Greiling.pdf

7/27/2019 Greiling.pdf

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Geol Rundsch (1994) 83 :48 4- 50 1 Springer-Verlag 1994

R . O . Gre i l i n g M . M . A b d e e n A . A . Da rd i rH . E 1 Ak h a l . M . F . E1 R a m l y G . M . Ka m a l E 1 D i nA. F . Os m a n A . A . R a s h w a n A . H . N . R i c eM. E Sadek

A structural synthesis of the Proterozoic Arabian-Nubian Shieldin Egypt

Received: 26 January 1994~Accepted: 24 May 1994Ab s t r a c t De t a i l e d s tru c t u ra l g e o l o g ic a l a n d r e l a t e d s t u -d ies were car r ied ou t in a num ber o f c r i t ica l a reas in theP ro t e r o z o i c b a s e m e n t o f e a s te rn E g y p t t o r e s o lv e th es t ruc tu ra l pa t te rn a t a reg iona l sca le and to assess theg e n e ra l c h a ra c t e r is t i c s o f t e c t o n i c e v o l u t i o n , o ro g e n y a n dt e r r a n e b o u n d a r i e s . F o l l o wi n g a b r i e f a c c o u n t o f t h et e c t o n o s t r a t i g r a p h y a n d t i m i n g o f t h e o ro g e n i c e v o lu t i o n ,t h e m a j o r s t ru c t u ra l c h a ra c t e r i s t i c s o f t h e c r i t ic a l a r e a sa re p r e s e n t e d . C o l l is i o n a l d e fo rm a t i o n o f th e t e r r a n e se n d e d a b o u t 6 1 5 - 6 0 0 M a a g o . S u b s e q u e n t e x t e n s i o n a lc o l l a p s e p ro b a b l y o c c u r r e d w i t h i n a r e l a t i v e l y n a r ro wt i m e s pa n o f a b o u t 2 0 M a ( 5 7 5 - 5 95 M a a g o ) o v e r t h eE a s t e rn De s e r t a n d wa s fo l l o we d b y a fu r t h e r p e r i o d o fa b o u t 5 0 M a o f la t e t o p o s t - t e c t o n i c a c t iv i t y . T h e r e g i o n a ls t ru c t u re s o r i g i n a t e d m a i n l y d u r i n g p o s t - c o l l i s i o n a leven ts , s t a r t ing wi th those re la ted to ex tens iona l co l lapse(m o l a s se b a s i n fo rm a t i o n , n o rm a l f a u l t in g , g e n e ra t i o n o fm e t a m o r p h i c c o r e c o m p l e x e s ) . S u b s e q u e n t N N W - S S Es h o r t e n i n g i s d o c u m e n t e d b y l a rg e - s c a l e t h ru s t i n g ( t o -wa rd s t h e NNW ) a n d fo l d i n g , d i s t r i b u t e d o v e r t h eE a s t e rn D e s e r t , a l t h o u g h w i t h v a r i a b l e in t e n s it y . T h ru s t sa r e o v e rp r i n t e d b y t r a n s p re s s i o n , w h i c h wa s l o c a l i z e d top a r t i c u l a r s h e a r z o n es . E a r l y t r a n s p re s s i o n p ro d u c e d , f o re x a m p l e , t h e A l l a q i s h e a r z o n e a n d f i n a l t r a n s p re s s i o n i sd o c u m e n t e d i n t he N a j d a n d W a d i K h a r i t- W a d i H o d e i n

R. O. Greiling (I~) - M. M. Abdeen - A. H. N. RiceGeologisch-Pal~iontologischesInstitut,Ruprecht-Karls-Universitfit, IN F 234, Fa x: (0 62 21) 56 55 03D-69120 Heidelberg, Germ anyM. M. Abdeen - A. A. D ardir " M. F. SadekEgyptian Geological Survey and Mining Authority, 3 Salah SalemRoad, Abbassiya, Cairo, EgyptH. E1 AkhalDepartment of Earth Science,University of Yarmouk, Irbid, Jor danM. F. E1 Rare ly A. F. OsmanGeology Department, Faculty o f Science, Ain Sham s University,Cairo, EgyptG. M. Kamal E1 Din - A. A. RashwanGeology Department, Quena Fac ulty of Science, Assiut University,Quena, Egypt

z o n e s . T wo t e r r a n e b o u n d a r i e s c a n b e d e f i n e d , t h e A l la q ia n d S o u t h Ha fa f i t S u t u re s , wh i c h a r e a p p a re n t l y l i n k e dby the h igh ang le s in i s t ra l s t r ike-s l ip Wadi Khar i t -WadiHo d e i n s h e a r z o n e w i t h a t e c t o n i c t r a n s p o r t o f a b o u t3 0 0 k m t o wa rd s t h e W / NW . In g e n e ra l , t h e t e c t o n i cevo lu t ion shows tha t ex tens iona l co l lapse i s no t necessa-r i l y t h e f i n al s t a ge o f o ro g e n y , b u t m a y b e fo l l o we d b yfu r t h e r c o m p re s s i o n a l a n d t r a n s p re s s i o n a l t e c t o n i s m .T h e l a t e P a n -Af r i c a n h i g h a n g l e f a u l t s we re r e a c t i v a t e dd u r i n g R e d S e a t e c t o n i c s b o t h a s R i e d e l s h e a r s a n dn o rm a l f a u l t s, wh e re t h e y we re o r i e n t e d f a v o u ra b l y w i t hrespec t to the ac tua l s t ress reg ime.K e y w o rd s A r a b i a n - N u b i a n S h ie l d E g y p t P a n -Af r i c a n o ro g e n y P ro t e r o z o i c - E x t e n s i o n a l c o l l a p s e T h ru s t t e c t o n i cs T ra n s p re s s i o n

IntroductionT h e s t ru c t u re o f t h e P a n -Af r i c a n b a s e m e n t i n E g y p t ,a s i t is e x p o s e d t o d a y , i s t h e p ro d u c t o f a c o m p l e x ,P ro t e ro z o i c o ro g e n i c e v o l u t i o n fo l l o wi n g t e r r a n e c o l -l i s i o n a n d a c c re t i o n o n t o a p r e -P a n -Af r i c a n c o n t i n e n tto the wes t o f the Ni le . As a con seque nce o f thec o m p l e x e v o l u t i o n , p r e - c o l l i s i o n a l a n d e a r l y o ro g e n i cs t ru c t u re s a r e s e v e re l y o v e rp r i n t e d a n d o n l y l o c a l lyp re s e rv e d a n d t h e r e g i o n a l s t ru c t u re i s d o m i n a t e d b ya la te o rogen ic s t ruc tu ra l g ra in . Th is reg iona l s t ruc tu re ,wh i c h i s th e m a j o r t o p i c o f t hi s p a p e r , c a n b e a t t r i b u t e dto phase 4 in the f ive phase t ec ton ic evo lu t ion o fm o u n t a i n b e l ts (De we y , 1 9 8 8 ; T a b le 1 ). Ho we v e r , a c o m -p a r i s o n o f De we y ' s p h a s e s w i t h t h e g e n e ra l e v o l u t i o ni n t h e E g y p t i a n b a s e m e n t r e v e a l s s o m e p a r t i c u l a r i t i e s .W h e r e a s l a t e o r o g e n ic m a g m a t i s m a n d t h e f o r m a t i o nof ex tens iona l bas ins a re wel l doc um ente d (e .g . Tab les2 - 4 ) , r e l a t e d s tru c t u re s, i n p a r t i c u l a r t h o s e a s so c i a t e dwi th ex tens ion a l co l lapse , a re on ly loca l ly observed .P e rh a p s e v e n m o re i m p o r t a n t l y , t h e fo rm a t i o n o f e x -t e n s i o n a l b a s i ns w i t h V e r ru c a n o - t y p e d e p o s i t s i s f o l lo we db y i n t en s e c o m p re s s i o n a n d / o r t r a n s p re s s i o n ( s e e b e l o w).


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Table 1. Five phase tectonic evolu tion of mo unta in belts , s implif iedfrom Dewey (1988; see also Dewey et al . 1993) and separated intogenera l and s t ruc tura l even ts . TBCL: the rmal boundary condi t ionlayer of the continental l i thosphere. B ased on the Pan-Africa nstructural e volution, the phase 4 is divided into an early, extensionalpar t (4 A) and a subsequent compress iona l pa r t (4 B) . Approximateages fo r some tec ton ic ep i sodes in the nor thwes te rn Arab ian-N ubianShield are given, for references see text .

5

4

4

Tectonic evolut ion of mou ntain belts(Dewey 1988)

Structure (andGeneral Pan-African timing)post extensional therm al recovery,thickening of TBCL, eventualretrograde metamorphism,marine transgression

(subsidence)

530 Ma

convectiveTBCL thinning,mantle partial melting,mafic magmatism, minimum-meltinggranite suites,HT mantle diapirs,irapid subsidence,;xtensional basins,/errucano-type deposits

subsequent thrust stacking575 Maaccelerating extensionalcollapse. (radial) extension,development of metamorphiccore complexes,little relationship betweendisplacement vectors andbounding plate slip vectors595 Ma

:atastrophic erosio n of the TBCL,"apid uplift,~ro-grade HT metamorphism,~osttectonic granite suite

600 Mabeginning extension

)ost or slow convergence,~low uplift,~0-few Ma thermal reequilibration,dow thinning of TBCL,nin or alkaline to silicic granites

thru st and strike-slipstructures,strong direct relationshipbetween shortening structuresand plate slip vector615 Ma

ithospheridcrustal shortening and:hickening,-IP/LT blueschist and kyanite)earing metamo rphic assemblages,:ontinental collision,"ift inversion,:ompressive continental margin arc

Such compression after extensional collapse may bedue, for example, to continued plate convergence aftercollision (e.g. Dewey, 1988). For that reason, Dewey'sphase 4 has been divided here into an early, extensionalphase (4A) and a late, compressional phase (4B; seeTable 1).Owing to the complex deformation al pattern and a lackof comprehensive, detailed structural inform ation ata regional scale, contrasting and apparently mutuallyincompatible m odels for the structural evolution of theA ra b i an -N ub ia n Sh ie ld have been proposed . Suchmodels include high angle block fault ing and 'blocktect oni cs' (e.g. Sabet , 1983; Su ltan et al., 1988), large-scale low angle norm al faulting (e.g. Sturchio et al., 1983;Ka ma l E1 Di n et al., 1992), rev erse faultin g (e.g. Rieset al., 1983; E1 Ramly et al., 1984) and wrench tectonics

48 5(e.g. Stern, 1985; Shimron, 1990), or a combination ofsome of these processes (e.g. Shimron, 1990; Abdeenet al., 1992). There fore, the prese nt wor king g roup stu-died a numb er of cri t ical areas to assess whether theShield as a whole is dominated by a single structuraldomain or whether there are various doma ins o f contrast-ing deformational type and tectonic evolution. Theinvestigated areas com prise the extreme so uth of theEastern D esert of Egypt (Wadi Allaqi to Abu Swayel) andseveral areas in the central parts (Wadi Hafafit , WadiGhadir, Wadi Igla, Gabal E1 Shallul, Gabal E1 Sibai,Wadi Queih ; see Figs 1, 2 and 6). These a reas w eresurveyed by detailed structural geological and strainstudies, supported by petrographic, metamorphic andgeochemical wor k and remote sensing. Following a briefaccount o f the tectonostratigrap hy of the rock typesinvolved and the tectonic evolution, the major structuralcharacterist ics of these areas are brief ly presented and areused, together with published data, as a base for a regio-nal synthesis and a discussion of new implications with

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2;0 311 3'30 3'5o 37Fig. 1. Distr ibutio n of Precambr ian base ment (vert ical ly hatched)as exposed in the footwall of the north ern Red Sea r if t and associatedrif t systems towards the nor th (compiled from E1 Gab y et al . , 1988;Schande lmeier et al ., 1988; Stoeser and Stacey, 1988). The Preca m-br ian is d iv ided in to the Pan-Afr ican , Ara b i an - Nubian Shie ld anda pre -Pan-Afr ican c ra ton towards the west , the Eas t Sahara Cra ton .A ten ta t ive boundary be tween these domains has been based onisotopic data (e .g. Harris et al . , 1990). The present pap er is concernedwi th the Nubian Shie ld in Egypt and in pa r t i cu la r wi th the a reasshown in detai l on Figs 2 and 6 (boxes)


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486re g a rd t o t e c t o n i c e v o l u ti o n , t e r r a n e m a rg i n s a n d p o t e n -t i al i n v e r si o n a n d r e a c t i v a t i o n o f t h e P a n -A f r i c a n s t ru c-tures .

