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International Geology Review
ISSN: 0020-6814 (Print) 1938-2839 (Online) Journal homepage: http://www.tandfonline.com/loi/tigr20
Age, geochemistry, and emplacement of the~40-Ma Baneh granite–appinite complex in atranspressional tectonic regime, Zagros suturezone, northwest Iran
Hossein Azizi, Sepideh Hadad, Robert J. Stern & Yoshihiro Asahara
To cite this article: Hossein Azizi, Sepideh Hadad, Robert J. Stern & Yoshihiro Asahara (2018):Age, geochemistry, and emplacement of the ~40-Ma Baneh granite–appinite complex in atranspressional tectonic regime, Zagros suture zone, northwest Iran, International Geology Review,DOI: 10.1080/00206814.2017.1422394
To link to this article: https://doi.org/10.1080/00206814.2017.1422394
Published online: 12 Jan 2018.
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ARTICLE
Age, geochemistry, and emplacement of the ~40-Ma Baneh granite–appinitecomplex in a transpressional tectonic regime, Zagros suture zone, northwestIranHossein Azizi a, Sepideh Hadadb, Robert J. Sternc and Yoshihiro Asaharad
aMining Department, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran; bEarth Sciences Department, Faculty of Basic Sciences,University of Kurdistan, Sanandaj, Iran; cGeosciences Department, University of Texas at Dallas, Richardson, TX, USA; dDepartment of Earthand Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
ABSTRACTThe Baneh plutonic complex is situated in the Zagros suture zone of northwest Iran between theArabian and Eurasian plates. This complex is divided into granite and appinite groups. Zircon U–Pb dating shows that granites crystallized 41–38 million years ago but appinites experience moreprotracted magmatic evolution, from at 52 to 38 Ma. Whole-rock chemical compositions showsignificant major and trace element variations between the two lithologies. Granitic rocks aremore evolved, with high contents of SiO2 (62.4–77.0 wt%), low contents of TiO2 (0.25 wt%), MgO(0.05–1.57 wt%), and Fe2O3 (0.40–4.06 wt%) and high contents of Na2O + K2O (≈10 wt%). Incontrast, appinites have low contents of SiO2 (51.0–57.0 wt%) and K2O (<2.1 wt%) and high Fe2O3
(6.4–9.35 wt%), MgO (2.0–9.9 wt%), and Mg number (Mg# = 35–76). The concentration of rareearth elements in the appinites is higher than in granitic rocks, making it difficult to form granitessolely by fractionation of appinite magma. (87Sr/86Sr)i and εNd(40 Ma) in both groups are similar,from 0.7045 to 0.7061 and −1.2 to +2.6, except for a primitive gabbroic dike with εNd(40 Ma) = +9.9.Appinites show mainly typical I-type characteristics, but granites have some S-type characteristics.The sigmoidal shape of the Baneh pluton and its emplacement into deformed Cretaceous shalesand limestone showing kink bands, asymmetric and recumbent folds in a broad contact zone,with pervasive ductile to brittle structures in both host rocks and intrusion, indicate that magmaemplacement was controlled by a transpressional tectonic regime, perhaps developed duringearly stages in the collision of Arabia and Eurasian plates.
ARTICLE HISTORYReceived 18 July 2017Accepted 2 December 2017
KEYWORDSGranite; appinite; Eocene;transpression tectonicregime; Zagros fault; Iran
1. Introduction
Plutonic rocks of broad granitic compositions are themain components of continental crust (Othman et al.1984; Krüner et al. 1991). Different types of granitoidsare generated with distinctive compositions and miner-alogies and are classified as I-, S-, and A-type granitesdepending on the nature of their source (e.g. Chappelland White 1974; Loiselle and Wones 1979; Pearce et al.1984; Whalen et al. 1987; Eby 1992; Frost et al. 2001).Because granitic magma cannot be produced directlyfrom partial melting of the mantle (Rudnick 1995), thismagma must evolve in the crust. In collision zones likeIran, factors such as thickness and thermal structure ofthe crust and the flux of mantle-derived basalt arecritical for generating granitic magma. Crustal thicken-ing leads to heating as a result of thermal blanketingand radioactive element decay, and such heating isfurthered by injection of mafic magma at the base ofthe crust (Le Fort et al. 1987; Zen 1988; Sylvester 1998;
Moyen et al. (2017); suggesting that granitic melts canbe produced by differentiation of basaltic magma andpartial melting of metabasites (Annen et al. 2006; Ulmeret al. 2008; Jagoutz 2010; Jagoutz et al. 2011;Nandedkar 2014) and metasediments (Pitcher 1983;Chappell et al. 1988, 2000; Patiño Douce 1995;Sylvester 1998; Clemens 2003; Miller et al. 2003;Chelle-Michou et al. 2015; Laurent et al. 2015).
In this contribution, we explore an example of gran-ite magmagenesis associated with crustal thickeningand magmatism in the Zagros of southwest Iran. TheZagros orogen is part of the Alpine-Himalayan orogenicbelt and consists of four main parts, from southwest tonortheast: (1) Zagros folded belt, (2) Zagros crush zone,(3) Sanandaj–Sirjan Zone (SNSZ), and (4) LateCretaceous ophiolites (Figure 1(A)) (e.g. Stöcklin 1968;Alavi 1980; Berberian and Berberian 1981; Hassanzadehet al. 2008; Agard et al. 2011; Moghadam and Stern2015; Davoudian et al. 2016; Hassanzadeh and
CONTACT Hossein Azizi [email protected] Mining Department, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran
INTERNATIONAL GEOLOGY REVIEW, 2018https://doi.org/10.1080/00206814.2017.1422394
© 2018 Informa UK Limited, trading as Taylor & Francis Group
Wernicke 2016). The Zagros orogen originated as anN-dipping subduction zone and now is evolving into acontinental collision zone between the Arabian andEurasian plates (Figure 1(a); Stöcklin 1968; Berberian
and King 1981; Alavi 1994; Agard et al. 2011). Thebeginning of this collision is controversial, partlybecause it was and is diachronous along strike. It mayhave begun as early as Late Cretaceous (Mohajjel and
Figure 1. (a) Simplified geology map of Iran (modified from Stöcklin 1968). (b) Location of the Baneh intrusion and other CenozoicS-type granite along the Zagros fault in northwestern Iran.
2 H. AZIZI ET AL.
Fergusson 2000) or as late as Miocene (Talebian andJackson 2002; Okay et al. 2010; Azizi et al. 2011; Ballatoet al. 2011; Mouthereau 2011; Ali et al. 2012, 2016;McQuarrie and Van Hinsbergen 2013). Collision beganin the northwest (Anatolia) and subduction continues inthe southeast (Makran).
Despite the abundance of igneous rocks of variousages in the Zagros orogen, there are few studies of itsgranitic bodies (Azizi et al. 2011; Nouri et al. 2016;Mohammad and Cornell 2017). The main graniticbodies are restricted to the SNSZ, which wereemplaced in Middle-to-Late Jurassic time (Sepahi andAthari 2006; Shahbazi et al. 2010; Azizi et al. 2011,2015, 2016; Mahmoudi et al. 2011; Azizi and Asahara2013; Chiu et al. 2013; Maanijou et al. 2013; Hunzikeret al. 2015; Yajam et al. 2015; Abdulzahra et al. 2016;Bayati et al. 2017).
In the northern SNSZ, there are some Cenozoic grani-toid bodies such as Naghadeh (Mazhari et al. 2011),Marivan (Sepahi et al. 2014), Marziyan (Darvishi et al.2015), and Baneh granites (Amini et al. 2005). These intru-sions follow the NW–SE grain of the Zagros orogen andshow typical S-type granite affinities (Amini et al. 2005;Sepahi et al. 2014; Darvishi et al. 2015). The Baneh pluton(Figures 1(b) and 2) is a particularly interesting examplebecause it is composite body ~10 km across that consistsof two groups: diorite–granodiorite (appinite) and granite.Appinite is a hornblende-rich, mafic-to-intermediate
igneous rock with calc-alkaline to shoshonitic affinitiesformed from water-rich mantle melts during late stagesof subduction and early stages of collision; many appinitecomplexes are associated with crustal melts (Murphy2013). This term and concept is rarely used in describingIranian intrusive bodies but may be useful, as our studyshows.
In this research, we focus on the Baneh intrusion andpresent new chemical, field relation, structures, radio-genic isotopes and U–Pb zircon ages. Based on theseresults, we discuss Baneh intrusion magmatic evolution,the relation of the granite and appinitic rocks andsuggest a new geodynamic model for emplacement ofEocene intrusions in the Zagros suture zone in westernIran. We also provide the first reliable age for this body,correcting the previous conclusion of Amini et al.(2005), who suggested that intruded in LateCretaceous–Palaeocene time.
2. Field relations
The Baneh appinite–granite complex covers more than100 km2 to the west of the small city of Baneh(Figure 1). This body intruded into Cretaceous shaleand limestone of the SNSZ (Figure 1(b)). These sedi-mentary host rocks are affected by a ~1-km wide ther-mal aureole, where they are converted to hornfels andskarn, respectively (Figure 2). Most of the Baneh
Figure 2. Geologic map of the Baneh intrusive complex and host rocks (modified from Fonoudi and Sadeghi 2009). Samplelocations are also shown.
INTERNATIONAL GEOLOGY REVIEW 3
complex is covered by grass but good outcrops arefound in roadcuts and deep valleys. In map view, theBaneh pluton has a balloon-and-tail shape, which canbe divided into three main components. The first isbiotite granite, which comprises most of the plutonand contains appinite enclaves. The second is appinite,which is diorite–granodiorite that is rich in hornblendeand is mainly observed in the centre of the body. Banehappinite contains some enclaves of granite with dia-meters of a few centimetres to a few metres. The thirdis leucogranite, which occurs as parallel dikes that cutthe main body and host rocks and have beendeformed, boudinaged and folded due to syn-emplace-ment deformation (Figure 3(a-c)). Mafic enclaves in thegranite body are variously aligned, elongated (Figure 3(d-g)), folded (Figure 3(h)), angular (Figure 3(i)), andsigmoidal (Figure 3(j)) that confirm that deformationaccompanied emplacement and crystallization of theBaneh pluton.
Appinitic bodies with circular-to-ellipsoidal shapesintruded the granite in the centre of the Baneh complex
(Figure 2); around its margins, appinites appear as smallblocks and dikes. In addition, the granite is full ofappinitic enclaves. The occurrence of appinite enclaves,dikes, and larger intrusions in the granitic body indi-cates that appinite and granitic magmatism happenedabout the same time.
