Precambrian Research 110 (2001) 357–383

Structural geology, single zircon ages and fluid inclusionstudies of the Meatiq metamorphic core complex:

Implications for Neoproterozoic tectonics in the EasternDesert of Egypt

J. Loizenbauer a,*, E. Wallbrecher a, H. Fritz a, P. Neumayr b, A.A. Khudeir c,U. Kloetzli d

a Department of Geology and Palaeontology, Uni�ersity of Graz, Heinrichstraße 26, A-8010 Graz, Austriab Centre for Global Metallogeny, Department of Geology and Geophysics, The Uni�ersity of Western Australia,

35 Stirling Highway, Crawley W.A. 6009, Australiac Department of Geology, Assiut Uni�ersity, Assiut, Egypt

d Laboratory for Geochronology, Institute of Geology, Uni�ersity of Vienna, Vienna, Austria

Received 15 September 1999; received in revised form 18 November 1999

Abstract

The Meatiq metamorphic core complex (MMCC) formed during the Precambrian as a result of multipledeformation and metamorphism in the Eastern Desert of Egypt. Structural, geochronologic, and fluid inclusionmicrothermometric analyses reveal a long formation/deformation history for the MMCC. This started with thebreak-up of Rodinia at ca. 800 Ma and continued until Pan-African collision at ca. 580 Ma. Between 800–780 Ma,rifting continued into sea floor spreading and oceanic crust formation. Synchronously, the Um Ba�anib graniteintruded into an approximately 1.14 Ga old crust comprising migmatic amphibolites. Rifting was accompanied by thedeposition of quartz- and mica-rich sediments. Between 660 Ma and 620 Ma, convergence between East and WestGondwanaland caused burial of sediments to a crustal depth of approximately 20 km and intrusion of calc-alkalinerocks. Subsequently, the meta-sediments were thrust across the Um Ba�anib granitoid. Deformation of both rockunits took place under amphibolite-facies metamorphic conditions. Fluid inclusions with moderate density provideevidence for the retrograde stage of this metamorphic event. Continued oblique convergence between East and WestGondwanaland resulted in a transpressional regime with displacement partition. While nappe stacking continued inforeland domains, the MMCC was exhumed to a depth of 12–15 km in hinterland domains. Extension-relatedgranitoids were emplaced between 620 and 580 Ma. Microthermometric analyses of fluid inclusions suggest a crustaldepth of approximately 10–12 km for the transpressional event. Rapid exhumation was accompanied by detachmentof the cover nappes and emplacement of syn-tectonic intrusions, which caused local contact metamorphism.Low-density fluid inclusions document high-T, low-P conditions for the contact metamorphism. The final stage of

www.elsevier.com/locate/precamres

* Corresponding author. Tel.: +43-316-3808725; fax: +43-316-3809870.E-mail address: juergen.loizenbauer@kfunigraz.ac.at (J. Loizenbauer).

0301-9268/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.

PII: S 0301 -9268 (01 )00176 -0

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383358

exhumation took place under brittle/ductile conditions at a crustal depth of approximately 3–6 km indicated bywater-rich fluid inclusions. The age of this event is constrained by the intrusion of the late- to post-tectonic Ariekiadamellite at approximately 580 Ma. © 2001 Elsevier Science B.V. All rights reserved.

Keywords: Egypt; Exhumation; Fluid inclusions; Metamorphic core complex; Pan-African orogen; Rodinia break-up

1. Introduction

The Meatiq metamorphic core complex(MMCC) represents the structurally lower unit inthe Central Eastern Desert of Egypt. This unit isexposed in a tectonic window through theNeoproterozoic cover nappes, which include ophi-olites and island-arc volcanic rocks. These coverunits were accreted by Pan-African plate tectonicswhich caused consolidation in NE-Africa (Engelet al., 1980; Kroner, 1984; Morgan, 1990). TheMMCC is one of several domes in the EasternDesert of Egypt which are arranged sub-parallelto the Najd fault system (Stern, 1985, 1994; Fig.1a). The eastern and western dome margins arebounded by sinistral strike-slip shear zoneswhereas the northern and southern margins aredefined by prominent normal faults (Wallbrecheret al., 1993). These structures are related to ESE-WNW compression with contemporary N-S ex-tension, accompanied by syn-tectonic granitoidemplacement (Fritz et al., 1996; Bregar et al.,1996).

Habib et al. (1985a,b) reported a poly-deforma-tional history for the Meatiq area. Using isotopicage data obtained from syn-tectonic granitoids,they identified two orogenies:1. the Meatiqian orogeny, which is defined by

high-grade metamorphic and deformation pro-cesses at 626�2 Ma; and

2. the Abu Ziran orogeny, defined by the obduc-tion of ophiolitic cover nappes under low-grade metamorphic conditions at 613�2 Ma.

In contrast, Neumayr et al. (1998) suggestedthat older crustal relics are preserved within theMMCC, so that tectonic processes began earlierthan what was proposed by Habib et al. (1985a).Other studies indicate that the 660 Ma and 580Ma magmatic events were related to continuousPan-African crustal evolution (Fritz et al., 1996;Neumayr et al., 1998; Loizenbauer, 1998; Bregaret al., in press).

The formation of metamorphic core complexesis commonly related to magmatic activity duringcontinental extension (Lister and Davis, 1989; Hillet al., 1992, 1995; Simony and Carr, 1997). Sev-eral mechanisms for the exhumation and/or upliftof the core complexes have been proposed; how-ever, two main mechanisms can be distinguished.One is related to crustal thickening and gravita-tional collapse (e.g. Platt, 1986; Hill et al., 1992;Kurz and Neubauer, 1996) and the other relies onenhancement of magmatic activity which accom-panied extensional tectonics of a thinning crust(e.g. Lister and Baldwin, 1993; Warren and Ellis,1996). The second mechanism explains the evolu-tion of MMCC, since there are no indicators forprominent crustal thickening (like high-pressureminerals and high-density fluid inclusions) in thispart of the Arabian Nubian Shield.

Dating of igneous and metamorphic rocks inthe Meatiq area reveals important informationabout the relationship between magmatism andcrustal extension (Sturchio et al., 1983; Stern andHedge, 1985; Fritz and Puhl, 1996). Althoughconsiderable research on the geology of the Mea-tiq area has already been carried out (Andrew,1931; Hume, 1934; Akaad and El-Ramly, 1960;Akaad and Shazly, 1972; Sturchio et al., 1983;Habib et al., 1985a,b), comprehensive understand-ing of the orogenic development of the dome isstill lacking. Now, 207Pb/206Pb zircon ages of ig-neous rocks and their metamorphic equivalentsfrom the MMCC add new data important tounderstanding the sequence of events which led tothe formation of the dome.

The aim of this study was to gain informationabout the structural evolution, timing of igneousintrusions, fluid regimes, and P-T conditions ofevents which led to the formation of MMCC.Detailed P-T paths for different structural andmetamorphic units have been established usingfluid-inclusion microthermometry and P-T data

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 359

Fig. 1. (a) Geographic position of the MMCC and the possible continuation of the Najd fault system (NFS) into Egypt. (b) Thedirections of shortening and extension during D3 transpression and lateral extrusion. (c) major tectonic units of the MMCC. Notethe ophiolitic remnants occurring as thrust nappes on top of the meta-sediments.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383360

previously published by Neumayr et al. (1996,1998), Fritz and Puhl (1996), and Puhl (1997).Data obtained from the different techniques areused to propose a model for the complex geologyof the MMCC, and this model is discussed withinthe framework of post-Rodinian and Pan-Africanorogenic processes in the Eastern Desert of Egypt.

2. Tectonic style and petrology of the Meatiqdome

2.1. Tectonostratigraphic units

The MMCC is located in the Central EasternDesert of Egypt, around 600 km SE of Cairo andcovers an area of about 500 km2 (Fig. 1). TheMMCC comprises two major tectonostratigraphicunits: (1) A high-grade metamorphic core; and (2)Low-grade metamorphic cover nappes. Thesewere referred to as infrastructure and suprastruc-ture, respectively (Habib et al., 1982; El Gaby etal., 1988, 1990). Both units were intruded by thesyn-tectonic Abu Ziran granitoid and Abu Fan-nani tonalite, and the post-tectonic Ariekiadamellite, together with small granite stocks andveins. The voluminous magmatic intrusionsplayed a major role in the thermal budget andalso for the exhumation of the MMCC (Loizen-bauer, 1998). Locally, magmatism triggered con-tact metamorphism (Fritz and Puhl, 1996).

2.1.1. The infrastructureThe infrastructure constitutes the structurally

lower Um Ba�anib granitic gneiss and upper meta-sediments (Habib et al., 1985b; Neumayr et al.,1996, 1998). The Um Ba�anib granitic gneiss is awithin-plate intrusion (Fig. 2.) which was em-placed into a pre-existing crust represented byxenolith lenses up to a few hundreds of metreslong within the granitic gneiss. These xenolithsconsist of metagabbro, amphibolite and partlymigmatised amphibolite, which have basalt tobasaltic andesite composition (Neumayr et al.,1996). Neumayr et al. (1996) proved that theselenses have two distinct geological settings: (1)MORB-type amphibolites; and (2) within-platebasaltic magmatism.The meta-sedimentary units

consist mainly of garnet-bearing quartz-rich meta-pelites and garnet-bearing quartzites. Small layersof amphibolite are also present, intercalated withthe meta-sediments (Puhl, 1997). In the southernpart of the MMCC there are small bands ofmeta-carbonates in the upper part of the se-quence. The contact with the Um Ba�anib granitic

Fig. 2. Discrimination diagrams for (a) Rb versus Y+Nb and(b) for Nb versus Y after Pearce et al., (1984). All samples arefrom the Um Ba’anib granite-gneiss and plot into the within-plate granites field (WPG). VAG+COLG, Volcanic arc andcollisional granites; ORG, Orogenic granites.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 361

gneiss is characterised by a well-developed my-lonitic foliation indicating the tectonic nature ofthe contact as reported by Habib et al. (1985a,b).Shear-sense indicators like S-C-fabrics andsheared clasts provide evidence for a northwest-wards thrust of the meta-sediments across the UmBa�anib granitic gneiss. The hanging wall is welldefined by reddish quartz-rich layers. Meta-con-glomerates occur in the southern part of theMMCC. The ellipsoidal pebbles consist ofgranitic material and show preferred orientationparallel to the foliation and lineation of the thrustand detached meta-sedimentary unit. In contrastto the Um Ba�anib granitic gneiss, the graniticpebbles are rich in plagioclase and weakly de-formed. Ries et al. (1983) suggested that the meta-sedimentary unit defines a continental faciesassemblage. Limited geochemical data analysedwith discrimination diagrams after Bhatia andCrook (1986) support a continental origin forthese meta-sediments, suggesting they might havebeen derived from either a continental island arcor a passive continental margin (Loizenbauer,1998).

2.1.2. The suprastructureThe suprastructure represents the upper unit of

the MMCC. Shackleton et al. (1980) described thesuprastructure as an ophiolitic melange of ob-ducted island-arc rocks, ophiolite materialand volcano-sedimentary sequences. These weredeformed under low-grade metamorphic condi-tions. Carbonatisation and alteration totalc are very common in the mafic and ultramaficrocks. Talc and magnesite are common alongshear zones. Shear bands and sheared quartzclasts indicate that the ophiolites were tectonicallyemplaced across the metamorphic core. Duringexhumation suprastructure rocks were dis-placed due to normal faulting as indicated byquartz boudins, extensional crenulation cleavage,and deformed quartz veins. Ophiolitic nappes ofthe MMCC (Fig. 1) comprise serpentinitesand hornblende-rich rocks which are intectonic contact with the meta-sediments. Thiscontact is marked by the occurrence of highlymylonitised quartz-rich meta-sediments (Loizen-bauer, 1998).

