Journal of African Earth Sciences 100 (2014) 510–523

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Journal of African Earth Sciences

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Provenance of the heavy mineral-enriched alluvial deposits at the westcoast of the Red Sea. Implications for evolution of Arabian–Nubian crust

http://dx.doi.org/10.1016/j.jafrearsci.2014.07.0151464-343X/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author.E-mail address: mali3@miners.utep.edu (M.A. Mahar).

Munazzam Ali Mahar a,⇑, Tarek M.M. Ibrahim b, Philip C. Goodell a

a Department of Geological Sciences, University of Texas at El Paso, El Paso, USAb Nuclear Materials Authority, Cairo, Egypt

a r t i c l e i n f o a b s t r a c t

Article history:Received 10 December 2013Received in revised form 15 July 2014Accepted 15 July 2014Available online 12 August 2014

Keywords:Arabian–Nubian ShieldDetrital zircon geochronologyMagmatic evolutionAlluvial fan depositsProvenanceJuvenile Neoproterozoic crust

Here we present the LA-ICP-MS U–Pb ages and Hf isotopic record of detrital zircons from the active allu-vial fans at the west coast of the Red Sea. The Ras Manazal alluvial fan (primarily composed of zircon,magnetite with some rutile, ilmenite and monazite) yielded a relatively restricted age population rangesfrom 765 to 666 Ma. These ages and present-day drainage pattern is consistent that the sediments areprimarily derived from erosion of nearby subduction related granitoids in the immediate west (i.e., notmore than 50 km from the Red Sea coast) of the fan. In contrast, approximately 160 km south, at theEgypt–Sudan border, the Wadi Diit fan is relatively more enriched in ilmenite and REE-bearing phases(e.g., thorite, monazite, xenotime, garnet, etc.) and yielded five zircon age populations of (1) 824–733 Ma, (2) 730–705 Ma, (3) 646–608 Ma, (4) 516–500 Ma, and (5) 134–114 Ma. The age populations1–3 if coupled with the present-day drainage pattern can be related to the earlier subduction relatedand later post collision granitoids in the southern part of the South Eastern Desert and Gebeit terraneof northern Sudan. Sparse Early Cretaceous zircons (134–114 Ma) are derived from the Mesozoic volcanicsuits in the source region. However, the age group 516–500 Ma is enigmatic. Wadi Diit zircons are pri-marily derived from granitoids in the broad S–N directed Hamisana Shear Zone and its subordinateSW to NE directed Onib-Sol-Hamed Suture Zone. These shear zones provided pathways for the pres-ent-day drainage system for sediment transportation to the Wadi Diit and adjacent coastal region. Weinfer that the ca. 500 Ma late-stage magmatic zircons represent a hitherto unknown magmatic event,possibly related to the shear heating associated with the crustal scale shear zones. This implies thatthe shear zones in the South Eastern Desert and northern Sudan remained thermally active as late as�500 Ma. The time resolved hafnium composition (eHf (t)) of both fans varies from +3.5 to +13.5. Ournew U–Pb ages and Hf isotopic composition suggests that the detrital zircons were derived from the Neo-proterozoic juvenile crust. This is consistent with the Neoproterozoic juvenile igneous and metamorphicrocks in the Eastern Desert and northern Sudan.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The combined U–Pb and Hf isotopic record of detrital zirconsprovides insight regarding source region history of parental magmawith which the zircon was in equilibrium at the time of crystalliza-tion. In the last two decades numerous studies have been devotedto the isotopic record of detrital zircons to establish detailed crustalevolution models (e.g., Griffin et al., 2006; Belousova et al., 2010;Kuznetsov et al., 2010; Matteini et al., 2010 and references therein)and sedimentary provenance interpretations (e.g., Koglin et al.,2010; Clements et al., 2012 and references therein).

The Eastern Desert of Egypt is a part of the Neoproterozoic Ara-bian–Nubian Shield formed between 900 and 550 Ma by accretionof several mainly intra-oceanic arcs along ophiolitic sutures(Kröner, 1985; Stoeser and Camp, 1985; Vail, 1985; Johnson,1998, 2014; Stern and Johnson, 2010; Ali et al., 2009, 2010a,b,2012a; Johnson et al., 2011; Fritz et al., 2013) (Fig. 1). One of thelongstanding controversies in this region is the origin of lower–middle crust beneath the Eastern Desert of Egypt forming the wes-tern part of the Arabian–Nubian Shield. Structurally lower granit-oid gneisses exhumed in the form of gneiss domes in the EasternDesert are suggested to have a component of the older, pre-Neo-proterozoic crust that is pre-Pan-African basement (e.g., El-Gabyet al., 1984, 1988; Khudier et al., 2008). Many other workers sug-gested that the Arabian–Nubian crust is juvenile and exclusivelyNeoproterozoic in age formed in an intra-oceanic arc setting within

Fig. 1. The age range based on U–Pb single and multi-grain zircon dating onplutonic and volcanic rocks of Eastern Desert and northern Sudan (compiled byJohnson, 2014 and references therein). The ages given in rectangles are protolithages (after Johnson et al., 2011 and references therein).

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the Mozambique Ocean, or along one or more magmatic arcs alongthe western margin of the Mozambique Ocean prior to the finalcollision of East and West Gondwana about 630 Ma (e.g., Greilinget al., 1984, 1988, 1994; Kröner et al., 1987; Stern, 1994; Liégeoisand Stern, 2010; Ali et al., 2012a,b).

The Red Sea coast in the Eastern Desert is accumulating thealluvial deposits by active erosion and transportation throughthe present-day drainage system during recent flash flooding.Several alluvial deposits enriched in REE bearing minerals havebeen identified in the coastal strip between Ras Banas in the northand at the Egypt–Sudan border in the south (Ibrahim et al., 2009).Accumulations of heavy minerals have been observed along RedSea beaches at Ras Manazal, Khudaa, Shalateen, Wadi Diit, andalong the coastal stretches between these locations. The morphol-ogy and positions of the alluvial fans with respect to the coast lineindicate that the sediments derived nearly exclusively from theinterior drainage areas, with marginal input from a longshore sed-iment transport. Therefore, it seems less likely that the alluvialfans have significant contribution from other parts of the RedSea coast by longshore currents. The denudation and erosion ofthe Eastern Desert have been investigated using apatite fissiontrack dating (e.g., Omar and Steckler, 1995; Bojar et al., 2001;Abbate et al., 2002; Balestrieri et al., 2009). This dating indicatesthat the Arabian–Nubian Shield underwent uplift in two stages,an early uplift stage in the Oligocene (±35 Ma) and a later majoruplift period in the Miocene (20–25 Ma). During these uplifts ofthe flanks of the rift zone, sediments might have transported tothe coastal areas of the Red Sea. However, if there were such earlycoastal deposits, they have since been eroded, submerged in theRed Sea or deeply buried (Moawad, 2013). Therefore, our samplesdo not belong to these ancient Oligocene to Miocene coastal sed-

iments, but instead represent the top 1 m of the active alluvialfans transported by present-day drainage system through recentflash flooding periods.

