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Sutures and shear zones in the Arabian-Nubian Shield
Abstract
Deformational belts in the Arabian-Nubian Shield (ANS) are divided into: (1) those associated with sutures, both arc-arc and arc-continental; and (2) post-accretionary structures which include north trending shortening zones and northwest trending strike-slip faults. The arc-arc sutures manifest collision between arc terranes at -800-700 Ma. They are orientated east to northeast in the northern part of the ANS and north to north-northeast in the south. North or south verging ophiolitic nappes are associated with the east to northeast trending sutures. These nappes were steepened by upright folds associated with the final stages of collision between terranes. East or west verging ophiolitic nappes are associated with the north to north-northeast trending sutures. These were deformed by upright folds and strike-slip faults related to oblique collision between terranes and/or post-accretionary deformations. The arc-continental sutures define the eastern and western boundaries of the ANS and are marked by north trending deformational belts which accompanied collision of the ANS with east and west Gondwana at -750-650 Ma. The post-accretionary structures were developed between -650-550 Ma due to continued shortening of the ANS. This produced north trending shortening zones which offset the east to northeast trending sutures in the northern part of the ANS but were superimposed as co-axial deformation on the north to north-northeast trending sutures in the south. The shortening deformation culminated with the development of northwest trending strike-slip faults and shear zones.
... The Western Ethiopian Shield (WES) is situated in a key location, relatively close to the transition between the Arabian Nubian Shield and the Mozambique Belt. It is also adjacent to and east of the 'Eastern Saharan Meta-craton' [4]. It is a metamorphic terrane that includes high-grade gneisses and low-grade metavolcanic and metasedimentary rocks with associated intrusions. ...
... Based on its lithological and metamorphic characteristics, the EAO can be broadly subdivided into two terranes, the Arabian Nubian Shield in the north and the Mozambique Belt in the south. The ANS is dominated by low-grade volcano-sedimentary rocks associated with plutons and ophiolitic remnants [4,[15][16][17][18][19], and represents the juvenile terrane. However, the MB in the south part of the EAO is a tract of largely older continental crust that was extensively deformed and metamorphosed in the Neoproterozoic/Cambrian ( [10,[20][21][22]; Figure 1). ...
... The Kemashi Domain consists of a sequence of metasedimentary rocks and abundant mafic to ultra-mafic volcanic material that has been metamorphosed to upper greenschist/epidote-amphibolite facies. The nature of these ultra-mafic/mafic plutonic rocks within the Kemashi Domain is controversial, with some scholars holding that they represent an ophiolite sequence [4,15,23], named the Tuludimtu Ophiolite. However, others [24][25][26] hold that these ultra-mafic/mafic plutonic rocks represent Alaskan-type, concentrically zoned intrusions, which were emplaced into an extensional arc or back-arc environment. ...