2.2. Metamorphic e�ents

Neumayr et al. (1996, 1998) described threemajor metamorphic events in the MMCC on thebasis of textural observations, microchemicalanalyses and thermodynamic modelling. These arefrom oldest to youngest: M1, M2, and M3. Thecover nappe rocks exhibit only the M3 metamor-phic assemblage and textures indicating an un-equivocal metamorphic break between basementand cover rocks of the MMCC.

M1 is recorded in the xenoliths enclosed in theUm Ba�anib granitic gneiss. These were metamor-phosed at �750 °C leading to migmatisation andformation of ductile fabrics in the amphibolitelenses. This migmatitic texture is absent in theUm Ba�anib granitic gneiss, hence M1 pre-datesthe emplacement of the Um Ba’anib graniticgneiss. M2 is characterised by a clockwise P-T-tpath with peak metamorphic conditions of 610–690 °C and 600–800 MPa followed by retrogres-sive P-T conditions of 530–600 °C andapproximately 580 MPa (Neumayr et al., 1998).Thermal equilibration of basement rocks tookplace during this metamorphic event.

M3 affected both infrastructure and suprastruc-ture rocks. Two different types of metamorphismcan be distinguished. A greenschist-facies regionalmetamorphic event (M3R), and a contact meta-morphic event (M3C). M3C developed locallyaround syn- to late-tectonic intrusions. The tem-perature conditions for M3R and M3C range from450 to 500 °C and 610–650 °C, respectively (Fritzand Puhl, 1996). M3R and M3C pressure condi-tions were just below 400 MPa.

3. Structure and kinematics

Buckling of the basement followed by detach-ment of cover rocks are responsible for thedomal appearance of the MMCC. The main pre-Pan-African and Pan-African structures are (Fig.3):1. thrust nappes;2. NNW-SSE trending sinistral strike-slip shear

zones bordering the basement of the MMCCin the east and in the west;

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383362

Fig. 3. (a) Structural map of the MMCC illustrating the major structures formed during D2, D3 and D4, (b) Plot of poles to foliationplanes in equal-area lower hemisphere stereonet. Plot illustrates the dome-like appearance of the MMCC defined by open F3

mega-folds and S3 normal fault planes dipping gently to the north and south planes (NNF, foliation of northern normal fault; SNF,foliation of southern normal fault). Poles of the NW-SE trending strike-slip shear zones (SZ) show the steep dip to the NE and tothe SW. (c) Plot of stretching lineations in equal-area lower hemisphere stereonet exhibit a consistent NW-SE orientation. Stretchinglineations of the northern (NNF) and southern normal faults (SNF) plunge gently to moderately to the NW and to the SE,respectively. In the strike-slip shear zones (SZ), stretching lineation plunges sub-horizontally NW-SE.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 363

3. normal faults in the north and in the south ofthe dome; and

4. NNW- and E-trending folds.Four phases of deformation are identified in the

MMCC.These are from older to youngest D1,D2, D3, and D4. D1 is believed to be pre-Pan-African in age, whereas D2, D3, and D4 are Pan-African.

3.1. D1 pre-Pan-African structures

D1 structures in the MMCC are confined to thepartly migmatised amphibolite xenoliths enclosedin the Um Ba�anib granitic gneiss. D1 is in theform of isoclinal folds (F1), penetrative metamor-phic foliation (S1), and associated stretching lin-eation (L1). S1 is truncated by emplacementfeatures of the Um Ba�anib granitic gneissand locally superimposed by fabrics formed dur-ing D3 strike-slip movement. D1 structures arerandomly oriented because of their enclosure andre-orientation during the emplacement of the UmBa�anib granite gneiss and subsequent deforma-tion. Metamorphic textural and structural rela-tionships indicate that D1 and M1 are closelyrelated.

3.2. D2 Thrust-related structures

These structures are well preserved in the loweststructural units of the basement of the MMCC.They formed by thrusting of the meta-sedimentsfrom SE to NW across the Um Ba�anib graniticgneiss. Thrust planes are well determined with L-Sfabrics. Planar fabric (S2) is defined by parallelalignment of Bt-Ms-Hbl-Qtz-minerals that form apenetrative spaced foliation. In quartz-rich my-lonites continuous foliation is also common. S2

dips gently to the SE. L2 stretching lineationplunges to the NW and to the SE. Shear senseindicators, like S-C fabrics, sheared quartz veins,and asymmetric lenses of quartz, indicate tectonictransport from SE to NW. Associated F2 folds areasymmetric NW-vergent shear-folds and partlyrecumbent shear folds which are characterised by(E)NE-(W)SW-facing sub-horizontal fold-axes. Inthe centre of the basement of the MMCC, contin-uous schistosity and tight to isoclinal folds indi-

cate a dominant flattening due to pure shearstrain. During D2, the rheological behaviour ofthe basement rocks enabled dominant plastic de-formation accompanied by dynamic recrystallisa-tion of quartz and feldspar. Although D2 fabric iscommonly modified by D3 structures, neverthe-less, it is well preserved in the lowermost parts ofthe dome. D2 took place under M2 upper amphi-bolite facies metamorphic conditions.

3.3. D3 transpressional structures and lateralextrusion

D3 is characterised by an overall NW-trending,sinistral transpressional regime combined with lat-eral extrusion, which produced NW-trending, sin-istral wrenching and N- and S-directed extension.Related structures are prominent sinistral strike-slip shear zones which define the eastern and thewestern boundary of the MMCC and low-anglenormal faults occurring in the southern and thenorthern parts of the Meatiq dome. Transpres-sional deformation took place under M3

conditions.Two major D3 NW-trending, sinistral strike-slip

faults deform both basement and cover rocks ofthe MMCC. In the NE part of the eastern strike-slip shear zone, migmatised amphibolite xenolithsincorporated into the Um Ba�anib granitic gneissare aligned parallel to the NW-trending shearzone. The shear zone is defined by sub-vertical,NW-trending, mylonitic foliation (S3) withstretching lineations (L3) plunging gently to NWand SE. Similar fabrics are present in the NW-trending, sinistral shear zone which defines theSW part of the MMCC. However, here a secondset of stretching lineations plunges steeply to theSE and is superimposed on the more sub-horizon-tal set. This second set of lineations is youngerand could have been formed during exhumationphase of the MMCC. Both strike-slip shear zonescontain numerous NNW- and SSE-plunging F3

transposition synforms and antiforms with ori-ented hinge lines. Microscopic shear sense indica-tors such as S-C fabrics, feldspar�-porphyroclasts, and garnet porphyroblasts withasymmetric pressure shadows, indicate a sinistralsense of shear. Microfabric analyses of feldspar

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383364

and quartz from the western shear zone revealedinitial ductile deformation accompanied by recov-ery processes and dynamic recrystallisation. Therheological behaviour of quartz and feldspar sug-gests a deformation temperature of approximately500–550 °C during the sinistral strike-slip fault-ing. This temperature is indicated by lattice pre-ferred orientation (LPO) patterns of Quartz c-and a-axes (Tullis, 1977; Lister and Hobbs, 1980;Schmid and Casey, 1986, Mainprice et al., 1986),which suggest non-coaxial deformation domi-nated by prism �a� slip mechanism.

The normal faults are characterised by S3 folia-tions dipping gently to moderately to the NW andSE, and L3 stretching lineation plunging gently tothe NW and SE (Fig. 3). Boudinaged quartzveins, crenulation cleavage and kink folds arecompatible with the normal-slip movement. Mi-croscopic shear-sense indicators such as ecc-fab-rics (extensional crenulation cleavage; Platt andVissers, 1980), �-porphyroclasts with asymmetricpressure shadows, and mica-fish indicate top tothe N(NW) and top to the S(SE) normal-slipmovement in the northern and the southern faultplanes, respectively (Fig. 3). The meta-sediments,the ophiolitic cover rocks, and parts of the UmBa�anib granitic gneiss were deformed by thesefaults. Detachment occurred along mylonitic lay-ers which consist of quartz-, talc-, and mica-richmineral assemblages. 40Ar/39Ar ages obtainedfrom syn-tectonic muscovite of ca. 590 Ma giveevidence for a synchronous activity of strike-slipfaults and low-angle normal faults (Fritz et al.,1996). The development of these faults indicatesESE-WNW-directed shortening, and NNW-SSE-directed extension. Intrusions were emplaced dur-ing extensional deformation.

3.4. D4 Brittle structure

The last stage of exhumation is characterised bybrittle deformation in the form of joints andextensional gashes filled with chlorite and quartz.D3 strike-slip shear zones show local slickensidesindicating a dextral shear sense of rocks previ-ously deformed by sinistral strike-slip shearing.D4 dextral shear sense is also supported by pole

diagrams of LPO patterns of quartz c- and a-axes. These patterns exhibit a single girdle asym-metric orientation due to dominant basal �a� slipwhich underlines the dextral shear sense caused bynon-coaxial strike-slip faulting under low temper-ature conditions. D4 extensional fractures arealigned sub-perpendicular to D3 mylonitic folia-tion. The LPO pattern, slickensides, and conju-gate shear fractures suggest progressive rotationof compression from SE-NW to NE-SW in ananticlockwise sense during exhumation (Loizen-bauer, 1998; Loizenbauer et al., 1999).

4. Geochronology

4.1. Analytical methods

Using a single zircon evaporation techniqueaccording to modified procedures described inKober (1987), Pb/Pb measurements were carriedout at the Laboratory for Geochronology, Insti-tute of Geology, University of Vienna, Austria.Data were obtained using a double re-filamentarrangement in a FINNIGAN MAT 262 massspectrometer. Depending on crystal quality, size,age, and Pb content of the zircons, one to sixevaporation analysis cycles with temperature stepsof ca. 20 °C were performed (see Klotzli, 1997,for detailed discussion)

4.2. Results

Four samples were analysed to obtain forma-tion ages of the MMCC and the ophiolitic coverrocks. The petrography of samples is described indetail by Neumayr et al. (1996, 1998) and Puhl(1997). An ortho-amphibolite xenolith enclosed inthe Um Ba�anib granitic gneiss (ED85); a samplefrom the Um Ba�anib granitic gneiss (NM84); asample from a calc-alkaline granite stock (NM90)which intruded the Um Ba�anib in the eastern partof the Meatiq dome; and a sample from theophiolitic nappes (MPJ239) located at the top ofthe meta-sedimentary rocks were collected. Theresults of 207Pb/206Pb ages are shown in Table 1.1. The ortho-amphibolite xenolith (ED85): Three

zircon grains were analysed for 207Pb/206Pb

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 365

Table 1Single zircon 207Pb/206Pb ages from the MMCC (individual zircons A, B, C, D)

Sample Grain 207Pb/206Pba 2 �b 2 �%b 207Pb/206Pb age Maa,c 2 � Maa,b 2�%b

ED85 0.06687A 0.00066 0.5 834 21 2.50.06579 0.00014 0.5B 800ED85 4 0.5

CED85 0.07809 0.00097 0.5 1149 25 2.10.06640 0.00122 0.5 819 38ED85 4.7A-B0.06553 0.00014 0.2A 791MPJ239 4 0.60.06555 0.00010 0.2MPJ239 792B 3 0.40.06622 0.00056 0.8C 813MPJ239 18 2.2

DMPJ239 0.06508 0.00009 0.1 777 3 0.40.06541 0.00039 0.6A-D 788MPJ239 13 1.6

ANM84 0.06451 0.00113 1.8 758 37 4.90.06534 0.00036 0.6 785 12NM84 1.5B0.06516 0.00079 1.2C 779NM84 25 3.30.06517 0.00023 0.4NM84 780D 7 1.00.06516 0.00011 0.2A-D 779NM84 4 0.5

BNM90 0.06118 0.00150 2.5 646 53 8.20.06113 0.00041 0.7C 644NM90 14 2.2

DNM90 0.06592 0.00021 0.3 804 7 0.80.06114 0.00056 0.9NM90 644B-C 20 3.1

a Weighted mean from individual scan ratios.b All errors reported are 2 standard errors of the mean.c Mean ages derived from individual scan ratios and not from individual scan ages.