In this paper we report ‘‘in-situ’’ U–Pb ages and time resolvedHf isotopic composition of detrital zircons from the two alluvialfans in the South Eastern Desert along the west coast of Red Seawhich have been recording the sediment accumulation arguablyfrom proximal and distant sources from Eastern Desert andnorthern Sudan. Our data not only provide additional con-straints regarding evolution of the Arabian–Nubian Shield inthe Eastern Desert of Egypt but also test the provenance of min-eralogically and geochemically distinct black sands alluvialdeposits along the west coast of Red Sea. The determination ofthe provenance of these sands has significant implications forthe economic development emphasizing the sources of REE-enriched deposits.

2. Geological setting

2.1. Eastern Desert of Egypt

The Eastern Desert of Egypt is primarily characterized as Neo-proterozoic crust of the Arabian–Nubian Shield formed duringthe accretion stage-2 between 760–650 Ma of East African Orogenyand is separated from Gebiet and Gabgaba terranes in the southformed during the accretion stage-1 between 890–710 Ma (Fritzet al., 2013 and references therein, Fig. 1). The Neoproterozoic crustis traditionally divided into two groups (Greiling et al., 1994), (1)the structurally lower, so-called infrastructure group (El-Gabyet al., 1984) composed of granitoid orthogneisses and migmatitesexposed in the domal structures in Meatiq, Sibai, Shalul and Hafafitgneiss complexes from north to south in the Central and SouthernEastern Desert and (2) surrounding Neoproterozoic ophiolite com-plexes, island arc-related low grade (green schist facies) metavol-canic and metasedimentary assemblages, referred as thesuprastructure group (Fig. 2). The infra- and suprastructures areseparated by the Eastern Desert Shear Zone (EDSZ; Andresenet al., 2010). Further to the west, these Neoproterozoic rocks arebordered by the pre-Neoproterozoic Sahara metacratonic crust,however this transition is poorly understood (e.g., Abdelsalamet al., 2002, Figs. 1 and 2).

The granitoids of Eastern Desert of Egypt are generally subdi-vided into two groups, ‘‘Older and Younger’’ granites (e.g., ElRamly and Akaad, 1960). The calc–alkaline to alkaline older granitesare typically deformed and have variable composition from quartzdiorite to tonalite/trondhjemite and quartz monzonite. Tectoni-cally, the older granites are interpreted as synorogenic, subductionrelated and emplaced at convergent plate boundaries. Geochrono-logical data suggest that these rocks were emplaced between 880and 610 Ma (Johnson, 2014 and references therein). The Youngeralkaline to peralkaline or metaluminous granites are post colli-sional, undeformed and shallowly emplaced. These rocks are char-acterized as within-plate A-type granites (Kröner et al., 1994;Bregar et al., 2002; Shalaby et al., 2005; Moussa et al., 2008;Andresen et al., 2009; Pease et al., 2010; Lundmark et al., 2012).Mineralogically, older subduction related granites in the EasternDesert are interpreted as magnetite series granites (e.g., Botrosand Wetait, 1997; El-Gaby et al., 1988; Hussein et al., 1982) whilelater post collision granites are suggested to be ilmenite series gran-ites (e.g., Hussein et al., 1982). Volcano-sedimentary rocks are alsopresent primarily in the Eastern Desert and northern Sudan (e.g.,Kröner et al., 1987). The Dokhan volcanics and Hammamat Groupcrops out in post amalgamation basins of Eastern Desert. Both unitsare of variable thicknesses with a maximum of 1300 m and 7000 m,respectively (e.g., Eliwa et al., 2006; Abd El-Wahed, 2010).

Fig. 2. Lithological units surrounding the alluvial fan deposits in the Central Eastern Desert (CED), South Eastern Desert (SED) and northern Sudan (after Kröner et al., 1987).The age range for CED (including southward Hafafit) granitoid gneisses are based on robust U–Pb zircon ID-TIMS, SIMS and LA-ICP-MS ages (Lundmark et al., 2012 andreferences therein). The age range shown for southern part of SED and northern Sudan are same as in Fig. 1. The dashed boxes around study area are the locations for Fig. 8.RS: Ras Manazal, WD: Wadi Diit.

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2.2. North Sudan

North Eastern Sudan mainly consists of Gebeit and Gabgabaterranes separated by the prominent Hamisana Shear Zone (e.g.,Kröner et al., 1987; Stern et al., 1989, Figs. 1 and 2). The Gebeit ter-rane is interpreted as the dissected block from western Arabiawhich is part of the Hijaz terrane (Stoeser and Camp, 1985). Similarrocks of the South Eastern Desert extend further south in the Gebe-it terrane (Fig. 2). The northernmost part of the Gebiet terrane ismainly composed of (1) earlier to syntectonic magmatic rocks,referred to as ‘‘batholithic granites’’ by Neary et al. (1976), (2) posttectonic granitoids (younger granitoids), (3) volcano-sedimentaryrock assemblages and (4) ophiolites (Kröner et al., 1987, Fig. 2).West of Hamisana Shear Zone and south of Allaqi Heiani suturezone the terrane is known as Gabgaba terrane and is bounded bythe pre-Neoproterozoic crust in the west (Almond and Ahmed,1987; Stern and Kröner, 1993).

2.3. Geochronology of Eastern Desert and northern Sudan

Much effort has been dedicated to establish the geochronology(based on zircon U–Pb single and multigrain dating) of the EasternDesert and northern Sudan regions (Fig. 1, see also Johnson, 2014;Lundmark et al., 2012; Johnson et al., 2011; Stern et al., 2010; andreferences therein). The magmatic and volcanic rocks of Northernand Central Eastern Desert are mainly dated at 699–550 Ma and749–550 Ma, respectively. However, few older ages, 880–800 Maand >880 Ma are also reported from Central Eastern Desert. Thenorthern part of South Eastern Desert is generally dated at 749–650 Ma while southern part, close to Egypt–Sudan border, olderages range from 880 to 750 Ma are also recognized (Figs. 1 and 2).

