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Available online at www.sciencedirect.com
Precambrian Research 160 (2008) 341–356
SHRIMP zircon dating and Sm/Nd isotopic investigations ofNeoproterozoic granitoids, Eastern Desert, Egypt
Ewais M.M. Moussa a,∗, Robert J. Stern b, William I. Manton b, Kamal A. Ali b
a Nuclear Materials Authority, P.O. Box 530, El Maadi, Kattamyia, Egyptb Geosciences Department, University of Texas at Dallas, Box 830688, Richardson, TX 75083-0688, USA
Received 26 January 2007; received in revised form 7 August 2007; accepted 23 August 2007
bstract
There is an increasing evidence for the involvement of pre-Neoproterozoic zircons in the Arabian–Nubian Shield, a Neoproterozoic crustal tracthat is generally regarded to be juvenile. The source and significance of these xenocrystic zircons are not clear. In an effort to better understandhis problem, older and younger granitoids from the Egyptian basement complex were analyzed for chemical composition, SHRIMP U–Pb zirconges, and Sm–Nd isotopic compositions. Geochemically, the older granitoids are metaluminous and exhibit characteristics of I-type granites andost likely formed in a convergent margin (arc) tectonic environment. On the other hand, the younger granites are peraluminous and exhibit
he characteristics of A-type granites; these are post-collisional granites. The U–Pb SHRIMP dating of zircons revealed the ages of magmaticrystallization as well as the presence of slightly older, presumably inherited zircon grains. The age determined for the older granodiorite is52.5 ± 2.6 Ma, whereas the younger granitoids are 595–605 Ma. Xenocrystic zircons are found in most of the younger granitoid samples; the
enocrystic grains are all Neoproterozoic, but fall into three age ranges that correspond to the ages of other Eastern Desert igneous rocks, viz.710–690, ∼675–650 and ∼635–610 Ma. The analyzed granitoids have εtNd (+3.8 to +6.5) and crystallization ages, which confirm previousndications that the Arabian–Nubian Shield is juvenile Neoproterozoic crust. These results nevertheless indicate that older Neoproterozoic crustontributed to the formation of especially the younger granite magmas.
2007 Published by Elsevier B.V.
sa(yggypte6o
eywords: Neoproterozoic; Arabian–Nubian Shield; Granite; Egypt
. Introduction
Neoproterozoic basement in Egypt outcrops over100,000 km2 in the Eastern Desert (ED), south Sinai
nd limited areas in the South Western Desert. Eastern Desertasement is divided into three main domains: north Easternesert (NED), central Eastern Desert (CED) and south Easternesert (SED) (Fig. 1). These domains are distinguished
ithologically (Stern and Hedge, 1985; El-Gaby et al., 1988).A wide range of granitic rocks are common in ED basement
xposures (Stern and Hedge, 1985). The NED in particular isharacterized by extensive felsic intrusions. There is a clear com-ositional temporal evolution of ED granitoids, from medium-K
alc-alkaline plutonic suites to alkaline granites, as has beenecognized for many decades.∗ Corresponding author. Tel.: +202 26429537; fax: +202 27585832.E-mail address: [email protected] (E.M.M. Moussa).
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301-9268/$ – see front matter © 2007 Published by Elsevier B.V.oi:10.1016/j.precamres.2007.08.006
Granitoid rocks in the Arabian–Nubian Shield include (1)yn- to late-orogenic granitoid assemblages (880–610 Ma)nd (2) post-orogenic to anorogenic granitoid assemblages600–475 Ma), previously identified as older granitoids andounger granitoids, respectively (Bentor, 1985). The olderranitoids range in compositions from trondhjemite, tonalite,ranodiorite and rarely granites while granites dominate theounger granitoids. Hassan and Hashad (1990) recognized threeossible events of igneous activity during which different plu-ons of older granitoids were emplaced, these are: Shaitianvent 850–800 Ma, Hafafit event 760–710 Ma and Meatiq event30–610 Ma. The older granitoids were derived from a mantler from (not much older primitive crust). A subduction relatedechanism was suggested for the generation of these grani-
oids. On the other hand, three possible tectonic settings andagma generation sources was suggested for the evolution of
he younger granitoids: (a) generation of granitic magma dur-ng subduction processes in volcanic-arc setting, (b) generationf granitic magma as a result of arc-continent collision eventnd (c) generation of granitic magma within attenuated conti-
342 E.M.M. Moussa et al. / Precambrian Research 160 (2008) 341–356
ypt sh
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Fig. 1. Simplified geologic map of the Eastern Desert of Eg
ental crust as a result of post-cratonization rifting. Beyth etl. (1994) divided the syntectonic granodiorites (compressionalhase) from post-tectonic A-type granite (extensional phase)pisodes at ∼610 Ma.
Much of the uncertainty about the age of ED granitic plutonsesults from a lack of modern geochronologic investigations,ith early investigations done by less reliable K–Ar and Rb–Sr
echniques, and all too few of the more reliable U–Pb analysisf zircon, which is generally the best way to date crystalliza-ion of old igneous rocks (Davis et al., 2003). This is due to itstrong preference for U over Pb during crystallization, the power
f the two complementary U–Pb geochronometers (235U–207Pbnd 238U–206Pb), and the ability to correct for non-radiogenicb using the abundance of 204Pb). In particular, the ion probe,ith its powerful ability to identify xenocrystic inherited zir-fpgM
owing study areas, modified after Stern and Hedge (1985).
ons (Hargrove et al., 2006) has not been exploited in Easternesert studies, with the notable exception of Wilde and Youssef
2000, 2002) studies of the Dokhan and Hammamat sequences.n view of the importance of granitic rocks in the developmentf the Egyptian basement, five felsic intrusions were selectedor geochemical and in situ analysis using an ion probe. This ishe first use of this technique to determine ages of ED graniticocks. This revealed crystallization ages of the igneous unitsnd allows evaluating whether or not older crust participated inhe generation of the granitic magmas, taking advantage of theact that granitic rocks sample the crust that they are generated
rom and interact with during ascent and thus serve as crustalrobes. The studied plutons are, from north to south: Abu Harbaranite, Qattar granite, Qena–Safaga road older granitoids; Alissikat younger granite and Um Ara younger granite (Fig. 1).
brian Research 160 (2008) 341–356 343
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he zircon geochronology is complemented by Sm–Nd isotopiceterminations of whole-rock samples.
. Experimental techniques
Thirty samples representing the studied Abu Harba, Qattar,ena–Safaga, Al Missikat and Um Ara granitoid rock varieties
six samples from each locations) were analyzed by conven-ional wet chemical techniques (Shapiro and Brannock, 1962)or major oxide compositions and by XRF for some trace ele-ents at the Nuclear Materials Authority, Cairo, Egypt (Table 1).alibration of the results was done using international standardsith precision of ±3% for major oxides and ±5% for trace
lements.Standard methods were used for crushing and separating
ircons, which were then hand-picked under a binocular micro-cope. Zircon grains were mostly between 70 and 170 meshize; 210–88 �m). Zircons were mounted in epoxy on glasslides, polished and imaged using reflected light. Mounts wereold coated and digital images were captured by cathodolumi-escence on a JEOL 5600 LLV scanning electron microscope.ircons were analyzed using sensitive high resolution ion micro-robe reverse geometry (SHRIMP-RG) at Stanford Universitysing an O2− primary ion beam that generated secondary ionsor analysis <http://shrimprg.stanford.edu/>. This instrumentllows a mass resolution of 6000–8000 which eliminates iso-aric interferences. Analyses were calibrated using R33 zircontandard (419 Ma quartz diorites of the Braintree complex,ermont, Black et al., 2004). Ages and uncertainties wereetermined using Isoplot/Ex.3 software (Ludwig, 2000, 2001).esults are listed in Table 2 and are discussed in the following
ection.Sm–Nd contents and isotopic compositions were carried
ut at the University of Texas at Dallas (UTD). Separation ofd from the samples solutions were carried out using stan-ard cation exchange columns. All isotopic analyses wereade on a Finnigan MAT 261 solid-source mass spectrom-
ter using Re filaments and dynamic multicollection. Duringhe analysis, the La Jolla Nd standard produced a mean of43Nd/144Nd = 0.511845 ± 1. Results are listed in Table 3; Ndodel ages are calculated using the depleted mantle curve ofePaolo (1981).
. Abu Harba area
The studied area is a mountainous region in the NED atbout 27◦20′N, 33◦10′E (Fig. 2A). Various geologic aspectsere studied (dikes west of Gebel Dokhan were studied by Stern
nd Gottfried (1986) and Stern and Voegeli (1987); Hammamatediments were studied by Willis and Stern (1988) and Rb–Sreochronology were studied by Moussa (1998)).
