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Simplified geological map of the Arabian–Nubian shield (modified after Worku & Schandelmeier 1996; Fritz et al. 2013; Blades et al. 2015) with the study area indicated (Fig. 2). The Gulf of Aden fracture zones are after Bosworth et al. (2005). Inset shows the location of the Arabian–Nubian Shield (ANS) and Mozambique Belt (MB) within the East African Orogen. WES, Western Ethiopian Shield; SES, Southern Ethiopian Shield; NED, Northern Eastern Desert; CED, Central Eastern Desert; SED, Southern Eastern Desert.
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New high spatial resolution secondary ion mass spectrometry (SIMS) zircon dating from the Dire Dawa Precambrian basement yields crystallization ages at c. 790 Ma and 600 – 560 Ma. Two of the youngest samples are pervasively deformed, indicating that orogenesis continued until c. 560 Ma. SIMS δ18Ozrn shows bimodality, with the oldest sample (c. 790...
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Context 1
... the Harar granite (Kazmin 1975), near Harar and c. 10 km SE of the location of our sample DD-1-3 gave a Pb-Pb age of c.782 Ma ( Teklay et al. 1998). Hence, the age of c. 568 Ma for our sample DD-1-3 indicates that the outcrop of this sample is not a continuation of the Harar pluton dated by Teklay et al. (1998). In the Southern Ethiopian Shield (Fig. 1), four magmatic episodes have previously been identified, at 890 -840, 790 -700, c. 660 (Moyale Event) and 630 -500 Ma ( Teklay et al. 1998;Yibas et al. 2002;Stern et al. 2012). Although the ages for the eastern Ethiopian granitoids from this and previous studies are broadly contemporaneous with granitic magmatism in the Southern ...
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... rocks elsewhere in the country are dominated by north-south-to NNE-SSW-trending structures (Silverstein et al. 2012). Similarly, east-west-trending structures dominate the Al- Mahfid terrane of Yemen. Pre-Gulf of Aden and Afar Depression reconstructions ( Silverstein et al. 2012), which are consistent with the Gulf of Aden fracture zone pattern (Fig. 1), place the Dire Dawa basement adjacent to the Archaean Al-Mahfid terrane of Yemen. This reconstruction coupled with the unique east-west structural grain of the Dire Dawa basement and the Al-Mahfid terrane prompted Silverstein et al. (2012) to conclude that these structures developed prior to the formation of Gondwana; thus the Dire ...
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The Permian-Triassic time interval was a period of high sedimentation rates in the intracontinental Karoo rift basin of northwestern Mozambique, reflecting high exhumation rates in the surrounding high ground Precambrian-Cambrian basement and juxtaposed nappes. U-Pb LA-MC-ICPMS dating and Lu-Hf isotopic analysis of detrital zircons from the Late Pe...
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... 640 Ma in the ANS and was followed by shield-wide post-tectonic calcalkaline and alkaline magmatism at ca. 635-580 Ma (Fleck et al. 1980;Stern 1994;Johnson and Woldehaimanot 2003;Avigad and Gvirtzman 2009;Morag et al. 2011a;Robinson et al. 2014;Yeshanew et al. 2015). Final assembly was not achieved farther south in the EAAO until late Ediacaran to early Cambrian (Collins and Pisarevsky 2005;Johnson et al. 2011;Yeshanew et al. 2017). Given the plate configuration of Gondwana at the time of deposition ca. ...
... 50%) have evolved ε Hf (t) compositions (Figure 7), suggesting a source(s) outside of the juvenile ANS. Unlike the ANS, Neoproterozoic crustal segments derived from reworking of Archaean and Palaeoproterozoic crust are conspicuous in the polydeformed and polycyclic Mozambique Belt (MB), southern segment of the EAAO (Kröner et al. 2003;Kröner and Stern 2004;Cawood and Buchan 2007;Yeshanew et al. 2015Yeshanew et al. , 2017. These crustal domains have highly evolved ε Nd (t) and ε Hf (t) isotopic compositions (Kröner et al. 2003) and ancient model ages (Stern 2002). ...