Based on new robust U–Pb ID-TIMS and previous agesLundmark et al. (2012) identified six pulses of magmatism andmetamorphism in the Central and South Eastern Desert that are,

(1) 705–680 Ma, (2) �660 Ma, (3) 635–630 Ma, (4) 610–604 Ma,(5) 600–590 Ma and (6) 540 Ma (Fig. 2). The authors suggested thatgranites with ages from 705 to 630 Ma have a syn-orogenic originwhile later magmatic rocks of ages between 610 to 590 Ma arerelated to the post orogenic exhumation of mid-crustal gneissesalong the Eastern Desert Shear Zone, while the last pulse is inter-preted to be unrelated to the East African Orogeny. However, basedon U–Pb SHRIMP zircon dating, Ali et al. (2012b) assigned slightlyolder ages of 630–620 Ma to the post collision A-type granites inCentral Eastern Desert. In addition to igneous and metamorphicrocks, volcano-sedimentary rocks are also widespread throughoutthe Eastern Desert and northern Sudan (e.g., Kröner, 1987). U–PbSHRIMP zircon ages including Rb–Sr and conventional U–Pb zircondating suggest that the Dokhan volcanics erupted during 630–592 Ma (e.g., Breitkreuz et al., 2010; Wilde and Youssef, 2000and references therein). The Hammamat Group was depositedbetween 593–579 Ma (U–Pb SHRIMP; Wilde and Youssef, 2000).

For northern Sudan, we mainly describe the ages from theGebeit terrane and the region around the Hamisana Shear Zoneadjacent to the study area (Fig. 2). The new multigrain and singlegrain zircon U–Pb dating assigns the Neoproterozoic ages from880 to 649 Ma to the volcano-magmatic suit of the northernmostpart of the Gebeit terrane (Johnson, 2014; Stern et al., 2010, Figs. 1and 2). Previously, batholithic granitoids were assigned youngerRb–Sr ages of 720–660 Ma (Cavanagh, 1979; Vail et al., 1984;Klemenic, 1985). Post collision granitoids are dated at 570–550 Ma (Rb–Sr ages, Almond et al., 1989). Sm–Nd isochron agesof volcanic rocks placed an age of 832 ± 26 Ma (Reischmannet al., 1985). The metavolcanics overlying Sol-Hamed suture zoneand the Kadaweb Group are dated at 712 ± 58 and 723 ± 6 Ma(whole rock Rb–Sr ages), respectively (Fitches et al., 1983;Klemenic, 1985). Stern and Kröner (1993) suggested that thenortheast Sudan crust formed during 810 and 580 Ma, with pre-dominant crust generation at around 700 Ma. Based on their ages,

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suturing between east and west Gondwana is suggested to occur at600–700 Ma.

In summary, available geochronological data suggest that mostof the Arabian–Nubian Shield in the Eastern Desert and northernSudan is related to the Neoproterozoic crust. The majority of theages from Eastern Desert fall in the range from 750 to 540 Ma,rocks in the Gebeit terrane in northern Sudan are as old as880 Ma. No zircons in the South Eastern Desert and northern Sudanhave yielded an older inherited Paleoproterozoic component (Sternet al., 2010).

2.4. Major structural features

The South Eastern Desert of Egypt has been affected by the N–Soriented Hamisana Shear Zone with two subordinate suturesnamely, the Onib-Sol-Hamid suture striking to the east (Red Sea)and Allaqi-Heiani suture striking to the west in southern Egypt(Fig. 2). These two suture zones separate the South Eastern Desert(Gerf ophiolitic nappe) terrane in the north from the 830–700 MaGebeit and Gabgaga terranes of northern Sudan on the south(Johnson et al., 2011 and references therein) (Fig. 2). The HamisanaShear Zone was active during the Pan-African Orogeny and hasimparted a strong directional fabric to the gneissic and metamor-phosed basement rocks in the region (Stern et al., 1989) (Fig. 2).The Hamisana Shear Zone is a broad zone of deformation, approx-imately 50 km wide and at least 300 km long, making it one of thelargest basement structures in NE Africa. This shear zone has beeninterpreted as a Precambrian suture, as a zone of strike-slip dis-placement, or as a zone of crustal shortening. The results of Rb–Sr and U–Pb zircon geochronological studies suggested that thenorthern Hamisana Shear Zone was thermally active during Pan-African Orogeny (Stern et al., 1989). They also implied that theShear Zone remained thermally active about 50–150 Ma followingthe collisional suturing and terrane assembly at �550 Ma in theArabian–Nubian Shield (Stern et al., 1989).

3. Study area

The study area lies east and northeast of the igneous and meta-morphic rocks of South Eastern Desert and northern Sudan, respec-tively (Figs. 2 and 3). At the Red Sea coastline, heavy mineral-enriched alluvial fans extend from Ras Banas to Egypt–Sudan bor-der (Fig. 3a). Black-sand deposits were accumulated as lensesthrough recent flash flooding operating in the Eastern Desert. Thealluvial sands are primarily transported by ephemeral river sys-tems in the desert with minimal input from the longshore currentsas evident by drainage pattern and river directions (Fig. 7). Itshould be noticed that the sediments transported to the ancientcoast of the Red Sea due to the Neogene uplifting are eroded, sub-merged or deeply buried, and hence are not the subject of thisstudy. The studied samples represent the top 1 m of active alluvialfans. The distal (towards the coast) section of the fans is deltashaped while the elevated medial and proximal part of the depositshas typical fan type morphology. All samples were collected fromup-land alluvial fan sediments, for comparison, one sample thatis D113 collected from the distal, possibly wave modified deltamaterial in the Wadi Diit (see slope profile BB0 in Fig. 3). For sim-plicity we will henceforth refer these coastal deposits as alluvialfans.

3.1. Ras Manazal

The Ras Manazal is an east-directed alluvial fan and is about3 km long with a width between 50 m and 500 m (Fig. 3a and b).The fan is relatively steep with an apex at 100 m elevation about

6 km from the coast (Fig. 3b, profile AA0). The sample, RS representsthe medial part of the fan �2 km from the coast, and is approxi-mately 29 m above sea level. The fan morphology, elevation anddistance from the Red Sea coast require a minimal influence oflongshore currents in transporting the sands from other parts ofthe Eastern Desert along the coast (Fig. 3; profile AA0). The sedi-ments are primarily deposited by the present-day west to eastdirected active alluvial channels. Fig. 3e and g represent the extentand thickness of the black sand accumulation.

3.2. Wadi Diit

The Wadi Diit is a SW–NE directed triangular alluvial fan. Thefan is broad and relatively flat with an apex 40 km from the shore-line (Fig. 3c, profile BB0). The alluvial fan features two lenses ofblack sand, which extend for 5 km along the shoreline with anaverage width of 30 m and a thickness varying from 30 to 80 cm(Fig. 3d and f). Concentrations of black sand occur in the form ofdetached patches, varying from a few meters to hundreds ofmeters in length.

