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Journal o f t h e Geological Society, London, Vol. 144, 1987,pp. 569-575, 4 figs, 2 tables. Printed in Northern Ireland

Age of Feiran basement rocks, Sinai: implications for late Precambrian crustalevolution in the northern Arabian-Nubian Shield

R. J . STERN & W . I . MANTONPrograms in Geosciences, The University of Texas at Dallas, Box 688, Richardson, Texas 75083-0688,USA

Abstrart: Basement exposed on th e perimeter of the Red Sea was created during he Pan-Africanevent at the end of the Precambrian. Pre-Pan-Africancrust in the northern part of this region has notyet been identified. This paper reports the results of Rb-Sr whole-rock and U-Pb zircon dating ofgneisses and related basement units from the Wadi Feiran area in th e Sinai peninsula, where heexistence of such older basement has previously been suggested. A post-tectonic extensional dykegives a Rb-Sr age of 591f Ma with an initial s7Sr/86Sr ratio f 0.7034f .0002. Rb-Sr whole-rockan d thin slab dating of paragneisses gives ages of c. 610 M a with an initial s7Sr/86Srratio of 0.7035. AU-Pb zircon ag e of 632 f Ma is interpreted as either the time of formation of these gneisses or theage of the crust sampled by protolith sediments. Granodiorite to th e east gives a U-Pb zircon age of782f M a and is interpreted as representing the westernmost extent of a 780 f 0 Ma terrane thatextends across Sinai into Jordan. Uplift and erosion of the 780 f 0 Ma terrane supplied detritus toflanking terranes in N and SE Sinai. This region thus acted as a foreland to the younger accretionaryand extensional units to the south and west that were active later in the Pan-African event. There isstill no evidence fo r pre-Pan-African basement in the Precambrian units around the northern Red Seaeast of the Nile.

Formation of the continental crust of N E Africa and Arabiaoccurredduring heend of th ePrecambrian (450-950MaPan-AfricanEvent of Kroner1984), argelymanifestingatelescopederie s of islandrcs,marginalasins, andaccreted terranes (e.g. Gass 1977; Kroner 1985). One of themost remarkable aspects of this episode of crust formation isth eppare nt lack of involvement of pre-Pan-Africancontinental crust, especially in the basement exp osed east ofth eiver Nile. Th ere is no directvidenceha twell-defined tabilized oreland xisted nyw heren thisregion, and the re is a paucity of igneous rocks with isotopicsignatures indicating the meltingof such crust . An importantexception to this generalization is the c. 1.6 G a Afif Terra nein the S Arabian Shield (Stacey & Hedg e 1984). Even thismay not represent a pre-Pan-A frican foreland, becaus e it isflanked east nd westbywide xpanses of Pan-Africanigneous rocks and so may b e an exotic terrane (Stoeser &Camp1985). t is suggested that c. 0.9-1.2 Ga crustmayexist in the s outhern part of the E astern Dese rt of Egypt (ElShazly et al. 1973; El Manharawy 1977 in Cahen et al. 1984).Thesenferencesreasednwhole-rockRb-Srgedeterminations hateither showa arge degree of scatterarou nd he regression line (El Shazly et al. 1973) or a reunpublished nd navailableElManharaw y 977).W esuspect hat c . 1 lGa crust does exist in the Ab u Swayelarea (El Shazly et al. 1973) but these ages need confirmationby U-Pb zircon studies. Th e presence of 1.1-2.3 Ga cobblesof granodiorite,uartzite,ndarble in theatePrecambrian Atud Conglomerate of the Eastern Desert ofEgypt indicates that a much older foreland mus t have beennearby Dixon1981),andprobably ay ustwest of th epresent NileSchandelmeir et al .nress).Withheexception of Archean basement at Uweinat, 1000 km westof the principal Pan-African exposures (Klerkx & Deutsch1977), this foreland has not b een found in situ.

