Precambrian Research 123 (2003)

Precambrian Research 123 (2003) 203–221

Neoproterozoic deformation in the northeastern part ofthe Saharan Metacraton, northern Sudan

Mohamed G. Abdelsalama,∗, El-Shaikh M. Abdel-Rahmanb,El-Fadil M. El-Fakib, Bushra Al-Hurb, Fathel-Rahman M. El-Bashierb,

Robert J. Sterna, Allison K. Thurmonda

a Center for Lithospheric Studies, The University of Texas at Dallas, Richardson, TX 75083-0688, USAb Regional Geological Mapping Department, Geological Research Authority of the Sudan, Khartoum, Sudan

Received in revised form 4 March 2002; accepted 5 March 2002

Abstract

The northeastern part of the Saharan Metacraton is dominated by medium to high-grade gneisses and migmatites, disruptedby belts of low-grade volcano-sedimentary sequences representing arc assemblages and highly dismembered ophiolites, andintruded by A-type granitoids. This part of the Saharan Metacraton is affected by three Neoproterozoic deformation events:(1) Emplacement of S- to SE-verging nappes of ophiolites and passive margin sediments. The most prominent of these nappesis the Atmur-Delgo fold and thrust belt which extends westward from the eastern margin of the Saharan Metacraton to justeast of the Third Cataract Nile. This belt is interpreted as manifesting the closure of a restricted oceanic basin between theBayuda and Halfa Terranes at∼700–650 Ma. (2) Development of N- to NE-trending folds as a result of E-W shortening thataccompanied NW-SE oblique collision between the Saharan Metacraton and the Arabian-Nubian Shield at∼650–590 Ma.This event, although dominantly localized along the Keraf Suture at the boundary between the Saharan Metacraton and theArabian-Nubian Shield, also resulted in deformation within the northeastern part of the Saharan Metacraton. N- to NE-trendingfolds occur either as broad belts (Wadi Halfa Fold Belt) or narrow and discrete zones (Third Cataract Shear Zone). Thruststacking and folding thickened the Saharan Metacraton lithosphere as shown by numerous gneissic domes, such as the DelgoDome, in the northern part of the Bayuda Terrane. Crustal thickening also generated A-type granitoids that intrude the north-eastern part of the Saharan Metacraton. E-W shortening culminated in the development of∼590–550 Ma, N- to NNW-trendingsinistral strike-slip shear zones, sometimes coinciding with the N-trending fold belts as in the case of the Third CataractShear Zone. (3) Thickening of the Saharan Metacraton lithosphere triggered orogenic collapse with N-trending moderate-anglenormal-slip faults developed after 550 Ma. Neoproterozoic deformation and igneous activity in the northeastern part of theSaharan Metacraton are interpreted as due to processes that involve collision, lithospheric mantle delamination, and regionalextension.© 2003 Elsevier Science B.V. All rights reserved.

Keywords: Saharan Metacraton; Northern Sudan; Neoproterozoic deformation

∗ Corresponding author.E-mail address: [email protected] (M.G. Abdelsalam).

1. Introduction

Africa comprises Archean cratons such as theCongo and West African Cratons and Neoprotero-zoic orogenic belts such as the Arabian-Nubian and

0301-9268/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.doi:10.1016/S0301-9268(03)00068-8

204 M.G. Abdelsalam et al. / Precambrian Research 123 (2003) 203–221

Fig. 1. The Saharan Metacraton (modified afterAbdelsalam et al., 2002).

the Tuareg Shields (Fig. 1). However, the tract ofcontinental crust that occupies the area between theArabian-Nubian Shield in the east and the TuaregShield to the west and the Congo Craton in the southand the Phanerozoic cover of the northern margin ofthe African continent in southern Egypt and Libya(Fig. 1) is not a craton nor an orogenic belt in theclassical meanings of the terms. Geochronologicaland isotopic data (Pegram et al., 1976; Klerkx andDeutsch, 1977; Meinhold, 1979; Abdel-Monem andHurly, 1979; Dixon, 1981; Barth et al., 1983; Harriset al., 1984; Ries et al., 1985; Curtis and Lenz, 1985;Pin and Poidevin, 1987; Toteu et al., 1987; Kroneret al., 1987; Wust et al., 1987; Pin and Poidevin, 1987;Schandelmeier et al., 1988; Wust, 1989; Davidsonand Wilson, 1989; Harms et al., 1990, 1994; Sultan

et al., 1990, 1992, 1993, 1994; Stern and Dawoud,1991; Stern et al., 1994; Küster and Liégeois, 2001)indicate that this crust contains heterogeneous mix-ture of Archean, Paleo-, Meso-, and Neoproterozoicrocks which have old continental as well as juvenileisotopic signature. This contrasts with the Neopro-terozoic juvenile crust of the Arabian-Nubian Shieldto the east and the Archean continental crust of theCongo Craton and the West Africa Craton in thesouth and west respectively. This region largely con-sist of pre-Neoproterozoic continental crust which isdominated by medium- to high-grade gneisses andmigmatites as well as containing a significant amountof Neoproterozoic juvenile material including arcassemblages and dismembered ophiolite belts andA-type granitoids.

M.G. Abdelsalam et al. / Precambrian Research 123 (2003) 203–221 205

Precambrian rocks exposed in this region werepreviously referred to as the Nile Craton (Rocci,1965), the Sahara-Congo Craton (Kroner, 1977), theEastern Saharan Craton (Bertrand and Caby, 1978),or the Central Saharan Ghost Craton (Black andLiegeois, 1993). Abdelsalam et al. (2002)reviewedgeochronologhical and isotopic data and proposed thename “Saharan Metacraton.” They defined the term“metacraton” as “a craton that has been mobilizedduring an orogenic event but that is still recognizabledominantly through its rheological, geochronological,and isotopic characteristics.” They further explainedthat the prefix “meta” abbreviates “metamorphosis”in the general sense of the term and not only therestricted geological meaning “metamorphosis.”Abdelsalam et al. (2002)also identified boundaries forthe Saharan Metacraton on the east, west, and southwhereas its northern boundary is not known becauseit is buried under Phanerozoic cover. The easternboundary of the Saharan Metacraton is defined bythe N-trending Keraf-Kabus-Sekerr Suture in easternSudan and northeastern Kenya (Fig. 1). This suture re-sulted from collision between the Saharan Metacratonin the west and the Arabian-Nubian Shield to the east(Vail, 1983, 1985, 1988; Almond and Ahmed, 1987;Abdelsalam and Dawoud, 1991; Abdelsalam et al.,1995, 1998, 2000; Abdelsalam and Stern, 1996). Thewestern boundary of the metacraton is assigned to theN-trending Raghane Shear Zone in Algeria and Niger(Fig. 1) and thought to be the product of collision be-tween the metacraton in the east and the Tuareg Shieldto the west (Liégeois et al., 1994, 2000; Abdelsalamet al., 2002). The southern boundary of the SaharanMetacraton is defined by the E-trending OubanguidesOrogenic Belt in Cameroon, Central African Republicand Congo (Fig. 1). This orogenic belt is interpretedas a suture between the Saharan Metacraton and theCongo Craton (Pin and Poidevin, 1987; Abdelsalamet al., 2002). Abdelsalam et al. (2002)further pro-posed a model that involves collision, sub-continentallithospheric mantle delamination, regional extensionand assembly of exotic terranes to explain remobiliza-tion of the Saharan Metacraton during Neoproterozoictime.