Three composite samples were taken covering the fan of WadiDiit from the apex to the beach. Sample D113, D111 and D116 rep-resents the distal, medial and proximal parts of the fan respectively(Fig. 3c). Two samples, D111 and D116 are 20 and 32 km up-landfrom the coast and thus represent the active alluvial fan deposits.The sample D113 is collected from the delta at the shoreline(Fig. 3c; profile BB0). Therefore, in sample D113, in addition tothe present-day fluvial channels, influence of the longshore cur-rents to transport material from other parts of the coast is likely.The coastal strip in the distal parts of Wadi Diit slopes down NWfrom SE, therefore, sediment contribution from Halaib region inEgypt is also expected (Figs. 2 and 3). Samples were obtained byusing either a 3 m auger or by digging trenches to a depth of 1 m(Fig. 3h and i).

3.3. Mineralogical and geochemical characteristics of Ras Manazal andWadi Diit fans

Black sand deposits from Ras Manazal and Wadi Diit fansshowed variable mineralogical and geochemical features. Ras Man-azal sands are generally enriched in magnetite, zircon and rutile,while Wadi Diit fan is strongly enriched in REE bearing phases,includes zircon, garnet, ilmenite, rutile, thorite monazites, xeno-time and Chevkinite. Wadi Diit ilmenite is enriched in TiO2, andin some ilmenite TiO2 concentration reaches up to 50%. This is veryhigh compared to the northward Ras Manazal fans (Ibrahim et al.,2011). The considerable higher REE-bearing phases and TiO2

enrichment indicates that the Wadi Diit black sand may have dif-ferent source region history than the 160 km northward Ras Man-azal sands. This implies that the Ras Manazal black sand depositsmight source from the magnetite series granites while Wadi Diitfan is accumulated from the ilmenite series lithologies. The magne-tite series granitoids has been reported from the Eastern Desert ofEgypt. Botros and Wetait, (1997), El-Gaby et al. (1988), Husseinet al. (1982) suggested that the subduction related older granitoidsare magnetite series granitoids of Ishihara’s (1977) formed in theold Benioff zone in the mantle wedge with no significant crustalinput. The younger post collision granites are interpreted as ilmen-ite series granitoids (Hussein et al., 1982).

3.4. Zircon morphology

Zircons were separated using standard procedures of magneticand heavy liquid at the University of Texas at El Paso. Backscat-tered electron (BSE) images of all the mounted grains wereacquired before U–Pb analyses to differentiate core and rim

Fig. 3. (a) Alluvial fan deposits at the west coast of Red Sea from Ra’s Banas to the Egypt–Sudan border. (b and c) Orientation and extent of the fans with sample locations(slope profiles from proximal to the distal part of the fan are also shown. (d and e) View of black sand accumulations at the coast. (f and g) Alternative thin layers of light andblack sands. (h and i) An example of augering to collect the composite sample (Image Landsat, US Dept of state Geographer @ 2014, ORION-ME, Data SIO, NOAA, U.S. Navy,NGA, GEBCO).

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domains and to identify metamictization, inheritance and mineralinclusions so that suitable undisturbed clean spots could beselected for isotopic analyses. After U–Pb analyses, selected grainswere re-imaged by high resolution Cathodoluminescence (CL) tolocate the Hf beam on top of U–Pb pits and to avoid the grainswhere U–Pb pits overlapped the multiple growth domains (Fig. 4).

Ras Manazal (RS) zircons are larger, subhedral to euhedral withlength to width ratio of 1:2, average length of grains is 100 to200 lm. The zircons are essentially magmatic characterized bystrong oscillatory and sector zoning (Fig. 4a). No inherited compo-nent is observed in almost all grains. In contrast to RS zircons,Wadi Diit (WD) zircons are smaller, subhedral to subrounded tosubangular with an average length range from 50 to 100 lm. LikeRS zircons, Wadi Diit zircons are also magmatic representing oscil-latory and sector zoning. No inherited component is observed inBSE and CL images (Fig. 4b). The zircon morphology and internal

structure from both WD and RS shows no evidence of sedimentaryrecycling.

4. Methodology

4.1. U–Pb geochronology using LA-MC-ICP-MS

U–Pb zircon geochronology was performed at the ArizonaLaserChron Center using LA-MC-ICP-MS instrument. The fullmethod is described in (Gehrels et al., 2008). Here we brieflydescribe our specific analytical protocol.

Separated zircons were mounted on a 1 inch epoxy mount alongwith Sri Lanka zircons, polished, imaged and cleaned prior to isoto-pic analysis. The analyses involve ablation of zircon with a PhotonMachines Analyte G2 excimer laser using a beam diameter of

Fig. 3 (continued)

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30 lm. The ablated material is carried in Helium into the plasmasource of a Nu HR ICPMS, which is equipped with a flight tube ofsufficient width that U, Th and Pb isotopes are measuredsimultaneously.

All the measurements were made in static mode using Faradaydetectors with 3 * 1011 O resistors for 238U, 232Th, 208Pb, 206Pb anddiscrete dynode ion counters for 204Pb and 202Hg. Each analysisconsists of one 15-s integration on peaks with the laser off (forbackgrounds), 15 one-second integrations with the laser firingand a 30 s delay to purge the previous sample and prepare forthe next analysis. Common Pb correction is accomplished byusing the Hg corrected 204Pb and assuming an initial Pb compo-sition from Stacey and Kramers (1975). Inter-elementfractionation of Pb/U is generally �5%, whereas apparent fraction-ation of Pb isotopes is generally <0.2%. In-run analysis of frag-ments of a large zircon crystal (generally every fifthmeasurement) with known age of 563.5 ± 3.2 Ma (2r error) isused to correct for this fractionation. The uncertainty resultingfrom the calibration correction is generally 1–2% (2r) for both206Pb/207Pb and 206Pb/238U ages. Concentration of U and Th werecalibrated relative to standard Sri Lanka zircons (U = 18 ppm andTh = 68 ppm).

4.2. LA-MC-ICP-MS zircon Hf isotope measurements

The Hf isotopes were measured at the LaserChron lab facility,University of Arizona by LA-MC-ICP-MS following the methoddescribed in Cecil et al. (2011). Lu–Hf measurements were carriedout with a laser beam diameter of 40 lm, with the ablation pitslocated on top of the pits generated during U–Pb analysis. CLimages are used to confirm that the ablation pit is inclusion freeand should not be overlapping multiple age domains.

First, instrument settings are established by analysis of 10 ppbsolutions of JMC475 and a Spex Hf solution, and then by analysisof 10 ppb solutions containing Spex Hf, Yb, and Lu. The mixturesrange in concentration of Yb and Lu, with 176(Yb + Lu) up to 70%of the 176Hf. Once all solutions yield 176Hf/177Hf of �0.28216,instrument settings are adjusted for laser ablation analyses andseven different standard zircons (Mud Tank, 91500, Temora, R33,FC52, Plesovice, and Sri Lanka) are analyzed. All these standardsare mounted on the same epoxy along with the unknowns. Whenprecision and accuracy are adequate, unknowns are analyzed usingexactly the same acquisition parameters. The MC-ICP-MS utilizes12 Faraday detectors equipped with 3 � 1011 O resistors and 4 dis-crete dynode ion counters. During Hf analysis masses 171, 173,

Fig. 4. CL images of detrital zircons from the Ras Manazal and Wadi diit alluvial deposits, the pit is generated during U–Pb analysis.