Tectonostratigraphy and time cons traintsTwo-t ie r subd iv i s ionA c o a r s e , t w o - t i e r s u b d i v i si o n h a s b e e n a p p l i e d t h ro u g h -o u t m u c h o f th e A r a b i a n - N u b i a n S h ie ld (e .g . E 1 R a r e l y ,1972 ; Her min a e t a l . , 1989 ; Sh imro n , 1990) . In the cen t ra lp a r t o f t h e Ea s t e rn D e s e r t B e n n e t a n d M o s l e y (1 9 8 7)es tab l i shed a su bd iv i s ion wi th su i t es o f gne i s ses a t theb o t t o m a s t ie r 1 a n d s t ru c t u r a ll y o v e r l y i n g lo w g ra d esuccess ions as t i e r 2 . E1 G ab y e t a l . (1988 ; 1990) ap p l ieda t w o - t i e r s u b d i v is i o n fo r t h e w h o l e Eg y p t i a n p a r t o f t h eA r a b i a n - N u b i a n S h ie ld u s in g t h e t e rm s ' in f r a s tr u c t u re 'a n d ' s u p ra s t ru c t u r e ' f o r t h e l o w e r a n d u p p e r l e v e l s ,respec t ive ly . The in f ras t ruc tu re i s imp l ied to cons i s tm a i n l y o f p r e -P a n -A f r i c a n ( c o n t i n e n ta l ) c ru s t a l r o c k s ,w h e re a s t h e s u p ra s t ru c t u r e i s o f P a n -A f r i c a n o r i g in ( e .g .E1 G a b y , i n p r es s ). H o w e v e r , t h i s i n t e rp r e t a t io n i s t n o tu n a n i m o u s l y a c c e p t e d ( e. g. K r6 n e r e t a l ., 1 9 8 8 ; H a r r i se t a l . 1990) and , therefo re , the ' ne u t ra l ' t e rm ino log y o ft w o t i e r s i s u s e d h e re . A c o m p re h e n s i v e r e v i e w o ffo rm a t i o n s a n d l i t h o l o g y a n d r e l e v a n t r e f e r e n c e s w a sc o m p i l e d b y H e rm i n a e t a l . ( 1 98 9 ) a n d o n l y a b r i e facc oun t i s g iven here . Th e up per l eve l , ti e r 2 , i s com pos edof es sen t ia l ly low (subgreensch is t to b io t i t e , wi th loca lh i g h p r e s s u re o r h i g h t e m p e ra t u r e a s s e m b l a g e s ) g r a d em e t a v o l c a n i c , m e t a s e d i m e n t a ry a n d p l u t o n i c ro c k s . Th et ie r 2 ro c k s c a n a l l b e r e la t e d t o i g n e o u s a n d s e d i m e n t a ryro c k s o f t h e o c e a n i c l i th o s p h e re , o f a c c r e t i o n a ry p r i s m sa n d s u b d u c t i o n z o n e s a n d e v o l v i n g i s l a n d a r c s o f N e o p ro -te rozo ic , Pan-A fr ica n ag e (e.g. R ies e t a l ., 1983 ; Kr6 nere t a l ., 1987) . Tie r 2 a l so con ta ins l a te t ec ton ic , m o lasse-t y p e s e d i m e n t s ( e. g. t h e H a m m a m a t G r o u p w i t h th e b a s a lIg l a F o rm a t i o n ; A k a a d a n d E1 R a re l y , 1 9 58 ), a n db i m o d a l , a n d e s i t i c D o k h a n v o l c a n i c s a n d t h e A t t a l aFe l s i t es (e .g . S te rn and Got t f r i ed , 1986 ; S te rn e ta l . ,1988) . Loca l ly , t i e r 2 may inc lude i so la ted s l i ces o fgne i s sic rocks (e .g. S h imron , 1984 ; E1 Ba you mi andGre i l ing , 1984 ; E1 Ak hal 1993) , bu t these rocks a re no ta majo r cons t i tuen t . In con t ras t , gne i s ses p reva i l in therock assem blage o f the low er l evel , ti e r 1 , wh ich i sg e n e ra l l y e x p o s e d s t ru c t u r a l l y b e n e a t h t h e h i g h e r u n i t s .A l t h o u g h d o m i n a t e d b y g r a n i t o i d g n e i s se s , t h e t ie r 1 s e-q u e n c e s a l so c o n t a i n u l t r a m a f i c , m a f i c a n d i n t e rm e d i a t ei g n e o u s ro c k s a n d m e t a s e d i m e n t s . Th e i r m e t a m o rp h i cg ra d e i s c h a ra c te r i z e d b y r e l a ti v e ly h i g h t e m p e ra t u r e(migma t i t es ) and p res su re (e .g . garne t , loca l ly kyan i te ;e .g . S t ie tze l, 1987 ; Rashw an , 1991 ; Ab del K hale k e t a l .,1992) , ind ica t ing lower c rus ta l cond i t ions . Li tho log ica l lya n d g e o c h e m i c a l l y th e s e ro c k s e q u e n c e s r e la t e t o t h o s e o fthe ocean ic l i thosphere and i s l and a rcs (e .g . Rashwan ,1991 ; Kamal El Din Saber 1993) . Therefo re , there i s noconclus ive ev idence tha t t i e r 1 i s cons iderab ly d i f fe ren tf ro m t i e r 2 w i th r e g a rd t o p ro t o l i t h a n d g e o c h e m i s t ry (e .g .

R a s h w a n , 1991 ; see , however , E1 G ab y e t a l . , 1988). T heg n e i s s e s a r e d i s t i n c t f r o m t h e l o w g ra d e ro c k s o n l y b yt h e i r m e t a m o rp h i c g r a d e a n d f a b r i c . Th i s d e fo rm a t i o n a lfab r ic has no age impl ica t ion (e .g . gne i s ses a re no tn e c e s s a ri l y o l d e r t h a n l o w g ra d e ro c k s ; K r6 n e r e t a l .,1988) bu t i s, apparen t ly , a n express ion o f the genera li n c r e a se in d e fo rm a t i o n i n t e n s i ty t o w a rd s d e p t h . C o n s e -quen t ly , gne i s s ic dom ains u sua l ly rep resen t re la t ive ly lowc ru s t a l le v e ls a n d t h e s u r ro u n d i n g l o w g ra d e ro c k s c a n b et a k e n a s r e p re s e n t i n g u p p e r c ru s t a l r o c k s .T i m i n g o f th e o ro g e n i c e v o l u t i o nA g e s o f e a r l y P a n -A f r i c a n i g n e o u s a n d m e t a m o rp h i ce v e n t s v a ry w i d e l y b e t w e e n a b o u t 9 0 0 a n d 6 0 0 M a a n da c r o ss th e A r a b i a n - N u b i a n S h ie ld (e .g . S te r n a n dHe dge , 1985 , Kr 6ne r e t a l . , 1987 ; 1988 ; 1992 ; S toeser andStacey , 1988 ; Mi l le r and D ixon , 1992) . A t the end o f th isear ly Pan-A fr ican evo lu t ion , B ey th e t al . (1994) recogn iz-e d a t r a n s i ti o n a l p e r i o d b e t w e e n t h e e a r ly c o m p re s s i o n a ltec ton ic phase wi th ca lc -a lka l ine , co l l i s iona l, I - type g ran i -t o i d b a t h o l i t h s a n d a s u b s e q u e n t e x t e n s i o n a l p h a s e w i t hA-type a lka l i g ran i tes . Th is t rans i t iona l ep i sode can bef o l lo w e d a c r o ss t he n o r th e r n p a r t o f t h e A r a b i a n - N u -b ian Sh ie ld and , in Egyp t , l as ted f rom abou t 615 to600 M a (B ey th e t a l ., 1994). The ages o f the igneous rocksa n d m o l a s s e s e d i m e n t s r e l a t e d t o t h e e x t e n s i o n a l e v e n tf a ll i n a s i m i la r ly n a r ro w t i m e s p a n b e t w e e n a b o u t 5 75and 595 M a ago (e .g . S te rn and H edge , 1985 ; Wi l li s e t a l .,1988 ; Mi l le r and Dixon , 1992) . Th is t ime in te rva l i sassum ed here to def ine the age o f the ex tens iona l co l lapse .Th e e n d o f P a n -A f r i c a n a c t i v i ty is m a rk e d b y s o m ep o s t - t e c t o n i c g r a n i t o i d s (Y o u n g e r G ra n i t e , e t c . ) a n dre l a t e d ro c k s , w h i c h v a ry i n a g e f ro m a b o u t 5 8 0 t o530 M a (e.g . Sturc hio et al . , 19 84; W il l is et al . , 1988).S o m e o f th e s e ro c k s i n t ru d e a n d ' s ea l ' t h e s h e a r z o n e sr e l a t e d w i t h c o m p re s s i o n a n d t r a n s p re s s i o n a f t e r t h eex tens iona l co l lapse (see l a te r ) .

Regional structureS h e a r z o n e s w i t h i n a n d b e t w e e n t h e l o w g ra d e ( t ie r 2 ) a n dgneis s ic domains ( t i e r 1 ) documen t subs tan t ia l t ec ton ict r a n s p o r t w h i c h e v e n t u a l l y l e d to t h e p r e s e n t m a p p a t t e rn .Th i s d e fo rm a t i o n a l s o fo rm e d s t ru c t u r a l c u l m i n a t io n s , i nt h e c o re o f w h i c h t h e g n e i s si c r o c k s a r e e x p o s e d . R e s u l t so f d e t ai l e d s t u d ie s o n m a j o r a n t i f o rm a l d o m a i n s ( e. g.S tu rch io e t a l . , 1983 ; Gre i l ing e t a l . , 1988 a ; K am al e l Dine t a l ., 1992 ; Abde l Kha lek e t a l ., 1992 ; Wal lb recher e t a l . ,1993) revea l tha t such s t ruc tu res a re domina ted by e i thercompress iona l , ex tens iona l o r s t r ike-s l ip l inked fau l t s .D e t a i l e d e x a m p l e s o f t h e s e r es p e c t iv e d e fo rm a t i o n a ltypes a re t rea ted in the fo l lowing , toge ther wi th ana c c o u n t o f t h e s t r u c t u r e o f p o t e n t ia l l y e x t e n s i o n - r e la t e dm o l a s s e b a si n s . Ta b le s 2 - -4 p ro v i d e a b r i e f s u m m a ry o ft h e s t r u c t u r a l e v o l u t i o n o f v a r i o u s d o m a i n s w h i c h a r erep resen ta t ive o f ti e rs 1 and 2 , respec t ive ly . I t i s remar-k a b l e i n t h is c o n t e x t t h a t a l l o f t h e k n o w n l a te o ro g e n i c ,m o l a s s e - t y p e s e d i m e n t s r e s t u n c o n fo rm a b l y o v e r t i e r


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487Fig. 2. Structuralsketchmap ofthe central part of the EasternDesert of Egypt, simplified romBennet and Mosley (1987),Greiling et al. (1988 b), Sultan etal. (1988), Tehrani et al. (1988).For location, see Fig. 1 furtherexplanations on the figure andin the text

metamorphic corecomplex and thrusting?Gabal Meatiq basin formation, thrusting andtranspression in Wadi Queih,Figure 7

Wadi ZeidunFigure 4 ..~

normalfaulting/shearingat GabalEl Shalulgranite

- 25ON

0L km

~.,~ SAFAGA

Wadi Meesar

f ...,"

"Wadi Shait

". 2 - _k~

sl,. 134E

QUSEIR

PHANEROZOICCOVERT I E R 2['--'-1 PAN-AFRICANLOW GRADESUCCESSIONS, INCL.LATE OROGENICIGNEOUS AND~ SEDIMENTARYROCKST I E R 1

[ - -~ GNEISSIC UNITS,STRIKE-SLIP FAULTLOW-ANGLESHEAR ZONE

,4' 5",

MARSA

extension andformation olmetamorphiccore complex,Gabal El Sibaireversefaulting in'WadiUmm Nar

extension/basinformation inWadi Igla,se e Figure 3thrust systemsof the Wadi HafafitCulmination, Wadi Ghadiretc.