Neoproterozoic remobilization of the northeasternpart of the Saharan Metacraton was in the form ofdeformation (Vail, 1971, 1976; Schandelmeier et al.,1987; Stern et al., 1994; Sultan et al., 1994; Denkler

et al., 1994; Harms et al., 1994; Abdelsalam et al.,1995, 1998; Küster and Liégeois, 2001), metamor-phism (Kroner et al., 1987; Stern and Dawoud,1991; Denkler et al., 1994) and emplacement ofA- and I-type granitoids (Harms et al., 1990, 1994;Stern et al., 1994; Sultan et al., 1990, 1992, 1994).Moreover, the northeastern part of the SaharanMetacraton might have been affected by openingof restricted oceanic basins that were subsequentlyclosed, resulting in collision between drifted blocks(Schandelmeier et al., 1991, 1994; Abdel-Rahmanet al., 1990; Stern et al., 1994). Nevertheless, ge-ological, geochronological and isotopic evidenceindicate the existence of continental crust beforeNeoproterozoic time: (1) The region is dominatedby medium to high-grade gneisses, migmatites andsupracrustal rocks that are fundamentally differentfrom the low-grade volcano-sedimentary-ophioliteassemblages of the Neoproterozoic Arabian-NubianShield; and (2) Rb/Sr and U/Pb zircon ages as well asNd model ages and initial Sr data indicate the pres-ence of pre-Neoproterozoic continental crust (Fig. 2;Klerkx and Deutsch, 1977; Abdel-Monem and Hurly,1979; Dixon, 1981; Kroner et al., 1987; Wust et al.,1987; Wust, 1989; Davidson and Wilson, 1989;Harms et al., 1990, 1994; Sultan et al., 1990, 1992,1993, 1994; Stern et al., 1994; Küster and Liégeois,2001).

This article outlines the nature of Neoproterozoicdeformation affecting the northeastern part of theSaharan Metacraton in northern Sudan. This is a suit-able place to study and understand what happened tothe Saharan Metacraton during Neoproterozoic time(Fig. 3). Field studies, remote sensing data includ-ing Shuttle Imaging Radar (SIR) C/X-band SyntheticAperture Radar (SAR) images and previously pub-lished structural and geochronological data are usedto synthesize the deformational history of the re-gion. Remote sensing techniques and applicationsof SIR-C/X-SAR images for mapping Precambrianstructures in arid regions especially in northern Su-dan have been discussed inAbdelsalam et al. (1995,1998, 2000)andAbdelsalam and Stern (1996), hencewill not be discussed here. Age constraints for dif-ferent deformation events are obtained from datapublished byRies et al. (1985); Harms et al. (1990,1994); Sultan et al. (1994); Stern et al. (1994); andAbdelsalam et al. (1998).


Fig. 2. The northeastern part of the Saharan Metacraton. Geochronological and isotopic data fromAbdel-Monem and Hurly (1979), Dixon(1981), Harris et al. (1984), Kroner et al. (1987), Schandelmeier et al. (1988), Wust (1989), Davidson and Wilson (1989), Harms et al.(1990, 1994), Sultan et al. (1990, 1994), and Küster and Liegeois (2001). Black circles denote pre-Neoproterozoic U/Pb Zircon ages. 1:Sabaloka granulite; 2 and 3: Wadi Miyah greywacke; 4, 5, and 6: Wadi Allaqi greywacke; 7: Aswan granite; 8: Wadi Allaqi dike; 9, 10,11, and 12: Duweishat gneiss; 13: Duweishat granitic conglomeratic cobble; 14 and 15: Jebel Kamil anorthosite; 16 and 17: Jebel Al Asranorthosite. Grey circles denoteISr higher than 0.704. 1: Shallal granite; 2: Deifallab granite; 3: Sabaloka granite; 4 and 5: Nubian Desertgranite; 6 and 7: Wadi Hower granite; 8: Bir Safsaf granite; 9: Wadi Halfa granite. White circles denoteTDM ages older than 1500 Ma. 1and 2: Karkur Murr charnockite; 3 and 4: Rahaba metasediment; 5: El Obeid granite; 6: Wadi Hafafit granitic conglomeratic cobble; 7:Sabaloka granite; 8: Nubian Desert gneiss; 9: Nubian Desert granite; 10: Wadi Hower migmatite; 11: Wadi Hower granite; 12, 13, and14: Jebel Marra xenolith; 15: Jebel Kamil gneiss; 16 and 17: Jebel El Asr gneiss; 18 and 19: Nubian Desert gneiss; 20: Nubian Desertgranite; 21: Nubian Desert granodiorite; 22: Wadi Hower migmatite; 23: Wadi Hower gneiss; 24: Wadi Hower granite; 25: Jebel Rahibgneiss; 26: Bir Safsaf gneiss; 27: Bir Safsaf diorite; 28 and 29: Bir Safsaf diorite enclave; 30: Bir Safsaf gabbro enclave; 31: Bir Safsafbasaltic dike; 32, 33, 34, 35, 36, and 37: Duweishat gneiss; 38: Nubian Desert granite; 39: Nubian Desert greywacke; 40: Nubian Desertcalc-silicate; 41: Delgo Ophiolite; 42: Jebel Rahib ophiolite; 43, 44, and 45: El Melagi gneiss; 46 and 47: El Had metasediment.

2. Tectonic elements

The northeastern part of the Saharan Metacratonis bounded by the Arabian-Nubian Shield in theeast. Its extent westward is unknown because Pre-cambrian outcrops are covered by the Phanerozoic

sediments and sand of the Sahara Desert in easternChad (Fig. 2). It is exposed south of Phanerozoicsediments of southern Egypt to the Cretaceous andyounger sediments of central and southern Sudan.Outcrops are dominantly uplifted massifs withinCretaceous and younger sedimentary cover. These


Fig. 3. Tectonic elements of the Nubian Desert. 1: Atmur Ophiolite; 2: Siniat Ophiolite; and 3: Delgo Ophiolite.

massifs include Jebel El Asr, Bir Safsaf and JebelKamil in southern Egypt, the Uweinat massif in theSudanese/Egyptian/Libyan triple boarder, and NubianDesert, Bayuda Desert, Sabaloka, Kordofan Massif,Nuba Mountains, Wadi Hower Massif, and DarfurMassif in the Sudan (Fig. 2). The outcrops of theNubian Desert are the focus of this study.

The eastern boundary of the Saharan Metacratonin northern Sudan is defined by the∼500 km long,∼50 km wide, N-trending Keraf Suture which sep-arates it from the Arabian-Nubian Shield (Fig. 3;Almond and Ahmed, 1987; Abdelsalam et al., 1995,1998, 2000; Abdelsalam and Stern, 1996). The ophi-olitic fragments that decorate part of the suture (Fig. 3)are interpreted as indicating the closure of a back-arcbasin developed between the Arabian-Nubian Shieldand the Saharan Metacraton (Abdel-Rahman et al.,1993). Marbles, carbonate-rich turbidites, andpara-and ortho-gneisses exposed along the Suture areinterpreted as Neoproterozoic passive margin sed-iments deposited along the eastern margin of the

Saharan Metacraton (Abdelsalam et al., 1995, 1998).The Keraf Suture was deformed by sinistral trans-pression (Fig. 3) that accompanied NW-SE obliquecollision between the Arabian-Nubian Shield and theSaharan Metacraton (Abdelsalam et al., 1995, 1998;Abdelsalam and Stern, 1996). Küster and Liégeois(2001)present geochronological and isotopic data thatsuggested that the Bayuda Desert west of the KerafSuture (Fig. 3) is dominantly underlain by Neopro-terozoic juvenile material. Hence, they concluded thatthe Keraf Suture can only be the boundary betweenthe Arabian-Nubian Shield and the Saharan Metacra-ton if the low-grade volcano-sedimentary rocks of theBayuda Desert were thrust westward across it.