Our ignoranceegardingheelationshipetween

Pan-Africanan dolderunitssevere ly limits our ability torecons truct this regions tectonic evolution accurately. O neplace to lookfo rpre-Pan-Africanbasement is amo ng hegneissic ocks of Afro-Arabia. t is imp ortan t o know ifthese gneissic terran es re significantly olderhanhesurroundinggreenschist-faciesophiolitic and rcmaterialand so may have represented a continental foreland duringthe Pan-African orogenies, or if these erranes are simplymetamorphosed equivalents of the lower grad e rocks. Thisproblemwas first addressed in studies of th eEgyptianbasem ent, where gneisses are principally exposed in threeareas (Fig. 1): (1)Sinai, ypified by theareadrained byWadi Feiran; 2)CentralEasternDe sert typified by therocks of Meatiqome;nd3)Eesert,nereprese ntative of which is the gn eissic terrane surroun dingGeb els Migif and H afafit.Earliernvestigators onsideredhese neisses to bepalimpsests 01 much older continenta l crust (Hum e 1934).Schiirmann (1966) grouped he Egyptia n gneisses into heMitiq Series which he inte rpreted to underlie (beneath oneor moreunconformities) heyoungerand less metamor-phosed parts of the basemen t. Subse quent studies have notsupportedhesenterpretations . turchio et al .1983a)interpreted the Meatiq Dom e gneisses to have formed fromshearedndecrystallized felsic igneou socks t 580-625 M a accompanying th e develop ment of a metamorphiccoreomplex.ow initial 87Sr/86Sr (c. 0.7030) wasinterpreted to indicate a lack of remelted older continentalcrust Sturchio et al. 19836).Gneisses romhe Migif-Hafafit areaaveore complexistory.levendeformational and five igneous events have been observed(Elbayoumi & Greiling984).yntectoniconaliteintruded into the gneisses has a U-Pb zircon age of 682 Maandan initial s7Sr/86Sr of 0.7024 (Stern & Hedge 1985).Metasedimentsand oliatedgranites rom he egion givevalues of cN d at 750 Ma ago) of +6.6 and +5 .4 (Har r is t al.

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281

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R .J .S T E R N & W . I . M A N T O N

1984), aurtherndicationha tre-laterecambriancontinentalrust was not involved in generatingheMigif-Hafafit gneisses.The neisses of Wad iFeiranepresent n xcellentopportunity to investigate further the origin of Pan-Africanhigh gradeerranes.This aper eports our ;efforts todetermine the t imingof the principal crust-forming eventsnth eFeiranareaan dpresents our interpretation of theirsignificance forecipheringat erecambrianrustalevolution in N Afro-Arabia.

Fig. 1. Locality map of NE Africa, Sinai, andNWArabia, modified to show the distributionofbasement terranes prior to openingf the Red Seaand Gulf of Suez. Also shown are the location fgneisses and associated high-grade rocks andserpentinized ultramafics. Reconstruction includes110 km translation a long the Dead Sea-Gulf fAqaba strike slip system and 30m closure of theGulf of Suez (Freund et a l. 1970). The designation ofbasement province boundaries in the Eastern Desertof Egypt are those of Stern & Hedge (1985);designation of basem ent province V, Sinai, is a newresult. Sources for the geological compilation are asfollows: Eastern Desertof Egypt, El-Ramly 1972;Sinai, Eyalet a l. 1980; Jordan, Bender, 1974; NWArabia, Johnson, 1983; Clark, 1985. Abbreviationsfor regions discussed in the text are as follows:M-H, Migif-Hafafit; MD, Meatiq Dome; F, Feiran;JE, Jebel Ess ophiolite; AW,AI Wask ophiolite; K,Wadi Kid; S , Sa'al. Also shown are the ages andlocations of more reliable whole-rockRb-Sr, U-Pb zircon, o r Sm-Nd dates with agesgreater than 700 Ma. Sources of geochronologicaldata: Hashad er al. 1972; Halpern& Tristan 1981;Dixon 1981; Bielski 1982; arrar er al. 1983;Claesson et al. 1984; Hedge 1984;Stem & Hedge1985; present study.