Wadi Ranga'{ Wadi K a s h a / ~ ( ~ Wadi Ghadir"accretionary prism/fore-arc sectionminor late-tectonic X restor es to south, of Wadi Hafafitextensio n 35OE Culmination

2 rock sequences and no p rimary sedimentary contact o fmolasse-type sediments over tier 1 gneisses has beenobserved (e.g. Egyptian Geological Survey, 1981; Bennetand Mosley, 1987). Together with structura l data (Table 2and below) this observation indicates that molasse-typesedimentation took place before or during the activity ofregional shear zones, which brought the tier 1 gneisses upto their present, relatively high level in the crust. Thisrelationship will be used to speculate on the absolutetiming of the Neoproterozoic structural evolution inEastern Egypt. Meanwhile, as a working hypothesis, allthe molasse-type deposits discussed here are taken ascontemporaneous, about 595-575 Ma old (e.g. Williset al., 1988). Consequently, extension related to molassebasins is of about the same age; subsequent compressionand wrench-faulting took place later but before the end o fthe intrusion of post-tectonic granitoids ca. 530 Ma ago(see previous section). According to this time sequence,

examples of structures related to the evolution of molassebasins are discussed first followed by examples of sub-sequent compressional deformation and wrench-faulting.

Structures related to the evolution of molasse basinsWadi [gla basinThe Wadi Igla basin (Fig. 2, Rice et al., 1993), is the typelocality of the Igla Formation , which is assumed to be theoldest part of the Pan-African molasse sequence (e.g.Akaad and E1 Rarely, 1958; Hermina et al., 1989). Thebasin occupies a half-graben structure with thick basalconglomerates along the south-eastern margin, associ-ated with several large Atalla Felsite intrusions , reflectingthe major (extensional?) fault zone. Some YoungerGranites were intruded before sedimentation as they areunconformably overlain by the basal conglomerate orform abundant clasts within the basal conglomerate while


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48 8A N B N

:e Veins nd~-~(i3rec cias. N=5 6 N=2~07Vector Mean 072 Vector Mea n 064 C N

NNormal Faults,da=6 4 * Poles to N orm al Faults.N=58.

Poles to Fibrous Quartz Veins.Mean 330-01, N=130F i g , 3 A - - D . O r i e n t a t i o n o f e x t e n s i o n a l f e a t u r e s f r o m t h e W a d i I g l ab a s i n ( se e F i g . 2 f o r l o c a t i o n ) . A D i r e c t i o n r o s e s h o w i n g o r i e n t a t i o no f e x t e n s io n a l q u a r t z c a r b o n a t e v e i n s in W a d i I g l a . B D i r e c t i o n r o s es h o w i n g t r e n d o f d y k e m a r g i n s . C D i r e c t i o n ro s e s h o w i n g t r e n d o fn o r m a l f a u l t s i n W a d i I g l a . D S t e r e o n e t s h o w i n g o r i e n t a t i o n o fn o r m a l f a u l t s a n d ( e x t e n s io n a l ) q u a r t z v e i n s

s o m e m i n o r i n t ru s i o n s a l o n g t h e n o r t h e rn m a rg i n c u t th emolasse sed imen ts . Do ler i t i c to andes i t i c dykes wi tha d o m i n a n t N E - S W t r e n d a r e p a r ti c u la r l y a b u n d a n t i n th en o r t h - e a s t (F i g. 3 B ) ; t h e se c u t b o t h t h e H a m m a m a t G ro u pand Ata l l a Fe l s i t e . The Ig la Bas in has been a f fec ted bym i n o r N N E - S S W d e x t r a l t r a n st e n s io n a l s t ri k e- s li p d e fo r -ma t ion (R ice e t a l . , 1993 ; S tanek e t a l . , 1993) . Al thoug h nom a j o r s t ri k e -s l ip f a u l t h a s b e e n fo u n d c u t t i n g t h e m o l a s s es e d i m e n t s , s u b h o r i z o n t a l s l i c k e n s i d e s a r e a b u n d a n t o nj o i n t s , d y k e a n d q u a r t z v e i n m a rg i n s , i n d i c a t i n g t h a td e f o r m a t i o n w a s p o s t- s e d im e n t a t io n . A b u n d a n t f i b r o u squa rtz veins lie paral lel to the m afic dyke s (Fig . 3); the fibresi n d i c a t e e x t e n s i o n n o rm a l t o t h e v e i n m a rg i n s . N o rm a lfau l ts a re a l so comm on, a l though d i f fi cu l t to in te rp re t due tot h e p r e se n c e o f o l d e r P a n -A f r i c a n f a u l t s a n d t h o s ea s s o c i a t e d w i t h t h e R e d S e a r i f t . La t e P a n -A f r i c a nc o m p re s s i o n a l s t r u c t u r e s ( fo l ds a n d t h ru s t f a u l ts ) a r e r a r eand a we ak subver t i ca l c leavage is loca lly deve loped (Abde lK h a l e k a n d H a fe z , 1 98 6) . H o w e v e r w e a k , t h e l at ec o m p re s s i o n m a y b e o f g e n e ra l i m p o r t a n c e a s a n i n d i c a t io no f la t e P a n -A f r i c a n i n v e r s i o n o f a m o l a s s e b a s i n .Minor basins near the Wadi Hafafit CulminationT o th e s o u t h- e a s t o f W a d i I gl a, H a m m a m a t G r o u ps e d i m e n t s in W a d i R a n g a a r e e x p o s e d c l o s e t o t h e c o a s t ,f o r m i n g a t h in N N W - S S E t r en d i ng s e ri es o f o u t c r o p so v e r l a i n b y M i o c e n e s e d i m e n t s (F i g . 2 ) . Th e y c o m p r i s ea re la t ive ly th in basa l cong lomera te wh ich , in tu rn , res t son vo lcan ic rocks . Ata l l a Fe l s i t es a re p resen t b o th as l a rgeb o d i e s c l os e to , o r u n d e r l y i n g , t h e b a s a l c o n g l o m e ra t eand as th in s i l l s wi th in the molasse . Andes i t i c s i l l s up to7 m t h ic k , w h i c h h a v e e x t e n s iv e l y b a k e d t h e m a rg i n a l

s e d im e n t s , a r e a l s o p r e s e n t w i t h in t h e m o l a s s e a n d c a n b et r a c e d a l o n g s t r i k e fo r s e v e ra l ki l o m e t r es . A p a r t f r o m t h ereg iona l t i l t ing to the wes t and loca l i zed nor th -so u th toN E - S W fa u l ti n g , b o t h o f w h i c h m a y b e r e l a te d t o e i th e rm o l a s s e b a s i n fo rm a t i o n o r R e d S e a ri f ti n g , n o d e fo rm a -t i o n h a s b e e n o b s e rv e d (A k a a d a n d E1 R a m l y , 1 95 8) .A s i m il a r l a c k o f s m a l l- s c a le d e fo rm a t i o n h a s b e e n n o t e di n t h e m o l a s s e s e d i m e n t s a t W a d i K a s h a b a n d a t W a d iS h a i t, i m m e d i a t e l y t o t h e s o u t h a n d n o r t h o f th e W a d iH a fa f i t C u l m i n a t i o n , r e s p e c ti v e l y (F ig . 2 ). H o w e v e r , t h ela t t e r occurrence i s fo lded in to a fau l t -bend fo ld (wh icho r i g i n a te d d u r i n g t h ru s t in g o v e r a r a m p ) a n d i s t h u s p a r to f a t h ru s t s y s t e m t h a t i s r e l a t e d t o t h e W a d i H a fa f i ta n t i f o rm a l s t a c k ( se e b e l o w ) . F ro m t h e r e g i o na l c o n t e x t i tc a n b e i n f e r r e d t h a t t h e m o l a s s e d e p o s i t s o f W a d i s R a n g aa n d K a s h a b a l s o fo rm p a r t o f t h ru s t s y s t e m s (Te h ra nie t a l ., 1988 ; Gre i l ing e t a l ., 1993) . Far th er sou th o f theW a d i H a fa f i t C u l m i n a t i o n n o m a j o r e x t e n s i o n a l d e fo r -m a t i o n h a s b e e n o b s e rv e d i n t h e Ea s t e rn D e s e r t ( e . g . i nt h e G a b a l M u q s i m ~ W a d i A l la q i a re a ). H o w e v e r , c o n-g l o m e ra t i c s e d i m e n t s t o t h e n o r t h o f A b u S w a y e l m a y b ecand ida tes fo r molasse sed imen ts (F ig . 6 ) and , therefo re ,a l so be ' re la ted to ba s in fo rm at ion and ex tens ion (see a l soE1 Gaby et al . , 1988).Normal fau lts and rnolasse basins northof Gabal El ShalulIn t h e a r e a t o t h e n o r t h a n d n o r t h - e a s t o f G a b a l E1 S h a l u lth ree molasse bas ins have been s tud ied , Wad i Ze ido un Eas t ,W a d i Ze i d o u n W e s t a n d W a d i M e e s a r (O s m a n , 1 9 9 4; se eF i g . 2) . Th e f i r s t t w o a r e d o m i n a t e d b y t h i c k d e p o s i t s o fbasa l cong lomera te . Do kha n vo lcan ics a re absen t , a l thoughA t a l la F e l s it e d y ke s w e r e e m p la c e d a l o n g e a s t - w e s t a n dN W - S E o r i en t e d f a ul ts a n d a Y o u n g e r G r a n i t e h ase x te n si v el y c o n t a c t m e t a m o rp h o s e d t h e H a m m a m a t G ro u pin Wa di Ze id oun Eas t (Os ma n e t a l ., 1993) . In WadiZe i d o u n n o d e fo rm a t i o n h a s b e e n r e c o rd e d , p o s s i b ly d u e t ot h e m a s s iv e n a t u r e o f th e ro c k s . I n W a d i Ze i d o u n Ea s t a n dW a d i M e e s a r a w e a k p e b b l e p r e f e r r e d o r i e n t a t io n t o w a rd sthe wes t and nor th has been reco rded (Fig. 4 A - C) . Pebb lesi n t h e m e t a v o l c a n i c b a s e m e n t s h o w a m a rk e d p r e f e r r e dor ien ta t ion to the no r th -wes t , re la ted to the ex tens iona lshear zone a t the G aba l E1 Shalu l g ran i te marg in (F ig . 4 D,E an d be low) . In W adi Ze idou n E as t a c leavage is developed ,assoc ia ted wi th l a rge-sca le up r igh t fo ld ing (Osman e t a l . ,1992) , documen t ing subsequen t ( loca l ) compress ion .Lo w a n g l e n o rm a l f a u l t i n g a n d t r a n s t e n s i o nGabal El Sibai AntiformTh e G a b a l E1 S i b a i a n t i f o rm c o n s i st s o f a m e t a m o rp h i cc o re o f g n e i ss e s, g a rn e t i f e ro u s m i g m a t i te s a n d a m p h i b o l i -t es wi th g ran i to id in t rus ives ( t i e r 1 ) , exposed benea tha r im o f l o w g ra d e m e t a v o l c a n i c a n d m e t a s e d i m e n t a ryrock s ( t i e r 2 ; Kam al E1 Din , 1993 ; F ig . 2 ). A s um ma ry o fthe t ec ton ic evo lu t ion i s g iven in Tab le 2 . The two t i e rs a res e p a ra t e d b y ( e a rl y ) l o w a n g l e s h e a r z o n e s (D 3 o f Ta b l e 2 )t o w a rd s t h e n o r t h - e a s t a n d s o u t h -e a s t, a h i g h a n g le s h e a rzone wi th s in i s tra l s t r ike-s lip towa rds the so u th an d ( l a te )