Extending west from the Keraf Suture is a∼50 kmwide,∼250 km long, E-W to NE-SW trending belt oflow-grade volcano-sedimentary and ophiolites includ-ing the Atmur and Siniat ophiolites in the east and theDelgo Ophiolite to the west near the Third CataractNile (Fig. 3). These ophiolites define the Atmur-DelgoSuture (Fig. 3; Schandelmeier et al., 1994), which


divides the northeastern part of the Saharan Metacra-ton into the Halfa Terrane in the north and the BayudaTerrane to the south (Fig. 3). Both terranes comprisemedium to high-grade gneisses and migmatites, sub-ordinate outcrops of low-grade volcano-sedimentaryrocks, and are intruded by numerous A-type grani-toids (Harms et al., 1990, 1994; Sultan et al., 1994;Stern et al., 1994). In the Bayuda Terrane north of theNile’s Great Bend exist numerous gneissic domes, thelargest of which is the∼10 km across Delgo Dome(Fig. 3). Many of these domes are not obvious in or-bital optical remote sensing images because they areeither covered with thin (∼2–3 m) sand sheets or theyare barely exposed on the surface. However, becauseradar penetrates dry sand in arid desert environment(Abdelsalam et al., 2000), these gneissic domes are ap-parent on SIR-C/X-SAR images. Intrusion of A-typegranitoids and the development of the gneissic domesare interpreted as indicating lithospheric thickening inthe northeastern part of the Saharan Metacraton as willbe discussed later.

A broad belt of marbles, which is intensivelyfolded about N-trending axes and intruded by circulargranitic bodies, dominates the southwestern part of theHalfa Terrane. This belt is here named the Wadi HalfaFold Belt (Fig. 3). North of the Atmur-Delgo Suturelies a belt of low-grade volcano-sedimentary rocks(Fig. 3) that are interpreted as intra-oceanic (Sternet al., 1994) or Andean-type (Harms et al., 1994) arcvolcanics that developed over a N-dipping subductionzone. This subduction zone lay along the northernmargin of an E-W elongated oceanic re-entrant whichextended west from the Neoproterozoic MozambiqueOcean (Stern et al., 1994). South of the Atmur-DelgoSuture lies a belt of marbles and carbonate-rich tur-bidites that extends west from the Keraf Suture butthins before it reaches the Delgo Ophiolite (Fig. 3).These are interpreted as slope sediments depositedon the northern margin of the Bayuda Terrane (Sternet al., 1994). The volcano-sedimentary and ophioliteassemblages were thrust southward across the slopesediments, which in turn might have thrust westwardacross the Bayuda Terrane (Fig. 3).

Near the Third Cataract Nile is a 40 km wide,200 km long zone of N-trending folds and sinis-tral, strike-slip shear zone, referred to as the ThirdCataract Shear Zone (Fig. 3; Stern and Abdelsalam,1996). The Third Cataract Shear Zone deforms

A-type granitoids and low-grade volcano-sedimentaryrocks and is decorated by streaks of serpentinite pos-sibly sheared off the Delgo Ophiolite. This shearzone separates the dominantly medium to high-gradegneisses and migmatites of the Bayuda Terrane in theeast and west from a N-trending belt of low-gradevolcano-sedimentary rocks that narrows southward(Fig. 3). These low-grade volcano-sedimentary rocksare dominantly exposed east of the Nile and ex-tend between the second and third Cataracts (Fig. 3;Vail et al., 1973). They include mafic metavolcanics,metaconglomerates, quartzite, calc-silicates, meta-greywackes, and streaks of serpentinite and amphibo-lite bodies. They are interpreted as island-arc/back-arcassemblage (Denkler et al., 1994).

3. Structure

Below is a description of the structural evolutionof the northeastern part of the Saharan Metacratonbased on field studies carried out in 1995 and inter-pretation of SIR-C/X-SAR images. Previous struc-tural (Schandelmeier et al., 1994; Harms et al., 1994;Denkler et al., 1994; Abdelsalam et al., 1995, 1998;Abdelsalam and Stern, 1996) and geochronologicalstudies (Ries et al., 1985; Harms et al., 1990, 1994;Sultan et al., 1994; Stern et al., 1994; Abdelsalamet al., 1998) are used for correlating and constrainingthe ages of deformation events.

Three deformation events are recognized in thestudy area: (1) Emplacement of S-verging ophio-lite nappes; (2) E-W shortening which producedN-trending folds followed by N- to NNW-trendingsinistral strike-slip shear zones; and (3) Developmentof N-trending moderate-angle normal faults.

3.1. S-verging ophiolitic nappes

Schandelmeier et al. (1994), Harms et al. (1994),and Denkler et al. (1994)discussed three ophioliticoutcrops. These are from east to west: the Atmur,Siniat, and Delgo Ophiolites (Fig. 3). Together theseform a∼250 km long belt that trends E-W in the eastand swings to a more NE-trend as it approaches theThird Cataract Shear Zone (Fig. 3). The Atmur andSiniat ophiolites occur as generally E-W trending,crescent-like outcrops whereas the Delgo Ophiolite


Fig. 4. The Delgo Ophiolite. (A) L-band (wavelength= 24 cm) SIR-C/X-SAR image. (B) Structural map. (C) Lower hemisphere, equalarea stereonet plot of structural elements. Solid circles: foliation. Open squares: minor fold axes.

occurs as a NE-trending linear belt (Fig. 3). The DelgoOphiolite is made up of pillowed basalts, sheeteddykes, gabbros, and serpentinites.Schandelmeieret al. (1994)concluded that these ophiolites consti-tuted a coherent S-verging nappe which was foldedabout N-trending axes and deformed by N-trendingshear zones. The NE-trend of Delgo Ophiolite mightbe due to folding and shearing that accompanied thedevelopment of the Third Cataract Shear Zone (Fig. 3)as will be discussed later. The intensity of deforma-tion related to the emplacement of the Atmur-Delgoophiolitic nappes decreases southward within themeta-sedimenatry belt south of the Atmur-Delgo Su-ture and disappears completely north of the Nile’sGreat Bend (Fig. 3; Abdelsalam et al., 1995). SimilarE-W to NE-trending structures including the Dam etTor and Abu Hamed Fold and Thrust Belts are ex-posed in the Bayuda Desert south of the Atmur-DelgoSuture (Fig. 3).

The Delgo Ophiolite is a∼20 km long,∼5–7 kmwide NNE- to NE-trending belt of dismembered ser-pentinite bodies, sheared gabbro, pillowed basaltsand sheeted dykes exposed northeast of Delgo city(Fig. 4a and b). The serpentinite bodies lie on thenorthwestern part of the Delgo belt where they formthree hills that extend for 10 km along strike (Fig. 4aand b). These serpentinite bodies are thrust fromnorthwest to southeast across the sheared gabbro,pillowed basalt and sheeted dykes (Fig. 4b). The ser-pentinites bodies and sheared gabbros are complexlydeformed as indicated by the wide range of planarfabric orientation (Fig. 4c). This complex structure isinterpreted to reflect: (1) Superimposition of N- andNNW-trending folds and sinistral strike-slip faults onearlier E-trending, sub-horizontal structures that arerelated to the emplacement of the ophiolitic nappes.Evidence for this strain superimposition includescross-cutting relationships between planar fabrics and


development of crenulation cleavage. Hence, it isconcluded that the Delgo Ophiolite had a more E-Wtrend before it was re-oriented by N-trending fold-ing and sinistral strike-slip shearing along the ThirdCataract Shear Zone. (2) The wide range of orien-tation of planar fabrics especially in the serpentinitebodies (Fig. 4c) might also be due to the ductilenature of these lithologies.

Geochronological data suggest that the emplace-ment of the Atmur-Delgo ophiolitic nappes occurbetween 700 and 650 Ma.Stern et al. (1994)ob-tained two whole rock Rb/Sr ages of 653± 20 and581 ± 38 Ma from arc volcanic rocks of the HalfaTerrane. They also obtained aTDM Nd-model age of660 Ma from these volcanics. They interpreted thesevolcanics as related to a subduction zone that co-incided with the traces of the Atmur-Delgo Suture.Harms et al. (1994)obtained whole rock and internalSm/Nd isochron ages of 707± 54 and 752± 48 Mafrom gabbros of the Delgo Ophiolite. These databracket the formation and closing of the oceanic basin,and collision between the Halfa and Bayuda Terranesto prior to 650 Ma. The 581±38 Ma Rb/Sr age of somearc volcanic rocks in the Halfa Terrane (Stern et al.,1994) might represent the age of greenschist faciesmetamorphism.