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175, 176,177, 178, 179, and 180 were all measured simultaneouslyin Faraday collectors.

The 176Hf/177Hf at time of crystallization is calculated frommeasurement of present-day 176Hf/177Hf and 176Lu/177Hf, using adecay constant of 176Lu (k = 1.867e�11) from Scherer et al. (2001)and Söderlund et al. (2004). Chondritic values of Bouvier et al.(2008) were adopted for the calculation of eHf (t) values.

5. Results

5.1. U–Pb geochronology

All the detrital zircon (DZ) U–Pb ages from Wadi Diit and RasManazal are listed in Supplementary material, Table 1. In thisstudy 196 and 52 zircons were randomly selected from WD and

RS deltas respectively and were individually dated in order to rec-ognize major age populations. The probability of missing a prove-nance component should not be higher than �5%, although it maybe higher in the Ras Manazal site because at least 59 randomlyselected grains are measured to reduce the probability of missingany provenance component to <5% (Dodson et al., 1988). However,Vermeesch (2004) suggested more than 100 detrital zircons areneeded to obtain an adequate statistic reliability of not missing sig-nificant age populations. The number of analyzed zircons from RasManazal (n = 52) are less than the recommended minimum of 100(Vermeesch, 2004). Therefore, a certain fraction of the age popula-tions, particularly one comprising less than 5% of the total analyzedgrains may be missed. However, this reconnaissance paper is moredirected to the general provenance of the sediments rather anexhaustive account of detailed geochronology.

Fig. 5. Summarize the LA-ICP-MS U–Pb geochronological data on detrital zircons.(a) Probability density plots for detrital zircon ages presented in this study. Since allthe ages are <825 Ma, we used 206Pb/U238 ages. (b) Represents the overall variationsin the U–Pb data from both fans. (c and d) are the concordia plots, most of the agesare concordant (analyses yielding <90% and >105% concordance shown as redellipses on the concordia plots, were not used in the age probability plots). (e) Th/Uratio of all the studied zircons, range for magmatic (>0.2–0.4) and metamorphiczircons (<0.1) is from Williams and Claesson (1987) and Rubatto and Gebauer(2000).

Fig. 6. Plots of detrital zircon U–Pb ages vs eHf (t). The 176Hf/177Hf at time ofcrystallization is calculated from measurement of present-day 176Hf/177Hf and176Lu/177Hf, using a decay constant of 176Lu (k = 1.867e�11) from Scherer et al.(2001) and Söderlund et al. (2004). Chondritic values of Bouvier et al. (2008) wereadopted for the calculation of eHf (t) values.

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5.1.1. Detrital zircon ages from Wadi Diit FanIn Wadi Diit at the Egypt-Sudan border, dominantly four Neo-

proterozoic age populations were identified, (1) 824–733 Ma, (2)730–705 Ma, (3) 646–608 Ma and (4) 516–500 Ma (Fig. 5a andb). The U–Pb zircon age populations shown in relative probabilityplots (Fig. 5a) and age histogram (Fig. 5b) do not include ages withconcordance less than 90 or greater than 105%. In sample D113, thedistal part of the fan, youngest ages of 134–114 Ma were also iden-tified. These Early Cretaceous ages were not found in other twosamples collected from up-land medial and proximal parts of thefan. The oldest age of 824 Ma (113-TOP-94) was also found inthe distal part of the fan, other older ages include 813 Ma (113-TOP-11) and 808 Ma (D111–43). No pre-Neoproterozoic compo-nent was identified through this study. One of the significantresults is that we report an age component of � 516–500 Ma(n = 27). Fig. 5c shows the concordia plot of all the ages from Wadi

Diit zircons, where red error ellipses are the ages with either lessthan 90 or greater than 105% concordance. The dominant propor-tion of the younger Neoproterozoic ages (516–500 Ma), identifiedin all Wadi Diit samples (Fig. 5a) are essentially concordant andplots onto or closer to the concordia line indicating that theseare not resulted from Pb loss (Fig. 5c). No evidence of inheritanceis observed with regards to U–Pb ages as well as zircon morphol-ogy studied through CL and BSE images (Fig. 4b). The Th/U ratiofrom the Wadi Diit zircons remains higher than 0.2 in most cases.This coupled with strong oscillatory zoning suggests that the zir-cons have predominantly magmatic origin. Only five grains yieldedTh/U ratio less than 0.2 (Fig. 5e).

5.1.2. Detrital zircon ages from Ras ManazalIn contrast to multiple age populations observed in Wadi Diit

zircons, Ras Manazal yielded ages ranging from 765–666 Ma(Fig. 5a and b). A total of 41 out of 51 ages fall in the narrow rangeof 729–690 Ma (Fig. 5a and b). No pre-Neoproterozoic agecomponent was identified in Ras Manazal sample. Also, in contrastto Wadi Diit, Ras Manazal zircons yielded neither younger Neopro-terozoic ages of 516–500 Ma nor the Early Cretaceous ages. Thismight be due to the less number of analyzed grains, particularlythe Cretaceous zircons found in Wadi Diit constitutes only lessthan 5 percent of the total. Except one analysis (RS-94; 82% concor-dant.), all the ages are essentially concordant with majority at <5%

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discordance (Fig. 5d). The Th/U ratio of all the zircons (except onegrain) is higher than 0.2 indicating their magmatic origin (Fig. 5e).

5.2. Hf isotopic data

All the Hf isotopic data on selected grains are listed in theSupplementary material (Table 2). The initial hafnium isotopecomposition (eHf (t)) of the individual samples from both fans isgiven in (Fig. 6). The Hf isotopic measurements are aimed on topof the pits created during U–Pb analysis (Fig. 4). The uncertaintyin the Hf composition of individual analysis shown in the datatable is at 1r.

5.2.1. Wadi Diit zircons5.2.1.1. Sample D113 (distal part of the fan). The majority of the zir-cons from Wadi Diit fan yielded a juvenile positive Hf composition.The eHf (t) for zircon populations with ages 804–701 Ma from thedistal part of the fan (D113) varies from +6.6 to +13.9. The youngerpopulation, 668–500 Ma yielded relatively evolved values rangingfrom +2.2 to +8.3. Two zircons (D113-28 and 29) dated at 634and 642 Ma yielded highly evolved eHf (t) values of �20 and�18.8. In addition, two of the youngest zircons dated at 114 and134 Ma yielded eHf (t) composition of +10.6 and +3.5.