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489T a b l e 2. The sequenc e of deformational, magm atic and m etamorph ic events in tier i gn eisses as tentatively related to the four major phase sof the tectonic evolution of m ountain belts (compare Ta ble 1), modified from Kam al E1 Din (1992), Rashw an (1991) and E1 Ram ly et al.(1993). For location see Figure 2.G a b a l E l S i b a i a r e a g n e i s s e sM a g m a t ic a c ti v it y D e f o r m a t i o n M e t a m o r p h i s m

b S reg iona l f o l ds w i th axia lsu r face NW-SE

la te tectonicin t rus ions, ElDabbah and El Sibaigrani tesD 4 i m b r i c a t i o n o f m a j o r

shea r -zone , ex tens iona lf a u l t sD 3 reg iona l l ow-ang le shea r -zone , my lon i t i c f o l i a t i on loca l re t rog ress io r

U m Luseifaporphyr i t ic grani teEt Mir i f iya~ UmShaddad int rus ions,alkaline grani te

D 2 f o l i a t i o n

calc-alkaline t ona l i t e ,El ShushD I p e n e t r a t i v e sch is tos i ty r eg ional meta-m o r p h i s m , g r e e n -sch is t and amphi -bo l i t e g rade , l oca lm i g m a t i t e s

amphibol i tes ,p r o b a b l y o p h i o l i t i c

B

A

3

2

I

M i g i f - H a f a f i t g n e i s s e s~ la g m a ti c a c ti v it y D e f o r m a t i o n M e t a m o r p h i s m

D 9 o p e n f o l d s , g e n e r a l l yf la t - ly ing ax ia l surface, up l i f to f g r a n i t o i d d o m e s/ o u n g e r g r a n i t e

D 8 th rust ing / fau lt ing , my lo n i te re t ro g ra def o r m a t i o n , r e gi o na l m e t a m o r p h i s m ,l o w - a n g l e t h r u s t s a n d m e t a s o m a t i cre la ted fau l t -bend fo l ds ,v a r i o u s d i r e c t i o n s c h a n g e sD 7 v a r i a b le o p e n t o t i g h t d r a g-f o ld s , N W - S E t o W N W -ESE d i rec t i ons , c renu la t i on/ f r a c t u r e c leav~e

n o t d o c u m e n t e d ?

; r a n i t e / p e g m a t i t eD 6 o p e n fo l d s , N E - S W t o E - Wd i rec t i ons , c renu la t i onc l e a v a g eD 5 local faul ts , myloni tesD 4 pene t ra t i ve fo l i a t i on , i so -c l i na l f o l ds , i r regu la r f o l ds

: a l c - a l k a l i n e: r o n d h j e m i t e

:a lc -a lkal ine tonal i te

:alc-alkaline gabbro

D 3 pene t ra t i ve fo l i a t i on ,isoc l inal fo lds

D 2 pen te t ra t i ve fo l i a t i on ,m e t a m o r p h i c b a n d i n g

D I p l ana r fab r i c

c o n t a c tm e t a m o r p h i s mreg iona l me tamor -phism ( s tau ro l i te-kyanite) , localm i g m a t i z a t i o n

n e t a g a b b r o s , u l t r a -naf ic complexes ,) p h i o l i t i c

n o r m a l f a u l t s t o w a r d s t h e w e s t a n d n o r t h ( D 4 ) . S h e a rc r it e r ia s u c h a s S - C f a b r ic s a n d a s y m m e t r i c a l p o r p h y -r o c l a s t s d o c u m e n t a t r a n s p o r t ( t o p ) t o t h e s o u t h - e a s t(120 ) , cons i s t en t wi t h s i n i s t r a l s t r i ke- s l i p a t t he sou t hernm a r g i n o f t h e a n t i f o r m ( G r e i l in g e t a l ., 1 9 93 ). F u r t h e r -m o r e , t h e w e s t e r n p a r t o f t he a n t i f o r m i s i n t r u d e d b y a tl e a s t t w o m a j o r , p o s t - d e f o r m a t i o n a l g r a n i t e p l u t o n s( K a m a l E 1 D i n e t a l ., 1 9 92 ). S i m i l a r t o t h e W a d i I g l a a r e a( s e e a b o v e ) t h e e x t e n s i o n a l d e f o r m a t i o n i s f o l l o w e d b y( w e a k ) c o m p r e s s i o n ( D 5 o n T a b l e 2 ). T o t h e w e s t o f t h eG a b a l E 1 S i b a i a r e a f u r t h e r e x t e n s i o n a l s t r u c t u r e s a r ee x p o s e d , r e l a t e d i n p a r t i c u l a r t o t h e G a b a l E 1 S h a l u lg r a n i t e a n d a n u m b e r o f m o l a s s e b a s i ns .

Gabal El Shalul culmination

A p p a r e n t l y s i m i l a r t o t h e G a b a l E 1 S i b a i a n t i f o r m , t h eG a b a l E l S h a l u l g r a n i t e ( g n e i s s ) f o r m s a n o p e n a n t i f o r m ,t h e w e s t e rn a n d p e r h a p s m a j o r p a r t o f w h i c h is c o v e re d b yP h a n e r o z o i c s e d i m e n t s . H o w e v e r , a t t h e n o r t h - e a s t e r na n d e a s t e r n m a r g i n s o f t h e G a b a l E 1 S h a l u l g r a n it ea m a j o r l o w a n g l e s h e a r z o n e i s e x p o s e d ( O s m a n e t a l. ,1 9 9 2 ) . T r a n s p o r t - p a r a l l e l s t r e t c h i n g l i n e a t i o n s a n d s h e a rc r i te r i a d o c u m e n t a t r a n s p o r t o f o v e r ly i n g l o w g r a d em e t a s e d i m e n t s t o w a r d s t h e s o u t h - e a s t ( s e e F i g . 4 D , E ) .T h e s t r u c t u r a l s i t u a t io n i s, t h e r e fo r e , c o m p a r a b l e t o t h a to f th e G a b a l E 1 S i b ai a r e a a n d i t is p r o p o s e d t h a t t h e


7/18

490X / Y N = 2 2 N

4 . 0 ] e l o n g a t i o n /3 1 / /[ -,,," flattening2 O l . , . , / .

N e

1 o " : ' " - . . / z2.0 3.0 4.0] e l o n g a t i o n /3 . o - I , > / . ./ U flattening2.04 - . ,~/ _ - Q

2.0 3.0 4.0X/Y N

4 .0 N=2 2] e l o n g a t i o n /3.01,* , , , /[ ' . " y flattening

Z . 0 e l o l Y " ' . .2.0 3.0 4.0

X/Y4.03.0,2.0" i1.0

N = 2 0 Ne l n g j t i U, & /~ z f la t tening~ 0 . / . . - "

2'.0 310 4.'*0 ''Y /Z

4 0 . x 231 , , /2.0~11 / ~ f la t tening1 '~ " 2 !0 3 :0 4 . 'o /Z

Fig. 4. Flinn plots and stereonets showing sha pe and lon g (X) axisorientation o f deformed pebbles, respectively.Diagrams A to C referto H am ma ma t (molasse) sediments, diagrams D an d E to underlyingvolcanogenic metasediments. A W adi E1 Gurd (northern p art ofWadi Zeidun - we st basin); B W adi Zeidun - west; C WadiMeesar; D at the contact w ith the E1 Shalul granite; E Wadi Me sat;see Fig. 2 for location

G a b a l E 1 S h a l u l c u l m i n a t i o n i s a s i m i l a r m e t a m o r p h i cc o r e c o m p l e x .Gabal Meatiq metamorphic core complexT h e G a b a l M e a t i q a r e a i s c h a r a c t e r i z e d b y a d o m a ls t r u c tu r e , w h i c h h a s o f t e n b e e n s t u d i e d d u r i n g t h e p a s td e c a d e . T h e r e i s , h o w e v e r , a s y e t n o g e n e r a l l y a c c e p t e dm o d e l f o r t h e o r i g i n o f t h e s t ru c t u r e . I n t e r p r e t a t i o n sr a n g e f r o m f o l d i n t e r f e r e n c e p a t t e r n s ( e .g . E 1 G a b y e t a l .,1 98 8) t o c u l m i n a t i o n s i n t h r u s t s y s t e m s ( e .g . R i e s e t al . ,1983 ; S tu rch io e t a l . , 1984 ; Wal lb recher e t a l . , 1993) andt o m e t a m o r p h i c c o r e c o m p l e x e s ( e .g . S t u r c h i o e t a l .,1 98 3) . I n t h e l i g h t o f t h e n e w r e c o g n i t i o n o f m e t a m o r p h i cc o r e c o m p l e x e s i n t h e G a b a l E 1 S i b a i a n d G a b a l E 1 S h a l u la r e a s a n d t h e o v e r p r i n t i n g r e l a t i o n s h i p s i n t h e W a d iQ u e i h a r e a ( s e e l a t e r ) , i t i s s p e c u l a t e d t h a t t h e G a b a lM e a t i q c o m p l e x o r i g i n a t e d a s a n e x t e n s i o n a l s t r u c t u r e ,w h i c h w a s o v e r p r i n t e d b y c o m p r e s s i o n .

L o w a n g l e re v e r se f a u l t i n g a n d t r a n s p r e s s io nWadi Hafafit CulminationT h e W a d i H a f a f i t C u l m i n a t i o n ( W H C ) i s t h e m o s tc o n s p i c u o u s p a r t o f a la r g e r s c al e a n t i fo r m a l d o m a i n ,w h e r e v a r i o u s g n e i s s e s a r e e x p o s e d b e n e a t h l o w g r a d esucce ss ions (F ig . 2 ). T he gne i sses r ep rese n t su i t es o fi g n e o u s r o c k s o f o c e a n f l o o r a n d v o l c a n i c a rc c h a r a c t e r is -t ic s a n d r e l a te d m e t a s e d i m e n t s , t o g e t h e r w i t h a m e t a s e d i-m e n t a r y u n i t d e r i v e d f r o m a p r e - P a n - A f r i c a n s o u r c e a r e a( R a s h w a n , 1 99 1) . T a b l e 2 g i v e s a s u m m a r y o f t h e c o m p l e xs t r u c t u r a l e v o lu t i o n . T h e s t r u c t u r e o f th e W H C i s d o m i -n a t e d b y l o w a n g l e t h r u s t s ( e .g . E1 R a r e l y e t a l ., 1 9 8 4 ; D 8o n T a b l e 2 ) a n d s e c t i o n s a c r o s s t he W H C s h o w t h e t h r u s t st o b e l i n k e d t o f l o o r a n d r o o f t h r u s t s , r e s p e c t i v e l y ( e . g .G r e i l i n g e t a l . , 1 9 8 8 a ; 1 9 9 3; G r e i l i n g a n d E 1 R a r e l y ,1 9 9 0 ) . T h e r e f o r e , t h e g n e i s s i c u n i t s f o r m a n a n t i f o r m a ls t a c k b e n e a t h o v e r l y i n g l o w g r a d e s u c c e s s i o n s . V a r i o u ss h e a r c r i t e r i a s h o w a t e c t o n i c t r a n s p o r t t o w a r d s t h en o r t h - w e s t ( e .g . G r e i l i n g e t a l ., 1 9 9 3; G r e i l i n g a n d R a s h -w a n , i n p re s s) a n d , c o n s e q u e n t l y , a n o v e r a l l c o m p r e s s i o ni n a N W - S E d i re c ti o n. A s t ee p ly d i p p in g S E - N Wt r e n d i n g l a t e r a l r a m p , m i s i d e n t i f i e d e a r l i e r a s a s t r i k e -s l ip f a u l t ( S u l t a n e t a l ., 1 9 88 ), b o u n d s t h e W H C a n t i -f o r m a l s t a c k t o w a r d s t h e n o r t h - e a s t , w h e r e i t i s o v e r l a i nb y t h r u s t u n i t s o f t h e l o w g r a d e s u c c e ss i o n (E l B a y o u m ia n d G r e i l i n g , 1 9 8 4 ) . T h e s e l o w g r a d e u n i t s i n c l u d e t h ew e l l k n o w n a n d w e l l d o c u m e n t e d o p h i o l i te f r a g m e n t s o fW a d i G h a d i r .Wadi Ghadir areaD e t a i l e d s t r u c t u r a l w o r k i n t h e W a d i G h a d i r a r e a ( E lA k h a l , 1 99 3) r e v e a l e d a g e n e r a l c o m p r e s s i o n o f t h e a r e at h r o u g h l o w a n g l e t h r u s t s . T h e s e t h r u s t s a r e p a r t o f t h er e g i o n a l t h r u s t s y s t e m t h a t e x t e n d s a s f a r w e s t a s t h e W a d iH a f a f i t C u l m i n a t i o n ( E l B a y o u m i a n d G r e i l i n g , 1 9 8 4 ) .H o w e v e r , in c o n t r a s t w i t h th e W a d i H a f a f i t C u l m i n a t i o ng n e is s e s o f ti e r 1 a n d , p r e s u m a b l y b e c a u s e o f t h e i r h i g h e rc r u s t a l le v e l, th e p r e - t h r u s t m e t a m o r p h i c a n d s t r u c t u r a l


8/18

49 1T a b l e 3 . S e q u e n c e o f t e c t o n i c e v e n t s i n t h e t i e r t g n e i s s es o f t h eG a b a l M u q s i m a r e a , m o d i f i e d f r o m S a d e k (1 99 4 ). F o r l o c a t i o n s e eF i g u r e 5 , t e c t o n i c p h a s e s 1 - 4 a s i n T a b l e 2 .