The oldest rocks exposed are the metavolcano-sedimentaryssociation (represented by the metavolcanics north of Gabal
bu Harba). They are overlain by the Dokhan volcanics (westernarts of G. Dokhan comprising basalt to rhyolite flows). The Abuarba granites intrude both the Dokhan volcanics and the olderetavolcanics. The young granites cover more than 90% of the Table
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.M.M
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etal./Precam
brianR
esearch160
(2008)341–356
Table 2SHRIMP-RG U–Pb isotopic data of the studied granitoids
Spot name %comm.206Pb
ppm Rad206Pb
ppm U ppm Th Total238/206
%err Total207/206
%err 4 Corr238/206r
%err 4 Corr207/206r
%err 4 Corr207r/235
%err 4 Corr206r/238
%err Err corr 204 Corr206Pb/238Uage
1s err 204 Corr207Pb/206Pbage
1s err App conc age
EW1-1 2.89 20.6 238 70 9.92 0.7 .0811 1.4 10.22 0.8 .0579 6.2 0.78 6.3 .0979 0.8 .127 602.1 4.6 524 136 601.6 ± 2.2EW1-2 0.03 41.3 498 412 10.36 0.5 .0604 1.1 10.36 0.5 .0601 1.2 0.80 1.3 .0965 0.5 .373 594.1 2.7 609 26 594.7 ± 1.2EW1-3 2.45 13.2 197 61 12.80 0.8 .0814 1.7 13.12 0.9 .0617 7.6 0.65 7.7 .0762 0.9 .123 473.6 4.3 665 163 474.2EW1-4 3.24 32.1 468 155 12.52 0.5 .0847 3.7 12.94 0.8 .0585 10.0 0.62 10.0 .0773 0.8 .079 479.9 3.7 550 218 480 ± 1.8EW1-5 8.65 73.4 688 236 8.05 0.5 .1311 4.1 8.82 1.0 .0617 14.9 0.96 14.9 .1134 1.0 .069 692.7 6.8 662 319 692.6 ± 3.4EW1-6 1.79 64.1 801 489 10.74 0.4 .0753 2.6 10.93 0.5 .0609 4.6 0.77 4.7 .0915 0.5 .098 564.2 2.5 636 100 564.4 ± 2.4EW1-7 0.13 22.2 268 103 10.37 0.6 .0614 1.5 10.38 0.6 .0603 1.8 0.80 1.9 .0963 0.6 .343 592.7 3.7 615 38 593.4 ± 1.7EW1-8 0.51 13.4 159 74 10.24 0.8 .0609 2.0 10.29 0.9 .0568 3.5 0.76 3.6 .0972 0.9 .238 597.9 4.9 483 77 595.8EW1-9 0.38 23.0 276 133 10.32 0.6 .0625 1.5 10.36 0.7 .0594 2.5 0.79 2.6 .0965 0.7 .253 594.0 3.7 582 54 593.7 ± 1.8EW1-10 0.94 52.8 644 433 10.47 0.4 .0697 1.0 10.57 0.4 .0621 2.2 0.81 2.2 .0946 0.4 .197 582.6 2.4 679 46 DiscorEW1-13 0.09 25.1 304 226 10.39 0.6 .0632 1.4 10.40 0.6 .0625 1.5 0.83 1.6 .0962 0.6 .378 592.1 3.4 691 32 DiscorEW1-14 0.14 35.5 433 328 10.49 0.6 .0604 1.2 10.51 0.6 .0593 1.5 0.78 1.6 .0952 0.6 .368 586.0 3.2 576 32 585.7 ± 1.5EW1-15 1.76 76.0 923 775 10.42 0.3 .0726 0.8 10.61 0.4 .0583 2.5 0.76 2.6 .0942 0.4 .152 580.5 2.2 543 55 580.3 ± 1.1EW1-16 13.76 18.3 534 90 25.01 0.5 .1733 0.9 29.00 1.1 .0631 12.8 0.30 12.8 .0345 1.1 .086 218.5 2.4 713 272 218.8EW2-2 0.04 321.7 3856 1303 10.30 0.2 .0605 0.4 10.30 0.2 .0602 0.5 0.81 0.5 .0971 0.2 .356 597.2 1.0 610 10 597.6EW2-4 0.01 375.1 4376 1434 10.02 0.2 .0603 0.4 10.02 0.2 .0601 0.4 0.83 0.4 .0998 0.2 .384 613.0 0.9 608 8 612.8 0. ± 43EW2-6 0.00 538.7 6174 2850 9.84 0.1 .0602 0.3 9.85 0.1 .0601 0.3 0.84 0.3 .1016 0.1 .390 623.6 0.8 609 7 DiscorEW2-6 0.60 256.3 3003 861 10.07 0.2 .0653 0.4 10.13 0.2 .0605 0.9 0.82 0.9 .0987 0.2 .221 607.0 1.1 620 19 607.2 ± 0.55EW2-7 0.02 792.6 8916 5023 9.66 0.1 .0604 0.3 9.67 0.1 .0602 0.3 0.86 0.3 .1035 0.1 .386 634.7 0.7 612 6 DiscorEW2-8 0.01 334.4 3963 1283 10.18 0.2 .0600 0.4 10.18 0.2 .0599 0.4 0.81 0.4 .0982 0.2 .383 603.9 1.0 600 9 603.7 ± 0.44EW2-9 0.01 507.2 6055 1651 10.26 0.1 .0602 0.3 10.26 0.1 .0602 0.3 0.81 0.4 .0975 0.1 .385 599.8 0.8 610 7 600.2EW2-10 0.19 408.7 4591 1490 9.65 0.2 .0619 0.4 9.67 0.2 .0604 0.5 0.86 0.5 .1034 0.2 .352 634.4 1.1 616 10 633.7EW2-11 0.91 354.6 3513 949 8.51 0.2 .0681 0.4 8.59 0.2 .0608 0.9 0.98 0.9 .1164 0.2 .207 710.0 1.2 631 19 DiscorEW2-12 0.02 377.5 4510 1538 10.26 0.2 .0603 0.4 10.27 0.2 .0601 0.4 0.81 0.4 .0974 0.2 .373 599.2 0.9 609 9 599.5 ± 0.41EW2-13 0.04 541.1 5931 1653 9.42 0.1 .0606 0.3 9.42 0.1 .0603 0.4 0.88 0.4 .1061 0.1 .380 650.3 0.9 614 8 DiscorEW2-14 0.01 324.5 3838 1198 10.16 0.2 .0601 0.4 10.16 0.2 .0600 0.4 0.81 0.4 .0984 0.2 .386 605.1 1.0 603 9 605.07 ± 0.89EW3-1 0.92 57.2 756 659 11.36 0.4 .0682 1.5 11.46 0.4 .0608 2.4 0.73 2.4 .0872 0.4 .164 539.2 2.0 633 51 DiscorEW3-2 0.10 10.0 111 52 9.53 0.9 .0629 2.2 9.53 1.0 .0621 2.3 0.90 2.5 .1049 1.0 .378 642.9 5.8 677 50 644.3 ± 2.6EW3-3 0.00 21.5 256 253 10.23 0.6 .0606 1.5 10.23 0.6 .0606 1.5 0.82 1.6 .0977 0.6 .382 601.0 3.6 625 33 601.9 ± 1.6EW3-4 0.16 134.7 1469 1817 9.37 0.3 .0632 0.6 9.38 0.3 .0619 0.9 0.91 0.9 .1066 0.3 .312 652.8 1.7 669 18 653.3 ± 0.8EW3-5 0.04 115.7 1233 388 9.16 0.3 .0622 1.1 9.16 0.3 .0619 1.1 0.93 1.2 .1091 0.3 .253 667.7 1.8 671 24 667.7 ± 0.88EW3-6 0.25 9.8 111 49 9.78 1.0 .0609 2.3 9.80 1.0 .0589 2.9 0.83 3.1 .1020 1.0 .317 626.1 5.8 564 63 624.2 ± 2.7EW3-7 0.32 11.7 127 45 9.33 0.9 .0630 2.1 9.36 0.9 .0605 2.9 0.89 3.0 .1069 0.9 .301 654.6 5.7 621 62 653.6 ± 2.6EW3-8 0.04 80.9 873 237 9.27 0.3 .0621 0.8 9.28 0.3 .0617 0.8 0.92 0.9 .1078 0.3 .382 660.0 2.2 665 18 660.2 ± 0.98EW3-9 0.00 25.3 268 154 9.11 0.7 .0624 1.4 9.11 0.7 .0624 1.4 0.94 1.6 .1098 0.7 .456 671.6 4.6 686 30 672.5 ± 2EW3-10 0.07 32.6 352 133 9.26 0.5 .0619 1.2 9.27 0.5 .0613 1.3 0.91 1.4 .1079 0.5 .370 660.3 3.3 651 29 659.9 ± 1.5EW3-11 0.00 42.5 464 339 9.38 0.5 .0608 1.2 9.38 0.5 .0608 1.2 0.89 1.3 .1066 0.5 .371 653.2 3.0 632 26 652.3 ± 1.3EW3-12 0.00 20.2 020 70 9.37 0.7 .0618 1.6 9.37 0.7 .0618 1.6 0.91 1.7 .1068 0.7 .395 653.9 4.3 666 34 654.5 ± 1.9EW3-13 0.43 8.0 91 34 9.77 1.1 .0616 2.5 9.81 1.1 .0581 4.0 0.82 4.1 .1019 1.1 .261 625.7 6.4 533 87 623.6EW3-14 0.12 13.3 148 65 9.51 0.8 .0615 1.9 9.52 0.8 .0605 2.1 0.88 2.3 .1050 0.8 .366 643.6 5.1 622 46 642.7 ± 2.3EW5-2 0.98 24.4 289 88 10.17 0.6 .670 1.4 10.27 0.6 .0590 3.3 0.79 3.3 .0974 0.6 .188 599.1 3.6 569 71 598.8 ± 1.7EW5-3 0.65 14.8 167 66 9.74 0.8 .0626 1.8 9.81 0.8 .0574 3.6 0.8.1 3.7 .1020 0.8 .211 625.9 4.7 507 80 624EW5-4 1.42 18.9 250 95 11.38 0.7 .0695 1.5 11.54 0.7 .0581 5.1 0.69 5.1 .0867 0.7 .145 535.8 3.8 533 111 535.8 ± 1.9EW5-5 0.44 71.4 891 715 10.71 0.3 .0638 0.9 10.76 0.4 .0603 1.4 0.77 1.5 .0929 0.4 .239 572.8 1.9 613 31 573.5EW5-6 0.61 29.1 335 155 9.89 0.6 .0646 1.3 9.95 0.6 .0597 2.5 0.83 2.6 .1005 0.6 .226 617.3 3.4 592 54 616.9 ± 1.6EW5-7 0.08 20.4 246 128 10.36 0.7 .0613 1.6 10.37 0.7 .0606 1.7 0.81 1.8 .0964 0.7 .364 593.3 3.7 626 36 594.5 ± 1.7EW5-8 1.29 62.5 705 335 9.69 0.4 .0693 1.1 9.82 0.4 .0590 2.5 0.83 2.5 .1018 0.4 .162 625.1 2.4 566 54 624.6EW5-9 2.34 24.9 301 126 10.36 0.6 .0754 1.3 10.61 0.7 .0564 6.6 0.73 6.6 .0942 0.7 .110 580.6 4.0 470 146 580.1 2EW5-11 0.30 262.1 2759 859 9.04 0.2 .0645 0.5 9.07 0.2 .0621 0.7 0.94 0.7 .1102 0.2 .269 674.1 1.2 678 14 674.3 ± 0.57EW6-1 0.00 11.8 148 160 10.71 1.0 .0623 2.3 10.71 1.0 .0623 2.3 0.80 2.5 .0934 1.0 .391 575.7 5.3 686 49 DiscorEW6-2 4.56 66.5 1230 845 15.89 0.4 .0949 2.1 16.65 0.5 .0582 5.9 0.48 5.9 .0601 0.5 .084 376.0 1.8 536 128 376.2EW6-3 1.70 15.7 195 141 10.64 0.8 .0758 1.9 10.82 1.1 .0622 9.2 0.79 9.3 .0924 1.1 .117 569.6 5.9 680 197 570.1 ± 2.9EW6-4 0.14 15.2 177 97 10.01 0.9 .0601 2.1 10.02 0.9 .0590 2.4 0.81 2.6 .0998 0.9 .341 613.1 5.1 566 53 611.5 ± 2.3EW6-5 1.44 14.0 184 81 11.30 0.9 .0727 2.0 11.47 1.0 .0611 5.5 0.74 5.6 .0872 1.0 .170 539.0 4.9 644 118 539.8 ± 2.4
EW1, EW2, EW3, EW5 and EW6 referred to Abu Harba, Qattar, Qena–Safaga, Al Missikat and Um Ara areas, respectively.
