Geological setting of the Meatiq metamorphic core complex ...utdallas.edu/~rjstern/egypt/PDFs/CE Desert/NeumayrMeatiqJAES96.pdf · en accord avec le diagramme AFM confirmant la composition

Pergamon Joumalo fA f r i can Earth Sciences, Vol. 23, No. 3, pp. 331-345, 1996

Copyright © 1997 Elsevier Science Ltd All rights reserved. Printed in Great Britain

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Geological setting of the Meatiq metamorphic core complex in the Eastern Desert of Egypt based on

amphibolite geochemistry

P. NEUMAYR, A. MOGESSIE, G. HOINKES and J. PUHL Institute of Mineralogy-Crystal lography and Petrology,

KarI-Franzens University, A-801 0 Graz, Austr ia

Abst rac t - -Large parts of the Central Eastern Desert of Egypt consist of Neoproterozoic nappes

of ophiolite and island-arc volcanic rocks. Beneath these nappes metamorphic basement domes

are exposed in tectonic w indows such as the Meatiq basement. The mineral and whole rock

chemistry of amphibol i tes included in the teconical ly lowermost granitoid gneiss, within the

metasedimentary cover of the gneiss and within shear zones bordering the Meatiq basement

dome, are invest igated to determine their geodynamic setting.

The amphiboli tes consist mainly of plagioclase, hornblende, quartz and, locally, c l inopyroxene.

The metamorphic mineral assemblage is retrograded f rom upper amphibol i te- facies peak

metamorphic condit ions to lower amphiboli te-facies. The Niggli c - m g plot identif ies them as

orthoamphiboli tes, and whole rock chemistry indicates a basalt to basaltic andesite composit ion

for most of the amphibolites. Immobile trace elements such as Zr, Y and Ti suggest that one

group of amphibol i tes is derived from within-plate basalts and another belongs to the MORB

tectonic setting. This is consistent with the result of the AFM plot, which indicates a tholei i t ic

composi t ion for all the amphibolites. REE patterns confirm the trace element results, wi th a

typical LREE deplet ion for the N-type MORB amphibolites. The f irst group of amphiboli tes is

enriched in LREE and displays a concave pattern. The amphibol i te inclusions in the Um Ba'anib gneiss record d i f ferent geologic sett ings - f rom

the format ion of oceanic crust to wi th in-plate basalt ic magmat ism - prior to the intrusion of

the Um Ba'anib granitoid. Copyright © 1997 Elsevier Science Ltd. All rights reserved

R~sum~- De vastes regions de la partie centrale du D~sert Oriental en Egypte sont const i tuees

de nappes N6oprot~rozoiques d 'ophio l i tes et de roches volcaniques d 'arcs insulaires. Sous

ces nappes des d6mes de soubassement metamorphique, tel celui de Meatiq, a f f leurent

dans des fen6tres tectoniques. Afin de d~terminer le contexte g~odynamique des amphiboli tes

fa isant part ie des gneiss grani t iques de I 'unit~ st ructurale inf~rieure, de la couver ture

m~tas~dimentaire des gneiss ainsi que des zones de cisai l lement en bordure du dSme de

Meatiq, la composi t ion chimique des mineraux et des roches tota les est ~tudi~e.

Les amphibol i tes sont pr incipalement cons t i tu tes de plagioclase, de hornblende, de quartz

et Iocalement de cl inopyrox~ne. La paragen~se metamorphique prograde appart ient au facies

amphibol i te superieur et est re t romorphosee dans des condi t ions du facies amphibol i te

inf~rieur. Dans le diagramme c - m g de Niggli ces amphibol i tes appart iennent aux ortho-

amphibol i tes et la chimie des roches to ta les montre, pour la plupart des roches, une

composi t ion de basalte A basalte and6sit ique. Les 616ments en trace immobiles tels que le

Zr, I'Y et le Ti sugg~rent qu 'un groupe d 'amphibol i tes est d~riv~ de basaltes d ' in ter ieur de

plaques tandis que I 'autre appart ient au contexte tectonique des MORB. Ces r~sultats sont

en accord avec le diagramme AFM conf i rmant la composi t ion thol~i i t ique de toutes les

amphibol i tes. Les profi ls de terres rares conf i rment les r~sultats des 61ements en trace avec

un appauvr issement typique en terres rares 16g~res pour les ampbibol i tes de type N-MORB.

L'autre groupe d'amphibol i tes est enrichi en terres rares I~g~res et presente un profil concave.

Les enclaves d 'amphibol i tes dans les gneiss d 'Um Ba'anib ont enregistre des contex tes

g~olog iques d i f f~rents , depuis la fo rmat ion de croQte oc~anique jusqu'& un magmat isme

basal t ique d ' in te r ieur de plaques ant~r ieur a I ' in t rus ion des grani to ldes d 'Um Ba'anib.

Copyr ight © 1997 Elsevier Science Ltd. All rights reserved

(Received 14 November 1995: revised version accepted 10 May 1996)

Journal o# African Earth Sciences 33~

R N E U M A Y R et al.

INTRODUCTION Several metamorphic basement domes, such as the Hafafit-Migif, the Sibai and the Meatiq, are exposed in tectonic w indows beneath Pan- African ophiolite and island-arc volcanic rock sequences in the Central Eastern Desert (CED) of Egypt (El Gaby et al., 1990). It is widely accepted that crustal consolidation of northeast A f r i ca has la rge ly been ach ieved by Neoproterozoic accretion of island-arcs without major crustal thickening (Gass, 1982; Stern, 1994), but there has been considerable debate about the origin and genesis of these basement domes.

El Gaby et al. (1988, 1990) subdivided the whole Egyptian part of the Arabian-Nubian Shield (ANS) into a lower (infrastructure) and an upper structural level (suprastructure). The infrastructure essen t i a l l y c o m p r i s e s the gne isses and metasedimentary rocks exposed in the basement domes and is considered as pre-Pan-African (continental) crustal basement (El Gaby et al., 1990). The suprastructure, which comprises the ophiolit ic melange (sensu Shackleton et al . , 1980), was obducted onto the infrastructure during the late Pan-African collision. However, Stern and Hedge (1985), Stern and Manton (1987) and Kr6ner e ta / . (1990, 1994) suggest that the basement domes formed during the Pan- Afr ican magmat ic evolut ion of is land-arcs without the involvement of older continental crust, based on isotopic age and geochemical cons t ra in ts . This model impl ies tha t the basement was metamorphosed by a single metamorphic event. However, Habib et al. (1985) distinguished at least two metamorphic events in the basement of the Meatiq dome and Neumayr et al. (in review) recognized an early M 1 migmatization, an upper amphibolite-facies M~ and a greenschist-facies M 3 metamorphic event in the Meatiq basement. This contrasts w~th the m e t a m o r p h i c e v o l u t i o n of the structurally upper units (Pan-African nappes, suprastructure) which suffered monophase greenschist-facies metamorphic conditions. Due to the polymetamorphic nature of the basement domains, a complex tectonic history can be assumed for the fo rmat ion of the Meat iq metamorphic core complex.