_ ~ M u q s i m a r e a g n e is s e s

IM a g m a t i c a c t iv i ty D e f o r m a t i o n M e t a m ,4 B

4 A

la te gran i to idi n t r u s i o n sD 4 we a k fo l ia t i o nD 3 reg iona l folds, crenu la t iona n d kink bandsA b u Fa s -Um co n ta c tDorn i -E I De iga me tamo rph isma b b r o i c i n t ru s i o n s

D 2 shear fabric, r n y l o n i t i cfo l ia t ion & stre tch ingl ineation, regional thrus-t ing and t r a n s p r e s s i o n

~r l y to n a l i t en t r u s i o n

D I ope n- t igh t fo lds, reg iona lp e n e t ra t i ve fo l ia t i o n , me ta mo rp h i smme tam orph ic band ing rn igmat i tes

s l a n d a r c a n d e s i te smd related tufts;,~eneratJono f a n3 c e a n i c C r U S tioph io l i t i c~erpentini tes,lrnphibol i tes andnetagabbro)

evolution in the tier 2 rocks of the Wadi Ghadir area, asshown in Table 4, is less complex th an in the gneisses. Thismay be why the early, pre-orogenic structures, as relatedto the island arc evolution, are relatively well preserved.For example, the fabric of a deep-sea trench tectonicm61ange can be clearly distinguished from later collisionalor post-collisional structures (El Bayoumi and Greiling,1984; E1 Akhal, 1993). These observations support thefundamental results from E1 Sharkawy and E1 Bayoumi(1979), Shackleton et al. (1980), E1 Bayoumi et al. (1983)and E1 Bayoumi (1984) about the existence of a tectonicm61ange in the area and rule out contras ting views (Sultanet al., 1988). Therefore, it can be concluded that the WadiGhadir area represents a section across a fossil deep-seatrench/accre tionary prism and forearc (e.g. E1 Akhal andGreiling, 1987; Greiling et al., 1988a; E1 Akhal, 1993).Both structural criteria and the magmatic succession ofarc-related intrusives from basic in the south-west toacidic in the north-east point to an island arc facingsouth-west, i.e. oceanic lithosphere in the south-west wassubducted north-eastwards. Restoration of the WadiHafaf it antiformal stack restores the Wadi Ghadir forearcdomain to the south-east of the Wadi Hafafit island arcdomain (Greiling eta l., 1993; see Fig. 2) and it issuggested that both domains are part of the same islandarc terrane.

Tab l e 4 . S e q u e n c e o f t e c t o n i c e v e n t s in t i e r 2 s e q u e n c e s o f t h e W a d i G h a d i r a n d W a d i Q u e i h a r e a s , r e s p e c t i v e ly . M o d i f i e d f r o m E 1 A k h a l( 19 9 3) a n d A b d e e n e t a l. ( 19 9 2) . F o r l o c a t i o n s e e F i g u r e 2 , t e c t o n i c p h a s e s 1 - 4 a s i n T a b l e 2 .W a d i G h a d i r a r e aM a g m a t i c a c t i v i ty D e f o r m a t i o n M e t a m o r p h i s ml a t e o r o g e n i c , re dg r a n i t e , d a r k d y k e s D 6 regional ope n folds

D 5 n a p p e t r a n sp o r t

g r a n i t e , grano-d i o r i te , f i n e - g r a i n e dg r a n i t e a p l i teD 4 k ink fo lds, a lmos thor izonta l ax ia l surfaceD 3 congru ent fo lds.crenulation fol iationd i o r i t e , g r a n i t e

c a l c - a l k a l i n e d a rkd y k e s , a p l i te , t o n a -l i te, g r a n i t e d ik e s

d a r k d y k e sD 2 isocl inal/t ight folds.penetra t ive fo l ia t ionD I meta mo rph ic band ing.f o l i a t i o n g r e e n s c h i s t grademetamorph ismm ~ l a n g e - f o r m a t i o n

g e n e r a t i o n o f a no c e a n i c c r u s t( o p h i o l i t h i cs e r p e n t i n i t e , gabbro.s h e e t e d d y k e s ,p i l l o w l a v a s )

e a r l y shear-zones and faults

4 1 3

4 ~

W a d i Q u e i h a r e aM a g m a t i c a c t i v i ty D e f o r m a t i o n M e t a m o r p h i s m

D 3 NW-SE trend ing le f t -la te ra lstrike-slip faultsD 2 NW - t re n d in g fo l ds w i thth ru s ts to wa rd s NE , a l o ngthe folds' axial surfaceD I th ru s t in g to wa rd s N /N Wand folding along E-W a x e sAtalla F e l s i t e s e x t e n s i o n 7 .

b a s i n f o rma t i o n

n o t d o c u m e n t e d 7 .

g r e e n s c N s t g r a d em e t a m o r h i s p h ~ misland-arcmagmat ism


9/18

W.ALLAQI33o'55

o 1[ I 3kmI

%

L E G E N DYounger granitoids

~ '] Layered gabbro, minor peridotiteMeta-a n desite, volcanoclasliclulls and pyroclastic rocksActinolite chlorite epldo teschists

[I T[ ] 8erpentinite,talc carbona terocks and amphibolilesGneissic tonafiteQuartzo-feldspathlc qneisses,micaschists, meta-greywackes,amphibolite bandsMassive meta-andes[lesand metagabbros

f~" Layering trend in gab bro--)(-- Axia l trace of syntorm4)- Axial trace of antlform

IJneaiion/ Layering strike and dip.- ~ Foliation strike and dip

Shear zoneThrust contact

i Faulls

~7

I34 E

W ALLAQI

~V~VVV~VVV~

49 2

Fig. 6. St ruc tu ra l compi la t ionmap based on a satel l i te imagein te rpre ta t ion and inc lud inginformat ion f rom Fig . 5 , Tay loret al . (1993) and our ownfield data. See Fig. 1 forlocation. The structure isdomina ted by the Al laq i shearzone as de f ined by Tay loret al. (1993) a nd is par t o f theWadi Al laq i -Gaba l He ian ibelt as identif ied towards theeast by Kr6n er e t al. (1987). Thisshear zone changes i t s charac te rgradually from sinistral s tr ike-sl ip in the south-east to reversefau l t / th rus t a t Wadi Al laq iand towards the nor th andchanges back to sinistral s tr ike-sl ip in the north-west . Relatedt ranspor t l inea t ions a re shownin the inset s tereonets , dividedinto the ar ea of Fig. 5 inthe sou th-eas t (GM, be low) andthe a rea a round Abu Swaye l(AS, above) . The loca t ionof Fig. 5 is mark ed in thesou th-eas t corner . For the sakeof clari ty, l i thology andstructure are simplif ied.Mylon i tes pa r t ly f rom Tayloret aL (1993)

. LakeNasser

N

[ ~ Late tectonicgranite[- ~ gabbro intrusionTier 2ophiolite remnants

[~ low grade sequenceTier 1[~ gneisses,migrnatites

N=44~ '~.,., GM

\ - - - \L?"- \str ike and dip \ x : r- l~ .\ '~ _'~J ~ ~ ?fault, shear zone ~ -- ~t ~ #' xx xX xX xL ~"~ ~- . \ ~~ , . - ,my,onite \ \ ,

- -T ' - - - " % , -~ '~ ~- ( " ~ I ! l I:< I I IH iMuq~mj


10/18

~1 Fig. 5. G eological map of the area between Wadi Un gat andGabal Muqsim south of Wadi Allaqi in south-eastern Egypt. Thestructure is dominated by a shear zone, extending from the south-east corner of the map towards the west and curving towards thenorth into the north-west corner. This shear zone separates lowgrade, calc-alkaline metavolcan ics in the south-e ast (tier 2) fromgneisses and associated rocks (tier 1) towards the north-east andnorth. Towards the east and north-east these gneisses are overlainalong low angle shear zones by (i.a.) ophiolitic fragments andassociated low grade sequences of tier 2. For loc ation, see Fig. 6,which also contain s a stereonet showing lineatio ns related to tectonictransport along the shear zone

FiB. 7. Structural geological map of the Wadi Queih area, north-west of Quseir (see Fig. 2 for location). Major structural elemen ts areNNW directed early thrusts and associated east--west trendingfolds (D1), followed by north-west trending folds and associatednorth-eas t directed late thrusts (D 2). These latter structures areaccompanied and followed by major N W - S E trending left-lateraltranscurrent faults, which are related to the regional Najd wrenchfault system (e.g. Stern, 1985). Normal faults are related to lateMesoz oic -Ce nozoic Red Sea rift ing

493The Gaba l M uqs im, Wadi A l l aq i and Abu Swayel ar easField studies in the Gabal Muqsim area revealed thepresence of a tier 1 succession of gneisses and schists(Sadek, 1994; Fig. 5). A summa ry o f the structuralevolution is shown in Table 3. Towards the east, the tier1 gneisses are overlain tectonically by the Gabal Muq-s im-Gabal Um Domi ophio l i t i c assemblage, towardsthe north by low grade metasediments (tier 2). Thenorthern boundary of the gneisses is an east-westtrending high angle shear zone (north of Wadi Allaqi;Fig. 5), characterized by steeply plun ging stretching linea-tions and associated stretched pebbles (orientation show nin stereonet in Fig. 6). The steep attitude of the shear zoneand related lineations is due to folding along east-westtrending folds (Fig. 5), which are related to north-westdirected transpression (D2 on Table 3) and, if restored,imply a shearing/transport in about a north-southdirection. This shear zone is only schematically show n inFig. 5, as it has not been ma pped in detail. Bot h thegneisses and the ophiolitic assemblage were juxtaposed

~'' ~x~ x x ...< >c< x x x x x x~x x x x x .~ .~ x x x< x ~ZxX x ,~ . X x X x X x >x x x x ~ : xXxXx> ~ x >< x x xIx x Xx :x xx ~ xXx x x x x

x x x .

x >~ xX x~ ~ x X x ~x >< x ~< x x x X x x . x X x X ~x x x x x x >~" x >< x >< ~: x ~< x x x x x x x x . _$x ~ x x x ~,",< x x x ,, .< Xx~ ,_ _~.. > . . . . . . x x x x x

x x x x x Xx x, ~,~,~.2x :~x x

:::.::.:..:::....:...:..:..::.::...~::.... ~..~:..:....~....~..::..:..:..:...~.`:...~..::..:

~xX~ xx x x

:::::::