3. Petrography
Baneh pluton lithologies are plotted on the modalquartz-alkali feldspar-plagioclase (QAP) diagram(Figure 4(a)). These can be divided into two maingroups: diorite–granodiorite (appinite) and granite. Inthe normative orthoclase (Or), albite (Ab), and anorthite(An) diagram (O’Connor 1965), the samples plot in twoseparate granodiorite and granite fields (Figure 4(b)).The petrography of the leucogranite dikes is very simi-lar to the main granite body. For this reason, we treatthe main granite body and leucogranite dikes together.
Appinites and granites are further described below.
Figure 3. Photographs of various rocks and structures in the Baneh complex. (a) Granitic dike injected into host Cretaceoussedimentary rocks. (b) Parallel dikes which cut the main granitoid body. (c) Boudinaged and folded granitic dikes. (d) Boudinageddike with sigmoidal mafic enclaves in the granitic body. (d–f) Arrangement of mafic enclaves in the granitic body, arrangement andreaction of the enclaves in the foliated granite. (g,h) Folded enclave, rounded and alignment of enclaves in the host granite andsigmoidal structures in granitic body, respectively.
4 H. AZIZI ET AL.
3.1. Appinite
Appinitic rocks show granular and foliated textures(Figure 5(a-f)). Based on the QAP modal diagram(Figure 4(a)), these rocks classify as diorite, quartz mon-zonite, monzodiorite, quartz monzodiorite, and tonalite.The main minerals are hornblende, plagioclase, alkalifeldspar, quartz, biotite, and clinopyroxene. Apatite,
zircon, and titanite are accessories. Hornblende withlong prismatic, tabular, or acicular shape is the mainmafic mineral and sometimes makes up >60% of therock. Hornblende shows high birefringence with stronggreen pleochroism and in some parts is converted to Fe-rich biotite (Figure 5(c-e)). Black-to-green hornblendeaggregates are locally abundant. Because of the abun-dance of hornblende, these rocks are usefully also
Figure 4. (a) Modal classification of the Baneh batholith rocks. Samples of appinite and granite plot in two-separate groups:Appinites plot in the fields of diorite–monzodiorite–quartz diorite–granodiorite–tonalite whereas granites plot in the fields ofmonzogranite and syenogranite. (b) Normative classification of the Baneh granitoid based on orthoclase (Or), albite (Ab), andanorthite (An) diagram (O’Connor 1965). The appinitic rocks plot in the field of granodiorite–tonalite, whereas granites plot in thegranite–granodiorite field.
INTERNATIONAL GEOLOGY REVIEW 5
described as appinite (Figure 5(b,c); Murphy 2013).Plagioclase with idiomorphic-to-sub-idiomorphic shapesand polysynthetic twins is the main leucocratic mineral(Figure 5(f)). Plagioclase – locally with poikilitic texture –
encloses finer grained hornblende, confirming that pla-gioclase crystallized after hornblende (Figure 5(h-i)).Some plagioclase grains show reacted or altered cores(Figure 5(f,g)). Alkali feldspars locally with perthitic
Figure 5. Microphotographs of appinitic rocks (a–c) with granular texture. The main minerals are hornblende, plagioclase, and alkalifeldspar. Hornblende was replaced by Fe-rich biotite (d,e) and plagioclase shows two stages of crystallization (f). Rotated plagioclaseis surrounded by hornblende (g). Hornblende grains are surrounded by coarse-grained plagioclase (h) and fine-grained plagioclaseis surrounded by alkali feldspars (i). Granitic rocks show granular (j,k) perthitic and graphic textures (l,m). Alkali feldspar megacrystssurrounded by plagioclase grains (n). The main mafic minerals are hornblende and biotite (o); in some samples, biotite was replacedby muscovite and iron oxide (p). Garnets with quartz inclusion are the main accessory minerals and formed between alkali feldspargrains (q,r). Bt: Biotite; Hbl: hornblende; Pl: plagioclase; Qtz: quartz; Grt: garnet; Ms: muscovite.
6 H. AZIZI ET AL.
texture surround the hornblende and plagioclase, show-ing that crystallization of alkali feldspar occurred afterthat of plagioclase (Figure 5(i)).
3.2. Granite
The main body of the Baneh intrusion is medium-to-coarse-grained granite, with graphic and perthitic tex-tures (Figure 5(j-r)). The major minerals are K-feldspar,sodic plagioclase, and quartz with minor hornblendeand biotite. Garnet, zircon, and apatite are accessoryminerals. Orthoclase with rectangular to elongatedhabit and perthite is common and locally microcline isobserved (Figure 5(i-o)). Mineral alignment imparts afoliation and some large K-feldspars poikiliticallyenclose plagioclase and biotite. K-feldspar is mostlyfresh but in some deformed and altered rocks isreplaced by muscovite and kaolinite (Figure 5(p)).Plagioclase is the second most abundant mineral andshows polysynthetic twins with recrystallized rims. Mostsamples show two generations of plagioclase.Plagioclase cores are replaced by secondary mineralssuch as epidote, muscovite, and some clay minerals butthe rims are fresh. Quartz is interstitial to feldspars andshows serrated texture. Biotite is the main mafic mineralin these rocks, varying in abundance from 0% to 20%.Most biotites are elongated and show high relief andstrong brown colour indicating high Fe (annite).Prismatic hornblende is a minor mineral and is replacedby biotite in cores and around rims. Minor subhedral-to-euhedral garnet is found in granite but not in appinite
(Figure 5(q,r)). The presence of garnet suggests involve-ment of sediment melts (Harrison 1988).
4. Microstructures
The Baneh pluton and surrounding metasedimentaryrocks were affected by dextral strike-slip shearing. Inhornfelsic rocks, biotites are oriented and show asym-metrical pressure shadows and quartz ribbons showsigmoidal, isoclinal, and refolded structures (Figure 6(a,b)). Asymmetric cordierites are rotated, indicatingsyntectonic growth (Figure 6(c,d)). Garnet porphyro-blasts with asymmetric pressure shadows (Figure 6(e)),micas with mica-fish texture, and coarse biotite frac-tured at high angles to the mylonitic foliation are themain microstructures in metasediments surroundingthe intrusion (Figure 6(f)).
The main intrusive body has also been deformed(Figure 7(a-c)). Hornblende and biotite definestretching lineations and sometimes surround plagi-oclase, indicating the rotation of plagioclase as itcrystallized (Figure 7(d)). Some coarse plagioclaseand alkali feldspars locally are surrounded by fine-grained aggregates of these minerals and quartz(Figure 7(e-g)), especially in high-strain zones(Figure 7(i-l)). Inclusions of biotite and plagioclasein coarse K-feldspars are aligned (Figure 7(h)).Quartz grains between larger feldspars show ser-rated textures, making folded ribbons (Figure 7(l)).Some granitic rocks with striped gneissic fabric showthat K-feldspars and plagioclase are either replaced
Figure 6. Host rocks with evidence for deformation during contact metamorphism (a,b) sigmoidal and refolded quartz ribbons inthe spotted schist; elongated and syn-tectonic cordierite (c) with continuous foliation inside and outside a cordierite porphyroblast(d). (e) Syn-tectonic garnet with asymmetric pressure shadow. (f) Parallel fracture perpendicular to the mylonitic foliation in a biotiteporphyroblast. Bt: Biotite; Hbl: hornblende; Pl: plagioclase; Qtz: quartz; Grt: garnet; Crd: cordierite; Ap1 and Ap2: axial planes forfolds 1 and 2 generations.
INTERNATIONAL GEOLOGY REVIEW 7
with finer grained material or are aligned to makestriped gneiss texture that demonstrates ductiledeformation while the granite was still partially mol-ten (Figure 7(l)). Rotated trails of quartz inclusions ingarnets and also asymmetric garnets confirm thatcrystallization occurred during ductile deformation(Figure 7(m-o)). We conclude that shear structuresbegan forming when the magma partially crystal-lized and continued until the magma solidified(Bouchez and Gleizes 1995; Vauchez et al. 1997).
5. Analytical techniques
5.1. Zircon morphology and age dating
For age determinations, 1–2 kg of three granites (BGR5–7) and two appinites (SAMD-2, SAMD-4) wereselected. The samples were crushed by jaw crusherand then passed through 60 and 80 mesh sieves. Theclay-sized fraction was rinsed in tap and pure water,then dried in 110°C for a few hours. Hand magnet andFrantz magnetic separator were used to remove
Figure 7. Microstructures in the granitic rocks showing evidence for ductile deformation. Hornblende (a) and biotite (b,c) arealigned and biotite is rotated around plagioclase (d). Coarse alkali feldspars are aligned and surrounded by subgrains of alkalifeldspars (e–g). Orientation of plagioclase and biotite as inclusions in alkali feldspar megacrysts (h). Surrounded and oriented ofsubgrains around coarse-grained alkali feldspar with striped forms (i–l). Snowball garnet grains with rotated quartz inclusions (m,n)and aligned garnets (o). Bt: Biotite; Hbl: hornblende; Pl: plagioclase; Qtz: quartz; Grt: garnet.
8 H. AZIZI ET AL.
magnetic minerals, and then bromoform was used toseparate zircons, which were then purified by handpicking and mounted in epoxy. After polishing themounts on glass slides, back-scattered electron andcathodoluminescence (CL) images were obtained witha scanning electron microscope (JEOL JSM-6510LV)equipped with CL system (GATAN Mini CL) at NagoyaUniversity. Most grains in the granitic rocks (BGR 5–7)were broken due to crushing but some show prismaticshape with zoning (Figure 8(a-c)). Some zircons in appi-nites (SAMD-2, SAMD-4) show prismatic shapes lackinginternal structures but most show irregular, curved,inward-penetrating, patchy reaction zones. This istaken as evidence for re-equilibration of zircons formedby diffusion reaction and dissolution reprecipitation(Tomaschek 2004; Geisler et al. 2007). These morpholo-gies suggest that most zircons formed under disequili-brium conditions, perhaps due to magma mixing(Figure 8(d-e)).
Polished mounts were analysed by laser-ablationinductively coupled plasma mass spectrometer (LA-ICP-MS) Agilent 7700× model at Nagoya University(Table 1). The NIST-SRM 610 glass (Goolaerts et al.2004) was used for correcting U/Pb fractionation dur-ing sample measurement. Baneh complex zircons wereanalysed together with two standard zircons, 91500(Wiedenbeck et al. 2004) and OD-3 (Iwano et al.2013). The average ages determined for 91500 andOD-3 zircons were 1037 ± 34 Ma (2σ error, n = 13)and 31.0 ± 2.0 Ma (2σ error, n = 13), respectively. Adetailed description of the LA-ICP-MS analysis is pro-vided in Kouchi et al. (2015) and Orihashi et al. (2008).U–Pb ages were calculated using ISOPLOT software(Ludwig 1999).