Metabasites occur in the Meatiq metamorphic core complex as inclusions within the Um Ba'anib gneiss in the tectonic lowermost section of the basement, as lenses within the metasedimentary rocks covering the Um Ba'anib gneiss and within the ophiolite and island-arc nappes on top of the metamorphic core complex (e.g. Neumayr et al., in p rep . ) . Inclusions and xenoliths of

metabasites can provide important insights in the tectonic evolution of a metamorphic terrane, as has been demons t ra ted for maf ic and intermediate granulite xenoliths in the ANS of western Saudi Arabia (McGuire and Stern, 1993). In order to gain information on the earliest history of the Meatiq metamorphic core complex, geological, petrological and geochemical data of the metabasites are presented in this study.

GEOLOGICAL SETTING Nor theas te rn A f r i ca conso l i da ted in the N e o p r o t e r o z o i c dur ing the Pan -A f r i can orogenesis between 550 Ma and 1100 Ma (KrSner, 1979, 1984; Morgan, 1990). During this tectonic event, Pan-African island-arcs were accreted on the western foreland. Two cycles of ophio l i tes of d i f ferent ages have been distinguished on an isotopic basis (Stern, 1994). The easternmost remnant of the old craton is interpreted to be the Archean G. Uweinat area (Schandelmeier et al., 1988). East of the Nile the pre-Pan-African history is only preserved in the isotopic systems of granites (Sultan et al., 1990, 1992). The complex st ructural and metamorphic history of some basement domes in the CED, such as the Gebel Hafafit and the Gebel Meatiq, is interpreted to indicate probable pre-Pan-African crust east of the Nile by some authors (El Gaby et aL, 1990). However, isotopic constraints on the age of these basement domes are all within the time interval defined for the Pan-African orogenic event (e.g. Stern and Hedge, 1985; Kr6ner et al., 1990, 1994).

Meatiq geology The Mea t iq basemen t dome is loca ted a p p r o x i m a t e l y 80 km wes t of Qusei r , immediately north of the Quseir-Qift road in the CED. The structurally lowest parts comprise the Um Ba 'an ib gne iss wh i ch loca l l y hosts amphibolite lenses (Figs 1 and 2). In contrast to the gneiss, some of the amphibolites are partially migmatized. The basal gneiss is overlain by a dominant metasedimentary succession of quartz- rich schists which are locally intercalated with metapelitic schists. Garnet- and biotite-bearing metapelites, which are up to several hundred metres thick, form the upper section of the m e t a m o r p h i c core c o m p l e x . Lenses of amphibolites and metagabbros occur within the metasedimentary succession, locally discordant to the main foliation. Marble bands associated with amphibolite lenses in the upper sections of the metapelites (Fig. 2) potentially indicate a

332 Journal of African Earth Sciences

Geological setting of the Meatiq metamorphic core complex in the Eastern Desert of Egypt

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Figure 1. Location of the Meatiq basement complex in the Central Eastern Desert of Egypt (inset) and geology, J)-nportant structures and sample locations in the basement.

Journa l o f A f r i can Earth Sciences 333

R NEUMAYR e t a l .

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;ONTACT

Amphibol i te and marble bands

Bt-quartzite, Bt-Grt schist

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Layers with abundant St, Sil

Bt-Grt schist (locally reduced)

Grt pseudomorphs after St Grt-Zn-rich Sp-Qtz schists

Um Ba "anib gneiss, inclusions of locally migmatized amphibolite

Figure 2. Schemat i c prof i le th rough the Mea t i q b a s e m e n t and the l ower sect ions o f the ophiof i te and is land-arc cover series.

sedimentary origin for some of the amphibolites. The metasedimentary succession is tectonical ly overlain by nappes of ophiolite and island-arc volcanic rocks (El Gaby et al . , 1990) . The gneisses and me tased imen ta ry schists are intruded by syn- to post-tectonic granitoids (Abu Fanani g r a n o d i o r i t e / t o n a l i t e , 614_+8 Ma convent ional U/Pb on zircon age ]Stern and Hedge, 1985] , Arieki grani te, 585_+14 Ma conventional U/Pb on zircon age [Sturchio et a/. , 1983] ) along ex tens iona l faul ts at the southern margin of the dome (Fritz et al., 1996) and as circular shaped intrusions wi th in the dome, respectively.

Structural f r amework The structural history of the Meatiq basement dome, the ophiolite and the island-arc volcanic rocks is summarized in Habib et al. (1985) and Fritz et al. (1996). The earliest deformation D 1 in the Meat iq basement is recorded in melt enhanced extensional fabrics of amphibol i te migmatites enclosed in the Um Ba'anib gneiss. Both the Um B a ' a n i b g r a n i t o i d and the metasedimentary cover have been deformed

during a high temperature D 2 deformation event, remnants of which are preserved in ductile t ight to isoclinal folds, outlined by ilmenite inclusion trails in garnets. Nappes of ophiolites and island- arc volcanic rocks have been obducted along low-ang le th rus t planes, w i th a cons is ten t displacement of the top parts of the section to the no r thwes t onto the basement , in a D 3 deformational event. The D 3 nappe stacking caused a penetrative S 3 foliation and non-coaxial fabr ics such as a pronounced L 3 s t retch ing lineation, F 3 shear folds and boudinage structures in the upper structural units of the basement.