... These crustal domains have highly evolved ε Nd (t) and ε Hf (t) isotopic compositions (Kröner et al. 2003) and ancient model ages (Stern 2002). The Mozambique Belt and other ancient micro-continental fragments such as Azania and the arcgneiss collage of the Precambrian basement of Yemen (Whitehouse et al. 1998;Collins and Windley 2002;Stern 2002;Collins and Pisarevsky 2005;Yeshanew et al. 2015Yeshanew et al. , 2017Al-Khirbash et al. 2021), which coalesced together with juvenile oceanic arc terranes during the final amalgamation of Gondwana, are suggested as the likely sources of the Neoproterozoic detrital zircon with evolved ε Hf (t) compositions. Therefore, the Mozambique Belt is interpreted to have supplied a significant amount of the sediment that blanketed the ANS and northern Gondwana in general. ...
The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined in-situ U-Pb, δ 18 O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8-0.55 Ga and 1.1-0.9 Ga with subordinate peaks at ca. 2.2-1.7 Ga and 2.7-2.5 Ga. The δ 18 O secular variation mirrors global compilations with Archaean zircon defining a restricted δ 18 O range of ca. 4.0-8.0 ‰ and younger zircon showing wide variation in δ 18 O up to ca. 14 ‰. The ca. 0.8-0.55 Ga age peak has the largest variation in ε Hf (t) with about half of all these Neoproterozoic zircon grains being juvenile (ε Hf (t) > 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved ε Hf (t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1-0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1-0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ 18 O of post-Archaean zircon, together with the evolved ε Hf (t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental-scale homogenization and dispersion process. ARTICLE HISTORY
... In contrast to the other Ethiopian Precambrian basements, the Precambrian of eastern Ethiopia contains 1997 Ma and 2489 Ma rocks as well as Archean xenocrysts in Neoproterozoic rocks (Supplementary Table S7; Teklay et al., 1998). The Neoproterozoic rocks with ages from 844 to 560 Ma, exhi-bit negative whole-rock Ɛ Nd (t) values ( Fig. 12a; Teklay et al., 1998;Yeshanew et al., 2016), also indicating their generation from Paleoproterozoic-Archean crust. Late Cryogenian to Ediacaran magmatism is recorded in all the terranes in the ANS (e.g., Johnson et al., 2001;Teklay et al., 2001;Asrat et al., 2004;Ali et al., 2013Ali et al., , 2014Eliwa et al., 2014;Robinson et al., 2014;Megerssa et al., 2020;Saeed et al., 2020;Zoheir et al., 2021;Pease et al., 2022). ...
... ,Yihunie et al. (2006),Woldemichael et al. (2010),Yeshanew et al. (2016),Ghebretensae et al. (2019a),Jiang et al. (2024) andZeng et al. (2024); Gerf ophiolite data are fromZimmer et al. (1995), and Hf isotopic data are compiled fromAli et al. (2012, 2015, 2016), Blades et al. (2015), Saeed et al. (2020), Gamal El Dien et al. (2021a,b), Zoheir et al. (2021), Adam et al. (2022), Gamaleldien et al. (2022b), Peng et al. (2022), Sami et al. (2023), Jiang et al. (2024), Khan et al. (2024) and Zeng et al. (2024).Zoheir et al., 2021). The oldest ages of about 780 Ma are recorded in all the three sectors of the Eastern Desert of Egypt (e.g.,Ali et al., 2009;Abd El-Rahman et al., 2017; ...
... Gneisses and schists. Medium-to high-grade metasediments occupy Asrat et al., 2001;Fritz et al., 2013;Yeshanew et al., 2016;Ibinoof et al., 2016). Keys: SED=Southern Eastern Desert; WES=Western Ethiopian Shield; NSB=Northern Somali Basement. ...
The Bensa-Girja area is located in northernmost part of the Neoproterozoic Adola belt, southern Ethiopia. It is
largely constituted of mafic rocks (amphibolite and metagabbro), ultramafic suite (serpentinite/serpentinized
peridotite, talc schist and subordinate pyroxenite), metasedimentary (metapelitic to semi-metapelitic schists,
minor marble and metasandstone) and metavolcaniclastic rocks. Geochemical analysis was carried out on the
mafic–ultramafic rocks to characterize their petrogenesis, magma source and paleotectonic setting. The results
indicate that the mafic rocks have tholeiitic to boninitic composition and represent primitive to evolved magma.
