eschweizerbart_xxx

Transformation of kyanite to andalusite in the Benamocarra Unit

(Betic Cordillera S Spain) Kinetics and petrological significance

ANTONIO SANCHEZ-NAVAS1 ELISA MACAIONE2 RITA DE CASSIA OLIVEIRA-BARBOSA1

ANTONIA MESSINA2 and AGUSTIN MARTIN-ALGARRA3

1 Departamento de Mineralogıa y Petrologıa and IACT (CSIC-UGR) Universidad de Granada E-18071 Granada SpainCorresponding author e-mail asnavasugres

2 Dipartimento di Dipartimento de Scienze della Terra-Universita di Messina Salita Papardo 98122 Messina Italy3 Departamento de Estratigrafıa y Paleontologıa and IACT (CSIC-UGR) Universidad de Granada E-18071

Granada SpainPresent address Instituto de Geociencias Faculdade de Geologia Universidade Federal do Para CampusUniversitario do Guama Rua Augusto Correa 1 - Campus Basico - CEP 66075-110 Belem Para Brasil

E-mail ritabarbosaufpabr

Abstract Kyanite is directly replaced by andalusite in quartzndashplagioclase veins included within graphite-bearing micaschists of theAlpine Benamocarra Unit (Betic Cordillera Spain) Electron back-scattered diffraction indicates that i) precursory kyanite containsplanar defects ii) andalusite growth was crystallographically controlled by the kyanite and iii) the structure of both Al2SiO5 phasesshares nearly the closest-packed oxygen array and chains of edge-sharing octahedra The small entropy difference of the kyani-tendashandalusite polymorphic inversion makes it difficult to overcome the energy barrier of this transformation The driving forceneeded for the kyanite-to-andalusite reaction was a temperature (T) increase during a pre-Alpine tectonometamorphic evolution Thelow-Pmedium-Tmetamorphic conditions that affected the rocks studied took place in relation to a late Variscan extensional collapseThe reaction pathway proposed here corresponds to the first part of a poly-orogenic tectonometamorphic evolution consisting of apre-Alpine metamorphism of high thermal gradient with mainly static growth of porphyroblasts followed by an essentially dynamicmetamorphism during the Alpine orogeny

Key-words polymorphic transformation kinetics kyanite andalusite aluminium silicate metamorphism

1 Introduction

Orogenic cores frequently record complex polymeta-morphic histories An example of a complex polymeta-morphic history can be found in pre-Mesozoicmetamorphic successions of the Alpine Internal Domainsof the Betic Cordillera (Spain) and the Rif (Morocco)Recent studies have demonstrated that the Alpine evolu-tion overprinted Variscan and older orogenic events in theNevado-Filabride the Alpujarride-Sebtide and theMalaguide-Ghomaride complexes (eg Puga et al 1975Bouybaouene et al 1998 Martın-Algarra et al 2009a andb Rosetti et al 2010 2013 Gomez-Pugnaire et al 2012Sanchez-Navas et al 2012 2014) Variscan U-Pb agesobtained from zircon and monazite single crystals in pre-Mesozoic rocks have been interpreted as related to high-grade metamorphic or magmatic events (Zeck ampWhitehouse 1999 2002 Montel et al 2000 Zeck ampWilliams 2001) Before zircon dating the isotopic agessupporting the existence of pre-Alpine tectono-

metamorphic events (eg Priem et al 1966 Boulinet al 1969 Bernard-Griffiths et al 1977 Andriessenet al 1991 Montel et al 1995) were considered incon-clusive or else lacking in regional significance In factbefore the publication of a few recent papers (Sanchez-Navas et al 2012 2014) no direct field or petrographicevidence related to the Variscan orogenesis had been foundby most workers in the Alpujarride Complex of the Beticzone (eg Torres-Roldan 1974 1981 Tubıa et al 1997Garcıa-Casco et al 1993 Garcıa-Casco amp Torres-Roldan1996 1999 Azanon et al 1998 Argles et al 1999 Sotoamp Platt 1999) Moreover Alpujarride-Sebtide rocks ofvariable metamorphic grades dated with different radio-metric systems (Rb-Sr K-Ar-Ar Sm-Nd and U-Pb) gavesystematically Alpine ages (eg Loomis 1975 Priemet al 1979 Michard et al 1983 Zeck et al 1989a andb 1996 Monie et al 1991 Monie et al 1994 Sanchez-Rodrıguez et al 1996 Platt ampWhitehouse 1999 Rossettiet al 2010 2013) Integrated field and detailed micro-structural studies of mineral transformations in relation to

0935-1221160028-2518 $ 765DOI 101127ejm20160028-2518 2015 E Schweizerbartrsquosche Verlagsbuchhandlung D-70176 Stuttgart

Eur J Mineral

2016 28 337ndash353

Published online 5 January 2016

eschweizerbart_xxx

the tectono-metamorphic evolution are essential to distin-guish the part of the metamorphic mineral associations andtectonic fabrics currently visible in the Alpujarride rocksthat belong to Alpine or to pre-Alpine (Variscan andperhaps older) events

The three polymorphs of Al2SiO5 are important indexminerals to unravel pressure (P) and temperature (T) con-ditions during regional and contact metamorphism TheP-T phase equilibria involving kyanite andalusite and silli-manite are affected by considerable uncertainty in calibra-tion experiments and erroneous petrological interpretationsof the presence of coexisting polymorphs in rocks derivefrom the sluggish kinetics of reactions involving the alumi-nium silicates (Kerrick 1990) The reaction mechanisms inthe transformation of pre-Alpine andalusite porphyroblaststo Alpine small-sized kyanite and fibrolite (both related toAlpine foliations) in metapelitic rocks of the UpperAlpujarride Torrox Unit were studied by Sanchez Navaset al (2012) In the present study we examine the transfor-mation of pre-Alpine kyanite porphyroblasts to pre-Alpineandalusite porphyroblasts in medium-T metapelites of theBenamocarra Unit which tectonically overlies the TorroxUnit This transformation was observed in the field first andfurther confirmed by microstructural studies This allows adetailed discussion of the crystallographic and kinetic con-trols of the KyAnd transformation and on the geologicalconsequences of this transformation We also describe tex-tural relations and mineral chemistry of the enclosing poly-metamorphic medium-T graphite-bearing Ms thorn Bt thorn Pl Cld Grt St Ky And Crd micaschists (abbre-viations after Whitney amp Evans 2010) Finally we discussthe geological significance of the KyAnd transformationas well as of the textures and mineral chemistry of the rocksstudied in order to decipher the pre-Alpine vs Alpinepolymetamorphic history of the Benamocarra Unit

2 Geological setting

The Alboran-Kabylia-Peloritani-Calabria (AlKaPeCa)Alpine metamorphic belt (Bouillin et al 1986) includesthe internal domains of the Western Mediterranean AlpineBelts before its post-collisional Mid- to Late Miocenedisintegration (Fig 1a) This belt resulted from the EarlyMiocene collision of Iberia and Africa against the Meso-Mediterranean Microplate (Durand-Delga amp Fontbote1980) which was a continental crustal block detachedfrom Pangaea and bounded by narrow oceanic basinssince mid-Jurassic times (Guerrera et al 1993) TheAlpujarride and Malaguide complexes of the BeticCordillera (Fig 1b) and the equivalent tectonic units ofthe Rif (Sebtide-Ghomaride units) of the AlgerianKabylias and of the Calabria-Peloritani Terrane of south-ern Italy were essential constituents of the AlKaPeCa belt(Perrone et al 2006)

The Malaguide Complex constitutes the highest tec-tonic thrust unit of the Betic internal domain and over-lies the Alpujarride Complex of which the highest

tectonic units in the Malaga area are totally made upof medium- to high-grade metamorphic rocks (Fig 1b)In this work we study rocks belonging to theBenamocarra Unit (Aldaya et al 1979 Elorza 1982)which is located just below the Malaguide Complex tothe east of Malaga (Fig 1c)

The Benamocarra Unit is composed of Alpujarride-like graphite-rich metapelites and metapsammites cross-cut by dikes of mafic subvolcanic rocks (Fig 1d) with agradual upward decrease in metamorphic grade (egElorza amp Garcıa-Duenas 1981 Ruiz-Cruz 1997 Ruiz-Cruz amp Rodrıguez-Jimenez 2002) The BenamocarraUnit overlies the Torrox Unit the widest and mosttypical Upper Alpujarride Unit in the area from whichit is detached by an extensional contact (Alonso-Chavezamp Orozco 2012) The Torrox Unit is made of a gneissiccomplex at its base (Sanchez-Navas 1999 Sanchez-Navas et al 2014) surrounded by a monotone succes-sion of dark-coloured and graphite-bearing St-Grt-Ky-And-Fi micaschists (Sanchez-Navas et al 2012) withmetamorphic grade decreasing upwards The upper partof the pre-Mesozoic succession of the Torrox Unit ismade of andalusite-bearing graphite-rich metapelites andmetapsammites that are similar to the rocks that consti-tute the lower part of the Benamocarra Unit

The rock succession of the Benamocarra Unit isdescribed in more detail below It underlies a thick succes-sion of fine-grained low-grade to very low-grade schistsslates psammites and stretched conglomerates of earlyPalaeozoic or older age which constitute the stratigraphicbase of the Malaguide Complex (Morales FormationMartın-Algarra 1987) and which are also crosscut bydikes identical to those of the Benamocarra Unit(Fig 1d) The contact between the two rock successionscorresponds to a low-angle extensional fault which oftenis difficult to recognize in the field (Fig 1c) Consequentlyaccording to regional geological studies it is debatedwhether the Benamocarra Unit constitutes the base of theMalaguide Complex or is a part detached by low-anglefaults of the top of the highest Alpujarride (Torrox) Unit inthe area (Aldaya et al 1979 Elorza amp Garcıa-Duenas1981 Elorza 1982)

The stratigraphically lower beds of the MalaguideComplex (Morales Fm) are strongly foliated metapelitesand metapsammites affected by low-grade metamorphism(Ruiz-Cruz 1997 Ruiz-Cruz amp Rodrıguez-Jimenez2002) The lowest part of the Morales Fm contains abun-dant sericitized relics of metamorphic minerals randomlyoriented in the foliation Among themmillimetric porphyr-oblasts of andalusite biotite and garnet are locally pre-served All these minerals gradually disappear upwardswhereas their amount and size increase downwards sothat the lowest part of the Malaguide succession becomesvery similar to the rocks of the upper part of theBenamocarra Unit Upwards the Morales Fm is stratigra-phically followed by a thick succession of UpperOrdovician to Upper Carboniferous siliciclastic and carbo-natic turbidites with pelagic horizons that have been datedmainly with conodonts (OrsquoDogherty et al 2000

338 A Sanchez-Navas et al

eschweizerbart_xxx

Fig 1 (a) Western Mediterranean Alpine belts with indication of the AlKaPeCa fragments (black) (b) Tectonic map of the Betic Cordillera(c) Geologic map of the Benamocarra area (modified from Elorza amp Garcıa Duenas 1981) The samples mentioned in the text figures andtables are indicated with their numbers (d) Lithological succession of the Benamocarra Unit and overlying rocks (online version in colour)

Transformation of kyanite to andalusite 339

eschweizerbart_xxx

Martın-Algarra et al 2009a Rodrıguez-Canero et al2010 Rodrıguez-Canero amp Martın-Algarra 2014) Thefoliation in the Morales Fm and in overlying Devonian(Santi Petri Fm) up to Lower Carboniferous beds datedwith conodonts (Falcona Fm) is crosscut by the maficdikes (Fig 1c) These dikes have provided 40K39Ar and40Ar39Ar ages between 22 Ma and 30 Ma (Torres-Roldanet al 1986 Platzman et al 2000)

The Malaguide Palaeozoic succession is followed byunmetamorphosed Permo-Triassic to Cretaceous clasticand carbonate rocks (Martın-Algarra 1987) An unconfor-mity between the Palaeozoic and the Triassic rocks hasbeen reported by Foucault amp Paquet (1971) These aspectshave led different authors (eg Balanya amp Garcıa Duenas1987) to assign the foliation in the Morales Formation tothe Variscan orogeny

3 Sampling and analytical procedures

The studied samples were collected from four sectionsin the Benamocarra Unit and in the lowest beds of theMalaguide Morales Fm along the roads MA-135 fromBenamocarra to Iznate MA-176 from Iznate to CajizMA-149 from Almachar to Moclinejo and MA-106 fromTorre de Benagalbon to Macharaviaya and Benaque(Fig 1c) Polished thin sections for petrographic andanalytical studies were prepared from 61 samples ofgraphite-rich micaschists fine-grained micaschists phyl-lites and quartz-rich veins either crosscutting or subpar-allel to the main foliation The chemical composition ofthe mineral phases was determined from fine-grained(samples Ben10 and Ben11 Fig 1c) and coarse-grainedmicaschists (sample Ben54 Fig 1c) by using a CamecaSX-50 electron microprobe Operating conditions were20 kV accelerating voltage 20 nA beam current and aspot size between 5 and 7 mm Standards were bothsynthetic oxides and minerals Structural formulae ofminerals were calculated using the software of Ulmer(1986) with the exception of chloritoid (12-oxygenanhydrous basis Chopin et al 1992 and Fe3thorn as 4ndash(Al thorn Ti) Azanon amp Goffe 1997)

Electron back-scattered diffraction (EBSD) images andpole figures of the KyAnd transformation from a quartz-rich vein (sample Ben43 Fig 1c) were made with a LeoGEMINI-1530 scanning electron microscope (SEM)equipped with an Inca Crystal detector The diffractionpattern once indexed provides information on the orienta-tion of the crystal lattice Data from different positionswere integrated to perform orientation maps and repre-sented as pole figures In the sample Z and Y axes coincidewith normal direction to the polished section and the traceof the main or more pervasive foliation respectivelyAndalusite is orthorhombic space group Pnnm withunit-cell parameters a frac14 77980 b frac14 79031 c frac14 55566A kyanite is triclinic space group P-1 with afrac14 71262 bfrac14 78520 c frac14 55724 A a frac14 8999 b frac14 10111 and g frac1410603 (from Winter amp Ghose 1979)

4 Results

41 Field relations

Metapelitic rocks of the Benamocarra Unit consist of alter-nating bands of quartz-rich and mica-rich domains inher-ited from the psammitic and pelitic layers of thesedimentary protolith (Figs 1d and 2a) The succession islithologically very monotonous and in the field a gradualdecrease in grain size is observed from bottom to top of thesuccession Porphyroblasts of And and Cld are sometimesvisible to the naked eye as dark crystals (Fig 2b) and thoseof Grt as orange-reddish spots the latter being most abun-dant towards the top of the succession The upwarddecrease in grain size is accompanied by the disappearanceof And preserved only as relic pseudomorphs in manycases towards the top of the succession

In addition to the lithological layering (S0) defined bythe alternation of minor amounts of pelites intercalatedwith psammite layers two foliations are visible in thefield within the Benamocarra schists (Fig 2a) The mostevident foliation in the field hereafter called S3 transposesprevious foliations S1 and S2 However S1 is observed onlyin thin section within Cld and Grt crystals and in graphite-rich microlithons (see below) The foliation S2 visible inthe field is found within the graphite-rich pelitic bandstransposed by S3 (arrows in Fig 2a) In these graphite-richmetapelitic layers andalusite prisms occur randomlyoriented in foliation S2 (Fig 2b) Quartz segregations fre-quently containing millimetric to centimetric Ab and pinkAnd crystals are very abundant and most of them certainlycrosscut the S2 foliation Nonetheless the late foliation S3frequently shears these And-bearing quartz-rich veinswhich are commonly found parallelized to the latter Theless deformed veins contain random aggregates of pinkAnd prisms (Fig 2c) However within the veins the pinkAnd crystals more frequently appear fractured and tecto-nically re-oriented boudinaged and strongly elongatedalong S3 Exceptionally blue kyanite prisms are inter-grown with andalusite prisms in deformed veins parallelto the S3 (Fig 2d) The KyAnd transformation has beenstudied in one of these samples collected near km 6 alongthe MA-149 road from Almachar to Moclinejo (sampleBen43 Fig 1c) Although the coexistence of blue Ky andpink And in veins has only rarely been mentioned in theliterature available on the Alpujarride Complex (Martın-Algarra 1987) the occurrence of quartzndashalbite veinsincluding Ky partially transformed to And is not exclusiveof the Benamocarra Unit and has also been observed insimilar schists of diverse Upper Alpujarride units N of theSierra de las Aguas in the Carratraca peridotite massif(Martın-Algarra 1987) close to Almunecar and in theSierra de la Alfaguara near Granada

42 Petrography

Two main mineral associations have been recognized inthe Benamocarra metapeliticmetapsammitic succession

340 A Sanchez-Navas et al

eschweizerbart_xxx

i) Ms thorn Bt thorn Pl thorn Cld thorn Grt And (upper part) ii)Ms thorn Bt thorn Pl thorn Cld thorn Grt thorn And Ky St thorn Crd(lower part) The petrographic study is focused mainlyon the textural relation between Cld And Grt Crd andfoliations S1 S2 and S3 Chloritoid crystals have grownrandomly oriented on a Gr-rich foliation (S1) in the Msthorn Bt thorn Pl thorn Cld thorn Grt thorn And schists of the upper partof the Benamocarra Unit (Fig 3a) Chloritoid frequentlyoccurs as post-S1 prismatic crystals within Gr-richmicaceous domains moderately affected by S3(Fig 3a) In some cases Cld prisms appear moderatelydeformed and partially or totally pseudomorphed by Qzthorn Ms thorn Bt and opaque phases (Fig 3b) In additionsome Cld crystals are clearly reoriented and sheared byS3 and embedded in a Bt-rich matrix (Fig 3c)

Andalusite appears strongly affected by the deformationD3 with tectonic reorientation boudinage and microfold-ing associated with the development of the S3 foliation(Fig 3dndashf) The And porphyroblasts are post-kinematicto S2 and formed after Cld Grt and St (Fig 3e) In somecases And overgrowsGrt crystals including Cld or containsrelics of St The foliation S3 is well defined by micro-shearbands filled by Qz deforming the Gr-rich domains and Andcrystals (Fig 3f)

Within the mica-rich and finer-grained domains that areless deformed by D3 in the Ms thorn Bt thorn Pl thorn Cld thorn Grt thornAnd Ky St thorn Crd micaschists of the lower part of theBenamocarra Unit the porphyroblasts of Cld and Grt grew

first and those of And and xenoblastic Crd formed laterenclosing both Grt and Cld (Fig 4andashb) The Bt and Andformed after destabilization of Grt (Fig 4c) Indents on110 of Grt indicate the dissolution of Grt perpendicularto these faces favoured by the presence of abundant inclu-sions of Qz distributed perpendicularly to these crystalfaces (Fig 4c) In some cases such small Qz inclusionsform a cross-like pattern that evokes the typical crystal-growth features of the And chiastolites (Fig 4c) Theplagioclase is prevalently albitic commonly encloses gra-phite layers defining S1 and is frequently fractured whencrossed by S3 Some relic St grains are preserved withinpoikilitic And crystals (Fig 3e) but form preferentiallysmall isolated and dismembered porphyroclasts shearedand wrapped by S2 Kyanite is very rarely present in theschists The And thorn Crd association postdating the Cld thornGrt association is strongly affected by the S3-relateddeformation (Fig 4bndashd)

The S3 foliation transposes the earlier foliations S1 andS2 which are preserved in graphite-rich micaceous micro-lithons or within porphyroblasts (S1 in early Cld Fig 3andashband S2 in later CrdAnd Figs 3dndashf 4b and d) in the micas-chists of the whole Benamocarra succession The S3 folia-tion forms a metamorphic banding made of alternating Qz-rich and micaceous layers (recrystallized Bt and Ms) ana-stomosed around the Qz grains and pelitic microlithons(Fig 3a) Syn-S3 micas also grew as pseudomorphs ofprevious minerals such as Cld and Crd A common

Fig 2 (a) Micaschists of Benamocarra Unit formed by light-grey quartzites alternating with black metapelite bands (arrows) transposed bythe S3 foliation (b) Surface view of the S2 foliation with randomly oriented post-kinematic andalusite porphyroblasts in black graphite-richmetapelites S3 foliation is here parallel to S2 and is defined by fine-grained muscovite (lighter areas) formed on and around andalusite (c)Andalusite rosettes in quartz-rich veins segregated within And-bearing graphite-rich schist (d) Kyanite partially transformed to And within asmall quartz segregation stretched along S3 blue pen for scale is 1 cm wide (online version in colour)

Transformation of kyanite to andalusite 341

eschweizerbart_xxx

secondary mineral phase is Chl which crystallizes as aproduct of destabilization of Bt Grt and Crd

Kyanite crystals partially replaced by andalusite (Fig 5)have been studied in detail from one QzndashAb vein from theintermediate part of the Benamocarra succession (sampleBen43) This post-S2 vein is strongly deformed and paral-lel to the S3 foliation (Fig 2d) which is defined by Mswithin the vein itself Both the Ky and the And crystals arefolded and fractured (Fig 5a) In some cases a single Kycrystal is directly replaced by more than one And prismthis is apparent in optical images by the different crystal-lographic orientations observed for replacing And(Fig 5b) and confirmed also in EBSD images (see below)

43 Mineral chemistry

Muscovite mineral chemistry shows two compositionalgroups (Table S1 freely available online asSupplementary material linked to this article on the GSWwebsite of the journal httpeurjmingeoscienceworldorgFig 6andashb) Most analyses belong to the first group which isconstituted of Ms flakes formed after D1 (primary Ms)with lower Si content (Si frac14 303ndash315 atoms per formulaunit apfu) low celadonitic substitution (Fe thorn Mg frac14003ndash012 apfu) and low K(K thorn Na thorn Ca) The secondgroup includes the Ms formed in relation to the D3 deforma-tion (recrystallized Ms) and exhibits a higher Si content