5.2. Whole-rock geochemistry
After studying thin sections, we selected fresh samplesfor chemical and isotope analyses. Powders were gen-erated with a jaw crusher, roller, and agate mill, respec-tively. Glass beads were produced by mixing 0.5 g ofsample powder with 5.0 g of lithium tetraborate andmelted at 1200°C. X-ray fluorescence WD-XRF (RigakuZSX Primus II) at Nagoya University was used to mea-sure the major oxides. Loss of ignition (LOI) was calcu-lated based on weight loss upon heating to 950°C. Foranalyses of trace and rare earth elements (REEs) and87Sr/86Sr and 143Nd/144Nd, ~100 mg of sample powderwas digested using concentrated hydrofluoric andpercholoric acids in Teflon (PTFE) bottles that remainedon the hot plate for 2 days at 120–140°C. After drying,the sample cakes were redissolved in a few millilitredilute HCl (2–6 M) and then the liquid was centrifuged
at 3000 rpm for 15 min. Sample residues were dried andredigested at 180°C in sealed Teflon containers in high-pressure steel jackets. Finally, the dissolved sampleswere divided into two parts for trace element andradiogenic isotope analyses. After drying these splitsin PTFE, sample cakes were dissolved in dilute HNO3
(2%) solution for ICP-MS analysis of trace elements andREEs (for more information, see Azizi et al. 2015; Nouriet al. 2016).
5.3. Sr and Nd isotopes
To purify Sr and Nd, ion exchange chromatography HClcolumn was used. Purified samples were loaded onsingle tantalum and triple rhenium filaments for Srand Nd, respectively. The 87Sr/86Sr of the samples wasmeasured using a VG Sector 54 thermal ionization massspectrometer (TIMS) with seven Faraday cups. NIST-SRM987 was used as a Sr standard. During measurement ofthe samples, the 87Sr/86Sr of the standard was analysed13 times yielding 0.710257 ± 0.000020. For 143Nd/144Nd,the TIMS machine Isoprobe-T model with nine Faradaycups was used. JNdi-1 (Tanaka et al. 2000) was used asNd standard. During the sample analyses, the JNdi-1standard was analysed nine times yielding 143Nd/144Ndof 0.512113 ± 0.000011.
6. Results
6.1. Zircon U–Pb ages
Concordant zircons yield indistinguishable ages of39.7 ± 0.9 Ma (BGR-5), 40.5 ± 0.6 Ma (BGR-6), and41.0 ± 1.0 Ma (BGR-7) for the granite samples(Figure 9(a-c)). Appinitic rocks (SAMD-2 and SAMD-4)show two ages: 52–50 and 39–38 Ma. In detail, theold grains in SAMD-2 show 50.7 ± 0.9 Ma and inSAMD-4 show 52.6 ± 5.3 Ma. The young peaks are38.8 ± 0.4 and 39.1 ± 0.6 Ma for SAMD-2 and SAMD-4,respectively. Based on these ages, appinites began tocrystallize before granites and continued to crystallize~1 million years after host granitic rocks (Figure 9(d-f)).
6.2. Whole-rock geochemistry
The results of 24 whole-rock analyses from both groupsare listed in Table 2. Chemical compositions show somedifferences between the granite and appinite groups.Granitic rocks have high contents of SiO2 (62.4–77.0 wt%) along with low contents of TiO2 (0.25 wt%), MgO(0.05–1.57 wt%), and Fe2O3 (<4.06 wt%), and variableAl2O3 contents (13.05–18.90 wt%). The granitic rocksalso show high contents of Na2O + K2O (≈10 wt%)
INTERNATIONAL GEOLOGY REVIEW 9
with low values for LOI (<1.0 wt%) and Mg# (=100×molar Mg/molar Mg + Fe; 10–39). In contrast, appiniteshave low contents of SiO2 (51.0–57.0 wt%) and K2O
(<2.1 wt%) and high Fe2O3 (6.4–9.35 wt%) and MgO(2.0–9.9 wt%). In addition, appinites are richer in V (91–230 ppm), Ni (11–300 ppm), Cr (14–570 ppm), and Sr
Figure 8. Cathodoluminescence (CL) images of zircon grains from granitic (BGR-1, BGR-2, and BGR-3) and appinitic rocks (SAMD-2and SAMD-4). Analysed spots and ages are shown in the zircon grains (a–e).
10 H. AZIZI ET AL.
Table1.
LA-IC
P-MSanalyses
forzircon
grains
from
theBanehgranite
intrusion.
Spot
Th/U
207 Pb/
235 U
Error
206 Pb/
238 U
Error
207 Pb/
206 Pb
Error
235 U–2
07Pb
age
Error
238 U–2
06Pb
age
Error
2σ2σ
2σMa
2σMa
2σ
A:BG
R-5
B-GR5-01
0.99
0.319
0.042
0.0072
0.0005
0.3211
0.0359
281.4
37.0
46.3
3.2
B-GR5-06a
0.31
0.051
0.009
0.0066
0.0003
0.0557
0.0094
50.5
8.8
42.7
1.7
B-GR5-07a
0.48
0.043
0.009
0.0065
0.0003
0.0483
0.0097
42.9
8.9
41.7
1.8
B-GR5-08a
0.61
0.055
0.012
0.0062
0.0003
0.0641
0.0142
54.1
12.3
39.8
2.2
B-GR5-09
0.74
0.050
0.007
0.0064
0.0002
0.0567
0.0077
49.3
6.9
40.9
1.4
B-GR5-10
0.71
0.051
0.008
0.0063
0.0003
0.0594
0.0092
50.9
8.1
40.3
1.6
B-GR5-13a
0.82
0.031
0.005
0.0061
0.0002
0.0368
0.0059
30.8
5.1
39.1
1.4
B-GR5-14a
0.34
0.043
0.008
0.0057
0.0003
0.0551
0.0104
42.8
8.3
36.4
1.7
B-GR5-15a
0.46
0.042
0.005
0.0058
0.0002
0.0534
0.0065
42.3
5.4
37.1
1.2
B-GR5-16
0.77
0.056
0.010
0.0064
0.0003
0.0642
0.0112
55.6
10.1
40.9
1.9
B-GR5-17a
0.40
0.039
0.006
0.0061
0.0002
0.0470
0.0066
39.1
5.6
38.9
1.3
B-GR5-18a
0.47
0.041
0.007
0.0065
0.0002
0.0463
0.0071
41.0
6.5
41.5
1.5
B-GR5-21a
0.33
0.043
0.007
0.0061
0.0003
0.0508
0.0080
42.3
6.9
39.1
1.7
B-GR5-22a
0.37
0.046
0.008
0.0061
0.0003
0.0548
0.0092
45.7
7.9
39.2
1.8
B-GR5-24
0.55
0.002
0.000
0.0062
0.0003
0.0022
0.0004
1.9
0.4
39.9
1.9
B-GR5-25a
0.60
0.029
0.006
0.0060
0.0003
0.0355
0.0066
29.5
5.6
38.7
1.8
B-GR5-26a
0.50
0.040
0.009
0.0059
0.0003
0.0490
0.0105
39.4
8.7
37.7
2.0
B-GR5-28a
0.46
0.046
0.009
0.0064
0.0003
0.0521
0.0097
45.4
8.7
40.9
1.7
B-GR5-29
0.52
0.021
0.007
0.0063
0.0004
0.0242
0.0073
21.3
6.5
40.8
2.3
B-GR5-30a
0.27
0.039
0.008
0.0065
0.0003
0.0428
0.0087
38.5
8.0
42.1
1.7
B-GR5-31a
0.30
0.028
0.005
0.0059
0.0002
0.0345
0.0061
28.1
5.1
38.0
1.5
B-GR5-32a
0.55
0.033
0.005
0.0065
0.0002
0.0370
0.0049
33.2
4.5
41.8
1.1
B-GR5-33
0.30
0.058
0.009
0.0063
0.0002
0.0664
0.0104
57.1
9.2
40.6
1.6
B-GR5-36a
0.55
0.046
0.006
0.0062
0.0002
0.0535
0.0068
45.3
5.9
39.7
1.1
B-GR5-37a
0.39
0.032
0.005
0.0065
0.0002
0.0357
0.0052
32.1
4.8
41.9
1.5
B-GR5-40
1.36
0.129
0.016
0.0047
0.0003
0.1978
0.0200
123.1
15.0
30.4
2.1
B-GR5-41
0.42
0.097
0.018
0.0067
0.0004
0.1048
0.0181
93.8
17.0
43.0
2.4
B-GR5-42a
0.51
0.033
0.006
0.0065
0.0003
0.0370
0.0066
33.3
6.1
42.0
1.7
B-GR5-43
0.59
0.096
0.014
0.0062
0.0003
0.1132
0.0160
93.4
14.0
39.7
1.9
B-GR5-44
0.28
0.007
0.002
0.0058
0.0003
0.0092
0.0022
7.5
1.8
37.4
2.0
B-GR5-45a
0.24
0.050
0.006
0.0072
0.0002
0.0501
0.0054
49.6
5.6
46.5
1.4
B:BG
R-6
B-GR6-01
0.30
0.059
0.007
0.0066
0.0002
0.0651
0.0076
58.5
7.1
42.5
1.4
B-GR6-04
1.04
0.440
0.092
0.0127
0.0015
0.2517
0.0437
370.2
77.6
81.2
9.5
B-GR6-10
2.10
0.650
0.092
0.0074
0.0006
0.6406
0.0739
508.5
71.8
47.3
3.8
B-GR6-15
0.43
0.034
0.004
0.0059
0.0002
0.0422
0.0045
34.0
3.8
37.6
1.4
B-GR6-16a
0.33
0.040
0.009
0.0059
0.0003
0.0493
0.0105
39.6
8.7
37.6
2.0
B-GR6-17
1.29
0.980
0.140
0.0126
0.0010
0.5629
0.0665
693.8
99.4
80.9
6.6
B-GR6-21
1.47
0.829
0.108
0.0113
0.0008
0.5316
0.0579
613.1
80.2
72.5
5.2
B-GR6-25a
0.46
0.039
0.011
0.0062
0.0004
0.0453
0.0129
38.6
11.3
39.9
2.5
B-GR6-27a
0.53
0.046
0.010
0.0061
0.0003
0.0544
0.0120
45.3
10.3
39.1
2.1
B-GR6-28
1.90
0.193
0.023
0.0061
0.0004
0.2285
0.0223
179.5
21.2
39.5
2.6
B-GR6-29a
0.96
0.047
0.006
0.0066
0.0002
0.0511
0.0063
46.3
5.9
42.6
1.4
B-GR6-30a
1.15
0.035
0.004
0.0063
0.0002
0.0408
0.0042
35.3
3.8
40.4
1.1
B-GR6-39a
0.68
0.041
0.007
0.0062
0.0002
0.0481
0.0084
40.9
7.3
39.8
1.6
B-GR6-40a
0.54
0.047
0.008
0.0063
0.0002
0.0541
0.0085
46.9
7.5
40.8
1.5
B-GR6-42a
0.53
0.040
0.008
0.0065
0.0003
0.0447
0.0090
39.7
8.2
41.6
1.8
B-GR6-44a
0.32
0.056
0.018
0.0064
0.0005
0.0639
0.0202
55.4
18.0
40.9
3.0
(Con
tinued)
INTERNATIONAL GEOLOGY REVIEW 11
Table1.