ED85, amphibolite xenolith from the basement; MPJ239, Hbl-rich ophiolite from a cover nappe of the centre of the MMCC; NM84,Um Ba�anib granitic gneiss; NM90, calc-alkaline granite intruded the Um Ba�anib granite-gneiss.

ages (A, B and C). Grain C gave an age of 1149Ma. Grains A and B gave ages of ca. 800 Maand their individual scan ratios gave a mean ageof ca. 819�38 Ma.

2. The ophiolitic cover (MPJ239): Four zircongrains gave ages varying from 777 to 813 Mawith a mean of 788�13 Ma.

3. The Um Ba�anib granitic gneiss (NM84): Fourzircon grains gave ages varying from 758 to 785Ma with a mean of 779�4 Ma.

4. The granitic stock (NM90): Three zircon grainswere analysed (A, B, C and D). B and C gaveages of 646�53 and 644�14 Ma, respectively,with a mean of 644�20 Ma. Grain D gave anage of 804�7 Ma

4.3. Age interpretation and correlation withexisting data

207Pb/206Pb age data suggest major magmaticevents at 800, 780, 650 Ma. The inherited core ageof 1.15 Ga for a single zircon of the ortho-amphi-

bolite xenolith suggests the existence of an oldercrust which was intruded by the Um Ba’anibgranite at approximately 780 Ma. The emplace-ment could have affected the xenolith zircons of theortho-amphibolites as suggested by the 800 Ma age.Furthermore, the data suggest a close time betweenthe emplacement of the Um Ba’anib granitic gneiss(780 Ma) and the ophiolites (800 Ma).

The 804�7 Ma age obtained from one zircongrain of the granitic stock (NM90) might reflect aninherited zircon from the Um Ba�anib graniticgneiss. The ages from other zircon grains areinterpreted as that of magmatic activity at 644�20Ma. In addition, 207Pb/206Pb ages obtained fromGroup II and Group III (meta-)granitoids occur-ring in the Sibai dome reveal evidence for magmaticactivity at 659�14 Ma and 645�5 Ma, respec-tively (Bregar et al., in press). Therefore, we suggestthat these magmatic events were triggered by NW-SE oriented convergent plate movements of Eastand West Gondwanaland at approximately 644�20 Ma.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383366

U/Pb zircon ages for the intrusion of the AbuZiran granitoid of 614�8 Ma (Stern andHedge, 1985) and 40Ar/39Ar muscovite ages of595�0.5 Ma for the western strike-slip fault, aswell as 588�0.5 Ma for the normal faults inthe south (Fritz et al., 1996) determine the tim-ing of transpressional tectonics and lateral extru-sion in the MMCC. Rb/Sr model ages of579�6 Ma (Sturchio et al., 1983) for the late-to post-kinematic Arieki adamellite are associ-ated with the latest magmatic event in theMMCC.

5. Fluid inclusion studies

5.1. Introduction

Investigation of fluid inclusions (FIs) providesinformation about the P-T conditions of faultingand exhumation of metamorphic core complexes(e.g. Reynolds and Lister, 1987, Craw et al.,1994; Hodgkins and Stewart, 1994). The role offluid during deformation and metamorphism isdiscussed in Hubbert and Rubey (1959), Ethe-ridge et al. (1983, 1984), Sibson (1990), DenBrok and Spiers (1991), Walther (1994), andLosh (1997). Deformation enables deep fluid cir-culation in shear zones (McCaig, 1988; Oliver,1996; Pili et al., 1997). A pioneer fluid inclusionstudy in the MMCC was carried out by Neu-mayr et al. (1998). They reported peak- to post-metamorphic fluid inclusions trapped in thebasement of the MMCC. The occurrence of dif-ferent fluid inclusion generations in deformedrocks of the MMCC enables detailed microther-mometric studies to reconstruct individual P-Tpaths for metamorphic events. Combining P-Tpaths with age data results in detailing the com-plex tectonic history of the MMCC.

5.2. Analytical techniques

5.2.1. Heating-freezing stageFor a detailed outline of microthermometric

analysis technique refer to Roedder (1984),Shepherd et al. (1985), and Goldstein andReynolds (1994). Petrographic investigations on

fluid inclusions were carried out with an Olym-pus BH-2 translight microscope. Microthermo-metric fluid inclusion measurements wereperformed using a Chaixmeca heating-freezingstage (Shepherd et al., 1985) mounted onto anOlympus BH-2 translight microscope. The stan-dard instrument was improved by: (1) AnOmega CN 3000 Thermo-Controller; (2) Videoequipment including a Panasonic CCTV-WV-BL600/G black and white video camera; (3) ANFK 6.7× ND 125 projective and an IC 80long-distance objective ULWD MSPLAN 80 −0.75 �/0 f=180; and (4) A Panasonic blackand white video monitor WV-BM1400. Theheating-freezing stage is controlled by TCS-Al-pha computer program V1.0© (Stegmuller,1996). For accuracy, the heating-freezing stagewas calibrated periodically using commerciallyavailable calibration standards listed in Table 2.

Fluid inclusions were studied on double-pol-ished wafers, about 150 �m thick. Quartz wasthe host mineral of all the fluid inclusions mea-sured, although some primary fluid inclusionswere also observed in calcite.

Table 2Performed calibration standards. Deviation is given for twodifferent long distance objectives (UT50 and IC80)

DeviationCalibration Temperature(°C)standard

UT50 ( °C) IC80 ( °C)

−1.0−95.00 XaToluol−0.1−56.79n-Octan −0.8

−56.60 −0.8pure natural −0.1CO2-FI

−29.70n-Decan +0.1 −0.5−9.60 +0.1 Xan-Dodecan

H2O distillate +0.10 to 0.10.00+0.2 +0.240.00Merck 9640

+1.065.00 +1.0Merck 9665+1.480.00 +1.5Merck 9680+1.4+1.5Merck 9730 130.00+1.5180.00 +1.6Merck 9780

+2.0200.00 +1.8Merck 9800+2.0+2.2306.80Natriumnitrat

a X not measured.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 367

5.2.2. Raman spectroscopySome CO2-rich fluid inclusion assemblages of

the MMCC had melting temperatures (Tm) below−56.6 °C. This suggests impurity in the CO2-sys-tem. Typical impurities in the CO2-system are N2

and/or CH4. It is impossible to determine whichof these impurities is present using standard mi-crothermometry. Thus, Raman analyses were per-formed using an OMARS89 (DILOR) Ramanspectrometer in conjunction with a 5 W Argon-laser model 2020 (SPECTRA PHYSICS) at theDepartment of Experimental Physics, Karl-Franzens-University in Graz. Detailed informa-tion about the equipment and the appliedtechniques are reported by Knoll et al. (1990).

5.3. Sample collection

Fluid inclusions are trapped in trails which arealigned orthogonal to the extensional stress andsub-parallel to compressional stress. Therefore,orientation of fluid inclusion trails can be corre-lated with strain during syn-tectonic entrapment(Fig. 4). Fluid inclusion samples were collectedfrom: (1) Oriented samples from sheared asym-metric quartz lenses and folded quartz veins de-formed and metamorphosed during D2/M2; (2)Oriented samples from quartz boudins and differ-ent quartz veins deformed during D3; (3) Orientedfluid samples from the eastern and the westernstrike-slip shear zones in order to constrain theirP-T conditions and penetration depths during D3.These samples comprise S3-parallel sheared andfolded quartz veins, asymmetric quartz lenses andquartz segregation occurring as saddle reefs in F3

vortex folds; (4) Oriented samples from miner-alised extensional quartz veins formed during D4;and (5) Quartz-rich extension veins occurring inthe Abu Ziran granitoid to understand P-T condi-tions of syn-tectonic emplacement and the M3Ccontact metamorphism.

5.4. Results

5.4.1. Fluid inclusions hosted by themeta-sedimentary basement

There are three generations of fluid inclusionsin the meta-sediments (Table 3). The older fluid

Fig. 4. (a) 3D-schematic model illustrating the spatial relation-ship of orientation of vein generations and boudins formed inmeta-volcanic rocks from the NE of MMCC: The occurrenceof quartz-rich sample GML12 (foliation parallel vein),GML13 (vein perpendicular to foliation), and GML14(boudin) is shown. (b) The orientation of �1 during formationof quartz boudin (sample GML14). (c) Sketch showing theorientation of CO2-H2O-rich D3 and H2O-rich D4 fluid trailsoccurring in GML14. Alignment of D3 fluid inclusion trails isrelated to orientation of �1. (d) Orientation of D3 and D4 fluidtrails shown in (c). Note that D4 fluid trails cross-cut D3 fluidsand are therefore younger.

generation (D2/M2 retrograde fluids) was trappedduring thrusting and comprises H2O-CO2-richfluids. The second generation (D3/M3 fluids) wastrapped during transpressional tectonics and con-sists of two assemblages:1. CO2-H2O-rich FIs; and2. CO2-rich FIs.

The third generation was trapped during D4

and constitutes H2O-rich fluid inclusions.

5.4.1.1. D2/M2 (retrograde) fluid inclusion genera-tion. These occur only in samples from the innerparts of the MMCC and were trapped during D2

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383368

NW-verging thrusting. FIs are present within re-crystallised quartz grains showing top-to-the-NWshearing. The FIs occur as single isolated inclu-sions and in clusters in the cores of recrystallised

quartz grains. Therefore, these FIs are interpretedto represent primary inclusions, trapped duringthrusting. They consist mainly of H2O and CO2

and show low salinity. XCO2 is low with an aver-age of 0.3 (Table 3). CO2 last-melting tempera-tures (TmCO2) range from −57.3 to −56.9 °C,which indicates minor quantities of volatiles suchas CH4 and/or N2. Homogenisation of CO2

(ThCO2) occurs into the vapour phase in the rangeof 21–29 °C. Decrepitation textures are commonin fluid inclusions larger than 20 �m. These tex-tures are characterised by clusters of small inclu-sions extending from the large original ones.Decrepitation textures suggest an isothermal de-compression path (Vityk and Bodnar, 1995) forthe meta-sediments associated with thrusting.

5.4.1.2. D3 (CO2-H2O-NaCl and CO2) and D4 fluidgenerations (H2O-NaCl Fls). These occur inquartz boudins and extensional quartz veins de-formed during S-directed normal faulting (Fig.4a,b). The orientations of fluid trails suggest aclose relationship to normal fault-related struc-tures. The relative chronology of D3 and D4 fluidinclusion entrapment is indicated by the texturalrelations in oriented sections, where trails of theD3 CO2-H2O-rich fluid inclusions are cross-cut bytrails consisting of D4 saline FIs (Fig. 4c). D3 fluidinclusions show TmCO2 of −57.4 to −56.8 °Cand Tclath of 7.5 °C (Table 3). Homogenisation ofCO2 occurs in the liquid phase at 17–30 °C. Fluidinclusions which are larger than 20 �m are com-monly decrepitated.

The CO2-rich fluid inclusion assemblage occursas trails and clusters. The last melting temperatureof CO2 varies from −57.0 to −57.4 °C. All fluidinclusions show homogenisation of CO2 in theliquid phase in a range of 10.2–29.0 °C.