Fig 3 (a) Photomicrograph (plane polarised light) of a Gr-rich microlithon located between two Qz-rich shear bands defining S3 foliationCld porphyroblasts (arrows) postkinematic to the S1 foliation are preserved within the microlithon (b) Bt Ms and Qz pseudomorph after Cld(c) Lath-shaped crystals of Cld elongated along a shear band defining the S3 foliation In adjacent domains that are less affected by shearingCld crystals remain unoriented (d) Post-S2 And porphyroclasts sheared (arrow) and wrapped up by the S3 foliation defined by Qz rich bandsBt Ms and pre-S3 transposed Gr (e) And porphyroblasts including St relic and arranged on the S2 foliation (f) And porphyroblasts folded byD3 and including the S2 foliation defined by trail inclusions of Gr (online version in colour)

342 A Sanchez-Navas et al

eschweizerbart_xxx

the tectono-metamorphic evolution are essential to distin-guish the part of the metamorphic mineral associations andtectonic fabrics currently visible in the Alpujarride rocksthat belong to Alpine or to pre-Alpine (Variscan andperhaps older) events

The three polymorphs of Al2SiO5 are important indexminerals to unravel pressure (P) and temperature (T) con-ditions during regional and contact metamorphism TheP-T phase equilibria involving kyanite andalusite and silli-manite are affected by considerable uncertainty in calibra-tion experiments and erroneous petrological interpretationsof the presence of coexisting polymorphs in rocks derivefrom the sluggish kinetics of reactions involving the alumi-nium silicates (Kerrick 1990) The reaction mechanisms inthe transformation of pre-Alpine andalusite porphyroblaststo Alpine small-sized kyanite and fibrolite (both related toAlpine foliations) in metapelitic rocks of the UpperAlpujarride Torrox Unit were studied by Sanchez Navaset al (2012) In the present study we examine the transfor-mation of pre-Alpine kyanite porphyroblasts to pre-Alpineandalusite porphyroblasts in medium-T metapelites of theBenamocarra Unit which tectonically overlies the TorroxUnit This transformation was observed in the field first andfurther confirmed by microstructural studies This allows adetailed discussion of the crystallographic and kinetic con-trols of the KyAnd transformation and on the geologicalconsequences of this transformation We also describe tex-tural relations and mineral chemistry of the enclosing poly-metamorphic medium-T graphite-bearing Ms thorn Bt thorn Pl Cld Grt St Ky And Crd micaschists (abbre-viations after Whitney amp Evans 2010) Finally we discussthe geological significance of the KyAnd transformationas well as of the textures and mineral chemistry of the rocksstudied in order to decipher the pre-Alpine vs Alpinepolymetamorphic history of the Benamocarra Unit

2 Geological setting

The Alboran-Kabylia-Peloritani-Calabria (AlKaPeCa)Alpine metamorphic belt (Bouillin et al 1986) includesthe internal domains of the Western Mediterranean AlpineBelts before its post-collisional Mid- to Late Miocenedisintegration (Fig 1a) This belt resulted from the EarlyMiocene collision of Iberia and Africa against the Meso-Mediterranean Microplate (Durand-Delga amp Fontbote1980) which was a continental crustal block detachedfrom Pangaea and bounded by narrow oceanic basinssince mid-Jurassic times (Guerrera et al 1993) TheAlpujarride and Malaguide complexes of the BeticCordillera (Fig 1b) and the equivalent tectonic units ofthe Rif (Sebtide-Ghomaride units) of the AlgerianKabylias and of the Calabria-Peloritani Terrane of south-ern Italy were essential constituents of the AlKaPeCa belt(Perrone et al 2006)

The Malaguide Complex constitutes the highest tec-tonic thrust unit of the Betic internal domain and over-lies the Alpujarride Complex of which the highest

tectonic units in the Malaga area are totally made upof medium- to high-grade metamorphic rocks (Fig 1b)In this work we study rocks belonging to theBenamocarra Unit (Aldaya et al 1979 Elorza 1982)which is located just below the Malaguide Complex tothe east of Malaga (Fig 1c)

The Benamocarra Unit is composed of Alpujarride-like graphite-rich metapelites and metapsammites cross-cut by dikes of mafic subvolcanic rocks (Fig 1d) with agradual upward decrease in metamorphic grade (egElorza amp Garcıa-Duenas 1981 Ruiz-Cruz 1997 Ruiz-Cruz amp Rodrıguez-Jimenez 2002) The BenamocarraUnit overlies the Torrox Unit the widest and mosttypical Upper Alpujarride Unit in the area from whichit is detached by an extensional contact (Alonso-Chavezamp Orozco 2012) The Torrox Unit is made of a gneissiccomplex at its base (Sanchez-Navas 1999 Sanchez-Navas et al 2014) surrounded by a monotone succes-sion of dark-coloured and graphite-bearing St-Grt-Ky-And-Fi micaschists (Sanchez-Navas et al 2012) withmetamorphic grade decreasing upwards The upper partof the pre-Mesozoic succession of the Torrox Unit ismade of andalusite-bearing graphite-rich metapelites andmetapsammites that are similar to the rocks that consti-tute the lower part of the Benamocarra Unit

The rock succession of the Benamocarra Unit isdescribed in more detail below It underlies a thick succes-sion of fine-grained low-grade to very low-grade schistsslates psammites and stretched conglomerates of earlyPalaeozoic or older age which constitute the stratigraphicbase of the Malaguide Complex (Morales FormationMartın-Algarra 1987) and which are also crosscut bydikes identical to those of the Benamocarra Unit(Fig 1d) The contact between the two rock successionscorresponds to a low-angle extensional fault which oftenis difficult to recognize in the field (Fig 1c) Consequentlyaccording to regional geological studies it is debatedwhether the Benamocarra Unit constitutes the base of theMalaguide Complex or is a part detached by low-anglefaults of the top of the highest Alpujarride (Torrox) Unit inthe area (Aldaya et al 1979 Elorza amp Garcıa-Duenas1981 Elorza 1982)

The stratigraphically lower beds of the MalaguideComplex (Morales Fm) are strongly foliated metapelitesand metapsammites affected by low-grade metamorphism(Ruiz-Cruz 1997 Ruiz-Cruz amp Rodrıguez-Jimenez2002) The lowest part of the Morales Fm contains abun-dant sericitized relics of metamorphic minerals randomlyoriented in the foliation Among themmillimetric porphyr-oblasts of andalusite biotite and garnet are locally pre-served All these minerals gradually disappear upwardswhereas their amount and size increase downwards sothat the lowest part of the Malaguide succession becomesvery similar to the rocks of the upper part of theBenamocarra Unit Upwards the Morales Fm is stratigra-phically followed by a thick succession of UpperOrdovician to Upper Carboniferous siliciclastic and carbo-natic turbidites with pelagic horizons that have been datedmainly with conodonts (OrsquoDogherty et al 2000

338 A Sanchez-Navas et al

eschweizerbart_xxx

Fig 1 (a) Western Mediterranean Alpine belts with indication of the AlKaPeCa fragments (black) (b) Tectonic map of the Betic Cordillera(c) Geologic map of the Benamocarra area (modified from Elorza amp Garcıa Duenas 1981) The samples mentioned in the text figures andtables are indicated with their numbers (d) Lithological succession of the Benamocarra Unit and overlying rocks (online version in colour)

Transformation of kyanite to andalusite 339

eschweizerbart_xxx

Martın-Algarra et al 2009a Rodrıguez-Canero et al2010 Rodrıguez-Canero amp Martın-Algarra 2014) Thefoliation in the Morales Fm and in overlying Devonian(Santi Petri Fm) up to Lower Carboniferous beds datedwith conodonts (Falcona Fm) is crosscut by the maficdikes (Fig 1c) These dikes have provided 40K39Ar and40Ar39Ar ages between 22 Ma and 30 Ma (Torres-Roldanet al 1986 Platzman et al 2000)

The Malaguide Palaeozoic succession is followed byunmetamorphosed Permo-Triassic to Cretaceous clasticand carbonate rocks (Martın-Algarra 1987) An unconfor-mity between the Palaeozoic and the Triassic rocks hasbeen reported by Foucault amp Paquet (1971) These aspectshave led different authors (eg Balanya amp Garcıa Duenas1987) to assign the foliation in the Morales Formation tothe Variscan orogeny

3 Sampling and analytical procedures

The studied samples were collected from four sectionsin the Benamocarra Unit and in the lowest beds of theMalaguide Morales Fm along the roads MA-135 fromBenamocarra to Iznate MA-176 from Iznate to CajizMA-149 from Almachar to Moclinejo and MA-106 fromTorre de Benagalbon to Macharaviaya and Benaque(Fig 1c) Polished thin sections for petrographic andanalytical studies were prepared from 61 samples ofgraphite-rich micaschists fine-grained micaschists phyl-lites and quartz-rich veins either crosscutting or subpar-allel to the main foliation The chemical composition ofthe mineral phases was determined from fine-grained(samples Ben10 and Ben11 Fig 1c) and coarse-grainedmicaschists (sample Ben54 Fig 1c) by using a CamecaSX-50 electron microprobe Operating conditions were20 kV accelerating voltage 20 nA beam current and aspot size between 5 and 7 mm Standards were bothsynthetic oxides and minerals Structural formulae ofminerals were calculated using the software of Ulmer(1986) with the exception of chloritoid (12-oxygenanhydrous basis Chopin et al 1992 and Fe3thorn as 4ndash(Al thorn Ti) Azanon amp Goffe 1997)

Electron back-scattered diffraction (EBSD) images andpole figures of the KyAnd transformation from a quartz-rich vein (sample Ben43 Fig 1c) were made with a LeoGEMINI-1530 scanning electron microscope (SEM)equipped with an Inca Crystal detector The diffractionpattern once indexed provides information on the orienta-tion of the crystal lattice Data from different positionswere integrated to perform orientation maps and repre-sented as pole figures In the sample Z and Y axes coincidewith normal direction to the polished section and the traceof the main or more pervasive foliation respectivelyAndalusite is orthorhombic space group Pnnm withunit-cell parameters a frac14 77980 b frac14 79031 c frac14 55566A kyanite is triclinic space group P-1 with afrac14 71262 bfrac14 78520 c frac14 55724 A a frac14 8999 b frac14 10111 and g frac1410603 (from Winter amp Ghose 1979)

4 Results

41 Field relations

Metapelitic rocks of the Benamocarra Unit consist of alter-nating bands of quartz-rich and mica-rich domains inher-ited from the psammitic and pelitic layers of thesedimentary protolith (Figs 1d and 2a) The succession islithologically very monotonous and in the field a gradualdecrease in grain size is observed from bottom to top of thesuccession Porphyroblasts of And and Cld are sometimesvisible to the naked eye as dark crystals (Fig 2b) and thoseof Grt as orange-reddish spots the latter being most abun-dant towards the top of the succession The upwarddecrease in grain size is accompanied by the disappearanceof And preserved only as relic pseudomorphs in manycases towards the top of the succession

In addition to the lithological layering (S0) defined bythe alternation of minor amounts of pelites intercalatedwith psammite layers two foliations are visible in thefield within the Benamocarra schists (Fig 2a) The mostevident foliation in the field hereafter called S3 transposesprevious foliations S1 and S2 However S1 is observed onlyin thin section within Cld and Grt crystals and in graphite-rich microlithons (see below) The foliation S2 visible inthe field is found within the graphite-rich pelitic bandstransposed by S3 (arrows in Fig 2a) In these graphite-richmetapelitic layers andalusite prisms occur randomlyoriented in foliation S2 (Fig 2b) Quartz segregations fre-quently containing millimetric to centimetric Ab and pinkAnd crystals are very abundant and most of them certainlycrosscut the S2 foliation Nonetheless the late foliation S3frequently shears these And-bearing quartz-rich veinswhich are commonly found parallelized to the latter Theless deformed veins contain random aggregates of pinkAnd prisms (Fig 2c) However within the veins the pinkAnd crystals more frequently appear fractured and tecto-nically re-oriented boudinaged and strongly elongatedalong S3 Exceptionally blue kyanite prisms are inter-grown with andalusite prisms in deformed veins parallelto the S3 (Fig 2d) The KyAnd transformation has beenstudied in one of these samples collected near km 6 alongthe MA-149 road from Almachar to Moclinejo (sampleBen43 Fig 1c) Although the coexistence of blue Ky andpink And in veins has only rarely been mentioned in theliterature available on the Alpujarride Complex (Martın-Algarra 1987) the occurrence of quartzndashalbite veinsincluding Ky partially transformed to And is not exclusiveof the Benamocarra Unit and has also been observed insimilar schists of diverse Upper Alpujarride units N of theSierra de las Aguas in the Carratraca peridotite massif(Martın-Algarra 1987) close to Almunecar and in theSierra de la Alfaguara near Granada

42 Petrography

Two main mineral associations have been recognized inthe Benamocarra metapeliticmetapsammitic succession

340 A Sanchez-Navas et al

eschweizerbart_xxx

i) Ms thorn Bt thorn Pl thorn Cld thorn Grt And (upper part) ii)Ms thorn Bt thorn Pl thorn Cld thorn Grt thorn And Ky St thorn Crd(lower part) The petrographic study is focused mainlyon the textural relation between Cld And Grt Crd andfoliations S1 S2 and S3 Chloritoid crystals have grownrandomly oriented on a Gr-rich foliation (S1) in the Msthorn Bt thorn Pl thorn Cld thorn Grt thorn And schists of the upper partof the Benamocarra Unit (Fig 3a) Chloritoid frequentlyoccurs as post-S1 prismatic crystals within Gr-richmicaceous domains moderately affected by S3(Fig 3a) In some cases Cld prisms appear moderatelydeformed and partially or totally pseudomorphed by Qzthorn Ms thorn Bt and opaque phases (Fig 3b) In additionsome Cld crystals are clearly reoriented and sheared byS3 and embedded in a Bt-rich matrix (Fig 3c)

Andalusite appears strongly affected by the deformationD3 with tectonic reorientation boudinage and microfold-ing associated with the development of the S3 foliation(Fig 3dndashf) The And porphyroblasts are post-kinematicto S2 and formed after Cld Grt and St (Fig 3e) In somecases And overgrowsGrt crystals including Cld or containsrelics of St The foliation S3 is well defined by micro-shearbands filled by Qz deforming the Gr-rich domains and Andcrystals (Fig 3f)

Within the mica-rich and finer-grained domains that areless deformed by D3 in the Ms thorn Bt thorn Pl thorn Cld thorn Grt thornAnd Ky St thorn Crd micaschists of the lower part of theBenamocarra Unit the porphyroblasts of Cld and Grt grew

first and those of And and xenoblastic Crd formed laterenclosing both Grt and Cld (Fig 4andashb) The Bt and Andformed after destabilization of Grt (Fig 4c) Indents on110 of Grt indicate the dissolution of Grt perpendicularto these faces favoured by the presence of abundant inclu-sions of Qz distributed perpendicularly to these crystalfaces (Fig 4c) In some cases such small Qz inclusionsform a cross-like pattern that evokes the typical crystal-growth features of the And chiastolites (Fig 4c) Theplagioclase is prevalently albitic commonly encloses gra-phite layers defining S1 and is frequently fractured whencrossed by S3 Some relic St grains are preserved withinpoikilitic And crystals (Fig 3e) but form preferentiallysmall isolated and dismembered porphyroclasts shearedand wrapped by S2 Kyanite is very rarely present in theschists The And thorn Crd association postdating the Cld thornGrt association is strongly affected by the S3-relateddeformation (Fig 4bndashd)

The S3 foliation transposes the earlier foliations S1 andS2 which are preserved in graphite-rich micaceous micro-lithons or within porphyroblasts (S1 in early Cld Fig 3andashband S2 in later CrdAnd Figs 3dndashf 4b and d) in the micas-chists of the whole Benamocarra succession The S3 folia-tion forms a metamorphic banding made of alternating Qz-rich and micaceous layers (recrystallized Bt and Ms) ana-stomosed around the Qz grains and pelitic microlithons(Fig 3a) Syn-S3 micas also grew as pseudomorphs ofprevious minerals such as Cld and Crd A common

Fig 2 (a) Micaschists of Benamocarra Unit formed by light-grey quartzites alternating with black metapelite bands (arrows) transposed bythe S3 foliation (b) Surface view of the S2 foliation with randomly oriented post-kinematic andalusite porphyroblasts in black graphite-richmetapelites S3 foliation is here parallel to S2 and is defined by fine-grained muscovite (lighter areas) formed on and around andalusite (c)Andalusite rosettes in quartz-rich veins segregated within And-bearing graphite-rich schist (d) Kyanite partially transformed to And within asmall quartz segregation stretched along S3 blue pen for scale is 1 cm wide (online version in colour)

Transformation of kyanite to andalusite 341

eschweizerbart_xxx

secondary mineral phase is Chl which crystallizes as aproduct of destabilization of Bt Grt and Crd

Kyanite crystals partially replaced by andalusite (Fig 5)have been studied in detail from one QzndashAb vein from theintermediate part of the Benamocarra succession (sampleBen43) This post-S2 vein is strongly deformed and paral-lel to the S3 foliation (Fig 2d) which is defined by Mswithin the vein itself Both the Ky and the And crystals arefolded and fractured (Fig 5a) In some cases a single Kycrystal is directly replaced by more than one And prismthis is apparent in optical images by the different crystal-lographic orientations observed for replacing And(Fig 5b) and confirmed also in EBSD images (see below)

43 Mineral chemistry

Muscovite mineral chemistry shows two compositionalgroups (Table S1 freely available online asSupplementary material linked to this article on the GSWwebsite of the journal httpeurjmingeoscienceworldorgFig 6andashb) Most analyses belong to the first group which isconstituted of Ms flakes formed after D1 (primary Ms)with lower Si content (Si frac14 303ndash315 atoms per formulaunit apfu) low celadonitic substitution (Fe thorn Mg frac14003ndash012 apfu) and low K(K thorn Na thorn Ca) The secondgroup includes the Ms formed in relation to the D3 deforma-tion (recrystallized Ms) and exhibits a higher Si content

Fig 3 (a) Photomicrograph (plane polarised light) of a Gr-rich microlithon located between two Qz-rich shear bands defining S3 foliationCld porphyroblasts (arrows) postkinematic to the S1 foliation are preserved within the microlithon (b) Bt Ms and Qz pseudomorph after Cld(c) Lath-shaped crystals of Cld elongated along a shear band defining the S3 foliation In adjacent domains that are less affected by shearingCld crystals remain unoriented (d) Post-S2 And porphyroclasts sheared (arrow) and wrapped up by the S3 foliation defined by Qz rich bandsBt Ms and pre-S3 transposed Gr (e) And porphyroblasts including St relic and arranged on the S2 foliation (f) And porphyroblasts folded byD3 and including the S2 foliation defined by trail inclusions of Gr (online version in colour)

342 A Sanchez-Navas et al

eschweizerbart_xxx

Fig 1 (a) Western Mediterranean Alpine belts with indication of the AlKaPeCa fragments (black) (b) Tectonic map of the Betic Cordillera(c) Geologic map of the Benamocarra area (modified from Elorza amp Garcıa Duenas 1981) The samples mentioned in the text figures andtables are indicated with their numbers (d) Lithological succession of the Benamocarra Unit and overlying rocks (online version in colour)

Transformation of kyanite to andalusite 339

eschweizerbart_xxx

Martın-Algarra et al 2009a Rodrıguez-Canero et al2010 Rodrıguez-Canero amp Martın-Algarra 2014) Thefoliation in the Morales Fm and in overlying Devonian(Santi Petri Fm) up to Lower Carboniferous beds datedwith conodonts (Falcona Fm) is crosscut by the maficdikes (Fig 1c) These dikes have provided 40K39Ar and40Ar39Ar ages between 22 Ma and 30 Ma (Torres-Roldanet al 1986 Platzman et al 2000)

The Malaguide Palaeozoic succession is followed byunmetamorphosed Permo-Triassic to Cretaceous clasticand carbonate rocks (Martın-Algarra 1987) An unconfor-mity between the Palaeozoic and the Triassic rocks hasbeen reported by Foucault amp Paquet (1971) These aspectshave led different authors (eg Balanya amp Garcıa Duenas1987) to assign the foliation in the Morales Formation tothe Variscan orogeny

3 Sampling and analytical procedures

The studied samples were collected from four sectionsin the Benamocarra Unit and in the lowest beds of theMalaguide Morales Fm along the roads MA-135 fromBenamocarra to Iznate MA-176 from Iznate to CajizMA-149 from Almachar to Moclinejo and MA-106 fromTorre de Benagalbon to Macharaviaya and Benaque(Fig 1c) Polished thin sections for petrographic andanalytical studies were prepared from 61 samples ofgraphite-rich micaschists fine-grained micaschists phyl-lites and quartz-rich veins either crosscutting or subpar-allel to the main foliation The chemical composition ofthe mineral phases was determined from fine-grained(samples Ben10 and Ben11 Fig 1c) and coarse-grainedmicaschists (sample Ben54 Fig 1c) by using a CamecaSX-50 electron microprobe Operating conditions were20 kV accelerating voltage 20 nA beam current and aspot size between 5 and 7 mm Standards were bothsynthetic oxides and minerals Structural formulae ofminerals were calculated using the software of Ulmer(1986) with the exception of chloritoid (12-oxygenanhydrous basis Chopin et al 1992 and Fe3thorn as 4ndash(Al thorn Ti) Azanon amp Goffe 1997)

Electron back-scattered diffraction (EBSD) images andpole figures of the KyAnd transformation from a quartz-rich vein (sample Ben43 Fig 1c) were made with a LeoGEMINI-1530 scanning electron microscope (SEM)equipped with an Inca Crystal detector The diffractionpattern once indexed provides information on the orienta-tion of the crystal lattice Data from different positionswere integrated to perform orientation maps and repre-sented as pole figures In the sample Z and Y axes coincidewith normal direction to the polished section and the traceof the main or more pervasive foliation respectivelyAndalusite is orthorhombic space group Pnnm withunit-cell parameters a frac14 77980 b frac14 79031 c frac14 55566A kyanite is triclinic space group P-1 with afrac14 71262 bfrac14 78520 c frac14 55724 A a frac14 8999 b frac14 10111 and g frac1410603 (from Winter amp Ghose 1979)

