Arabian Shield Research Articles

Constraints of Mantle and Crustal Sources Interaction during Orogenesis of Pre‐ and Post‐collision Granitoids from the Northern Arabian‐Nubian Shield: A Case Study from Wadi El‐Akhder Granitoids, Southern Sinai, Egypt

AbstractThe Egyptian older and younger granitic rocks emplaced during pre‐ and post‐collision stages of Neoproterozoic Pan‐African orogeny, respectively, are widely distributed in the southern Sinai Peninsula, constituting 70% of the basement outcrops. The Wadi El‐Akhder, southwestern Sinai, is a mountainous terrain exposing two granitoid suites, namely the Wadi El‐Akhder Older Granites (AOG) and the Homra Younger Granites (HYG). The AOG (granodiorites with subordinate tonalite compositions) have geochemical characteristics of medium‐K calc‐alkaline, metaluminous to mildly peraluminous granitoids formed in an island‐arc environment, which are conformable with well‐known Egyptian older granitoids rocks, whereas the HYG display calc‐alkaline to slightly alkaline nature, peraluminous syeno‐, monzogranites and alkali feldspar granites matching well those of the Egyptian younger granites. With respect to the AOG granitoids, the HYG granites contain lower Al2O3, FeO∗, MgO, MnO, CaO, TiO2, Sr, Ba, and V, but higher Na2O, K2O, Nb, Zr, Th, and Rb. The AOG are generally characterized by enrichment in LILE and LREE and depletion in HFSE relative to N‐MORB values (e.g., negative Nb and Ta anomalies). The geochemical features of the AOG follow assimilation‐fractional crystallization (AFC) trends indicative of extensive crustal contamination of magma derived from a mantle source. The chemical characteristics of the AOG are remarkably similar to those of subduction‐related granitoids from the Arabian‐Nubian Shield (ANS). The compositional variations from monzogranites through syenogranites to alkali feldspar granite within HYG could not be explained by fractional crystallization solely. Correlating the whole‐rock composition of the HYG to melts generated by experimental dehydration melting of meta‐sedimentary and magmatic rocks reveals that they appear to be derived by extended melting of psammitic and pelitic metasediments, which is similar to the most of younger granitic suites in the ANS.

Field, textural, geochemical, and isotopic constraints on the origin and evolution of the magmatic microgranular enclaves from the Gharib Granitoid Complex, North Eastern Desert, Egypt

The Neoproterozoic Gharib Granitoid Complex (GGC), in the North Eastern Desert (NED) of Egypt, is characterized by the occurrence of varieties of granitoids. Monzogranite, the most abundant granite variety, contains abundant magmatic microgranular enclaves (MMEs) of mafic to intermediate composition. The MMEs are more mafic than their host and marked by a greater amount of amphibole and biotite. They are finer grained and have porphyritic/poikilitic textures.The sharp, crenulated, and fine-grained quenched contacts of the elongated, rounded, and ellipsoid form of the MMEs with their felsic host indicate rapid cooling during a magma mixing/mingling event. Micro-textural evidence supports the mechanical transfer of minerals that crystallized in felsic magma to the mafic melt (e.g., feldspar phenocrysts cross-cutting the MME-host boundaries, stubby apatite, quartz ocelli, and poikilitic outermost rims of K-feldspar phenocrysts), supercooling/quenching process (e.g., acicular apatite and elongated hornblende and biotite crystals), and disequilibrium growth (e.g., hornblende-biotite clots replaced early crystallized clinopyroxene), which also favour a magma mingling/mixing origin. Linear to curvilinear chemical variations of the MMEs and the host monzogranites on Harker diagrams, highly similar trace element contents, and Sr-Nd isotopic systematics together with mineral-chemical features also support mixing/mingling as the main process in magma genesis and strongly suggest that the MMEs were supercooled hybrid globules within cooler, partially crystallized host felsic magma. The crust-like geochemical signatures (i.e., SiO2 content, metaluminous nature, and lack of upper crustal xenoliths and typical peraluminous minerals), along with low [MMEs: (87Sr/86Sr)initial = 0.70136–0.70373; monzogranites: (87Sr/86Sr)initial = 0.70202–0.70320)] along with zircon and apatite U-Pb age data indicate the possible involvement of juvenile lower continental crust (LCC) of the Arabian-Nubian Shield (ANS) in their genesis. The medium- to high-K calc-alkaline affinity, the LILE enrichment, and the HFSE depletion along with low Nb/La ratios and positive εNd(t) (MMEs = +4.01 - +5.62, monzogranites = +2.29 - +6.03) indicate the contribution of depleted lithospheric mantle in the magma genesis, whereas the low δEu and fairly high δCe values, stable La/Sm, and variable Sr/Th ratios in apatites from the monzogranites and MMEs indicate the contribution of volatile/fluids from the remnants of the oceanic slab in facilitating melting in the source region. The genesis of the monzogranites and MMEs started with asthenosphere upwelling, followed by melting of the remnants of lithospheric mantle, and underplating of mantle magma, which led to partial melting of the LCC. Multi-element modelling postulates that the low degree mixing between partially crystallized mantle magma and LCC-derived felsic melt (Fmix ∼ 0.1) could produce the parent magma for the monzogranites. Further mixing/mingling of the crystal-charged monzogranite parent magma with new pulses of mafic melts (Fmix ∼ 0.25) developed a hybrid zone and formed the hybrid MMEs. Thus, the final episode of the ANS evolution was associated with a complex post-collisional interplay between asthenosphere, lithospheric mantle, and the LCC caused by the removal of delaminated lithospheric root and dense lower crust following the collision between East and West Gondwana in the Neoproterozoic time.