E.M.M. Moussa et al. / Precambrian Research 160 (2008) 341–356 345
Table 3Sm and Nd concentrations and Nd isotopic compositions
Locality no. Sm (ppm) Nd 147Sm/144Nd 143Nd/144Nd εtNd Model age TDM (Ga)
1 5.79 31.5 0.1111 0.51259 ± 1 5.75 0.672 13.0 33.4 0.2353 0.51302 ± 1 4.67 High Sm/Nd3 3.82 33.2 0.06956 0.51243 ± 1 6.74 0.655 12.2 35.0 0.2107 0.51295 ± 1 5.19 High Sm/Nd6 6.10 47.8 0.07714 0.51236 ± 1 3.97 0.76
Fig. 2. (A) Geologic map of Gabal Abu Harba area (locality no. 1, EW1). (B) Geologic map of Gabal Qattar area (locality no. 2, EW2). (C) Geologic map of GabalUmm Taghir-Gabal Al Missikat area (locality nos. 3 and 5, EW3 and EW5 respectively). (D) Geologic map of Um Ara area (locality no. 6, EW6).
346 E.M.M. Moussa et al. / Precambrian
Tabl
e4
Mod
alm
iner
alog
ical
com
posi
tions
ofth
est
udie
dgr
anito
ids
Sam
ple
no.
12
34
56
78
910
1112
1314
1516
1718
1920
2122
2324
2526
2728
2930
Qz
3433
.538
3139
3837
4237
3531
.536
.529
2632
2827
3334
3833
35.5
35.5
3536
3834
.539
3636
K-f
eld.
3943
4244
4042
4140
5246
5054
1413
1514
13.5
1641
4247
5044
5438
3537
31.5
3735
Plag
.18
1816
1715
1415
129
14.5
148
4044
4043
4439
1613
1015
817
1818
.520
1719
Mafi
cs7
43
65
46
51
34
113
1512
1314
116
54
34
27
7.5
88.
58
9O
p.an
dA
cc.
21.
51
21
21
11
1.5
0.5
0.5
42
12
1.5
13
21
1.5
1.5
12
1.5
21
21
Qz,
Qua
rtz;
K-f
eld.
,Pot
ash
feld
spar
;Pla
g.,P
lagi
ocla
se;O
p.,O
paqu
es;A
cc.,
Acc
esso
ry.
Sam
ple
nos.
asin
Tabl
e1.
sAAsalbd
iot(pdcctiama1mss
pfittrti
t
Fo
Research 160 (2008) 341–356
tudy area (Fig. 2A). They form high mountains including Gabalbu Harba, Gabal Urf El O‘rr, Gabal El-Shehaila and Gabalbu Marwa. These granitic rocks are light to pinkish grey and
ometimes pink or red. They are classified into two distinct typesccording to field characteristics; earlier biotite granites and aater perthitic leucogranites (Salman et al., 2006). The contactsetween the two granite types vary from clearly intrusive toiffuse.
Petrographically, the Abu Harba granites exhibit hypid-omorphic granular texture. Some samples are porphyritic withrthoclase phenocrysts. They are mostly medium but some-imes coarse-grained. They are mainly composed of K-feldsparsorthoclase and microcline with coarse patchy string and rip-le perthites) and quartz (undulose extinction due to strain oreformation), with subordinate plagioclase (An = 10–18, havingarlsbad and albite twins) and biotite (subhedral to anhedral flakyrystals bent due to deformation). Wedge-shaped euhedral crys-als of sphene are mainly associated with biotite and opaques ands the dominant accessory mineral along with zircon, magnetite,nd subordinate ilmenite. The secondary alteration minerals areuscovite (alteration product of feldspar) and chlorite (alter-
tion product of biotite). The QAP modal analysis, (Streckeisen,976) listed in Table 4 and shown in Fig. 3 indicates that theajority of granites samples plot in the syenogranite field. All
amples contain two feldspars indicating crystallization underubsolvus condition (Tuttle and Bowen, 1958).
Geochemically, in terms of alumina saturation, the graniteslot on the Shand (1951) diagram (Fig. 4A) in the peraluminouseld. The relationship between Ga/Al and Zr (Fig. 4B) indicates
hat the granites are A-type granites (Whalen et al., 1987). Tec-onic setting of formation can be inferred from Rb vs. Nb + Yelationships (Fig. 4C; Pearce et al., 1984; Pearce, 1996) where
he granites plot in the superimposed fields for within-plate andn the post-collisional granites.Zircons separated from Abu Harba granite (EW1) areransparent to translucent, typically 150–230 �m long and
ig. 3. Modal quartz (Qz)–alkali feldspar (A)–plagioclase (P) ternary diagramf the studied granitoids (Streckeisen, 1976).
E.M.M. Moussa et al. / Precambrian
Fig. 4. (A) Shand’s index diagram of the studied granitoids. (B) Whalen etal. (1987) diagram of the studied granitoids. (C) Tectonic discrimination dia-gram of the studied granitoids (Pearce et al., 1984; post-collisional granite fieldag
1mpt
MlcaTaTcp2abg(wTo
4
3ateb
ac(taawmcEstei
GEGaTmBa
mmpatch types), quartz (undulose extinction due to deformation),
fter Pearce, 1996). Abu Harba granites (©); Qattar granites (�); Qena–Safagaranitoids (×); Al Missikat granites (�); Um Ara granites (�).
00–120 �m wide (Fig. 5). Most exhibit prismatic and pyra-
idal crystal faces. Pupin (1980) related the development ofrismatic faces mainly due to the temperature of crystalliza-ion whereas pyramidal faces were linked to chemical factors.
pai
Research 160 (2008) 341–356 347
ost zircons show well-developed growth zoning in cathodo-uminescence images. Metamict zircons are very dark underathodoluminescence. Fourteen grain spots were analyzed, withverage U contents (459 ppm), Th contents (256 ppm) andh/U (0.56). Generally, Th/U of igneous zircon ≥0.5 (Hoskinnd Schaltegger, 2003) while metamorphic zircons have lowh/U < 0.07 (Rubatto, 2002). Most of the analyzed spots defineoncordant 206Pb/238U ages between 580.5 and 602.1 Ma. Fouroints give lower ages due to lead loss (206Pb/238U ages between19 and 564 Ma) while one data point (spot EW1-5) givesconcordant 206Pb/238U age 693 Ma. This grain is proba-
ly a xenocryst, inherited from slightly older crust. The mainroup of five concordant ages defines an age of 595.3 ± 3.3 MaMSWD = 0.017) as shown in Tera-Wasserburg diagram (Fig. 6),hich is interpreted as the age of magmatic crystallization.his age is consistent with a Rb–Sr whole-rock isochron agef 590 ± 4 Ma for the same granites (Moussa, 1998).
. Gabal Qattar area
The Gabal Qattar environs lies in the NED, ∼27◦10′N,3◦20′E. Several studies have been carried out as Shalaby (1990)nd Moussa (1994, 1998). This area is characterized by ruggedopography, especially the Qattar batholith and comprises sev-ral high mountains to the east that are separated from G. Qattary small low hills of older granites.
The oldest rocks exposed are the metavolcano-sedimentaryssociation, represented by metavolcanics exposed at the SWorner and as roof pendants (G. Kehala) of the Qattar batholithFig. 2B). Older granitoids form small, isolated masses dis-ributed N–S to NNW between the younger granitic batholithsnd at the eastern and western peripheral zones of the studyrea. They have sharp contacts with younger granites in theestern part of the study area. They range from coarse- toedium-grained diorites to granodiorites. The Dokhan vol-
anics (rhyolites to basalts) are exposed at the type locality G.l Dokhan in the NW corner of the study area forming a thickequence of lava flows and minor pyroclastics. The contact withhe pink granite is sharp intrusive. Hammamat sediments arexposed in the NW corner of the study area (G. Um Tawat)nterfingering with the Dokhan volcanics.