4 Results

41 Field relations

Metapelitic rocks of the Benamocarra Unit consist of alter-nating bands of quartz-rich and mica-rich domains inher-ited from the psammitic and pelitic layers of thesedimentary protolith (Figs 1d and 2a) The succession islithologically very monotonous and in the field a gradualdecrease in grain size is observed from bottom to top of thesuccession Porphyroblasts of And and Cld are sometimesvisible to the naked eye as dark crystals (Fig 2b) and thoseof Grt as orange-reddish spots the latter being most abun-dant towards the top of the succession The upwarddecrease in grain size is accompanied by the disappearanceof And preserved only as relic pseudomorphs in manycases towards the top of the succession

In addition to the lithological layering (S0) defined bythe alternation of minor amounts of pelites intercalatedwith psammite layers two foliations are visible in thefield within the Benamocarra schists (Fig 2a) The mostevident foliation in the field hereafter called S3 transposesprevious foliations S1 and S2 However S1 is observed onlyin thin section within Cld and Grt crystals and in graphite-rich microlithons (see below) The foliation S2 visible inthe field is found within the graphite-rich pelitic bandstransposed by S3 (arrows in Fig 2a) In these graphite-richmetapelitic layers andalusite prisms occur randomlyoriented in foliation S2 (Fig 2b) Quartz segregations fre-quently containing millimetric to centimetric Ab and pinkAnd crystals are very abundant and most of them certainlycrosscut the S2 foliation Nonetheless the late foliation S3frequently shears these And-bearing quartz-rich veinswhich are commonly found parallelized to the latter Theless deformed veins contain random aggregates of pinkAnd prisms (Fig 2c) However within the veins the pinkAnd crystals more frequently appear fractured and tecto-nically re-oriented boudinaged and strongly elongatedalong S3 Exceptionally blue kyanite prisms are inter-grown with andalusite prisms in deformed veins parallelto the S3 (Fig 2d) The KyAnd transformation has beenstudied in one of these samples collected near km 6 alongthe MA-149 road from Almachar to Moclinejo (sampleBen43 Fig 1c) Although the coexistence of blue Ky andpink And in veins has only rarely been mentioned in theliterature available on the Alpujarride Complex (Martın-Algarra 1987) the occurrence of quartzndashalbite veinsincluding Ky partially transformed to And is not exclusiveof the Benamocarra Unit and has also been observed insimilar schists of diverse Upper Alpujarride units N of theSierra de las Aguas in the Carratraca peridotite massif(Martın-Algarra 1987) close to Almunecar and in theSierra de la Alfaguara near Granada

42 Petrography

Two main mineral associations have been recognized inthe Benamocarra metapeliticmetapsammitic succession

340 A Sanchez-Navas et al

eschweizerbart_xxx

i) Ms thorn Bt thorn Pl thorn Cld thorn Grt And (upper part) ii)Ms thorn Bt thorn Pl thorn Cld thorn Grt thorn And Ky St thorn Crd(lower part) The petrographic study is focused mainlyon the textural relation between Cld And Grt Crd andfoliations S1 S2 and S3 Chloritoid crystals have grownrandomly oriented on a Gr-rich foliation (S1) in the Msthorn Bt thorn Pl thorn Cld thorn Grt thorn And schists of the upper partof the Benamocarra Unit (Fig 3a) Chloritoid frequentlyoccurs as post-S1 prismatic crystals within Gr-richmicaceous domains moderately affected by S3(Fig 3a) In some cases Cld prisms appear moderatelydeformed and partially or totally pseudomorphed by Qzthorn Ms thorn Bt and opaque phases (Fig 3b) In additionsome Cld crystals are clearly reoriented and sheared byS3 and embedded in a Bt-rich matrix (Fig 3c)

Andalusite appears strongly affected by the deformationD3 with tectonic reorientation boudinage and microfold-ing associated with the development of the S3 foliation(Fig 3dndashf) The And porphyroblasts are post-kinematicto S2 and formed after Cld Grt and St (Fig 3e) In somecases And overgrowsGrt crystals including Cld or containsrelics of St The foliation S3 is well defined by micro-shearbands filled by Qz deforming the Gr-rich domains and Andcrystals (Fig 3f)

Within the mica-rich and finer-grained domains that areless deformed by D3 in the Ms thorn Bt thorn Pl thorn Cld thorn Grt thornAnd Ky St thorn Crd micaschists of the lower part of theBenamocarra Unit the porphyroblasts of Cld and Grt grew

first and those of And and xenoblastic Crd formed laterenclosing both Grt and Cld (Fig 4andashb) The Bt and Andformed after destabilization of Grt (Fig 4c) Indents on110 of Grt indicate the dissolution of Grt perpendicularto these faces favoured by the presence of abundant inclu-sions of Qz distributed perpendicularly to these crystalfaces (Fig 4c) In some cases such small Qz inclusionsform a cross-like pattern that evokes the typical crystal-growth features of the And chiastolites (Fig 4c) Theplagioclase is prevalently albitic commonly encloses gra-phite layers defining S1 and is frequently fractured whencrossed by S3 Some relic St grains are preserved withinpoikilitic And crystals (Fig 3e) but form preferentiallysmall isolated and dismembered porphyroclasts shearedand wrapped by S2 Kyanite is very rarely present in theschists The And thorn Crd association postdating the Cld thornGrt association is strongly affected by the S3-relateddeformation (Fig 4bndashd)

The S3 foliation transposes the earlier foliations S1 andS2 which are preserved in graphite-rich micaceous micro-lithons or within porphyroblasts (S1 in early Cld Fig 3andashband S2 in later CrdAnd Figs 3dndashf 4b and d) in the micas-chists of the whole Benamocarra succession The S3 folia-tion forms a metamorphic banding made of alternating Qz-rich and micaceous layers (recrystallized Bt and Ms) ana-stomosed around the Qz grains and pelitic microlithons(Fig 3a) Syn-S3 micas also grew as pseudomorphs ofprevious minerals such as Cld and Crd A common

Fig 2 (a) Micaschists of Benamocarra Unit formed by light-grey quartzites alternating with black metapelite bands (arrows) transposed bythe S3 foliation (b) Surface view of the S2 foliation with randomly oriented post-kinematic andalusite porphyroblasts in black graphite-richmetapelites S3 foliation is here parallel to S2 and is defined by fine-grained muscovite (lighter areas) formed on and around andalusite (c)Andalusite rosettes in quartz-rich veins segregated within And-bearing graphite-rich schist (d) Kyanite partially transformed to And within asmall quartz segregation stretched along S3 blue pen for scale is 1 cm wide (online version in colour)

Transformation of kyanite to andalusite 341

eschweizerbart_xxx

secondary mineral phase is Chl which crystallizes as aproduct of destabilization of Bt Grt and Crd

Kyanite crystals partially replaced by andalusite (Fig 5)have been studied in detail from one QzndashAb vein from theintermediate part of the Benamocarra succession (sampleBen43) This post-S2 vein is strongly deformed and paral-lel to the S3 foliation (Fig 2d) which is defined by Mswithin the vein itself Both the Ky and the And crystals arefolded and fractured (Fig 5a) In some cases a single Kycrystal is directly replaced by more than one And prismthis is apparent in optical images by the different crystal-lographic orientations observed for replacing And(Fig 5b) and confirmed also in EBSD images (see below)

43 Mineral chemistry

Muscovite mineral chemistry shows two compositionalgroups (Table S1 freely available online asSupplementary material linked to this article on the GSWwebsite of the journal httpeurjmingeoscienceworldorgFig 6andashb) Most analyses belong to the first group which isconstituted of Ms flakes formed after D1 (primary Ms)with lower Si content (Si frac14 303ndash315 atoms per formulaunit apfu) low celadonitic substitution (Fe thorn Mg frac14003ndash012 apfu) and low K(K thorn Na thorn Ca) The secondgroup includes the Ms formed in relation to the D3 deforma-tion (recrystallized Ms) and exhibits a higher Si content

Fig 3 (a) Photomicrograph (plane polarised light) of a Gr-rich microlithon located between two Qz-rich shear bands defining S3 foliationCld porphyroblasts (arrows) postkinematic to the S1 foliation are preserved within the microlithon (b) Bt Ms and Qz pseudomorph after Cld(c) Lath-shaped crystals of Cld elongated along a shear band defining the S3 foliation In adjacent domains that are less affected by shearingCld crystals remain unoriented (d) Post-S2 And porphyroclasts sheared (arrow) and wrapped up by the S3 foliation defined by Qz rich bandsBt Ms and pre-S3 transposed Gr (e) And porphyroblasts including St relic and arranged on the S2 foliation (f) And porphyroblasts folded byD3 and including the S2 foliation defined by trail inclusions of Gr (online version in colour)

342 A Sanchez-Navas et al

eschweizerbart_xxx

Martın-Algarra et al 2009a Rodrıguez-Canero et al2010 Rodrıguez-Canero amp Martın-Algarra 2014) Thefoliation in the Morales Fm and in overlying Devonian(Santi Petri Fm) up to Lower Carboniferous beds datedwith conodonts (Falcona Fm) is crosscut by the maficdikes (Fig 1c) These dikes have provided 40K39Ar and40Ar39Ar ages between 22 Ma and 30 Ma (Torres-Roldanet al 1986 Platzman et al 2000)

The Malaguide Palaeozoic succession is followed byunmetamorphosed Permo-Triassic to Cretaceous clasticand carbonate rocks (Martın-Algarra 1987) An unconfor-mity between the Palaeozoic and the Triassic rocks hasbeen reported by Foucault amp Paquet (1971) These aspectshave led different authors (eg Balanya amp Garcıa Duenas1987) to assign the foliation in the Morales Formation tothe Variscan orogeny

3 Sampling and analytical procedures

The studied samples were collected from four sectionsin the Benamocarra Unit and in the lowest beds of theMalaguide Morales Fm along the roads MA-135 fromBenamocarra to Iznate MA-176 from Iznate to CajizMA-149 from Almachar to Moclinejo and MA-106 fromTorre de Benagalbon to Macharaviaya and Benaque(Fig 1c) Polished thin sections for petrographic andanalytical studies were prepared from 61 samples ofgraphite-rich micaschists fine-grained micaschists phyl-lites and quartz-rich veins either crosscutting or subpar-allel to the main foliation The chemical composition ofthe mineral phases was determined from fine-grained(samples Ben10 and Ben11 Fig 1c) and coarse-grainedmicaschists (sample Ben54 Fig 1c) by using a CamecaSX-50 electron microprobe Operating conditions were20 kV accelerating voltage 20 nA beam current and aspot size between 5 and 7 mm Standards were bothsynthetic oxides and minerals Structural formulae ofminerals were calculated using the software of Ulmer(1986) with the exception of chloritoid (12-oxygenanhydrous basis Chopin et al 1992 and Fe3thorn as 4ndash(Al thorn Ti) Azanon amp Goffe 1997)

Electron back-scattered diffraction (EBSD) images andpole figures of the KyAnd transformation from a quartz-rich vein (sample Ben43 Fig 1c) were made with a LeoGEMINI-1530 scanning electron microscope (SEM)equipped with an Inca Crystal detector The diffractionpattern once indexed provides information on the orienta-tion of the crystal lattice Data from different positionswere integrated to perform orientation maps and repre-sented as pole figures In the sample Z and Y axes coincidewith normal direction to the polished section and the traceof the main or more pervasive foliation respectivelyAndalusite is orthorhombic space group Pnnm withunit-cell parameters a frac14 77980 b frac14 79031 c frac14 55566A kyanite is triclinic space group P-1 with afrac14 71262 bfrac14 78520 c frac14 55724 A a frac14 8999 b frac14 10111 and g frac1410603 (from Winter amp Ghose 1979)

4 Results

41 Field relations

Metapelitic rocks of the Benamocarra Unit consist of alter-nating bands of quartz-rich and mica-rich domains inher-ited from the psammitic and pelitic layers of thesedimentary protolith (Figs 1d and 2a) The succession islithologically very monotonous and in the field a gradualdecrease in grain size is observed from bottom to top of thesuccession Porphyroblasts of And and Cld are sometimesvisible to the naked eye as dark crystals (Fig 2b) and thoseof Grt as orange-reddish spots the latter being most abun-dant towards the top of the succession The upwarddecrease in grain size is accompanied by the disappearanceof And preserved only as relic pseudomorphs in manycases towards the top of the succession

In addition to the lithological layering (S0) defined bythe alternation of minor amounts of pelites intercalatedwith psammite layers two foliations are visible in thefield within the Benamocarra schists (Fig 2a) The mostevident foliation in the field hereafter called S3 transposesprevious foliations S1 and S2 However S1 is observed onlyin thin section within Cld and Grt crystals and in graphite-rich microlithons (see below) The foliation S2 visible inthe field is found within the graphite-rich pelitic bandstransposed by S3 (arrows in Fig 2a) In these graphite-richmetapelitic layers andalusite prisms occur randomlyoriented in foliation S2 (Fig 2b) Quartz segregations fre-quently containing millimetric to centimetric Ab and pinkAnd crystals are very abundant and most of them certainlycrosscut the S2 foliation Nonetheless the late foliation S3frequently shears these And-bearing quartz-rich veinswhich are commonly found parallelized to the latter Theless deformed veins contain random aggregates of pinkAnd prisms (Fig 2c) However within the veins the pinkAnd crystals more frequently appear fractured and tecto-nically re-oriented boudinaged and strongly elongatedalong S3 Exceptionally blue kyanite prisms are inter-grown with andalusite prisms in deformed veins parallelto the S3 (Fig 2d) The KyAnd transformation has beenstudied in one of these samples collected near km 6 alongthe MA-149 road from Almachar to Moclinejo (sampleBen43 Fig 1c) Although the coexistence of blue Ky andpink And in veins has only rarely been mentioned in theliterature available on the Alpujarride Complex (Martın-Algarra 1987) the occurrence of quartzndashalbite veinsincluding Ky partially transformed to And is not exclusiveof the Benamocarra Unit and has also been observed insimilar schists of diverse Upper Alpujarride units N of theSierra de las Aguas in the Carratraca peridotite massif(Martın-Algarra 1987) close to Almunecar and in theSierra de la Alfaguara near Granada

42 Petrography

Two main mineral associations have been recognized inthe Benamocarra metapeliticmetapsammitic succession

340 A Sanchez-Navas et al

eschweizerbart_xxx

i) Ms thorn Bt thorn Pl thorn Cld thorn Grt And (upper part) ii)Ms thorn Bt thorn Pl thorn Cld thorn Grt thorn And Ky St thorn Crd(lower part) The petrographic study is focused mainlyon the textural relation between Cld And Grt Crd andfoliations S1 S2 and S3 Chloritoid crystals have grownrandomly oriented on a Gr-rich foliation (S1) in the Msthorn Bt thorn Pl thorn Cld thorn Grt thorn And schists of the upper partof the Benamocarra Unit (Fig 3a) Chloritoid frequentlyoccurs as post-S1 prismatic crystals within Gr-richmicaceous domains moderately affected by S3(Fig 3a) In some cases Cld prisms appear moderatelydeformed and partially or totally pseudomorphed by Qzthorn Ms thorn Bt and opaque phases (Fig 3b) In additionsome Cld crystals are clearly reoriented and sheared byS3 and embedded in a Bt-rich matrix (Fig 3c)

Andalusite appears strongly affected by the deformationD3 with tectonic reorientation boudinage and microfold-ing associated with the development of the S3 foliation(Fig 3dndashf) The And porphyroblasts are post-kinematicto S2 and formed after Cld Grt and St (Fig 3e) In somecases And overgrowsGrt crystals including Cld or containsrelics of St The foliation S3 is well defined by micro-shearbands filled by Qz deforming the Gr-rich domains and Andcrystals (Fig 3f)

Within the mica-rich and finer-grained domains that areless deformed by D3 in the Ms thorn Bt thorn Pl thorn Cld thorn Grt thornAnd Ky St thorn Crd micaschists of the lower part of theBenamocarra Unit the porphyroblasts of Cld and Grt grew

first and those of And and xenoblastic Crd formed laterenclosing both Grt and Cld (Fig 4andashb) The Bt and Andformed after destabilization of Grt (Fig 4c) Indents on110 of Grt indicate the dissolution of Grt perpendicularto these faces favoured by the presence of abundant inclu-sions of Qz distributed perpendicularly to these crystalfaces (Fig 4c) In some cases such small Qz inclusionsform a cross-like pattern that evokes the typical crystal-growth features of the And chiastolites (Fig 4c) Theplagioclase is prevalently albitic commonly encloses gra-phite layers defining S1 and is frequently fractured whencrossed by S3 Some relic St grains are preserved withinpoikilitic And crystals (Fig 3e) but form preferentiallysmall isolated and dismembered porphyroclasts shearedand wrapped by S2 Kyanite is very rarely present in theschists The And thorn Crd association postdating the Cld thornGrt association is strongly affected by the S3-relateddeformation (Fig 4bndashd)

The S3 foliation transposes the earlier foliations S1 andS2 which are preserved in graphite-rich micaceous micro-lithons or within porphyroblasts (S1 in early Cld Fig 3andashband S2 in later CrdAnd Figs 3dndashf 4b and d) in the micas-chists of the whole Benamocarra succession The S3 folia-tion forms a metamorphic banding made of alternating Qz-rich and micaceous layers (recrystallized Bt and Ms) ana-stomosed around the Qz grains and pelitic microlithons(Fig 3a) Syn-S3 micas also grew as pseudomorphs ofprevious minerals such as Cld and Crd A common

Fig 2 (a) Micaschists of Benamocarra Unit formed by light-grey quartzites alternating with black metapelite bands (arrows) transposed bythe S3 foliation (b) Surface view of the S2 foliation with randomly oriented post-kinematic andalusite porphyroblasts in black graphite-richmetapelites S3 foliation is here parallel to S2 and is defined by fine-grained muscovite (lighter areas) formed on and around andalusite (c)Andalusite rosettes in quartz-rich veins segregated within And-bearing graphite-rich schist (d) Kyanite partially transformed to And within asmall quartz segregation stretched along S3 blue pen for scale is 1 cm wide (online version in colour)

Transformation of kyanite to andalusite 341

eschweizerbart_xxx

secondary mineral phase is Chl which crystallizes as aproduct of destabilization of Bt Grt and Crd

Kyanite crystals partially replaced by andalusite (Fig 5)have been studied in detail from one QzndashAb vein from theintermediate part of the Benamocarra succession (sampleBen43) This post-S2 vein is strongly deformed and paral-lel to the S3 foliation (Fig 2d) which is defined by Mswithin the vein itself Both the Ky and the And crystals arefolded and fractured (Fig 5a) In some cases a single Kycrystal is directly replaced by more than one And prismthis is apparent in optical images by the different crystal-lographic orientations observed for replacing And(Fig 5b) and confirmed also in EBSD images (see below)

43 Mineral chemistry

Muscovite mineral chemistry shows two compositionalgroups (Table S1 freely available online asSupplementary material linked to this article on the GSWwebsite of the journal httpeurjmingeoscienceworldorgFig 6andashb) Most analyses belong to the first group which isconstituted of Ms flakes formed after D1 (primary Ms)with lower Si content (Si frac14 303ndash315 atoms per formulaunit apfu) low celadonitic substitution (Fe thorn Mg frac14003ndash012 apfu) and low K(K thorn Na thorn Ca) The secondgroup includes the Ms formed in relation to the D3 deforma-tion (recrystallized Ms) and exhibits a higher Si content

Fig 3 (a) Photomicrograph (plane polarised light) of a Gr-rich microlithon located between two Qz-rich shear bands defining S3 foliationCld porphyroblasts (arrows) postkinematic to the S1 foliation are preserved within the microlithon (b) Bt Ms and Qz pseudomorph after Cld(c) Lath-shaped crystals of Cld elongated along a shear band defining the S3 foliation In adjacent domains that are less affected by shearingCld crystals remain unoriented (d) Post-S2 And porphyroclasts sheared (arrow) and wrapped up by the S3 foliation defined by Qz rich bandsBt Ms and pre-S3 transposed Gr (e) And porphyroblasts including St relic and arranged on the S2 foliation (f) And porphyroblasts folded byD3 and including the S2 foliation defined by trail inclusions of Gr (online version in colour)

342 A Sanchez-Navas et al

eschweizerbart_xxx

i) Ms thorn Bt thorn Pl thorn Cld thorn Grt And (upper part) ii)Ms thorn Bt thorn Pl thorn Cld thorn Grt thorn And Ky St thorn Crd(lower part) The petrographic study is focused mainlyon the textural relation between Cld And Grt Crd andfoliations S1 S2 and S3 Chloritoid crystals have grownrandomly oriented on a Gr-rich foliation (S1) in the Msthorn Bt thorn Pl thorn Cld thorn Grt thorn And schists of the upper partof the Benamocarra Unit (Fig 3a) Chloritoid frequentlyoccurs as post-S1 prismatic crystals within Gr-richmicaceous domains moderately affected by S3(Fig 3a) In some cases Cld prisms appear moderatelydeformed and partially or totally pseudomorphed by Qzthorn Ms thorn Bt and opaque phases (Fig 3b) In additionsome Cld crystals are clearly reoriented and sheared byS3 and embedded in a Bt-rich matrix (Fig 3c)

Andalusite appears strongly affected by the deformationD3 with tectonic reorientation boudinage and microfold-ing associated with the development of the S3 foliation(Fig 3dndashf) The And porphyroblasts are post-kinematicto S2 and formed after Cld Grt and St (Fig 3e) In somecases And overgrowsGrt crystals including Cld or containsrelics of St The foliation S3 is well defined by micro-shearbands filled by Qz deforming the Gr-rich domains and Andcrystals (Fig 3f)