3.2. N- to NE-trending folds and N- toNNW-sinistral strike-slip faults

The N- to NE-trending folds and N- to NW-sinistralstrike-slip faults will be discussed together sinceit is believed that they represent the response ofthe northeastern part of the Saharan Metacratonto collision between the Saharan Metacraton andthe Arabian-Nubian Shield along the Keraf Suture(Fig. 3). This deformation event is represented by theThird Cataract Shear Zone and the Wadi Halfa FoldBelt (Figs. 3, 5 and 6).

The Third Cataract Shear Zone (Stern andAbdelsalam, 1996) is ∼40 km wide and∼200 km longcomplex structure exposed near the Third CataractNile where the river flows north through Precam-brian structure (Fig. 5). This shear zone is dominatedby early N- to NE-trending folds followed by N- toNNW-trending, sinistral strike-slip faults (Fig. 5Aand B). These represent early and late deformationdeveloped during E-W shortening where strain was

accommodated ductily in the early stages and culmi-nated with the development of N- and NNW-trendingzones of high shear strain.

The early stage in the evolution of the ThirdCataract Shear Zone is characterized by the devel-opment of N- to NE-trending folds (Fig. 5C) andsteep N- to NE-trending axial planar cleavage. Thesefolds deform, about sub-horizontal, NE-plungingaxes (Fig. 5C), early foliation possibly developedduring the emplacement of S-verging nappes alongthe Atmur-Delgo Suture. Together with the devel-opment of mesoscopic-scale folds, this deformationresulted in the development of three mappable-scaleN-trending folds that dominate the northern part ofthe Third Cataract Shear Zone (Fig. 5A and B). Theaxial traces of these folds are dominantly N-trending(Fig. 5B) but their axes plunge shallowly northeast(Fig. 5C) indicating that these folds have moderatevergence to the west. Both mesoscopic-scale andmappable-scale folds have open to tight in geometries(Fig. 5C). Granitic bodies intrude the cores of themappable-scale folds (Fig. 5A and B). The limbs ofthese folds consist of psammitic meta-sedimentaryrocks and streaks of serpentinites that include pocketsof chromite (Fig. 5B).

Mesoscopic structures suggest that the N-trendingfolds within the Third Cataract Shear Zones were de-veloped as a response to E-W shortening. Quartz veinsoriented at high angle to the N- to NE-trending folia-tion were folded about N- to NE-trending fold axes andhave steeply dipping axial planar surfaces that coin-cides with the trend of the regional foliation (Fig. 6A).Some of these mesoscopic-scale folds were sinistrallyor dextrally displaced along NNE- or NNW-trendingfault planes that are sub-parallel to the inflectionplanes of the folds. This indicates that accommodationof the E-W shortening progressed from dominantlyductile flow represented by folding to the stage ofdevelopment of zones of high shear strain that areoriented at∼30◦ on both sides of the flattening plane(manifested by the N-trending axial planar cleavage offolds). This indicates that the orientation of the strainellipsoid semi-principal shortening axis is dominantlyE-W. On the other hand, quartz veins that are orientedparallel to or at low angles to the N- to NE-trendof the regional foliation is dominantly boudinaged(Fig. 6B) indicating dominant elongation in this di-rection. This shows that the orientation of the strain


Fig. 5. The Third Cataract Shear Zone. (A) L-band (wavelength= 24 cm) SIR-C/X-SAR image. (B) Structural map. (C) Lower hemisphere,equal area stereonet plot of structural elements related to N-trending folds. Solid circle: early foliation. Open squares: minor fold axes. (D)Lower hemisphere, equal area streonet plot of structural elements related to N-trending sinistral strike-slip faults. Open circles: myloniticfabric. Solid squares: stretching lineation.

ellipsoid semi-principal extension axis is dominantlyN-S.

The late stage of development of the Third CataractShear Zone is marked by N-to NNW-trending, sinistralstrike-ship shear zones (Fig. 5A and B). These shearzones form 2–3 km wide discrete belts between the N-to NE-trending folds, at spacings of∼10 km (Fig. 5Aand B). Three of these shear zones are exposed eastand west of the Nile around Kosha and Akasha citieswhere they deform low-grade volcano-sedimenatryrocks and A-type granitoids (Figs. 5A and B and 6C).These shear zones are defined by well-developed my-

lonitic fabrics either sub-vertical or dip moderatelyto steeply to the east and west (Fig. 5D) as a resultof later folding about N-trending axes. This suggeststhat E-W shortening continued well after the forma-tion of the N- to NNW-trending, sinistral strike-slipshear zones. The well-developed mylonitic fabriccontains sub-horizontal, N-plunging stretching lin-eation (Fig. 5D) and kinematic indicators that suggestdominant sinistral strike-slip movement.

The relationship between the N- and NE-trendingfolds and the N- to NNW-trending sinistral strike-slipfaults as early and late deformation related to E-W


Fig. 6. (A) Contraction folds. (B) Boudinage structure. (C) A-type granitoid body deformed by N- to NNW-trending sinistral strike-slipshearing. (D) Minor thrust related to N- to NNW-trending sinistral strike-slip shearing.

shortening is evident in both mesoscopic and map-pable structures. Limbs of some of the N- to NE-trend-ing folds are sinistrally displaced by the N- toNNW-trending faults along the inflection planes.Moreover, the sinistral strike-slip movement has re-sulted in local N-verging thrusts across the hinges ofmappable-scale N-trending folds (Figs. 5B and 6D).This is because the hinges of these folds are orientedat high angle to the shear direction, a geometry thatfavors the accommodation of strain in a compressionstyle, hence, producing local N-verging thrusts.

The N- to NNW-trending sinistral strike-slip shearzones deform, together with the volcano-sedimentaryrocks, A-type granitoids. A-type granites of the north-eastern part of the Saharan Metacraton range in agebetween 550 and 590 Ma (Ries et al., 1985; Harmset al., 1990, 1994; Stern et al., 1994; Sultan et al.,

1994). This suggests that deformation along the N-to NE-trending sinistral strike-slip shear zones of theThird Cataract Shear Zone post-dates∼590–550 Ma.Abdelsalam et al. (1998)obtained 40Ar/39Ar ageof 577 ± 5 Ma from hornblendes and biotites ex-tracted from A-type granitoids deformed by a N- toNNW-trending sinistral strike-slip shear zone alongthe Keraf Suture (Fig. 3). They interpreted this toindicate the age of shearing along the Keraf Suture.They also suggested that the A-type granitoids mighthave been emplaced along the N- to NNW-trendingfaults during the sinistral strike-slip shearing. Hence,it is concluded that the N- to NNW-trending sinistralstrike-slip shearing along the Third Cataract ShearZone occurred between 590 and 550 Ma.

The Wadi Halfa Fold Belt is exposed south ofWadi Halfa city and north of the Atmur-Delgo Suture


Fig. 7. The Wadi Halfa Fold Belt. (A) L-band (wavelength= 24 cm) SIR-C/X-SAR image. (B) Structural map. (C) Lower hemisphere,equal area stereonet plot of structural elements related to N-trending folds. Stars: axial planar cleavage and folds axial surfaces. Opensquares: minor fold axes.

(Figs. 3 and 7). Here, a thick sequence of marbles inter-calated with dominantly psammitic meta-sedimentaryrocks and serpentinite bodies are folded aboutN-trending axes (Fig. 7A and B). Numerous foldsare recognized on SIR-C/X-SAR images (Fig. 10a).These folds are dominantly tight, plunge to the north,and have sub-vertical axial surfaces (Fig. 7C). Mesos-copic-scale folds have similar geometry (Fig. 7C).The cores of the mapable-scale folds are sometimesintruded by granitoids (Fig. 7B). The intrusion ofthese granitoids might have modified the geometry ofthe mappable-scale folds to a limited extent.

Broad, N-trending shear zones also occur withinthe Wadi Halfa Fold Belt (Fig. 7B). Some of these

shear zones are decorated with serpentinite fragments(Fig. 7B). A few shear zones show development ofandalusite crystals that dominantly aligned along thegeneral shear fabric. This suggests that shearing mighthave occurred in mid-crustal depth.