Systematics of detrital zircon U–Pb ages from Cambrian–Lower Devonian rocks of northern Morocco with implications for the northern Gondwanan passive margin

The systematic acquisition of U–Pb geochronological data from detrital zircon grains has become an essential tool in tectonic studies focused on reconstructing the pre–Variscan geography of the northern Gondwanan passive margin. New detrital zircon ages for 16 samples from the Cambrian–Lower Devonian succession of the Moroccan Mesetas (northern Morocco) are reported here. The results, combined with previously published data, reassert the strong West African Craton affinity of the Paleozoic sedimentary rocks, characterized by dominant Cadomian/Pan–African (c. 850–540 Ma) and Eburnean (c. 2.2–1.9 Ga) detrital zircon populations and a minor Leonian/Liberian (c. 2.5 Ga) population. Primary sources of these zircon grains are well established as the West African Craton located just to the south, but also in the Precambrian basement that locally crops out in the Moroccan Mesetas themselves. During the Cambrian–Early Ordovician, erosion preferentially dismantled Cadomian (c. 590–540 Ma) arc–derived rocks of the Gondwanan continental margin, while later, the slightly older Pan–African (c. 650–600 Ma) basement became the main sediment source. In the studied samples, irregularly present minor detrital zircon populations suggest additional sediment provenance from secondary sources such as: (i) remote northeastern African cratons (e.g., Saharan Metacraton and/or Arabian–Nubian Shield) that likely could have provided the c. 1.1–0.9 Ga and, possibly, the c. 1.9–1.7 Ga zircon grains, and (ii) rift–related Cambrian–Early Ordovician volcanic centers in the Moroccan Mesetas that supplied heterogeneously distributed – although locally dominant in small areas – sedimentary detritus before rift abortion and burial underneath the overlying passive margin sedimentary succession.

Simulation of strong ground motions onshore the southeastern coast of the Red Sea, Saudi Arabia

In the southernmost part of the Arabian Shield, southeastern onshore of the Red Sea, damage earthquakes were historically reported implying that the region may be susceptible to have a potential seismic hazard in future. To understand the potential seismic hazard in the region, we present an analysis to simulate the peak ground accelerations (PGA) from future large earthquakes of Mw 6.0, and 6.5 in the region using an empirical Green's function (EGF) summation technique. The waveform recordings for a small-sized earthquake of Mw 4.4, that occurred in 23rd of January 2014, were used as an element earthquake. The estimated PGA values are consistent with the corresponding values of ground motion prediction equations (GMPEs) that derived for California, Japan, and Western Saudi Arabia, indicating that these equations are applicable for rock site conditions in the region. The results of response spectra reveal periods vary from 0.2 s to 3.0 s, implying potential hazard impacts for short and tall buildings.

Magmatic and hydrothermal evolution of highly-fractionated rare-metal granites at Gabal Nuweibi, Eastern Desert, Egypt

The Nuweibi intrusion was emplaced during the final tectono-magmatic stage of Arabian-Nubian Shield development (ANS). Two cogenetic phases of intrusion can be recognized in the field: the early phase is represented by porphyritic albite granite and the final phase by non-porphyritic albite granite. Mineralogically, both phases are essentially composed of albite, quartz, and K-feldspars with subordinate muscovite. Accessory minerals include fluorite, zircon, NbTa oxides, cassiterite, beryl, topaz, and garnet. Geochemically, the Nuweibi intrusion consists of extensively fractionated rare-metal granite with low contents of TiO2, FeOt, CaO, MgO, P2O5, Sr, and Ba in contrast to elevated concentrations of alkalis, Rb, Nb, Ta, and Hf. Their peraluminous (molar Al2O3/[CaO + Na2O + K2O] = 1.06–1.15) and low-P (P2O5 < 0.008 wt%) character identify them as highly fractionated I-type granites. The primary magma of the Nuweibi intrusion was most likely generated by partial melting of the juvenile crust of the ANS. We document numerous lines of evidence that the Nuweibi albite granite was formed by extensive fractional crystallization followed by interaction with magmatically-derived, F-rich hydrothermal solutions. The REE patterns of the Nuweibi albite granite show marked negative Eu anomalies (Eu/Eu⁎ = 0.01–0.15) as well as prominent M-type tetrad effects (TE1,3 = 1.332–3.536), typically seen in highly differentiated granites and attributed to exchange with hydrothermal fluid. Anomalous ratios of isovalent “twin” elements such as Nb/Ta, Zr/Hf, and Y/Ho likewise indicate exchange with hydrothermal fluid. The primary rare-metal accessory minerals are restricted to the Mn-rich part of the columbite-tantalite series; this manganoan trend is characteristic of highly fractionated granites. Likewise, the presence of wodginite, a Sn-bearing mineral, is a unique fingerprint of highly evolved rare-metal granites. Late-stage hydrothermal overprint of the primary rare-metal mineralization is preserved by rims of fluorcalciomicrolite partly replacing columbite-(Mn) and tantalite-(Mn). Accumulation of residual volatile-rich melt and exsolved fluids in the upper part of the magma chamber produced stockscheider pegmatite, greisen, and quartz veins that cut the peripheries of the Nuweibi intrusion and the surrounding country rocks.