Geological setting and previous workTheFeiran gneisses are ocatednear he NW corner ofexposed asement in SinaiFig. ).The neissesndassociatedsynorogenicgranodioritesar ebracketed to henorthan dsouth by post-orogenicgranites (Fig. 2), datedelsew here in Sinai and Egyp t at 570-600Ma (Bielski et al .1979; Halpern 1980; Fullagar 1980; Halpe rn & Tristan 1981;Stern & Hedge 1985). El Gaby & Ahm ed (1980) interpretedth eeiran gneisses toepresen t thick (X 0 00 m)

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A G E OF F E I R A N B A S E M E N T ,S I N A I33'40'F

571

.28"46'30"N

?8'36'08"NFig. 2. Geological mapof the area around Wadi Feiran, modified after El-GabyAhmed (1980), showing the distributionf samplesanalysed here along with the approximate location of the suite analysed by Bielski (1982).sedimentary succession, with minor mafic intercalations,that was foldedntohreeNW - SErending anticlinesoverturned to the west and separated by NW-SE trendingthrust faults.Previousnvestigatorsav eonsidered theeirangneisses to be of pre-Pan-Africanage Schurmann1966;Shimron1980). Shim ron (1980) argued hat he gneissesform ed prior to 1100 Ma largely on the basis of unpublishedgeochronological data . Bielski (1982) report ed Rb-Srwhole rock age of 643 f 41 Ma and an initial 87Sr/86Sr ratioof 0.7032 f 0.0007 for five sam ples of gneiss collected w ithinthe present study area. The gneisses are f lanked to the eastby an extensive ody of foliated ranodiorite nd redissected by abundant N30"E trendingimodalykes(Voegeli985). Theatterostdate allompressionaldeformationndre manifestations of lateegionalextension (Stem 1985).Analy t ica l techniquesSamples for Rb-Srwhole-rock eochronologywere rocessedaccording to standard procedures, including cleaning, crushing, andcolumn separation. Rb and Sr were analysed by isotope dilution onthe UTD 6 - and 12"-radius solid source mass spectrometers. Totalprocessing blanks are S 3 ng Sr and 0.1 ng R b. Age regressionswere carried out using the Yo rk I1 treatment of data (York 1969)and ll ncertainties re 2a. Samples ontaining irconswerecrushed, sized, and he nonmagnetic zircons isolated. These werecleaned byoilingnHNO,ndHCleforeissolutionnKrogh-type bombs. Total processing blanks for Pb are 0.5-1.0 "g.Analyseswere arried out on he UTD 12"-radius nstrument.

Regression calculations o concordia are hose ofLudwig(1980);uncerta inties are at the 95% confidence level. A lower intercept of15f 0 Ma was forced; the justificationor this procedurefor datingrocks in the Arabian Shield has been presented elsewhere (Staceytal. 1984).ResultsTh e location of the four suites studied here along with thatof the suite analysed by Bielski (1982) are show n in Fig. 2.analyticalesults are listednTables 1 and 2 and representedn Figs 3 nd 4. Th e Rb-Sr results will bediscussed first.The ate dykeswarms are epresented by 10 samples,ED-1B to12B , ake n rom a ingle ompositebasalt-rhyolite dyke (Voegeli 1985). These give an excellent spreadin 87Rb/86Sr, defining an age of 59 1 f 9 Ma and an initial87Sr/86Sr atio of 0.70 34 f0. 00 02 (Fig. 3a). The MS WD of1.8 is less than the F-va riate of 2.02, so this is an isochronage, taken to represent the t ime of emplac emen t of this andother NE-trending dykes in the region.Eight samples of hornblende-biotite quartzo-feldspathicgneiss were collected from outcropsseparate d by a otaldistance of no more than 400 m. These rocks were mapp edas metasediments by El Gab y & Ahm ed (1980); we describethese as paragneisses in th e field. T he eight points define aregression ine with an age of 614 f 27 Ma a nd an initial%r/%Sr ratio of 0.703 4f0. 000 3 (Fig. 3b). The MSW D of4.7 is significantlyigherhan the F-variate of 2.18,indicating that this is not an isochron. Nevertheless, the lowintercept and m oderate deg ree of scatter indicate this age is

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572 R . J . S T E R N & W . I . M A N T O NTable 1. R b , Sr , and s7Sr/ssSr data