Atalla FelsiteHammat-(molasse) clasticsediments:~ Sand/siltstone,conglomerate[ - ~ Basal conglomerateF~ pre-Hammamat"basement"

early thrustlate thrust

'~ . normal fault".. Direction and\ plunge ofstretching lineation.~'x~ ~l~n~es2fs,.~ slickensides-~ on fault, ~i-~ surfaces

1Ikm

x x

X x X x >~x Xx Xx x

X x X x X x X x X x >

xXx Z~x Xx >z-: < X x X x X x X x > < x x x ;~< x ~< x x x X x ~ x x x x xx x x x x >c~>~ x ~


11/18

494against low grade meta-andesites and their pyroclasticequivalents towards the south and west along a majorshear zone (Fig. 5). This shear zone is part o f the so-calledAllaqi-Heiani Belt (Kr6ner et al., 1987), which can befollowed for over 200 km in the southern Eastern Desertof Egypt (Fig. 6 and below). Along the main shear zonethe meta-andesites are highly sheared, mylonitized andtransformed into actinolite-chlorite-epidote schists.They show a pencil-like structure and exhibit minerallineations marked by the alignment of epidotized feld-spars. Several lenticular slices of serpentinite andtalc-carbonate rock are incorporated within theseschists. They are mostly remnants of (thrust) slabs fromthe main ophiolitic ultramafic body, their trend is gene-rally N W - S E, concordant with the general trend of theshear zone. Most of the recorded stretching lineations(low angle lineations in stereonet in Fig. 6) and thekinematic criteria indicate a sense of movement witha general orientation of the top towards the north-west.In these meta-andesites of Wadi Abu Fas-Wadi Ungat(south-west corner of Fig. 5) and in the schists to thenorth, the foliation essentially strikes WN W - E SE andlocally N W - S E , generally with a dip towards thenorth-east (Fig. 5). North-westwards this trend graduallyswings towards the north-west and cuts through WadiAllaqi, Wadi Murra and Wadi Umm Rilan (Taylor et al.,1993). It continues to reach the Abu Swayel area, where itcurves back into a WNW direction. Figure 6 showsa structural compilation map based on a satellite imageinterpretation, which includes both the Gabal Muqsimand the Abu Swayel areas. From this map it becomesclear that the fault systems documented around WadiAllaqi (Taylor et al., 1993), in the Gabal Muqsim areatowards the east (Sadek, 1994) and in the Abu Swayelarea towards the north-west (e.g. E1 Shazly et al., 1977;our da ta) form a linked system of (mainly) thrusts in thecentral part with transitions towards transpressional andsinistral strike-slip systems towards the north-west andsouth-east, respectively.

Wadi Queih basinA complex structural evolution after (molasse) basinformation has also been documented in the northernEastern Desert, in the Wadi Queih area (Fig. 2). The WadiQueih basin (Fig. 7) lies between two major Red Searifting faults. Basal conglomerate mainly crops out at thenorthern margin, overlying Dokha n Volcanics, and theasymmetry of these conglomeratic deposits within thebasin suggest an e as t- west oriented half-graben geomet-ry. After emplacement of the Atalla Felsites (penecon-temporaneous with molasse sedimentation), three mainphases of defo rmation affected the basin (Abdeen et al.,1992; Table 4). In the first event, compression resul ted inthe development of essentially ea st -w es t oriented thrustsand folds, locally overturned, along the nor thern marg in.Along the southern margin, thrusts define most of thebasin margin, with the pre-H ammamat basement thrust

N

4-

OO

AN=23

0

BN=I/.

N

Fig. 8. Stereonets showing ineation orientation n the Wadi Queiharea. A Stretching lineations and orientation of long axes ofstretched pebbles. B Slickensides related to north-west directed(early) low angle hrust surfaces. C Slickensides elated o left-lateralhigh angle wrench faults. Contours at 2 - 4 - 6 - 8-10-12%

both over the Atalla Felsite and the Ha mmam at Group.These thrusts moved towards the NNW and are associat-ed with the development of a marked preferred orienta-tion in conglomeratic pebbles (Fig. 8A and 8 B). Theparallelism of the early structures with the east-westorientation of the basal conglomerates in the northsuggests that their orien tation may have been controlledby inversion of the extensional structures; a similar modelis less easy to sustain in the south, due to the lack ofprimary da ta on the basin margin orientation. These earlystructural elements are overprinted by north-west trend-ing folds and some associated north-east directed thrusts.These latter were observed by Ries et al. (1983) and


12/18

495interpreted as backthrusts synchrono us with (north) westdirected thrusts. However, the observed geometric andoverprinting relationships imply a two-phase origin forthese two sets of thrusts. In the last phase of deform ationsinistral strike-slip faulting occurred along a number ofd isc re te N W - S E to W N W - E S E o r ien ted cu rv il in earand branching subvertical faults (Figs 7 and 8 C). Thesecu t bo th the Ham mam at Group , wi th it s re la ted volcan icsuites, and the metavolcanic sequences to the south.These faults form a large posit ive f lower structure, whichis cutt ing the earlier thrust with an associated footwallsyncline . Far ther aw ay f rom the fau l t, o ther N W -S Etrending folds, probably t ip folds over blind imbricatethrusts o f the f lower structure, are developed.

DiscussionRegional structureFigure 9 shows a compilation m ap of the structural grainof the Proterozoic base ment in the Eastern De sert ofEgypt. I t shows a number of domains which can bedistinguished by their contrasting structural grain. Basedon the orientation of structures, the basement can bed iv ided , f rom nor th to sou th , in to a domain of N W - SEtrending grain (Najd trend, e.g. Stern 1985), followed byone of b road ly e as t - w es t g rain , inc lud ing the WadiHafa fit Culmination. South of the Wadi Hafafit Culmi-na t ion ano ther domain of N W -S E grain is de limi tedsouthward by the equally N W -S E t rend ing zone ofWadi Kh ar i t -W ad i Hodein . South o f th is zone andtowards the Allaqi-Heiani Belt is an area with variableo r i en ta t io n s , m a in ly ea s t - wes t an d n o r th - so u th .Whereas the N W - SE grain domains can be easily relatedto late stage Najd (transpressional) faulting (e.g. Stern,1985; Shimron, 1990; Stern et al., 1990; Hussein et al.,1992), the origin of the structural grain in the otherdomains may be more complex (Tables 2 -4) . Thesouthern area is characterized by essentially compressio-nal/ transpressional deformation and a major extensionalcollapse structure has yet to be documented, apart fromminor extensional structures at the southern margin ofthe Wadi Haf afit Culm ination (Rice et al ., 1992; Fig. 2).Possibly, north o fA bu Swayel (see Fig. 6), this compres-sional regime has ove rprinted mi no r molasse basins,which can be interpreted as extensional features. How-ever, there is no direct structural evidence of extension inthis domain. In contrast , a bund ant extensional structurescharacterize the domain in the north (see section onmolasse basins and, e.g. Stanek et al., 1993). In the areamarke d as 'extension-dominated doma in ' in Fig. 9 , exten-sional basins and metamorphic core complexes are onlyweakly affected by later deformation, whereas extensio-nal features far ther north are overprint both by reversefaulting and (transpressional) strike-slip faulting (e.g.Wadi Queih basin; see Fig. 7 and 8) .

Tectonic evolutionEarly evolutionEarly coll ision in the south of the Eastern Desert wasprobably relatively gentle (e.g. Shackleton, 1986; Millerand D ixon, 1992) and led to an accretion of a number ofterranes with only weak deformation. Alternatively,traces of a more violent coll ision may have been severelyoverprinted during the subsequent structural evolutionand are no longer readily recognizable at a regional scale,as has been found, for example, in the Wadi HafafitCulmination (e.g. E1 Rarely et al., 1993). Tables 2 and3 show local examples of pre-coll isional structures, whichoriginated in an oceanic island arc stage as they areintimately related to island arc igneous activity (e.g. E1Akha l, 1993; E1 Rar ely et al., 1984; Rash wan , 1991; seealso Miller and Dixon, 1992). Although coll ision mayhave been rather gentle, at least in the north i t wassucceeded at a bou t 600 M a ago by crustal extension(Table 1) , documented both by molasse basin formationand extensive magmatism, which was at least partlyderived from mantle sources (e.g. Stern and Gottfr ied,1986; Stern et al., 1988) and thus implies mantle uplift.This si tuation is comparable to that of late orogenicextensional collapse (Dewey, 1988) and of convectiveremoval of upper mantle l i thosphere and cons equentuplift of asthen osphe re (e.g. Moln ar et al., 1993). Bo ththese scenarios are the consequence of earlier l i thosphericthickening due to plate collisions. By inference, sucha l i thospheric thickening must have also preceded thecrusta l th inn ing in the Arab ian-Nubian Shie ld .Development of regional structuresThe post-collisional extensional stage, lasting fromabout 59 5-5 75 Ma ago (Table 1 ), was fol lowed byshortening , mainly in a N N W -S S E d i rec t ion , whichled to folding and thrusting towards NNW (e.g. WadiHafafit, Wadi Queih, Tables 2 and 4; Greiling, 1987).Although of varying intensity, traces of this shorteninghave been found in all the areas studied. Subsequently,these compressional structures were overprinted bytranspression, which is localized to particular zones, forexample the Allaqi-Heiani shear zone and the WadiKh a r i t - W ad i Ho d e in , t h e Ham isan a an d th e Na jdfault zones (Fig. 10). As is clear particularly from theHam isana shear zone this transpression in itself ispolyphase (e.g. Miller and Dixon, i992). This is consis-tent with the geometric relationship between the easternextension of the Allaqi shear zone and the Ha misa nashear zone. Figure 10 shows that the Allaqi-Heianishear zone is apparently cut by the Hamisana shearzone. No Pan-African structures younger than thoserelated to this wrench-fault ing event have been ob-served.If this evolution is interpreted in terms of orogenicprocesses, the regional compression after extension in-dicates a continuation of plate convergence and con-sequent compression/transpression after an episode of


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49 6

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K O M O M I 3 0 "6

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PHANEROZOICCOVERTIER 2--'-]PAN-AFRICANLOW GRADESUCCESSIONS,INCL.LATE OROGENICIGNEOUS ANDSEDIMENTARYROCKSTIER 1GNEISSIC UNITSEXTENSION-DOMINATED DOMAIN~ STRIKE-SLIP AULT

,~ LOW-ANGLESHEAR ZONE;f~t FOLIATION,BANDING

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33 E " ~\ ' k , \ \ ~34 ."E,F ig . 9 . S t ruc tura l compi la t ion map o f the Pan-Afr ican basement inthe Eas te rn Deser t o f Egypt , compi led f rom Figs 2 and 6 , Dixon e tal . (1987), E1 Ram ly (unpublished ma p of gneisses between 23 and25 N), E1 Ram ly an d Sallou m (1974), Egyp tian Geol ogical Survey(1981), Gre iling et al. (1988 b), Hassa n and H ash ad (1990), Huss einet al. (1992) a nd Tehr ani et al. (1988). Mo st o f the tier 1 gneissic units

in ~che north ern part of the map a rea for m structu ral culm inations,whereas a num ber o f gnei ssic uni t s in the sou th fo rm fau l t -boundedslices or horsts , im bricated in to t ier 2 low grade successions. Fo r thesake of clari ty the t ier 1 gneisses are shown without their internalstructural grain, which is usually discontinuous across the marginsand mo re complex than tha t o f the sur rounding t i e r 2 .