During D 4, S 3 foliation planes have been bent into northwest-str iking transcurrent shear zones along the southwestern and northeastern margin of the dome (Wa l l b reche r e t a / . , 1993)~ Southeast of the Meatiq dome, east-northeast striking faults interpreted as Riedel shear zones indicate overall sinistral slip along the main D 4 str ike-sl ip shear zone. East -west or ientated compression caused megascale F~ folding with northwest trending fold axes, and resulted in the updoming of the Meatiq basement. During the updoming, low-angle normal faults at the southern and northern margin of the dome were associated with transport of the upper nappes to the south and the north, respectively. F 4 folds are refolded by F S cross folds (Habib et a/., 1985). The age of the D 4 strike-slip shear zones, and hence the updoming, is constrained by 4°Ar/ 39Ar dating of micas to 5 9 5 . 9 + 0 . 5 Ma (Fritz et al., 1996) and the end of the tectonic evolution in the Meatiq area is constrained by the post- kinematic tonalites to 585_+ 14 Ma (Stern and Hedge, 1985).

M E T A M O R P H I C EVOLUTION The me tamorph i c evo lu t ion of the Meat iq metamorphic core complex is summarized in Neumay r e t a / . ( in p r e p . ) . Three d i s t i nc t m e t a m o r p h i c even ts are i den t i f i ed in the basement, whereas only the last one, M 3, is recognized in the ophiolite and island-arc volcanic rocks. Therefore, a distinct metamorphic break between the basement and the cover nappes is evident.

The migmatization of some of the amphibolite lenses in the Um Ba'anib gneiss represents the only record of the M1 metamorphic event. The m in imum m e t a m o r p h i c t e m p e r a t u r e s are estimated to be > 750 ° C for the M 1 event based on publ ished exper imen ta l resul ts of melt reactions of metabasites (Neumayr et al., in p r e p ) . The b a s e m e n t was s u b s e q u e n t l y



metamorphosed in a high temperature, medium pressure M~ metamorph ic event. The high temperature conditions of M 2 a r e indicated by

i) the breakdown reaction of muscovite to alkali feldspar and sillimanite in the presence of quartz;

ii) chemically uniform cores of garnets, which formed due to diffusional equilibration of the garnet composition at high temperature; and

i i i) the breakdown of Fe-staurolite to the peak assemblage of garnet and sillimanite.

Peak M 2 conditions are also constrained by garnet- biotite and garnet-staurolite thermometers and the GASP, GRIPS and GRAIL barometers to be at least 620°C to 690°C and 6 to 8.5 kbar. Assuming peak M 2 pressures of 6 to 8 kbar and water saturated conditions, the muscovite out reaction would indicate temperatures of at least 650°C (Spear, 1993) for the peak of the M 2 e v e n t .

The intensity of the a 3 metamorphic event increases towards the contact of the basement and the ophiolite and island-arc volcanic nappes in the south. Peak M 3 metamorphic conditions in the basement are calculated to be < 5 5 0 ° C and < 4 kbar (stability of andalusite). Peak M3 temperatures in the ophiolite and island-arc volcanic rocks are limited to < 5 4 0 ° C by the mineral assemblage a n t i g o r i t e + t a l c in the serpentinites.

PETROGRAPHY OF THE METABASITES AND THE UM BA'ANIB GNEISS

The majority of the amphibol i tes occurs as inclusions within the Um Ba'anib gneiss (Fig. 1). Minor amphibolite occurrs as lenses within the metasedimentary cover of the Um Ba'anib gneiss. Some amphibolites have been deformed in the D 4 strike-slip shear zones which border the Meatiq basement dome in the southwest and northeast.

All metabasites are mineralogically similar and range in compos i t ion from amphibo l i te to hornblende gneiss. The metabasites contain dark green to brown-green hornblende, plagioclase, quartz and, locally, biotite, which typically forms rims around subhedral hornblende grains. Plagioclase is common ly zoned and hosts abundant f ine-grained muscovi te alteration, whereas hornblende is unzoned in all samples. Bands of pale-green clinopyroxene, which are up to 2 cm in t h i ckness , a l te rna te w i t h hornblende-plagioclase bands in some samples. Fine-grained, subhedral t itanite and magnetite are present as accessory phases.

The well-foliated, compositionally homogeneous Um Ba'anib gneiss is medium-grained and

contains plagioclase, microcline and quartz. Minor phases of the Um Ba'anib gneiss contain aegirine and riebeckite.

ANALYTICAL TECHNIQUES Mineral analyses have been obtained using an ARL-SEMQ electron microprobe at the Institute of Mineralogy-Crystallography and Petrology at the KarI-Franzens University Graz. The analytical conditions were set to 15 kV accelerating voltage and 20 nA sample current on brass. The analyses were calibrated using a set of international mineral standards and a standard ZAF correction procedure. Addit ional mineral analyses were performed wi th a JEOL-JSM6310 scanning e lec t ron m i c r o s c o p e at the I ns t i t u te of Mineralogy-Crystallography and Petrology at the Kar I -F ranzens U n i v e r s i t y Graz us ing an accelerating voltage of 15 kV and a LINK ISIS energy dispersive system.

Major, trace and rare earth elements of 19 unmigmatized metabasites were performed at XRAL Laboratories, Ontario, Canada. Precision and accuracy of the data were guaranteed by the ca l ibra t ion against in te rnat iona l rock standards and the performance of blank and repeat analyses. The major element oxides (minimum detection limit [radii =0.01 wt%) and Rb, Sr, Y, Zr, Ba and Nb (mdl= 10 ppm) have been analyzed using XRF techniques, Sc, Cr, Co, Ta, Th, Hf, La, Ce, Nd, Sm, Eu, Tb and Lu (mdl better than 0.5 ppm, Ce= 1 ppm, Nd = 3 ppm) using neutron activation techniques and V, Ni, Cu, and Zn (md l=2 ppm) using ICP-MS techniques.

MINERAL CHEMISTRY Representative mineral analyses of the Meatiq amphibolites are listed in Table 1.

Feldspars The anorthite content ranges from An20 to An40 and locally plagioclase recrystallizes to fine- gra ined unzoned a lb i te w i t h An s. Some plagioclases are zoned from An24 in the core to An36at the rim of the grain. There is no significant difference in plagioclase composition between different amphibolites.