(Con
tinued).
Spot
Th/U
207 Pb/
235 U
Error
206 Pb/
238 U
Error
207 Pb/
206 Pb
Error
235 U–2
07Pb
age
Error
238 U–2
06Pb
age
Error
2σ2σ
2σMa
2σMa
2σ
B-GR6-45
0.76
0.022
0.003
0.0061
0.0002
0.0266
0.0039
22.4
3.4
39.1
1.4
C:BG
R-7
B-GR7-01a
0.13
0.042
0.003
0.0065
0.0002
0.0472
0.0037
42.0
3.5
41.7
1.1
B-GR7-03
1.19
0.022
0.002
0.0060
0.0002
0.0266
0.0028
22.0
2.4
38.4
1.2
B-GR7-04a
0.60
0.041
0.004
0.0063
0.0002
0.0464
0.0041
40.3
3.7
40.7
1.1
B-GR7-05a
1.04
0.031
0.006
0.0058
0.0003
0.0389
0.0067
31.0
5.5
37.1
1.7
B-GR7-06a
0.88
0.034
0.005
0.0053
0.0002
0.0467
0.0063
34.2
4.7
34.2
1.2
B-GR7-07
0.51
0.002
0.000
0.0061
0.0003
0.0020
0.0003
1.7
0.2
39.5
1.7
B-GR7-08a
0.45
0.049
0.007
0.0072
0.0003
0.0488
0.0070
48.2
7.2
46.4
1.8
B-GR7-09a
0.56
0.037
0.005
0.0058
0.0002
0.0471
0.0059
37.3
4.9
37.0
1.4
B-GR7-10a
0.51
0.044
0.006
0.0059
0.0002
0.0547
0.0077
44.1
6.4
37.8
1.4
B-GR7-11a
1.22
0.036
0.005
0.0058
0.0002
0.0450
0.0065
36.0
5.3
37.4
1.3
B-GR7-12a
0.36
0.034
0.004
0.0067
0.0002
0.0366
0.0046
34.0
4.5
43.3
1.5
B-GR7-13
0.43
0.074
0.018
0.0065
0.0004
0.0827
0.0198
72.1
17.9
41.5
2.8
B-GR7-14
0.36
0.115
0.027
0.0061
0.0006
0.1369
0.0293
110.3
25.9
39.1
3.7
B-GR7-15a
0.66
0.039
0.010
0.0063
0.0004
0.0444
0.0116
38.4
10.3
40.5
2.3
B-GR7-16a
0.47
0.034
0.006
0.0071
0.0003
0.0346
0.0055
33.7
5.5
45.4
1.8
B-GR7-17a
1.01
0.045
0.007
0.0066
0.0003
0.0491
0.0079
44.4
7.4
42.4
1.9
B-GR7-18
0.57
0.058
0.010
0.0085
0.0004
0.0491
0.0084
57.0
10.1
54.7
2.3
B-GR7-19
0.66
0.026
0.003
0.0059
0.0002
0.0321
0.0031
26.2
2.7
38.0
1.1
B-GR7-20
0.58
0.054
0.006
0.0058
0.0002
0.0675
0.0076
53.6
6.3
37.5
1.3
B-GR7-21a
0.12
0.042
0.006
0.0066
0.0002
0.0457
0.0067
41.4
6.2
42.4
1.5
B-GR7-22
0.31
0.108
0.036
0.0065
0.0007
0.1203
0.0382
104.4
34.9
41.9
4.3
B-GR7-23a
0.16
0.031
0.005
0.0061
0.0002
0.0365
0.0058
30.9
5.0
39.5
1.6
B-GR7-24
0.18
0.004
0.001
0.0061
0.0003
0.0043
0.0010
3.7
0.9
39.2
2.0
B-GR7-25
1.04
0.001
0.000
0.0056
0.0003
0.0010
0.0002
0.8
0.2
36.2
2.1
B-GR7-26a
1.18
0.049
0.010
0.0068
0.0003
0.0529
0.0099
48.9
9.5
43.5
2.1
B-GR7-28a
0.28
0.049
0.007
0.0062
0.0003
0.0565
0.0075
48.2
6.7
40.1
1.6
B-GR7-30
0.80
0.070
0.006
0.0064
0.0002
0.0791
0.0059
69.0
5.5
41.4
1.2
B-GR7-31
1.03
0.043
0.004
0.0063
0.0002
0.0495
0.0047
42.5
4.2
40.2
1.3
B-GR7-33a
0.69
0.042
0.009
0.0067
0.0003
0.0458
0.0093
42.0
8.8
43.0
2.1
B-GR7-34
0.76
0.054
0.008
0.0066
0.0003
0.0595
0.0088
53.7
8.2
42.5
1.8
B-GR7-35a
0.93
0.038
0.004
0.0062
0.0002
0.0442
0.0041
37.9
3.7
40.1
1.2
B-GR7-36a
0.49
0.043
0.007
0.0067
0.0003
0.0468
0.0075
42.8
7.1
42.8
1.8
D:SA
MD-2
SAMD2-01
a0.64
0.038
0.009
0.0051
0.0003
0.0541
0.0119
37.6
8.5
32.6
1.7
SAMD2-02
a0.70
0.039
0.004
0.0058
0.0002
0.0490
0.0054
39.3
4.5
37.5
1.2
SAMD2-03
a0.71
0.058
0.011
0.0077
0.0004
0.0550
0.0101
57.5
10.9
49.4
2.3
SAMD2-04
a0.43
0.049
0.019
0.0081
0.0006
0.0439
0.0167
48.4
18.8
51.8
4.0
SAMD2-05
0.82
0.029
0.007
0.0042
0.0003
0.0490
0.0112
28.6
6.9
27.2
2.1
SAMD2-06
0.47
0.203
0.033
0.0037
0.0003
0.3980
0.0549
187.9
30.4
23.8
2.0
SAMD2-08
0.63
0.472
0.065
0.0063
0.0005
0.5443
0.0633
392.3
53.8
40.4
2.9
SAMD2-09
0.48
0.017
0.004
0.0078
0.0004
0.0156
0.0040
16.9
4.4
50.1
2.8
SAMD2-10
a0.68
0.043
0.011
0.0063
0.0004
0.0491
0.0123
42.5
10.9
40.6
2.3
SAMD2-11
a0.43
0.067
0.018
0.0088
0.0005
0.0552
0.0142
65.9
17.4
56.5
3.4
SAMD2-12
a0.47
0.038
0.013
0.0086
0.0005
0.0317
0.0110
37.6
13.2
55.4
3.4
SAMD2-13
a0.41
0.061
0.019
0.0067
0.0005
0.0658
0.0202
59.7
18.9
42.9
3.3
SAMD2-14
0.43
0.039
0.011
0.0063
0.0005
0.0445
0.0121
38.6
10.9
40.6
3.0
SAMD2-17
a1.39
0.039
0.008
0.0063
0.0003
0.0449
0.0093
38.7
8.3
40.4
2.2
SAMD2-18
a1.12
0.045
0.011
0.0060
0.0004
0.0551
0.0129
45.0
10.9
38.3
2.4
SAMD2-19
1.28
0.006
0.001
0.0053
0.0003
0.0076
0.0014
5.7
1.1
34.2
1.8
SAMD2-20
0.87
0.000
0.000
0.0057
0.0003
0.0006
0.0001
0.4
0.1
36.5
2.2
(Con
tinued)
12 H. AZIZI ET AL.
Table1.
(Con
tinued).