5.2.1.2. Sample D111 (Medial part of the fan). Ten zircons with ages753–691 Ma yielded similar and indistinguishable juvenile initialeHf (t) composition ranges from +7.5 to +12.5. The younger compo-nent with ages 634–502 Ma rendered similar juvenile eHf (t) val-ues of +4.0 to +9.2. One sample dated at 659 yielded negative Hfcompositions of �3.8 while one sample (665 Ma) yielded extremeevolved Hf composition of �30.4.

5.2.1.3. Sample D116 (proximal part of the fan). Nine analyses withU–Pb ages ranging from 729–694 Ma yielded initial eHf (t) compo-sition ranging from +7.2 to +10.9. Two samples with younger ages

Fig. 7. (a and b) Size and orientation of drainage basins and river flow directions (over-laHSZ: Hamisana hear Zone, SH: El-Shalul, S: El-Sibai, M: Meatiq, NED: North Eastern Deseavailable at <http://hydrosheds.cr.usgs.gov/data.php>.

516 and 644 Ma show Hf composition of +3 and +6.7. One zircondated at 643 Ma rendered non radiogenic value of �10.9.

5.2.2. Ras Manazal zirconsThe initial eHf (t) composition of Ras Manazal zircons dated at

723–688 Ma is ranging from +4.1 to +12.4. Hf composition of 27out of 31 zircons varies from +7.9 to +12.4. The youngest zircondated at 606 Ma yielded eHf (t) composition of +3.5. The Hf isoto-pic composition of Ras Manazal zircons is indistinguishable fromthe Wadi Diit zircons of comparable ages (725–690 Ma).

6. Discussion

6.1. Drainage system and structural trend in the Eastern Desert andnorthern Sudan

The first order observation is that all the present-day drainagebasins along the coastal regions are predominantly confinedwithin the 50 km from the Red Sea coast (Fig. 7). In the northernand central part of the Desert, drainage basins are either east-directed or WSW to ENE oriented. In the Ras Manazal area, thedrainage is west to east and confined within the 30–40 km fromthe coast indicating that the Ras Manazal sediments are providedby the proximal coastal mountains by active fluvial channels. Fur-ther south, close to Wadi Diit, a change in the orientation of thedrainage system can be noticed that is SSW–NNE directed, partic-ularly within the 150 km along the coast (Fig. 7a). Notably, thecatchment area is relatively larger and nucleating from the prox-imal mountains of South Eastern Desert of Halaib region andadjacent Gebeit terrane in the northern Sudan (Fig. 7a). The Riverflow directions follow the general trend of the basins describedabove and primarily originating from the mountains locatedwithin the 50–70 km of the coast (Figs. 7b, 8a and b). Drainagebasins and River directions suggest that the alluvial deposits donot have larger and more distant sources. This is particularly truefor the Ras Manazal alluvial fan (Figs. 7b and 8a). It is observed

id on Digital Elevation Model) in the Eastern Desert and northern Sudan. H: Hafafit,rt. Drainage basins, DEM and River flow directions are compiled from the shape files

M.A. Mahar et al. / Journal of African Earth Sciences 100 (2014) 510–523 519

that the drainage patterns in the Ras Manazal and Wadi Diitregion are not consistent with sediment transportation fromnorthward located Central Eastern Desert (Fig. 8a and b). SampleD113 is collected from the distal part of the fan at the coast andsediment transport from the longshore currents is likely for thissample. The coastal strip at the Wadi Diit slopes from SE toNW (Fig. 2, Fig. 8). Therefore, the contribution from longshorecurrents should be from SE-ward located deltas in the Halaibregion. Nonetheless, in both cases (fluvial and longshore currents)the sources would still be confined in the southern part of theSouth Eastern Desert and northern Sudan.

In the Ras Manazal, structural foliation trends are essentially E–W oriented and only confined to the coastal mountains (Fig. 8c). InWadi Diit, shear zones, particularly S–N directed Hamisana ShearZone and its subordinate SW–NE directed Onib-Sol-Hamed suturezone primarily controls the structural grain (Figs. 2 and 8d). Thesemajor structures and their associated weak zones provided theconduits for present-day drainage basins running through SouthEastern Desert and NS to the coastal region of Wadi Diit (Fig. 8band d).

Fig. 8. (a and b) Drainage patterns and river directions around Ras Manazal and Wadi DiitJohnson et al., 2011). Relative probability plots of U–Pb detrital zircon ages (this study) aunits in the southern part of South Eastern Desert and northern Sudan. AH: Allaqi–HeianiSudan, ONSH: Onib-Sol-Hamed Suture, OSZ: Oko Shear Zone RS: Ras Manazal, WD: Wa

6.2. Origin of detrital zircons in Ras Manazal

Our new U–Pb detrital zircon ages predominantly range from765 to 666 Ma, broadly coinciding with the U–Pb zircon ages(750–650 Ma) from the South Eastern Desert in the immediatewest of the alluvial fan (Figs. 1 and 2). This coupled with the drain-age pattern and structural trends suggest that the early subductionrelated granitoids are the most likely sources for Ras Manazal zir-cons (Fig. 8a, c and e). As discussed in the previous sections, the RSsample represents the up-land medial part of the active fan about2 km from the coast. Hence, the probability of sediment transportby longshore currents from other parts of the Red Sea coast is lesslikely. The Late Cryogenian–Ediacaran (650–542 Ma) age popula-tion is a predominant component in the Central Eastern Desertand North Eastern Desert and is virtually absent in the Ras Manazal(Fig. 2). This further strengthens the interpretation that the RasManazal zircons are (1) predominantly derived from early subduc-tion related granitoids, and (2) sediments were provided from theproximal sources. This is likely because in the 30–50 km west ofthe Ras Manazal, early subduction related granitoids are the

alluvial fans respectively, (c and d) shear zones and structural foliation trends (afternd zircon U–Pb age range in the source regions are also given, (e and f) lithological(suture zone), Gab: Gabgaba, Geb: Gebeit, HSZ: Hamisana Shear Zone, NS: Northern

di Diit.