Within the mica-rich and finer-grained domains that areless deformed by D3 in the Ms thorn Bt thorn Pl thorn Cld thorn Grt thornAnd Ky St thorn Crd micaschists of the lower part of theBenamocarra Unit the porphyroblasts of Cld and Grt grew

first and those of And and xenoblastic Crd formed laterenclosing both Grt and Cld (Fig 4andashb) The Bt and Andformed after destabilization of Grt (Fig 4c) Indents on110 of Grt indicate the dissolution of Grt perpendicularto these faces favoured by the presence of abundant inclu-sions of Qz distributed perpendicularly to these crystalfaces (Fig 4c) In some cases such small Qz inclusionsform a cross-like pattern that evokes the typical crystal-growth features of the And chiastolites (Fig 4c) Theplagioclase is prevalently albitic commonly encloses gra-phite layers defining S1 and is frequently fractured whencrossed by S3 Some relic St grains are preserved withinpoikilitic And crystals (Fig 3e) but form preferentiallysmall isolated and dismembered porphyroclasts shearedand wrapped by S2 Kyanite is very rarely present in theschists The And thorn Crd association postdating the Cld thornGrt association is strongly affected by the S3-relateddeformation (Fig 4bndashd)

The S3 foliation transposes the earlier foliations S1 andS2 which are preserved in graphite-rich micaceous micro-lithons or within porphyroblasts (S1 in early Cld Fig 3andashband S2 in later CrdAnd Figs 3dndashf 4b and d) in the micas-chists of the whole Benamocarra succession The S3 folia-tion forms a metamorphic banding made of alternating Qz-rich and micaceous layers (recrystallized Bt and Ms) ana-stomosed around the Qz grains and pelitic microlithons(Fig 3a) Syn-S3 micas also grew as pseudomorphs ofprevious minerals such as Cld and Crd A common

Fig 2 (a) Micaschists of Benamocarra Unit formed by light-grey quartzites alternating with black metapelite bands (arrows) transposed bythe S3 foliation (b) Surface view of the S2 foliation with randomly oriented post-kinematic andalusite porphyroblasts in black graphite-richmetapelites S3 foliation is here parallel to S2 and is defined by fine-grained muscovite (lighter areas) formed on and around andalusite (c)Andalusite rosettes in quartz-rich veins segregated within And-bearing graphite-rich schist (d) Kyanite partially transformed to And within asmall quartz segregation stretched along S3 blue pen for scale is 1 cm wide (online version in colour)

Transformation of kyanite to andalusite 341

eschweizerbart_xxx

secondary mineral phase is Chl which crystallizes as aproduct of destabilization of Bt Grt and Crd

Kyanite crystals partially replaced by andalusite (Fig 5)have been studied in detail from one QzndashAb vein from theintermediate part of the Benamocarra succession (sampleBen43) This post-S2 vein is strongly deformed and paral-lel to the S3 foliation (Fig 2d) which is defined by Mswithin the vein itself Both the Ky and the And crystals arefolded and fractured (Fig 5a) In some cases a single Kycrystal is directly replaced by more than one And prismthis is apparent in optical images by the different crystal-lographic orientations observed for replacing And(Fig 5b) and confirmed also in EBSD images (see below)

43 Mineral chemistry

Muscovite mineral chemistry shows two compositionalgroups (Table S1 freely available online asSupplementary material linked to this article on the GSWwebsite of the journal httpeurjmingeoscienceworldorgFig 6andashb) Most analyses belong to the first group which isconstituted of Ms flakes formed after D1 (primary Ms)with lower Si content (Si frac14 303ndash315 atoms per formulaunit apfu) low celadonitic substitution (Fe thorn Mg frac14003ndash012 apfu) and low K(K thorn Na thorn Ca) The secondgroup includes the Ms formed in relation to the D3 deforma-tion (recrystallized Ms) and exhibits a higher Si content

Fig 3 (a) Photomicrograph (plane polarised light) of a Gr-rich microlithon located between two Qz-rich shear bands defining S3 foliationCld porphyroblasts (arrows) postkinematic to the S1 foliation are preserved within the microlithon (b) Bt Ms and Qz pseudomorph after Cld(c) Lath-shaped crystals of Cld elongated along a shear band defining the S3 foliation In adjacent domains that are less affected by shearingCld crystals remain unoriented (d) Post-S2 And porphyroclasts sheared (arrow) and wrapped up by the S3 foliation defined by Qz rich bandsBt Ms and pre-S3 transposed Gr (e) And porphyroblasts including St relic and arranged on the S2 foliation (f) And porphyroblasts folded byD3 and including the S2 foliation defined by trail inclusions of Gr (online version in colour)

342 A Sanchez-Navas et al

eschweizerbart_xxx

secondary mineral phase is Chl which crystallizes as aproduct of destabilization of Bt Grt and Crd

Kyanite crystals partially replaced by andalusite (Fig 5)have been studied in detail from one QzndashAb vein from theintermediate part of the Benamocarra succession (sampleBen43) This post-S2 vein is strongly deformed and paral-lel to the S3 foliation (Fig 2d) which is defined by Mswithin the vein itself Both the Ky and the And crystals arefolded and fractured (Fig 5a) In some cases a single Kycrystal is directly replaced by more than one And prismthis is apparent in optical images by the different crystal-lographic orientations observed for replacing And(Fig 5b) and confirmed also in EBSD images (see below)

43 Mineral chemistry

Muscovite mineral chemistry shows two compositionalgroups (Table S1 freely available online asSupplementary material linked to this article on the GSWwebsite of the journal httpeurjmingeoscienceworldorgFig 6andashb) Most analyses belong to the first group which isconstituted of Ms flakes formed after D1 (primary Ms)with lower Si content (Si frac14 303ndash315 atoms per formulaunit apfu) low celadonitic substitution (Fe thorn Mg frac14003ndash012 apfu) and low K(K thorn Na thorn Ca) The secondgroup includes the Ms formed in relation to the D3 deforma-tion (recrystallized Ms) and exhibits a higher Si content

Fig 3 (a) Photomicrograph (plane polarised light) of a Gr-rich microlithon located between two Qz-rich shear bands defining S3 foliationCld porphyroblasts (arrows) postkinematic to the S1 foliation are preserved within the microlithon (b) Bt Ms and Qz pseudomorph after Cld(c) Lath-shaped crystals of Cld elongated along a shear band defining the S3 foliation In adjacent domains that are less affected by shearingCld crystals remain unoriented (d) Post-S2 And porphyroclasts sheared (arrow) and wrapped up by the S3 foliation defined by Qz rich bandsBt Ms and pre-S3 transposed Gr (e) And porphyroblasts including St relic and arranged on the S2 foliation (f) And porphyroblasts folded byD3 and including the S2 foliation defined by trail inclusions of Gr (online version in colour)

342 A Sanchez-Navas et al

eschweizerbart_xxx

(321ndash323 Si apfu) and intermediate celadonitic substi-tution (XMg frac14 095ndash1)

Biotite composition is intermediate between phlogopiteand annite (XMg frac14 044ndash054 Table S2 in SupplementrayMaterial) Some chemical analyses indicate that Bt is par-tially transformed to Chl Sometimes Bt that formed alongS3 is completely transformed to Chl even if it preserves theusual optical features of Bt

Garnet composition is close to that of almandine Almfrac1463ndash74 Grs frac14 5ndash20 Prp frac14 4ndash10 and Sps frac14 0ndash9 (Table S3 Fig 6cndashd) In addition representative Grt com-position data reveal differences between cores and rims(Table S3) cores show a higher content of spessartine(XSps frac14 004ndash009) and a relative lower abundance inalmandine (XAlm frac14 063ndash070) whereas rims are depletedin spessartine (XSpsfrac14 000ndash004) with correlative increasein almandine (XAlm frac14 070ndash074) The Mg number doesnot change from cores to rims however Ca is slightlyhigher in garnet cores than in rims (Fig 6c)

Chloritoid is a Fe-Cld (Table S4) with a very low Mncontent (001ndash003 apfu) The Mg content invariablyincreases from cores (XMg frac14 011ndash013) to rims (XMg frac14013ndash016)

Chlorite forms at the expense of Bt and composition-ally is a chamosite with an XMg from 037 to 039

44 EBSD study of andalusite pseudomorphs afterkyanite

As mentioned above in the deformed QzndashAb vein withabundant Ky and And of sample Ben43 elongated Kycrystals are topotactically transformed to And Firstwe describe the partial replacement of a single Kycrystal by two And crystals with a different crystal-lographic orientation (Figs 5b 7 8) and later thetextural relations between Ky relics and enclosing neo-formed And (Fig 9)

Figure 7 shows the results of the EBSD study corre-sponding to Zone 1 of Fig 5b Poles corresponding to thedirection normal to the (100) Ky planes locate close to theZ axis in some pieces of the Ky crystal eg central part andlower left-hand side of the Ky (Z) orientation map(Fig 7e) Nevertheless in other pieces of the Ky crystalthe poles of the (010) planes are located along the Z axis(upper and lower parts of the main Ky crystal in Fig 7e)As shown by the Ky (X) orientation map and the corre-sponding 001 pole figure different orientations are alsoobservable for Ky (Fig 7f) However the poles corre-sponding to the normal to the (001) planes of the Ky crystalmainly locate near the X direction in the sample The ccrystallographic axis of the And crystal is sub-parallel to

Fig 4 (a) Photomicrograph (cross-polarised light) showing the textural relationship between Cld Grt altered Crd and And with fine-grainedMsand Bt And and Crd grow surrounding Grt and Cld Note the accumulations of Gr at the ends of the skeletal arms of the And crystal (arrows) (b)Xenoblastic Crd around Cld prims within mica-rich (fine-grained Ms) domains (crossed nicols) S3 foliation is defined by Qz-rich shear bandscrosscutting Crd whereas S1 and S2 foliations are parallelized and wrapped by Crd in the micaceous domains (c) Grt porphyroclasts wrapped byAnd both affected by the foliation S3 Grt appears partially dissolved and surrounded by Bt and Qz When well-preserved as in the Grt grain atthe bottom right-hand side of the image it exhibits crystal-growth features similar to those visible in And as is the development of the lsquolsquoxrsquorsquo-shaped inclusions pattern (arrows) And Bt and Qz formed after destabilization of Grt (d) Optical image of a Bt-schist with Crdthorn And relicsCrd is altered to fine-grained sericitic Ms Chl and minor Bt and appears dismembered and elongated along the Qz-rich bans related to the S3foliation the S2 defined by trails of Gr inclusions is preserved within relic And (white dotted line) (online version in colour)

Transformation of kyanite to andalusite 343

eschweizerbart_xxx

the Z direction in the And (Z) orientation map and thecorresponding 001 pole figure (Fig 7d)

Figure 8 shows the orientation of the second And crystalreplacing Ky in Zone 2 of Fig 5b In this case the c

crystallographic axis of the And crystal is sub-parallel tothe poles corresponding to the normal to the (001) planes ofthe precursory kyanite single crystal (compare Fig 8 withFig 7f)

Fig 6 Mineral chemistry data from the Benamocarra metapelites (units apfu) (a) Fe2thornthornMg vs Si ofMs (solid squares primaryMs blanksquares recrystallizedMs) (b) K(KthornNathornCa) vs Si diagram ofMs (c) Fe2thornndashMnndashCa diagram of garnet (blank circles cores solid circlesrims) (d) MnndashMgndashFe2thorn diagram of garnet

Fig 5 Optical images of folded And prims after Ky within QzndashPl veins within Msthorn Btthorn Plthorn Grtthorn Kythorn Stthorn And schists from the lowerpart of the Benamocarra Unit (a) Crossed-nicol images of elongated Ky crystals partially transformed to And Deformation of And and Kysingle crystals formed subgrains as revealed by undulatory extinction in crossed nicols (b) Two crystallographic orientations are visible inzones 1 and 2 for the And replacing Ky (crossed nicols) (online version in colour)

344 A Sanchez-Navas et al

eschweizerbart_xxx

Figure 9 corresponds to the EBSD study of an Andpseudomorph after Ky In this case small non-transformedrelics of the precursory Ky single crystal still remain withinthe And crystal (high-relief areas in background electro-nic-image) The crystallographic relations between the Kysingle crystal and the And are similar to those visible inZone 2 of Fig 5b Because EBSD orientation mappingcovers a large area it results in a large numbers of maximain the pole figures (Fig 9g) due to the presence of smallpieces of Ky and And with different orientation When thescanned region is restricted to a small area (so that onlyAnd close to the almost completely transformed Ky istaken into account) it can be appreciated that the c crystal-lographic axes of both phases are parallel whereas the a

and b axes are interchanged with an angular deviation of 6and 13 between the aAnd and bKy and between the bAnd andaKy respectively (Fig 9hndashi)

5 Discussion

51 Crystallography of the transformation of kyaniteto andalusite

The KyAnd transformation described here is a solution-mediated solid-solid reaction in which Al2SiO5 undergoesstructural changes without compositional changeAccording to the crystallographic relationships observed

Fig 7 EBSD results for zone 1 of Fig 5b (a) Optical image with indication of the area studied by EBSD (b) Phase map And (yellow) Ky(purple) and Qtz (red) (c) Electronic image with indication of the directions corresponding to the reference system in the sample Keyorientation colour maps for both And and Ky are also included (d) And orientationmap along Z (And (Z)) superposed onto the pattern qualitymap 001 pole figure for And is shown in the right-hand side of figure 7d (e) Ky orientationmap along Z (Ky (Z)) is projected onto the patternquality map Ky crystal has a lamellar structure with some packets having 010 parallel to Z (in green) whereas other packets have 100parallel to Z (in blue) (f) Orientation map for Ky along X (Ky (X)) and 001 pole figure of Ky (right-hand side) (online version in colour)

Transformation of kyanite to andalusite 345

eschweizerbart_xxx

for Ky and And this transformation is structurally con-trolled It means that the crystallographic orientation of theAnd was controlled by the orientation of Ky The structu-rally controlled Ky And transformation began at areaction site of high-energy density that in the studycase corresponds to a particular crystallographic plane ofthe Ky crystal structure At that site the atoms of the Kyreactant have enough energy to surmount the activationbarrier and to reorganize themselves to form And Aspreviously shown the Ky crystals partially transformedto And contain planar defects (Fig 7e)

Figure 10a shows the projection of diverse close-packedoxygen layers that form the anion sub-lattice in the Kystructure onto the (110) Ky crystallographic plane Thecoordination environment of anions forming the close-packed layers appears in Fig 10b Anion (110) layers(here designated as A B and C) form a closely packedroughly cubic array of oxygen atoms The closest-packed

array occurring in the Ky structure allows the developmentof complex stacking sequences (Fig 10c) and can beresponsible for the occurrence of planar defects in Ky(disoriented domains in the map of Fig 7e)

One specific crystallographic relation between reactionproduct and reactant is found in topotactic replacementsamong Al-silicates ie in the case of replacement of anda-lusite by mullitesillimanite (cAndjjcSilcMul aAndjjbSilbMul bAndjjaSilaMul Hulsmans et al 2000 Cesare et al2002) The mutual crystallographic orientation of Ky andAnd obtained from EBSD data in small areas of bothphases (Fig 10hndashi) deviates slightly from those topotacticrelationship proposed in the literature Nevertheless theAnd follows at least two main orientations when replacingKy (Figs 5b 7 and 8) It has been illustrated in Fig 11andashbwhere two And crystals grow with their c crystallographicaxes contained in Ky (110) planes that one of them coin-cides with cKy

Fig 8 EBSD results for zone 2 of Fig 5B (a) Pattern quality map (b) Optical image (crossed nicols) with indication of the area studied byEBSD (c) The same area is indicated on the background electronic image (d) Orientation map along X and 001 pole figure of And (left-handside) (online version in colour)

346 A Sanchez-Navas et al

eschweizerbart_xxx

Worden et al (1987) made a noteworthy observation inrelation to structurally controlled replacements amongoxygen-bearing minerals of different compositionAccording to these authors the crystallographic plane par-allel to the interface between reactant and product corre-sponds to a close-packed plane of the oxygen sub-lattice oftheir respective structures The two coexisting phases sharenearly the closest-packed anion layers in topotactic repla-cements where a definite crystallographic relation isobserved between host and inclusions (eg Shau et al1991) Lattice strain is reduced at the interface defined bythe shared closest-packed anion layers because intera-tomic distances and type of arrangement (hexanet) in oxy-gen layers are approximately the same on both sides of theinterface Figures 11c and d show the oxygen packing in(110) and (320) planes of the structures of Ky and Andrespectively The oxygen arrangement along the c

crystallographic axis of the And structure indicated inFig 11d fits any of the three directions within the (110)plane of the Ky (Fig 11c)

Atoms at the interface of one phase are partiallybonded to different neighbours in the adjacent phaseConsequently the change of oxygen coordination environ-ment at the interface with respect to the atom within thecrystal lattice affects the energy of the anion coordinationpolyhedron Burdett amp McLarnan (1984) established theidea that there is a tight positive correlation between theelectron-band structure energy of polymorphs and energycomputed by adding only local contribution from eachanion coordination polyhedron These authors emphasizedthe importance of the environment of anions where most ofthe valence electrons are located Moreover in their orbitalinterpretation of Paulingrsquos second rule they concluded thatthe anions with higher coordination numbers lead to a

Fig 9 EBSD study of And pseudormoph after Ky performed in an area preserving relics of precursory Ky (a) Phase map with And in yellowand Ky in purplish red (b) Orientation map for And along X (c) The area studied by EBSD is indicated on the background electronic image(d) Optical image (crossed nicols) (e) Orientation map for Ky along Z projected onto the quality map (f) Orientation map for Ky along X (g)001 100 and 010 pole figures of And and Ky The diverse number of maxima (at least two) in these pole figures is due to the presence ofsmaller pieces of And and Ky with different orientation than the main crystals (h) Pole figures of both phases from a smaller area includingonly And close to the transformed Ky and providing a single orientation (i) Pole figure for all three axes of both Ky and And deducedfrom G (online version in colour)

Transformation of kyanite to andalusite 347

eschweizerbart_xxx

structural destabilization In the case of silicates theseanions correspond to the so-called oversaturated oxygenanions of Zachariasen-Baur (Baur 1970) which areresponsible for unusually long Si-O bonds thus favouringbond-breaking Experimental evidence of minor structuralstability around oxygen atoms with higher coordinationnumber was provided by Bell amp Wilson (1977) andMeike (1989) who demonstrated that muscovite requiredmore strain energy to bring about dislocations than didbiotite and that faulting goes through the octahedrallayer (closest-packed oxygen layers with chains of edge-sharing octahedra within these anion layers)

The presence of chains of edge-sharing octahedra in thestructures of the three polymorphs of Al2SiO5 also weak-ens their stability according to rule 3 of Pauling Burdett ampMcLarnan (1984) showed that structures with edge or facesharing have distorted anion environments resulting inpoor anion hybridization and weaker metal-anion bondsThe weathering series KyAnd Sil has been explainedfrom a crystal chemical standpoint In Ky all Al atoms

locate in octahedral sites whereas in And half the Alatoms occupy five-coordinated sites and in Sil halfoccupy four-coordinated sites According to Velbel(1999) relative weathering rates within the Al2SiO5

group vary with the coordination number of Al theAl2SiO5 polymorph weathers more easily when the coor-dination number of Al is higher Nevertheless the traditionof considering only the cation coordination was con-demned as early as Bragg (1930) if the environment ofanions (and therefore half of the atoms of the structurewhere most of the valence electrons are located) is ignoredthe structural transformations among minerals cannot bewell explained

As illustrated in Fig 10b the oxygen coordination num-ber in the close-packed (110) planes of Ky is higher than 3whereas it is 3 or lower in the oxygen atoms of the And andSil structure Consequently according to the above discus-sion high-coordinated oxygen atoms in close-packedstructures are responsible for high local structural instabil-ities that favour the breaking andor reorganization of SindashObonds in response to the change in P-T conditions duringthe Ky And replacement

52 Kinetics of the Ky And reaction

In previous studies the Ky And polymorphic inversionin Alpujarride rocks has been interpreted in relation todecompression during the Alpine orogeny (Garcıa-Cascoamp Torres-Roldan 1996 Argles et al 1999) Grambling(1981) and Grambling amp Williams (1985) described theoccurrence of Ky And and And Sil reactions duringprograde conditions in rocks affected by a low-pressureregional metamorphism Nevertheless Pattison (2001)indicates that these Al2SiO5-bearing rocks were involvedin decompressional P-T paths traversing in order the KySil and And fields Kerrick (1988) studied the transforma-tion of Ky And in Al2SiO5-bearing segregations duringretrograde decompression of rocks from the LepontineAlps He concluded that the Ky And reaction wascatalysed by fluids derived from metamorphic dehydrationreactions in the host rock Sanchez-Navas et al (2012)have shown that the dissolutionprecipitation of alumino-silicate minerals is easier if the reaction involves OH-bearing minerals These authors studied the opposite trans-formation (And Ky) in Grt St Ky And Fi Crd Gr-bearing micaschists of the Torrox Unit whichtectonically underlies the Benamocarra Unit and con-cluded that dehydration reactions of Ms and Bt providedthe chemical driving force needed to break SindashO bonds

In the Benamocarra Unit the energy necessary to over-come the activation barrier of the KyAnd reaction couldhave been provided by a temperature increase instead of apressure increase To envisage how a pressure increasehelps the activation energy barrier to be overcome weneed to consider only the fact that energy density is(dimensionally) equivalent to pressure Nevertheless it ismuch easier to interpret the Ky And reaction foundwithin the Benamocarra schist sequence in relation to a

Fig 10 (a) Projection onto (110) planes of the layers of type A (bluespheres) B (red spheres) and C (green spheres) forming a lsquolsquopseudo-cubicrsquorsquo closest-packed array of oxygen atoms in the Ky structure (b)First coordination sphere around the oxygen atoms (red spheres)forming one closest-packed layer The cations coordinating the Oatoms are Si (grey spheres) and Al (blue and purple spheres) (c)Stacking sequence corresponding to the crystallographic orienta-tions shown in the Fig 7E for the Ky The trace of the (110) latticeplanes and the orientation of the crystallographic axes for the differ-ent coherent domains within the structure are also shown in thefigure (online version in colour)

348 A Sanchez-Navas et al

eschweizerbart_xxx

high- thermal-gradient metamorphism and maximum tem-perature close to 550 C that reached a maximum pressurearound 04 GPa close to that defined by the Al2SiO5 triplepoint (see below)