Amphiboles Amphibole analyses have been reduced using a computer program by Mogessie et al. (1990) fo l lowing the recommendat ion of the IMA

Journal o f Afr ican Earth Sciences 335


Table 1. Microprobe anlyses of metamorphic amphibole, cl inopyroxene and plagioclase from amphibolite inclusions within the Um Ba'anib gneiss

Sample GML79 M4 M145 NM6/1 Analysis Cpx791 Am60 PI30 Cpx794 Am69 PI34 Am423 PI9 Am18 PI24 Am1 PI20

SiO2 53.53 44.56 60.22 53.32 44.38 57.94 39.85 61.00 47.87 68.72 47.06 62.53 TiO2 0.04 0.79 0.03 0.10 0.82 bdl 1.22 0 . 0 9 0.63 bdl 1.03 bdl

AI203 0.31 10.28 25.00 0 . 9 3 11.20 26.11 12.29 24.18 9 .31 20 .04 13.57 23.42 FeO 9.59 14.05 0.22 7 . 6 5 12.23 0 .14 13.44 0 .11 11 .25 0 . 0 3 14.43 0.62

Fe203 nd 3.37 nd nd 3.75 nd 6.85 nd 3.96 nd bdl bdl MnO 0.41 0.28 bdl 0.32 0.23 bdl 0.23 bdl 0.58 bdl 0.18 0.11 MgO 11 .78 10.23 bdl 12 .97 11.10 bdl 8.75 bdl 10 .84 0.40 5.93 bdl CaO 23.62 11.86 6.26 23.78 11.97 8 .16 11.24 4 . 2 2 10.62 0.42 8.51 5.69 Na20 0.29 1.39 7.41 0.31 1.45 6.79 1.61 8.90 1.23 10.54 4.77 7.48 K20 bdl 0.64 0.44 bdl 0.69 0.16 1.71 0 . 3 0 0.09 0,04 0.77 0.09

Total 99 .57 97.45 99.58 99.38 97.82 99.30 97.19 98.80 96.38 100.19 96.25 99.94

Si 2.02 6.66 2.69 2.00 6.55 2.61 6.21 2 . 7 4 7.04 2.99 6.99 2.77 Ti 0.001 0.080 0.001 0 .003 0.09 bdl 0.14 0.003 0.070 bdl 0.120 bdF AI 0.01 1.81 1 . 3 2 0.04 1.95 1.39 2.26 1.28 1.61 1.02 2.37 1.22

Fe2+ 0.30 1.76 0.01 0.24 1.51 0.01 1.72 0 .004 1 . 3 8 0.001 1.79 0.02 Fe3+ nd 0.38 bdl nd 0.42 bdl 0.79 nd 0.44 nd bdl bdl Mn 0.01 0.04 bdl 0.01 0.03 bdl 0.03 bdl 0.07 bdl 0.02 0.004 Mg 0.66 2.28 bdl 0.73 2.45 bdl 2.03 bdl 2.38 0.03 1.31 bdl Ca 0.96 1.90 0.30 0.96 1.90 0.39 1.88 0.20 1.67 0.02 1.35 0.27 Na 0.02 0.40 0.64 0.02 0.42 0.59 0.49 0.77 1.23 0.89 1.37 0.64 K bdl 0.12 0.02 bdl 0.13 0.01 0.34 0 . 0 2 0.09 0 .002 0 . 1 4 0.005

Total 3.98 15.43 4.98 4 . 0 0 15.45 5 .00 15.89 5 . 0 2 15.98 4 . 9 5 15.47 4.929

Mg# 0.55 0.56 nd 0.63 0.62 nd 0.54 nd 0.63 nd 0.42 nd

bdl = below detection limit; nd= not determined

nomenclature by Leake (1 978). The amphiboles vary in composition from magnesio-hornblende, tschermakit ic hornblende to tschermakite and hastingsite with Mg/(Mg +Fe) ratios of 0.44 to 0.60. Some hornblendes are retrograded to actinolite either patchily or along the margins. Hornblendes are character ized by low TiO~ concentrations from 0.75 w t% to 1.5 wt%.

Clinopyroxenes Clinopyroxenes occur locally in bands alternating w i th ho rnb lende -p lag ioc lase layers . Most cl inopyroxenes are diopside, calculated using the IMA c lassi f icat ion of Mor imoto (1988). C l i n o p y r o x e n e s in the m idd le of the clinopyroxene-plagioclase layers are characterized by an enstatite component of 33.5% to 35.2%, whereas cl inopyroxenes at the margin of the layers show higher enstat i te components of 37.2% to 37.6%, potential ly indicating a whole

rock chemica l con t ro l on the g r o w t h of metamorphic cl inopyroxene.

BULK ROCK CHEMISTRY According to field evidence, structural position and geochemica l charac te r i s t i cs , six main groups of amphibolites have been distinguished (Fig. 1 ):

i) amphibolite lenses in the core and along the eastern margin w i th in the Um Ba'anib gneiss;

i i) amphibol i te lenses wi th in the western margin of the Um Ba'anib gneiss;

i i i ) amph ibo l i tes in the me tased imen ta ry sequence;

i v ) amph ibo l i tes w i th in the nor theastern shearzone;

v) amphibolites within the southwestern shear zone; and


Geological setting of the Meatiq metamorphic core complex in the Eastern Desert o f Egypt

15

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I I I I I 35 40 45 50 55 60 65 70 75

Si02 (wt%) Figure 3. Meatiq amphiborltes plotted in the total a/karl-sir/ca classification of volcanic rocks (after Le Bas et aL, 1986). (0 = amphiborlte lenses in the core and along the western margin within the Um Ba 'anib gneiss, © = amphiborlte lenses within the western margin o f the Um Ba'anib gneiss, 0 = amphiborltes in the metasedimentary sequence, [ ] = amphibolites within the south western shear zone, • = amphiborltes within the northeaszern

shear zone, 4- = one sample of an amphibofite in the ophiorlte and island-arc nappes).

vi) amphibolites in the ophiolite and island- arc nappes (one comparative sample).

All major element oxide, trace element and rare earth element analyses are reported in Table 2. The Meatiq amphibolites are typically mafic to slightly intermediate in composit ion (45.00 to 51.70 w t% SiO 2) and plot in the total alkali- silica diagram of Le Bas eta/ . (1986), mostly in the basalt field (Fig. 3). Two samples are classified as basaltic andesite and andesite (54.30 and 58.60 w t% SiO2), respectively. The amphibol i tes are medium-K rocks wi th K20 ranging from 0.24 to 2.05 wt%.

The amphibolites from the ophiolite and island- arc nappes are dist inct from the basement amphibolites in almost all elements (Table 2) and are not considered further. Niobium is very low and close to the detection limit (10 ppm) in all samples. Amphibol i tes from the western margin of the Um Ba'anib gneiss (Group 2) are distinct in a number of features. They generally have low K20 + Na20 values and very low TiO 2 c o n c e n t r a t i o n s . C o m p a r e d to Group 1 amphibolites, P2Os is generally lower in Group 2. Scandium and V are enriched compared to all other amphibolites, and Zr and Y are depleted

compared to Group 1 amphibolites. Hafnium is marginal ly lower in Group 2 amphibol i tes compared to all other groups. Light rare earth elements are generally depleted in the Group 2 compared to Group 1 amphibolites, whereas HREEs are similar in both groups.