The Neoproterozoic Bure adakitic rock in the western Ethiopia shield is a newly discovered magmatic rock type. However, the physicochemical conditions during its formation, and its source characteristics are still not clear, restricting a full understanding of its petrogenesis and geodynamic evolution. In this study, in order to shed light on the physicochemical conditions during rock formation and provide further constraints on the petrogenesis of the Bure adakitic rock, we conduct electron microprobe analysis on K-feldspar, plagioclase, and biotite. Additionally, we investigate the trace elements and Hf isotopes of zircon, and the Sr-Nd isotopes of the whole rock. The results show that the K-feldspar is orthoclase (Or = 89.08~96.37), the plagioclase is oligoclase (Ab = 74.63~85.99), and the biotite is magnesio-biotite. Based on the biotite analysis results, we calculate that the pressure during rock formation was 1.75~2.81 kbar (average value of 2.09 kbar), representing a depth of approximately 6.39~10.2 km (average value of 7.60 km). The zircon thermometer yields a crystallization temperature of 659~814 °C. Most of the (Ce/Ce*)D values in the zircons plotted above the Ni-NiO oxygen buffer pair, and the calculated magmatic oxygen fugacity (logfO2) values vary from −18.5 to −4.9, revealing a relatively high magma oxygen fugacity. The uniform contents of FeO, MgO, and K2O in the biotite suggest a crustal magma source for the Bure adakitic rock. The relatively low (87Sr/86Sr)i values of 0.70088 to 0.70275, positive εNd(t) values of 3.26 to 7.28, together with the positive εHf(t) values of 7.64~12.99, suggest that the magma was sourced from a Neoproterozoic juvenile crust, with no discernable involvement of a pre-Neoproterozoic continental crust, which is coeval with early magmatic stages in the Arabian Nubian Shield elsewhere. Additionally, the mean Nd model ages demonstrate an increasing trend from the northern parts (Egypt, Sudan, Afif terrane of Arabia, and Eritrea and northern Ethiopia; 0.87 Ga) to the central parts (Western Ethiopia shield; 1.03 Ga) and southern parts (Southern Ethiopia Shield, 1.13 Ga; Kenya, 1.2 Ga) of the East African Orogen, which indicate an increasing contribution of pre-Pan-African crust towards the southern part of the East African Orogen. Based on the negative correlation between MgO and Al2O3 in the biotite, together with the Lu/Hf-Y and Yb-Y results of the zircon, we infer that the Bure adakitic rock was formed in an arc–arc collision orogenic environment. Combining this inference with the whole rock geochemistry and U-Pb age of the Bure adakitic rock, we further propose that the rock is the product of thickened juvenile crust melting triggered by the Neoproterozoic Pan-African Orogeny.
... This gap in the literature raises fundamental questions regarding the mechanisms that govern orebody development in the context of the syn-and post-tectonic intrusions of granitic rocks and shear zones in the study area. The intricate structural evolution of the Nakasib deformation belt, resulting from the oblique collision between the Haya and Gebeit Terranes, adds further complexity to the geological setting of the region ( Fig. 1; Abdelsalam and Stern, 1993;Stern and Abdelsalam, 1998;Abdelsalam and Stern, 1996;Malavieille et al., 2002;Johnson and Woldehaimanot, 2003;Hargrove et al., 2006). ...
... In the study area D2 is represented by the F2 folds (refolded limbs of F1), a reverse fault in the eastern part of the Amgififa deposit, and the foliation of the ore-siliceous breccia within the Amgififia pull-apart ( Fig. 8a-b, and 9c-e). Abdelsalam and Stern (1996) suggested that the F2 folds (in the SW of the Nakasib Suture) were formed by a convergent terrane moving on top of the NW-dipping subduction zone (Wipfler, 1996). However, the regional stress direction from the stereographic projection of the D2 structures portrayed an NNW-SSE-trending maximum compression direction (Fig. 9c-e), which is slightly different from the regional horizontal stress direction of D1. ...
... Wadi Um Gheig area lies in the Central Eastern Desert, south west of Quseir City forming a part of the Neoporeterozoic evolution of the Nubian Shield in NE Africa. The Shield of NE Africa was Developed because of accretion of intraoceanic island arc, continental microplates, and oceanic plateaus during consolidation of Gondwana (Gass, 1982, Stern, 1994, Kröner et al., 1994, Abdelsalam and Stern, 1996. Geological and tectonic setting of the basement rocks in the CED of Egypt particularly Umm Gheig-Umm Naggat area has been the focus of many workers (e. ...
The area of Wadi Umm Gheig-Umm Naggat is located at the central part of the Eastern desert, Egypt, 50km south to El-Quseir city at the Red Sea coast. The area is dominated by metavolcanics, Older Granites, Dokhan Volcanics, intrusive cumulate gabbro and Younger Granites. This works focuses on heavy minerals distributed in dry stream sediments of Wadi Umm Gheig and Gabal Umm Nagat. The study has followed up the traditional methods for sample collection from the stream sediments and the plane study for investigation and prospecting, as well as evaluation of heavy mineral deposits. The studied bed rocks are represented mainly by monzogranite, alkali feldspar granite, syenogranite and alkali granite. The investigated heavy minerals dominating the stream sediments are given by magnetite, ilmenite, rutile, leucoxene, zircon, fluorite and apatite arranged in decreasing orderas percentages of abundances. Few trace minerals are detected in some samples like thorite and monazite, and xenotime as well. The evaluation of heavy minerals concentration reveals higher concentration of magnetite, ilmenite and zircon at the western sector, while fluorite show random distributions within the stream sediments area.