Spot
Th/U
207 Pb/
235 U
Error
206 Pb/
238 U
Error
207 Pb/
206 Pb
Error
235 U–2
07Pb
age
Error
238 U–2
06Pb
age
Error
2σ2σ
2σMa
2σMa
2σ
SAMD2-23
0.92
0.050
0.013
0.0048
0.0003
0.0757
0.0186
49.7
12.7
30.9
2.2
SAMD2-26
0.46
0.097
0.023
0.0049
0.0004
0.1453
0.0323
94.4
22.3
31.3
2.5
SAMD2-27
a0.39
0.047
0.023
0.0062
0.0006
0.0546
0.0267
46.6
23.3
40.1
4.0
SAMD2-29
a0.14
0.040
0.002
0.0062
0.0001
0.0470
0.0024
39.7
2.2
39.6
0.7
SAMD2-30
a0.14
0.040
0.002
0.0062
0.0001
0.0470
0.0020
39.8
1.8
39.7
0.7
SAMD2-32
0.44
0.084
0.023
0.0058
0.0005
0.1041
0.0268
81.8
22.0
37.6
2.9
SAMD2-34
0.50
0.135
0.038
0.0057
0.0006
0.1722
0.0460
128.2
36.6
36.4
3.7
SAMD2-35
0.73
0.001
0.000
0.0046
0.0002
0.0017
0.0003
1.1
0.2
29.7
1.3
SAMD2-36
0.77
0.020
0.002
0.0047
0.0001
0.0316
0.0035
20.4
2.3
30.1
0.8
SAMD2-38
0.46
0.008
0.003
0.0062
0.0004
0.0091
0.0029
7.9
2.6
40.2
2.6
SAMD2-39
1.00
0.054
0.011
0.0058
0.0003
0.0668
0.0131
53.2
10.8
37.6
1.9
SAMD2-40
a0.50
0.060
0.014
0.0081
0.0004
0.0538
0.0123
59.3
13.9
52.0
2.7
SAMD2-42
a0.79
0.055
0.008
0.0080
0.0003
0.0497
0.0074
54.2
8.4
51.4
1.9
SAMD2-43
a0.65
0.056
0.012
0.0087
0.0004
0.0462
0.0098
54.9
11.9
55.9
2.7
SAMD2-44
a0.45
0.032
0.012
0.0055
0.0004
0.0422
0.0160
31.8
12.3
35.1
2.7
SAMD2-45
0.72
0.078
0.015
0.0058
0.0003
0.0980
0.0179
76.4
14.6
37.2
2.1
SAMD2-46
a0.45
0.055
0.015
0.0067
0.0004
0.0595
0.0160
54.4
15.0
43.1
2.8
SAMD2-47
0.62
0.037
0.008
0.0065
0.0004
0.0416
0.0088
37.3
8.2
41.9
2.4
SAMD2-48
a0.41
0.044
0.014
0.0051
0.0004
0.0623
0.0196
43.4
14.1
32.7
2.5
E:SA
MD-4
SAMD-4-1
a0.69
0.045
0.009
0.0061
0.0003
0.0541
0.0104
45.1
9.0
39.2
39.6
SAMD-4-2
0.60
0.006
0.002
0.0059
0.0003
0.0077
0.0018
6.3
1.5
37.8
2.1
SAMD-4-7
a0.49
0.041
0.008
0.0062
0.0003
0.0488
0.0085
41.3
7.5
39.6
1.9
SAMD-4-9
0.40
0.063
0.017
0.0057
0.0004
0.0797
0.0205
61.9
16.6
36.7
2.2
SAMD-4-19a
0.44
0.056
0.012
0.0084
0.0005
0.0479
0.0102
55.0
12.2
54.1
2.0
SAMD-4-20a
0.39
0.052
0.013
0.0069
0.0005
0.0544
0.0132
51.5
13.0
44.6
2.9
SAMD-4-21a
0.38
0.052
0.011
0.0090
0.0005
0.0424
0.0086
51.8
10.9
57.5
3.1
SAMD-4-22a
0.88
0.042
0.007
0.0064
0.0003
0.0477
0.0077
42.1
7.1
41.3
2.1
SAMD-4-25
0.63
0.024
0.006
0.0061
0.0003
0.0291
0.0069
24.5
6.0
39.1
2.1
SAMD-4-26a
0.66
0.045
0.011
0.0058
0.0003
0.0559
0.0134
44.7
11.0
37.5
2.1
SAMD-4-27
0.43
0.023
0.004
0.0060
0.0003
0.0274
0.0052
22.7
4.5
38.5
1.9
SAMD-4-30a
0.85
0.038
0.007
0.0059
0.0002
0.0470
0.0080
38.1
6.6
37.9
1.5
SAMD-4-32
0.68
0.061
0.014
0.0064
0.0004
0.0682
0.0150
59.8
13.5
41.4
2.4
SAMD-4-33a
0.40
0.034
0.009
0.0058
0.0004
0.0420
0.0115
33.6
9.5
37.4
1.9
SAMD-4-34a
0.38
0.024
0.008
0.0055
0.0004
0.0311
0.0100
23.7
7.8
35.5
2.7
SAMD-4-36a
0.44
0.026
0.009
0.0074
0.0006
0.0256
0.0087
26.1
9.1
47.4
3.6
SAMD-4-37
0.37
0.045
0.014
0.0067
0.0005
0.0486
0.0142
44.8
13.6
43.3
3.4
SAMD-4-41a
0.39
0.050
0.011
0.0081
0.0004
0.0446
0.0092
49.2
10.5
51.9
3.3
SAMD-4-42a
0.18
0.033
0.005
0.0065
0.0002
0.0373
0.0049
33.4
4.5
41.8
1.5
SAMD-4-43a
0.57
0.069
0.009
0.0091
0.0003
0.0550
0.0071
67.5
9.0
58.2
2.1
SAMD-4-44a
0.63
0.035
0.009
0.0058
0.0003
0.0441
0.0104
35.4
8.5
37.5
2.0
SAMD-4-46
0.78
0.020
0.003
0.0075
0.0003
0.0196
0.0027
20.4
2.9
48.2
1.8
SAMD-4-47a
0.74
0.047
0.008
0.0073
0.0003
0.0460
0.0080
46.2
8.3
47.1
2.0
SAMD-4-48a
0.53
0.063
0.014
0.0073
0.0004
0.0623
0.0138
61.9
14.2
47.0
2.7
SAMD-4-49
0.52
0.006
0.001
0.0082
0.0003
0.0053
0.0007
6.1
0.8
52.8
2.1
SAMD-4-50a
0.38
0.060
0.014
0.0073
0.0005
0.0598
0.0135
59.2
13.9
46.8
2.9
SAMD-4-51
0.66
0.006
0.001
0.0060
0.0003
0.0077
0.0016
6.4
1.4
38.4
2.1
SAMD-4-52a
0.71
0.036
0.008
0.0060
0.0003
0.0443
0.0100
36.4
8.4
38.4
2.1
SAMD-4-53a
0.47
0.051
0.010
0.0061
0.0003
0.0604
0.0117
50.5
10.1
39.4
2.2
SAMD-4-54a
0.62
0.062
0.010
0.0100
0.0005
0.0449
0.0073
61.2
10.3
64.4
3.0
a Selectedforconcordia.
INTERNATIONAL GEOLOGY REVIEW 13
Figure 9. Concordia diagrams for analysed zircons. Concordant ages are determined for three granite samples: 39.69 ± 0.88 Ma(BGR-5), 40.5 ± 0.56 Ma (BGR-6), and 41.0 ± 0.98 Ma (BGR-7) (Figure 7(a-c)). The two appinite samples (SAM-2 and SAMD-4) yieldtwo groups of ages. The old grains show 50.7 ± 0.9 and 52.6 ± 5.3 Ma for SAMD-2 and SAMD-4, respectively (d–f) but the younggrains (g,h) show 38.8 ± 0.4 Ma (SAMD-2) and 39.1 ± 0.6 Ma (SAMD-4). Based on this dating, appinitic rocks crystallized ~1 millionyears after the host granitic rocks.
14 H. AZIZI ET AL.
Table2.
Who
le-rocks
compo
sitio
nof
Banehintrusion.
Sample
Unit
SAMG-
1SA
MG-
2SA
MG-
6SA
MG-
7SA
MG-
8SA
MG-
9SA
MG-
10SA
MG-
11SA
MG-
12SA
MG-
14SA
MP-
1SA
MP-
2SA
MP-
3SA
MD-
1SA
MD-
2SA
MD-
3SA
MD-
4SA
MD-5
SAMD-
6SA
MD-
7SA
MG-
3SA
MG-
4SA
MG-
5SA
MD-8
Rock
type
Granite
Diorite–
Appinite
Gabbroic
dike
SiO2
%76.0
76.7
62.4
68.2
74.0
75.6
71.8
73.9
75.4
74.7
77.0
76.9
76.1
56.8
56.4
55.1
57.0
53.1
54.8
51.4
56.0
55.6
53.6
51.0
TiO2
%0.01
0.00
0.50
0.25
0.00
0.03
0.21
0.03
0.00
0.01
0.02
0.04
0.02
0.48
0.57
0.61
0.51
0.62
0.49
0.53
0.73
0.79
0.66
0.57
Al2O
3%
14.0
13.1
18.9
15.6
16.1
13.6
15.0
13.6
14.1
14.2
13.5
13.1
14.0
9.6
13.9
15.5
12.7
13.2
13.5
17.3
17.1
19.8
12.3
16.6
Fe2O
3%
1.33
1.29
4.62
2.97
1.53
2.00
2.59
1.82
1.28
1.38
0.54
0.99
0.40
7.12
7.54
7.57
7.04
8.50
7.44
5.99
7.17
7.25
9.35
6.43
MnO
%0.10
0.11
0.08
0.07
0.11
0.17
0.06
0.10
0.19
0.09
0.04
0.01
0.00
0.15
0.14
0.13
0.132
0.17
0.14
0.10
0.14
0.11
0.19
0.11
MgO
%0.08
0.07
1.47
0.67
0.09
0.12
0.68
0.10
0.11
0.09
0.05
0.08
0.08
9.9
7.27
6.42
8.48
8.91
8.27
9.04
5.56
2.04
9.06
10.3
CaO
%0.37
0.51
3.94
1.97
0.46
0.56
1.85
0.69
0.63
0.67
0.87
0.67
0.52
11.6
8.80
9.09
9.47
10.64
9.76
8.90
8.50
6.16
9.94
8.85
Na 2O
%4.28
3.94
4.44
4.50
3.38
3.78
4.22
4.23
2.68
5.04
4.87
4.19
3.17
1.89
2.35
2.43
2.26
2.09
2.50
3.08
2.95
3.71
2.69
2.98
K 2O
%3.97
4.46
2.88
3.36
5.16
4.61
3.52
4.09
6.38
3.88
3.38
4.03
6.43
1.45
1.78
1.92
1.39
1.45
1.50
1.35
1.38
2.74
0.91
0.88
P 2O5
%0.14
0.08
0.20
0.14
0.10
0.08
0.14
0.08
0.07
0.19
0.03
0.02
0.02
0.11
0.13
0.18
0.13
0.11
0.11
0.08
0.13
0.28
0.16
0.10
LOI
%0.56
0.21
0.65
1.03
0.30
0.37
0.53
0.44
0.25
0.23
0.21
0.46
0.29
0.74
1.12
1.06
1.25
1.25
1.11
2.42
0.94
0.77
1.21
2.47
TOTA
L%
100.8
100.4
100.1
98.8
101.2
100.9
100.6
99.0
101.1
100.5
100.5
100.5
101.0
99.9
100.0
100.0
100.3
100.1
99.6
100.2
100.6
99.3
100.1
100.3
Mg#
11.0
9.9
38.6
31.0
9.9
10.2
34.1
10.2
14.8
11.3
15.0
13.5
27.9
73.4
65.7
62.7
70.5
67.5
68.8
74.9
60.6
35.8
65.7
76.1
Scpp
m1.83
2.28
9.03
3.15
1.78
1.95
3.74
2.05
2.07
1.55
1.81
1.47
0.817
37.6
28.8
27.4
27.8
31.0
33.4
23.5
24.6
11.1
32.0
21.7
Vpp
m1.24
1.39
57.2
11.1
1.59
1.89
22.4
3.90
2.01
2.46
1.17
4.76
2.06
178
191
203
167
206
200
123
203
91.1
145
123
Crpp
m12.8
4.29
24.3
8.72
8.60
8.18
10.3
5.59
10.5
25.7
12.1
6.56
8.66
454
314
202
437
438
319
362
40.2
15.6
571
473
Copp
m0.369
0.432
7.88
2.94
0.407
0.676
3.41
0.643
0.726
0.471
0.261
0.483
0.598
34.2
28.5
25.3
29.3
30.4
28.5
27.7
21.5
11.8
32.1
30.7
Ni
ppm
3.60
3.84
12.5
3.62
2.85
5.94
6.64
4.13
2.65
2.54
2.30
4.36
4.12
123
67.2
50.1
118
101
69.4
150
7.78
6.98
129
223
Cupp
m11.0
7.91
7.34
3.95
4.98
9.19
5.03
6.83
14.2
4.82
4.57
9.00
5.41
101
46.0
46.8
49.2
45.3
62.4
50.5
19.2
17.5
13.7
54.6
Znpp
m37.3
4.26
59.5
43.7
5.71
16.0
43.6
16.2
6.99
26.1
5.09
6.76
4.73
56.0
66.9
71.4
64.9
76.3
63.9
43.2
58.2
88.8
124
44.9
Ga
ppm
17.3
11.2
21.6
16.1
10.9
10.9
16.3
12.0
10.8
18.9
13.1
12.5
11.9
11.0
15.1
16.6
14.2
14.2
14.2
12.3
15.8
22.6
17.6
12.2
Rbpp
m182
69.8
102
91.4
97.6
92.2
106
67.5
121
114
164
159
179
47.8
60.2
56.5
41.5
39.4
52.0
53.5
47.0
120
24.5