The current serpentinite and serpentinized peridotite were formed after harzburgites that are interpreted as a
refractory mantle wedge peridotite, and pyroxenites are considered as cumulate rocks crystallized from partial
melts of the peridotite. The geochemical data further suggest that the mantle sources of the mafic-ultramafic
rocks were modified by both slab-derived fluids and melts in a supra-subduction zone. The rocks thus display
geochemical characteristics typical of island arc system with slight MORB-like affinity, inferred to have formed in
a sub-arc or spreading forearc setting. It is interpreted that the studied rocks are representing remnants of a
fragmented oceanic lithosphere. This together with field geological data supports the arc accretion model
postulated for the crustal growth of the Arabian-Nubian Shield.
... Also, it distinguished the low-grade metavolcano-sedimentary rocks of the Bulbul Terrane from the medium-to high-grade gneissic, migmatites, and granulites of the Alghe Terrane. The Bule Hora Fritz et al., 2013;Blades et al., 2015;Fitsum et al., 2016). (b) Geologic map of Ethiopia, with emphasis on the southern Ethiopian Shield. ...
... On the other hand, the petrogenesis of meta-volcano-sedimentary rocks from Mai Kenetal, central Tigray, northern Ethiopia suggests a calc-alkaline suite resulted from mantle-derived magmas and a subducted slab of continental crust equivalent to Sudan, Egypt, and Saudi Arabia's meta-volcano-sedimentary rocks that evidence Arabian-Nubian Shield Neoproterozoic growth (Alene et al., 2000;Solomon, 2009). The western Ethiopian Shield (WES) super-crustal rocks are correlated with the Dire Dawa basement rocks of eastern Ethiopia and the northeastern Uganda shield (Blades et al., 2015;Fitsum et al., 2016), but older than the southern and northern Ethiopian Shield, southeast Kenya basement rocks, and the Eritrea Arabian Nubian Shield. ...
The granite gneiss complexes and mafic-ultramafic-sedimentary ophiolitic belts are mostly exposed in southern Ethiopia, but the Bule Hora ophiolitic belt is not well studied yet. For the first time, this paper reveals the petrogenesis and geochemical nature of the rocks from the Ropi Megda area in the Bule Hora ophiolitic belt, southern Ethiopia, through ore rock geochemical and field studies. Major oxides and trace elements were analyzed using ICP-MS and ICP-AES to understand the geochemical trends, petrogenesis and tectonic settings of the Ropi Megada. The SiO2 and TiO2 content in the hornblende-biotite-quartz-plagioclase schist range from 35-50 Wt. % and 0.07–6.38 Wt. %, respectively. Among the major oxides, Fe2O3, MgO, CaO show negative trends with silica content. Similarly, some trace elements like V and Sr show negative trends with SiO2. The rocks are LREE-enriched and HREE-depleted [(La/Yb)N = 0.64–12.77], with a positive Eu anomaly [(Eu/Eu*)N = 0.56–2.32]. Hornblende-biotite-quartz-plagioclase schist has higher gold content (0.001–0.489 ppm) than the biotite-quartz-feldspathic gneiss (0.001–0.003 ppm). Based on the geochemical and field data, the brittle-ductile deformations and hydrothermal fluid reactions with the ophiolitic rocks might have been the primary agents for the gold leaching and transportation from the source to the deposit in the sheared and fractured zone within the host rocks. Hornblende-biotite-quartz-plagioclase schist and quartz-hornblende-biotite schist geochemical data studies from the Ropi Megada area, supposedly associated with the upper mantle composition, show tholeiitic, calc-alkaline, metaluminous, and boninite affinity that formed in the island arc and mid-oceanic ridge basalt tectonic settings.