The H2O-rich FIs occur either as secondarytrails in the high-temperature rocks, or as primaryinclusions within quartz crystals of late-tectonicmineralised extensional veins. Secondary fluid in-clusions are commonly arranged along trails,which parallel chlorite-filled extensional gashes ingarnet. The degree of fill varies between 0.90 and�0.95. First melting of ice (Te) occurred at ap-proximately −22.0 °C, suggesting the presence ofan NaCl-dominated solution probably with minor

Table 3Microthermometric data for D2–D4 fluid inclusions of themeta-sediments

D2 H2O-(NaCl)-CO2 FIsSample GML24a n=50

6 to 30 �m (12 �m)Size rangeNumber/type of phases (at RT) 2/L, V and 3/L, L, V

−57.3 to −56.9 °CTmCO2

(−57.1 °C)8.4 to 9.0 °C (8.5 °C)Tclath

wt% NaCl equivalent 2.0 to 3.2 (3.0)ThCO2 21.0 to 28.8 °C (24.0 °C)aMode of homogenisation VbXCO2 0.3 to 0.5 (0.4)

0.62 to 0.78 (0.70)Bulk density (g·cm−3)

D3 CO2-H2O-NaCl FIn=72Sample GML495 to 12 �m (8 �m)Size range

Number/type of phases (at RT) 2/L, L and 3/L, L, V−57.4 to −56.8 °CTmCO2

(−57.1 °C)6.6 to 7.6 °C (7.5 °C)Tclath

wt% NaCl equivalent 4.7 to 6.5 (4.9)17.0 to 30.2 °C (27.8 °C)ThCO2

aMode of homogenisation LbXCO2 0.8 to�0.9 (0.85)Bulk density (g·cm−3) 0.65 to 0.83 (0.72)

D4 H2O-NaCl�KCln=60Samples GML24a, GML57 and

GML59Size range 6 to 15 �m (12 �m)

1/L and 2/L, VNumber/type of phases (at RT)bDegree of fill 0.90 to �0.95cTe −22.0 to −19.3 °CSystem H2O-NaCl�KClTm −1.6 to −2.5 °C

(−2.0 °C)wt% NaCl equivalent 2.6 to 3.3 (3.27)

140 to 220 °C (154 °C)ThLaMode of homogenisation0.87 to 0.95 (0.94)Bulk density (g.cm-3)

Note: mean values shown in brackets:a Mode of homogenisation: to liquid, L; to vapour, V.b Estimated visually at room temperature (RT) from the

charts of Shepherd et al. (1985).c Here apparent Te values are given, because real Te was

commonly hard or even impossible to measure. n number ofmeasurements.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 369

quantities of KCl. Lowest Tm of −1.5 °C revealslow salinity for these inclusions (Table 3). Allfluid inclusions homogenise into the liquid phaseat ca. 140–220 °C.

5.4.2. Fluid inclusions from the eastern andwestern strike-slip shear zones

5.4.2.1. The eastern strike-slip shear zone. Twodistinct fluid inclusion assemblages have been ob-served. The first assemblage is rich in CO2-H2Oand exhibits three phases. The second assemblagecomprises one- and two-phase H2O-rich inclu-sions which are mainly decrepitated, and hence donot provide useful microthermometric data. TheCO2-H2O-rich FIs show constant XCO2 content of0.5–0.6 and exhibit rounded to negative crystalshape. They range in size between 5 and 15 �m.Fluids are arranged mainly in trails and rarely inclusters. The orientation of the trails is controlledby sinistral strike-slip regime. Thus, microthermo-metric data of the three-phase CO2-H2O-rich FIsconstrain P-T conditions prevalent during sinistralstrike-slip faulting. TmCO2

near −56.6 °C sug-gests that fluid inclusions contain nearly pureCO2. The homogenisation occurs in the liquidphase in a range between 22 and 27 °C with amaximum at 26.6 °C.

5.4.2.2. The Western strike-slip shear zone. Thissystem comprises three-phase FIs (CO2(V)-CO2(L)-H2O(L)) occurring either as primary single inclu-sions arranged in clusters in the centres of quartzgrains or as secondary inclusions aligned in trailsthat may cross grain boundaries. Rounded tonegative crystal shapes are very common. The sizeof FIs ranges from �4 to �16 �m. Two differ-

ent inclusion assemblages can be distinguished.One is oriented by the sinistral shear movementand the other shows orientation due to dextralshear movement (Fig. 5c). In some samples, theformer are cross-cut by the latter, indicating thatthe sinistral movement is older. Fluid inclusionsoriented according to sinistral movement aresmall and comprise two (CO2(L)-H2O(L)) and three(CO2(V)-CO2(L)-H2O(L)) phases with XCO2 rangingfrom 0.5–0.6 (Fig. 5d). Last melting temperaturesfor CO2 range from −57.5 to −58.6 °C. ThCO2

ranges from 11.8 to 21.0 °C. All fluid inclusionsindicate a ThCO2

into the liquid phase.Fluid inclusions oriented according to dextral

movement are larger than fluid inclusions trappedduring sinistral faulting. They comprise two(CO2(L)-H2O(L)) and three (CO2(V)-CO2(L)-H2O(L))phases with XCO2 ranging from 0.6–0.7. Three-phase FIs are more common than 2-phase FIs.The melting temperatures of CO2 range from−57.5 to −59.2 °C with a maximum at −58.6°C. ThCO2 ranges from 18.1 to 24.5 °C with amaximum at 24.3 °C. All fluid inclusions indicatea ThCO2

in the liquid state.

5.4.3. Fluid inclusions hosted by ophiolitic co�ernappes

To gain information about the detachment ofthe cover nappes, fluid inclusions from coverrocks in the northeastern and southern parts ofthe MMCC were analysed. The ophiolites in thesouth experienced contact metamorphism owingto emplacement of the Abu Ziran granitoid. How-ever, evidence for high-temperature events in thecover rocks from the northern part of the dome islacking.

Fig. 5. Photomicrographs of polished wafers showing fluid inclusions (Fls). (a) Re-equilibration textures of Fls from an extensionalquartz vein (Sample GML13). Clusters of small inclusions extending from the large original inclusion indicate re-equilibration inresponse to isothermal decompression. (b) Fls trapped within rocks of the contact aureole (sample GML46). Irregular dendriticre-equilibration pattern provides evidence for a non-isochoric P-T path in response to isobaric cooling. (c) Two CO-H2O-rich fluidinclusion assemblages (FIA) hosted by quartz minerals from the western strike-slip shear zone (sample GML 130). One ischaracterised by trails trending from upper right to lower left (white arrow) that terminate at the grain boundary. These fluids showalignment according sinistral (top to the left) deformation (Fl-sin). Second FIA is defined by fluid trails trending from upper left tolower right, parallel to the extension crack which cross-cuts the recrystallised quartz grains (black arrow). These fluids suggestentrapment during dextral strike-slip movement (FI-dex). Inset in the upper right indicates the alignment of the two fluid inclusionassemblages. (d) Magnification of ‘Fl-sin’ fluid inclusions shown in (c). All sections are taken parallel to stretching lineation andnormal to the foliation; width of view is: (a) 200 �m; (b) 420 �m; (c) 3.3 mm; (d) 385 �m.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383370

Fig

.5.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 371

Table 4Microthermometric data for D3-D4 fluid inclusions of thesouthern ophiolitic cover

D3 CO2-H2O-NaCl FIsGML41a GML46

(n=35)(n=12)5 to 10 �mSize range 6 to 16 �m

(12 �m)(7 �m)Number/type of 3/L, L, V 2/L, V

phases (at RT)−57.3 to −56.8 °CTmCO2 −59.5 to −58.5

°C (-58.9 °C)(−57.0 °C)Tclath 8.5 to 9.2 °C 5.7 to 9.3 °C

(8.2 °C)(9.0 °C)wt% NaCl 1.6 to 3.0 (2.0) 1.4 to 8 (3.6)

equivalent26.1 to 29.0 °CThCO2 8.1 to 9.3 °C

(9.2 °C)(28.7 °C)aMode of V L, V

homogenisationbXCO2 0.4 to 0.5 (0.5) 0.5 to 0.6 (0.5)

0.72 to 0.73 (0.73) 0.49 to 0.58Bulk density(g·cm−3) (0.50)

0.91 to 0.94(for Th=�L)

D4 H2O-NaCl�CaCl2 FIs (low salinity)GML41 GML46

(n=12)(n=40)5 to 20 �m (6 �m)Size range 4 to 8 �m (6 �m)1/L and 2/L, VNumber/type of 1/L and 2/L, V

phases (at RT)bdegree of fill 0.90 to �0.950.70 to �0.95

−54.8 to −49.5 °CcTe −51.8 to−48.1 °C−22.0 to−22.5 to −19.8 °C−20.2 °C

H2O-NaCl-CaCl2System H2O-NaCl-CaCl2

�KCl�KClTm −1.8 to −0.7 °C −1.2 to −0.8 °C

(−1.0° C)(−1.2 °C)wt% NaCl 1.0 to 3.0 (2.0) 1.0 to 2.0 (1.7)

equivalent145 to 220 °C144 to 220 °CTh

(150 °C) (150 °C)aHomogenisation LLBulk density 0.86 to 0.94 (0.94) 0.85 to 0.94

(0.93)(g·cm−3)

D4 H2O-NaC l�CaCl2 FIs (mod. salinity)GML41 (n=25) GML46 (n=30)

9 to 25 �m12 to �20 �mSize range(16 �m) (15 �m)

Number/type of 1/L and 2/L, V 1/L and 2/L, Vphases (at RT)

bDegree of fill 0.90 to �0.950.70 to �0.95−53.2 to −49.8−52.8 to −49.8 °CcTe°C (51.0 °C)

Table 4 (Continued)

−22 °C to−22.5 to −20.8 °C−18.9 °CH2O-NaCl-CaCl2System H2O-NaCl-CaCl2

�KCl�KCl−8 to −5 °C −3.0 to −6.7 °CTm

(−3.4 °C)(−7.7 °C)7.8 to 11.7 (11.3)wt% NaCl 4.9 to 10.1 (5.5)

equivalent155 to 220 °CTh 190 to 250 °C

(200 °C) (185 °C)LLaHomogenisation

0.90 to 0.96 (0.95) 0.89 to 0.95 (0.92)Bulk density(g·cm−3)

Notes as in Table 3.

5.4.3.1. The Southern ophiolites. Fluid-inclusionthermobarometry was performed on two orientedsamples (GML46, GML41) collected from north-south opening quartz veins in the southern part ofthe MMCC. Three different fluid-inclusion assem-blages are present (Table 4). Two CO2-H2O-richassemblages distinguished by homogenisation ofCO2 either in the liquid or in the vapour phase (thiswas observed only in sample GML46) and a salineH2O-rich fluid inclusion generation. The H2O-richassemblage constitutes low and moderate salinityfluids. Trails of D3-related CO2-H2O-rich fluidinclusions are cross-cut by D4 inclusions.

The microthermometric results for these fluidinclusions are summarised in Table 4. Ramanspectroscopy gives evidence for the presence of CH4

and N2 in both CO2-H2O-rich FI assemblages. Anaverage Tclath of 8.5 °C indicates a salinity ofapproximately 3 wt% NaClequiv. for the CO2-H2O-rich fluids. In the D3 CO2-H2O-rich fluid, inclusionre-equilibration textures due to a non-isochoric P-Thistory are common (Fig. 5b). Clusters of smallsecondary FIs surrounding the parent inclusion, aswell as textures defined by irregular dendritic inclu-sions, indicate re-equilibration under isobaric cool-ing. Vityk and Bodnar (1995) described similarre-equilibration textures of synthetic FIs derived byisobaric cooling at 5 kbar and decreasing tempera-tures from 700 to 500 and 400 °C.