31.6
Srpp
m4.27
33.9
324
186
27.5
30.0
154
69.9
86.9
18.5
18.9
25.9
20.3
180
293
404
239
349
349
329
332
449
233
298
Zrpp
m42.0
55.6
156
147
56.6
57.8
29.0
43.9
43.1
33.1
69.5
47.7
64.1
41.2
55.4
58.6
36.5
41.5
37.8
62.7
47.8
62.9
48.3
62.0
Nb
ppm
6.08
0.316
11.9
10.5
1.02
1.05
10.4
3.13
1.00
7.33
6.26
9.14
2.11
6.14
8.46
6.32
6.08
5.52
4.76
3.25
5.42
6.84
8.84
3.43
Cspp
m12.4
1.36
5.34
3.32
2.18
1.89
5.45
1.22
2.60
3.13
10.5
4.01
4.37
1.75
2.12
2.29
2.90
2.45
3.17
2.04
3.56
8.54
1.99
1.41
Bapp
m15.2
280
537
461
268
290
324
475
612
69.4
35.2
66.5
135
136
175
234
136
253
159
100
179
548
85.9
92.7
Pbpp
m18.0
31.8
28.2
22.1
27.6
31.8
22.6
35.8
35.8
15.0
24.4
32.0
34.7
6.57
8.12
8.25
6.96
6.44
7.26
4.39
7.72
10.9
6.65
3.93
Thpp
m4.78
1.88
9.68
11.6
1.74
1.69
8.82
2.67
4.48
2.31
14.6
12.0
10.5
4.69
5.28
4.37
4.93
1.86
4.04
2.02
4.49
3.12
3.75
2.14
Upp
m2.51
0.724
1.24
3.054
0.532
0.232
0.831
0.369
0.649
0.767
2.75
1.41
2.33
1.19
1.48
0.833
1.31
0.432
1.25
0.253
1.39
1.63
1.20
0.342
Tapp
m2.14
2.21
3.88
3.99
2.30
2.12
1.01
1.63
1.72
1.88
3.13
2.40
3.18
1.58
2.20
1.98
1.59
1.75
1.58
1.72
1.69
2.06
2.15
1.70
Hf
ppm
0.979
0.108
0.739
0.846
0.218
0.168
0.729
0.221
0.171
0.842
0.745
0.766
0.446
0.515
0.797
0.452
0.525
0.417
0.371
0.238
0.430
0.623
0.484
0.265
Ypp
m8.05
19.0
15.8
14.1
12.1
19.6
12.2
21.0
16.1
6.48
9.31
5.15
9.29
14.5
17.9
17.8
15.2
18.8
13.9
11.8
14.8
24.8
32.0
12.3
Lapp
m2.46
3.52
30.1
23.4
3.38
4.17
15.6
6.08
6.69
1.34
15.0
12.4
12.1
11.4
14.0
15.9
11.7
10.1
11.1
6.63
11.8
11.5
23.2
6.16
Cepp
m6.92
5.98
56.7
41.5
5.84
7.33
30.3
11.0
13.5
3.54
29.7
23.0
20.8
22.1
30.8
33.1
26.8
24.0
21.8
13.9
24.0
29.4
54.0
13.1
Prpp
m0.878
0.608
6.12
4.34
0.654
0.775
3.22
1.18
1.49
0.470
3.13
2.27
2.12
2.63
3.77
3.85
3.29
3.27
2.60
1.68
2.78
3.73
7.21
1.65
Nd
ppm
3.46
2.12
22.95
14.7
2.23
2.63
11.8
4.23
5.11
1.82
10.4
7.41
7.07
10.6
14.8
15.3
13.0
14.6
11.1
7.09
11.2
15.8
31.2
7.20
Smpp
m1.33
0.549
4.199
2.65
0.530
0.612
2.45
0.977
1.16
0.900
2.14
1.41
1.53
2.44
3.31
3.24
2.74
3.45
2.44
1.64
2.40
3.64
6.64
1.80
Eupp
m0.012
0.121
1.230
0.552
0.094
0.098
0.254
0.222
0.243
0.052
0.060
0.076
0.076
0.686
0.968
0.891
0.727
0.945
0.728
0.633
0.986
1.10
1.57
0.608
Gd
ppm
1.26
1.15
3.851
2.36
0.880
1.13
2.29
1.59
1.36
1.201
1.69
1.14
1.41
2.66
3.42
3.19
2.76
3.44
2.50
1.90
2.51
3.60
6.50
2.03
Tbpp
m0.265
0.316
0.531
0.366
0.241
0.343
0.377
0.426
0.321
0.243
0.266
0.168
0.236
0.411
0.516
0.489
0.404
0.539
0.387
0.329
0.414
0.586
0.964
0.346
Dy
ppm
1.60
2.92
2.95
2.36
1.86
2.96
2.38
3.48
2.63
1.36
1.59
0.994
1.52
2.71
3.34
3.28
2.73
3.43
2.59
2.17
2.71
4.14
6.02
2.29
Ho
ppm
0.264
0.663
0.579
0.486
0.428
0.649
0.420
0.731
0.606
0.200
0.322
0.201
0.301
0.558
0.662
0.682
0.570
0.705
0.531
0.426
0.573
0.841
1.19
0.488
Erpp
m0.670
2.08
1.60
1.47
1.32
1.84
1.16
2.019
1.84
0.529
1.02
0.578
0.876
1.64
2.08
1.98
1.69
2.14
1.53
1.33
1.62
2.63
3.39
1.43
Tmpp
m0.103
0.327
0.218
0.225
0.213
0.284
0.162
0.271
0.284
0.083
0.176
0.095
0.136
0.231
0.305
0.303
0.253
0.308
0.225
0.188
0.258
0.380
0.486
0.209
Ybpp
m0.588
2.27
1.48
1.60
1.38
1.84
0.989
1.65
1.98
0.513
1.29
0.657
0.959
1.48
1.87
1.93
1.67
1.90
1.50
1.31
1.59
2.46
3.17
1.36
Lupp
m0.071
0.321
0.223
0.243
0.212
0.258
0.138
0.197
0.265
0.070
0.202
0.103
0.144
0.232
0.289
0.301
0.264
0.296
0.226
0.187
0.235
0.333
0.467
0.211
Mg#
=[M
gO]/([M
gO]+[FeO
]).
INTERNATIONAL GEOLOGY REVIEW 15
(179–449 ppm) and have higher Mg number(Mg# = 35–76); some have Mg# and Ni and Cr contentsexpected for primitive mantle-derived magmas. Thechemical data confirm different compositions for separ-ating appinites and granites into two distinct groups.
Harker diagram variations (Figure 10(a-h)) confirm dif-ferent patterns for rocks of the Baneh appinite–granite
complex and show that the appinites are distinguished bysignificantly higher contents of CaO, TiO2, MgO, and FeOt.Chondrite-normalized REE patterns (McDonough and Sun1995) for both groups show strong light REE enrichment(Figure 11) and flat heavy REE patterns (HREE).Surprisingly, the concentrations of REEs in the appinitesare higher than in the granitic rocks. The strongly negative
Figure 10. Harker diagrams (a–h) confirm the mafic nature of Baneh appinites and the felsic nature of Baneh granites.
16 H. AZIZI ET AL.
Eu anomaly observed for granitic rocks implies an impor-tant role for fractionation of or residual feldspar (Weill andDrake 1973).
In plots of FeOt/(FeOt + MgO) (wt%) versus SiO2 (wt%)(Frost et al. 2001), the granitic rocks mostly plot in theferroan field whereas appinitic rocks mostly plot in themagnesian field (Figure 12(a)). In the plot ofNa2O + K2O − CaO (wt%) versus SiO2, the granitic rocksplot in the alkali-calcic or calc-alkaline field, whereas appi-nites plot in the calcic field (Figure 12(b)). In the Shanddiagram, granitic rocks have A/CNK > 1.0 and classify asslightly peraluminous, plotting near the boundary of I- andS-typegranites; appinites classify asmetaluminouswith lowA/CNK (Figure 12(c)). In variation diagrams using Zr, Nb, Ce,andY versus 10,000Ga/Al (Whalen et al. 1987), bothgranitesand appinites plot in the I–S granite fields (Figure 13(a-d)).High contents of Rb and Ta with low contents of Yb in bothgroups plot as volcanic arc (Figure 14(a-b)) but based onTa–Yb concentrations, the samples extend to the syn-oro-genic domain (Pearce et al. 1984) (Figure 14(c)). In theHarriset al. (1986) Hf–Rb–Ta triangle diagram, all samples plot ingroups 2 and 3 as syn-orogenic to post-orogenic granitewithmodest affinities to the activemargin andwithin-platefields (Figure 14(d)). Based on the R1–R2 cationic classifica-tion (Batchelor and Bowden 1985), the granitic and appini-tic rocks mainly plot in the syn-collision and mantle-fractionate granite field, respectively (Figure 14(e)).
6.3. Sr–Nd isotope ratios
Table 3 lists 87Sr/86Sr and 143Nd/144Nd measured andinitial ratios for 24 whole-rock samples. The initial ratiosand Nd epsilon notation (εNd(t)) are calculated based on
zircon U–Pb ages (40 Ma). To calculate initial ratios, the87Rb/86Sr and 147Sm/144Nd were calculated based on thechemical composition of whole rocks. In addition,because of some alteration and fractionated nature ofthe granite samples, two-stage Nd model ages (TDM2)were calculated based on the method of Keto andJacobsen (1987). 87Rb/86Sr shows a wide range for thegranitic rocks (0.914–124) but is much lower (<0.77) inthe appinites. Initial 87Sr/86Sr and 143Nd/144Nd ratios inboth groups are broadly similar. If we filter out graniticsamples with high 87Rb/86Sr (>2) because propagation ofthe 87Rb/86Sr or age error can result in mis-correcting87Sr/86Sr(i), three granites have 87Sr/86Sr(i) = 0.7051–0.7062 compared to 11 appinites with (87Sr/86Sr)i = 0.7045–0.7057; the 87Sr/86Sr(i) ratios for appinites areslightly lower than the granites. In contrast, εNd(40 Ma) forboth types are mostly similar – with one exception – withvalues around zero. The exception is a primitivemafic dikewith asthenosphere-like εNd(40 Ma) ~+9.9. The
87Sr/86Sr(i)versus εNd(40 Ma) diagram (Figure 15(a)) shows that mostsamples plot near the Bulk Earth. One appinitic sample(SAMD-3) has an unusually high 87Sr/86Sr(i), for which wehave no explanation. The variation of 87Sr/86Sr(i) and εNd
(40 Ma) versus SiO2 for most samples shows horizontal trendfor both groups and varies little with SiO2 supporting anoverall interpretation of magma differentiation for bothappinitic and granitic groups (Figure 15(b,c)).