Younger granites cover an extensive part of the study area.abal Qattar granite batholith extends N–S ∼30 km and ∼20 km–W. The Qatar batholith comprises the following high peaks:. Qattar, G. Um Disi, G. Kehala and G. Thalma. The granites
re red to pink and both varieties pass gradually into each other.hey intrude the Hammamat sediments to the NW where contactetamorphism has produced a hornblende hornfels along Wadiali. The age of this granite indirectly constrains the depositionalge of the Hammamat sediments in the area.
Petrographically, the Gabal Qattar rocks are pink to red,edium-grained, show hypidiomorphic granular texture and areainly composed of orthoclase perthites (string and sometimes
lagioclases (An = 6–12, prismatic crystals with carlsbad andlbite twins) and biotite (subhedral flaky crystals with opaquenclusions). Accessory minerals include zircon, fluorite and iron
348 E.M.M. Moussa et al. / Precambrian Research 160 (2008) 341–356
zirco
ocTs
Fe
Fig. 5. Cathodoluminescence images of selected
xides. The secondary alteration minerals are sericite and mus-ovite. The QAP modal analysis (Streckeisen, 1976) listed inable 4 and shown in Fig. 3 indicates that the majority of granitesamples plot in the syenogranite field except one sample plot in
ig. 6. Tera-Wasserburg Concordia diagram for the Abu Harba granite, dashedllipses for Pb-loss or inherited grains.
tbss
mUivtsg
t6cd(y(r
n crystals separated from the studied granitoids.
he alkali feldspar granite field and other two samples plot at theoundary between the alkali feldspar and syenogranite fields. Allamples contain two feldspars indicating crystallization underubsolvus condition (Tuttle and Bowen, 1958).
Geochemically, the granites plot on the Shand (1951) alu-ina saturation diagram (Fig. 4A) in the peraluminous field.sing Ga/Al and Zr diagram (Fig. 4B) indicates that the gran-
tes are A-type granites (Whalen et al., 1987) whereas the Rbs. Nb + Y (Fig. 4C; Pearce et al., 1984; Pearce, 1996) tec-onic setting diagram indicates that the granites plot in theuperimposed fields for within-plate and in the post-collisionalranites.
The separated zircons from Qattar granite (EW2) areranslucent to opaque euhedral crystals 130–200 �m long and0–100 �m wide (Fig. 5). Most exhibit prismatic and pyramidalrystal faces. Most zircons are dark under cathodoluminescenceue to radiation damage caused by high U and Th contents
metamict), which is also obliterated zoning. Twelve spot anal-ses of individual zircons were done, with high average of U4894 ppm) and Th (1769 ppm). The low mean Th/U (0.36) mayeflect U enrichment or Th loss by the damaged zircons. Seven
E.M.M. Moussa et al. / Precambrian
Fec
o5adFEaFaaiatg
5
aogm
ma(eaxfapSbeU
tT
ap(dw1eabcTscc
afiQortiyocci(
s6pFa(gt6dw(6SifbQ
6
ob
ig. 7. (A) Tera-Wasserburg Concordia diagram for Qattar granite, dashedllipses for Pb-loss or inherited grains. (B) Part from Fig. 7A represent fiveoncordant grains using a Concordia-intercept age model.
f the analyses define concordant 206Pb/238U ages between97.2 and 613 Ma. The other five points give older 206Pb/238Uges, ranging from 624 to 710 Ma, but these are not concor-ant (Fig. 7A) and may reflect Pb gain in metamict grains.ive concordant grains (EW2-6, EW2-8, EW2-9, EW2-12 andW2-14) yield an age of 604.8 ± 3.3 Ma (MSWD = 1.7) usingConcordia-intercept ages (model 1 solution, 95% confidence;ig. 7B) which is taken as the crystallization age. The obtainedge is significantly older than previous ages of the pluton. Sternnd Hedge (1985) reported a 579 Ma zircon model age and a sim-lar Rb/Sr model age of 575 Ma. Also, Moussa (1998) reportedRb–Sr isochron age of 570 ± 17 Ma. The difference between
hese results and ours suggests that multiple episodes of intrusionenerated the Qattar batholith.
. Qena–Safaga road
The study area lies at 26◦30′N, 33◦30′E. The investigatedrea comprises the following rock units from oldest to youngest:phiolitic melange, metavolcano-sedimentary association, olderranitoids younger granitoids, Dokhan volcanics and Hamma-at sediments (Fig. 2C).The metavolcao-sedimentary association, represented by
etavolcanics cropping out at the eastern part of the studyrea (represent part of the older metavolcanic successionStern, 1981)). The older granitoids form a huge batholith,xtending across the entire width of the NED–CED bound-ry along the Qena–Safaga road. Within the batholith, smallenoliths of mafic minerals and pegmatites are common. Theeatures of this batholith suggest an intrusive igneous body,nd not an autochthonous granitoid detached from remobilizedre-Neoproterozoic basement, as proposed by El-Shazly and El-ayed (2000). The pluton is mostly a medium to coarse-grainediotite hornblende tonalite showing mafic phenocryst flow lin-ations. The batholith is intruded by younger granitoids as G.
rf Salih and Al Missikat pluton.Petrographically, the Qena–Safaga granitoids are mediumo coarse-grained with hypidiomorphic equigranular texture.hey are composed of plagioclase (An = 9–26, zoned and albite
baAf
Research 160 (2008) 341–356 349
nd carlsbad twinning), quartz (undulose extinction), orthoclaseerthite, biotite and hornblende together with sphene, zirconassociated with biotite), apatite and epidote as accessories. Epi-ote crystallized after hornblende and shows a reaction relationith it suggesting a magmatic origin (Zen and Hammarstrom,984). Iron oxides are magnetite which may contain ilmenitexolutions of anhedral grains or as rods associated with biotitend hornblende. Minor deformation is shown by kinked andent plagioclase twins, undulose extinction in quartz and kinkedhlorite. The QAP modal analysis (Streckeisen, 1976) listed inable 4 and shown in Fig. 3 indicates that the older granitoidamples plot in the granodiorite fields as well as all samplesontain two feldspars indicating crystallization under subsolvusondition (Tuttle and Bowen, 1958).
Geochemically, the granitoids plot on the Shand (1951)lumina saturation diagram (Fig. 4A) in the metaluminouseld. Using Ga/Al and Zr diagram (Fig. 4B) indicates that theena–Safaga granitoids plot in the I-type field. Tectonic settingf formation of the granitoids can be inferred from Rb vs. Nb + Yelationships (Fig. 4C; Pearce et al., 1984; Pearce, 1996) wherehey plot in the volcanic-arc field. Hilmy et al. (2004) stud-ed the pressure, temperature and oxygen fugacities of someounger and older granitoids in the NED, including Um Taghirlder granitoid pluton and concluded that the pressure data dis-riminate three categories of granitoid emplacement at differentrustal levels ranging from 9 to 20 km (Um Taghir older gran-toid pluton <21 km) at a temperature between 650 and 819 ◦CUm Taghir older granitoid pluton 724–800 ◦C).
Zircons separated from the Qena–Safaga granodiorite con-ist of transparent euhedral crystals 130–400 �m long and5–100 �m wide (Fig. 5). The zircons exhibit prismatic andyramidal crystal faces with well-developed growth zoning.ourteen zircons were analyzed (EW3) with moderate aver-ge contents of U (463 ppm) and Th (307 ppm); high Th/U0.66) further indicates that these are igneous zircons. Tenrains yield 206Pb/238U ages between 643 and 672 Ma, andhe other four points show younger ages, between 539 and26 Ma, perhaps reflecting variable Pb loss. Five of the tenata points yield an age of 652.5 ± 2.6 Ma (MSWD = 0.017)hich is taken as the crystallization age of the granodiorite
Fig. 8). The obtained age is slightly younger than the nearby66 Ma Mons Claudianus granodiorite (U/Pb zircon model age;tern and Hedge, 1985) and somewhat older than the Rb–Sr
sochron age of 632 ± 4.6 Ma reported by El-Debeiky (1994)or tonalite/granodiorite/monzogranite suite of the Qena–Safagaatholith. It appears that granodiorite plutonism to form theena–Safaga batholith persisted between about 670 and 630 Ma.
. Al Missikat granite
The Al Missikat pluton is located in the central Eastern Desertf Egypt at 26◦20′N and 33◦26′E (Fig. 2C). Several studies haveeen carried out, including those of Moussa (2006). The granite
ody exposed at the southwestern corner of the mapped area issemi-circular post-tectonic pluton, which encompasses G. Ril Jarrah, G. Al Missikat and G. Al Jidami. Gabal Al Missikatorms ∼30 km2 oval shaped pluton.
350 E.M.M. Moussa et al. / Precambrian Research 160 (2008) 341–356
Fd
fitpcsazCQsptbss
pfittrti
e(fNTcpnc5tz
Fe
pE(oUzF
7
Etagtgal
hpmMnaFtsc1
t
ig. 8. Tera-Wasserburg Concordia diagram of Qena–Safaga older granitoids,ashed ellipses for Pb-loss or inherited grains.