The amphibolites from the shear zones have the lowest K20 values and are characterized by mostly low P205 concentrations. Amphibolites from the shear zones have been distinguished based on their tectonic position as samples from the nor theast and sou thwes t shear zone, respectively. However, in each shear zone two chemically different amphibolites are present. One group is characterized by high Zr and Hf concentrations, whereas the other group has low c o n c e n t r a t i o n s in these e l emen ts . Additionally, REEs are enriched in the first group of shear zone amphibolites. The second group of shear zone amphibo l i tes show a LREE enrichment and HREE depletion. The different chemical compositions of amphibolites within one single shear zone may indicate either selective element mobil i ty during deformation or structural juxtaposition of amphibolites which have formed in different tectonic settings. The

Journal of African Earth Sciences 337


E

O J~

C ¢-

00 O u) C O

O

c"

E (~

©

c-

¢)

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O

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~ m ~ r n

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o ~ o

~ ~ o ~ ~ ~ ~ ~ ~ - ~ ~ ~ ~ • • . ~ • ~ o ~ d ~ m ~ d

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~ o ~ ~ . • . ~ ~ ~ ~ ~ ® © ~ - ~ ~ ~ ~ o ~ ~ .

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~ O o ~ • . ° ~ ~ o ~ ~ ~ ~ ~ ~ - ~

~ d ~ d d N ~ d ~ " ~ d O ~ d

o ~ o ~

~ d ~ N d d ~ ~ d ~ ~ E ~ - ~ d

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. . . . . ~ • . ~ ~

• . o ~ ~ ~ © . ~ ~ . ~. ~ • ~ ~ ~

" ~ ~ ~ d

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o ~ ~ - ~ = ~ ~ - - ~

~ m ~ o ~ o o ~ o° o m ~ ~ ~ . . . . . ~ O ~ o

o ~ ~ - - ~ ~ ~ ~ ~ ~ ~ ~ ~ © ~ ~ ~ d ~ d

~ m ~ o o o ~ = ~ o


Geological sett ing o f the Meat/q metamorphic core complex in the Eastern Desert o f Egypt

wt% TiO 2 3

2 - •o O=•

1 - ~ o •

0 + Or I wt% P2 5

0.8

0.6

0.4

0.2 []

r

wt% K20

om

2

1

• o •

I l r

1 O0 200 300 Zr (ppm)

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]

ppm Nb 5o

40

20

10

I I

ppm Rb 5 0 -

a0

30 ~

20 ~-0 D

10 • D

I

400 1 O0

o • []

0

m

<>i

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200 300 400 Zr (ppm)

Figure 4. Variation diagrams for selected major element oxide and trace elements o f the amphibo f i tes in the Meat iq basement to test e lement mob i l i t y dur ing h igh-grade metamorphism. Yttrium, TiO 2 and P205 show a minor scatter and a linear correlation with Zr which indicates immobi le behaviour. Niobium, Rb and K20 show a wide scatter and may have been mobi le during metamorphism (symbols as in Fig. 3).

intense deformation along the shear zones does not allow a decision as to whether element mobility or primary differences were the cause for these chemical variations. Therefore, the fol lowing discussion about the origin of the Meatiq amphibolites deals mainly with Group 1 and 2 amphibolites, which form enclaves within the Um Ba'anib gneiss. Chemical analyses of amphibolites from the shear zones are only plotted for comparison.

Element mobility In any geochemical study of metabasites, the possible modi f icat ions to rock composi t ion imposed by alteration and metamorphism are an important considerat ion. This is part icularly significant in this study of amphibolites in the Meatiq metamorphic core complex since these

rocks have been af fected by a high-grade m e t a m o r p h i c o v e r p r i n t . For the Meat iq amphibol i tes, good linear correlat ions exist between incompatible elements (Ti, Zr, Y, P and REE; e.g. Figs 4, 10 and 11 ) which are apparently immobile under most metamorphic conditions (e.g. Pearce and Cann, 1973; Winchester and Floyd, 1 977; Floyd and Winchester, 1 978). Only one sample (NM7/1) appears to be anomalous in almost all trace element plots and was, therefore, probably affected by remobilization (Fig. 4). Rare earth element and trace element patterns normalized to MORB (Pearce, 1982) show distinct trends and permit distinction of different groups of amphibolites (Figs 10 and 11). Although REE mobility and fractionation during high-grade metamorphism is indicated in some studies (Janardhan et al. , 1 982; Collerson

Journal of African Earth Sctences 339

R NEUMAYR et al.

60 T

50 f

40 t

30 t

20 t

10t

/ / / / / oo'om"e9 P e l i t e - l i m e s t o n e ~

mixtures / J

. / / ~ o o dolerite * ~ ~______ trend

[_~_~Pel i te and semipelite 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90

m g

Figure 5. Nl~Tg// c-mg plot (after Leake, 1964) for Meatiq amphlbolites. Note that all amph/bohtes fol low the Karoo do/erlte trend,

30

A

o

10

+ °o~ Basalt tiqu~s Oe J 'roctolites • ~ 0 lOCI • r'l • •J I

W e h t l i t e , , , , I , r , , I r ~ r

1 2 TiO 2 (wt%)

Figure 6. A/203 versus 7-/02 p lot (after Pearce, 1983) for Meatiq amphibofites. Note that most amphibofites plot in the basalt field. (Symbols as in Figure 3).

and Fryer, 1978), numerous studies suggest that the REEs probably remain immobi le dur ing amphibolite- to granulite-facies metamorphism (Dupuy et aL, 1979; Hamilton et al., 1979). Hence, the regu lar i ty o f t h e REE pat te rns observed for the Meatiq amphibolites and the correlation of REE contents wi th abundances of major and trace elements is interpreted to reflect the most likely unmodif ied igneous distributions (c. f . Sivel l , 1986) . In a f e w cases whe re disruption of element-pair correlations results from preferential trace element mobil i ty and red is t r ibut ion of e lements by metamorph ic p r o c e s s e s (K20-Zr , Rb-Zr ; Fig. 4) t hen petrogenetic interpretation in terms of a primary process is not justif ied.