53 Evidence of a high-thermal-gradientmetamorphism

The reaction pathway proposed above for the Ky Andtransformation found within QzndashAb veins is compatiblewith the metamorphic evolution inferred from the enclos-ing schists The petrographic data indicate an early pro-grade metamorphic stage related to burial and heatingevidenced in the schists by blastesis of post-S1 Cld andGrt porphyroblasts (Figs 3andashc 4andashc) The growth of CldGrt St and Ky in the schists was probably slightly olderthan (or coeval to) the opening of QndashAb veins and relatedformation of cm-sized Ky crystals

The blastesis of Cld Grt St and Ky predated the para-morphic replacement of Ky crystals by And in the veinswhich was probably associated with the generalized blast-esis of post-S2 And (and locally of Crd) in the schists Thisreflects the evolution from an initial intermediate-PBarrovian metamorphism to medium-T and low-P meta-morphic conditions Deformation during decompressionled to the formation of the S2 foliation sealed by Andand in the widespread occurrence of post-S2 veins filledby Qz Ab and And prisms which is a common featureof medium-grade schists equivalent to those ofBenamocarra frequently found in many Alpujarride units

When well preserved which is not always the case dueto younger deformation events in the Benamocarra micas-chists the larger porphyroblasts postdating the foliationsS1 and S2 in particular some of Grt and especially thoseof And show textural evidence of crystal growth understatic conditions (Fig 4a and c) In chiastolitic andalusitethe crystal-growth features consist of graphite accumula-tions at the edges of the prism faces resulting from crystalgrowth normal to the flat faces (Fig 4a) In relation to Grtthe same conditions favoured the development of cross-like inclusion patterns of Qz grains perpendicular to rhom-bododecahedral faces (Fig 4c) Both patterns result from atype of crystal-growth mechanism related to static blastesisand for pre-Alpine And in the rocks of the Torrox Unitthis was called layeritic growth by Sanchez-Navas et al(2012) According to this mechanism the crystal-growthfeatures of both And chiastolites and Grt porphyroblastsresulted from a thermally activated fast growth normal tothe flat faces of crystals This growth was controlled byscrew dislocations emergent at the centre of the F-facesunder low-supersaturation conditions due to slow diffusionrates where the low matter supply was related to lowdeformation rate (Sanchez-Navas et al 2012) Thereforethe blastesis of And and Grt in the schists also occurredthrough a thermally activated process related to a progrademetamorphism in the same way as previously proposedfor the Ky And transformation in the veins

The normal chemical zoning pattern observed fromcores to rims in Grt also indicates a prograde growthcertainly due to a T increase (Fig 6cndashd Table S3) The

Fig 11 (a) and (b) Model proposed for the polymorphic inversion studied According to this model two And crystals nucleate and growwiththeir c crystallographic axes parallel to the (110) plane of Ky (c) Close-packed layer formed by O atoms parallel to the (110) plane of Kystructure (d) Close-packed array of O atoms along the c crystallographic axis of And (online version in colour)

Transformation of kyanite to andalusite 349

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

the Z direction in the And (Z) orientation map and thecorresponding 001 pole figure (Fig 7d)

Figure 8 shows the orientation of the second And crystalreplacing Ky in Zone 2 of Fig 5b In this case the c

crystallographic axis of the And crystal is sub-parallel tothe poles corresponding to the normal to the (001) planes ofthe precursory kyanite single crystal (compare Fig 8 withFig 7f)

Fig 6 Mineral chemistry data from the Benamocarra metapelites (units apfu) (a) Fe2thornthornMg vs Si ofMs (solid squares primaryMs blanksquares recrystallizedMs) (b) K(KthornNathornCa) vs Si diagram ofMs (c) Fe2thornndashMnndashCa diagram of garnet (blank circles cores solid circlesrims) (d) MnndashMgndashFe2thorn diagram of garnet

Fig 5 Optical images of folded And prims after Ky within QzndashPl veins within Msthorn Btthorn Plthorn Grtthorn Kythorn Stthorn And schists from the lowerpart of the Benamocarra Unit (a) Crossed-nicol images of elongated Ky crystals partially transformed to And Deformation of And and Kysingle crystals formed subgrains as revealed by undulatory extinction in crossed nicols (b) Two crystallographic orientations are visible inzones 1 and 2 for the And replacing Ky (crossed nicols) (online version in colour)

344 A Sanchez-Navas et al

eschweizerbart_xxx

Figure 9 corresponds to the EBSD study of an Andpseudomorph after Ky In this case small non-transformedrelics of the precursory Ky single crystal still remain withinthe And crystal (high-relief areas in background electro-nic-image) The crystallographic relations between the Kysingle crystal and the And are similar to those visible inZone 2 of Fig 5b Because EBSD orientation mappingcovers a large area it results in a large numbers of maximain the pole figures (Fig 9g) due to the presence of smallpieces of Ky and And with different orientation When thescanned region is restricted to a small area (so that onlyAnd close to the almost completely transformed Ky istaken into account) it can be appreciated that the c crystal-lographic axes of both phases are parallel whereas the a

and b axes are interchanged with an angular deviation of 6and 13 between the aAnd and bKy and between the bAnd andaKy respectively (Fig 9hndashi)

5 Discussion

51 Crystallography of the transformation of kyaniteto andalusite

The KyAnd transformation described here is a solution-mediated solid-solid reaction in which Al2SiO5 undergoesstructural changes without compositional changeAccording to the crystallographic relationships observed

Fig 7 EBSD results for zone 1 of Fig 5b (a) Optical image with indication of the area studied by EBSD (b) Phase map And (yellow) Ky(purple) and Qtz (red) (c) Electronic image with indication of the directions corresponding to the reference system in the sample Keyorientation colour maps for both And and Ky are also included (d) And orientationmap along Z (And (Z)) superposed onto the pattern qualitymap 001 pole figure for And is shown in the right-hand side of figure 7d (e) Ky orientationmap along Z (Ky (Z)) is projected onto the patternquality map Ky crystal has a lamellar structure with some packets having 010 parallel to Z (in green) whereas other packets have 100parallel to Z (in blue) (f) Orientation map for Ky along X (Ky (X)) and 001 pole figure of Ky (right-hand side) (online version in colour)

Transformation of kyanite to andalusite 345

eschweizerbart_xxx

for Ky and And this transformation is structurally con-trolled It means that the crystallographic orientation of theAnd was controlled by the orientation of Ky The structu-rally controlled Ky And transformation began at areaction site of high-energy density that in the studycase corresponds to a particular crystallographic plane ofthe Ky crystal structure At that site the atoms of the Kyreactant have enough energy to surmount the activationbarrier and to reorganize themselves to form And Aspreviously shown the Ky crystals partially transformedto And contain planar defects (Fig 7e)

Figure 10a shows the projection of diverse close-packedoxygen layers that form the anion sub-lattice in the Kystructure onto the (110) Ky crystallographic plane Thecoordination environment of anions forming the close-packed layers appears in Fig 10b Anion (110) layers(here designated as A B and C) form a closely packedroughly cubic array of oxygen atoms The closest-packed

array occurring in the Ky structure allows the developmentof complex stacking sequences (Fig 10c) and can beresponsible for the occurrence of planar defects in Ky(disoriented domains in the map of Fig 7e)

One specific crystallographic relation between reactionproduct and reactant is found in topotactic replacementsamong Al-silicates ie in the case of replacement of anda-lusite by mullitesillimanite (cAndjjcSilcMul aAndjjbSilbMul bAndjjaSilaMul Hulsmans et al 2000 Cesare et al2002) The mutual crystallographic orientation of Ky andAnd obtained from EBSD data in small areas of bothphases (Fig 10hndashi) deviates slightly from those topotacticrelationship proposed in the literature Nevertheless theAnd follows at least two main orientations when replacingKy (Figs 5b 7 and 8) It has been illustrated in Fig 11andashbwhere two And crystals grow with their c crystallographicaxes contained in Ky (110) planes that one of them coin-cides with cKy

Fig 8 EBSD results for zone 2 of Fig 5B (a) Pattern quality map (b) Optical image (crossed nicols) with indication of the area studied byEBSD (c) The same area is indicated on the background electronic image (d) Orientation map along X and 001 pole figure of And (left-handside) (online version in colour)

346 A Sanchez-Navas et al

eschweizerbart_xxx

Worden et al (1987) made a noteworthy observation inrelation to structurally controlled replacements amongoxygen-bearing minerals of different compositionAccording to these authors the crystallographic plane par-allel to the interface between reactant and product corre-sponds to a close-packed plane of the oxygen sub-lattice oftheir respective structures The two coexisting phases sharenearly the closest-packed anion layers in topotactic repla-cements where a definite crystallographic relation isobserved between host and inclusions (eg Shau et al1991) Lattice strain is reduced at the interface defined bythe shared closest-packed anion layers because intera-tomic distances and type of arrangement (hexanet) in oxy-gen layers are approximately the same on both sides of theinterface Figures 11c and d show the oxygen packing in(110) and (320) planes of the structures of Ky and Andrespectively The oxygen arrangement along the c

crystallographic axis of the And structure indicated inFig 11d fits any of the three directions within the (110)plane of the Ky (Fig 11c)

Atoms at the interface of one phase are partiallybonded to different neighbours in the adjacent phaseConsequently the change of oxygen coordination environ-ment at the interface with respect to the atom within thecrystal lattice affects the energy of the anion coordinationpolyhedron Burdett amp McLarnan (1984) established theidea that there is a tight positive correlation between theelectron-band structure energy of polymorphs and energycomputed by adding only local contribution from eachanion coordination polyhedron These authors emphasizedthe importance of the environment of anions where most ofthe valence electrons are located Moreover in their orbitalinterpretation of Paulingrsquos second rule they concluded thatthe anions with higher coordination numbers lead to a

Fig 9 EBSD study of And pseudormoph after Ky performed in an area preserving relics of precursory Ky (a) Phase map with And in yellowand Ky in purplish red (b) Orientation map for And along X (c) The area studied by EBSD is indicated on the background electronic image(d) Optical image (crossed nicols) (e) Orientation map for Ky along Z projected onto the quality map (f) Orientation map for Ky along X (g)001 100 and 010 pole figures of And and Ky The diverse number of maxima (at least two) in these pole figures is due to the presence ofsmaller pieces of And and Ky with different orientation than the main crystals (h) Pole figures of both phases from a smaller area includingonly And close to the transformed Ky and providing a single orientation (i) Pole figure for all three axes of both Ky and And deducedfrom G (online version in colour)

Transformation of kyanite to andalusite 347

eschweizerbart_xxx

structural destabilization In the case of silicates theseanions correspond to the so-called oversaturated oxygenanions of Zachariasen-Baur (Baur 1970) which areresponsible for unusually long Si-O bonds thus favouringbond-breaking Experimental evidence of minor structuralstability around oxygen atoms with higher coordinationnumber was provided by Bell amp Wilson (1977) andMeike (1989) who demonstrated that muscovite requiredmore strain energy to bring about dislocations than didbiotite and that faulting goes through the octahedrallayer (closest-packed oxygen layers with chains of edge-sharing octahedra within these anion layers)

The presence of chains of edge-sharing octahedra in thestructures of the three polymorphs of Al2SiO5 also weak-ens their stability according to rule 3 of Pauling Burdett ampMcLarnan (1984) showed that structures with edge or facesharing have distorted anion environments resulting inpoor anion hybridization and weaker metal-anion bondsThe weathering series KyAnd Sil has been explainedfrom a crystal chemical standpoint In Ky all Al atoms

locate in octahedral sites whereas in And half the Alatoms occupy five-coordinated sites and in Sil halfoccupy four-coordinated sites According to Velbel(1999) relative weathering rates within the Al2SiO5

group vary with the coordination number of Al theAl2SiO5 polymorph weathers more easily when the coor-dination number of Al is higher Nevertheless the traditionof considering only the cation coordination was con-demned as early as Bragg (1930) if the environment ofanions (and therefore half of the atoms of the structurewhere most of the valence electrons are located) is ignoredthe structural transformations among minerals cannot bewell explained

As illustrated in Fig 10b the oxygen coordination num-ber in the close-packed (110) planes of Ky is higher than 3whereas it is 3 or lower in the oxygen atoms of the And andSil structure Consequently according to the above discus-sion high-coordinated oxygen atoms in close-packedstructures are responsible for high local structural instabil-ities that favour the breaking andor reorganization of SindashObonds in response to the change in P-T conditions duringthe Ky And replacement

52 Kinetics of the Ky And reaction

In previous studies the Ky And polymorphic inversionin Alpujarride rocks has been interpreted in relation todecompression during the Alpine orogeny (Garcıa-Cascoamp Torres-Roldan 1996 Argles et al 1999) Grambling(1981) and Grambling amp Williams (1985) described theoccurrence of Ky And and And Sil reactions duringprograde conditions in rocks affected by a low-pressureregional metamorphism Nevertheless Pattison (2001)indicates that these Al2SiO5-bearing rocks were involvedin decompressional P-T paths traversing in order the KySil and And fields Kerrick (1988) studied the transforma-tion of Ky And in Al2SiO5-bearing segregations duringretrograde decompression of rocks from the LepontineAlps He concluded that the Ky And reaction wascatalysed by fluids derived from metamorphic dehydrationreactions in the host rock Sanchez-Navas et al (2012)have shown that the dissolutionprecipitation of alumino-silicate minerals is easier if the reaction involves OH-bearing minerals These authors studied the opposite trans-formation (And Ky) in Grt St Ky And Fi Crd Gr-bearing micaschists of the Torrox Unit whichtectonically underlies the Benamocarra Unit and con-cluded that dehydration reactions of Ms and Bt providedthe chemical driving force needed to break SindashO bonds

In the Benamocarra Unit the energy necessary to over-come the activation barrier of the KyAnd reaction couldhave been provided by a temperature increase instead of apressure increase To envisage how a pressure increasehelps the activation energy barrier to be overcome weneed to consider only the fact that energy density is(dimensionally) equivalent to pressure Nevertheless it ismuch easier to interpret the Ky And reaction foundwithin the Benamocarra schist sequence in relation to a

Fig 10 (a) Projection onto (110) planes of the layers of type A (bluespheres) B (red spheres) and C (green spheres) forming a lsquolsquopseudo-cubicrsquorsquo closest-packed array of oxygen atoms in the Ky structure (b)First coordination sphere around the oxygen atoms (red spheres)forming one closest-packed layer The cations coordinating the Oatoms are Si (grey spheres) and Al (blue and purple spheres) (c)Stacking sequence corresponding to the crystallographic orienta-tions shown in the Fig 7E for the Ky The trace of the (110) latticeplanes and the orientation of the crystallographic axes for the differ-ent coherent domains within the structure are also shown in thefigure (online version in colour)

348 A Sanchez-Navas et al

eschweizerbart_xxx

high- thermal-gradient metamorphism and maximum tem-perature close to 550 C that reached a maximum pressurearound 04 GPa close to that defined by the Al2SiO5 triplepoint (see below)

53 Evidence of a high-thermal-gradientmetamorphism

The reaction pathway proposed above for the Ky Andtransformation found within QzndashAb veins is compatiblewith the metamorphic evolution inferred from the enclos-ing schists The petrographic data indicate an early pro-grade metamorphic stage related to burial and heatingevidenced in the schists by blastesis of post-S1 Cld andGrt porphyroblasts (Figs 3andashc 4andashc) The growth of CldGrt St and Ky in the schists was probably slightly olderthan (or coeval to) the opening of QndashAb veins and relatedformation of cm-sized Ky crystals

The blastesis of Cld Grt St and Ky predated the para-morphic replacement of Ky crystals by And in the veinswhich was probably associated with the generalized blast-esis of post-S2 And (and locally of Crd) in the schists Thisreflects the evolution from an initial intermediate-PBarrovian metamorphism to medium-T and low-P meta-morphic conditions Deformation during decompressionled to the formation of the S2 foliation sealed by Andand in the widespread occurrence of post-S2 veins filledby Qz Ab and And prisms which is a common featureof medium-grade schists equivalent to those ofBenamocarra frequently found in many Alpujarride units

When well preserved which is not always the case dueto younger deformation events in the Benamocarra micas-chists the larger porphyroblasts postdating the foliationsS1 and S2 in particular some of Grt and especially thoseof And show textural evidence of crystal growth understatic conditions (Fig 4a and c) In chiastolitic andalusitethe crystal-growth features consist of graphite accumula-tions at the edges of the prism faces resulting from crystalgrowth normal to the flat faces (Fig 4a) In relation to Grtthe same conditions favoured the development of cross-like inclusion patterns of Qz grains perpendicular to rhom-bododecahedral faces (Fig 4c) Both patterns result from atype of crystal-growth mechanism related to static blastesisand for pre-Alpine And in the rocks of the Torrox Unitthis was called layeritic growth by Sanchez-Navas et al(2012) According to this mechanism the crystal-growthfeatures of both And chiastolites and Grt porphyroblastsresulted from a thermally activated fast growth normal tothe flat faces of crystals This growth was controlled byscrew dislocations emergent at the centre of the F-facesunder low-supersaturation conditions due to slow diffusionrates where the low matter supply was related to lowdeformation rate (Sanchez-Navas et al 2012) Thereforethe blastesis of And and Grt in the schists also occurredthrough a thermally activated process related to a progrademetamorphism in the same way as previously proposedfor the Ky And transformation in the veins

The normal chemical zoning pattern observed fromcores to rims in Grt also indicates a prograde growthcertainly due to a T increase (Fig 6cndashd Table S3) The

Fig 11 (a) and (b) Model proposed for the polymorphic inversion studied According to this model two And crystals nucleate and growwiththeir c crystallographic axes parallel to the (110) plane of Ky (c) Close-packed layer formed by O atoms parallel to the (110) plane of Kystructure (d) Close-packed array of O atoms along the c crystallographic axis of And (online version in colour)

Transformation of kyanite to andalusite 349

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

Figure 9 corresponds to the EBSD study of an Andpseudomorph after Ky In this case small non-transformedrelics of the precursory Ky single crystal still remain withinthe And crystal (high-relief areas in background electro-nic-image) The crystallographic relations between the Kysingle crystal and the And are similar to those visible inZone 2 of Fig 5b Because EBSD orientation mappingcovers a large area it results in a large numbers of maximain the pole figures (Fig 9g) due to the presence of smallpieces of Ky and And with different orientation When thescanned region is restricted to a small area (so that onlyAnd close to the almost completely transformed Ky istaken into account) it can be appreciated that the c crystal-lographic axes of both phases are parallel whereas the a

and b axes are interchanged with an angular deviation of 6and 13 between the aAnd and bKy and between the bAnd andaKy respectively (Fig 9hndashi)

5 Discussion

51 Crystallography of the transformation of kyaniteto andalusite

The KyAnd transformation described here is a solution-mediated solid-solid reaction in which Al2SiO5 undergoesstructural changes without compositional changeAccording to the crystallographic relationships observed

Fig 7 EBSD results for zone 1 of Fig 5b (a) Optical image with indication of the area studied by EBSD (b) Phase map And (yellow) Ky(purple) and Qtz (red) (c) Electronic image with indication of the directions corresponding to the reference system in the sample Keyorientation colour maps for both And and Ky are also included (d) And orientationmap along Z (And (Z)) superposed onto the pattern qualitymap 001 pole figure for And is shown in the right-hand side of figure 7d (e) Ky orientationmap along Z (Ky (Z)) is projected onto the patternquality map Ky crystal has a lamellar structure with some packets having 010 parallel to Z (in green) whereas other packets have 100parallel to Z (in blue) (f) Orientation map for Ky along X (Ky (X)) and 001 pole figure of Ky (right-hand side) (online version in colour)

Transformation of kyanite to andalusite 345

eschweizerbart_xxx

for Ky and And this transformation is structurally con-trolled It means that the crystallographic orientation of theAnd was controlled by the orientation of Ky The structu-rally controlled Ky And transformation began at areaction site of high-energy density that in the studycase corresponds to a particular crystallographic plane ofthe Ky crystal structure At that site the atoms of the Kyreactant have enough energy to surmount the activationbarrier and to reorganize themselves to form And Aspreviously shown the Ky crystals partially transformedto And contain planar defects (Fig 7e)

Figure 10a shows the projection of diverse close-packedoxygen layers that form the anion sub-lattice in the Kystructure onto the (110) Ky crystallographic plane Thecoordination environment of anions forming the close-packed layers appears in Fig 10b Anion (110) layers(here designated as A B and C) form a closely packedroughly cubic array of oxygen atoms The closest-packed

array occurring in the Ky structure allows the developmentof complex stacking sequences (Fig 10c) and can beresponsible for the occurrence of planar defects in Ky(disoriented domains in the map of Fig 7e)

One specific crystallographic relation between reactionproduct and reactant is found in topotactic replacementsamong Al-silicates ie in the case of replacement of anda-lusite by mullitesillimanite (cAndjjcSilcMul aAndjjbSilbMul bAndjjaSilaMul Hulsmans et al 2000 Cesare et al2002) The mutual crystallographic orientation of Ky andAnd obtained from EBSD data in small areas of bothphases (Fig 10hndashi) deviates slightly from those topotacticrelationship proposed in the literature Nevertheless theAnd follows at least two main orientations when replacingKy (Figs 5b 7 and 8) It has been illustrated in Fig 11andashbwhere two And crystals grow with their c crystallographicaxes contained in Ky (110) planes that one of them coin-cides with cKy

Fig 8 EBSD results for zone 2 of Fig 5B (a) Pattern quality map (b) Optical image (crossed nicols) with indication of the area studied byEBSD (c) The same area is indicated on the background electronic image (d) Orientation map along X and 001 pole figure of And (left-handside) (online version in colour)