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- 26ON

"Barramiya

22N ' ~ U t u r e

0 50 100I r /km33OE 34OE

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Fig . 10. Tec ton ic ske tch map o f the Ara b i an -N ub ian Shie ld ineastern Egypt, s implif ied from Fig. 9 and extend ed southw ard toinc lude the Hamisa na shear zone ( f rom Dixon e t a l ., 1987; Kr6ner e ta l ., 1987) . The s in i s tra l Wadi Kh ar i t - W adi Hode in shear zone mayhave connec ted the - pe rhaps once con t inuous - Al laq i and SouthHafaf i t su tures (be fore be ing overpr in ted by the Hamisana shearzone?) . Poss ib le corre la t ives ac ross the Wadi Kh ar i t -W ad i Hode inZone m ay be the t ier 1 gneisses to the nor th of the sutures (darkpattern) , s tructu ral ly overlying ophioli t ic nappes (cross-hatched)and the late tectonic granites (G, crosses). Res torat io n of about300 km of s in is t ral d i sp lacement a long the Wadi Kh ar i t - W ad iHode in Zone ma y br ing toge ther the ophio l i t e remnants o f theGaba l Ger fand Bar ramiya nappes and the l ate t ec ton ic g ran ites nearAswan and in the north-eastern Desert and l ink the sutures ina g e n er a l W N W - E S E t r e nd

extensional collapse of the Pan-African orogen. In ge-neral terms, this example shows that extensional collapse(Dewey, 1988) is not necessarily the final stage oforogeny, but is one episode in the complex evolutionof mountain belts and the l i thosphere as a whole.

497Potential sutures and terrane marginsAs is clear from the structural evolution outlined ab ove,potential ' sutures' and terrane margins were overprintedintensely by post-coll isional deform ation. Consequently,the most obvious, late orogenic shear zones cannota pr ior i be correlated with terrane margins (see discussionin Church, 1988; Miller and Dixon, 1992) A morereliable means of identifying terrane margins is the com-bination of a numbe r of cri ter ia that d ocum ent terranemargins, for example a destructive plate margin withtraces of accretionary prism and forearc basins, subduc-t ion- re la ted h igh pressure- low tempera ture metamor-phic assemblages and a diagnostic sequence of island arcrelated igneous rocks in the hangingwall of the (former)subduction zone. At present at least two such terranemargins can be identif ied in the Eastern D esert of Egyptwith reasonably reliabil i ty: the Wadi Ghadir assemblagerelated to a 'South Ha fafit suture ' to the south of the WadiHafafit island are terrane and the 'Allaqui suture ' to thesouth-east o f lake Nasser (see Fig. 10): The Wadi G hadirassemblage combines sedimentological and structuralfeatures of an accretiona ry prism and an igneous sequen-ce of calc-alkaline mafic to felsic intrusives, which istypical of island arcs (e.g. E1 Sha rkaw y and E1 Bay oum i,1979; E1 Bayoumi et al., 1983; E1 Bayoumi, 1984; E1Bay oum i and Greiling, 1984; E1 Alkh al and Greiling,1987; El Akhal, 1993) and thus documents its palaeotec-tonic si tuation at an d/or above a destructive plate margin.The Allaqi suture may be the f irst where high pressure-low temperature metamorphic assemblages have beenobserved in the Eastern Desert of Egypt (Taylor et al . ,1993). These asse mblages oc cur in the footwa ll of the (eastto north-east dipping) Allaqi shear zone (Fig. 6), togetherwith island arc volcanics and marbles In the hangingwallof this shear zon e, relatively high grade gneisses representthe uplifted and/o r thrusted parts o f lower ( island arc)crust. This situation m ay imply the (simplistic) interpreta-t ion that the gneisses were obducted towards the WSWduring the final stage of collision and overridin g thesubduction-related high pressure rock assemblages.However, due to intense post-coll ision/accretion defor-mation (see Table 3) it is not yet clear whether the Allaqishear zone represents the original suture or a more or lessunrelated later structure. As defined earlier, the terrane tothe south of the Allaqi suture is called the Gabgabaterrane (K r6ner et al. , 1987) and co mpo sed essentially ofPan-African island arc associations The Gabgaba terra-ne is dist inct from the 'Asw an terrane' to the north of theAllaqi suture by the occurrence of marbles, which prob -ably represent shallow water carbonates fr inging islandarcs. The Aswan terrane as defined in Fig. 10 representsthe western part of the Gerf terrane of Kr6ner et al . (1987)and is comp osed of ensimatic island arcs, ophioli tenappes (e.g.G. Mu qsim, Fig. 5; Ge rfN app e, Fig. 10) andlate tectonic granitoids. The Aswan terrane is boundedtowards the nor th-east by a N W -S E t rending s in ist ra lshear zon e which w as identified earlier (e.g. E1 Ga by et al.,1988; Shimron, 1990; Stern et. al., 1990) and is called here


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498the Wadi Kh ar it - Wadi Hodein zone (Fig. 10). The WadiKharit-Wadi Hodein zone is interpreted as an equivalentof the Najd Fault zone farther north, in the northern partof the Central Eastern Desert (e.g. E1 Gaby et al., 1988;Shimron, 1990; Stern et al., 1990) and as the youngestmajor structural element in the Eastern Desert (e.g. Stern,1985). Such a relationship is supported by structuralevidence in the Wadi Queih area (Table 4) of the Najdfault zone bu t there is as yet no conclusive evidence fromthe Wadi Kha rit -W ad i Hodein zone.The importance of this shear zone, however, and itssinistral displacement sense are clear from the map byHussein et al. (1992). Consequently, the domain to thenorth-east of the Wadi Kharit-Hodein shear zonerestores towards the south-east and probably to the southof the (eastward continuation of the) Allaqi suture.Therefore, this domain is probably no t part of the Aswanterrane. (This distinction was not known when the Gerfterrane was defined as covering the whole of south-eastern Egypt (Kr6ner et al., 1987) and to avoid confu-sion, the term Gerf terrane is not used here.) As a furthe rconsequence of the sinistral sense of the Wadi Kharit-Wadi Hodein shear zone, the South Hafafit suturerestores to the south-east, perhaps as far as to form theeastward continuation of the Allaqi suture. In that case,the Aswan terrane is the equivalent and westward conti-nuation of the 'Hafafit terrane' and the terrane to thesouth of the South Hafafit suture, perhaps extending asfar south as the Onib-Sol Hamed Belt, is an equivalent ofthe Gabgaba terrane (Fig. 10). Such a restoration impliesa lateral transport distance of at least 300 km, a figurethat is comparable with those o f late tectonic strike-slipdeformation in Phanerozoic fold belts (e.g. Ratschbacheret al., 1991 ; Soper et al., 1992). The re storation implies thehuge Gabal Gerf ophiolite nappe to be an equivalent ofthe equally extensive Barramyia 'nappe' of ophioliticfragments in the central Eastern Desert. Following theresults of Hussein et al. (1992), the extensive ultrama-fic/mafic associations to the south-west of Baranis andnorth-east of the Wadi Khar it -Wa di Hodein zone arepost-ophiolitic intrusives and no t ophiolite fragments assuggested by Shackleton et al. (1980), amongst others.Consequently, these intrusives may not be the northwardextension of the Gabal Ger f ophiolite nappe. Finally, thevast domains of late tectonic granites in the Aswan are/tmay be the equivalents of the late tectonic granites whichdominate the northern part of the Eastern Desert(Fig. 10). Lithological similarities between bot of thesegranites (Klitzsch et al., 1987) support such a model.However, further structural information is required, forexample on the relationships between the Wadi Kha-rit-- Wadi Hodein Zone and the Hamisana shear zone, totest the proposed restoration.Correlations towards the east, across the Red Sea, areextremely difficult (see Kr6ner et al., 1987; Church, 1988;Vail, 1988; Shimron, 1990; Stern et al., 1990). Potentialcandidates for the eastward continuation of the SouthHafaf it suture may be the Jabal Ess ophiolite towards thenorth-eas t in Arabia (Church, 1988), or ophiolites in Sinai

and north-westernmost Saudi Arabia, if latest Protero-zoic transcurrent faulting along the Red Sea is assumed(Shimron, 1990). Correlations towards the Sudan aresimilary problematic, due to intense overprinting of thesutures (e.g. Miller and Dixon, 1992; Abdelsa!am andStern, 1993). As the Allaqi suture at the northe rn bound-ary of the Gabga ba terrane trends towards the north-westat its western limit of exposure, it is unlikely to join upwith the newly discovered Atmur-Delgo suture in thesouth-west (Schandelmeier et al., 1993).

Phanerozoic reactivation of Proterozoic structuresThe extent and distribution of the Phanerozoic cover asshown in Figs 9 and 10 gives some indi cati on of thepotential reactivation of Pan-African structures. Mostobvious and discussed earlier are the reactivated portionsof the Najd Fault zone and the related Wadi Kha-rit-Wadi Hodein zone (e.g. Stern, 1985; El Gaby et al.,1988; Greiling et al., 1988b). There, high angle Pan-African fault zones were reactived during late Mesozoicand Cenozic Red Sea tectonics, probably due to theirfavourable ori entation during transtension between Afri-ca and Arabia in a position of Riedel shears. High anglenormal faulting parallel to the present Red Sea coast andassociated reactivation of fault surfaces of appropriateorientation may be related to footwall uplift of Red Seamarginal faults and may have led to a horst-like structureof the Pan-African basement in eastern Egypt (e.g.Egyptian Geological Survey, 1981; Klitzsch et al., 1987;Greiling et al., 1988 b). In con tras t with the reactivation ofhigh angle faults, low angle fault zones appear to be lessaffected by Phanerozoic tectonics, apart from small scalereactivation near the Red Sea coast (e.g. Greiling et al.,1988 b).

ConclusionsA comprehensive review of structures in the Pan-Africanbasement of the Eastern Desert of Egypt revealed theregional structure to be due to post-collisional structuralevents, which affected the area to various degrees.Features of extensional collapse dominate some domainsin the north, whereas other domains acquired theirdominant structural grain during subsequent phasesof compression and (late) transpression, respectively.The latter are characterized by a NW-- SE trend, relatedto Najd faulting. The post-collisional tectonic evolutionstarted with extensional collapse (at least in the north),which was followed by NN W - SS E shortening andrelated large-scale thrusting (towards the NNW) andfolding, distibuted all over the Eastern Desert, alt houghwith variable intensity. Subsequent transpression waslocalized to particular shear zones. Early transpressionproduced, for example, the Allaqi shear zone (Allaqi-Heinai Belt) and final transpression is documented inthe Najd and Wadi Kharit-Wadi Hodein zones. The


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49 9e x t e n s i o n a l c o l l a p s e p r o b a b l y o c c u r r e d w i t h i n a r e la t i v e lyn a r r o w t i m e sp a n o f a b o u t 2 0 M a ( 5 7 5 - 5 9 5 M a a g o )a l l o v e r t h e E a s t e r n D e s e r t a n d w a s f o l l o w e d b y a f u r t h e rp e r i o d o f a b o u t 5 0 M a o f la t e to p o s t - t e c t o n i c a c t i v it y .F i g u r e 1 0 s h o w s a t e c t o n i c i n t e r p r e t a t i o n o f t h e N u b i a nS h i e l d i n E a s t e r n E g y p t w i t h p o t e n t i a l s u t u re s a n dt e r r a n e m a r g i n s . B a s e d o n a n u m b e r o f c r i te r i a, s u c ha s d e e p - s e a t r e n c h , f o r e a r c a n d a r c s e d i m e n t a r y , i g n e o u sa n d m e t a m o r p h i c s e q u e n c e s , tw o s u t u r e s c a n b e d e fi n e d ,t h e A l l a q i a n d S o u t h H a f a f i t S u t u r e s , r e s p e c t iv e l y . B o t ht h e s e s u t u r e s a r e a p p a r e n t l y l i n k e d b y a h i g h a n g l es i n is t ra l s t r i k e - s l i p s h e a r z o n e ( W a d i K h a r i t - W a d i H o -d e i n ) w i t h a te c t o n i c t r a n s p o r t o f a b o u t 3 0 0 k m t o w a r d st h e W / N W ( F i g . 1 0) . A s a c o n s e q u e n c e , t h e G a b a lG e r f N a p p e o f u l t r a m a f i c ro c k s a n d o p h i o l i t e r e m n a n t sm a y l in k w i t h th e B a r r a m y i a ' n a p p e ' c o m p l e x a n dt h e l a te t e c t o n i c g r a n i t e s a t A s w a n m a y l i n k w i t ht h o s e in n o r t h e r n E g y p t .