Rb (ppm) Sr (ppm) 87Rb/S6Sr 87Sr/ssSr'1. D y k eED-1B3B4B6B7B8B9B10B11B12B2. Gnei ssE-210AZADAL210B210c210D210E

210F210G210H

78.781.410116418418216610278.476.335.563.118.480.853.436.219.416.846.082.13. Single samplesE-210eg.36207G6.5 213

699.326 639.368 518.564 35.04.05 27.20.38 16.24.19 22.12.46 573.515 687.330 672.328342.283 326 0.560346.154 309.757 395.391 393.267 407.138313.155 466.286 482.492161.44 358.295 299.718

0.70597f0.70639 f0.70819f0.82307f 130.87689f0.99169f 00.88791f 30.70765f0.70620f0.70631 f0.70606f0.70862f0.70506 f0.71000 f0.70677 f0.70587f0.70445f0.70518f 00.70595 f0.70775 f 110.72430 f0.70654 f0.71139 f

87Sr/86Srnormalized to E + A SrCO, 87Sr/ssSr= 0.70800.'E-210A, 210AD, and 210AL are whole rock, dark ayers, andlight layers, respectively, of sample E-210A.probably close to he rue age; whethe r variablenitial87Sr/86Sr ormetamorphicdisturbancesare responsible orthe scatter is not clear. Analyses of adjacent 5-cm-thick lightanddark ayers rom E-210AFig. bnset) efine anisochronage of 610 f 44Ma with an initial "Sr/"Srof0.7037 f .0002 K-feldspar-rich pegm atite from this locality(E-210 peg.) gives model ages of 606 M a (I.R. = 0.7032) to586 Ma ( I .R . = 0.7039).Zircons were separated from a gneiss sample (E-207G)that has a very similar field appea rance and petrograph y toth esamplesdated by Rb-Srwhole-rock echniques. Th ezircons were few in number and of small size (< l4 0 mesh).Microscopic examination disclosed that all wereeuhedra lwith no appa rent overgrown or metamict cores. Th e singlefractionanalysedgave a nearly concordant modelage of

I n.'."I F E I R A N D Y K EAG E = 5 9 1 i 9 M AM S W D = 1.8

(e7Sr/86Sr)i=.7034i20.9 n =10

e7Rb/B6SrFig. 3. Rb-Sr whole rock isochron diagrams for rocks from theFeiran area. (a) Late extensional dyke; (b) Paragneiss (inset showsresults for thin-layer datingof one sample).

0.15 1 1 1 1 1 1F E IRA N Z IRCONS

3mm5U)0N

a0.09t

Fig. 4. U-Pb zircon concordia diagram for ocks from the Feiranarea.Table 2. U, b , a n d P b i s o t o p i c c o m p o s i t io n d a t a

Corrected ratiosConcentrationMeasured Pb ratiosSample,mesh U (ppm)Pbppm) 06/204 07/206 07Pb/235 U 206 b/238 U 207 b/206 Pb~~