3.3. N-trending normal-slip faults

The final stage in the Neoproterozoic deformationin the northeastern part of the Saharan Metacraton wasin the form of N-trending normal-slip faults that areinterpreted as due to tectonic collapse in response toNeoproterozoic lithospheric thickening (Harms et al.,1994; Denkler et al., 1994). Lithospheric thickening


Fig. 8. N-trending normal-slip folds and Delgo Dome. (A) L-band (wavelength= 24 cm) SIR-C/X-SAR image. (B) Structural map. (C)Lower hemisphere, equal area stereonet plot of structural elements related to N-trending normal-slip faults. Open circles: mylonitic fabric.Solid squares: stretching lineation.

is evident in the northern part of the Bayuda Ter-rane where it resulted in the development of gneissicdomes; the most prominent of these is the DelgoDome, east of Delgo city (Fig. 3). The Delgo Domeis dominated by garnet-bearing gneisses, which aredeformed into a complex folding structure (Fig. 8Aand B). The possibility that these structures resultedfrom fold superimposition is ruled out due to a lackof cross-cutting foliations. Instead, the Delgo Domeis interpreted as manifesting ductile flow related todiapric rise of lower lithospheric material due tolithospheric thickening.

Between the Delgo Ophiolite and the Delgo Domelies a well-developed, N-trending,∼5 km wide and

∼25 km long zone of normal-slip faults (and 8Aand B) with N-trending foliation that dips moderatelyto the west (Fig. 8C). Well-developed mylonitic fabricthat deforms granitic and gneissic rocks defines thezone. The mylonitic fabric is interpreted as developedduring normal-slip shearing because: (1) Stretchinglineation is dominantly down-dip (Fig. 8C) and is fun-damentally different from the sub-horizontal stretch-ing lineation associated with the N-trending sinistralstrike-slip shear zones. These down-dip stretchinglineations indicate either normal-slip or reverse move-ment across the N-trending planes. (2) Mesoscopicfolds observed on sections sub-parallel to the dipdirection have dominantly S-type geometry which


indicates down-dip movement. These folds havesub-horizontal hinges indicating little or no strike-slipshearing. (3) Microscopic structures observed on ori-ented sections of the mylonitic fabric such as mica fishand shelf book sliding indicate normal-slip movement.

Denkler et al. (1994)identified another zone ofnormal-slip movement west of the Nile (Fig. 3). Thiszone is also strike N-S and mylonitic fabrics dip mod-erately to the east. They showed that this zone myloni-tized gneisses and migmatites west of the low-gradevolcano-sedimentary belt (Fig. 3). Moreover,Denkleret al. (1994)concluded that the mylonite fabrics weredeveloped under retrograde amphibolite to greenschistfacies metamorphic conditions and post-date migma-tization. Harms et al. (1994)obtained whole rockRb/Sr isochron age of 546± 19 Ma from migmatitesof the Nubian Desert. They suggested that extensionand moderate-dip normal-slip movement along theN-trending planes shortly followed migmatization.Hence, they took the∼550 Ma age as indicating thetiming of extension in the Nubian Desert.

4. Structural and tectonic evolution

Fig. 9 is a three-dimensional illustration of thestructural evolution of the northeastern part of theSaharan Metacraton during Neoproterozoic time.Deformation started with the emplacement of ophi-olitic nappes from north to south (Fig. 9A). TheseS-verging nappes formed when the Halfa Terranecollided with the Bayuda Terrane between∼700 and650 Ma. This collision followed the consumption ofan oceanic basin, which extended westward from theMozambique Ocean (Stern, 1994). The emplacementof these nappes occurred during the early stages ofcollision and resulted in sub-horizontal, S-vergingfolds and thrusts. Continuation of convergence be-tween the Halfa and Gebeit Terranes deformed thesub-horizontal structures about E-trending fold axes.The latter were superimposed on the earlier as co-axialbut non-co-planar deformation. Deformation relatedto the emplacement of the ophiolitic nappes affectedthe carbonate-rich rocks on the northern margin ofthe Bayuda Terrane (Fig. 9A). Orientation and styleof structures along the Atmur-Delgo Suture suggest itis related to a N-dipping subduction zone beneath thesouthern margin of the Halfa Terrane. Intra-oceanic

(Stern et al., 1994) or Andean-type (Harms et al.,1994) island-arc system have been suggested to formover this N-dipping subduction zone. The N-trendingbelt of the low-grade volcano-sedimentary rocks thatexist along the Second and Third Cataract Nile mightbe related to this convergent margin system (Denkleret al., 1994). The present trend of this belt is due toyounger deformation.

Similar E-W and NE-trending structures are presentin the Bayuda Desert. These include the Dam et TorFold and Thrust Belt in the south and the Abu HamedFold and Thrust belt to the north (Fig. 3). Thesestructures, similar to the Atmur-Delgo Suture, havebeen interpreted as resulting from closure of oceanicre-entrants extending westward from the Mozam-bique Ocean (Abdelsalam et al., 1998). Closure ofthese oceanic re-entrants might be due to an overallNW-SE convergence between East and West Gond-wana before the consumption of the MozambiqueOcean and sandwiching the Arabian-Nubian Shieldbetween East and West Gondwana. Evidence for suchoblique convergence include sinistral transpressionzones in the Arabian-Nubian such as the Barka (deSouza Filho and Drury, 1998; Drury and Berhe, 1993)and the Keraf Sutures (Abdelsalam et al., 1995, 1998;Abdelsalam and Stern, 1996) as well as the presenceof consistent NW-trending stretching lineation inter-preted as indicating an overall NW-SE convergencebetween East and West Gondwana (Shackleton andRies, 1984).

NW-SE convergence culminated with the con-sumption of the Mozambique Ocean and collisionbetween East and West Gondwana, with intra-oceanicisland-arcs preserved in the north as the Arabian-Nubian Shield. The Arabian-Nubian Shield collidedwith West Gondwana, fragments of which are nowpreserved as the Saharan Metacraton, along theKeraf-Kabus-Sekerr Suture at∼600 Ma (Vail, 1983,1985, 1988; Almond and Ahmed, 1987; Abdelsalamand Dawoud, 1991; Abdelsalam et al., 1995, 1998,2000; Abdelsalam and Stern, 1996). The northeasternmargin of the Saharan Metacraton is defined by theN-trending Keraf Suture (Abdelsalam et al., 1995,1998; Abdelsalam and Stern, 1996). The NW-SE di-rected collision between the Arabian-Nubian Shieldand the Saharan Metacraton produced sinistral trans-pression along the Keraf Suture (Abdelsalam et al.,1995, 1998; Abdelsalam and Stern, 1996). In the

216M

.G.

Abdelsalam

etal./P

recambrian

Research

123(2003)

203–221

Fig. 9. Three-dimensional cartoon illustrating structural evolution of the northeastern part of the Saharan Metacraton. (A) Emplacement of the S-verging Atmur-Delgoophiolitic nappes due to collision between the Halfa and Bayuda Terranes along the Atmur-Delgo Suture at∼700–650 Ma. (B) Development of N-trending folds due toNW-SE oblique collision between the Saharan Metacraton and the Arabian-Nubian Shield along the Keraf Suture at∼650–600 Ma. (C) Development of N- to NW-trendingsinistral strike-slip faults at∼590–550 Ma due to continuation of convergence between the Saharan Metacraton and the Arabian-Nubian Shield. (D) Development of N-trendinglow-angle normal-slip faults as a response to lithospheric thickening in the northeastern part of the Saharan Metacraton that resulted from thrust stacking and folding.


northern part of the suture, N-trending folds domi-nate whereas the southern part is dominated by N- toNNW-trending sinistral strike-slip faults (Fig. 3). Thiscollision might have produced far-reaching stressesthat affected the northeastern part of the SaharanMetacraton. The N-trending contraction structuresparallel to the Keraf Suture are observed up to 300 kmwest of the SutureFigs. 3 and 9B). The Third CataractShear Zone and the Wadi Halfa Fold Belt (Figs. 3,5 and 7) might be related to this collision. Similarly,convergence between the Arabian-Nubian Shield andthe Saharan Metacraton might have imposed overallshortening in the Arabian-Nubian Shield producingN-trending structure such as the Hamisana and OkoShear Zones (Fig. 3; Stern et al., 1989, 1990; Millerand Dixon, 1990; Abdelsalam, 1994). It is not clearwhy deformation related to this collision localizedalong certain zones east and west of the Keraf Suture.Crustal attenuation is called for as a model to explainsuch strain localization along the Hamisana ShearZone (Stern et al., 1989, 1990). This might be alsothe case of the Third Cataract Shear Zones wherea back-arc basin (Denkler et al., 1994) might havelocalized strain. In addition, the Third Cataract ShearZone and the Wadi Halfa Fold Belt coincide withlow-grade volcano-sedimentary rocks and carbonates,respectively. This suggests that strain localization isalso controlled by the rheological difference betweenthe medium to high-grade gneisses and migmatitesand the more ductile volcano-sedimentary rocks andcarbonates.