Petrographically, G. Al Missikat granites are pink to red,ne- to medium-grained, and exhibit panidiomorphic and some-
imes porphyritic textures. They are composed mainly ofotash feldspars (microcline and microcline perthites present asracked, crushed as well as exhibit filament and feather types),trained quart, plagioclase (An = 7–12), biotite (sometimesltered to chlorite), opaques together with fluorite, muscovite,ircon, monazite, allanite and apatite as accessory minerals.hlorite and epidote are recorded as alteration minerals. TheAP modal analysis (Streckeisen, 1976) listed in Table 4 and
hown in Fig. 3 indicates that the majority of granites sampleslot in the syenogranite field, except one sample which plot inhe alkali feldspar granite field and two other samples plot at theoundary between the alkali feldspar and syenogranite fields Allamples contain two feldspars indicating crystallization underubsolvus condition (Tuttle and Bowen, 1958).
Geochemically, in terms of alumina saturation, the graniteslot on the Shand (1951) diagram (Fig. 4A) in the peraluminouseld. The relationship between Ga/Al and Zr (Fig. 4B) indicates
hat the granites are A-type granites (Whalen et al., 1987). Tec-onic setting of formation can be inferred from Rb vs. Nb + Yelationships (Fig. 4C; Pearce et al., 1984; Pearce, 1996) wherehe granites plot in the superimposed fields for within-plate andn the post-collisional granites.
Zircons from Al Missikat granite are translucent to opaqueuhedral crystals, 100–230 �m long and 60–100 �m wideFig. 5). Most zircons exhibit prismatic and pyramidal crystalaces well-developed growth zoning in the translucent crystals.ine zircons from the Al Missikat granite (EW5) were analyzed.hese contained moderately high U (mean = 660 ppm) and Thontents (mean = 285 ppm) and slightly low mean Th/U (0.43)ossibly indicating U enrichment. The analyzed nine zircons doot define a tight cluster and it is not easy to identify a magmatic
206 238
rystallization age. Four points define Pb/ U ages between73 and 599 Ma, which probably approximates the crystalliza-ion age. Four other points probably reflect inherited, xenocrysticircons, with ages between 617 and 674 Ma. One very young(avt
ig. 9. Tera-Wasserburg Concordia diagram of Al Missikat granite, dashedllipses for Pb-loss or inherited grains.
oint (EW5-4) shows clear Pb loss. Two points (EW5-2 andW5-7 yield Tera-Wasserburg Concordia with 596.5 ± 7 Ma
MSWD = 1.1) which is taken as tentative crystallization agef Al Missikat granite (Fig. 9). This age is consistent with–Pb zircon upper intercept 583 ± 21 Ma age of a discordant
ircon suites of the nearby El-Erediya granite (Abu Dief, 1992),ig. 2C.
. Um Ara area
The Um Ara area is located in the south Eastern Desert ofgypt at 22◦38′N, 33◦50′E (Fig. 2D). The granitic rocks intrude
he ophiolitic melange, metavolcano-sedimentary associationnd Dokhan volcanics (G. Um Dubr). The intrusion of Um Araranites appears to have been controlled by deep-seated tec-onic zones and block faulting (Abdalla, 1996). The Um Araranites is an oval shaped pluton trending N–S. It generally hashomogenous pinkish equigranular coarse-grained texture but
ocally porphyritic.Petrographically, G. Um Ara granites are red to pink,
omogenous, equigranular coarse-grained texture (in placesorphyritic). They are mainly composed of microcline andicrocline perthite, plagioclase (An = 8–15), quartz and biotite.inute flakes of muscovite are present. Sphene, zircon and mag-
etite are the common accessory minerals. The QAP modalnalysis (Streckeisen, 1976) listed in Table 4 and shown inig. 3 indicates that the majority of granites samples plot in
he monzogranite field, except one sample which plot in theyenogranite field. All samples contain two feldspars indicatingrystallization under subsolvus condition (Tuttle and Bowen,958).
Geochemically, the granites exhibit peraluminous charac-ers as indicated from Shand (1951) alumina saturation diagram
Fig. 4A) as well as exhibit A-type characteristics from Ga/Alnd Zr diagram (Fig. 4C) (Whalen et al., 1987). Using Rbs. Nb + Y (Fig. 4C; Pearce et al., 1984; Pearce, 1996) tec-onic setting diagram, which indicates the granites plot in the
E.M.M. Moussa et al. / Precambrian Research 160 (2008) 341–356 351
Ff
sg
c(fm((zdfbnh(a5s
8
sfZrhgc
arspbml
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ig. 10. Tera-Wasserburg Concordia diagram of Um Ara granite, dashed ellipsesor Pb-loss or inherited grains.
uperimposed fields for within-plate and in the post-collisionalranites.
Zircons from Um Ara granites are transparent to translu-ent euhedral crystals, 160–300 �m long and 130–150 �m wideFig. 5). The zircons exhibit prismatic and pyramidal crystalaces with well-developed growth zoning as seen in cathodolu-inescence images (Fig. 5). Five zircon grains were analyzed
EW6) with moderate mean contents of U (387 ppm) and Th265 ppm); mean Th/U (0.68) is high, as expected for igneousircons. Error ellipses of zircon grains are shown on the Concor-ia diagram (Fig. 10), where three of the 206Pb/238U ages scatterrom 570 to 613 Ma. The other two points have 206Pb/238U agesetween 376 and 539 Ma, probably reflecting Pb loss. The smallumber of points and the large scatter makes this age unreliable,owever, a 4 points produces an intercept age of 603 ± 14 MaMSWD = 2.1) (model 1 solution (95% confidence) which takens the crystallization age. The obtained age is consistent with the89 Ma K–Ar age on mica separates of Abdalla (1996) for theame granite.
. Nd isotopic results
Neodymium isotopic data for the studied granitoids are pre-ented in Table 3. The 147Sm/144Nd of granitoids vary widely,rom 0.06956 to 0.2353. These variations are consistent withr/Y ratios (Table 2) where the granitoids with low 147Sm/144Nd
atios have high Zr/Y ones (4.45–10) whereas the granitoids withigh 147Sm/144Nd ratios have low Zr/Y ones (2.2–4.14). Theranitic samples with high 147Sm/144Nd also have notably highontents of Y (64–100 ppm) and low Sr contents (<22 ppm).
Initial εtNd was calculated using the preferred crystallization
ge and adjusting the isotopic value for the chondritic uniformeservoir to be consistent with our analyses of the La Jolla Ndtandard. Initial epsilon Nd (εt
Nd) for the older granitoid sam-
le is +6.74, whereas the younger granitoid samples rangesetween +3.97 and +5.75. These εtNd values indicate that theagma sources were dominated by juvenile crust and mantle,
ike most other ANS samples (Dixon and Golombek, 1988).
ig. 11. Initial epsilon Nd vs. crystallization ages of the studied granitoids. Greyeld outlines distribution of isotopic composition of ANS juvenile crust, afterargrove et al. (2006). Solid line is depleted mantel curve of DePaolo (1981).
n a plot of εtNd against time (Fig. 11), the samples fall in the
NS field, indicating their juvenile nature and derivation fromelting of juvenile crust or fractionation of melts from depletedantle. Nd isotopic compositions are similar to that predicted
or the depleted mantle by the DePaolo (1981) model for theena–Safaga granodiorite but fall below the DePaolo curve for
he younger granites. This may reflect the role for slightly lessepleted mantle or a minor contribution from older crust.
A Nd model age (TDM), sometimes called a crust forma-ion age, marks when the initial 143Nd/144Nd of a sample wasqual to that of its depleted mantle source (DePaolo, 1981).amples with high 147Sm/144Nd produce unreliable model agesnd should not be reported. Stern (2002) inferred that samplesith147Sm/144Nd >0.165 should be excluded from calculatingd model ages, so we only calculated three Nd model ages
Table 3). The Qena–Safaga older granitoid (EW3) has a TDM0.65 Ga) that is indistinguishable from its crystallization age653 Ma). The younger granitoids of Abu Harba (EW1) and Umra (EW6) reflect slightly older Nd model ages of 0.67 and.76 Ga, respectively, which are nevertheless significantly olderhan their crystallization ages. This also agrees with the resultf Stern (2002), indicating tight clustering of ANS Nd modelges around 750 Ma taken to indicate juvenile Neoproterozoicature of this crustal tract.
. Discussion
Seven points from the present study and previous efforts areorthy of further comment:
. Previous geochronological and Nd isotopic work on the
granitoids of the Eastern Desert is summarized in Fig. 12and Appendix 1, suggests that the interval 550–600 Ma wasmost important in the formation of Egyptian granitoids, butbecause the older granitoids constitute about 27% of the base-
352 E.M.M. Moussa et al. / Precambrian
Fig. 12. Frequency diagram (histogram) for the previous geochronological stud-ies of granitoids of Egypt by different techniques. Data sources: Hashad (1980),Stern and Hedge (1985), Abdel-Rahman and Doig (1987), Hassan and Hashad((A
2
3
4
5
1990), Abu Dief (1992), El-Debeiky (1994), Moghazi et al. (1998), Moussa1998), Loizenbauer et al. (2001), Bregar et al. (2002), Shalaby et al. (2005) andbdel-Rahman (2006).
ment outcrops while the younger granites constitute ∼16%of the total outcrops in the Eastern Desert, the histogramis certainly biased towards the ages of younger granites.This reflects the reality that the K-rich younger granites areeasily dated by Rb–Sr whole-rock techniques, the dominantsource of information for the age of Egyptian granitic rocks.Stern and Hedge (1985) used Rb–Sr and U–Pb zircon tech-niques but found no granitic rocks older than ∼710 Ma in theED. U–Pb zircon dating favors the older granitoids, becausethese zircons have lower U contents and thus have muchless radiation damage, generally yielding reliable ages, andfuture histograms should reflect this, Our results are con-sistent with the temporal subdivision at 610–625 Ma whichseparates convergent margin-related orogenic “older grani-toids” from extensional anorogenic plutonic suites “youngergranites” (Fig. 12; Beyth et al., 1994).