207 G paragneiss'213 granodiorite'

~~~ ~

-140 + 20034.40.59812.06255.8096.09662.06077-100 + 140 475.8 51.06 2667 0.07054 0.9010 0.1002 0.06520-140 + 200 552.9 53.20 1873 0.07279 0.7968 0.08883 0.06506-200 + 270 629.0 63.32 6211 0.06736 0.8499 0.09476 0.06505

'Corrected for common lead at 620 Ma (Stacey & Kramers 1975).Corrected for common lead at 790 Ma (Stacey& Kramers 1975).

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A G E O F F E I R A NB A S E M E N T ,S I N A I 513632 f 3 Ma (Fig. 4). Using this age and the Rb-Sr data inTab le 1, E-207G h ad an initial 87Sr/86Sr atio of 0.7039.Stronglyoliatedranodioritesomprise an extensiveterraneeast of th eparagneiss.Thre e racti ons of zirconsseparated from samp le 213 were euhedral, with no obviousovergrown cores or metamict components. Analytical esultswere quite discordant but defined an agef 782 f Ma (Fig.4). Interpreting hisas he crystallizationage, the Rb-Srdata in Table 1 indicate that this granodiorite had an initial87Sr/86Sr atio of 0.7034.DiscussionThe re are two possible interpretations of the gneiss zirconag e of 632M a. This age represents either the t ime of themetamorphism hat ormed hegneisses, or he ime ofigneous activity sampled by theedimentaryrotolith.Selection of the correct interpretation is critically dependenton etter nderstanding of the ature of the gneissprotoli th.The gneisses are quartzo-feldspathic ndac kminerals that would be found in metamorphosed polycyclicsediments, especially aluminosilicates and garnet; there arenoquartzites m ong hegneisses.Theprotolith for heFeiranaragneisseswasrobablyer ymmature,ol-canigenic wack6s or pe rhaps lithic arenites interbedded withfelsic tuffs. Suchedimentsredominatenheat ePrecambrian of this region and were deposited very rapidlyfollowing consolidation of their source rocks (Engel et al.1980; Massey 1984). Th e zircons from the gneiss may haveformed n granitic rocks hat cooled and were eroded ustprior to the deposition of these sediments and tuffs; in thiscase,he 632 Ma ge orresponds to pre-metamorphicigneous activity and the time of g neiss formation is betterdefined by the Rb-Srwhole ock and thin-slab gesof610-615 Ma.Alternativelyhe32Ma age dateshegneiss-forming event. This could be the result of eithe r theloss of all lead from detrital zirconsor growth of new zirconsin metasedimentshatwere riginally eposited ree ofzircon. In this c ase, the 632 Ma refers to peak metamorphicconditionswith 14, 10, nd 06-586MaRb-Sr gescorresponding to later time s of cooling through whole-rock,thin layer, and K-feldspar blocking temperatures.Inithernterpretation,here was veryittleim ebetwee n the igneous activity and sedimentation resulting inprotolithormation,metamorphism,nd uplift. This isdem ons trated by t he relatively ow initial 87Sr/86Sr atios(0.7034-0.7039) of th e gneisses and the ov erlap be twe en theages given by U-Pb zircon, whole rock R b-Sr and thin slabRb-Sr, and the mode l age of the late pegmatite. Regardlessof which interpretation is preferred, the gneiss formed at orjust af ter 632M a. The high-grade m etamorphic event musthave been complete by the t ime that the 591f Ma dykeswere emplaced. Th e tectono-magmatic episode responsiblefor gneissormationmayav eee nelated toh e610-630 Ma compressional events imp ortant in the evolutionof the Central and NE Deserts of Egypt (Stem & Hedge1985). Themajor NW-SE trendingtructures clearlydeveloped during this event.Th e 780 M agero mheeiranranodiorite isespecially significant for egional ectonic econs tructionsbut is mo re difficult to interpret within the local geologicalcontext. The contact between the paragneisses to the westand the granodiorite arallelshe aragneisstructuraltrends and on the basis of the geochronological date must