520 M.A. Mahar et al. / Journal of African Earth Sciences 100 (2014) 510–523

dominant rock type with considerable scarcity of younger grani-toids (Fig. 2, Fig. 8e). Previously Ali et al., 2010a reported Paleopro-terozoic U–Pb SHRIMP ages (i.e., 2.9–1.9 Ga and 2.7–2.1 Ga.) fordetrital zircons from the diamictites in the Central Eastern Desert.Alluvial fans in the study area did not sample this pre-Neoprotero-zoic component of Central Eastern Desert. It can be argued that theanalyzed grains (n = 52) are not sufficient to represent all the zir-con age populations (Vermeesch, 2004) and we do not contest thispitfall. However, given the W–E directed drainage pattern, riverdirections, orientation of structure foliations, similar ages (749–650 Ma) in the immediate west of the alluvial fan and absence ofinherited ages with predominance of older subduction relatedgranitoids (Fig. 8), we propose that the Ras Manazal sedimentsare not derived from northward granitoid gneisses. The presenceof the subhedral–euhedral larger zircon crystals is also consistentwith the proximal source interpretation. Previously, subductionrelated older granitoids were interpreted to be magnetite seriesgranitoids of Ishihara’s (1977) (Botros and Wetait, 1997; El-Gabyet al., 1988; Hussein et al., 1982). Considerable deficiency of TiO2

content in the Ras Manazal (Ibrahim et al., 2011) corroboratesour interpretation that the zircons were provided from magnetiteseries older subduction related granitoids of South Eastern Desert.The younger post collision granites are interpreted as ilmenite ser-ies granitoid (Hussein et al., 1982) which makes the smaller pro-portion of rock types in the source region.

6.3. Origin of detrital zircons in Wadi Diit

As previously discussed, the drainage pattern around the WadiDiit fan are SSW–NNE directed suggesting that the sediments areprimarily provided from the southward Halaib region of the SouthEastern Desert and Gebeit terrane. The fluvial channels stronglyfollow the shear zones of the primarily N–S oriented HamisanaShear Zone, its SW–NE directed subordinate Onib-Sol-Hamed(ONSH) suture zone and associated structures providing the path-ways for sediment transportation (Fig. 8b, d and f). The multipleage populations in the Wadi Diit are consistent with the presenceof a variety of rocks in the source region, primarily matching rocksalong the ONSH shear zone (Figs. 2 and 8d and f). These rocksinclude earlier-to-syntectonic to post collision granitoids, migma-tites and volcano-sedimentary assemblages (Fig. 8f). Our U–Pbdetrital ages of 824–550 Ma, in combination with the drainage sys-tem and associated fluvial channels are consistent with a prove-nance from the southernmost part of South Eastern Desert andGebeit terrane in the northern Sudan, with no significant compo-nent from north and far westerly located rocks.

The unusual age population ranging from 516–500 Ma and afew Early Cretaceous ages remain to be explained. Johnson(2014) did not include the U–Pb ages younger than 540 Ma(Fig. 1). Stern et al. (2010) suggested that the ages <550 Ma inthe Arabian–Nubian Shield are not related to the Pan-African Orog-eny, as no igneous rocks intrudes the unconformity (forming at550 Ma) between Cambrian sandstone and underlying basement(Stern et al., 2010). Therefore, zircon ages from the igneous base-ment <550 Ma should not be related to the Pan-African Orogeny(e.g., Stern et al., 2010). However, zircons yielding U–Pb postPan-African ages ca. 500 Ma were identified in all three samples(n = 27) and nonetheless are the part of Arabian–Nubian crust.

Drainage pattern and structural foliations suggest that thedetrital zircons in the Wadi Diit are related to the Neoproterozoicjuvenile magmatic rock assemblages associated with the HamisanaShear Zone and its subordinate Onib-Sol-Hamed suture zonelocated in the south eastern desert and northern Sudan (Fig. 8f).Therefore, we infer that these U–Pb ages represent a post Africanmagmatic event in deep crust and the magmatic zircons were crys-talized from the melt generated by shear heating associated with

the crustal scale shear zones. The magmatic origin of these zirconsis further supported by strong oscillatory zoning and higher Th/Uratio (>0.2) predominantly ranging from 0.2 to 2.5 (Fig. 5e). There-fore, we propose that the data reveal hitherto unknown magma-tism in relation to the shear zones. Since Wadi Diit sand isenriched in ilmenite and higher in TiO2 content, we suggest thatthe new zircons potentially crystalized from melt generated bypartial melting of ilmenite series post collision granites (Husseinet al., 1982) emplaced within the shear zones at �540 Ma. Sternet al. (1989) implied that the Hamisana Shear Zone remained ther-mally active about 50–150 Ma following the collisional suturingand terrane accretion in the Arabian–Nubian Shield. This couldbe possibly true as evident by these younger ages from the WadiDiit zircons which are primarily sourced from the granitoids ofSouth Eastern Desert and northern Sudan Shear zones. Alterna-tively, there is possibility that the ca. 500 Ma zircons formed inresponse to the metamorphic conditions in the shear zones. Zir-cons crystallize and grow at a variety of temperature and condi-tions (e.g., Harley et al., 2007; Watson et al., 2006). Along thecooling path new zircons can grow at any temperature between>1000 �C to below 600 �C (e.g., Harley et al., 2007). Processes andthe causes that formed these late-stage zircons may include sub-solidus post-peak reactions and fluid–rock interactions at �30–20 Ma following the emplacement of ilmenite rich post collisiongranitoids at �540 Ma. Zircons can potentially grow below600 �C as interpreted based on their lower Ti concentration(Watson et al., 2006). These late-stage zircons could have formedunder subsolidus conditions and are related to reheating of postcollision granites. In this case, most of the Ti has already beentaken up by the ilmenite and the late-stage Ti-deficient zirconscan grow at temperatures lower than 600 �C under subsolidus con-ditions while the shear zones in the South Eastern Desert andnorthern Sudan were still thermally active around 520–500 Ma.Other metamorphic conditions to form zircons include Zr liberat-ing from the breakdown of minerals like garnet and rutile duringdecompression melting (Harley et al., 2007) or by Zr-liberationfrom ilmenite as a reaction product (Bingen et al., 2001). These lat-ter interpretations require the knowledge of REE and Ti content ofthe zircons. Also, strong oscillatory zoning and higher Th/U ratiosuggest the magmatic origin of these zircons.

A few zircons with the youngest ages of 134–114 Ma (only foundin sample D113) are potentially derived from the mantle derivedMesozoic volcanics (191–74 Ma) of South Eastern Desert and north-ern Sudan (e.g., Franz et al., 1987; Satir et al., 1991; El-Hemaly et al.,2012). These rocks are widespread in the southern Desert andnorthern Sudan and their composition varies from olivine basaltto trachyte. It is likely that these Early Cretaceous zircons in the dis-tal part of Wadi Diit fan are transported by longshore currents.

6.4. Implications for the crust in the Eastern Desert and northernSudan

U–Pb ages and other isotopic records (e.g. Sr, Nd and Hf) fromthe individual igneous and metamorphic rocks may identify theages and origin of different magmatic pulses and episodes. How-ever, the isotopic composition of detrital zircons records the com-posite response in a particular crustal tract and provides furtherconstraints on the source region history and crustal evolution.