The continuation of E-W shortening producedzones of high shear strain oriented at 30◦ to the flat-tening planes. These zones of high shear strain mighthave been rotated to a more northerly trend as short-ening continued (Fig. 9C). The N- to NNW-trendingsinistral strike-slip shear zones along the Third Catat-act Shear Zones and their relationship with the olderN- NE-trending folds are good examples of pro-gressive accommodation of E-W shortening fromearly contraction structures represented by the N-to NE-trending fold to late N- to NNW-trendingstrike-slip shear zone.

The superimposition of the N- to NE-trendingfolds and the N- to NNW-trending sinistral strike-slipshear zones significantly modified the orientationof S-verging nappes along the Atmur-Delgo Suture.Ophiolitic nappes were re-folded to form crescent-like

outcrop patterns as in the case of the Atmur and Siniatophiolites in the east (Fig. 3) or completely sheared toa NE-orientation as in the case of the Delgo Ophioliteto the westFigs. 3 and 9C).

Thrust stacking along the Atmur-Delgo Suture andshortening along the Third Cataract Shear Zone andthe Wadi Halfa Fold Belt resulted in lithosphericthickening manifested by the development of gneissicdomes in the northern part of the Bayuda Terrane(Fig. 3) as well as emplacement of A-type grani-toids. Other evidence for lithospheric thickening inthe northeastern part of the Saharan Metacraton in-cludes Neoproterozoic granulite facies metamorphismalong the interface between the metacaton and theArabian-Nubian Shield (Kroner et al., 1987; Sternand Dawoud, 1991). This resulted in lithosphericinstability that was compensated for by orogeniccollapse. Orogenic collapse tectonic in the north-eastern part of the Saharan Metacraton is manifestedby the development of N-trending, moderate-anglenormal-slip faults (Fig. 9D) such as the one betweenthe Delgo Ophiolite and the Delgo Dome (Figs. 3and 8) signaling the final phase of Neoproterozoicdeformation in the northeastern part of the SaharanMetacraton. Since these N-trending moderate-anglenormal-slip faults deform older Neoproterozoicstructures in the northeastern part of the SaharanMetacraton, one concludes that they were formed550 Ma ago.

5. Significance of Neoproterozoic deformation

A craton is the part of a continent that has actedas a stable interior during orogenic events at its mar-gins and has since suffered little deformation (Batesand Jackson, 1980). This is due to a thick and coldlithosphere, strong crust-mantle coupling and an elas-tic thickness that provides high lithospheric strengththat prevents subsequent deformation (Black andLiegeois, 1993). Margins of the cratons behave aspassive margins during orogenic events and the cratonmay be destablized when subduction initiation turnsthe passive margins into active margins. Due to col-lision, only fragments of a partially reworked cratonmay be preserved within the orogenic belt. However,there might be an intermediate phase due to thrustingacross passive margins that might result in flexure


of the cratonic lithosphere, lower crust fluxing, orcrust-mantle decoupling (Brown and Philipps, 2000)that could lead to decratonization, but retaining relicsand/or isotopic inheritance of the former craton.

Review of Neoproterozoic deformation and igneousactivity suggests that three lithospheric processes havecontributed to the remobilization of the northeasternpart of the Saharan Metacraton during Neoprotero-zoic time: (1) Collision; (2) Delamination of thesub-continental mantle lithosphere; and (3) Extension.

Remobilization due to Neoproterozoic collision hasbeen suggested bySchandelmeier et al. (1988)anddiscussed byStern et al. (1994). The eastern marginof the northeastern part of the metacraton is definedby the N-trending Keraf Suture (Fig. 2) thought torepresent an arc-continental suture between the Sa-haran Metacraton and the Arabian-Nubian Shield(Vail, 1983, 1985, 1988; Almond and Ahmed, 1987;Abdelsalam and Dawoud, 1991; Abdel-Rahman et al.,1993; Abdelsalam et al., 1995, 1998; Abdelsalam andStern, 1996). Scarce geochronologic data (Abdelsalamet al., 1998) constrained collision along this sutureto be at∼630–560 Ma. In addition, structural stylesalong the sutures can be interpreted as due to anoverall NW-SE collision which is oblique to theN-trending Keraf fronts. This oblique collision pro-duced sinistral transpression along the N-trendingeastern margin of the metacraton. Such collisionmight have been responsible for E-W shortening andcrustal thickening within the northeastern part of theSaharan Metacraton where deformation related to col-lision was accommodated in the form of NE- (Vail,1971, 1972, 1976; Schandelmeier et al., 1987, 1994;Sultan et al., 1994; Abdelsalam et al., 1995, 1998;Küster and Liégeois, 2001) and N-trending fold beltsfollowed by N- to NNW-trending sinistral strike-slipfaults (Denkler et al., 1994; Harms et al., 1994; Sternet al., 1994; Abdelsalam et al., 2002) with the de-velopment of N-trending moderate-angle normal-slipfaults (Denkler et al., 1994; Abdelsalam et al., 2002).Lithospheric thickening might have triggered lowercrustal melting and emplacement of A-type granitoidswithin the northeastern part of the Saharan Metacra-ton (Harms et al., 1990, 1994; Sultan et al., 1994;Stern et al., 1994) as well as granulite facies metamor-phism close to the interface between the metacratonand the Arabian-Nubian Shield (Kroner et al., 1987;Stern and Dawoud, 1991).

Contemporaneous shortening event is also evi-dent in the Arabian-Nubian Shield as exemplifiedby the N-trending Hamisana and Oko Shear Zonewhich crops out∼100 km east of the Keraf Suture(Stern et al., 1989, 1990; Miller and Dixon, 1990;Abdelsalam, 1994).

Black and Liegeois (1993)suggested that Neopro-terozoic deformation and igneous activities in the Sa-haran Metacraton might be due to delamination of thelithospheric mantle of the Saharan Metacraton that oc-curred at∼700 Ma. Similar examples of lithosphericmantle delamination include the Colorado Plateau(Bird, 1979); Tibetan plateau (Houseman et al., 1981;and other parts of North Africa (Ashwal and Burke,1989). Black and Liegeois (1993)added that destabi-lization of the Saharan Metacraton was due to the lossof its thick mechanical boundary layer during Neo-proterozoic time. They used this to explain why theNeoproterozoic orogenic belts in northern Africa arecharacterized by high heat flow indicated by A-typegranitoids and high-temperature low-pressure meta-morphism. Such delamination process is probably theresult of collision (Black and Liegeois, 1993), whichinduced regional extension due to the collapse of thehot lower crust.