346 A Sanchez-Navas et al

eschweizerbart_xxx

Worden et al (1987) made a noteworthy observation inrelation to structurally controlled replacements amongoxygen-bearing minerals of different compositionAccording to these authors the crystallographic plane par-allel to the interface between reactant and product corre-sponds to a close-packed plane of the oxygen sub-lattice oftheir respective structures The two coexisting phases sharenearly the closest-packed anion layers in topotactic repla-cements where a definite crystallographic relation isobserved between host and inclusions (eg Shau et al1991) Lattice strain is reduced at the interface defined bythe shared closest-packed anion layers because intera-tomic distances and type of arrangement (hexanet) in oxy-gen layers are approximately the same on both sides of theinterface Figures 11c and d show the oxygen packing in(110) and (320) planes of the structures of Ky and Andrespectively The oxygen arrangement along the c

crystallographic axis of the And structure indicated inFig 11d fits any of the three directions within the (110)plane of the Ky (Fig 11c)

Atoms at the interface of one phase are partiallybonded to different neighbours in the adjacent phaseConsequently the change of oxygen coordination environ-ment at the interface with respect to the atom within thecrystal lattice affects the energy of the anion coordinationpolyhedron Burdett amp McLarnan (1984) established theidea that there is a tight positive correlation between theelectron-band structure energy of polymorphs and energycomputed by adding only local contribution from eachanion coordination polyhedron These authors emphasizedthe importance of the environment of anions where most ofthe valence electrons are located Moreover in their orbitalinterpretation of Paulingrsquos second rule they concluded thatthe anions with higher coordination numbers lead to a

Fig 9 EBSD study of And pseudormoph after Ky performed in an area preserving relics of precursory Ky (a) Phase map with And in yellowand Ky in purplish red (b) Orientation map for And along X (c) The area studied by EBSD is indicated on the background electronic image(d) Optical image (crossed nicols) (e) Orientation map for Ky along Z projected onto the quality map (f) Orientation map for Ky along X (g)001 100 and 010 pole figures of And and Ky The diverse number of maxima (at least two) in these pole figures is due to the presence ofsmaller pieces of And and Ky with different orientation than the main crystals (h) Pole figures of both phases from a smaller area includingonly And close to the transformed Ky and providing a single orientation (i) Pole figure for all three axes of both Ky and And deducedfrom G (online version in colour)

Transformation of kyanite to andalusite 347

eschweizerbart_xxx

structural destabilization In the case of silicates theseanions correspond to the so-called oversaturated oxygenanions of Zachariasen-Baur (Baur 1970) which areresponsible for unusually long Si-O bonds thus favouringbond-breaking Experimental evidence of minor structuralstability around oxygen atoms with higher coordinationnumber was provided by Bell amp Wilson (1977) andMeike (1989) who demonstrated that muscovite requiredmore strain energy to bring about dislocations than didbiotite and that faulting goes through the octahedrallayer (closest-packed oxygen layers with chains of edge-sharing octahedra within these anion layers)

The presence of chains of edge-sharing octahedra in thestructures of the three polymorphs of Al2SiO5 also weak-ens their stability according to rule 3 of Pauling Burdett ampMcLarnan (1984) showed that structures with edge or facesharing have distorted anion environments resulting inpoor anion hybridization and weaker metal-anion bondsThe weathering series KyAnd Sil has been explainedfrom a crystal chemical standpoint In Ky all Al atoms

locate in octahedral sites whereas in And half the Alatoms occupy five-coordinated sites and in Sil halfoccupy four-coordinated sites According to Velbel(1999) relative weathering rates within the Al2SiO5

group vary with the coordination number of Al theAl2SiO5 polymorph weathers more easily when the coor-dination number of Al is higher Nevertheless the traditionof considering only the cation coordination was con-demned as early as Bragg (1930) if the environment ofanions (and therefore half of the atoms of the structurewhere most of the valence electrons are located) is ignoredthe structural transformations among minerals cannot bewell explained

As illustrated in Fig 10b the oxygen coordination num-ber in the close-packed (110) planes of Ky is higher than 3whereas it is 3 or lower in the oxygen atoms of the And andSil structure Consequently according to the above discus-sion high-coordinated oxygen atoms in close-packedstructures are responsible for high local structural instabil-ities that favour the breaking andor reorganization of SindashObonds in response to the change in P-T conditions duringthe Ky And replacement

52 Kinetics of the Ky And reaction

In previous studies the Ky And polymorphic inversionin Alpujarride rocks has been interpreted in relation todecompression during the Alpine orogeny (Garcıa-Cascoamp Torres-Roldan 1996 Argles et al 1999) Grambling(1981) and Grambling amp Williams (1985) described theoccurrence of Ky And and And Sil reactions duringprograde conditions in rocks affected by a low-pressureregional metamorphism Nevertheless Pattison (2001)indicates that these Al2SiO5-bearing rocks were involvedin decompressional P-T paths traversing in order the KySil and And fields Kerrick (1988) studied the transforma-tion of Ky And in Al2SiO5-bearing segregations duringretrograde decompression of rocks from the LepontineAlps He concluded that the Ky And reaction wascatalysed by fluids derived from metamorphic dehydrationreactions in the host rock Sanchez-Navas et al (2012)have shown that the dissolutionprecipitation of alumino-silicate minerals is easier if the reaction involves OH-bearing minerals These authors studied the opposite trans-formation (And Ky) in Grt St Ky And Fi Crd Gr-bearing micaschists of the Torrox Unit whichtectonically underlies the Benamocarra Unit and con-cluded that dehydration reactions of Ms and Bt providedthe chemical driving force needed to break SindashO bonds

In the Benamocarra Unit the energy necessary to over-come the activation barrier of the KyAnd reaction couldhave been provided by a temperature increase instead of apressure increase To envisage how a pressure increasehelps the activation energy barrier to be overcome weneed to consider only the fact that energy density is(dimensionally) equivalent to pressure Nevertheless it ismuch easier to interpret the Ky And reaction foundwithin the Benamocarra schist sequence in relation to a

Fig 10 (a) Projection onto (110) planes of the layers of type A (bluespheres) B (red spheres) and C (green spheres) forming a lsquolsquopseudo-cubicrsquorsquo closest-packed array of oxygen atoms in the Ky structure (b)First coordination sphere around the oxygen atoms (red spheres)forming one closest-packed layer The cations coordinating the Oatoms are Si (grey spheres) and Al (blue and purple spheres) (c)Stacking sequence corresponding to the crystallographic orienta-tions shown in the Fig 7E for the Ky The trace of the (110) latticeplanes and the orientation of the crystallographic axes for the differ-ent coherent domains within the structure are also shown in thefigure (online version in colour)

348 A Sanchez-Navas et al

eschweizerbart_xxx

high- thermal-gradient metamorphism and maximum tem-perature close to 550 C that reached a maximum pressurearound 04 GPa close to that defined by the Al2SiO5 triplepoint (see below)

53 Evidence of a high-thermal-gradientmetamorphism

The reaction pathway proposed above for the Ky Andtransformation found within QzndashAb veins is compatiblewith the metamorphic evolution inferred from the enclos-ing schists The petrographic data indicate an early pro-grade metamorphic stage related to burial and heatingevidenced in the schists by blastesis of post-S1 Cld andGrt porphyroblasts (Figs 3andashc 4andashc) The growth of CldGrt St and Ky in the schists was probably slightly olderthan (or coeval to) the opening of QndashAb veins and relatedformation of cm-sized Ky crystals

The blastesis of Cld Grt St and Ky predated the para-morphic replacement of Ky crystals by And in the veinswhich was probably associated with the generalized blast-esis of post-S2 And (and locally of Crd) in the schists Thisreflects the evolution from an initial intermediate-PBarrovian metamorphism to medium-T and low-P meta-morphic conditions Deformation during decompressionled to the formation of the S2 foliation sealed by Andand in the widespread occurrence of post-S2 veins filledby Qz Ab and And prisms which is a common featureof medium-grade schists equivalent to those ofBenamocarra frequently found in many Alpujarride units

When well preserved which is not always the case dueto younger deformation events in the Benamocarra micas-chists the larger porphyroblasts postdating the foliationsS1 and S2 in particular some of Grt and especially thoseof And show textural evidence of crystal growth understatic conditions (Fig 4a and c) In chiastolitic andalusitethe crystal-growth features consist of graphite accumula-tions at the edges of the prism faces resulting from crystalgrowth normal to the flat faces (Fig 4a) In relation to Grtthe same conditions favoured the development of cross-like inclusion patterns of Qz grains perpendicular to rhom-bododecahedral faces (Fig 4c) Both patterns result from atype of crystal-growth mechanism related to static blastesisand for pre-Alpine And in the rocks of the Torrox Unitthis was called layeritic growth by Sanchez-Navas et al(2012) According to this mechanism the crystal-growthfeatures of both And chiastolites and Grt porphyroblastsresulted from a thermally activated fast growth normal tothe flat faces of crystals This growth was controlled byscrew dislocations emergent at the centre of the F-facesunder low-supersaturation conditions due to slow diffusionrates where the low matter supply was related to lowdeformation rate (Sanchez-Navas et al 2012) Thereforethe blastesis of And and Grt in the schists also occurredthrough a thermally activated process related to a progrademetamorphism in the same way as previously proposedfor the Ky And transformation in the veins

The normal chemical zoning pattern observed fromcores to rims in Grt also indicates a prograde growthcertainly due to a T increase (Fig 6cndashd Table S3) The

Fig 11 (a) and (b) Model proposed for the polymorphic inversion studied According to this model two And crystals nucleate and growwiththeir c crystallographic axes parallel to the (110) plane of Ky (c) Close-packed layer formed by O atoms parallel to the (110) plane of Kystructure (d) Close-packed array of O atoms along the c crystallographic axis of And (online version in colour)

Transformation of kyanite to andalusite 349

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

for Ky and And this transformation is structurally con-trolled It means that the crystallographic orientation of theAnd was controlled by the orientation of Ky The structu-rally controlled Ky And transformation began at areaction site of high-energy density that in the studycase corresponds to a particular crystallographic plane ofthe Ky crystal structure At that site the atoms of the Kyreactant have enough energy to surmount the activationbarrier and to reorganize themselves to form And Aspreviously shown the Ky crystals partially transformedto And contain planar defects (Fig 7e)

Figure 10a shows the projection of diverse close-packedoxygen layers that form the anion sub-lattice in the Kystructure onto the (110) Ky crystallographic plane Thecoordination environment of anions forming the close-packed layers appears in Fig 10b Anion (110) layers(here designated as A B and C) form a closely packedroughly cubic array of oxygen atoms The closest-packed

array occurring in the Ky structure allows the developmentof complex stacking sequences (Fig 10c) and can beresponsible for the occurrence of planar defects in Ky(disoriented domains in the map of Fig 7e)

One specific crystallographic relation between reactionproduct and reactant is found in topotactic replacementsamong Al-silicates ie in the case of replacement of anda-lusite by mullitesillimanite (cAndjjcSilcMul aAndjjbSilbMul bAndjjaSilaMul Hulsmans et al 2000 Cesare et al2002) The mutual crystallographic orientation of Ky andAnd obtained from EBSD data in small areas of bothphases (Fig 10hndashi) deviates slightly from those topotacticrelationship proposed in the literature Nevertheless theAnd follows at least two main orientations when replacingKy (Figs 5b 7 and 8) It has been illustrated in Fig 11andashbwhere two And crystals grow with their c crystallographicaxes contained in Ky (110) planes that one of them coin-cides with cKy

Fig 8 EBSD results for zone 2 of Fig 5B (a) Pattern quality map (b) Optical image (crossed nicols) with indication of the area studied byEBSD (c) The same area is indicated on the background electronic image (d) Orientation map along X and 001 pole figure of And (left-handside) (online version in colour)

346 A Sanchez-Navas et al

eschweizerbart_xxx

Worden et al (1987) made a noteworthy observation inrelation to structurally controlled replacements amongoxygen-bearing minerals of different compositionAccording to these authors the crystallographic plane par-allel to the interface between reactant and product corre-sponds to a close-packed plane of the oxygen sub-lattice oftheir respective structures The two coexisting phases sharenearly the closest-packed anion layers in topotactic repla-cements where a definite crystallographic relation isobserved between host and inclusions (eg Shau et al1991) Lattice strain is reduced at the interface defined bythe shared closest-packed anion layers because intera-tomic distances and type of arrangement (hexanet) in oxy-gen layers are approximately the same on both sides of theinterface Figures 11c and d show the oxygen packing in(110) and (320) planes of the structures of Ky and Andrespectively The oxygen arrangement along the c

crystallographic axis of the And structure indicated inFig 11d fits any of the three directions within the (110)plane of the Ky (Fig 11c)

Atoms at the interface of one phase are partiallybonded to different neighbours in the adjacent phaseConsequently the change of oxygen coordination environ-ment at the interface with respect to the atom within thecrystal lattice affects the energy of the anion coordinationpolyhedron Burdett amp McLarnan (1984) established theidea that there is a tight positive correlation between theelectron-band structure energy of polymorphs and energycomputed by adding only local contribution from eachanion coordination polyhedron These authors emphasizedthe importance of the environment of anions where most ofthe valence electrons are located Moreover in their orbitalinterpretation of Paulingrsquos second rule they concluded thatthe anions with higher coordination numbers lead to a

Fig 9 EBSD study of And pseudormoph after Ky performed in an area preserving relics of precursory Ky (a) Phase map with And in yellowand Ky in purplish red (b) Orientation map for And along X (c) The area studied by EBSD is indicated on the background electronic image(d) Optical image (crossed nicols) (e) Orientation map for Ky along Z projected onto the quality map (f) Orientation map for Ky along X (g)001 100 and 010 pole figures of And and Ky The diverse number of maxima (at least two) in these pole figures is due to the presence ofsmaller pieces of And and Ky with different orientation than the main crystals (h) Pole figures of both phases from a smaller area includingonly And close to the transformed Ky and providing a single orientation (i) Pole figure for all three axes of both Ky and And deducedfrom G (online version in colour)

Transformation of kyanite to andalusite 347

eschweizerbart_xxx

structural destabilization In the case of silicates theseanions correspond to the so-called oversaturated oxygenanions of Zachariasen-Baur (Baur 1970) which areresponsible for unusually long Si-O bonds thus favouringbond-breaking Experimental evidence of minor structuralstability around oxygen atoms with higher coordinationnumber was provided by Bell amp Wilson (1977) andMeike (1989) who demonstrated that muscovite requiredmore strain energy to bring about dislocations than didbiotite and that faulting goes through the octahedrallayer (closest-packed oxygen layers with chains of edge-sharing octahedra within these anion layers)

The presence of chains of edge-sharing octahedra in thestructures of the three polymorphs of Al2SiO5 also weak-ens their stability according to rule 3 of Pauling Burdett ampMcLarnan (1984) showed that structures with edge or facesharing have distorted anion environments resulting inpoor anion hybridization and weaker metal-anion bondsThe weathering series KyAnd Sil has been explainedfrom a crystal chemical standpoint In Ky all Al atoms

locate in octahedral sites whereas in And half the Alatoms occupy five-coordinated sites and in Sil halfoccupy four-coordinated sites According to Velbel(1999) relative weathering rates within the Al2SiO5

group vary with the coordination number of Al theAl2SiO5 polymorph weathers more easily when the coor-dination number of Al is higher Nevertheless the traditionof considering only the cation coordination was con-demned as early as Bragg (1930) if the environment ofanions (and therefore half of the atoms of the structurewhere most of the valence electrons are located) is ignoredthe structural transformations among minerals cannot bewell explained

As illustrated in Fig 10b the oxygen coordination num-ber in the close-packed (110) planes of Ky is higher than 3whereas it is 3 or lower in the oxygen atoms of the And andSil structure Consequently according to the above discus-sion high-coordinated oxygen atoms in close-packedstructures are responsible for high local structural instabil-ities that favour the breaking andor reorganization of SindashObonds in response to the change in P-T conditions duringthe Ky And replacement

52 Kinetics of the Ky And reaction

In previous studies the Ky And polymorphic inversionin Alpujarride rocks has been interpreted in relation todecompression during the Alpine orogeny (Garcıa-Cascoamp Torres-Roldan 1996 Argles et al 1999) Grambling(1981) and Grambling amp Williams (1985) described theoccurrence of Ky And and And Sil reactions duringprograde conditions in rocks affected by a low-pressureregional metamorphism Nevertheless Pattison (2001)indicates that these Al2SiO5-bearing rocks were involvedin decompressional P-T paths traversing in order the KySil and And fields Kerrick (1988) studied the transforma-tion of Ky And in Al2SiO5-bearing segregations duringretrograde decompression of rocks from the LepontineAlps He concluded that the Ky And reaction wascatalysed by fluids derived from metamorphic dehydrationreactions in the host rock Sanchez-Navas et al (2012)have shown that the dissolutionprecipitation of alumino-silicate minerals is easier if the reaction involves OH-bearing minerals These authors studied the opposite trans-formation (And Ky) in Grt St Ky And Fi Crd Gr-bearing micaschists of the Torrox Unit whichtectonically underlies the Benamocarra Unit and con-cluded that dehydration reactions of Ms and Bt providedthe chemical driving force needed to break SindashO bonds

In the Benamocarra Unit the energy necessary to over-come the activation barrier of the KyAnd reaction couldhave been provided by a temperature increase instead of apressure increase To envisage how a pressure increasehelps the activation energy barrier to be overcome weneed to consider only the fact that energy density is(dimensionally) equivalent to pressure Nevertheless it ismuch easier to interpret the Ky And reaction foundwithin the Benamocarra schist sequence in relation to a

Fig 10 (a) Projection onto (110) planes of the layers of type A (bluespheres) B (red spheres) and C (green spheres) forming a lsquolsquopseudo-cubicrsquorsquo closest-packed array of oxygen atoms in the Ky structure (b)First coordination sphere around the oxygen atoms (red spheres)forming one closest-packed layer The cations coordinating the Oatoms are Si (grey spheres) and Al (blue and purple spheres) (c)Stacking sequence corresponding to the crystallographic orienta-tions shown in the Fig 7E for the Ky The trace of the (110) latticeplanes and the orientation of the crystallographic axes for the differ-ent coherent domains within the structure are also shown in thefigure (online version in colour)

348 A Sanchez-Navas et al

eschweizerbart_xxx

high- thermal-gradient metamorphism and maximum tem-perature close to 550 C that reached a maximum pressurearound 04 GPa close to that defined by the Al2SiO5 triplepoint (see below)

53 Evidence of a high-thermal-gradientmetamorphism

The reaction pathway proposed above for the Ky Andtransformation found within QzndashAb veins is compatiblewith the metamorphic evolution inferred from the enclos-ing schists The petrographic data indicate an early pro-grade metamorphic stage related to burial and heatingevidenced in the schists by blastesis of post-S1 Cld andGrt porphyroblasts (Figs 3andashc 4andashc) The growth of CldGrt St and Ky in the schists was probably slightly olderthan (or coeval to) the opening of QndashAb veins and relatedformation of cm-sized Ky crystals

The blastesis of Cld Grt St and Ky predated the para-morphic replacement of Ky crystals by And in the veinswhich was probably associated with the generalized blast-esis of post-S2 And (and locally of Crd) in the schists Thisreflects the evolution from an initial intermediate-PBarrovian metamorphism to medium-T and low-P meta-morphic conditions Deformation during decompressionled to the formation of the S2 foliation sealed by Andand in the widespread occurrence of post-S2 veins filledby Qz Ab and And prisms which is a common featureof medium-grade schists equivalent to those ofBenamocarra frequently found in many Alpujarride units

When well preserved which is not always the case dueto younger deformation events in the Benamocarra micas-chists the larger porphyroblasts postdating the foliationsS1 and S2 in particular some of Grt and especially thoseof And show textural evidence of crystal growth understatic conditions (Fig 4a and c) In chiastolitic andalusitethe crystal-growth features consist of graphite accumula-tions at the edges of the prism faces resulting from crystalgrowth normal to the flat faces (Fig 4a) In relation to Grtthe same conditions favoured the development of cross-like inclusion patterns of Qz grains perpendicular to rhom-bododecahedral faces (Fig 4c) Both patterns result from atype of crystal-growth mechanism related to static blastesisand for pre-Alpine And in the rocks of the Torrox Unitthis was called layeritic growth by Sanchez-Navas et al(2012) According to this mechanism the crystal-growthfeatures of both And chiastolites and Grt porphyroblastsresulted from a thermally activated fast growth normal tothe flat faces of crystals This growth was controlled byscrew dislocations emergent at the centre of the F-facesunder low-supersaturation conditions due to slow diffusionrates where the low matter supply was related to lowdeformation rate (Sanchez-Navas et al 2012) Thereforethe blastesis of And and Grt in the schists also occurredthrough a thermally activated process related to a progrademetamorphism in the same way as previously proposedfor the Ky And transformation in the veins

The normal chemical zoning pattern observed fromcores to rims in Grt also indicates a prograde growthcertainly due to a T increase (Fig 6cndashd Table S3) The

Fig 11 (a) and (b) Model proposed for the polymorphic inversion studied According to this model two And crystals nucleate and growwiththeir c crystallographic axes parallel to the (110) plane of Ky (c) Close-packed layer formed by O atoms parallel to the (110) plane of Kystructure (d) Close-packed array of O atoms along the c crystallographic axis of And (online version in colour)

Transformation of kyanite to andalusite 349

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

Worden et al (1987) made a noteworthy observation inrelation to structurally controlled replacements amongoxygen-bearing minerals of different compositionAccording to these authors the crystallographic plane par-allel to the interface between reactant and product corre-sponds to a close-packed plane of the oxygen sub-lattice oftheir respective structures The two coexisting phases sharenearly the closest-packed anion layers in topotactic repla-cements where a definite crystallographic relation isobserved between host and inclusions (eg Shau et al1991) Lattice strain is reduced at the interface defined bythe shared closest-packed anion layers because intera-tomic distances and type of arrangement (hexanet) in oxy-gen layers are approximately the same on both sides of theinterface Figures 11c and d show the oxygen packing in(110) and (320) planes of the structures of Ky and Andrespectively The oxygen arrangement along the c

crystallographic axis of the And structure indicated inFig 11d fits any of the three directions within the (110)plane of the Ky (Fig 11c)