Origin of the Meatiq amphibolites All Meatiq amphibolites plot in a Niggli c-rag diagram (Leake, 1964) along the Karoo dolerite trend (Fig. 5). This diagram is commonly used to d i s t i n g u i s h b e t w e e n o r tho - and para- amphibolites. Since all Meatiq amphibolites plot along the dolerite trend and no relationship to the various sediment trends can be recognized, the Meatiq amphibolites are classified as ortho- amphibolites. This is consistent wi th the field occurrence of Group 1 and 2 amphibolites, since metasedimentary rocks or marbles, which may indicate a metased imenta ry origin of these amphibolite xenoliths in the Um Ba'anib gneiss, are absent. Only one amphibolite sample in the metasedimentary cover sequence is intercalated with metapelites and marbles. Since this sample is c h e m i c a l l y i n d i s t i n g u i s h a b l e f rom the amphibolites within the Um Ba'anib gneiss, it is

also interpreted as ortho-amphibol i te. In the AI203-TiO 2 plot of Pearce (1983) most Meatiq amphibolites plot in the field of basaltic liquids (Fig. 6).

Most of the Group 1 amphibolite inclusions in the Um Ba'anib gneiss plot in the within-plate basalt field in the Zr/Y versus Zr diagram (Fig. 7) of Pearce and Norry ( 1 9 7 9 ) . Group 2 amph ibo l i t es p lot in the ove r lapp ing f ie ld between island-arc basalts and mid-ocean ridge basalts. Some shear zone amphibolites lie outside the def ined f ields and may be altered wi th r e s p e c t to t he p l o t t i n g e l e m e n t s . Th is classification is supported by the (Ti/1OO)-Zr- (Yx3) plot (Fig. 8) of Pearce and Cann (1973) in which most of the Group 1 amphibolites plot also in the within-plate basalt field. Group 2 amphibolites plot in the fields defined for island- arc, ocean floor or calc-alkali basalts. Since the Ti-Zr-Y plot does not permit a more detailed discrimination of the tectonic setting, no further distinction can be made.

In the FeO-AIk-MgO diagram of Irvine and Baragar (1971) most Meatiq amphibolites plot in the tholeiit ic field and only a few appear to have alkaline aff inity (Fig. 9). Al though there may have been some trace element migration due to metamorphic processes, an attempt has been made to distinguish the amphibolite groups by trace elements also (Fig. 10). Group 1 and 3 amphibolites are characterized by an element enrichment increasing from Sr to Rb and from Ti to Rb in the Rock/MORB normalized plot after Pearce (1982), whereas Y and Yb are close to unity. Group 2 amphibolites show positive Rb, and Ta and Nb anomalies, but are close to unity from Ce to Sc. The amphibolites from the shear


Geological sett ing o f the Meat iq metamorphic core complex in the Eastern Desert o f Egypt

E {3 .

N

[ ] I I I I I I I I 1 I I I I I

1 0 / . A y ; /

• / . / . +/:/./y /B /

1 I I I I I I I I I I I I I I I I

1 0 1 0 0 1 0 0 0

Zr (ppm)

Figure 7. Zr /Y versus Zr (ppm) discrimination diagram (after Pearce and Norry, 1979) for Meat iq amphibol i tes (symbols as in Fig. 3). Fields: A = within-plate basalts; B = mid- ocean ridge basalts; C = island-arc basalts.

zones show variable patterns and cannot be distinguished by their trace element signature.

Group 1 amphibolites are distinguished from Group 2 amphibolites by their REE pattern (Fig. 11). Whereas the latter show a depletion in the LREEs and a flat pattern in the HREEs, the former are typically enriched in the LREEs and show a slight negative slope in the HREE patterns. Amphibol i tes from the shear zones have no distinct REE pattern (Fig. 12), but tend to have similar patterns as the amphibolite inclusions in the core and the eastern margin of the Um Ba'anib gneiss. Two amphibolites from the shear zone show a positive Eu anomaly, which may relate to preferential plagioclase fractionation.

DISCUSSION It has been demonstrated that certain elements (e.g. K20, Rb and Nb) in the Meatiq amphibolites have been remobil ized during a high-grade me tamorph i c ove rp r in t . There fo re , these elements are not used for a classification of the tectonic setting. However, REEs and most of the trace e lements show d is t inc t pr imary patterns and hence are significant in constraining the geological setting of the Meatiq amphibolites. All amphibolites investigated fol low the Karoo dolerite trend in the Niggli c-rag diagram and are hence or tho-amphibol i tes. Furthermore, amphibolite inclusions in the Um Ba'anib gneiss form two distinct groups with different trace and RE-element characteristics, but both fol low a tholeiitic trend. Lower Ti and Zr concentrations in Group 2 amphibolites indicate a MORB or island-arc setting, whereas enriched Zr and Ti values suggest a within-plate setting for Group 1

amphibolites in the core and the eastern margin of the Um Ba'anib gneiss.

Trace e lemen t p a t t e r n s for Group 1 amphibolites with a moderate enrichment from Sr to Nb and values close to unity for Y and Yb are typical for within-plate basaltic rocks (Pearce, 1982). Group 2 amphibolites show a typical MORB pattern, with a weak enrichment from Sr to Nb and flat patterns close to unity from Ce to Sc (Pearce, 1982). The classification into two different groups of amphibolites is also indicated in the REE/chondrite patterns. The REE patterns of the Group 1 amphibolites with moderate LREE enrichment, and the concave patterns with unfractionated HREEs (CeN/Yb N ratios 2.3 to 4.7 for most amph ibo l i tes of th is group) are comparable to patterns for continental tholeiitic basalts (Basaltic Volcanism Study Project, 1981 ) and are clearly classified as within-plate basalts by various trace elements. In addition, the REE patterns are similar to those of basic granulites from the Qianxi Group, China (Jahn and Zhang, 1984 ) and the Oonagalabi gneiss complex, Central Australia (Sivell, 1986). In contrast, the LREE depletion compared to the HREEs in Group 2 amphibolites (CeN/Yb N ratios 0.45 to 0.62) resembles patterns of N-type MORB basalts and are similar to those described for the East Taiwan ophiolite (Jahn, 1986). The flat REE patterns of some Group 1 samples, intermediate between continental tholeiitic basalts and N-type MORB, may actually indicate an island-arc setting for these samples (island-arc tholeiites, Wilson, 1989), although the trace element patterns do not favour this interpretation (Fig. 10; Pearce, 1982).