. Cause of discordance in younger granites: There is a lot ofdiscordance in especially the younger granite zircon ages.This is mostly due to the presence of slightly older, xenocrys-tic zircons and to the fact that radiation damage in high Uzircons causes these to act as open systems (Ewing et al.,2003) subject to gain and loss of U, Pb and intermediateradiogenic daughters. CL imaging identifies many of thesedamaged zircons. Unaltered zircon lattices lose very little orno Pb while metamict zircons lose Pb readily. The xenocrys-tic zircons are especially interesting because they reveal thecrustal sources involved in generating the younger granitemelts, as discussed further in (3) below.
. Signficance of older zircons in ED granitic rocks: Zircon inigneous rocks either precipitated from the melt or is pre-magmatic, i.e., entrained as a solid and never dissolved.Pre-magmatic zircon may be accidental, entrained from wallrock through late stage contamination, or inherited, derived
at a deeper level from a contributing source material. Zirconsanalyzed from Qena–Safaga granodiorite show no evidenceof older crust, but the studied younger granites reveal slightlyolder Neoproterozoic components that correspond to igneousResearch 160 (2008) 341–356
rocks that outcrop elsewhere in the ED. Inheritance from pre-Neoproterozoic crust – or any crust older than ∼710 Ma –was not identified. The inherited, xenocrystic Neoproterozoicages can be grouped into three periods that are remarkablysimilar to those defined for ED igneous rocks by Stern andHedge (1985) as follows:(a) 710–690 Ma: Zircons from two plutons define this
period: ∼710 Ma from the Qattar granite (EW2-11,206Pb/238U age) and ∼693 Ma from the Abu Harbagranite (EW1-5; Concordia age). This is similar to715–700 Ma igneous pulse of Stern and Hedge (1985),heretofore only identified in the SE Desert.
(b) 674–650 Ma: Zircons from two plutons define thisperiod: ∼674 Ma from Al Missikat granite (EW5-11;Concordia age) and ∼650 Ma from the Qattar granite(EW2-13, 206Pb/238U age). This episode is similar to665–685 Ma igneous pulse of Stern and Hedge (1985).
(c) 635–610 Ma: Six zircons from three plutons define thisperiod: two ∼635 Ma zircons from Qattar granite (EW2-10; concordant age and EW2-7 206Pb/238U age); two∼624 Ma zircons from Qattar (EW2-6; 206Pb/238U age)and Al Missikat (EW5-8; concordant age). The ∼612 Maage is found in zircons from Um Ara (EW6-4; concor-dant age) and Qattar (EW2-4; 613 Ma concordant age).This period is similar to the 625–610 Ma igneous pulseof Stern and Hedge (1985).
. Evidence for 640–680 Ma magmatic pulse: Based on 666 Mafor Mons Claudianus granodiorite (Stern and Hedge, 1985);644 ± 20 Ma 207Pb/206Pb single-zircon age for Meatiq gran-itoids (Loizenbauer et al., 2001); Sibai ages of 659 ± 14 Ma(Pb/Pb single-zircon ages) and 645 ± 5 Ma for Groups II andIII meta-granodiorite to tonalite (Bregar et al., 2002) andsingle-zircon ages of 654 and 690 Ma from the El Umragranite complex in the Wadi Mubarak belt (Shalaby et al.,2005), it is clear that a major magmatic pulse occurred in theinterval 640–680 Ma, especially in the Central Eastern Desertand perhaps in the NED. The obtained SHRIMP 652 Ma ageand the presence of two similar-age zircons in the youngergranites reveal that the 640–680 Ma episode was an impor-tant time for the generation of older granitoids in the EasternDesert. The studied older Qena–Safaga granitoids (652.5 MaConcordia age) further indicates that the huge older gran-itoid batholith along the discontinuity between NED andCED domains was generated during this interval, but fur-ther zircon geochronology is needed to resolve the age andtectonic significance of this huge batholith. Direct evidencefor this episode has not been found in the NED, but Wildeand Youssef (2000) identified two concordant zircon cores ofDokhan Volcanics (685 ± 16 Ma) and the bulk zircon popula-tion in Hammamat sediments range between 750 and 600 Mawith peak values around 685 and 640 Ma (Wilde and Youssef,2002).
. Age of younger granitoids: The studied younger granitoids
ages range in age between 595 and 605 Ma for NED granites(Abu Harba, 595 Ma and Qattar: 605 Ma); ∼597 Ma for CEDgranites (Al Missikat) and 603 Ma for SED granites (UmAra). These ages represent the second cycle igneous and tec-
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tonic (Stern and Hedge, 1985) and suggest that the youngergranite pulse was significantly shorter than the 620–530 Maage range reported by Hassan and Hashad (1990). It is note-worthy that the ages reported for Abu Harba and Qattaroverlap with those reported by Wilde and Youssef (2000) forthe Dokhan Volcanics (593–602 Ma), supporting the conclu-sion of Stern and Gottfried (1986) that these units developedsynchronously.
. Significance of Nd isotopic compositions: The calculated ini-tial epsilon Nd (εt
Nd) varies between +3.97 and +6.74 for thegranitoids reflecting the juvenile Neoproterozoic nature ofED crust (Dixon and Golombek, 1988). Also, the Nd modelages indicate that the juvenile crust formed ultimately fromdepleted asthenospheric mantle only a few millions to tens ofmillions of years before the granites were produced, either byanatexis of this crust or coupled fractionation of mafic meltsand assimilation of slightly older juvenile crust. The Nd iso-topic results are consistent with results from zircon dating inthis regard.
. No evidence for pre-Neoproterozoic crust beneath the East-ern Desert: The Arabian–Nubian Shield (ANS) is composedlargely of Late Proterozoic volcano-sedimentary arc assem-blages separated by linear belts of ophiolitic sequences thatwere assembled and accreted onto the older African craton600–950 Ma (Stoeser and Camp, 1985). The ANS representsone of the largest such tracts of juvenile crust on Earth occu-pies the northern part of the East African Orogen (EAO) of(Stern, 1994) a major Neoproterozoic orogen that resultedfrom the collision of the East and West Gondwana conti-nents to form the Gondwana supercontinent near the end ofthe Neoproterozoic (Johnson and Woldehaimanot, 2003).
Dixon and Golombek (1988) indicated that the central part ofhe exposed Arabian–Nubian Shield consists mainly of juvenile,
antle-derived oceanic and intra-oceanic island-arc Precam-rian crust, whereas the eastern and western margins consistainly of older continental crust. Also they reported that the
rigin of many granitic intrusions in the shield as resulting fromnteraction of primitive mafic melts with older crustal compo-ents. These melts probably resulted from partial melting ofantle-derived material that had a short residence time in the
ower crust or the mantle itself. The crustal components couldave been derived from an underlying pre-Pan-African basementr from detritus introduced from an adjacent continent.
The extent of involvement of the older craton in the forma-ion of the shield is a subject of debate. Different studies argueor the presence of pre-Neoproterozoic sialic continental crustn Arabian–Nubian Shield (ANS) igneous rocks (Stacey andgar, 1985; Pallister et al., 1988; Kroner et al., 1994; Sultan et
l., 1990; Kennedy et al., 2004; Hargrove et al., 2006). Stoesernd Frost (2006) using Nd, Sr, and Pb isotopic data to con-rm the previous interpretations that the bulk of the Arabianhield is ensimatic in character, and the only older cratonic crust
ithin the region of the exposed Shield is that of the Khidaerrane that are composed of pre-Neoproterozoic continentalrust. More direct evidence for older basement in the core of theNS may come from Zabargad Island of Egypt where granulite
ifra
Research 160 (2008) 341–356 353
neisses yield metamorphic dates of 669 ± 34 Ma (Sm–Nd) and55 ± 8 Ma (Rb–Sr), but initial Nd isotopic data were interpretedo indicate extraction of the protoliths from depleted mantle after200 Ma, and possibly as early as 1700 Ma (Lancelot and Bosch,991). Those model ages are comparable to Mesoproterozoicges for inherited zircon in the Arabian Shield (Hargrove et al.,006). Post-tectonic granites in the CED that contain inheritedircon are possibly anatectic melts of that or a similar continentalomponent (Sultan et al., 1990). Although much of the ANS issotopically juvenile, some Neoproterozoic igneous rocks in theorthern NAS contain zircon inherited from pre-Neoproterozoicources (Hargrove et al., 2006).
From the above discussions, it is clear that the inheritance isecognized in some parts of the ANS but our results indicate nore-Neoproterozoic zircons in the granitoids investigated.
0. Conclusions
Our study of older and younger granitoids in the Egyptianasement complex reveal the following:
. The older and younger granitoids intruded surroundingmetasediments and metavolcanic rocks with sharp contacts.The older granitoids are represented by Qena–Safaga gran-odiorites whereas the younger granitoids are represented bybiotite granites of Abu Harba, Qattar (NED), Al Missikat(CED) and Um Ara (SED).
. Geochemically, the older granitods are metaluminous andformed in a volcanic-arc setting while the younger gran-ites are A-type granites that formed during a post-collisionalphase.
. Crystallization ages for granites studied here ranged from652.5 ± 2.6 Ma for the older granodiorite to 595–605 Ma forthe younger granites.
. The zircon U–Pb SHRIMP isotopic data indicate the presenceof inherited zircon grains derived from slightly older Neo-proterozoic crust. Three magmatic and igneous activities arereported from the inherited zircon grains: 710–690, 675–650,and 635–610 Ma. The 675–650 Ma episode is particularlyimportant because it represents the formation of granitoidsat Qena–Safaga, Meatiq and Sibai.