Atoms at the interface of one phase are partiallybonded to different neighbours in the adjacent phaseConsequently the change of oxygen coordination environ-ment at the interface with respect to the atom within thecrystal lattice affects the energy of the anion coordinationpolyhedron Burdett amp McLarnan (1984) established theidea that there is a tight positive correlation between theelectron-band structure energy of polymorphs and energycomputed by adding only local contribution from eachanion coordination polyhedron These authors emphasizedthe importance of the environment of anions where most ofthe valence electrons are located Moreover in their orbitalinterpretation of Paulingrsquos second rule they concluded thatthe anions with higher coordination numbers lead to a

Fig 9 EBSD study of And pseudormoph after Ky performed in an area preserving relics of precursory Ky (a) Phase map with And in yellowand Ky in purplish red (b) Orientation map for And along X (c) The area studied by EBSD is indicated on the background electronic image(d) Optical image (crossed nicols) (e) Orientation map for Ky along Z projected onto the quality map (f) Orientation map for Ky along X (g)001 100 and 010 pole figures of And and Ky The diverse number of maxima (at least two) in these pole figures is due to the presence ofsmaller pieces of And and Ky with different orientation than the main crystals (h) Pole figures of both phases from a smaller area includingonly And close to the transformed Ky and providing a single orientation (i) Pole figure for all three axes of both Ky and And deducedfrom G (online version in colour)

Transformation of kyanite to andalusite 347

eschweizerbart_xxx

structural destabilization In the case of silicates theseanions correspond to the so-called oversaturated oxygenanions of Zachariasen-Baur (Baur 1970) which areresponsible for unusually long Si-O bonds thus favouringbond-breaking Experimental evidence of minor structuralstability around oxygen atoms with higher coordinationnumber was provided by Bell amp Wilson (1977) andMeike (1989) who demonstrated that muscovite requiredmore strain energy to bring about dislocations than didbiotite and that faulting goes through the octahedrallayer (closest-packed oxygen layers with chains of edge-sharing octahedra within these anion layers)

The presence of chains of edge-sharing octahedra in thestructures of the three polymorphs of Al2SiO5 also weak-ens their stability according to rule 3 of Pauling Burdett ampMcLarnan (1984) showed that structures with edge or facesharing have distorted anion environments resulting inpoor anion hybridization and weaker metal-anion bondsThe weathering series KyAnd Sil has been explainedfrom a crystal chemical standpoint In Ky all Al atoms

locate in octahedral sites whereas in And half the Alatoms occupy five-coordinated sites and in Sil halfoccupy four-coordinated sites According to Velbel(1999) relative weathering rates within the Al2SiO5

group vary with the coordination number of Al theAl2SiO5 polymorph weathers more easily when the coor-dination number of Al is higher Nevertheless the traditionof considering only the cation coordination was con-demned as early as Bragg (1930) if the environment ofanions (and therefore half of the atoms of the structurewhere most of the valence electrons are located) is ignoredthe structural transformations among minerals cannot bewell explained

As illustrated in Fig 10b the oxygen coordination num-ber in the close-packed (110) planes of Ky is higher than 3whereas it is 3 or lower in the oxygen atoms of the And andSil structure Consequently according to the above discus-sion high-coordinated oxygen atoms in close-packedstructures are responsible for high local structural instabil-ities that favour the breaking andor reorganization of SindashObonds in response to the change in P-T conditions duringthe Ky And replacement

52 Kinetics of the Ky And reaction

In previous studies the Ky And polymorphic inversionin Alpujarride rocks has been interpreted in relation todecompression during the Alpine orogeny (Garcıa-Cascoamp Torres-Roldan 1996 Argles et al 1999) Grambling(1981) and Grambling amp Williams (1985) described theoccurrence of Ky And and And Sil reactions duringprograde conditions in rocks affected by a low-pressureregional metamorphism Nevertheless Pattison (2001)indicates that these Al2SiO5-bearing rocks were involvedin decompressional P-T paths traversing in order the KySil and And fields Kerrick (1988) studied the transforma-tion of Ky And in Al2SiO5-bearing segregations duringretrograde decompression of rocks from the LepontineAlps He concluded that the Ky And reaction wascatalysed by fluids derived from metamorphic dehydrationreactions in the host rock Sanchez-Navas et al (2012)have shown that the dissolutionprecipitation of alumino-silicate minerals is easier if the reaction involves OH-bearing minerals These authors studied the opposite trans-formation (And Ky) in Grt St Ky And Fi Crd Gr-bearing micaschists of the Torrox Unit whichtectonically underlies the Benamocarra Unit and con-cluded that dehydration reactions of Ms and Bt providedthe chemical driving force needed to break SindashO bonds

In the Benamocarra Unit the energy necessary to over-come the activation barrier of the KyAnd reaction couldhave been provided by a temperature increase instead of apressure increase To envisage how a pressure increasehelps the activation energy barrier to be overcome weneed to consider only the fact that energy density is(dimensionally) equivalent to pressure Nevertheless it ismuch easier to interpret the Ky And reaction foundwithin the Benamocarra schist sequence in relation to a

Fig 10 (a) Projection onto (110) planes of the layers of type A (bluespheres) B (red spheres) and C (green spheres) forming a lsquolsquopseudo-cubicrsquorsquo closest-packed array of oxygen atoms in the Ky structure (b)First coordination sphere around the oxygen atoms (red spheres)forming one closest-packed layer The cations coordinating the Oatoms are Si (grey spheres) and Al (blue and purple spheres) (c)Stacking sequence corresponding to the crystallographic orienta-tions shown in the Fig 7E for the Ky The trace of the (110) latticeplanes and the orientation of the crystallographic axes for the differ-ent coherent domains within the structure are also shown in thefigure (online version in colour)

348 A Sanchez-Navas et al

eschweizerbart_xxx

high- thermal-gradient metamorphism and maximum tem-perature close to 550 C that reached a maximum pressurearound 04 GPa close to that defined by the Al2SiO5 triplepoint (see below)

53 Evidence of a high-thermal-gradientmetamorphism

The reaction pathway proposed above for the Ky Andtransformation found within QzndashAb veins is compatiblewith the metamorphic evolution inferred from the enclos-ing schists The petrographic data indicate an early pro-grade metamorphic stage related to burial and heatingevidenced in the schists by blastesis of post-S1 Cld andGrt porphyroblasts (Figs 3andashc 4andashc) The growth of CldGrt St and Ky in the schists was probably slightly olderthan (or coeval to) the opening of QndashAb veins and relatedformation of cm-sized Ky crystals

The blastesis of Cld Grt St and Ky predated the para-morphic replacement of Ky crystals by And in the veinswhich was probably associated with the generalized blast-esis of post-S2 And (and locally of Crd) in the schists Thisreflects the evolution from an initial intermediate-PBarrovian metamorphism to medium-T and low-P meta-morphic conditions Deformation during decompressionled to the formation of the S2 foliation sealed by Andand in the widespread occurrence of post-S2 veins filledby Qz Ab and And prisms which is a common featureof medium-grade schists equivalent to those ofBenamocarra frequently found in many Alpujarride units

When well preserved which is not always the case dueto younger deformation events in the Benamocarra micas-chists the larger porphyroblasts postdating the foliationsS1 and S2 in particular some of Grt and especially thoseof And show textural evidence of crystal growth understatic conditions (Fig 4a and c) In chiastolitic andalusitethe crystal-growth features consist of graphite accumula-tions at the edges of the prism faces resulting from crystalgrowth normal to the flat faces (Fig 4a) In relation to Grtthe same conditions favoured the development of cross-like inclusion patterns of Qz grains perpendicular to rhom-bododecahedral faces (Fig 4c) Both patterns result from atype of crystal-growth mechanism related to static blastesisand for pre-Alpine And in the rocks of the Torrox Unitthis was called layeritic growth by Sanchez-Navas et al(2012) According to this mechanism the crystal-growthfeatures of both And chiastolites and Grt porphyroblastsresulted from a thermally activated fast growth normal tothe flat faces of crystals This growth was controlled byscrew dislocations emergent at the centre of the F-facesunder low-supersaturation conditions due to slow diffusionrates where the low matter supply was related to lowdeformation rate (Sanchez-Navas et al 2012) Thereforethe blastesis of And and Grt in the schists also occurredthrough a thermally activated process related to a progrademetamorphism in the same way as previously proposedfor the Ky And transformation in the veins

The normal chemical zoning pattern observed fromcores to rims in Grt also indicates a prograde growthcertainly due to a T increase (Fig 6cndashd Table S3) The

Fig 11 (a) and (b) Model proposed for the polymorphic inversion studied According to this model two And crystals nucleate and growwiththeir c crystallographic axes parallel to the (110) plane of Ky (c) Close-packed layer formed by O atoms parallel to the (110) plane of Kystructure (d) Close-packed array of O atoms along the c crystallographic axis of And (online version in colour)

Transformation of kyanite to andalusite 349

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

structural destabilization In the case of silicates theseanions correspond to the so-called oversaturated oxygenanions of Zachariasen-Baur (Baur 1970) which areresponsible for unusually long Si-O bonds thus favouringbond-breaking Experimental evidence of minor structuralstability around oxygen atoms with higher coordinationnumber was provided by Bell amp Wilson (1977) andMeike (1989) who demonstrated that muscovite requiredmore strain energy to bring about dislocations than didbiotite and that faulting goes through the octahedrallayer (closest-packed oxygen layers with chains of edge-sharing octahedra within these anion layers)

The presence of chains of edge-sharing octahedra in thestructures of the three polymorphs of Al2SiO5 also weak-ens their stability according to rule 3 of Pauling Burdett ampMcLarnan (1984) showed that structures with edge or facesharing have distorted anion environments resulting inpoor anion hybridization and weaker metal-anion bondsThe weathering series KyAnd Sil has been explainedfrom a crystal chemical standpoint In Ky all Al atoms

locate in octahedral sites whereas in And half the Alatoms occupy five-coordinated sites and in Sil halfoccupy four-coordinated sites According to Velbel(1999) relative weathering rates within the Al2SiO5

group vary with the coordination number of Al theAl2SiO5 polymorph weathers more easily when the coor-dination number of Al is higher Nevertheless the traditionof considering only the cation coordination was con-demned as early as Bragg (1930) if the environment ofanions (and therefore half of the atoms of the structurewhere most of the valence electrons are located) is ignoredthe structural transformations among minerals cannot bewell explained

As illustrated in Fig 10b the oxygen coordination num-ber in the close-packed (110) planes of Ky is higher than 3whereas it is 3 or lower in the oxygen atoms of the And andSil structure Consequently according to the above discus-sion high-coordinated oxygen atoms in close-packedstructures are responsible for high local structural instabil-ities that favour the breaking andor reorganization of SindashObonds in response to the change in P-T conditions duringthe Ky And replacement

52 Kinetics of the Ky And reaction

In previous studies the Ky And polymorphic inversionin Alpujarride rocks has been interpreted in relation todecompression during the Alpine orogeny (Garcıa-Cascoamp Torres-Roldan 1996 Argles et al 1999) Grambling(1981) and Grambling amp Williams (1985) described theoccurrence of Ky And and And Sil reactions duringprograde conditions in rocks affected by a low-pressureregional metamorphism Nevertheless Pattison (2001)indicates that these Al2SiO5-bearing rocks were involvedin decompressional P-T paths traversing in order the KySil and And fields Kerrick (1988) studied the transforma-tion of Ky And in Al2SiO5-bearing segregations duringretrograde decompression of rocks from the LepontineAlps He concluded that the Ky And reaction wascatalysed by fluids derived from metamorphic dehydrationreactions in the host rock Sanchez-Navas et al (2012)have shown that the dissolutionprecipitation of alumino-silicate minerals is easier if the reaction involves OH-bearing minerals These authors studied the opposite trans-formation (And Ky) in Grt St Ky And Fi Crd Gr-bearing micaschists of the Torrox Unit whichtectonically underlies the Benamocarra Unit and con-cluded that dehydration reactions of Ms and Bt providedthe chemical driving force needed to break SindashO bonds

In the Benamocarra Unit the energy necessary to over-come the activation barrier of the KyAnd reaction couldhave been provided by a temperature increase instead of apressure increase To envisage how a pressure increasehelps the activation energy barrier to be overcome weneed to consider only the fact that energy density is(dimensionally) equivalent to pressure Nevertheless it ismuch easier to interpret the Ky And reaction foundwithin the Benamocarra schist sequence in relation to a

Fig 10 (a) Projection onto (110) planes of the layers of type A (bluespheres) B (red spheres) and C (green spheres) forming a lsquolsquopseudo-cubicrsquorsquo closest-packed array of oxygen atoms in the Ky structure (b)First coordination sphere around the oxygen atoms (red spheres)forming one closest-packed layer The cations coordinating the Oatoms are Si (grey spheres) and Al (blue and purple spheres) (c)Stacking sequence corresponding to the crystallographic orienta-tions shown in the Fig 7E for the Ky The trace of the (110) latticeplanes and the orientation of the crystallographic axes for the differ-ent coherent domains within the structure are also shown in thefigure (online version in colour)

348 A Sanchez-Navas et al

eschweizerbart_xxx

high- thermal-gradient metamorphism and maximum tem-perature close to 550 C that reached a maximum pressurearound 04 GPa close to that defined by the Al2SiO5 triplepoint (see below)

53 Evidence of a high-thermal-gradientmetamorphism

The reaction pathway proposed above for the Ky Andtransformation found within QzndashAb veins is compatiblewith the metamorphic evolution inferred from the enclos-ing schists The petrographic data indicate an early pro-grade metamorphic stage related to burial and heatingevidenced in the schists by blastesis of post-S1 Cld andGrt porphyroblasts (Figs 3andashc 4andashc) The growth of CldGrt St and Ky in the schists was probably slightly olderthan (or coeval to) the opening of QndashAb veins and relatedformation of cm-sized Ky crystals

The blastesis of Cld Grt St and Ky predated the para-morphic replacement of Ky crystals by And in the veinswhich was probably associated with the generalized blast-esis of post-S2 And (and locally of Crd) in the schists Thisreflects the evolution from an initial intermediate-PBarrovian metamorphism to medium-T and low-P meta-morphic conditions Deformation during decompressionled to the formation of the S2 foliation sealed by Andand in the widespread occurrence of post-S2 veins filledby Qz Ab and And prisms which is a common featureof medium-grade schists equivalent to those ofBenamocarra frequently found in many Alpujarride units

When well preserved which is not always the case dueto younger deformation events in the Benamocarra micas-chists the larger porphyroblasts postdating the foliationsS1 and S2 in particular some of Grt and especially thoseof And show textural evidence of crystal growth understatic conditions (Fig 4a and c) In chiastolitic andalusitethe crystal-growth features consist of graphite accumula-tions at the edges of the prism faces resulting from crystalgrowth normal to the flat faces (Fig 4a) In relation to Grtthe same conditions favoured the development of cross-like inclusion patterns of Qz grains perpendicular to rhom-bododecahedral faces (Fig 4c) Both patterns result from atype of crystal-growth mechanism related to static blastesisand for pre-Alpine And in the rocks of the Torrox Unitthis was called layeritic growth by Sanchez-Navas et al(2012) According to this mechanism the crystal-growthfeatures of both And chiastolites and Grt porphyroblastsresulted from a thermally activated fast growth normal tothe flat faces of crystals This growth was controlled byscrew dislocations emergent at the centre of the F-facesunder low-supersaturation conditions due to slow diffusionrates where the low matter supply was related to lowdeformation rate (Sanchez-Navas et al 2012) Thereforethe blastesis of And and Grt in the schists also occurredthrough a thermally activated process related to a progrademetamorphism in the same way as previously proposedfor the Ky And transformation in the veins

The normal chemical zoning pattern observed fromcores to rims in Grt also indicates a prograde growthcertainly due to a T increase (Fig 6cndashd Table S3) The

Fig 11 (a) and (b) Model proposed for the polymorphic inversion studied According to this model two And crystals nucleate and growwiththeir c crystallographic axes parallel to the (110) plane of Ky (c) Close-packed layer formed by O atoms parallel to the (110) plane of Kystructure (d) Close-packed array of O atoms along the c crystallographic axis of And (online version in colour)

Transformation of kyanite to andalusite 349

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

high- thermal-gradient metamorphism and maximum tem-perature close to 550 C that reached a maximum pressurearound 04 GPa close to that defined by the Al2SiO5 triplepoint (see below)

53 Evidence of a high-thermal-gradientmetamorphism

The reaction pathway proposed above for the Ky Andtransformation found within QzndashAb veins is compatiblewith the metamorphic evolution inferred from the enclos-ing schists The petrographic data indicate an early pro-grade metamorphic stage related to burial and heatingevidenced in the schists by blastesis of post-S1 Cld andGrt porphyroblasts (Figs 3andashc 4andashc) The growth of CldGrt St and Ky in the schists was probably slightly olderthan (or coeval to) the opening of QndashAb veins and relatedformation of cm-sized Ky crystals

The blastesis of Cld Grt St and Ky predated the para-morphic replacement of Ky crystals by And in the veinswhich was probably associated with the generalized blast-esis of post-S2 And (and locally of Crd) in the schists Thisreflects the evolution from an initial intermediate-PBarrovian metamorphism to medium-T and low-P meta-morphic conditions Deformation during decompressionled to the formation of the S2 foliation sealed by Andand in the widespread occurrence of post-S2 veins filledby Qz Ab and And prisms which is a common featureof medium-grade schists equivalent to those ofBenamocarra frequently found in many Alpujarride units

When well preserved which is not always the case dueto younger deformation events in the Benamocarra micas-chists the larger porphyroblasts postdating the foliationsS1 and S2 in particular some of Grt and especially thoseof And show textural evidence of crystal growth understatic conditions (Fig 4a and c) In chiastolitic andalusitethe crystal-growth features consist of graphite accumula-tions at the edges of the prism faces resulting from crystalgrowth normal to the flat faces (Fig 4a) In relation to Grtthe same conditions favoured the development of cross-like inclusion patterns of Qz grains perpendicular to rhom-bododecahedral faces (Fig 4c) Both patterns result from atype of crystal-growth mechanism related to static blastesisand for pre-Alpine And in the rocks of the Torrox Unitthis was called layeritic growth by Sanchez-Navas et al(2012) According to this mechanism the crystal-growthfeatures of both And chiastolites and Grt porphyroblastsresulted from a thermally activated fast growth normal tothe flat faces of crystals This growth was controlled byscrew dislocations emergent at the centre of the F-facesunder low-supersaturation conditions due to slow diffusionrates where the low matter supply was related to lowdeformation rate (Sanchez-Navas et al 2012) Thereforethe blastesis of And and Grt in the schists also occurredthrough a thermally activated process related to a progrademetamorphism in the same way as previously proposedfor the Ky And transformation in the veins

The normal chemical zoning pattern observed fromcores to rims in Grt also indicates a prograde growthcertainly due to a T increase (Fig 6cndashd Table S3) The

Fig 11 (a) and (b) Model proposed for the polymorphic inversion studied According to this model two And crystals nucleate and growwiththeir c crystallographic axes parallel to the (110) plane of Ky (c) Close-packed layer formed by O atoms parallel to the (110) plane of Kystructure (d) Close-packed array of O atoms along the c crystallographic axis of And (online version in colour)

Transformation of kyanite to andalusite 349

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

increase in Mg content of Cld from core to rim (Table S4)further supports this T increase The occurrence of Grt andCld in these rocks is due to their Fe-rich composition anddoes not necessarily indicates much higher pressure thanthat of the Al2SiO5 triple point Almandine Grt and Fe-richCld (XMg frac14 011ndash013) can form at relatively low pres-sures because of the strong stabilizing effect of iron andother transition elements when they are incorporated intothe structures of both minerals (Spear 1993)

As stated above Cld and Grt porphyroblasts were laterpartially consumed in the prograde reactions that formedAnd and Crd In fact Crd grew over Cld and And chiasto-lites that formed in the matrix instead of replacing Cldporphyroblasts directly (Fig 4andashb) The persistence ofCld and Grt in And-Crd metapelites indicates that theirbreakdown extended across the growth interval of And andCrd (Fig 4) It represents a chemical disequilibrium prob-ably conditioned by a very rapid decompression or simplymetastable persistence

54 Tectono-metamorphic history

In diverse zones of the Iberian Variscan Belt the Variscancrustal thickening induced a prograde metamorphism ofBarrovian type which was followed by a HT-LP meta-morphism after the collapse of the thickened continentalcrust (Abalos et al 2002 Valle-Aguado et al 2005 Beaet al 2006) This transition took place through isothermaldecompression and resulted in high thermal gradients andwidespread intrusions of granitoids (eg Abalos et al2002) In the Upper-Alpujarride Torrox Unit located struc-turally below the Benamocarra Unit the coexistence of Andand Crd in leuco-granitic dykes intruding high-grade para-gneisses and schists (Sanchez-Navas et al 2014) as well asthe breakdown of large pegmatitic Ms forming And thorn Kfsintergrowths in orthogneisses (Sanchez-Navas 1999) havebeen interpreted as result of a high-T low-P Variscan meta-morphic event Moreover the strong metamorphic gradientobserved through the crustal sequence in many Upper andIntermediate Alpujarride units including those related tothe Ronda peridotite emplacement has been recently rein-terpreted as developed under low-P and high-T conditionsduring the Variscan Orogeny (eg Acosta Vigil et al2014) According to our interpretation Cld St Grt andKy are syn- to post- kinematic to D1 and formed in relationto a Barrovian-type metamorphism of medium-P thataffected the Benamocarra Unit probably during Variscantimes It reflects an initial episode of prograde metamorph-ism resulting from crustal thickening represented by D1 inthe clockwise P-T path (I) of Fig 12 This early Variscantectono-metamorphic evolution reached a maximum pres-sure around 04 GPa (Fig 12) The second episode con-sisted of a late Variscan decompression (D2) that endedwith the blastesis of post-S2 And and Crd at low P (around02 GPa) and medium T (around 550 C) conditions(Fig 12)