I n g e n e r a l , th e t e c t o n i c e v o l u t i o n s h o w s t h a t e x t e n s io -n a l c o l l a p s e i s n o t n e c e s s a r i l y th e f i n a l s ta g e o f o r o g e n yb u t m a y b e f o l l o w e d b y f u r th e r c o m p r e s s i o n a l a n dt r a n s p r e s s i o n a l t e c to n i s m . D u r i n g t h e P h a n e r o z o i c e v o -l u t io n , t h e l a te P a n - A f r i c a n h i g h a n g l e f a u l ts w e r er e a c t i v a t e d d u r i n g R e d S e a te c t o n i c s b o t h a s R i e d e ls h e a r s a n d n o r m a l f a u l t s , a l b e i t o n l y w h e r e t h e y w e r eo r i e n t e d f a v o u r a b l y w i t h r e s p e c t t o t h e a c t u a l s t re s sr e g i m e .Acknowledgements Thi s pape r pr esent s some of t he r esul t s ofa c o - o p e r a t i o n p r o je c t b e tw e e n E G S M A a n d G e o l o g i sc h - P a l f io n t o l o -g i sc h e s I n s t i tu t , R u p r e c h t - K a r l s - U n i v e r s i t y H e i d e l b e rg , w h i c h i sf u n d e d b y B M F T , t h r o u g h F o r s c h u n g s z e n t r u m J / il ic h , I n t e r n a t i o n a lB u r e a u . S a t e l l it e i m a g e s u s e d f o r t h i s w o r k w e r e a l s o f u n d e d b y t h ep r o j e c t a n d p r o c e s s e d a t I n s t i t u t f f i r G e o l o g i e , G e o p h y s i k u n dG e o i n f o r m a t i k , F U B e r l in ; P r o f e s so r F . K . L i s t. M . M . A b d e e n w a sal so funded by a s cholar ship f rom G raduier t enf6rderung, Univer s i t y ofH e i d e l b e r g , G . M . K a m a l E1 D i n b y a s c h o l a r s h i p f r o m t h e E g y p t i a nG o v e r n m e n t ( p o s t g r a d u a t e m i s s i o n st u d e n t o f A s s i u t U n i v e r s it y ) ,A s s i u t a n d A . F . O s m a n b y t h e G e r m a n A c a d e m i c E x c h a n g e S er vi ce( D A A D ) . W e t h a n k a l l t h e s e in s t i t u ti o n s f o r t h e ir s u p p o r t . T h i s w o r kal so benef i ted f rom di scus sions wi th num erous col l eagues n Eg ypt andG e r m a n y , i n p a r ti c u l a r G . M . N a i m a n d A . A . H u s s e in ( E G S M A ) , S .E 1 G a b y ( A s s i u t U n i v e r s i ty ) , M . E . H i l m y , A . I . R a g a b ( A i n S h a m sU n i v e r s it y , C a i r o ) , p a r t i c i p a n t s o f M a r s a 'A l a m W o r k s h o p 1 9 9 3 , E K .Li s t (F U Ber l in) , G . M athei s (TU Ber lin), K . -R Stanek (T U Fre iberg) .E x t e n s iv e r e v ie w s a n d h e l p f u l su g g e s t io n s f o r t h e i m p r o v e m e n t o f t h ep a p e r b y A . K r 6 n e r ( M a i n z ) , A . E . S h i m r o n ( J e r u s al e m ) a n d W . E . G .T a y l o r ( L u t o n ) a r e g r a t e f u ll y a c k n o w l e d g e d .

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A k a a d M K , E 1 R a m l y M F ( 19 5 8) S e v e n n e w o c c u r r e n c e s o f th e I g l aF o r m a t i o n i n t h e E a s e r n D e s e r t o f E g y p t . G e o l S u r v M i n R e sD e p t P a p 3 : 1 - 3 7A k a a d M K , E 1 R a m l y M F ( 19 6 3) G e o l o g y a n d s t r u c t u re o f th eU m m L a s s a f - - U m m N a r i r o n b e l t ( E a s t e r n D e s e r t o f E g y p t ) .G e o l Su rv M i n R e s D e p t P a p 1 7 : 1 - 2 3B e n n e t t J D , M o s l e y P N ( 19 8 7) T i e r e d - t e c t o n i c s a n d e v o l u t i o n ,E D e s e r t a n d S i n a i , E g y p t . I n : M a t h e i s G , S c h a n d e l m e i e r H ( e d s )C u r r e n t R e s e a r c h i n A f r i c a n E a r t h S c i e n c e s . B a l k e m a , R o t t e r -d a m , p p 7 9 - 8 2B e y t h M , S t e r n R J , A l t h e r r R , K r 6 n e r A ( 19 8 4 ) T h e L a t e P r e c a m -b r i a n T i m n a i g n e o u s c o m p l e x , S o u t h e r n I s r a e l : e v i d e n c e f o rc o m a g m a t i c - t y p e s a n u k i t o i d m o n z o d i o r i t e a n d a l k a l i g r a n it em a g m a . L i t h o s 31 : 1 0 3 - 1 2 4C h u r c h W R ( 19 8 8 ) O p h i o l it e s , su t u r e s, a n d m i c r o - p l a t e s o f th eA r a b i a n - N u b i a n S h i e ld : a cr it ic a l c o m m e n t . I n : E 1 G a b y S ,G r e i l i n g R O ( e d s) T h e P a n - A f r i c a n B e l t o f N o r t h e a s t A f r i c a a n dA d j a c e n t A r e a s . F r i e d r V ie w e g S o h n , B r a u n s c h w e i g / W i e s b a d e n ,p p 2 8 9 - 3 1 6D e w e y J F ( 1 9 8 8 ) E x t e n s i o n a l c o l l a p s e o f o r o g e n s . T e c t o n i c s 7 :1 1 2 3 - 1 1 3 9D e w e y J F , R y a n P D , A n d e r s e n T B ( 1 9 9 3 ) O r o g e n i c u p l i f t a n dc o l l a p se , c r u s ta l t h i c k n e s s, f a b r ic s a n d m e t a m o r p h i c p h a s e c h a n -g e s : t h e r o l e o f e c l o g it e s. I n : P r i c h a r d H M , A l a b a s t e r T , H a r r i sN B W , N e a r y C R ( e d s ) M a g m a t i c P r o c e s s e s a n d P l a t e T e c to n ic s.S p ec P u b l G e o l S o c L o n d o n 7 6 : 3 2 5 - 3 4 3D i x o n T H , S t e r n R J , H u s s e i n I M ( 19 8 7 ) C o n t r o l o f R e d - S e a r if tg e o m e t r y b y P r e c a m b r i a n s t ru c t u r e s. T e c t o n ic s 6 : 5 5 1 - 5 7 1E g y p t i a n G e o l o g i c a l S u r v e y ( 19 8 1) G e o l o g i c M a p o f E g y p t .1 : 2 .000.000. Egy pt i an G eolog ica l Survey, Ca i roE1 Ak hal H (1993) A t r ansect f rom a t ec tonic m61a nge to ani s l a n d - a r c i n t h e P a n - A f r i c a n o f S E E g y p t ( W a d i G h a d i r a r e a ) . S c iSer In t Bur 20: 1 - 244E 1 A k h a l H , G r e i l i n g R O ( 19 8 7 ) A s e c t io n t h r o u g h a L a t eP r o t e r o z o i c f o r e -a r c d o m a i n f r o m t h e E a s t e r n D e s e r t o f E g y p t .T e r ra C o g n i t a 7 : 1 5 0E 1 B a y o u m i R M ( 19 8 4 ) O p h i o l i te s a n d m + l an g e c o m p l e x o f W a d iG h a d i r a r e a , E a s t e r n D e s e r t , E g y p t . B u l l F a c E a r t h S c i K i n gA b d u l a z i z U n i v . 6: 3 2 9 - 3 4 2

E 1 B a y o u m i R M A , G r e i l i n g R O ( 19 8 4) T e c t o n ic e v o l u t io n o fa P a n - A f r i c a n p l a t e m a r g i n i n s o u t h e a s te r n E g y p t - - A s u t u r e z o n eo v e r p r i n t e d b y l o w - a n g l e th r u s t in g . I n : K l e r k x J , M i c h o t J ( e d s)A f r i c a n G e o l o g y . M u s R o y A f r C e n t T e r v u r e n B e l g p p 4 7 - 5 6E l B a y o u m i R M , E 1 R a r e l y M F , G r e i l i n g R , K r 6 n e r A , S h a l a b y I M( 1 9 8 3 ) G u i d e - b o o k f o r a n e x c u r s i o n t o t h e E a s t e r n D e s e r t o fE g y p t . N e w s l P a n A f r i c a n C r u s t a l E v o l u t i o n i n t h e A r a -b i a n - N u b i a n S h ie ld 5 : 6 2 - 1 0 5E l G a b y S . G e o l o g i c a n d t e c t o n ic f r a m e w o r k o f t h e P a n - A f r i c a no r o g e n i c b e l t i n E g y p t . I n : S a d e k A ( e d ) P r o c 2 n d l n t C o n f o nG e o l o g y o f t h e A r a b W o r l d . C a i r o , in p r e s sE l G a b y S , L i s t F K , T e h r a n i R ( 19 8 8) G e o l o g y , E v o l u t i o n a n dm e t a l l o g e n e s is o f t h e P a n A f r i c a n b e l t in E g y p t . I n : E 1 G a b y S ,G r e i l i n g R O ( e d s) T h e P a n - A f r i c a n B e l t o f N o r t h e a s t A f r i c a a n dA d j a c e n t A r e a s . V i ew e g & S o h n , B r a u n s c h w e i g / W i e s b a d e n ,p p 1 7 - 6 8E l G a b y S , L i st F K , T e h r a n i R ( 19 9 0 ) T h e b a s e m e n t c o m p l e x o f t h eE a s t e r n D e s e r t a n d S i n a i. I n : S a i d R ( e d ) T h e G e o l o g y o f E g y p t .B a l k e m a , R o t t e r d a m , p p 1 7 5 - 1 8 4E 1 R a r e l y M F ( 19 7 2 ) A n e w g e o l o g i c a l m a p f o r t h e b a s e m e n t r o c k sin the Eas t ern and Sou th-We s tern Deser t s of Egyp t . 1 : 1 .000.000.A n n G e o l S u rv E g y p t 2 : 1 - 1 8E 1 R a r e l y M F , S a l l o u m G J ( 19 7 4 ) T h e t e c t o n i c r e g i o n i n g o f t h eb a s e m e n t r o c k s o f t h e E a s t e r n D e s e r t o f E g y p t , A c t a M i n e r a lP e t r o g r S z e g e d 21 : 1 7 3 - 1 8 1E 1 R a m l y M F , G r e i l i n g R , K r 6 n e r A , R a s h w a n A A ( 19 9 4 ) O n t h et e c t o n i c e v o l u t i o n o f t h e W a d i H a f a f i t a r e a a n d e n v i r o n s , E a s t e rnD e s e r t o f E g y p t . B u l l F a c E a r t h S c i K i n g A b d u l a z i z U n i v 6 :1 1 3 - 1 2 6E 1 R a m l y M F , G r e i l in g R O , R a s h w a n A A , R a s m y A H (1 9 93 )E x p l a n a t o r y n o t e t o a c c o m p a n y t h e g e o l o g i c a l a n d s t r u c tu r a l


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500maps of Wadi Hafafit area, Eastern Desert of Egypt. Geol SurvEgypt Pap 68: 1 - 53E1 Sharkawy MA, E1 Bayoumi RM (1979) The ophiolites of WadiGhadir area, Eastern Desert, Egypt. A nn Geol Surv Egypt 9:125-135E1 Shazly EM, Bassyoumi FA, Abdel Khalelk ML (1977) Geologyof the Greater Abu Swayel Area, Eastern Desert Egypt. EgyptJ Geol 19: 1-4 1

Greiling RO (1987) Directions of Pan-African thrusting in theEastern Desert of Egypt derived from linea tion and strain data.In: Matheis G, Schandelmeier H (eds) Current Research inAfrican Earth Sciences. Balkema, Rotterdam, pp 83 -8 6Greiling RO, E1 Ramly MF (1990) Wadi Hafafit area. Map,structural geology, 1 : 100.000. TFH, BerlinGreiling RO, Rashwan AA. Large-scale

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