7. Discussion
In this section, we use our new results to discuss thegeodynamic setting, magma source, and emplacementstyle of the Baneh pluton.
Figure 11. Chondrite-normalized REE diagrams (normalization following McDonough and Sun 1995). Note the strong Eu negativeanomalies for the granite group, which are not observed in the appinitic rocks.
INTERNATIONAL GEOLOGY REVIEW 17
Figure 12. Major element characterization of Baneh complex igneous rocks. On the plot of SiO2 (wt%) versus FeO(t)/(FeO(t) + MgO) (Frost et al. 2001), the appinitic and granite samples plot in the magnesian and ferroan granite fields, respectively(a). On the plot of SiO2 (wt%) versus Na2O + K2O − CaO, the appinitic rocks show typical calcic features but granitic rocks aremore similar to calc-alkaline and alkali-calcic rocks (b). In the Shand (1951), appinitic rocks plot as metaluminous and graniticrocks plot as peraluminous (c).
18 H. AZIZI ET AL.
7.1. Geodynamic setting
The satellite ETM+ data (processed as bands 7, 4, and 1processed as R, G, and B; Figure 16(a)) and also theimage filtered to remove shadows confirm a sigmoidalform for the Baneh intrusion (Figure 16(a,b)). As wediscussed in Section 2, structures at all scales confirman important role for shear during magma emplace-ment. The asymmetric folds of the host rocks nearcontacts with the intrusion and also folded and boudi-naged intrusions and enclaves, with mineral stretchinglineation of elongated plagioclase and mafic minerals,in addition to some S–C structures (Passchier andTrouw 2005) confirm shearing during injection andafter emplacement of the granitic magma.
Magma generation and injection in transpressionalshear zones has been studied by many researchers(Hollister and Crawford 1986; Clemens and Mawer1992; Hutton and Reavy 1992; Vauchez et al. 1997; Pe-Piper et al. 1998; Acocella and Rossetti 2002; Annenet al. 2006; Ciancaleoni and Marquer 2006; Dong et al.2011). Transpression has been suggested to be impor-tant along the main Zagros fault and in the SNSZ(Mohajjel and Fergusson 2000; Authemayou et al.2006; Sarkarinejad 2007; Sarkarinejad and Azizi 2008;Moosavi et al. 2014). Mohajjel and Fergusson (2000),based on sheared structures that overprint marble,
schist and granitoid bodies in the SNSZ, suggestedthat dextral transpressional system occurred in theLate Cretaceous due to early convergence betweenAfro-Arabia and Iran. Sarkarinejad and Azizi (2008)reported clear flexural duplex structures in the Zagrosshear zone, consistent with transpressional conver-gence. Moosavi et al. (2014) documented multiple epi-sodes of deformation of granitic rocks in the centre ofthe SNSZ with shallow dipping reverse and dextralstrike-slip faults; on this basis, they concluded that atranspressional tectonic regime existed in LateCretaceous–Palaeocene time. Asymmetric and recum-bent folds of Cretaceous sediments around the Banehpluton, along with the asymmetric-to-rhombohedralshape of the granitic body, confirm that intrusionoccurred along the Zagros strike-slip fault while it wasactive, and our U–Pb zircon ages indicate that thisepisode of transpression occurred in late Eocene time,~38–41 Ma.
Transpression along the Zagros dextral strike-slipfault made an asymmetric pull-apart basin wherelower crustal and upper mantle partial melts couldinvade. Geodynamic models suggest that pull-a-partbasins form with low angle to the main fault trendduring the lateral movement in shear zones (Castroand Fernández 1998; Fernández and Castro 1999;
Figure 13. Whalen et al. (1987) diagrams for discriminating granitic types. Both granite and appinites show low Ga/Al, Zr, Nb, Ce,and Y compared to A-type granites and plot in the I and S-type granite fields (a–d).
INTERNATIONAL GEOLOGY REVIEW 19
Tikoff et al. 1999; Vigneresse et al. 1999). During shear-ing, lower crustal and upper mantle melts flowed intothe extended region beneath the pull-apart basin.During magma injection, minerals aligned with flowand deformation, partially digested enclaves werefolded and stretched, and asymmetric folds in the sur-rounding sediments reflected the ductile deformationdeveloped in and around semi-crystallized magma.
Rotated foliation and ring structures in the centre ofthe intrusion indicate that shear intensity varied overthe complex. In the late stage of magma injection dur-ing shearing, the solidifying granitoid body continuedto be affected and the final stage of magmatic activityoccurred as parallel dikes with low angles to the mainfault orientation. Our conceptual model is summarizedin Figure 17(a-f). A similar mechanism may be
Figure 14. Tectonic setting discrimination of granitic rocks in Pearce et al. (1984), Harris et al. (1986), and Batchelor and Bowden(1985) diagrams. In Pearce et al. (1984) diagrams, the samples for both groups show clear relation with typical volcanic arc and syn-collision granites (a–c). In the Harris et al. (1986) diagram (d), most granites plot in fields for group 2 (collision granite) whereasappinites mostly plot in the group 3 field (late-to-post-orogenic granite). In the R1–R2 cationic diagram of Batchelor and Bowden(1985) (e), granitic rocks plot in the syn-collision granite field and appinitic rocks plot in the field for mantle fractionates.VAG: Volcanic arc granite; WPG: within plate granite; ORG: oceanic ridge granite; COLG: collision granite.
20 H. AZIZI ET AL.
Table3.
Who
lerockspresentandinitial
ratio
sof
SrandNdisotop
esforBanehIntrusion.
Sample
RbSr
Nd
Sm87Rb
/86 Sr
87Sr/86 Sr
±IS
E87Sr/86 Sr
147 Sm/144Nd
143 Nd/
144 Nd
±IS
E143 Nd/
144 Nd
EpsNdi
T DM
ppm
ppm
ppm
ppm
Present
Initial
Present
Initial
Ga
Granite
SAMG-1
182
4.27
3.46
1.33
124
0.76922
0.000009
0.232
0.51259
0.000007
0.5013
−1.20
SAMG-2
7033.9
2.12
0.549
5.97
0.70881
0.000006
0.157
0.51260
0.000006
0.5126
−0.59
1.36
SAMG-6
102
324
23.0
4.20
0.914
0.70673
0.000007
0.7061
0.111
0.51250
0.000005
0.5125
−2.28
0.93
SAMG-7
91.4
186
14.7
2.65
1.42
0.70648
0.000007
0.7056
0.109
0.51258
0.000004
0.5126
−0.59
0.79
SAMG-8
97.6
27.5
2.23
0.530
10.3
0.70999
0.000005
0.144
0.51259
0.000004
0.5126
−0.56
1.13
SAMG-9
92.2
30.0
2.63
0.612
8.90
0.70932
0.000006
SAMG-10
106
154
11.8
2.45
1.95
0.70630
0.000006
0.7051
0.125
0.51262
0.000003
0.5126
−0.04
0.87
SAMG-11
67.5
69.9
4.23
0.977
2.80
0.70800
0.000006
0.7062
0.140
0.51257
0.000004
0.5125
−0.94
1.12
SAMG-12
121
86.9
5.11
1.16
4.04
0.70749
0.000007
0.138
0.51260
0.000004
0.5126
−0.35
1.03
SAMG-14
114
18.5
1.82
0.900
17.8
0.70528
0.000007
SAMP-1
164
18.9
10.4
2.14
25.2
0.71698
0.000005
0.125
0.51257
0.000004
0.5125
−0.99
0.95
SAMP-2
159
25.9
7.41
1.41
17.8
0.71397
0.000007
0.115
0.51256
0.000004
0.5125
−1.07
0.87
SAMP-3
179
20.3
7.07
1.53
25.6
0.71870
0.000006
0.115
Diorite–app
inite
SAMD-1
47.8
180
10.6
2.44
0.770
0.70553
0.000006
0.7050
0.139
0.51254
0.000007
0.5125
−1.60
1.17
SAMD-2
60.2
293
14.8
3.31
0.595
0.70611
0.000006
0.7057
0.135
0.51249
0.000004
0.5124
−2.56
1.20
SAMD-3
56.5
404
15.3
3.24
0.405
0.71350
0.000006
0.7132
0.128
0.51256
0.000004
0.5125
−1.22
1.00
SAMD-4
41.5
239
13.0
2.74
0.502
0.70553
0.000006
0.7052
0.127
0.51254
0.000004
0.5125
−1.45
1.01
SAMD-5
39.4
349
14.6
3.45
0.327
0.70524
0.000005
0.7050
0.143
0.51256
0.000004
0.5125
−1.14
1.17
SAMD-6
52.0
349
11.1
2.44
0.431
0.70524
0.000006
0.7050
0.134
0.51257
0.000005
0.5125
−1.01
1.04
SAMD-7
53.5
329
7.09
1.64
0.471
0.70480
0.000006
0.7045
0.139
0.51275
0.000005
0.5127
2.56
0.77
SAMG-3
47.0
332
11.2
2.40
0.409
0.70505
0.000007
0.7048
0.129
0.51264
0.000004
0.5126
0.43
0.87
SAMG-4
120
449
15.8
3.64
0.777
0.70606
0.000006
0.7056
0.139
0.51255
0.000004
0.5125
−1.46
1.15
SAMG-5
24.5
233
31.2
6.64
0.305
0.70582
0.000007
0.7056
0.129
0.51255
0.000004
0.5125
−1.39
1.02
Maficdike
SAMD-8
31.6
298
7.20
1.80
0.307
0.70493
0.000007
0.7047
0.151
0.51313
0.000022
0.5131
9.86
0.05
The
Nd
and
Srnaturalisotop
eratio
swere
norm
alized
based
onthe
146 Nd/
144 Nd
=0.7219
and
86Sr/88 Sr=
0.1194.Averages
and
ISE
forisotop
eratio
standards,
JNdi-1
and
NIST-SRM987,
are
143 Nd/
144 Nd=0.512113
±0.00006(n
=9)
and
87Sr
/86 Sr=0.710244
±0.000009
(n=11).TheCH
UR(Cho
ndriticUniform
Reservoir)values,1
47Sm
/144Nd=0.1967
and
143 Nd/
144 Nd=0.512638,w
ereused
tocalculate
theε N
d(0)(DePaolo
andWasserburg1979).TheBA
BI(Basaltic
Acho
driticBestInitial)value,
87Sr/86 Sr=0.69899,
and
87Rb
/86 Srratio
sof
UR(und
ifferentiatedreservoir)=0.0827
wereused.p
:Present;I:initialratios.