either be an unconformity or a fault. This contact has notbeendentified in t he field as ither, robably ueooverprintingyhe 610-630Mavent. Moreetailedstructural studies will be requi red to resolve this problem .The granodiorite is thewesternmost knownepre-sentative of 780 f 50 M a crust which extends across Sinaiinto Jordan but has not been found in adjacent portions ofEgyptrArabia.norda n, sillimanite-garnet schists,2-mica granite,andparagneis s give U-Pbzirconagesof742-820 M a (Jarra r et al . 1983). Pelitic schists from a highgrade etamorphicerraneroundlat,srael, givewhole-rock Rb-Sr ages of 807 f 35 Ma (I.R. = 0.7032 f0.0005; Halpern & Tr is t an 1 98 1) o r 8 0 0 f 4 3 M a ( I.R . =0.7030 f 0.0006;Bielski1982).Metavolcanic rocksof theSa'al Groupn SinaiieldRb-Srwhole-rockge sf734 f 1 7 Ma (I .R . = 0.7029;Bielski1982). Th ere is thusclearly an xten sive erran e of 780 f 50 M abasementunderlyingmuch of N Sinai and S Jordan. These are heoldest reliable ages from this region, and suggestions f agesgreater than 1100 Ma (Shim ron 1980) cannot be confirmed.T he 780 f 5 0 M a t e r ran e in n o rth er nmo s t Af ro - Arab iahas not been recognized in adjacent terranes immediately tothe south and west (Fig. 1). Rocks older than 700Ma havenot been found north of 25"N in Egypt in spite of efforts todate heoldes t rocks there Stern & Hedge 1985).Unitsolder than 700 Ma are quite common in Egypt southf 25"N(Fig. 1) and in S udan (Fitches et al. 1983; Klemenic 1985).In heArabianShield,unitsolder han 700 Ma arenotcommonorth of 27"N (H edg e 1984). Toheouth ,780 f 50Ma ages are first encountered for the 782 f 38 M aJ. Ess ophiolites at 26'20'N (Fig. 1; Claesson et al . 1984).Basement dominated by >700 Ma rocks is only found southof 23"30'N in Arabi a (Co ope r et al. 1979; Fleck et al. 1980;J. S. Stacey pers. comm. 1986).Further support for the interpretation that 780f 0 M acrust is commonnSinai nd ordan nd bsent romterranes mmediately to he southan dwestcomes romconsideration of initial 87Sr/ffiSr atios. Paragneiss and thedyke analys ed have initial 87Sr/86Sr atio s of 0.7034-0.7039,similar to th e initial ratios for rocks of like age elsewhere inSinai (R = 0.7040; M ittlefehldt & Rey me r 1986) but slightlyhigher han initial 87Sr/86Sr ratios for rocks of sim ilar agefrom the Eastern Desert of Eg ypt (0.7025-0.7035; S tern &Hedge 1985) orro mWrabia (0.7028-0.7035;Duyverman et al . 1982; Hedge 1984). The consistentlyhigher initial 87Sr/s6Sratios of Sin aiasementocksprobably reflects theparticipation of 780 f 50Ma crustand/or litho sphere in the gene ration of the Sinai melts. Thiscomponentwasotresenturingmeltvolution inadjacent regions to the south and west.The juxtaposition of 630M a aragneiss against the780 f 50M abasement n the Feiranarea is especiallyinteresting.Thismay epresentamajorcrustalboundarywithin the Precam brian basem ent, separating 540-670 Masialic crust of province I11 in theN EDesert from780 f 50Ma basement of Sinai and Jordan that was never-theless everely overprintedduring he youngergneouspulses. The atter is identifiedas anew ectono-magmaticbasementprovince (IV in Fig. 1) to differentiate t romotherparts of th eEgyptianbasement,even hough hedefinition of its southern limits will require further detailedstudies in NW Arabia and Sinai.Finally, these data permit us for the first time to identifyan erosional unconformity that was developed early in the

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514 R . J . S T E R N & W . I . M A N T O NPan-African evolut ion of N Afro-A rabia . Priem et al. (1984)producedU-Pbircongesorraniticebblesro mmetaco nglom erates from he Sa 'a l an d Kid areas (Fig. 1).Thea 'a le taconglomera teebbles gaven upperintercept age of 757 f 8M a while the Kid pebbles gave anupper intercept age 735 f 8 Ma. These pebbles must havebeenrodedrom asementimilarohat of the78 0 f 50Ma e rrane dent i f iedhere .This is a urtherindicat ion that much of the basem ent of Sinai and Jordanhad been consolidated an d was being subjected to uplift anderosion while rocesses of accret ionary nd xtensionaltectonics were continuing to the south and west .