... 1. Yanbu suture: This suture comprises a highly deformed greenschist to amphibolite grade volcanosedimentary metamorphosed rock assemblage. It 2014), which was modified from Abdelsalam and Stern (1996). Structures orthogonal to the coast are shown in detail, whereas others are shown simplified with bold lines. ...
Associating lithospheric suture zones of the Arabian-Nubian Shield on either side of the central Red Sea is important for constraining Arabia-Nubia plate motion and potentially testing plate rigidity during continental breakup. However, that association is difficult because of the non-unique character of the shield suture zones, some shield areas are obscured by later volcanics and sediments, and because some intervening shield crust that was extended during continental rifting now lies submerged beneath thick Miocene evaporites in the Red Sea and is thus obscured. Here, we show that an association is clearly favoured if shield structures are interpreted along with an oceanic segmentation revealed by the satellite-derived gravity field. The Proterozoic subduction suture zones associated include: the Bi’r Umq on the Arabian shield with a previously unrecognised suture zone in the Nubian Shield (herein called Shagara), Fatma with Nakaseib, and Ad Damm with Ashat suture zone. Bouguer gravity anomaly lows, produced by oceanic spreading discontinuities of the new mid-ocean ridge formed in the Red Sea, connect two sets of suture zones: Bi’r Umq-Shagara and Fatma-Nakaseib. As far as we are aware, these are the first short-offset oceanic discontinuities to be clearly linked to adjacent shield structures.
... Bogens, gefolgt von der Akkretion des Hijaz-Magmatischen Bogens gegen den Nilkraton und die Überarbeitung des akkretierten Bogens nach der Akkretion (Stoeser und Camp, 1985;Abdelsalam und Stern, 1996;Fritz et al., 1996;Augland et al., 2012). ...
The Sukari granites are elongated in a NNE direction and surrounded by two steep shear zones from east and west directions. These granites belong to the within–plate A–type magmatism and display a trondhjemitic affinity. They comprise alkali feldspar granite together with syenogranite and monzogranite. Their geochemical signatures suggest emplacement in an extensional tectonic regime associated with the post–collisional collapse of the Pan–African Orogeny. They range in compositions from metaluminous to peraluminous and classified as ferroan alkali–calcic to calc–alkalic rocks. These calc–alkalic granites were formed by partial melting of tonalitic to granodioritic crust at low–pressure conditions. Magmatic temperatures are around 930°C as deduced from zircon saturation estimate. This inference is supported by the high SiO2 (> 70 wt. %) and low CaO (< 2 wt. %) contents that are similar to those of melts produced experimentally by partial melting of tonalites and granodiorites. Moreover, the Rb–Sr systematic indicates that these granitic magmas were formed at relatively shallow depth (around 20 km). The rocks show enrichment in the LILE (Rb, Ba, Ta and K) relative to HFSE (P, Ti and Y). The overall similarity of the trace element patterns suggests that the Sukari granites were derived from a similar parental magma source. The gold mineralizations in the Eastern Desert of Egypt including Sukari gold mine region principally controlled by the conjugate shear zones of the Najd Fault System and are associated with E–W directed shortening accompanying oblique convergence between East and West Gondwana. The nature of the mineralized structures include essentially the first shear set which is N-S trending and stacked shear set that dips between 45º to 60º E. The sheared rock commonly contains strong kaolinite, where the kaolinite occurs the gold grades and sulphide content increases.