The fact that at least two different tectonic settings are recorded in the Meatiq amphibolites points to a complex geological history prior to the intrusion of the Um Ba'anib gneiss. Since all these amphibol i tes are included in the Um Ba'anib gneiss, the timing of the formation of the i nd i v idua l a m p h i b o l i t e s canno t be determined. The different settings may indicate a history from the formation of oceanic crust to within-plate basaltic magmatism. On the other hand, the magmatic precursor of the Um Ba'anib gneiss may have enclosed amphibolite xenoliths from different geological settings, which have been assembled tectonically prior to the intrusion of the granitoid.

Engel et al. (1980) determined chondrite normalized REE patterns for selected pil low basalts, arc andesites and one sample of a late tectonic granite from various locations in the CED. The shape of the REE pattern (Fig. 11b) indicates a MORB setting for the pillow basalts

Journal of African Earth Sciences 341

Ti/1 O0

R NEUMAYR et al.

Zr Y*3

FeO*

AIk MgO

Figure 8. (Ti/ l OO)-Zr-(Yx3) p lot (after Pearce and Cann, 1973) for Meatiq amphibo/ites (symbols as m FI~?. 3). F/elds: A, B -/s/and-arc basa/ts; B = ocean-f loor basalt;B, C = calc-a/ka# basalt; D = w/thin-plate basalt).

Figure 9. FeO-alkalis-MgO plot (after Irvtne and Baragar, 1971) for Meat iq amphibohtes. Note that most samples fo l low a thole#tic trend (symbols as in Fig. 3).

100

. . . . . . . . . . . . . . . . i IB . . . . . . . . . . . . . . . ! o,Of

0.1 0.1

i L i i i i i i i i i ~ L i h i I ~ i i , i i i i , J 1

I r Sr O RbBaThTaNbCa(:~Zr HfSm(~Y YbSc Cr 100 "~ o , ~

m I0

Figure 10. MORB normalized trace element pattems (after 1

t r Pearce, 1982) for (A) Groups 1 and 3, (B) Group 2 and 0.1 (C) Groups 4 and 5 amphibofites, symbols as i# Fig. 3.

i i i L I i , i t i , , ; , i i i t

Sr 0 RbBaThTaNbCeo~Zr HfSmc__~Y YbSc Cr CL I.--


Geological setting o f the Meatiq metamorphic core complex in the Eastern Desert o f Egypt

I00

6

100

0 )

o 10

rc

I I I I I I I I I I I I I I I

j • Meatiq core a n d e a s t margin !__tll

A I I I I I I I I t I f I t I

La Ce Nd Sm Eu Tb Yb Lu I I I 1 1 1 I I 1 1 1 1

B 1 I I

La Ce Figure 1 1.

I I 1 I I i I I I I I I I Nd Sm Eu Tb Yb Lu

Chondr i te no rma l i zed REE pat te rns . (,4) Amphibofite lenses within the Um Ba 'anib gneiss. Group 1 amphibofites show a LREE enrichment and a typically concave pattern, whereas Group 2 amph/bofites are characterized by LREE depletion relative to Group I. (B) Pillow lavas (OMV) and arc andesites (YMV) o f representative samples from the CED (after Engel et aL, 1980). Note that the REE patterns for the pi l low basalts are similar to those o f the Group 2 Meatiq amph/bolltes. The shape o f the REE pattern o f the arc andesites is similar to Group I amphibofites o f the Meatiq basement, but LREE enrichment is less in the arc andesites of Engel et aL (1980).

and an island-arc setting for the calc-alkaline andesites. Engel e t al. (1980) concluded that the Afro-Arabian oceanic arc consolidated from an island-arc to continental crust within 300 Ma.

Al though the shape of the REE patterns, determined by Engel et al. (1980), are similar to the pa t te rns d e t e r m i n e d for the Mea t iq

IO0

e

,o 8

n-

I I I I I I ! I I I I I I I I

i B S h e a r z o n e w e s t ~ ' - I a S h e a r z o n e e a s t i - " I + O p h i o U t e a n d i s l and a r c i - I naive I

I I I I I I t I I I I I I I 1

La Ce Nd Sm Eu Tb Yb Lu

Figure 12. Chondrite normalized FlEE plot o f amphibo/ites from the northeastern and southwestern D~strike-s/ip shear zones o f the Meatiq dome and one pattern from the ophio/ite and is/and-arc nappe for comparison. Note the dist inct positive Eu anomaly in some of the shear zone samples, which contrasts with the REE patterns from the amphibofite lenses in the Um Ba "an/b gneiss (Figure 11A). The sample o f the ophiofite and island-arc nappe shows a REE pattern different from all groups.

amphibol i tes, there are marked dif ferences between the two settings. Whereas Engel et al. (1980) determined crustal consolidation in the CED using basalts and andesites, (between 750 and 550 Ma in age), the Meatiq amphibolites are included in the tectonically lowermost Um Ba'anib gneiss in the Meatiq basement complex. A probable magmatic age of 780___ 25 Ma for the Um Ba'anib gneiss has been determined using single zircon U/Pb techniques (KI6tzi pers.

c o m m . , 1995). Thus, the Meatiq amphibolites record the tectonic evolution of the basement at, or prior to, 780 Ma and are hence older than most of the rocks used by Engel et al. (1980). In addition, the intrusion of the Um Ba'anib gneiss in the Meatiq basement was followed by one upper a m p h i b o l i t e - f a c i e s and one greenschist-facies metamorphic event (Neumayr e t al., in p rep . ) . The latter was associated with the obduction of ophiolite and island-arc volcanic nappes onto the basement, which ceased at approximately 600 Ma (Fritz e t al. , 1996). Therefore, the metamorphic and structural histories of the Meatiq metamorphic core complex and the geochemistry of the amphibolite inclusions in the Um Ba'anib gneiss indicate a complex


R NEUMAYR et al.

g e o l o g i c a l h i s t o r y p r io r to , as we l l as s u b s e q u e n t

to , t h e i n t r us i on of t h e U m B a ' a n i b g r a n i t o i d .