A much more dynamic metamorphism was relatedessentially to the strong deformational Alpine history

which caused mylonitization and grain-size reduction ofthe previous larger minerals in the rocks studied TheAlpine overprint which occurred along shear zones inrelation to D3 gradually decreased from bottom to topof the metapelitic-metapsammitic sequence It gave riseto zones at different degrees of re-equilibration frompartly re-crystallized medium-fine grained micaschistswith abundant pre-Alpine minerals to pervasivelyrestructured fine-grained mica phyllites The T condi-tions of the Alpine metamorphic peak in theBenamocarra Unit were between 400C and 450C inaccordance to the formation of biotite and muscovite inthe foliation (Figs 3ndash4) and in the case of biotite alsoaround garnet (Fig 4c) According to phengite geobaro-metry (Massonne amp Schreyer 1987) the pressure of thisAlpine event was around 05ndash06 GPa as deduced fromSi (323ndash321 apfu) and Fe2thornthornMg content(019ndash014) of phengitic muscovite (Table S1 Fig 6a)The partial replacement of chiastolitic And by fine-grained Ky and fibrollitic sillimanite in the TorroxUnit (Sanchez-Navas et al 2012) indicates that P andT were higher during the Alpine orogeny in tectonicunits structurally below the Benamocarra Unit Theinferred metamorphic P-T path related to the majorAlpine deformation phase D3 is represented by thecurve (II) of Fig 12 which agrees well with intense

Fig 12 Variscan (I) and Alpine (II)P-T paths and their relation with themaindeformationphases (D1D2D3) for theMsthornBtthorn PlthornAndGrt Ky St Crd graphite schists of the lower part of the BenamocarraUnit The garnet-in reaction (1) defined by the Fe end-member reactionFe-Cld thorn Ann frac14 Alm thorn Ms (Spear amp Cheney 1989) is representedtogetherwith reaction 2 of destabilization of the St (StthornQzthornChlthornMsfrac14 BtthornAndthorn H2O Thompson 1982) reaction 3 forming Crd from StGrt andAnd (StthornQzfrac14CrdthornAndthornH2O Thompson 1982) the phasediagram for Al2SiO5 polymorphs (Pattison 2001) and the Si isoplethsfor reaction 3K2Al6Si6O20(OH)4 thorn 6SiMgAl-2 frac14 4KAlSi3O8 thorn 6SiO2

thorn K2Mg6Al2Si6O20(OH)4thorn 4H2O (Massonne amp Schreyer 1987)

350 A Sanchez-Navas et al

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

contractional tectonics associated with nappe emplace-ment during the Alpine orogeny

Acknowledgements We thank Bernard Grobety DavidPattison and one anonymous reviewer as well as AssociateEditor Bernardo Cesare for their very detailed and carefulreviews and suggestions that helped us to improve thepaper This work is supported by grants CGL2012-32169(DGICYT Spain) and P11-RNM-7067 RNM-179 andRNM-208 (Junta de Andalucıa Spain)

References

Abalos B Carreras J Druguet E Escuder Viruete J Gomez

Pugnaire MT Lorenzo Alvarez S Quesada C Rodrıguez

Fernandez L R Gil-Ibarguchi J I (2002) Variscan and pre-

Variscan tectonics in lsquolsquoThe Geology of Spainrsquorsquo W Gibbsons

and T Moreno eds The Geological Society London

Acosta-Vigil A Rubatto D Bartoli O Cesare B Meli S

Pedrera A Azor A Tajcmanova L (2014) Age of anatexis

in the crustal footwall of the Ronda peridotites S Spain Lithos

210ndash211 147ndash167

Aldaya F Garcıa-Duenas V Navarro-Vila F (1979) Los mantos

alpujarrides del tercio central de las Cordilleras Beticas Ensayo

de correlacion tectonica de los Alpujarrides Acta Geol Hisp 1

154ndash166

Alonso-Chaves FM amp Orozco M (2012) The Alpujarride

Complex in La Axarquıa Malaga province Crustal-scale duc-

tile shear zones and associated recumbent folds Geogaceta 52

5ndash8

Andriessen PMA Hebeda EH Somon OJ Verschure RH

(1991) Tourmaline K-Ar ages compared to other radiometric

dating systems in Alpine anatetic leucosomes and metamorphic

rocks (Cyclades and southern Spain Chem Geol 91 33ndash48

Argles T W Platt J P Waters DJ (1999) Attenuation and

excision of a crustal section during extensional exhumation

the Carratraca Massif Betic Cordillera southern Spain J

Geol Soc London 156 149ndash162

Azanon JM amp Goffe B (1997) Ferro- and magnesiocarpholite

assemblages as record of high-P low-T metamorphism in the

Central Alpujarrides Betic Cordillera (SE Spain Eur J

Mineral 9 1035ndash1051

Azanon JM Garcıa-Duenas V Goffe B (1998) Exhumation of

high-pressure pelites and coeval crustal extension in the

Alpujarride complex (Betic Cordillera) Tectonophysics 285

231ndash252

Balanya JC amp Garcıa-Duenas V (1987) Les directions structur-

ales dans le Domaine drsquoAlboran de part et drsquoautre du Detroit de

Gibraltrar C R Acad Sci Paris 304 929ndash933

Baur WH (1970) Bond length variation and distorted coordination

polyhedra in inorganic crystals Trans Am Cryst Ass 6

129ndash155

Bea F Montero PG Gonzalez-Lodeiro F Talavera C Molina

JF Scarrow JH Whitehouse MJ Zinger T (2006) Zircon

thermometry and UPb ion-microprobe dating of the gabbros

and associated migmatites of the Variscan Toledo Anatectic

Complex Central Iberia J Geol Soc London 163 847ndash855

Bell IA amp Wilson CJL (1977) Growth defects in metamorphic

biotite Phys Chem Minerals 2 153ndash169

Bernard-Griffiths J Cantagrel JM Kornprobst J (1977) Ages

des gneiss du Hacho de Ceuta un evenement thermique

Hercynien dans la zone interne du Rif R A S T Rennes

(Abstracts) 64

Bouillin JP Durand-Delga M Oliver P (1986) Betic-Rifian and

Tyrrhenian arcs distinctive features genesis and development

stages in lsquolsquoThe Origin of Arcsrsquorsquo FC Wezel ed Amsterdam

Elsevier 281ndash304

Boulin J Ledent D Pasteels P (1969) Reperes geochronologi-

ques dans les zones internes des cordilleres betiques au sud-

ouest de la Sierra Nevada (Espagne Ann Soc Geol Bel 92

377ndash381

Bouybaouene ML Michard A Goffe B (1998) High-pressure

granulites on top of the Beni Bousera peridotites Rif belt

Marocco a record of an ancient thickened crust in the Alboran

domain Bull Soc Geol France 169 153ndash162

Bragg WH (1930) The structure of silicates Zeitsch Krist 74

237ndash305

Burdett JK amp McLarnan TJ (1984) An orbital interpretation of

Paulingrsquos rules Am Mineral 69 601ndash621

Cesare B Gomez-Pugnaire MT Sanchez-Navas A Grobety B

(2002) Andalusite-sillimanite replacement (Mazarron SE Spain)

A microstructural and TEM study Am Mineral 87 433ndash444

Chopin C Seidel E Theye T Fenaris G lvaldi G Catti M

(1992) Magnesiochloritoid and the Mg-Fe series in the chlor-

itoid group Eur J Mineral 4 67ndash57

Durand-Delga M amp Fontbote JM (1980) Le cadre structurale de

la Mediterranee occidentale Mem BRGM 15 677ndash685

Elorza JJ (1982) Peculiaridades y disposicion de la unidad de

Benamocarra en la transversal de Sierra Tejeda (zona Betica

Bol Geol Min 5 379ndash389

Elorza JJ amp Garcıa Duenas V (1981) Hoja y memoria explicativa

de la hoja n 1054 (Velez-Malaga) del Mapa Geologico de

Espana 150000 (serie Magna) IGME

Foucault A amp Paquet J (1971) Sur lrsquoimportance drsquoune tectogenese

hercynienne dans la region centrale des Cordilleres Betiques (S

de la Arana prov Grenade EspagneC R Acad Sci Paris 272

2756ndash2758

Garcıa-Casco A amp Torres-Roldan RL (1996) Disequilibrium

induced by fast decompression in St-Bt-Grt-Ky-Sil-And meta-

pelites from the Betic belt (S Spain) J Petrol 37 1207ndash1240

mdash mdash (1999) Natural metastable reactions involving garnet staur-

olite and cordierite implications for petrogenetic grids and the

extensional collapse of the Betic-Rif Belt Contrib Mineral

Petrol 136 131ndash153

Garcıa-Casco A Sanchez-Navas A Torres-Roldan RL (1993)

Disequilibrium decomposition and breakdown of muscovite in

high P-T gneisses Betic alpine belt (southern Spain) Am

Mineral 78 158ndash177

Gomez-Pugnaire MT Rubatto D Fernandez-Soler JM

Jabaloy A Lopez-Sanchez-Vizcaıno V Gonzalez-Lodeiro

F Galindo-Zaldıvar J Padron-Navarta JA (2012) Late

Variscan magmatism in the Nevado-Filabride Complex U-Pb

geochronologic evidence for the pre-Mesozoic nature of the

deepest Betic complex (SE Spain Lithos 146ndash147 93ndash111

Grambling JA (1981) Kyanite andalusite sillimanite and related

mineral assemblages in the Truchas Peaks region New Mexico

Am Mineral 66 702ndash722

Transformation of kyanite to andalusite 351

eschweizerbart_xxx

Grambling JA amp Williams ML (1985) The effects of Fe3thorn and

Mn3thorn on aluminium silicate phase relations in north-central

New Mexico USA J Petrol 26 324ndash354

Guerrera F Martın-Algarra A Perrone V (1993) Late

Oligocene-Miocene syn--late-orogenic successions in Western

and Central Mediterranean Chains from Betic Cordillera to

Southern Apennine Terra Nova 5 525ndash544

Hulsmans A Schmucker M Mader W Schneider H (2000)

The transformation of andalusite to mullite and silica Part 1

Transformation mechanism in [001]A direction Am Mineral

85 980ndash986

Kerrick DM (1988) Al2SiO5-bearing segregations in the

Lepontine Alps Switzerland Aluminium mobility in metape-

lites Geology 16 636ndash640

Kerrick DM (1990) The Al2SiO5 polymorphs Reviews in

Mineralogy 22 Chantilly VAMineralogical Society of America

Loomis TP (1975) Tertiary mantle diapirism orogeny and plate

tectonics East of the Strait of Gibraltar Am J Sci 275 1ndash30

Martın-Algarra A (1987) Evolucion geologica alpina del contacto

entre las Zonas Internas y las Zonas Externas de la Cordillera

Betica PhD dissertation University of Granada

Martın-Algarra A Mazzoli S Perrone V Rodrıguez-Canero R

Navas-Parejo P (2009a) Variscan tectonics in the Malaguide

Complex (Betic Cordillera southern Spain) stratigraphic and

structural Alpine versus pre-Alpine constraints from the Ardales

area (Province of Malaga) I Stratigraphy J Geol 117

241ndash262

Martın-Algarra A Mazzoli S Perrone V Rodrıguez-Canero R

(2009b) Variscan tectonics in the Malaguide Complex (Betic

Cordillera southern Spain) stratigraphic and structural Alpine

versus pre-Alpine constraints from the Ardales area (Province of

Malaga) II Structure J Geol 117 263ndash284

Massonne HJ amp Schreyer W (1987) Phengite geobarometry

based on limiting assemblage with K-feldspar phlogopite and

quartz Contrib Mineral Petrol 96 212ndash224

Meike A (1989) In situ deformation of micas a high-voltage

electron-microscope study Am Mineral 74 780ndash796

Michard A Chalouan A Montigny R Quazzani-Touhami M

(1983) Les nappes cristallophylliennes du Rif (Sebtides

Maroc) temoins drsquoun edifice alpin de type pennique incluant

le manteau superieur C R Acad Sci Paris 296 1337ndash1340

Monie P Galindo-Zaldıvar J Gonzalez-Lodeiro F Goffe B

Jabaloy A (1991) 40Ar39Ar geochronology of Alpine tecton-

ism in the Betic Cordilleras (southern Spain) J Geol Soc

London 148 288ndash297

Monie P Torres-Roldan R L Garcıa-Casco A (1994) Cooling

and exhumation of the Western Betic Cordilleras 40Ar39Ar

thermochronological constraints on a collapsed terrane

Tectonophysics 238 353ndash379

Montel J M Kornprobst J Vielzeuf D Veschambre M (1995)

Shielding effect of garnet for the U-Th-Pb system in monazite

an e-probe study at Beni Bousera (Maroc) Terra Abstr 7 348

Montel J M Kornprobst J Vielzeuf D (2000) Preservation of

old U-Th-Pb ages in shielded monazite example from the Beni

Bousera Hercynian kinzigites (Morocco J Metamorphic Geol

18 335ndash342

OrsquoDogherty L Rodrıguez-Canero R Gursky HJ Martın-

Algarra A Caridroit M (2000) New data on Lower

Carboniferous stratigraphy and palaeogeography of the

Malaguide Complex (Betic Cordillera Southern Spain C R

Acad Sci Paris 331 533ndash541

Pattison DRM (2001) Instability of Al2SiO5 triple point assem-

blages in muscovitethorn biotitethorn quartz-bearing metapelites with

implications Am Mineral 86 1414ndash1422

Perrone V Martın-Algarra A Critelli S Decandia FA

DrsquoErrico M Estevez A Iannace A Lazzarotto A

Martın-Martın M Martın-Rojas I Mazzoli S Messina

A Mongelli G Vitale S Zaghloul NM (2006)

Verrucanorsquorsquo and lsquolsquoPseudoverrucanorsquorsquo in the Central-Western

Mediterranean Alpine Chains in lsquolsquoTectonics of the Western

Mediterranean and North Africarsquorsquo G Moratti amp A Chalouan

eds Geological Society London Special Publications

London 262 1ndash43

Platt JP ampWhitehouse MJ (1999) Early Miocene high-tempera-

ture metamorphism and rapid exhumation in the Betic Cordillera

(Spain) evidence from U-Pb zircon ages Earth Planet Sci

Lett 171 591ndash605

Platzman E Platt JP Kelley SP Allerton S (2000) Large

clockwise rotations in an extensional allochthon Alboran

Domain (southern Spain J Geol Soc London 157 1187ndash1197

Priem HNA Boelrijk NAIM Hebeda EH Verschure RH

(1966) Isotopic age determination on tourmaline granite-

gneisses and a metagranite in the eastern Betic Cordilleras

(southeastern Sierra de Los Filabres) SE Spain Geol

Mijnbouwn 45 184ndash187

Priem HNA Boelrijk NAIM Hebeda EH Oen EH

Verdurmen EAT (1979) Isotopic dating of the emplacement

of the ultramafic masses in the Serranıa de Ronda southern

Spain Contrib Mineral Petrol 70 103ndash109

Puga E Fontbote JM Martın-Vivaldi JL (1975) Kyanite pseu-

domorphs after andalusite in polymetamorphic rocks of Sierra

Nevada (Betic Cordillera Southern Spain Schweiz Mineral

Petrogr Mitt 55 227ndash241

Rodrıguez-Canero R amp Martın-Algarra A (2014) Frasnian

Famennian crisis in the Malaguide Complex (Betic Cordillera

Spain) stratigraphic discontinuities and a new pebbly mudstone

horizon with shallow marine carbonate clasts and conodonts

Palaeogeographic significance Terra Nova 26 38ndash54

Rodrıguez-Canero R Martın-Algarra A Sarmiento GN Navas-

Parejo P (2010) First Late Ordovician conodont fauna in the

Betic Cordillera (South Spain) a palaeobiogeographical contri-

bution Terra Nova 22 330ndash340

Rossetti F Theye T Lucci F Bouybaouene ML Dini A

Gerdes A Phillips D Cozzupoli D (2010) Timing and

modes of granite magmatism in the core of the Alboran

Domain Rif chain northern Morocco implications for the

Alpine evolution of the western Mediterranean Tectonics

29(2) DOI 1010292009TC002487

Rossetti F Dini A Lucci F Bouybaouene ML Faccenna C

(2013) Early Miocene strike-slip tectonics and granite emplace-

ment in the Alboran Domain (Rif Chain Morocco) significance

for the geodynamic evolution of Western Mediterranean

Tectonophysics 608 774ndash791

Ruiz-Cruz MD (1997) Very low-grade chlorite with anomalous

chemistry and optical properties from the Malaguide Complex

Betic Cordilleras Spain Can Mineral 35 923ndash935

Ruiz-Cruz MD amp Rodrıguez-Jimenez P (2002) Correlation

between crystallochemical parameters of phyllosilicates and

mineral facies in very low-grade metasediments of the Betic

Cordillera (Spain) A synthesis Clay Minerals 37 169ndash185

Sanchez-Navas A (1999) Sequential kinetics of a muscovite-out

reaction A natural example Am Mineral 84 1270ndash1286

352 A Sanchez-Navas et al

eschweizerbart_xxx

Sanchez-Navas A Oliveira-Barbosa RC Garcıa-Casco A

Martın-Algarra A (2012) Transformation of andalusite to kya-

nite in the Alpujarride Complex (Betic Cordillera S Spain)

Geologic implications J Geol 120 557ndash574

Sanchez-Navas A Garcıa-Casco A Martın-Algarra A (2014)

Pre-alpine discordant granitic dikes in the metamorphic core of

the Betic Cordillera Tectonic implications Terra Nova 26

477ndash486 DOI 101111ter12123

Sanchez-Rodrıguez L Gebauer D Tubıa J M Gil Ibarguchi J

I Rubatto D (1996) First SHRIMP-ages on pyroxenites eclo-

gites and granites of the Ronda complex and its country-rocks

Geogaceta 20 487ndash488

Shau YH Yang HY Peacor DR (1991) On oriented titanite

and rutile inclusions in sagenitic biotite Am Mineral 76

1205ndash1217

Soto JI amp Platt JP (1999) Petrological and structural evolu-

tions of high-grade metamorphic rocks from the floor of the

Alboran Sea Basin Western Mediterranean J Petrol 40

21ndash60

Spear FS (1993) Metamorphic Phase Equilibria and Pressure-

Temperature-Time paths Mineralogical Society of America

(Monograph) 799 p

Spear FS amp Cheney JT (1989) A petrogenetic grid for pelitic

schists in the system SiO2-Al2O3-FeO-MgO-K2O-H2OContrib

Mineral Petrol 101 149ndash164

Thompson AB (1982) Dehydration melting of pelitic rocks and

the generation of H2O-undersaturated granitic liquids Am J

Sci 282 1567ndash1595

Torres-Roldan RL (1974) El metamorfismo progresivo y la evo-

lucion de la serie de facies en las metapelitas alpujarrides al SE

de Sierra Almijara (sector Central de las Cordilleras Beticas S

de Espana Cuad Geol 5 21ndash77

mdash (1981) Plurifacial metamorphic evolution of the Sierra Bermeja

peridotite aureole (southern Spain Estud Geol 37 115ndash133

Torres-Roldan RL Poli G Peccerillo A (1986) An Early

Miocene arc tholeitic magmatic dike event from the Alboran

Sea Evidence for precollisional subduction and back-arc crustal

extension in the westernmost Mediterranean Geol Rundschau

75 219ndash234

Tubıa JM Cuevas J Gil-Ibarguchi JI (1997) Sequential devel-

opment of the metamorphic aureole beneath the Ronda perido-

tites and its bearing on the tectonic evolution of the Betic

Cordillera Tectonophysics 279 227ndash252

Ulmer P (1986) NORM-Program for cation and oxygen mineral

norms Zurich Computer Library Institute fur Mineralogie und

Petrographie ETH-Zentrum

Valle Aguado B Azevedo M R Schaltegger U Martınez Catalan

J R Nolan J (2005) UndashPb zircon and monazite geochronology

of Variscan magmatism related to syn-convergence extension in

Central Northern Portugal Lithos 82 169ndash184

Veldel MA (1999) Bond strength and the relative weathering rates

of simple orthosilicates Am J Sci 299 679ndash696

Walther JV ampWood BJ (1984) Rate and mechanism in prograde

metamorphism Contrib Mineral Petrol 88 246ndash259

Whitney DL amp Evans BW (2010) Abbreviations for names of

rock-forming minerals Am Mineral 95 185ndash187

Winter J K amp Ghose S (1979) Thermal expansion and high-

temperature crystal chemistry of the Al2SiO5 polymorphs Am

Mineral 69 573ndash586

Worden RH Champness PE Droop GTR (1987)

Transmission electron microscopy of pyrometamorphic break-

down of phengite and chlorite Mineral Mag 51 107ndash121

Zeck HP (1996) Betic-Rif orogeny subduction of Mesozoic

Tethys under E-ward drifting Iberia slab detachment shortly

before 22 Ma and subsequent uplift and extensional tectonics

Tectonophysics 254 1ndash16

Zeck HP amp Whitehouse MJ (1999) Hercynian Pan-African

Proterozoic and Archean ion-microprobe zircon ages for a

Betic-Rif core complex Alpine belt W Mediterranean conse-

quences for its P-T-t path Contrib Mineral Petrol 134

134ndash149

mdash mdash (2002) Repeated age resetting in zircons from Hercynian-

Alpine polymetamorphic schists Betic-Rif tectonic belt S

Spaina U-Th-Pb ion microprobe study Chem Geol 182

275ndash292

Zeck HP amp Williams IS (2001) Hercynian metamorphism in

nappe core complexes of the Alpine Betic-Rif belt western

Mediterranean a SHRIMP zircon study J Petrol 42

1373ndash1385

Zeck HD Albat F Hansen BT Torres-Roldan RL Garcıa-

Casco A Martın-Algarra A (1989a) A 21 2 Ma age for the

termination of the ductile Alpine deformation in the internal

zone of the Betic Cordilleras south Spain Tectonophysics

169 215ndash220

Zeck HD Albat F Hansen BT Torres-Roldan RL Garcıa-

Casco A (1989b) Alpine tourmaline-bearing leucogranites

intrusion age and petrogenesis Betic Cordilleras SE Spain N

Jb Mineral Mh 1989(11) 513ndash520

Received 15 April 2015

Modified version received 15 September 2015

Accepted 17 November 2015

Transformation of kyanite to andalusite 353