In Northeast Africa, a greenschist to lower amphibolite facies dominated collisional Pan-African belt extends along the Western flank of the Red Sea. The belt is known as the Egyptian Nubian Shield (ENS) in Egypt. The ENS represents the northern tip of the Arabian-Nubian Shield (ANS) and exhibits most of the essential lithological/structural features of the Midyan terrane exposed in western Saudi Arabia. The low-grade ANS was regarded as the upper crustal equivalent of the high granulite facies-dominated Mozambique Belt (MB), with both forming the N–S oriented East African Orogen (EAO), which formed during a ~200 Ma prolonged stage of closure of the Pacific-sized Mozambique Ocean, and convergence of East and West Gondwana that culminated in arc suturing and terrane accretion. The main objective of the present chapter is to introduce the ENS belt exposed in Northeast Africa. The Neoproterozoic ENS litho-units are typically juvenile and experienced a polyphase deformation history. Following this introduction, the setting of the ANS in Northeast Africa, the broad relations of the ANS with the EAO, and the tectonic components of the ANS will be addressed with reference to their lithotectonic associations, geochemistry and geochronology, and structural and tectonic framework. The chapter provides an opportunity to review the magmatic-metamorphic-tectonic history of the Pan-African belt in Northeast Africa.
The tectonic settings and petrogenesis of Neoproterozoic gabbroic rocks are critical to understand the formation and evolution of the Arabian-Nubian accretionary orogen. We present the whole-rock chemistry and amphibole chemistry of the Gattar gabbro in the northern Eastern Desert of Egypt to better understand the formation of this part of the orogen. The Gattar gabbro is composed of variable proportions of amphibole and plagioclase, which imply the hydrous nature of its parent magma. Trace element patterns of the gabbro and the calculated liquids in equilibrium with its amphibole show enrichment in large ion lithophile elements relative to high field strength elements, which indicate that the Gattar magma formed above a subduction zone. The low abundances of high field strength element in the gabbro are consistent with a depleted mantle source similar to intra-oceanic island arc rocks. However, the high Nb/La ratio of the Gattar gabbro (0.46–10.71) is reminiscent to Nb-enriched mafic rocks from subduction settings. The amphibole chemistry suggests that the hydrous magma of the gabbro crystallized at temperature and pressure estimates of 930 °C and 8 kbar and under oxidizing conditions. The Gattar gabbro is affiliated with the Tonian-Cryogenian arc-related mafic gabbro, which is rarely recorded in this northernmost segment of the Arabian-Nubian orogen. In terms of comparison with the Ediacaran post-orogenic gabbros from the northern Eastern Desert, the Gattar gabbro shows lower concentrations of incompatible elements and Ti/V ratio.
Based on new field, petrographic, and whole-rock geochemistry data, we investigated three discrete metagabbro-diorite complexes (MGDC) across the E-W Sinai to contribute to increasing knowledge of the evolution of the juvenile continental crust of the Neoproterozoic Arabian–Nubian Shield. The three MGDCs vary in the dominance of the gabbroic versus dioritic rock types among each of them. Gabbroids are distinguished into pyroxene-hornblende gabbros and hornblende gabbros, whereas dioritic rocks have been subdivided into diorites and quartz diorites. The studied MGDC rocks are almost metaluminous and possess prevalent calc-alkaline characteristics over subsidiary tholeiitic and alkaline affinities. The most distinctive feature in the profiles of the investigated MGDCs on the N-MORB-normalized spider diagrams is the coincidence of stout negative Nb anomalies and projecting positive Pb spikes, which is typical of igneous rocks evolved in subduction zones. The three MGDC samples exhibit variably LREE-enriched patterns [(La/Yb)N = 4.92–18.55; av. = 9.04], either lacking or possessing weak to negligible positive and negative Eu anomalies. The calculated apatite and zircon crystallization temperatures reveal the earlier separation of apatite at higher temperatures, with the obvious possibility of two genetic types of apatite and zircon in the magma (cognate vs. xenocrystic) since both accessories have yielded very wide ranges of crystallization temperatures. The investigated MGDCs were formed in a continental arc setting, particularly a thick-crust arc (>39 km). The parent magmas comprised components derived from the melting of the mantle wedge, subducting oceanic lithosphere, and subducting overlying sediments. The mantle input was from a spinel–garnet transitional mantle source at a depth of ca. 75–90 km. The impact of slab-derived fluids was much greater than that of slab-derived melts, and so subduction-related fluids had a crucial effect on metasomatizing the partially melted mantle source. The parent mantle-derived magma has been subjected to substantial crustal contamination as a dominant mechanism of differentiation.