The D4 H2O-rich FIs are characterised by differ-ent salinity and different salt composition (Table 4).Primary and secondary FIs are trapped in quartz

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383372

Table 5Microthermometric data from D3-D4 fluid inclusions of the northeastern ophiolitic

GML13 (n=107)GML12a (n=30) GML14 (n=51)

D3 CO2-H2O-NaCl Fis8 to 30 �m (20 �m)Size range 8 to 15 �m (12 �m)5 to 20 �m (15 �m)

3/L, L, V 3/L, L, V 3/L, L, VNumber/type of phases(at RT)

−57.0 to −56.6 °C −57.5 to -57.0 °CTm CO2 −57.1 to −56.8 °C(−57.2 °C) (−56.9 °C)(−56.9 °C)7.5 to 8.0 °C (7.8 °C)6.5 to 7 °C (6.8 °C) 7.5 to 8.3 °C (8.0 °C)Tclath

5.7 to 6.6 (6.1)wt% NaCl equivalent 4.0 to 4.9 (4.3) 3.4 to 4.9 (4.0)26.6 to 30.2 °C (28.5 °C)26.1 to 30.7 °C (30.5 °C) 26.6 to 30.2 °C (28.1 °C)Th CO2

LaMode of homogenisation L L0.6 to �0.9 (0.8)bXCO2 0.3 to 0.5 (0.45) 0.35 to 0.6 (0.5)

0.80 to 0.89 (0.82)0.64 to 0.74 (0.65) 0.76 to 0.87 (0.80)Bulk density (g·cm−3)

D4 H2O-NaCl�CaCl2 FIsGML13 (n=20)GML12a (n=15) GML14 (n=20)5 to �10 �m (6 �m)Size range 4 to 8 �m (5 �m)8 to 16 �m (10 �m)

1/L and 2/L, V 1/L and 2/L, V 1/L and 2/L, VNumber/type of phases (atRT)

0.90 to �0.95 0.90 to �0.95bDegree of fill 0.90 to �0.95−21.8 to -19.3 °C−52.0 to −49.6 °C −51.8 to −48.1 °C (51.0 °C)cTe

−20.5 to −19.8 °CH2O-NaCl�KClSystem H2O-NaCl-CaCl2H2O-NaCl-CaCl2

H2O-NaCl�KCl−12.6 to −2.7 °CTm −3.5 to −2.0 °C −13.8 to −11.8 °C(−3.0 °C) (−12.2 °C)(−2.2 °C)

3.3 to 5.6 (3.6)4.4 to 16.5 (4.8) 15.7 to 17.6 (16.0)wt% NaCl equivalent152 to 180 °C (162 °C)Th 136 to 150 °C (145 °C)150 to 180 °C (160 °C)LL LaHomogenisation

Bulk density (g·cm−3) 0.92 to 0.95 (0.93)0.92 to 0.95 (0.94) 1.03 to 1.05 (1.04)

Notes as in Table 3.

and carbonate minerals where inclusions exhibitirregular and rounded shapes, with few negativecrystal shapes.

5.4.3.2. The Northeastern ophiolites. Fluid-inclu-sion measurements were performed on three sam-ples, GML12a, GML13 and GML14 derived froma concordant and a discordant extensional quartzvein, and from a boudin, respectively (Table 5; Fig.4). Structures formed during and after D3 trans-pressional deformation and lateral extrusion. Mi-crothermometric analyses reveal two fluid inclusionassemblages. One is rich in CO2-H2O-NaCl (D3-re-lated), and a second constitutes H2O-NaCl�CaCl2solution (D4-related). The H2O-rich FIs are ar-ranged in trails which cross-cut the CO2-H2O-NaClfluid inclusions and hence represent the youngersystem. The composition of the fluid assemblages

and the changes in physical and chemical propertiesare summarised in Table 5. Re-equilibration tex-tures formed in response to isothermal decompres-sion are common (Fig. 5a).

5.4.3.3. FIs in the Abu Ziran granitoid. Two samples(ED107 and ED117) from E-trending quartz veinsin the Abu Ziran granitoid were analysed. Fluidtrails are oriented parallel to the pluton margins,suggesting entrapment during N-S directed exten-sion. Three-phase CO2-H2O-(salt) fluid inclusionsare common. Most inclusions show irregular shapeand rare negative crystal shape. Necking-down anddecrepitation features are common. The size of thefluid inclusions ranges from 5–100 �m. The CO2

phase is nearly pure, because Tm of the solidcarbonic phases ranges between −57.2 and −56.6°C. Raman spectroscopy revealed the presence of

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 373

minor quantities of H2S and N2. A salinity of 4wt% NaClequiv. is indicated by an average Tclath

of 7.7 °C. Th of CO2 ranges from 22 to 30 °C.The CO2 phases of all fluid inclusions ho-mogenise in the liquid phase. FIs show a homo-geneous XCO2

of approximately 0.50.

5.5. P-T-t paths

Calculated fluid densities are used to constructisochores after FLINCOR computer code(Brown, 1989). Fluid inclusion analyses com-bined with petrologic studies reveal the P-T con-ditions predominant during deformationstages. In addition, re-equilibration textures offluid inclusions formed due to non-isochoric tec-tonic development provide information aboutthe P-T path a rock unit experienced subsequentto fluid entrapment (e.g. Bodnar et al., 1989;Sterner and Bodnar, 1989; Vityk and Bodnar,1995).

5.5.1. P-T path for the meta-sedimentarybasement

The P-T path of the meta-sedimentary base-ment rocks shows an early clockwise loop (Neu-mayr et al., 1998). The isochores fromD2-related H2O-CO2-rich FIs pass just below theM2 peak metamorphic conditions (Fig. 6a). Re-equilibration textures indicate nearly isothermaldecompression after the M2 peak metamor-phism. CO2-H2O D3 FIs close to the Abu Ziranpluton show flat isochores suggesting entrap-ment during the low-P and high T-conditions ofM3C followed by isobaric cooling. CO2-H2O FIsoutside the pluton followed a P-T path withmoderate slope. Late H2O-rich FIs were trappedunder low P-T conditions of 200 MPa and 300–350 °C determined from FIs cross-cutting quartzdeformation lamellae (Passchier and Trouw,1996). This FI assemblage has steep isochoreswhich suggests nearly isothermal decompressionin the late stage of exhumation.

5.5.2. P-T path of the strike-slip shear zonesIntersection of the fluid isochores with the

temperature range estimated from mineral rheol-ogy reveals two distinct P-T boxes that define

the deformation conditions during sinistral anddextral strike-slip movement (Fig. 6b). Initialstrike-slip movement must have been sinistralunder pressure conditions of 380–550 MPa andtemperatures between 450 and 550 °C. Subse-quent dextral movement took place under tem-perature conditions ranging from 300 to 400 °Cand pressures between 250–350 MPa. Low-grade metamorphosed ophiolitic rocks probablyapproached higher P-T conditions from 400–500to 500–550 °C during strike-slip deformation,whereas amphibolite-facies meta-pelites mighthave experienced a decrease in P-T conditions(from 610–690 to 500–550 °C). During andafter strike-slip deformation both units followeda similar clockwise P-T path.

5.5.3. P-T path of the ophiolitic co�er in thesouthern MMCC

M3R peak metamorphic conditions in theophiolites not disturbed by the emplacement ofAbu Ziran granitoid is in the range of 450–500°C and 300–400 MPa (Fritz and Puhl, 1996;Puhl, 1997; Neumayr et al., 1998). The tempera-ture at the contact with the pluton is con-strained by the growth of garnet andhornblende and ranges from 670–690 °C (Puhl,1997). Microthermometric analyses of succes-sively entrapped fluid generations suggest thefollowing P-T path: (1) Isochores constructedfor the first generation of D3-related CO2-H2O-rich fluids inclusions have moderate slope (Fig.6c) and intersect the M3R field; (2) The secondgeneration of D3-related CO2-H2O-rich FI haveflat isochores. Saline aqueous FI trapped in latequartz precipitates define moderate to steepslopes in P-T space. Intersection of isochoreswith the P-T fields and with interpreted re-equi-libration textures reveal an isobaric to anti-clockwise P-T loop for the ophiolitic nappes.The P-T path starts with M3R conditions docu-mented by first generation CO2-H2O-rich FIs.The flat isochores of the second generation offluid inclusions pass through M3C P-T box. Af-ter the high-T, low-P event, the P-T loop indi-cates isobaric cooling. H2O-rich saline FIs withsteep isochores suggest nearly isothermal decom-pression in the late stage of exhumation.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383374

Fig. 6.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 375

5.5.4. P-T path of the ophiolitic co�er in thenortheastern MMCC

The P-T path constructed for the ophiolitic coverrocks of the northeastern MMCC is characterisedby a clockwise loop with isothermal decompression(Fig. 6d). The isothermal decompression texturesare well developed in the early-formed discordantquartz vein and boudins. This suggests rapid ex-humation during the initial stage of D3 deforma-tion. The isochores obtained from CO2-H2O-NaClFIs reveal pressure values ranging from 300 to 400MPa and temperatures between 400 and 500 °C forearly stage D3 deformation. During this event thediscordant quartz vein and boudins were formed.The concordant vein formed under P-T conditionsof 150–250 MPa and 400–500 °C. This suggests anisothermal exhumation of the cover rocks from adepth of ca 12 km to about 8 km. The H2O-NaCl�CaCl2 FIs are younger and were trapped at depthsof ca. 3 km and temperatures above 180 °C duringD4 deformation.

5.5.5. P-T path of the Abu Ziran granitoidMicrothermometric data indicate isochores with

moderate slope (Fig. 6e). The P-T path of the AbuZiran granitoid is controlled by the emplacementof the pluton, by M3C contact metamorphism andsubsequently by isothermal cooling to M3R meta-morphic conditions. Because isochores passthrough the M3R field, quartz vein formation andentrapment of fluid inclusions are considered tohave happened during D3/M3R. Minimum temper-atures of entrapment are determined by total ho-mogenisation of CO2-H2O-rich FIs at temperatures

ranging from 370 to 390 °C and minimum pressuresof 250–300 MPa during onset of north-southextension. Maximum trapping conditions of 650 °Cand 400–600 MPa are defined by intersection of theisochores with the dry solidus (Fig. 6e).

6. Discussion

6.1. Tectonic and structural e�olution of theMMCC

Since there is little information about D1 pre-Pan-African structures, considerable reconstruc-tion of the structural and tectonic evolution of theMMCC is possible only from the beginning of D2

to D4 (Fig. 6 and Table 6). Structural analyses fromfield work as well as microfabric analyses giveevidence for three deformation stages with differentorientation of principal stresses during evolution ofMMCC. The early stage of deformation (D2) tookplace under a NNW-SSE-directed compression,which translated, into NNW-verging thrusting.Thrusting caused the formation of NW-vergingtight to isoclinal folds and S-C fabrics. SubsequentD3 transpression combined with lateral extrusionresulted in the development of N-S directed exten-sion accompanied by an E-W directed compres-sion. NW-trending thrust-related structures havebeen overprinted by structures formed by N-Sdirected normal-fault movement, such as boudins,extensional crenulation cleavage, and extensionalgashes. Hence, the stress field must have changedduring D2 and D3 from NNW-SSE compression to

Fig. 6. P-T paths and isochores for the MMCC. (a) P-T path for the meta-sedimentary basement during amphibolite faciesmetamorphic event (M2). Grey arrow represents the clockwise P-T path reported by Neumayr et al. (1998). After M2 peak-metamor-phism the rocks experience isothermal decompression (ITD). During D3/M3 two P-T paths developed. One is characterised bylow-P, low-T conditions due to regional metamorphism (M3R); the other one shows low-P, high-T conditions during M3C contactmetamorphism indicated by flat isochores. (b) P-T path for the strike-slip shear zones developed during D3/M3 transpression. Anearly sinistral deformation under higher P-T conditions (Tsin) followed by right-lateral displacement under lower P-T conditions(Tdex.). (c) The southern ophiolites show an anti-clockwise P-T path caused by M3 contact metamorphism (M3C) followed byisobaric cooling (IBC) to pass the field of M3 regional metamorphism (M3R). In the final stage rapid exhumation is suggested bysteep isochores. (d) The P-T path of the northeastern ophiolites starts at M3R conditions and show rapid exhumation indicated byisothermal decompression (ITD) and flat isochores. (e) P-T path for the D3 syn-tectonic Abu Ziran granitoid. This path isconstrained by the P-T conditions of crystallisation (I) after Fritz and Puhl (1996), the solidus (after Luth et al., 1964), M3C andM3R conditions, as well as from the total homogenisation of CO2-H2O fluid inclusions(Thtot). (f) Summarised P-T-t path of theMMCC; dark arrows indicate the P-T-t loop for the basement rocks, grey arrows for the ophiolitic cover. Striped areas in (a) to(d) indicate P-T conditions resulting from intersection of isochores with temperatures assessed from quartz and feldspar mineralrheology as well as from LPO patterns of quartz.