... 879 Ma) and the assembly of Gondwana (ca. 550 Ma) (Stern et al. 1994;Johnson and Woldehaimanot 2003;Jacobs and Thomas 2004;Li et al. 2008;Stern and Johnson 2010;Yeshanew et al. 2017). ...
The “Supercontinents” constitute the majority of the ancient Earth’s surface and play an important role in Earth’s history.
... Also, it distinguished the low-grade metavolcano-sedimentary rocks of the Bulbul Terrane from the medium-to high-grade gneissic, migmatites, and granulites of the Alghe Terrane. The Bule Hora Fritz et al., 2013;Blades et al., 2015;Fitsum et al., 2016). (b) Geologic map of Ethiopia, with emphasis on the southern Ethiopian Shield. ...
... On the other hand, the petrogenesis of meta-volcano-sedimentary rocks from Mai Kenetal, central Tigray, northern Ethiopia suggests a calc-alkaline suite resulted from mantle-derived magmas and a subducted slab of continental crust equivalent to Sudan, Egypt, and Saudi Arabia's meta-volcano-sedimentary rocks that evidence Arabian-Nubian Shield Neoproterozoic growth (Alene et al., 2000;Solomon, 2009). The western Ethiopian Shield (WES) super-crustal rocks are correlated with the Dire Dawa basement rocks of eastern Ethiopia and the northeastern Uganda shield (Blades et al., 2015;Fitsum et al., 2016), but older than the southern and northern Ethiopian Shield, southeast Kenya basement rocks, and the Eritrea Arabian Nubian Shield. ...
... 630-550 Ma) (Bentor 1985;Be'eri-Shlevin et al. 2009a;Johnson et al. 2011;Fritz et al. 2013;Robinson et al. 2014;Yeshanew et al. 2015). While the core of the ANS is a collage of juvenile island-arc terranes, its margins were influenced by either pre-Neoproterozoic crust reworked during Neoproterozoic amalgamation or by the involvement of older continental material (Agar et al. 1992;Windley et al. 1996;Teklay et al. 1998;Whitehouse et al. 1998;Be'eri-Shlevin et al. 2009b;Yeshanew et al. 2015Yeshanew et al. , 2017. ...
... Determinations of Sm and Nd isotope ratios were made on a Thermo Scientific TRITON thermal isonization mass spectrometer using the total spiking method with a mixed 147 Sm/ 150 Nd spike at the Swedish Museum of Natural History. Detailed sample preparation and analytical conditions closely resemble those described in Yeshanew et al. (2017). Samarium concentrations were determined in multi-collector static mode, neodymium was run in static mode, and both elements were run using rhenium double filaments. ...
New U-Pb zircon geochronology using high-spatial resolution secondary ion mass spectrometry fills a data gap and provides crystallization ages for granitoids from the Asir composite terrane in the southernmost Arabian Shield of Saudi Arabia. Ages of c. 810–685 Ma, c. 663–636 Ma, and 625–610 Ma reflect oceanic island arc genesis, subduction-related arc accretion (syn-collisional), and post-collisional stabilization, respectively. All samples have juvenile εNd(t) compositions with no evidence of older material being involved in their genesis, indicating that this part of the Arabian Shield grew through juvenile magmatic addition and that assimilation by syn- and post-tectonic magmatism involved an isotopically juvenile component(s). The crustal thickness derived from the (La/Yb)N proxy indicates significant thickening from 10–20 km to c. 70 km at c. 650 Ma, consistent with timing of orogenic uplift and increasing crustal thickness post-dating peak Nabitah orogeny. The age of an intrusion cross-cutting the Atura formation, when combined with other data, provides a well-constrained depositional age of c. 646–625 Ma for the Atura formation and indicates that erosion of the orogenic edifice in this part of the Arabian Shield began at latest by 625 Ma. Our new data indicate that denudation occurred 80–100 m.y. before the development of the prominent sub-Cambrian peneplain, consistent with previous assertions that major pulses of denudation occurred prior to the waning stages of Nabitah orogenesis.