Vermiculite deposit, about 65 mt, reported by Ezana Mining Company in northern Ethiopia is studied for petrography and geochemistry. The deposit, located near Digum village, is confined to a small elongated intrusive complex, about 0.7 Km2. The complex is comprised of ultramafic, syenite, and alkali granitic rocks. The intrusive rocks have been emplaced into the Neoproterozoic basement rocks comprised of metavolcanic and phyllite rocks of Tsaliet Group. Vermiculite occurs up to a depth of ~ 25 m, formed by weathering of phlogopite present in ultramafic rocks. Petrography indicates the presence of phlogopite, and XRD data also suggest presence of vermiculite. Intrusive rocks geochemical data plot in fields of Ijolite/Ijolite-gabbro, syenite, and alkali granite. Data also suggest volcanic-arc tectonic setting. These rocks are comparable, spatially and temporally, with the nearby post-tectonic Negash igneous complex which varies in composition from ultramafic to felsic though dominantly intermediate. Digum complex is conspicuous in rock composition and facilitate vermiculite and provides an opportunity to study the petrogenesis of the intrusive complexes.
Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egypt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terrane boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristics of the critical areas are presented. Collisional deformation of the terranes ended about 615-600 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma (575 - 595 Ma ago) over the Eastern Desert and was followed by a further period of about 50 Ma of late to post-tectonic activity. The regional structures originated mainly during post-collisional events, starting with those related to extensional collapse (molasse basin formation, normal faulting, generation of metamorphic core complexes). Subsequent NNW-SSE shortening is documented by large-scale thrusting (towards the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, which was localized to particular shear zones. Early transpression produced, for example, the Allaqi shear zone and final transpression is documented in the Najd and Wadi Kharit-Wadi Hodein zones. Two terrane boundaries can be defined, the Allaqi and South Hafafit Sutures, which are apparently linked by the high angle sinistral strike-slip Wadi Kharit-Wadi Hodein shear zone with a tectonic transport of about 300 km towards the W/NW. In general, the tectonic evolution shows that extensional collapse is not necessarily the final stage of orogeny, but may be followed by further compressional and transpressional tectonism. The late Pan-African high angle faults were reactivated during Red Sea tectonics both as Riedel shears and normal faults, where they were oriented favourably with respect to the actual stress regime.
The petrography of rocks of the Upper Proterozoic mafic-ultramafic complex of Tulu Dimitri (approx 35.5oE, 9oN) are briefly described. On the basis of 17 XRF analyses for major, minor and some trace elements, and of REE analyses, an AMF diagram and several discriminating diagrams are presented, without giving the detailed results of the analyses. With the exception of the REE analyses, which are considered to be inconclusive, the chemical investigation supports the earlier conclusion, based on geological arguments, that this is an ophiolitic complex.-J.Ze.
The Al-Amar fault, one of the most important geological features of the E corner of the Arabian Shield, separates a dominantly metavolcanic sequence overlying gneissis granodiorite of the basement to the E, from an essentially metasedimentary sequence to the W. Intrusive rocks of the region include: grabbro, diorite, granodiorite, and alkalic granite. The Al-Amar- Idsas region, evaluated in the light of the plate tectonic theory, appears to represent a continental volcanic arc and a contiguous back-arc basin. -Author