2022

ConclusionThe Precambrian basement exposed n Wadi Fe i ran recordsalmost 200 Ma of rustalgrowth.The mplacement ofgranodiori teat 782 Ma is par t of amajorepisode ha tresulted in the formation of large port ions of the basem entof Sinai, southe rn Israel, and Jordan at 780 f 50Ma. Thisterrane was u plifted and eroded, supplying course debris toflanking basins. A second major episode is reflected in theformation of paragneissesat or slightly after 632 M a; thismay representnasternxtensio n of tectonicndma gm atic activity of this ge, co-mmonly foun d in theEastern Desert of Egypt. Finally, extensional tectonism andmagmaticctivityccompaniedhemplacement ofN30"E-trending dyke swarms at 591Ma and related A-typegranites. Altho ugh it is becoming increasingly clear that anolderorelandor ccretederrane?) xisted in north-ernm ost Afro-Ara bia early in the Pan-African, there is st il lno evidenceoritherre-Pan-Africanoreland orreworkedre-Pan-Africanasement in northernmostAfro -Arab ia east of the R iver N ile .Field work in Sinai was made possible by the co-operative researchprogramme of Professors E . M , El-Shazly and W . H. anes (NSFINT-7801469). Laboratoryesearchasupported bySFEAR-8205802. The assistance of David Voegeli in the field and inthe laboratory was appreciated. David Mittlefehldt made it possibleto reviewriticalarts ofMiriamBielski's dissertation.Thecomments of P. D. Fullager, H . N . A. Priem, A. Reymer, J. S.Stacey and two anonymous reviewers are gratefully acknowledged.This sUniversity of Texas at DallasPrograms nGeosciencescontribution num ber 499.ReferencesBENDER,F. 1974. Explanatory notes on the geological map of the Wadi

Araba, Jordan. Geologische Jahrbuch, B10,3-62.BIELSKI,M. 1982. Stages n he evolution of the Arabian-Nubian massif in

Sinai. PhD thesis, Hebrew University.-, JAGER,E. & STEINITZ, . 1979. The geochronology of Iqna Granite(Wadi Kid Pluton), Southern Sinai. Contributions oMineralogy andPetrology, 70, 159-65.CAHEN,L., SNELLING,N. J. , DELHAL, . & VAIL, J. R. 1984.heGeochronology and Evolution of Africa.OxfordUniversity Press,London.

CLAESSON,. , PALLISTER,. S. & TATSUMOTO,M.984.amarium-neodymium data on two late Proterozoic ophiolites of Saudi Arabia andimplications for crustal and mantle evolution. ContributionsoMineralogy and Petrology, 85, 244-52.

CLARK,. D . 1985. Late Proterozoic crustal evolution of the Midyan region,northwestern Saudi Arabia. Geology, U, 611-5.COOPER,. A., STACEY,. S . , STOESER, . G. & FLECK,R. J. 1979.An

Arabian craton. Contributions to Mineralogy and Petrology, 68,429-39.evaluation of the zircon method of isotopic dating in the southernDIXON, T. . 1981. Age and chemicalcharacteristicsof some pre-Pan-African

rocks in the Egyptian Shield. Precambrian Research, 14, 119-33.DUYVERMAN, H.., HARMS, . B. W. & HAWKESWORTH, C. J. 1982. Crustal

Arabian Shield. Earth and Planetary Science Letters, 59, 315-26.accretion in the PanAfrican: Nd and Sr isotope evidence rom the

ELBAYOUMI, . M. A. & GREILING, . 1984. Tectonic evolution of aPan-African plate marginn southeastern Egypt-a suture zoneAfrican Geology. Tervuren, 47-56.overprinted by ow angle thrusting?. I n : KLERKX,. & MICHOT,. (eds)

EL-GABY, . & AHMED,A. M. A. 1980. The Feiran-Solaf gneiss belt, SW ofSinai, Egypt. Bulletin of thenstitute of AppliedGeology,KingAbdulaziz University (Jeddah), 4,95-105.

EL-MANHARAWY, S. 1977.eochronologicalnvestigation of somebasement ocks n heCentralEasternDesert,Egypt,between Lat. 25"and 26"N. PhD thesis, University of Cairo.

EL-RAMLY, M. . 1972. A new geological map for the basement rocks in theeastern and southwestern deserts of Egypt.Annals of theGeologicalSurvey of Egypt, 2, 1-18.EL-SHAZLY,. M,, HASHAD, A. H., SAWAH, T. A. & BASSYUNI,. A. 1973.Geochronology of the Abu Swayel area, south Eastern Desert. Egyptian

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Received 16 June 1986; revised typescript accepted 29 September 1986.