... Although most geochronological studies (e.g., Reisberg et al., 2004;Yeshanew et al., 2017) suggest the southern Ethiopian mantle lithosphere is Neoproterozoic in age, Stern et al. (2012) and Bianchini et al. (2014) attribute the presence of abundant 2.5 Ga zircons to Archean lithosphere at depth in the southern Ethiopian Shield. Xenoliths around Mega (Figure 10b) also preserve evidence of ancient Precambrian depletion events, unlike elsewhere in the northern sector of the EAR (e.g., Beccaluva et al., 2011). ...
Abstract The Turkana Depression, a topographically subdued, broadly rifted zone between the elevated East African and Ethiopian plateaus, disrupts the N–S, fault-bounded rift basin morphology that characterizes most of the East African Rift. The unusual breadth of the Turkana Depression leaves unanswered questions about the initiation and evolution of rifting between the Main Ethiopian Rift (MER) and Eastern Rift. Hypotheses explaining the unusually broad, low-lying area include superposed Mesozoic and Cenozoic rifting and a lack of mantle lithospheric thinning and dynamic support. To address these issues, we have carried out the first body-wave tomographic study of the Depression's upper mantle. Seismically derived temperatures at 100 km depth exceed petrological estimates, suggesting the presence of mantle melt, although not as voluminous as the MER, contributes to velocity anomalies. A NW–SE-trending high wavespeed band in southern Ethiopia at <200 km depth is interpreted as refractory Proterozoic lithosphere which has likely influenced the localization of both Mesozoic and Cenozoic rifting. At <100 km depth below the central Depression, a single localized low wavespeed zone is lacking. Only in the northernmost Eastern Rift and southern Lake Turkana is there evidence for focused low wavespeeds resembling the MER, that bifurcate below the Depression and broaden approaching southern Ethiopia further north. These low wavespeeds may be attributed to melt-intruded mantle lithosphere or ponded asthenospheric material below lithospheric thin-spots induced by the region's multiple rifting phases. Low wavespeeds persist to the mantle transition zone suggesting the Depression may not lack mantle dynamic support in comparison to the two plateaus.
... It is clear that the Sahara Metacraton has a complicated history with multiple phases of magmatism occurring during the Mesoproterozoic and Neoproterozoic, though there is sparse data available from these regions. This map hap has been gridded using QGIS nearest neighbour interpolation, with set age bins to act as a visual aid for the relative distribution of ages in northern Africa (Abdelsalam et al., 2002;Abdelsalam et al., 2003;Abdelsalam et al., 2011;Be'eri-Shlevin et al., 2012;Couzinié et al., 2020;de Wit and Linol, 2015;Djerossem et al. 2020;Djerossem et al., 2021;Henry et al., 2009;Johnson et al., 2011;Johnson, 2014;Küster et al., 2008;Robinson et al., 2014;Robinson et al.,2015a;Robinson et al.,2015b;Robinson et al.,2017;Shellnutt et al. 2017;Shellnutt et al., 2020;Whitehouse et al., 1998;Whitehouse et al., 2001b;Windley et al., 1996;Yeshanew et al., 2015;Yeshanew et al., 2017;Zhang et al. 2019a;Zhang et al., 2019b). The pie charts show the distribution of detrital zircon U-Pb ages in the metasedimentary samples-all samples from this study, except the purple asterisks, which are data from Djerossem et al. 2021. ...
... Saharan Metacraton), with the oldest juvenile magmatism at ca. 840 Ma and subsequent magmatism at ca. 787 Ma. Magmatism and metamorphism at ca. 790-780 Ma are also seen in western Ethiopia, in the Dire Dawa Basement in eastern Ethiopia as well as in the Tokar/Barka Terrane (Andersson et al., 2006;Blades et al., 2015;Teklay et al., 2003;Yeshanew et al., 2017). The bimodal ε Hf (t) signature and model ages, in the western most sample (BU2 + BU6) in Butana (Fig. 8a) suggest that when this granite crystallised, the magma assimilated older continental crust. ...