Italicsindicate
samples
with
high
87Rb
/86 Sr(>2)
notpreferredforcalculating.
INTERNATIONAL GEOLOGY REVIEW 21
responsible for the concentration of ~40 Ma S-typegranites along the Main Zagros Fault between 35° and37°N (Figure 1(b)).
Figure 17 shows how subduction and beginningcollision may have caused the NW-trending dextralshear zone and drawn in melts from a lower crustalshear zone. In Figure 17(a), an N-dipping subductionzone is active beneath Anatolia and Iran ~50 Ma, form-ing a ‘deep crustal hot zone’ (Annen et al. 2006) wherehydrous mantle melts (appinites) were stored andmelted older crust and sediments. This is consistentwith the age of old zircons in appinites. In Figure 17(b), collision is underway in Anatolia by ~42 Ma but Iranis still the site of normal subduction. This progressivelydisplaced the western part of the convergence zonenorthwards, forming a dextral shear zone that con-nected the two convergence zones and drew in meltsfrom the lower crustal hot zone into local regions oftranstension. The lower crustal hot zone was a hetero-geneous mixture of lower crustal S-type felsic melts(mostly on top) and mantle-derived mafic melts (mostlyon bottom). In Figure 17(c), movement of the magmaentrained previously crystallized mafic portions and
these are preserved as enclaves. As these heteroge-neous melts were emplaced to form the Baneh intru-sion, it formed a mega-sheath fold, with originally lowerappinite melts surrounded by higher granitic melts.
7.2. Magma evolution
Field relations, radiometric ages, and chemical compo-sitions confirm that rocks of the Baneh complex can bedivided into three main groups. The main body is bio-tite granite deformed by shear and accompanied byelliptical bodies of less deformed appinite, especiallyin the centre of the larger granite intrusion. Youngerintrusions of granite fill extensional dikes. The chemicalcomposition of granites and appinites shows they aredifferent, in spite of the fact that they have mostlysimilar initial ratios of 87Sr/86Sr and 143Nd/144Nd.
Low silica contents and high MgO, Mg#, Ni, and Crcontents indicate that the appinites are partial melts ofhydrous mantle. The flat HREE patterns of appinitesindicate that garnet was not a residual mineral; there-fore, the appinitic melts formed by partial melting ofspinel peridotite in the upper mantle, at depths <70 km
Figure 15. Variation of 87Sr/86Sr (40 Ma) versus ?Nd (40 Ma) in granitic and appinitic rocks. Without dike sample SAMD-8, mostsamples show slightly negative ?Nd (40 Ma) and extend into the continental field (a). The nearly horizontal pattern in the 87Sr/86Sr(t)and 143Nd/144Nd (t = 40 Ma) versus SiO2 (wt%) for both groups supports an interpretation of magma differentiation (b,c). Nd TDMmodel ages are 0.7–0.9 Ga for both groups, further supporting a similar source (d).
22 H. AZIZI ET AL.
or so. Mafic dike SAMD-8 with initial 87Sr/86Sr = 0.7047and εNd(t) = +9.9 with 51 wt% SiO2, 10.3 wt% MgO,Mg# = 76, 473 ppm Cr, and 223 ppm Ni may berepresentative of these unmodified mantle melts.Other appinites have been modified by significant frac-tionation and mixing with crustal melts, probably in a‘deep crustal hot zone’ (Annen et al. 2006), where dif-ferentiation of mantle-derived magmas and interactionwith pre-existing crust form MASH (combined mixing,assimilation, storage, and homogenization processes)zones. The more evolved nature of most Baneh com-plex appinites relative to mafic dike SAMD-8 can beseen in their higher silica (57.0–51.4 wt%) and lowerMgO (9.9–2.0 wt%), Mg# (73–36), Ni (150–7 ppm), andCr (454–16 ppm) contents. In addition to long-livedmagma mixing, the role of hornblende is key to under-standing differentiation of the appinite suite.Separation of hornblende along with plagioclaseallowed residual melts to evolve to higher concentra-tions of silica and Large Ion Lithophile Elements (LILEs).Blocks of amphibole-rich rocks brought up in the appi-nites may be relicts of earlier episodes of amphiboleaccumulation, as suggested by zircons that are ~10 Maolder than the Baneh intrusion.
If our interpretation of SAMD-8 as a mantle endmem-ber is correct, then other appinites must have a
significant crustal input to explain their much lower εNd(t), which is indistinguishable from the granites. This isdifficult to quantify because some appinite samples (e.g.SAMD-5 and -7) have elevated MgO (~9 wt%), Mg# (68–75), Ni (100–150 ppm), and Cr (438–362 ppm) indicatinglittle fractionation of mafic minerals but εNd(t) = +2.6 to−1.1 that are essentially identical to the granites. Giventhat appinite Nd contents are generally greater than thatof granites, changing Nd isotopic compositions of appi-nites so much requires more mixing of crustal melts thanthe elevated contents of MgO, Ni, and Cr warrants. It willrequire a focused effort to better constrain the mantleendmember of the appinite suite and track its evolution.
It is also difficult to understand formation of thegranitic rocks. These are not easily interpreted as purefractionates of appinitic melts because the two suitesare distinct in many ways: appinites are magnesian,calcic, metaluminous and contain more REE whereasgranites are ferroan, alkali-calcic to calc-alkaline, pera-luminous and contain less REE. Granites also show evi-dence of interaction with the crust in terms of presenceof garnet and association with a broad metamorphicaureole. We do infer from Harker variation diagrams(Figure 10(a-h)) that magma differentiation had animportant role in producing Baneh complex igneousrocks, but it was a very open system, with primitive
Figure 16. Red–green–blue (RGB) false colour (bands 7, 4, and 1, respectively) from the ETM+ sensor (Landsat satellite) showing theasymmetric shape of the Baneh granitoid and asymmetric folding of the host rocks (a). The digital elevation filter applied to the ETM+ data confirms the mainly sigmoidal and parallel shapes for the main granitic body (b). These images indicate injection of graniticand dioritic magma (c–f) during a transpressional tectonic regime in the shear zone (modified from Castro and Fernández 1998).
INTERNATIONAL GEOLOGY REVIEW 23
magmas due to hydrous mantle melting interactingwith the crust to produce a vertically stratified mag-matic mush zone in the lower crust, dominated bymore recent mafic additions at the base gradingupwards into older, more evolved, and more felsiczones above this. Baneh granites and appinites havemean Nd model ages of 1.0 Ga, indicating significantinvolvement of older (~530 Ma) Cadomian crust. Exceptfor primitive sample SAMD-8, the appinites have similarNd model ages of 1.0 Ga. How such remarkable isotopichomogenization happened between mantle melts and
crustal melts suggests that mantle melts formed bypartial melting of sub-continental lithospheric mantlein the spinel peridotite facies. Either that or processes ofradiogenic isotope equilibration are much faster thanchemical homogenization in this lower crustal MASHzone than generally recognized.
8. Conclusions
Middle-to-late Eocene (Lutetian–Bartonian) igneousrocks of the Baneh complex were injected in a
Figure 17. Schematic illustration of how subduction and diachronous collision may have caused the NW-trending dextral shearzone and drawn in melts from a lower crustal hot zone. (a) Scenario at ~50 Ma. Active N-dipping subduction zone beneath Anatoliaand Iran forms a lower crustal hot zone where hydrous mantle melts (appinites) were stored and melted older crust and sedimentsto form S-type granites. (b) Scenario just before emplacement of the Baneh pluton (~42 Ma). Collision is underway in Anatolia butIran is still the site of normal subduction. Collision in the west and subduction in the east resulted in progressive northwarddisplacement of the western part of the convergence zone, forming a dextral shear zone that connected the two convergence zonesand drew melts from the lower crustal hot zone into local regions of transtension. (c) Scenario at the time of Baneh plutonemplacement, ~39 Ma. Movement of the magma entrained previously crystallized mafic portions and these are preserved asenclaves. As these heterogeneous melts were emplaced to form the Baneh intrusion, it formed a mega sheath fold, with originallylower appinite melts surrounded by originally higher granitic melts.
24 H. AZIZI ET AL.
transpressional tectonic regime along the Zagros faultin northwest Iran. Our research reveals the role of par-tial melting, both of metasomatized mantle over thesubduction zone to form appinites which fractionatedand partially melted Iranian continental crust and sedi-ments to form granites. Appinite and granitic meltsinteracted in a deep crustal hot zone. Furthermore,the compositional similarity of Baneh granites to globalsyn-collision granites confirms the association of theformer with collision of the Arabian and Eurasian platesin northwest Iran. This documented example of Eocenemagmatism in western Iran may provide insights intothe nature of supposed ophiolites of Eocene age, forexample in the southern part of our study area in theKamyaran area. Intrusive bodies of similar age andcomposition rocks are reported along the Zagros fault,but new radiometric ages and isotope data, along withpressure and temperature estimates, are needed beforewe can develop a comprehensive geodynamic modelfor Eocene tectonic and magmatic evolution of theZagros orogen in western Iran.
Acknowledgements
The chemical data and analyses were supported by NagoyaUniversity in Japan and JSPS KAKENHI: [Grant Number17H01671], Japan. A part of this work was carried out bythe join research programme of the Institute for Space –Earth Environmental Research (ISEE), Nagoya University,Japan. We thank M. Aghazadeh and F. Rezaei for theirtechnical assistance and fieldwork. The authors speciallythank Prof. S. Wallis and K. Mano for BSE and CL imagesat Nagoya University and F. Nouri for technical support.This version benefited greatly from the comments of HadiShafaii Moghadam (editor) and two anonymous reviewers.This is UTD Geosciences contribution number 1309.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The chemical data and analyses were supported by NagoyaUniversity in Japan and JSPS KAKENHI: [Grant Number17H01671], Japan. A part of this work was carried out by thejoin research programme of the Institute for Space –EarthEnvironmental Research (ISEE), Nagoya University, Japan.
ORCIDHossein Azizi http://orcid.org/0000-0001-5686-4340
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