Lithospheric extension can subject broad crustaltracts to high heat flow, uplift and intrusion or under-plating of melts from the asthenosphere as exemplifiedby the 1000 km wide Basin and Range Province of theUnited States of America (Eaton, 1982). Large-scaleextension brings the asthenosphere nearer to the sur-face leading to high heat flow, resulting in metamor-phism and emplacement of A-type granitoids (Lumet al., 1989). Similar relationships have been inferredfor the northeastern part of the Saharan Metacraton(Denkler et al., 1994). Thus, such large-scale ex-tension might have contributed significantly to theremobilization of the northeastern part of the SaharanMetacraton during Neoproterozoic time.

Acknowledgements

The National Aeronautic and Space Agency(NASA) through its Jet Propulsion Laboratory (JPL)supported this work. The authors would like to thankthe Geological Research Authority of the Sudan(GRAS) for its co-operation and help during the field


phase of this work. This is the University of Texasat Dallas—Department of Geosciences contributionnumber 1000.

References

Abdel-Monem, A.A., Hurly, P.M., 1979. U–Pb dating of zirconfrom psammitic gneisses, Wadi Abu Rosheid-Wadi Sikait area,Egypt. Institute of Applied Geology Bulletin, King AbdulazizUniversity, Jeddah 2, 165–170.

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

Abdelsalam, M.G., Dawoud, A.S., 1991. The Kabus ophioliticmelange, Sudan, and its bearing on the W boundary of theNubian Shield. J. Geol. Soc. Lond. 148, 83–92.

Abdelsalam, M.G., Liegeois, J.-P., Stern, R.J., 2002. The SaharanMetacraton. J. Afr. Earth Sci. 34, 119–136.

Abdelsalam, M.G., Stern, R.J., 1996. Mapping Precambrianstructures in the Sahara Desert with SIR-C/X-SAR Radar: TheNeoproterozoic Keraf Suture, NE Sudan. J. Geophys. Res. 101,23063–23076.

Abdelsalam, M.G., Stern, R.J., Copeland, P., Elfaki, E.M., Elhur,B., Ibrahim, F.M., 1998. The Neoproterozoic Keraf Suture inNE Sudan: sinistral transpression along the eastern margin ofWest Gondwana. J. Geol. 106, 133–148.

Abdelsalam, M.G., Stern, R.J., Schandelmeier, H., Sultan, M.,1995. Deformational history of the Keraf Zone in NE Sudan,revealed by Shuttle Imaging Radar. J. Geol. 103, 475–491.

Abdelsalam, M.G., Robinson, C., El-Baz, F., Stern, R.J., 2000.Applications of Orbital Imaging Radar for geological studies inarid regions: the Saharan testimony. J. Photogrammetric Eng.Remote Sens. 66, 717–726.

Abdel-Rahman, E.M., Harms, U., Schandelmeier, H., Franz, G.,Darbyshire, D.P.F., Horn, P., Muller-Sohnius, D., 1990. Anew ophiolite occurrence in NW Sudan—constraints on lateProterozoic tectonism. Terra Nova 2, 363–376.

Abdel-Rahman, E.M., Matheis, G., Schandelmeier, H., Karfis,M.A., Abdel Gadir, I., El Khedir, M., 1993. Evolution of theKeraf back-arc basin: constraints on the Nubian Shield margin.In: Thorweihe, U., Schandelmeier, H. (Eds.), GeoscientificResearch in NE Africa. Balkema, pp. 93–98.

Almond, D.C., Ahmed, F., 1987. Ductile shear zones on N RedSea Hills, Sudan and their implication for crustal collision.Geol. J. 22, 175–184.

Ashwal, L.D., Burke, K., 1989. African lithospheric structure,volcanism and topography. Earth Planet. Sci. Lett. 96, 8–14.

Barth, H., Besang, C., Lenz, H., meinhold, K.-D., 1983. Resultsof petrographical investigation and Rb/Sr age determinationson non-orogenic ring complexes in the Bayuda Desert, Sudan.Geologisches Jahrbuch 51, 3–34.

Bates, R.L., Jackson, J.A., 1980. Glossary of Geology. AmericanGeological Institute, Falls Church, VA, USA, 751 pp.

Bertrand, J.-M., Caby, R., 1978. Geodynamic evolution of thePan-African orogenic belt: a new interpretation of the HoggarShield (Algerian Sahara). Geologische Rundsch. 67, 357–388.

Bird, P., 1979. Continental delamination and the Colorado Plateau.J. Geophys. Res. 84, 7561–7571.

Black, R., Liegeois, J.-P., 1993. Cratons, mobile belts, alkalinerocks and continental lithospheric mantle: the Pan-Africantestimony. J. Geol. Soc. Lond. 150, 89–98.

Brown, C.D., Philipps, R.J., 2000. Crust-mantle decoupling byflexure of continental lithosphere. J. Geophys. Res. 105, 13221–13237.

Curtis, P., Lenz, H., 1985. Geologic and geochronologicalinvestigations of selected alkali ring igneous complexes inthe Nuba Mountains, southern Kordofan, Sudan. GeologischesJahrbuch 69, 3–24.

Davidson, J.P., Wilson, I.R., 1989. Evolution of the alkali basalt—trachyte suite from Jebel Marra volcano, Sudan, throughassimilation and fractional crystallization. Earth Planet. Sci.Lett. 95, 141–160.

Denkler, T., Franz, G., Schandelmeier, H., 1994. Tectonometa-morphic evolution of the Neoproterozoic Delgo PrecambrianRes. zone, northern Sudan. Geologische Rundschau 83, 578–590.

de Souza Filho, C.R., Drury, S.A., 1998. A Neoproterozoicsupra-subduction terrane in northern Eritrea, NE Africa. J. Geol.Soc. Lond. 155, 551–566.

Dixon, T.H., 1981. Age and chemical characteristics of somepre-Pan-African rocks in the Egyptian Shield. Precambrian Res.14, 119–133.

Drury, S.A., Berhe, S.M., 1993. Accretion tectonics in northernEritrea revealed by remotely sensed imagery. Geol. Magazine130, 177–190.

Eaton, G.P., 1982. The Basin and Range Province: origin andtectonic significance. Annu. Rev. Earth Planet. Sci. 10, 409–440.

Harms, U., Darbyshire, D.P.F., Denkler, T., Hengst, M.,Schandelmeier, H., 1994. Evolution of the NeoproterozoicDelgo Suture Zone and crustal growth in northern Sudan:geochemical and radiogenic isotope constrains. GeologischeRundsch. 83, 591–603.

Harms, U., Schandelmeier, H., Darbyshire, D.P.F., 1990. Pan-African reworked early/middle Proterozoic crust in NE AfricaW of the Nile: Sr and Nd isotope evidence. J. Geol. Soc. Lond.147, 859–872.

Harris, N.B.W., Hawkesworth, C.J., Ries, A.C., 1984. Crustalevolution in NE and E Africa from model Nd ages. Nature309, 773–776.

Houseman, G.A., McKenzie, D.P., Molnar, P., 1981. Convectiveinstability of a thickened boundary layer and its relevance for thethermal evolution of continental convergent belts. J. Geophys.Res. 86, 6115–6132.

Klerkx, J., Deutsch, S., 1977. Resultats preliminaires obtenus parla methode Rb/Sr sur l’age des formations precambriennes de laregion d’Uweinat (Libye). Musee Royal de l’Afrique Centrale,Dept. Geol. Min. Rapp. Ann, 83–94.

Kroner, A., 1977. The Precambrian geotectonic evolution of Africa:plate accretion vs. plate destruction. Precambrian Res. 4, 163–213.

Kroner, A., Stern, R.J., Dawoud, A.S., Compston, W., Reischmann,T., 1987. The Pan-African continental margin in NE Africa:


evidence from a geochronological study of granulites atSabaloka, Sudan. Earth Planet. Sci. Lett. 85, 91–104.

Küster, D., Liégeois, J.-P., 2001. Isotopic and geochronologicalstudy of high-grade metamorphic lithologies from BayudaDesert, Sudan—New insights into the Neoproterozoic evolutionof the Eastern Saharan Ghost Craton. Precambrian Res. 109,1–23.