J.L

oizenbaueret

al./P

recambrian

Research

110(2001)

357–

383376

Table 6Summary of geologic and petrologic data from the MMCC

1.14 Ga to 800 Ma �580 Ma800–780 Ma 660–620 MaTime 620–580 MaD4D3

bD2Deformation Not knownaD1

eventRetrograde M3M3R and M3CbM2Metamorphic Not knownaM1

eventbIntrusion of granite stocksMagmatic event awithin-plate and Syn- to late tectonic Alkaline Arieki adamelliteWithin-plate type Um

calc-alkaline magmatismin the Eastern parts of theBa�anib granitoid; oceanicMORB-type basaltsMMCCcrust formation (Abu Ziran granitoid, Abu

Fannani tonalite)Fluid regime Not known Not known bH2O-CO2-rich FIs CO2-H2O-rich FIs H2O-rich FIs

N-S directed quartz-richFluid inclusion N-S dipping quartz- andNot known Not known bNW-wards thrusted quartzlenses calcite-rich mineralisedhost mineral extension gashes; quartz

joints and extensionboudins Qtz-saddle reefs inF3 folds; Qtz pods sheared gashes;due to sinistral strike-slipfaulting

N(N)W directed thrustNot known E-W compression and N-SKinematics and Rift tectonics N(N)E-S(S)W compressiontectonics brittle deformationextension Transpressiontectonic style

regimeconvergence of E. and W.Interpretation pre-Pan-African break-up of Rodinia final stage of exhumationisland arc accretion;Gondwana; formation of collision of East and West(Rodinian?) tectonics of MMCC

Gondwana; main stage ofthe metamorphic core;exhumation of MMCCincipient exhumation of

MMCC and subsequentisland arc accretion

a Restricted to ortho-amphibolite xenolithes.b Restricted to basement rocks (Um Ba�anib granitic-gneiss and meta-sediments).

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 377

E-W compression. Synchronously, the NW-trend-ing sinistral strike-slip shear zones developed.Habib et al. (1985a,b) described these steeplydipping fault zones with sub-horizontal stretchinglineations as thrust faults, which is in contrast toour observations. However, these shear zones showsimilar orientation as the left-lateral shear zones ofthe prominent Najd fault system in the Arabian-Nubian Shield (e.g. Stern, 1985, 1994; Abdelsalam,1994). Therefore, the sinistral shear zones of theMMCC might be the Egyptian continuation of theprominent Najd fault system in the Arabian-Nu-bian Shield (Fig. 1a). In the latest stage of exhuma-tion brittle/ductile D4 deformation occurred. Lowtemperatures, orientation of structures, and kine-matics of shear zones contrast with those of D2 andD3. Orientation of fracture planes as well as dextralstrike-slip shear zones suggest NNE-SSW directedcompression during D4. This suggests a rotation ofthe principal stress from NNW-SSE to NNE-SSWfrom D2 to D4. The orogenic process was continu-ous and was accompanied by successive emplace-ment of plutons before and during exhumation ofthe MMCC. This conclusion contrasts with Habibet al. (1985a) who inferred two distinct orogeniesfor the MMCC. Petrographic and geochemicaldata from the metasediments lead to the assump-tion that these sediments were deposited on apassive continental margin. This formation/defor-mation history points to a complete Wilson-cycleorogeny similar to that proposed for the Nakasibsuture, in the Red Sea Hills of Sudan (Abdelsalamand Stern, 1993; Stern and Abdelsalam, 1998).

6.2. Geochronological constraints for the MMCC

Previously published geochronological datafrom the Eastern Desert of Egypt did not supportthe presence of pre-Pan-African (�900 Ma) crust(e.g. Sturchio et al., 1983; Stern and Hedge, 1985;Kroner et al., 1994; Shackleton, 1994; Furnes et al.,1996). The inherited 207Pb/206Pb single zircon ageof 1,149�25 Ma from the ortho-amphibolite xeno-lith within the Um Ba�anib granitic gneiss nowindicates the presence of a pre-Pan-African crust.Additional geochronological work is required tosupport further the presence of older crust in theEastern Desert of Egypt.

207Pb/206Pb single zircon ages from the ophiolites(788�13 Ma) and from the Um Ba�anib graniticgneiss (779�4 Ma) are indistinguishable withinprecision limits. We interpret the ages as the timeof formation of oceanic crust and the emplacementof the Um Ba�anib granitic gneiss due to an earlierrift event, probably during Rodinia break-up(Stern, 1994). Similar ages around 800 Ma forrifting and break-up of Rodinia are reported byKampunzu et al. (1998), Dirks and Sithole (1999),and Rozendaal et al. (1999), although Handke etal. (1999) interpreted their data to represent sub-duction below a continental magmatic arc.

207Pb/206Pb single zircon ages for granitoids em-placed into the western part of the Um Ba�anibindicate magmatic activity at 644�20 Ma. Thisand similar intrusions in the Arabian-Nubianshield (Stern and Hedge, 1985; Stern et al., 1989;Kroner et al., 1992; Furnes et al., 1996; Bregar etal., in press) could be related to convergence duringcollision between East and West Gondwanaland.The D3 transpressional regime is geochronologi-cally constrained by Sturchio et al. (1983), Sternand Hedge (1985), and Fritz et al. (1996) and tookplace between 620 Ma and 580 Ma. Consistent agesfor the strike-slip shear zones and the Najd faultsystem (Abdelsalam and Stern, 1993; Stern, 1985,1994; Stern et al., 1989) as well as constraints fromthe orientation and kinematics suggest that thestrike-slip faults are part of this prominent wrench-fault system. Late-tectonic D4 deformation proba-bly accompanied the intrusion of the weakly toundeformed Arieki adamellite at ca 575 Ma.

6.3. Origin of fluid inclusion assemblages andtiming of entrapment

Three principal fluid inclusion generations areidentified and correlated with different deformationevents (Table 6):1. H2O-CO2-rich;2. CO2− (�N2/CH4)-H2O-rich; and3. H2O-rich fluid inclusions.

The first generation of H2O-CO2 fluid inclu-sions is related to D2/M2 and shows a dominanceof water. Fluid inclusions exhibit elevated densityvalues due to high-P, high-T conditions. Theiroccurrence within D2 sheared quartz lenses and

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383378

their orientation give evidence for entrapment and/or re-equilibration during D2/M2 event. Domi-nance of water might be the result of H2O-releaseduring prograde reaction of M2 mineral assem-blages (Neumayr et al., 1998). CO2 fluids arecommon in amphibolite facies metamorphism(Mullis, 1979). Since D2 temperature conditionswere far above the solvus of the system H2O-CO2

+2 wt% NaClequiv. (Hendel and Hollister, 1981),entrapment of a homogeneous H2O-CO2 fluid isproposed. Microthermometric analyses reveal thatthe first generation of fluid inclusions is trapped atdepth of approximately 20 km. Metamorphic fluidwas produced during M2 peak conditions andsubsequently entrapped. This is consistent withconclusions reached by Neumayr et al. (1998) forfluid inclusions trapped in D2/M2 garnet.

The second generation of CO2-H2O-rich FIA ischaracterised by higher quantities of CO2. Theorientation of fluid trails is structurally controlledby D3 deformation. Newton (1990) argued thatcrustal sources for CO2-rich fluids are not likely. Hesuggested that a CO2-dominated fluid derivespreferably from asthenospheric carbonatite, kim-berlite, and alkali basalt liquids, as well as fromvolatile-enriched lithosphere. The close spatial as-sociation of CO2-rich fluid to the shear zones, theplutons and to the normal faults, and its homoge-neous occurrence, suggests that this fluid wasderived from the mantle, from where it channelisedinto dilational jogs, opened by a transpressiveregime.

The third generation of fluid inclusions is inter-preted to represent syn- to late-tectonic D4 inclu-sions, trapped at a shallow depth of approximately6–7 km and was produced by sericitisation reac-tions during retrograde metamorphism. These reac-tions require major amounts of water. Considering

that the fluid of D3 transpression tectonics isCO2-rich, the water-rich fluid must represent eitherthe latest magmatic fluid released after emplace-ment of plutons or downwards migrating meteoricfluid. Since the fluid inclusions exhibit a wide-rangeof salinity, a mixture of the two sources is likely.

6.4. P-T-t paths

Neumayr et al. (1998) proposed a progradeclockwise P-T loop for the metasediments of theMMCC during M2/D2, followed by a retrogradepath (Fig. 6a). Combining our microthermometricdata with previously published P-T data revealsdifferent P-T-t paths for the MMCC (Fig. 6). Thesepartly contrasting P-T-t paths result from thediachronous tectonic development of the in-frastructure and the suprastructure as well as fromlocal magmatic activity. Whereas the ophiolitesexperienced large-scale sub-horizontal displace-ment under D3/M3 greenschist-facies conditions,the rocks from the metamorphic core were de-formed under amphibolite facies conditions (D2/M2). D3-related emplacement of voluminousmagmatic intrusions was responsible for enhancedheat input which caused an isobaric to anti-clock-wise P-T loop. Thus, contrasting P-T paths are onlyrecorded for D3. Contrasting P-T paths for high-T,low-P terranes are reported by Sisson and Hollister(1988) and Stuwe and Sandiford (1994). Flat iso-chores from D3 fluid inclusions trapped near theAbu Ziran pluton indicate high-T, low-P condi-tions for D3. Fluid inclusions trapped during D3 inthe same stratigraphic unit but outside the igneousintrusions, exhibit moderate isochores indicatinglow-T, low-P conditions. This illustrates the impor-tance of the role the igneous intrusions played inenhancing the heat budget in the MMCC. Mag-

Fig. 7. Schematic model of the geologic development of the MMCC. (a) Between 800–780 Ma rifting caused crustal thinning, theformation of oceanic crust (inset), and emplacement of the Um Ba’anib granite accompanied by deposition of sediments. (b)Between 660 Ma and 640 Ma, convergence caused burial of sediments and intrusion of calc-alkaline rocks. Subsequently, themeta-sediments were thrust across the Um Ba’anib granitoid accompanied by entrapment of H2O-CO2-rich fluid inclusions. (c)Continued oblique convergence resulted in a transpressional regime with displacement partition. While nappe stacking continued inforeland domains the MMCC were exhumed from ca. 20 km to a depth of 12–15 km in hinterland domains. (d) and (e) aresynchronous E-W and N-S cross-sections. Between 620 and 580 Ma extension-related granitoids were emplaced. Rapid exhumationwas accompanied by detachment of the cover nappes and emplacement of syn-tectonic intrusions. Low density CO2-H2O mantlefluid was entrapped. The final stage of exhumation took place under brittle/ductile conditions at a crustal depth of approximately3–6 km, as indicated by H2O-rich fluid inclusions. Diagrams are not to scale.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 379

Fig. 7.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383380

matic underplating, as reported by Warren andEllis (1996), was probably a major mechanismresponsible for the exhumation of the MMCCduring D3. Therein, they suggested that emplace-ment of a pluton might cause dragging down ofadjacent rocks to deeper crustal levels and thusleading to P-increase. This model might also be apossible explanation for the slightly higher pres-sures of 400–500 MPa assessed for the strike-slipshear zones.