Recent geochronological and isotopic data (Sr, Nd and Hf) fromthe Eastern Desert suggested that the Arabian–Nubian Shield ispredominantly composed of Neoproterozoic juvenile crust (Aliet al., 2009, 2012a,b; Liégeois and Stern, 2010; Andresen et al.,2009; Moussa et al., 2008; Stoeser and Frost, 2006; Bregar et al.,2002). The eNd values for the Neoproterozic crust (�560–820 Ma) varies from �+3 to +10. And these values are similar tothe Abu Hamamid mafic–ultramafic complex and Shadli

M.A. Mahar et al. / Journal of African Earth Sciences 100 (2014) 510–523 521

metavolcanics (south of Hafafit) in the South Eastern Desert witheNd ranges from +6.9 to +7.7 (Sm/Nd modal age of 770 ± 20 Ma)and +6.3 to +7.8 (Rb–Sr ages of 712 ± 24) respectively (Helmyet al., 2005; Stern et al., 1991). Zircons from the calc–alkaline,gneissic El Shalul granites dated at 637 ± 5 Ma and 630 ± 6 Mashowed a time resolved eHf (t) values ranging from +12.0 and+6.1 with a mean of +9.3 (Ali et al., 2012a). Similarly, Stern andKröner (1993) suggested that the crust in the NE-Sudan is mainlygenerated during 810 and 580 Ma, with dominant magmatic eventaround 700 Ma. Isotopic data (e.g., Rb–Sr and Sm–Nd) from the NESudanese crust is indistinguishable from the eastern Egypt and isprimarily derived from the juvenile sources with initial 87Sr/86-

Sr = 0.7019 to 0.7030, eNd (t) = +5.1 to +7.7 with no evidence ofpre-Neoproterozoic evolved crust. However, based on SIMS,U–Pb ages and oxygen isotopic measurements of detrital zirconsfrom the Sa’al schist in Sinai and whole rock Nd isotopic recordfrom the northern most part of Arabian–Nubian Shield, involve-ment of pre-Neoproterozoic crust (1.0–1.1 Ga) is suggested(Be’eri-Shlevin et al., 2009 and references therein). Based on theirzircon oxygen (6.1–9.4‰) and lower Nd isotopes (�+2), supracru-stal recycling was interpreted in the formation of c. 1.1–1.0 Gacrust. The pre-Neoproterozoic ages on detrital zircons and evolvedcomposition of multiple isotopes (Nd, Sr, Pb, and O) from Sinai isattributed to crust formed at the northeastern margin of westernGondwana prior to the Arabian–Nubian Shield formation(Be’eri-Shlevin et al., 2009 and references therein).

Detrital zircons in our region neither sampled pre-Neoprotero-zoic ages nor an evolved crustal signature. This further supportsour interpretation that the studied zircons are not sourced fromcontaminated pre-Neoproterozoic crust at the northern margin ofArabian–Nubian Shield. It also implies that the South EasternDesert and northern Sudan may not directly correlate with theigneous-metamorphic evolution of northern part of the Arabian–Nubian Shield in the Sinai region.

Our new detrital zircon U–Pb ages and Hf isotope composition(eHf (t) = +3 to +13) from Ras Manazal and Wadi Diit areas atteststhat the Arabian–Nubian Shield is predominantly composed ofNeoproterozoic juvenile crust, formed by accretion of severalmainly intra-oceanic arcs (e.g., Kröner, 1985; Stoeser and Camp,1985; Vail, 1985; Quick, 1991; Johnson, 1998, 2014; Ali et al.,2009, 2010b, 2012a; Stern and Johnson, 2010; Fritz et al., 2013)between 900 and 550 Ma as the Mozambique Ocean closed(Stern, 1994). This contradicts with other interpretations in whichrole of pre-Neoproterozoic non radiogenic component is advocated(e.g. Khudier et al., 2008).

Despite the predominant juvenile signature, five zircons withages 659 to 634 Ma showed variable none-radiogenic values witheHf (t) ranging from �3.8 to �30.4. These zircons may representminor partial melting of supracrustal lithologies (metapelites)present at the margin of colliding plates. The ages of these zirconsare consistent with the timing of collision of west and east Gondw-ana. The two Hf analyses on youngest zircons of ages 114 and134 Ma also showed juvenile character with eHf (t) of +10.6 and+3.4, respectively. These youngest zircons may be correlated withthe Mesozoic magmatism in the Arabian–Nubian Shield.

7. Conclusion

� U–Pb detrital zircon ages (765–666 Ma) from the Ras Manazalcoincide with the zircon U–Pb ages from South Eastern Desertin the immediate west of the alluvial fan. U–Pb ages, zirconmorphology, drainage pattern and structural trends are consis-tent with the provenance from proximal sources through thepresent-day drainage system, predominantly by materialeroded from nearby older subduction related granitoids.

� In contrast, Wadi Diit alluvial deposits show five distinctage populations, (1) 824–733 Ma, (2) 730–705 Ma, (3)646–608 Ma and (4) 516–500 Ma, (5) 134–114 Ma. Based onthese ages, present-day drainage pattern and orientation ofshear zones; we suggest that the alluvial fan sediments weresourced from the southern part of South Eastern Desert andthe Gebeit terrane in the northern Sudan. The U–Pb ages areconsistent with a source region that includes rocks of variableages, including earlier arc related and post tectonic granitoids� Our U–Pb ages, with absence of pre-Neoproterozoic inherited

component and Hf composition of the detrital zircons suggeststhat the sources of these zircons are essentially juvenile andNeoproterozoic in age. No contribution from evolved pre-Neo-proterozoic crust is identified. This interpretation is consistentwith previous age and isotopic data from the Arabian–NubianShield.� A younger post tectonic concordant age population (516–

500 Ma) is only found in the detrital zircons from Wadi Diit.These zircons are interpreted to be derived from rock assem-blages along the Hamisana Shear Zone and its subordinatebranch Onib-Sol-Hamed suture zone. We infer that these postPan-African magmatic zircons crystalized from the melt gener-ated by shear heating related to the crustal scale shear zones inthe source region. This provides further constraints on the pre-vious interpretation that the shear zones in South Eastern Des-ert were thermally active about 50–150 Ma following thecollisional suturing (Stern et al., 1989). However, presentU–Pb and Hf isotopic data are insufficient to conclude thishypothesis. Additional studies focusing trace element geochem-istry of zircons and coexisting phases, microstructures andTi-in-zircon temperatures are suggested to provide furtherconstraints.

Acknowledgements

We are grateful to Dominique Giesler, Mark Pecha and Dr.Clayton Loehn at LaserChron, University of Arizona for technicalassistance in the sample preparation, analysis, and data reductionisotopic data (U-Pb and Hf) acquisition and zircon BSE & CL-imaging. Discussions with Dr. T.L. Pavlis and Dr. Gail L. Arnoldhelped improve this manuscript. The collaborative research isfunded by US-AID Program for science and technology cooperation.Anders Mattias Lundmark and an anonymous reviewer areacknowledged for helpful comments and suggestions.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.jafrearsci.2014.07.015.

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