Liégeois, J.-P., Black, R., Navez, J., Latouche, L., 1994. Earlyand late Pan-African orogenies in the Air assembly ofterranes (Tuareg Shield, Niger). Precambrian Res. 67, 59–88.

Liégeois, J.P., Latouche, L., Navez, J., Black, R., 2000. Pan-Africancollision, collapse and escape tectonics in the Tuareg Shield:relations with the East Saharan Ghost Craton and the WestAfrican Craton. 18th Colloquium of African Geology, Graz,Austria. J. Afr. Earth Sci. 30, 53–54.

Lum, C.C.L., Leeman, W.P., Foland, K.A., Kargell, J.A., Fitton,J.G., 1989. Isotopic variation in continental basaltic lavas asindicators of mantle heterogeneity: examples from the westernU.S. Cordillera. J. Geophys. Res. 94, 871–884.

Meinhold, K.-D., 1979. The Precambrian basement complex ofBayuda Desert, northern Sudan. Rev. Geol. Geogr. Phys. 21,359–401.

Miller, M.M., Dixon, T.H., 1990. Late Proterozoic evolution ofthe north part of the Hamisana Shear Zone, northeast Sudan:constraints on Pan-African accretionary tectonics. J. Geol. Soc.Lond. 149, 743–750.

Pegram, W.J., Register, J.K., Fullagar, P.D., Ghuma, M.A., Rogers,J.J.W., 1976. Pan-African ages from A Tibesti massif batholith,southern Lybia. Earth Planet. Sci. Lett. 30, 123–128.

Pin, C., Poidevin, J.L., 1987. U–Pb zircon evidence for aPan-African granulite facies metamorphism in the CentralAfrican Republic. A new interpretation of the high-grade seriesof the northern border of the Congo Craton. Precambrian Res.36, 303–312.

Ries, A.C., Shackleton, R.M., Dawoud, A.S., 1985. Geochrono-logy, geochemistry and tectonics of the NE Bayuda Desert innorthern Sudan: Implication for the western margin of the lateProterozoic fold belt of NE Africa. Precambrian Res. 30, 43–62.

Rocci, G., 1965. Essai d’interpretation de mesures geochrono-logiques. La structure de l’Ouest africain. Sci. Terre. Fr. 10,461–479.

Schandelmeier, H., Darbyshire, D.P.F., Harms, U., Richter, A.,1988. The E Saharan Craton: evidence for pre-Pan-Africancrust in NE Africa W of the Nile. In: El Gaby, S., Greiling,R.O. (Eds.), The Pan-African belts of NE Africa and Adjacentareas. Friedr Vieweg and Sohn, Utrecht University, Utrecht,The Netherlands, pp. 69–94.

Schandelmeier, H., Richter, A., Harms, U., 1987. Proterozoicdeformation of the East Sahara Craton in southeast Libya,south Egypt and north Sudan. Tectonophysics 140, 233–246.

Schandelmeier, H., Wipfler, E., Kuster, D., Sultan, M., Becker,R., Stern, R.J., Abdelsalam, M.G., 1994. Atmur-Delgo Suture:A Neoproterozoic oceanic basin extending into the interior ofnortheast Africa. Geology 22, 563–566.

Shackleton, R.M., Ries, A.C., 1984. The relation between region-ally consistent stretching lineation and plate motions. J. Struct.Geol. 6, 111–117.

Stern, R.J., 1994. Arc assembly and continental collision in theNeoproterozoic E African Orogen: implication for the consoli-dation of Gondwanaland. Annu. Rev. Earth Planet. Sci. 22,319–351.

Stern, R.J., Abdelsalam, M.G., 1996. The origin of the great bendof the Nile from SIR-C/X-SAR imagery. Science 274, 1696–1698.

Stern, R.J., Dawoud, A.S., 1991. Late Precambrian (740 Ma)charnockite, enderbite, and granite from Jebel Moya, Sudan:a link between the Mozambique Belt and the Arabian-NubianShield? J. Geol. 99, 648–659.

Stern, R.J., Kroner, A., Manton, W.I., Reischmann, T., Mansour,M., Hussein, I.M., 1989. Geochronology of the late PrecambrianHamisana shear zone, Red sea Hills, Sudan and Egypt. J. Geol.Soc. Lond. 146, 1017–1030.

Stern, R.J., Kroner, A., Reischmann, T., Bender, R., Dawoud,A.S., 1994. Precambrian basement around Wadi Halfa: a newperspective on the evolution of the Central Saharan GhostCraton. Geol. Rund. 83, 564–577.

Stern, R.J., Nielsen, K.C., Best, E., Sultan, M., Arvidson, R.E.,Kroner, A., 1990. Orientation of late Precambrian sutures inthe Arabian-Nubian Shield. Geology 18, 1103–1106.

Sultan, M., Bickford, M.E., El Kaliouby, B., Arvidson, R.E., 1992.Common Pb systematics of Precambrian granitic rocks of theNubian Shield (Egypt) and tectonic implications. Geol. Soc.Am. Bull. 104, 456–470.

Sultan, M., Chamberlin, K.R., Bowring, S.A., Arvidson, R.E.,Abuzied, H., El Kaliouby, B., 1990. Geochronologic andisotopic evidence for involvement of pre-Pan-African crust inthe Nubian Shield, Egypt. Geology 18, 761–764.

Sultan, M., Tucker, R.D., El Alfy, Z., Attia, R., Ragab, A.G., 1994.U–Pb (Zircon) Ages for the Gneissic Terrane West of the Nile,Southern Egypt.

Sultan, M., Tuckler, R.D., Gharbawi, R.I., Ragab, A.I., El Alfy,Z., 1993. On the location of the boundary between theNubian Shield and the old African continent: inferences fromU–Pb (zircon) and common Pb data. In: Thorweihe, U.,Schandelmeier, H. (Eds.), Geoscientific Research in NE Africa.Balkema, Rotterdam, The Netherlands, pp. 75–77.

Toteu, S.F., Michard, A., Bertrand, J.M., Rocci, G., 1987. U/Pbdating of Precambrian rocks from the northern Cameroon,orogenic evolution and chronology of the Pan-African belt ofcentral Africa. Precambrian Res. 37, 71–87.

Vail, J.R., 1971. Geological reconnaissance in part of BerberDistrict, Northern Province, Sudan. Sudan Geol. Surv. Dept.Bull. 13, 76.

Vail, J.R., 1972. Geological reconnaissance in the Zalingei andJebel Marra areas of western Darfur Province. Sudan Geol.Surv. Dept. Bull. 14, 50.

Vail, J.R., 1976. Outline of the geochronology and tectonic unitsof the basement complex of Northeast Africa. Proceedings ofthe Royal Society of London A350, 127–141.

Vail, J.R., 1983. Pan-African crustal accretion in NE Africa. J.Afr. Earth Sci. 1, 285–294.


Vail, J.R., 1985. Pan-African (late Precambrian) tectonic terranesand reconstruction of the Arabian-Nubian Shield. Geology 13,839–842.

Vail, J.R. 1988. Tectonics and evolution of the Proterozoicbasement of NE Africa. In: El Gaby, S., Greiling, R.O. (Eds.),The Pan-African Belts of NE Africa and Adjacent Areas. FriedrVieweg and Sohn, pp. 185–226.

Vail, J.R., Dawoud, A.S., Ahmed, F., 1973. Geology of the ThirdCataract, Halfa District, Northern Province, Sudan. Sudan Geol.Surv. Dept. Bull. 22, 34.

Wust, H.J., 1989. Geochronologie und geochemie Prakambrischermetasedimente und metavulkanite der Sudlichen Eastern Desert,Agypten. M.Sc. thesis. Johannes-Gutenberg-Universitat, Mainz,Germany, 71 pp.

Wust, H.J., Todt, W., Kroner, A., 1987. Conventional and singlegrain zircon ages for meta-sediments and granitic clasts fromthe E Desert of Egypt: evidence for active continental marginevolution in Pan-African times. Terra Cognita Abstr. 7, 333–334.

Documents

Precambrian Research 123 (2003)