Microthermometric analyses on FIs oriented bysinistral movement of shear zones (Fig. 5c) revealthat the initial strike-slip faulting happened dur-ing sinistral movement under P-T conditions of400–550 MPa and 450–550 °C whereas dextralmovement happened under P-T conditions of250–350 MPa and 300–400 °C. Calculated pres-sures suggest that sinistral and dextral strike-slipdeformation took place at depths of approxi-mately 15 km and ca 9 km, respectively. Fluidinclusion studies also reveal peak-pressure condi-tions of approximately 600–700 MPa for the in-frastructure rocks and ca 200–400 MPa for thecover ophiolites. Since the ophiolites directly over-lie the metamorphic core, there is an averageP-difference of 300 MPa between the cover andthe basement which equals approximately 9 km ofcrustal depth. Hence, we conclude that the meta-morphic core exhumed from ca 20 km to 11–12km depth before the tectonic emplacement of thecover. Eroded material was deposited at the baseof the intramontane molasse basins (Messner etal., 1996; Fritz and Messner, 1999). Steep iso-chores from fluid inclusions of the cover nappesindicate a nearly isothermal decompression pathduring and subsequent to D3. We interpret thesteep slope as rapid exhumation of the core ac-companied by detachment of the cover.

7. Conclusions

The formation of the MMCC started between780 and 800 Ma with the break-up of an oldcontinent, probably Rodinia (Fig. 7a). Rifting andsubsequent events caused the formation of ophio-lites and the emplacement of the Um Ba�anibgranitoid into an 1.14 Ga old crust comprising

partly migmatised ortho-amphibolites. At thesame time, quartz- and mica-rich sediments weredeposited on a passive continental margin.

Between 660 Ma and 620 Ma convergence be-tween East and West Gondwanaland caused thesubduction of quartz- and mica-rich sedimentaryrocks to a crustal depth of approximately 20 km(Fig. 7b). Synchronously, calc-alkaline granitoidsemplaced into the western part of MMCC. Dur-ing D2/M2 the metamorphosed sediments werethrust over the Um Ba�anib granitic gneiss underamphibolite facies metamorphic conditions. H2O-CO2-rich fluid inclusions trapped during D2/M2

give evidence for high-P, high-T conditions duringnorthwestward thrusting. After the thrusting, theMMCC was exhumed to a crustal depth of ap-proximately 12–15 km. Continuous convergenceresulted in thrusting from ESE to WNW of coverrocks over the MMCC (Fig. 7c).

Between 620 Ma and 580 Ma ongoing obliqueconvergence culminated in D3 sinistral transpres-sion and lateral extrusion (Fig. 7d,e). Syn-chronous activity of strike-slip faults andlow-angle normal faults took place under green-schist-facies metamorphic conditions (M3R). Mi-crothermometric analyses of CO2-H2O-rich fluidinclusions suggest a crustal depth of approxi-mately 10–12 km for D3/M3. Fluid-inclusionstudies indicate rapid exhumation accompaniedby detachment of the cover nappes. Extensionwas accompanied by emplacement of numerousgranitoids, which caused contact metamorphism(M3C). At 580 Ma, the final stage of exhumation,D4 deformation occurred under brittle/ductileconditions at crustal depth of approximately 3–6km as indicated by H2O-rich fluid inclusions. Theformation/deformation history of the MMCC ischaracterised by a long time process (more than200 Ma), whereas the Pan-African orogenic pro-cesses (in s.s.) started at ca 660–640 Ma in theMMCC area. The long orogenic history, the lackof high-pressure mineral assemblages, and syn-kinematic low-density fluid inclusions indicate ex-humation as a mechanism for the evolution ofMMCC, which is enhanced by magmatic activityand accompanied by shear extension within athin-skinned crust.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 381

Acknowledgements

This work presented here was part of the FWF-project P09703-GEO and was financed by theAustrian ‘‘Fonds zur Forderung der wis-senschaftlichen Forschung’’. Helpful discussionfrom members of the project and from the De-partments of Mineralogy and Petrology and Geol-ogy and Palaeontology at KFU Graz is gratefullyacknowledged. We thank J. Puhl for fruitful geo-chemical and petrologic discussion, P. Knoll andR. Kaindl for help in Raman spectroscopy, andthe members of the University of Assiut-particu-larly S. El Gaby — for logistic support. Wegratefully acknowledge B. Wallbrecher for reviewof the manuscript. The authors want to thank M.G. Abdelsalam and R. O. Greiling for their criti-cal reviews and constructive comments. This pa-per is a contribution to IGCP 440: Assembly andBreakup of Rodinia.

References

Abdelsalam, M.G., 1994. The Oko Shear Zone, Sudan: post-accretionary deformation in the Arabian-Nubian Shield. J.Geol. Soc. London 151, 767–776.

Abdelsalam, M.G., Stern, R.J., 1993. Tectonic evolution of theNakasib suture, Red Sea Hills, Sudan: evidence for a latePrecambrian Wilson Cycle, J. Geol. Soc. London 150,393–404.

Akaad, M.K., El-Ramly, M.E., 1960. Geological history andclassification of the basement rocks of the Central EasternDesert of Egypt. Geol. Surv. Egypt 9, 1–24.

Akaad, M.K., Shazly, A.G., 1972. Description and petrogra-phy of the Meatiq Group. Ann. Geol. Surv. Egypt 2,115–138.

Andrew,G., 1931. Note on the geology of Gabal Mitiq. In:W.F. Hume (Ed.), Geology of Egypt. Geol. Surv. Egypt,Cairo. II, I, 295–296.

Bhatia, M.R., Crook, K.A.W., 1986. Trace element character-istics of graywackes and tectonic setting discrimination ofsedimentary basins. Contrib. Mineral. Petrol. 92, 181–193.

Bodnar, R.J., Binns, P.R., Hall, D.L., 1989. Synthetic fluidinclusions. VI. Quantitative evaluation of the decrepitationbehaviour of fluid inclusions in quartz at one atmosphereconfining pressure. J. Metamorphic Geol. 7, 229–242.

Bregar, M., Fritz, H., Unzog, W., 1996. Structural evolutionof low-angle normal faults SE of the Gebel El SibaiCrystalline Dome; Eastern Desert, Egypt: evidence frompaleopiezometry and vorticity analysis. Zbl. Geol. Palaont.I 3/4, 243–256.

Bregar,M., Bauernhofer, A., Pelz, K., Klotzli, U., Fritz, H.,Neumayr, P., in press. A late Panafrican magmatic corecomplex in the Eastern Desert of Egypt: Emplacement ofgranitoids in a shear extensional setting. Prec. Res. (Inpress)

Brown, P.E., 1989. FLINCOR: A fluid inclusion data reduc-tion and exploration program. Second Biennial Pan-Amer-ican Conference on Research on Fluid Inclusions. Programwith Abstracts, Blacksburg, Virginia Polytechnic Institute,14

Craw, D., Koons, P.O., Winslow, D., Chamberlain, C.P.,Zeitler, P., 1994. Boiling fluids in a region of rapid uplift,Nanga Parbat Massif, Pakistan. Earth Planet. Sci. Lett.128, 169–182.

Den Brok, S.W.J., Spiers, C.J., 1991. Experimental evidencefor water weakening of quartzite by microcracking plussolution-precipitation creep. J. Geol. Soc. Lond. 148, 541–548.

Dirks, P.H.G.M., Sithole, T.A., 1999. Eclogites in the MakutiGneisses of Zimbabwe — Implications for the tectonicevolution of the Zambezi Belt in Southern Africa. J. Meta-morphic Geol. 17 (6), 593–612.

El Gaby, S., List, F.K., Tehrani, R., 1988. Geology, evolutionand metallogenesis of the Pan African belt in Egypt. In: ElGaby, S., Greiling, R.O. (Eds.), The Pan African belt ofNortheast Africa and adjacent areas. Vieweg, Braun-schweig, pp. 17–68.

El Gaby, S., List, F.K., Tehrani, R., 1990. The basementcomplex of the Eastern Desert and Sinai. In: Rushdi, S.(Ed.), The Geology of Egypt. Balkema, Rotterdam, pp.175–184.

Engel, A.E.J., Dixon, T.H., Stern, R.J., 1980. Late Precam-brian evolution of the Afro-Arabian crust from ocean arcto craton. Geol. Soc. Am. Bull. 91, 699–706.

Etheridge, M.A., Wall, V.J., Vernon, R.H., 1983. The role ofthe fluid phase during regional metamorphism and defor-mation. J. Metamorph. Geol. 1, 205–226.

Etheridge, M.A., Wall, V.J., Cox, S.F., Vernon, R.H., 1984.High fluid pressures during regional metamorphism anddeformation: implications for mass transport and deforma-tion mechanisms. J. Geophys. Res. 89, 4344–4358.

Fritz, H., Wallbrecher, E., Khudier, A.A., Abu El Ela, F.A.,Dallmeyer, D.R., 1996. Formation of Neoproterozoicmetamorphic core complexes during oblique convergence,(Eastern Desert, Egypt). J. Afr Earth Sci. 23 (3), 311–329.

Fritz, H., Puhl, J., 1996. Granitoid emplacement in a shear-ex-tensional setting: A semiquantitative approach from physi-cal parameters (Eastern Desert, Egypt), Zbl. Geol. Palaont.I. H.3/4, 257-276

Fritz, H., Messner, M., 1999. Intramontane basin formationduring oblique convergence in the Eastern Desert of Egypt:magmatically versus tectonically induced subsidence. Tec-tonophysics 315, 145–162.

Furnes, H., El-Sayed, M.M., Khalil, S.O., Hassanen, M.A.,1996. Pan-African magmatism in the Wadi El-Imra dis-trict, Central Eastern Desert, Egypt: geochemistry andtectonic environment. J. Geol. Soc. Lond. 153, 705–718.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383382

Goldstein, R.H., Reynolds, T.J., 1994. Systematics of fluidinclusions in diagenetic minerals. Society for SedimentaryGeology. SEPM Short Course 31, 199.

Habib, M.E., Ahmed, A.A., El Nady, O.M., 1982. Lithos-tratigraphy and tectonic evolution of the Meatiq in-frastructure, Central Eastern Desert, Egypt. In: Al Shanti,A.M.S (Ed.), Pan-African Crustal Evolution in Arabia andNorth-East Africa. Elsevier, Amsterdam, p. 23.

Habib, M.E., Ahmed, A.A., El Nady, O.M., 1985a. Twoorogenies in the Meatiq area of the Central Eastern Desert,Egypt. Prec. Res. 30, 83–111.

Habib, M.E., Ahmed, A.A., El Nady, O.M., 1985b. Tectonicevolution of the Meatiq infrastructure, Central EasternDesert, Egypt. Tectonics 4 (7), 613–627.

Handke, M.J., Tucker, R.D., Ashwal, L.D., 1999. Neoprotero-zoic continental arc magmatism in west-central Madagas-car. Geology 27 (4), 351–354.

Hendel, E.M., Hollister, L.S., 1981. An empirical solvus forCO2-H2O-2.6 wt% salt. Geochim. Cosmochim. Acta. 45,225–228.

Hill, E.J., Baldwin, S.L., Lister, G.S., 1992. Unroofing ofactive metamorphic core complexes in the D�EntrecasteauxIslands, Papua New Guinea. Geology 20, 907–910.

Hill, E.J., Baldwin, S.L., Lister, G.S., 1995. Magmatism as anessential driving force for formation of active metamorphiccore complexes in eastern Papua New Guinea. J. Geophys.Res. 100, 10441–10451.

Hodgkins, M.A., Stewart, K.G., 1994. The use of fluid inclu-sions to constrain fault zone pressure, temperature andkinematic history: an example from the Alpi Apuane, Italy.J. Struct. Geol. 16 (1), 85–96.