CONCLUSIONS T h e a m p h i b o l i t e e n c l a v e s in t h e U m B a ' a n i b

gne i ss r e c o r d t h e o l d e s t t e c t o n i c h i s t o r y in t h e

M e a t i q b a s e m e n t . T h e c h e m i c a l v a r i a t i o n

i n d i c a t e s t h a t d i f f e r e n t t e c t o n i c s e t t i n g s h a v e

b e e n r e c o r d e d in t h e s e a m p h i b o l i t e s , r a n g i n g

f r o m w i t h i n - p l a t e b a s a l t s t o N - t y p e M O R B

s e t t i n g s . The g e o l o g i c a l h i s t o r y m a y i n c l u d e t h e

f o r m a t i o n o f o c e a n i c c r u s t t o w i t h i n - p l a t e

m a g m a t i s m e i t h e r in an o c e a n i c or c o n t i n e n t a l

s e t t i n g , a l t h o u g h t h e e x a c t t i m i n g b e t w e e n t h e

d i f f e r e n t a m p h i b o l i t e l enses is n o t e s t a b l i s h e d .

ACKNOWLEDGEMENTS Th is s t u d y is pa r t o f t h e F W F o p r o j e c t P O 9 7 0 3 -

G e o and is f i n a n c e d by t h e A u s t r i a n " F o n d s zur

F 6 r d e r u n g de r w i s s e n s c h a f t l i c h e n F o r s c h u n g " .

D i s c u s s i o n s a n d h e l p f r o m al l o t h e r p r o j e c t

m e m b e r s o f t h e D e p a r t m e n t o f G e o l o g y and

P a t a e o n t o l o g y , K a r I - F r a n z e n s U n i v e r s i t y Graz are

g r a t e f u l l y a c k n o w l e d g e d . T h e a u t h o r s a l s o

a c k n o w l e d g e t h e l o g i s t i c a l s u p p o r t o f t h e

U n i v e r s i t y o f A s s i u t ( E g y p t ) , p a r t i c u l a r l y b y Prof .

S. El G a b y . T h e p e r t i n e n t c o m m e n t s o f t w o

J o u r n a l r e f e r e e s i m p r o v e d t h e q u a l i t i y o f t h e

p a p e r c o n s i d e r a b l y .

REFERENCES Basal t ic Vo l can i sm S tudy Pro jec t 1981 . Basal t ic

volcanism on the terrestr/a/ planets. 1286p. Pergamon Press, New York.

Collerson, K. D. and Fryer, B. J. 1978. The role of fluids in the formation and subsequent development of early cont inental crust. Contributions to Mineralogy and Petrology 67, 151 - 167.

Dupuy, C., Dostal, J. and Capedri, S. 1979. Rare-earth elements in high grade metamorphic rocks from the western Alps. Lithos 12, 41 49.

El Gaby, S., List, F. K. and Tehran~, R. 1988. Geology, evolution and metallogenesis of the Pan African belt in Egypt. In: The Pan African belt of northeast Africa and adjacent areas (Edited by El Gaby, S. and Greiling, R. O.) pp17-68. Vieweg, Braunschweig.

El Gaby, S., List, F. K. and Tehrani, R. 1990. The basement complex of the Eastern Desert and Sinai. In: The Geology of Egypt (Edited by Rushdi, S.) pp175-184. Balkema, Rotterdam.

Engel, A. E. J., Dixon, T. H. and Stern, R. J. 1980. Late Precambrian evolution of the Afro-Arabian crust from ocean arc to craton. Geological Society America Bulletin 91, 699-706.

Floyd, P. A. and Winchester, J. A. 1978. Identif ication and d iscr iminat ion of al tered and metamorphosed volcanic rocks using immobi le elements. Chemical Geology 21, 231-306.

Fritz, H., Wallbrecher, E., Khudeir, A. A., Abu El Ela, F. A., El Gaby, S. and Dallmeyer, D. R. 1996. Formation of Neoproterozoic metamorphic core complexes during oblique convergence - Eastern Desert, Egypt. Journal of African Earth Sciences 23, 311-329.

Gass, I. G. 1982. Upper Proterozo ic (Pan-Afr ican) calcalkaline magmatism in northeastern Africa and Arabia. In: Andesites (Edited by Thorpe, R. S.) pp591-609. Wiley, New York.

Habib, M. E., Ahmed, A. A. and El Nady, O. M. 1985. Two orogenies in the Meatiq Area of the Central Eastern Desert, Egypt. Precambrian Research 30, 83-111.

Hamilton, P. J., Evensen, N. M., O'Nions, R. K. and Tarney, J. 1979. Sm-Nd sys temat ics of Lewisian gneisses: implications of the origin of granulites. Nature 277, 25-28.

Irvine, T. N. and Baragar, W. R. A. 1971. A guide to the chemical classification of the common volcanic rocks. Canadian Journal Earth Sciences 8, 523-548.

Jahn, Bor-ming, and Zhang, Z. 1984. Archean granulite gneisses from Eastern Hebei Province, China: rare earth geochemistry and tectonic implications. Contributions Mineralogy Petrology 85, 224 243.

Jahn, Bor ming, 1986. Mid-ocean ridge or marginal basin origin of the East Taiwan Ophiolite: chemical and isotopic evidence. Contributions Mineralogy Petrology 92, 194-206.

Janardhan, A. S., Newton, R. C. and Hansen, E. C. 1982. The transformation of amphibolite gneiss to charnockite in southern Karnataka and northern Tamil Nadu, India. Contributions Mineralogy Petrology 79, 130 149.

KrOner, A. 1979. Pan African plate tectonics and its repercuss ions on the crust of nor theas t Af r ica. Geologische Rundschau 68, 565-583.

Kr6ner, A. 1984. Late Precambrian plate tectonics and orogeny: a need to redefine the term Pan-African. In: G~o/ogie africaine (Edited by Klerkx, J. and Michot, J.) pp23-28. Musee Royal de I'Afrique Centrale, Tervuren, Belgium.

Kroner, A., Eyal, M. and Eyal, Y. 1990. Early Pan-African evolution of the basement around Elat, Israel, and the Sinai Penninsula revealed by single-zircon evaporation dating, and implication for crustal accretion rates. Geology 18, 545-548.

Kroner, A., KrQger, J. and Rashwan, A. A. 1994. Age and tectonic setting of granitoid gneisses in the Eastern Desert of Egypt and south west Sinai. Geo/ogische Rundschau 83, 502 513.

Leake, B. E. 1964. The chemical distinction between ortho and para-amphibolites. Journal Petrology 5, 238 254.

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Documents

Geological setting of the Meatiq metamorphic core complex ...utdallas.edu/~rjstern/egypt/PDFs/CE Desert/NeumayrMeatiqJAES96.pdf · en accord avec le diagramme AFM confirmant la composition