. We found no evidence for pre-Neoproterozoic crust beneaththe Eastern Desert, either in zircon ages or Nd isotopic com-positions. Therefore, future efforts to this end would bestbe served by combining detailed Nd and Pb isotopic stud-ies with U–Pb single-zircon geochronology employing theion microprobe, which is ideally suited to discriminatingbetween juvenile and inherited zircon.
cknowledgments
The authors would like to thank the SHRIMP-RG Lab. Groupt Stanford University especially Prof. J. Wooden for their help
n analyzing zircons. They acknowledge the efforts and help-ul comment of Prof. Brenda Kaldenbach and two anonymouseviewers which greatly improved the manuscript. The firstuthor (Ewais Moussa) would like to thank Prof. R.J. Stern
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or allowing him the opportunity to be a visitor at Universityf Texas at Dallas. Thanks are due to Prof. A. Abdel-Monemor fruitful discussions during the revision of the manuscript.inally, the help offered by my wife (Prof. Bothaina Moussa)ith the computer writing and figure drafting of the manuscript
s greatly appreciated.
ppendix A. Previous geochronologic and Nd isotopictudies in the Eastern Desert
Greenberg (1981) suggested that the younger granitic plutonsepresent a single magmatic episode 603–575 Ma ago whicharked the end of cratonization and the beginning of truly
norogenic activity in the Egyptian Red Sea Hills.Harris et al. (1984) from model Nd ages of Pan African rocks
n northeast Africa, concluded that the range of εtNd reflects
ifferences in the tectonic regime and in the age of the pre-xisting crust. Juvenile areas of significant crustal accretion havetNd = +2 to +7.
Six crust-forming episodes and two major cycles with dis-inct magmatic and tectonic characteristics were defined for theastern Desert by Stern and Hedge (1985) based on the agesf 24 geological units (15 granitoids) using Rb–Sr and U–Pbircon techniques. The older cycle (765–610 Ma) is character-zed by calc-alkaline igneous products. They concluded thathe 600–575 Ma episode is especially important in the crustalvolution of the north Eastern Desert.
Abdel-Rahman and Doig (1987) carried out a Rb–Sreochronological study of the Ras Gharib segment of theorthern Nubian Shield. They reported ages from oldesto youngest: gabbro-diorite–tonalite (881 Ma), volcanic rocks620 Ma), granodiorite–adamellite and leucogranite (552 Ma),uscovite trondhjemite (516 Ma) orogenic Pan-African suites,
yke swarms (493 Ma) and anorogenic peralkaline granites476 Ma). The old age is 150 Ma older than the next oldest rockn the Eastern Desert and has not been verified with U–Pb zirconating yet. The lower Paleozoic ages for igneous rocks are alsouch younger than any other dates and need to be verified with–Pb zircon techniques.Hassan and Hashad (1990) summarized the literature and
oncluded that eight older granitoids range between a maximumf 850 and a minimum of 614 Ma. For the younger grani-oids (22 granitoid masses), the ages lie within the 620–530 Maange: this 90 Ma time span resolved into two major eventspanning 620–570 (Dokhan event) and 570–530 Ma (Katherinavent).
Nd isotopic studies indicate that gneisses and granites fromouthern Egypt and northern Sudan west of the Nile involvedeworking of older continental crust (Harms et al., 1990), butuch isotopic indications of older crust are not found east of theile in Egypt.El-Debeiky (1994) reported 632 Ma for the old granite
atholith between Safaga and Qena. This comprises a suite of
onalite–granodiorite–monzogranite and in some parts trond-jemites.Moghazi et al. (1998) reported Rb–Sr ages of the Kidabbro-diorite plutonic suite in southeast Sinai; quartz mon-
Research 160 (2008) 341–356
odiorite (581 Ma); granodiorite–monzogranite association576 Ma) and syenogranite (570 Ma). Also, they reported εt
Ndf +4.4 for quartz monzodiorite; εt
Nd of +1.5 to +2.7 forranodiorite–monzogranite and εt
Nd of +4.5 for syenogranitesf Neoproterozoic granitoids in the Kid area (southeast Sinai)eflecting derivation from a mantle source and contradicts theresence of pre-Neoproterozoic sialic crust in Sinai.
Moussa (1998) dated seven granitoids in the NED by theb–Sr whole-rock method (north Wadi Hawashiya granodiorites
841 Ma), Abu Marwa hornblende–biotite granites (641 Ma),mm Araka-Loman (606 Ma) and Milaha (584 Ma), and theiotite granites of Abu Harba (590 Ma), Gabal Qattar (570 Ma)nd north Wadi Hawashiya (556 Ma)).
Loizenbauer et al. (2001) used 207Pb/206Pb single-zircon agesor granitoids at Meatiq metamorphic core complex to indicateagmatic activity at 644 ± 20 Ma. Also, they concluded that the
nherited core age of 1.15 Ga for a single zircon of the ortho-mphibolite xenolith suggests the existence of an older crusthich was intruded by the Um Ba’anib granite at approximately80 Ma.
Bregar et al. (2002) obtained 659 ± 14 Ma and 645 ± 5 Ma forroups II and III meta-granitoids from the Sibai dome (Pb/Pb
ingle-zircon ages). These correspond with older granites ofgypt by Kroner et al. (1994).
Stern (2002) summarized 449 samples from the East Africanrogen (EAO) indicate that the crust of the ANS yields over-helmingly Neoproterozoic model ages and is composed of
uvenile Neoproterozoic crust sandwiched between reworkedlder crust.
Shalaby et al. (2005) dated El Umra granite complex (gran-diorite to tonalite), Wadi Mubarak belt (CED) by single-zirconges as 654 and 690 Ma.
Abdel-Rahman (2006) carried out Rb–Sr radiometric age dat-ng of Gebels Abu-Kharif and El-Dob (central Eastern Desert)hat produced a Cambrian age of 522 ± 21 Ma.
eferences
bdalla, H.M.A., 1996. Geochemical and mineralogical studies at Um Ararare metals prospect, southeastern Desert, Egypt. Ph.D. Thesis. HokkaidoUniversity, Sapporo, Japan, 148 pp.
bdel-Rahman, A.M., 2006. Petrogenesis of anorogenic peralkaline graniticcomplexes from eastern Egypt. Mineral. Mag. 70 (1), 27–50.
bdel-Rahman, A.M., Doig, R., 1987. The Rb–Sr geochronological evolutionof the Ras Gharib segment of the northern Nubian Shield. J. Geol. Soc. Lond.144, 577–586.
bu Dief, A., 1992. The relation between uranium mineralization and tectonicsin some Pan-African granites, West of Safaga, Egypt. Ph.D. Thesis. Al AssiutUniversity, Assiut, 218 pp.
entor, Y.K., 1985. The crustal evolution of the Arabo-Nubian massif withspecial reference to the Sinai Peninsula. Precamb. Res. 28 (1), 1–74.
eyth, M., Stern, R.J., Altherr, R., Kroner, A., 1994. The late Precambrian Timnaigneous complex, southern Israel: evidence for comagmatic-type sanukitoidmonzodiorite and alkali granite magma. Lithos 31, 103–124.
lack, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley,
J.W., Mundil, R., Campbell, I.H., Korsch, R.J., Williams, I.S., Foudoulis, C.,2004. Improved 206Pb/238U microprobe geochronology by the monitoringof a trace-element-related matrix effect: SHRIMP, ID-TIMS, ELA-ICP-MSand oxygen isotope documentation for a series of zircon standards. Chem.Geol. 205 (1–2), 115.
brian
B
D
D
D
E
E
E
E
G
H
H
H
H
H
H
H
J
K
K
L
L
L
L
M
M
M
M
P
P
P
P
R
S
S
S
SS
S
S
S
S
S
S
S
S
S
S
E.M.M. Moussa et al. / Precam
regar, M., Bauernhofer, A., Pelz, K., Kloetzli, U., Fritz, H., Neumayr, P., 2002.A late Neoproterozoic magmatic core complex in the Eastern Desert ofEgypt: emplacement of granitoids in a wrench-tectonic setting. Precamb.Res. 118, 59–82.
avis, D.W., Williams, I.S., Krogh, T.E., 2003. In: Hanchar, J.M., Hoskin,P.W.O. (Eds.), Historical Development of Zircon Geochronology: Reviewsin Mineralogy and Geochemistry, pp. 145–181.
ePaolo, D.J., 1981. Neodymium isotopes in the Colorado Front Range andcrust-mantle evolution in the Proterozoic. Nature 291, 193–196.
ixon, T.H., Golombek, M.P., 1988. Late Precambrian crustal accretion rates inNortheast Africa and Arabia. Geology 16, 991–994.
l-Debeiky, S.A., 1994. Petrology, geochemistry and geochronology of theold granite batholith between Safaga and Hurghada, Eastern Desert, Egypt.M.Sc. Thesis. Faculty of Science, Ain Shams University, 203 pp.
l-Gaby, S., List, F.K., Tehrani, R., 1988. Geology, evolution and metallogenesisof the Pan-African belt in Egypt. In: El-Gaby, S., Greiling, R.O. (Eds.),The Pan-African Belt of Northeast Africa and Adjacent Areas, Vieweg, pp.17–70.
l-Shazly, S.M., El-Sayed, M.M., 2000. Petrogenesis of the Pan-African El-Bulaigneous suite, Central Eastern Desert, Egypt. J. Afr. Earth Sci. 31, 317–336.
wing, R.C., Meldrum, A., Wang, L., Weber, W.J., Corrales, L.R., 2003. Radi-ation effects in zircon. Rev. Mineral. Geochem. 53, 387–425.
reenberg, J.K., 1981. Characteristics and origin of Egyptian younger granites.Geol. Soc. Am. Bull. 92 (pt. 2), 749–840.
argrove, U.S., Stern, R.J., Kimura, J.-I., Manton, W.I., Johnson, P.R., 2006.How juvenile is the Arabian–Nubian Shield? Evidence from Nd isotopesand pre-Neoproterozoic inherited zircon. Earth Planet. Sci. Lett. 252 (3–4),308–326.