Hubbert, M.K., Rubey, W.W., 1959. Role of fluid pressure inthe mechanics of overthrust faulting. Geol. Soc. Am. Bull.70, 115–205.

Hume,W.F., 1934. Geology of Egypt, the metamorphic rocks.Surv. of Egypt, Cairo. II, I, pp. 293.

Kampunzu, A.B., Kramers, J.D., Makutu, M.N., 1998. Rb-Srwhole rock ages of the Lueshe, Kirumba and Numbiigneous complexes (Kivu, Democratic Republic of Congo)and the break-up of the Rodinia supercontinent. J. Afr.Earth Sci. 26, 29–36.

Klotzli, U.S., 1997. Zircon evaporation: TIMS Method andProcedures. The Analyst 122, 1239–1248.

Kober, B., 1987. Single-zircon evaporation combined withPb+ emitter bedding for 207Pb/206Pb-age investigationsusing thermal ion mass spectrometry, and implications tozirconology. Contrib. Mineral. Petrol. 96, 63–71.

Knoll, P., Finger, R., Kiefer, W., 1990. Improving spectro-scopic techniques by a scanning multichannel method.Appl. Spectrosc. 44, 776–782.

Kroner, A., 1984. Late Precambrian plate tectonics andorogeny: a need to redefine the term Pan-African. In:Klerkx, J., Michot, J. (Eds.), African Geology Tervuren:Musee. R. l�Afrique Centrale, pp. 23–28.

Kroner, A, Todt, W., Hussein, I.M., Mansour, M., Rashwan,A.A., 1992. Dating of late Proterozoic ophiolites in Egyptand the Sudan using the single grain zircon evaporationtechnique. Prec. Res. 59, 15–32.

Kroner, A., Kruger, J., Rashwan, A.A., 1994. Age and tec-tonic setting of granitoid gneisses in the Eastern Desert ofEgypt and south-west Sinai. Geol. Rundschau. 83 (3),502–513.

Kurz, W., Neubauer, F., 1996. Deformation partitioning dur-ing updoming of the Sonnblick area in the Tauern Window(Eastern Alps, Austria). J. Struct. Geol. 18 (11), 1327–1343.

Lister, G.S., Hobbs, B.E., 1980. The simulation of fabricdevelopment during plastic deformation and its applicationto quartzite: fabric transitions. J. Struct. Geol. 1, 99–115.

Lister, G.S., Davis, G.A., 1989. The origin of metamorphiccore complexes and detachment faults formed during Ter-tiary continental extension in the northern Colorado Riverregion. USA, J. Struct. Geol. 11, 65–94

Lister, G.S., Baldwin, S.L., 1993. Plutonism and the origin ofmetamorphic core complexes. Geology 21, 607–610.

Loizenbauer,J., 1998. Exhumation History of the MeatiqMetamorphic Core Complex and gold mineralisation dur-ing Pan-African Orogeny in the Eastern Desert, Egypt —Evidence from Fluid Inclusion studies and Structural Geol-ogy. PhD. Thesis, Univ. Graz, Austria.

Loizenbauer, J., Wallbrecher, E., Fritz, H., 1999. Formationand structural evolution of the Meatiq Metamorphic CoreComplex during post-Rodinian tectonics — a reconstruc-tion by the use of fluid inclusion studies, structural geologyand age dating. In: de Wall, H., Greiling, R.O. (Eds.),Aspects of Pan-African Tectonics. In: Schriften desForschungszentrums Julich. Bilateral Seminars of the In-ternational Bureau, vol. 32, pp. 143–148.

Losh, S., 1997. Stable isotope and modelling studies of fluid-rock interaction associated with the Snake Range andMormon Peak detachment faults, Nevada. Geol. Soc. Am.Bull. 109 (3), 300–323.

Luth, W.D., Jahns, R.H., Tuttle, O.F., 1964. The granitesystem at pressures of 4 to 110 kilobars. J. Geophys. Res.69, 659–773.

Mainprice, D., Bouchez, J.L., Blumenfeld, P., Tubia, J.M.,1986. Dominant c-slip in naturally deformed quartz: impli-cations for dramatic plastic softening at high temperature.Geology 14, 819–822.

McCaig, A.M., 1988. Deep fluid circulation in fault zones.Geology 16, 867–870.

Messner,M., Fritz, H., Pelz, K., Unzog, W., 1996. Beckenbil-dung in verschiedenen tektonischen Settings: StrukturelleRahmen und Abbildung der Tektonik in der Sedimenta-tion. Symposium Tektonik Strukturgeologie Kristallinge-ologie 6. Facultas, Salzburg, 275−278.

Morgan, P., 1990. Egypt in the framework of global tectonics.In: Said, R. (Ed.), The Geology of Egypt. Balkema, Rot-terdam, pp. 91–111.

Mullis, J., 1979. The system methane-water as a geologicthermometer and barometer from the external part of thecentral Alps. Bull. Mineral. 102, 526–536.

Neumayr, P., Mogessie, A., Hoinkes, G., Puhl, J., 1996.Geological Setting of the Meatiq metamorphic core com-plex in the Eastern Desert of Egypt based on amphibolitegeochemistry. J. Afr. Earth Sci. 23, 331–345.

J. Loizenbauer et al. / Precambrian Research 110 (2001) 357–383 383

Neumayr, P., Hoinkes, G., Puhl, J., Mogessie, A., Khudeir,A.A., 1998. The Meatiq dome (Eastern Desert, Egypt) aPrecambrian metamorphic core complex: petrological andgeological evidence. J. Metamorph. Geol. 16, 259–279.

Newton, R.C., 1990. Fluids and shear zones in the deep crust.Tectonophysics. 182, 21–37.

Oliver, N.H.S., 1996. Review and classification of structuralcontrols on fluid flow during regional metamorphism. J.Metamorph. Geol. 14, 477–492.

Passchier, C.W., Trouw, R.A.J., 1996. Microtectonics.Springer-Verlag, Germany.

Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace ele-ment discrimination diagrams for the tectonic interpreta-tion of granitic rocks. J. Petrol. 25, 956–983.

Pili, E., Sheppard, S.M.F., Lardeaux, J., Martelat, J., Nicollet,C., 1997. Fluid flow vs. scale of shear zones in the lowercontinental crust and the granulite paradox. Geology 25,15–18.

Platt, J.P., 1986. Dynamics of orogenic wedges and the upliftof high-pressure metamorphic rocks. Geol. Soc. Am. Bull.97, 1037–1053.

Platt, J.P., Vissers, R.L.M., 1980. Extensional structures inanisotropic rocks. J. Struct. Geol. 2, 397–410.

Puhl,J., 1997. Die Petrogenese des Meatiq-Kristallindomes,O� stliche Zentralarabische Wuste, A� gypten. M.Sc.Thesis.Univ. Graz, Austria.

Reynolds, S.J., Lister, G.S., 1987. Structural aspects of fluid-rock interactions in detachment zones. Geology 15, 362–366.

Ries, A.C., Shackleton, R.M., Graham, R.H., Fitches, W.R.,1983. Pan-african structures, ophiolites and melange in theEastern Desert of Egypt: a traverse at 26°N. J. Geol. Soc.Lond. 140, 75–95.

Roedder, E., 1984. Fluid inclusions. Rev. Min. Chelsea MI 12,644.

Rozendaal, A., Gresse, P.G., Scheepers, R., Leroux, J.P.,1999. Neoproterozoic to Early Cambrian Crustal Evolu-tion of the Pan-African Saldania Belt, South-Africa. Prec.Res. 97, 303–323.

Schmid, S.M., Casey, M., 1986. Complete fabric analysis ofsome commonly observed quartz C-axis patterns.Geophys. Monogr. 36, 263–286.

Shackleton, R.M., 1994. Review of Late Proterozoic sutures,ophiolitic melanges and tectonics of eastern Egypt andnorth-east Sudan. Geol. Rundschau. 83 (3), 537–546.

Shackleton, R.M., Ries, A.C., Graham, R.H., Fitches, W.R.,1980. Late Precambrian ophiolite melange in the EasternDesert of Egypt. Nature 285, 472–474.

Shepherd, T.J., Rankin, A.H., Alderton, D.H.M., 1985. APractical Guide to Fluid Inclusion Studies. Blackie, Lon-don, p. 239.

Sibson, R.H., 1990. Faulting and fluid flow. In: Nesbitt, B.E.(Ed.), Short Course on Fluids in Tectonically ActiveRegimes of the Continental Crust, pp. 93–132.

Simony, P.S., Carr, S.D., 1997. Large lateral ramps in theEocene Valkyr shear zone: extensional ductile faulting

controlled by plutonism in southern British Columbia. J.Struct. Geol. 19, 769–784.

Sisson, V.B., Hollister, L.S., 1988. Low-pressure facies seriesmetamorphism in an accretionary sedimentary prism,southern Alaska. Geology. 16, 358–361.

Stegmuller,G., 1996. Entwurf und Implementierung derSteuerung eines Temperaturkontrollsystems. M.Sc Thesis,IICM-Ordinariat fur Softwaretechnologie, Technische Uni-versitat Graz.

Stern, R.J., 1985. The Najd Fault System, Saudi Arabia andEgypt: A late Precambrian rift-related transform system?Tectonics 4, 497–511.

Stern, R.J., 1994. Arc assembly and continental collision in theNeoproterozoic East African orogen: Implications for theconsolidation of Gondwanaland. Ann. Rev. Earth Planet.Sci. 22, 319–351.

Stern, R.J., Hedge, C.E., 1985. Geochronologic and isotopicconstraints on late Precambrian crustal evolution in theEastern Desert of Egypt. Am. J. Sci. 285, 97–127.

Stern, R.J., Kroner, A., Manton, W.I., Reischmann, T., Man-sour, M., Hussein, I.M., 1989. Geochronology of the latePrecambrian Hamisana shear zone, Red Sea Hills, Sudanand Egypt. J. Geol. Soc. London 146, 1017–1029.

Stern, R.J., Abdelsalam, M.G., 1998. Formation of juvenilecontinental crust in the Arabian-Nubian shield: evidencefrom granitic rocks of the Nakasib suture, NE Sudan.Geol. Rundschau 87, 150–160.

Sterner, S.M., Bodnar, R.J., 1989. Synthetic fluid inclusions.VII. Reequilibration of fluid inclusions in quartz duringlaboratory simulated metamorphic burial and uplift. J.Metamorph. Geol. 7, 243–260.

Sturchio, N.C., Sultan, M., Batiza, R., 1983. Geology andorigin of Meatiq dome, Egypt: A Precambrian metamor-phic core complex? Geology 11, 72–76.

Stuwe, K., Sandiford, M., 1994. Contribution of deviatoricstresses to metamorphic P-T paths: an example appropriateto low-P, high-T metamorphism. J. Metamorph. Geol. 12,445–454.

Tullis, J., 1977. Preferred orientation of quartz produced byslip during plane strain. Tectonophysics 39, 87–102.

Vityk, M.O., Bodnar, R.J., 1995. Textural evolution of syn-thetic fluid inclusions in quartz during reequilibration, withapplications to tectonic reconstruction. Contrib. MineralPetrol. 121, 309–323.

Wallbrecher, E., Fritz, H.E., Khudier, A.A., Farahad, F.,1993. Kinematics of Panafrican thrusting and extension inEgypt. In: Thorweihe, U., Schandelmeier, H. (Eds.), Geo-scientific Research in Northeast Africa. Proceedings of theinternational conference on geoscientific research in North-east Africa. Balkema, Rotterdam, pp. 27–30.

Walther, J.V., 1994. Fluid-rock reactions during metamor-phism at mid-crustal conditions. J. Geol. 102, 559–570.

Warren, R.G., Ellis, D.J., 1996. Mantle underplating, granitetectonics, and metamorphic P-T-t paths. Geology 24, 663–666.

.