The Saharan Metacraton is a poorly known tract of pre-Neoproterozoic continental crust that occupies the area between the juvenile Arabian Nubian Shield, in the east, and the Tuareg Shield to the west. Neoproterozoic orogenesis (i.e. Oubanguides and East African orogenies) affect the west, the south and the east of the metacraton, respectively, which led to deformation, emplacement of igneous bodies, and localised episodes of rift-related magamatism. Details about interior regions of the Saharan Metacraton are poorly known, with much of it covered by Phanerozoic rocks. The basement outcrops in Sudan, Chad, Algeria and Libya have been the subject of few modern geochronological studies. Here we present results from the first zircon geochronology and in-situ zircon hafnium isotope investigations from both the Sudanese Butana and central Chad. The terranes in Butana, formed to the east of pre-Neoproterozoic continental crust of the Saharan Metacraton, with the oldest juvenile magmatism (ƐHf(t) of +4.89 to +7.89) at ca. 839 Ma, followed by subsequent magmatism at ca. 787 Ma. The ca. 787 Ma event (seen elsewhere in the East African Orogen) is interpreted to represent volcanic-arc collision and accretion with the kernel of the Saharan Metacraton. The ca. 839 Ma magmatism is contemporaneous with the accretion of the Tonian (ca. 850 Ma) arc terranes of the Arabian Nubian Shield and marks subduction to the east of the Saharan Metacraton. The magmatic history of the Ouaddaï region in Chad begins in the late Mesoproterozoic, with localised rifting, resulting in the emplacement of juvenile granites (ca. 1030 Ma). The Cryogenian and Ediacaran in the Saharan Metacraton reveal a complicated history of magmatism and deformation. Age data from Chad show the emplacement of granites (from melting of Mesoproterozoic crust: ƐHf(t) = +2.04 and −4.07) at ca. 665–654 Ma, coeval with the main East African Orogeny and accretion of the other ANS terranes to the Saharan Metacraton at ca. 650–580 Ma. The youngest tectonothermal event within the Saharan Metacraton is recorded by emplacement of granites between 580 and 550 Ma (ƐHf(t) values of −17 to −31) in southern Chad.
... The Western Ethiopian Shield hosting the Tulu Dimtu ophiolites gave model ages between 0.92 and 1.5 (Kebede and Koeberl 2003;Johnson et al. 2004;Woldemichael et al. 2010), and from the southern Ethiopian Shield, older ages (1.42-1.72 Ga) were reported by Yeshanew et al. (2016). Mean model ages of southern Ethiopia and Kenya yield intermediate ages (mean 1.1-1.2 ...
The Arabian–Nubian Shield (ANS), as a tract of Neoproterozoic juvenile island-arc suites and intervening oceanic basin, extends from Egypt/Saudi Arabia southwards along eastern Africa and is considered to end in southern Kenya where the southernmost ophiolite remnants occur. It consolidated by closure of the Mozambique Ocean and final collision of West- and East-Gondwana fragments. Juvenile Neoproterozoic crust that experienced tectonic and metamorphic histories similar to the northern ANS, however, extends further south to Tanzania, Madagascar, and northern Mozambique. Here, the Mozambique or Neomozambique Ocean opened by separating Azania from cratonic Africa (wider Congo Craton) in the late Mesoproterozoic. The ocean started closing by formation of the Galana—Vohibory arc by c. 970 Ma that extended from southern Kenya to southeastern Madagascar. Successively evolving island arcs (Usambara Arc, Uluguru Arcs, and Ntaka Arc) and intervening oceanic basins amalgamated finally by c. 620 Ma to build the East African high-grade granulite belt. The high- to ultra- high-grade metamorphism in Tanzanian, Kenyan, and Ugandan granulites is explained by magmatic underplating in the back of retreating subduction zones. When the ANS is defined as a suite of Neoproterozoic oceanic basins and arcs that formed by closure of the Mozambique Ocean, it has to be traced further South to northern Mozambique-western Madagascar. That questions the meaning of the conventional understanding of the term “Arabian–Nubian Shield.” It is neither a shield nor limited to Arabia and ancient Nubia. Apparent differences between the northern (Egypt–Saudi Arabia–Ethiopia) and southern portions of the Mozambique Belt (Kenya–Tanzania–northeastern Mozambique) are considered artificial arising from the fact that different nomenclatures are used.