arms, U., Schandelmeir, H., Darbyshire, D.P.F., 1990. Pan African reworkedearly/middle Proterozoic crust in NE Africa west of the Nile: Sr and Ndisotope evidence. J. Geol. Soc. Lond. 147, 859–872.
arris, N.B.W., Hawkesworth, C.J., Ries, A.C., 1984. Crustal evolution in north-east and east Africa from model Nd ages. Nature 309, 773–776.
ashad, A.H., 1980. Present status of geochronological data on the Egyptianbasement complex. In evolution and mineralization of the Arabian–NubianShield. Inst. Appl. Geol. Jeddah Bull. 3 (3), 31–46.
assan, M.A., Hashad, A.H., 1990. Precambrian Egypt. In: Said, R. (Ed.),Geology of Egypt. Balkema Publications, Netherlands, 734 pp.
ilmy, H.M., Ahmed, A.F., El Mahallawi, M.M., Ali, S.M., 2004. Pressure, tem-perature and oxygen fugacity conditions of calc-alkaline granitoids, EasternDesert of Egypt, and tectonic implications. J. Afr. Earth Sci. 38, 255–268.
oskin, P.W.O., Schaltegger, U., 2003. The composition of zircon and igneousand metamorphic petrogenesis. Rev. Mineral. Geochem. 53, 27–62.
ohnson, P.R., Woldehaimanot, B., 2003. Development of the Arabian–Nubianshield: perspectives on accretion and deformation in the northern EastAfrican Orogen and the assembly of Gondwana. In: Yoshida, M., Dasgupta,S., Windley, B. (Eds.), Proterozoic East Gondwana: Supercontinent Assem-bly and Breakup 206. Special Publication No. 206. Geological Society ofLondon, London, pp. 289–325.
ennedy, A., Johnson, P.R., Kattan, F.H., 2004. SHRIMP geochronology in thenorthern Arabian Shield. Part 1. Data acquisition. Saudi Geological SurveyOpen File Report SGS-OF-2004-11, 28 pp.
roner, A., Kruger, J., Rashwan, A.A., 1994. Age and tectonic setting of gran-itoid gneisses in the Eastern Desert of Egypt and south-west Sinai. Geol.Rundsch. 83, 502–505.
ancelot, J.R., Bosch, D., 1991. A Pan-African age for the HP-HT granulitegneisses of Zabargad Island: implication for the early stages of the Red Searifting. Earth. Planet. Sci. Lett. 107, 539–549.
oizenbauer, J., Wallbrecher, E., Fritz, H., Neumayr, P., Khudeir, A.A., Kloetzli,U., 2001. Structural geology, single zircon ages and fluid inclusion studiesof the Meatiq metamorphic core complex: implications for Neoproterozoictectonics in the Eastern Desert of Egypt. Precamb. Res. 110, 357–383.
udwig, K.R., 2000. Isoplot/Ex 3.0: A Geological Toolkit for Microsoft Excel.
Berkeley Geochronology Center Special Publication, p. 1.udwig, K.R., 2001. 2001 SQUID 1.02 Add-In for ExcelTM. BerkeleyGeochronology Center.
oghazi, A.M., Andersen, T., Oweiss, G.A., El Bouseily, A.M., 1998. Geo-chemical and Sr–Nd–Pb isotopic data bearing on the origin of Pan African
S
Research 160 (2008) 341–356 355
granitoids in the Kid area, southeast Sinai, Egypt. J. Geol. Soc. Lond. 155,697–710.
oussa, E.M.M., 1994. Geochemistry of some granitic masses and their relationto the tectonic evolution of the northern Eastern Desert, Egypt. M.Sc. Thesis.Ain Shams University, Cairo, 212 pp.
oussa, E.M.M., 1998. Geochronological studies of some granitoids: applica-tion to geochemical evolution and tectonic history of the northern EasternDesert, Egypt. Ph.D. Thesis. Ain Shams University, 284 pp.
oussa, E.M.M., 2006. Post-collisional A-type granites at Al Missikat and AlAradiya, Eastern Desert, Egypt: geochemical characteristics and REE pet-rogenetic modeling. In: Proceedings of the 7th International Conference onGeochemistry. Alex. University, Egypt, 1, 1–16.
allister, J.S., Stacey, J.S., Fischer, L.B., Premo, W.R., 1988. Precambrianophiolites of Arabia: geologic settings, U–Pb geochronology, Pb-isotopecharacteristics, and implications for continental accretion. Precamb. Res. 38(1), 1–54.
earce, J.A., 1996. Sources and settings of granitic rocks. Episodes 19 (4),120–125.
earce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace element discrimina-tion diagrams for the tectonic interpretation of granitic rocks. J. Petrol. 25,956–983.
upin, J.P., 1980. Zircon and granite typology. Contrib. Mineral. Petrol. 73,207–220.
ubatto, D., 2002. Zircon trace element geochemistry: partitioning with gar-net and the link between U–Pb ages and metamorphism. Chem. Geol. 184,123–138.
alman, A.B., Shalaby, M.H., Moussa, E.M.M., Roz, M.A., 2006. Rare earthelements petrogenitic modelling of Gabal Abu Harba granites, North East-ern Desert, Egypt. In: Proceedings of the 7th International Conference onGeochemistry. Alex. University, Egypt, 1, 59–72.
halaby, A., Stiiwe, K., Makroum, F., Fritz, H., Kebede, T., Klotzli, V., 2005. TheWadi Mubarak belt, Eastern Desert of Egypt: a Neoproterozoic conjugateshear system in the Arabian–Nubian Shield. Precamb. Res. 136, 27–50.
halaby, M.H., 1990. Uranium mineralization in northen Gabal Qattar local-ity, northern Eastern Desert, Egypt. In: Proceedings of the Symposium onPhanerozoic and Development, Faculty of Science, Al-Azhar University, 19pp.
hand, S.J., 1951. Eruptive Rocks. John Wiley, New York.hapiro, L., Brannock, W.W., 1962. Rapid analysis of silicate, carbonate and
phosphate rocks. U.S. Geol. Surv. Bull. 1144A, 56 pp.tacey, J.S., Agar, R.A., 1985. U–Pb isotopic evidence for the accretion of a
continental micro-plate in the Zalm region of the Saudi Arabian Shield. J.Geol. Soc. Lond. 142 (6), 1189–1203.
tern, R.J., 1981. Petrogenesis and tectonic setting of late Precambrian ensimaticvolcanic rocks, central Eastern Desert, Egypt. Precamb. Res. 16, 195–230.
tern, R.J., 1994. Arc assembly and continental collision in the NeoproterozoicEast African Oroge: implications for the consolidation of Gondwanaland.Annu. Rev. Earth Planet. Sci. 22, 319–351.
tern, R.J., 2002. Crustal evolution in the East African Orogen: a neodymiumisotopic perspective. J. Afr. Earth Sci. 9, 109–117.
tern, R.J., Gottfried, D., 1986. Petrogenesis of late Precambrian (575–600 Ma)bimodal suite in north-east Africa. Contrib. Mineral. Petrol. 92, 492–501.
tern, R.J., Hedge, C.E., 1985. Geochronologic and isotopic constraints on latePrecambrian crustal evolution in the Eastern Desert of Egypt. Am. J. Sci.285, 97–127.
tern, R.J., Voegeli, D.A., 1987. Geochemistry, geochronology, and petrogenesisof a late Precambrian (∼590 Ma) composite dike from the north EasternDesert of Egypt. Geol. Rundschau. 76, 325–341.
toeser, D.B., Camp, V.E., 1985. Pan-African microplate accretion of the Ara-bian Shield. Geol. Soc. Am. Bull. 96, 817–826.
toeser, D.B., Frost, C.D., 2006. Nd, Pb, Sr and O isotopic characterization ofSaudi Arabian Shield terraines. Chem. Geol. 226, 163–188.
treckeisen, A., 1976. To each plutonic rock its proper name. Earth Sci. Rev.
12, 1–33.ultan, M., Chamberlain, K.R., Bowring, S.A., Arvidson, R.E., Abu Zied, H.,El Kaliouby, B., 1990. Geochronologic and isotopic evidence for involve-ment of pre-Pan-African crust in the Nubian Shield, Egypt. Geology 18,761–764.
3 brian
T
W
W
W
56 E.M.M. Moussa et al. / Precam
uttle, O.F., Bowen, N.L., 1958. Origin of granites in the light of experimentalstudies in the system of NaAlSi3O8–KAlSi3O8–H2O. Geol. Soc. Am. Mem.74, 153 pp.
halen, J.B., Curri, K.L., Chappell, B.W., 1987. A-type granites: geochemical
characteristics, discrimination and petrogenesis. Contrib. Mineral. Petrol.95, 407–419.ilde, S.A., Youssef, K., 2000. Significance of SHRIMP U–Pb dating of theImperial Porphyry and associated Dokhan Volcanics, Gabal Dokhan, northEastern Desert, Egypt. J. Afr. Earth Sci. 31 (2), 403–413.
W
Z
Research 160 (2008) 341–356
ilde, S.A., Youssef, K., 2002. A re-evaluation of the origin and setting of theLate Precambrian Hammamat Group based on SHRIMP-U–Pb dating ofdetrital zircons from Gebel Umm Tawat, North Eastern Desert, Egypt. J.Geol. Soc. Lond. 159, 595–604.
illis, K.M., Stern, R.J., 1988. Age and geochemistry of late Precambriansediments of the Hammamat series from the north Eastern Desert, Egypt.Precamb. Res. 42, 173–187.
en, E., Hammarstrom, J.M., 1984. Magmatic epidote and its petrologic signif-icance. Geology 12, 515–518.