Petrology and Geochemistry of Some Ophiolitic Metaperidotites from the Eastern Desert of Egypt: Insights into Geodynamic Evolution and Metasomatic Processes

AbstractOphiolitic peridotites exposed in the Eastern Desert (ED) of Egypt record multiple stages of evolution, including different degrees of partial melting and melt extraction, serpentinization, carbonatization and metamorphism. The present study deals with metaperidotites at two selected localities in the central and southern ED, namely Wadi El‐Nabá and Wadi Ghadir, respectively. They represent residual mantle sections of a Neoproterozoic dismembered ophiolite that tectonically emplaced over a volcano‐sedimentary succession that represents island–arc assemblages. The studied metaperidotites are serpentinized, with the development of talc‐carbonate and quartz‐carbonate rocks, especially along shear and fault planes. Fresh relics of primary minerals (olivine, orthopyroxene and Cr‐spinel) are preserved in a few samples of partially‐serpentinized peridotite. Most of the Cr‐spinel crystals have fresh cores followed by outer zones of ferritchromite and Cr‐magnetite, which indicates that melt extraction from the mantle protolith took place under oxidizing conditions. The protoliths of the studied metaperidotites were dominated by harzburgites, which is supported by the abundance of mesh and bastite textures in addition to some evidence from mineral and whole‐rock chemical compositions. The high Cr# (0.62–0.69; Av. 0.66) and low TiO2 (&lt;0.3 wt%) contents of the fresh Cr‐spinels, the higher Fo (89–92; Av. 91) and NiO (0.24–0.54 wt%, Av. 0.40) contents of the primary olivine relics, together with the high Mg# (0.91–0.93; Av. 91) and low CaO, Al2O3 and TiO2 of the orthopyroxene relics, are all comparable with depleted to highly depleted forearc harzburgite from a suprasubduction zone setting. The investigated peridotites have suffered subsequent phases of metasomatism, from ocean‐floor hydrothermal alteration (serpentinization) to magmatic hydrothermal alteration. The enrichment of the studied samples in light rare earth elements (LREEs) relative to the heavy ones (HREEs) is attributed to most probably be due to the contamination of their mantle source with granitic source hydrothermal fluids after the obduction of the ophiolite assemblage onto the continental crust. The examined rocks represent mantle residue that experienced different degrees of partial melting (∼10% to 25% for W. El‐Nabá rocks and ∼5% to 23% for W. Ghadir rocks). Variable degrees of partial melting among the two investigated areas suggest mantle heterogeneity beneath the Arabian‐Nubian Shield (ANS).

Trace element and Pb and Sr isotope investigation of tooth enamel from archaeological remains at El-Kurru, Sudan: Evaluating the role of groundwater-related diagenetic alteration

This study reports new trace element and Pb and Sr isotope compositions of tooth enamel from archaeological remains at a Medieval (Christian) cemetery located adjacent to the Kushite royal cemetery of El-Kurru, Sudan. The archaeological site of El-Kurru is located along the Nile River on the southern edge of the Nubian Plateau; the bedrock geology consists of Neoproterozoic crystalline basement and is overlain by fluvial sandstones and mudstones of Cretaceous age. El-Kurru is situated between two well-developed drainage basins, and in the past has been subjected to periodic (wadi-related) flooding as a result of intense local precipitation events. Enamel samples were taken from 18 individuals of varying ages and both sexes. Trace element abundances for a significant number of samples record elevated concentrations relative to modern (“in-vivo”) enamel, including Pb and U; however, the abundances for both elements do not correlate significantly with the contents of the remaining trace elements (Ba, Fe, Mg, Mn, Nd, Sr) investigated here. The calculated enrichment factors for all trace elements studied here relative to average crustal values are not consistent with exposure to Pb ores for human purposes, which is corroborated by the Pb isotope results. The Sr isotope compositions define 2 main groups that yield 87Sr/86Sr ratios that are either higher or lower than 0.7072 with similar Sr abundances (range between ~100 and ~400 ppm). The Pb isotope compositions are extremely variable and correlate well with their corresponding U/Pb ratios; the former overlap Pb isotope ratios for proximal Neoproterozoic rocks belonging to the Saharan Metacraton and Arabian Nubian Shield tectonic provinces. The combined trace element abundances and Sr and Pb isotope compositions for the enamel samples located within the Christian cemetery at El-Kurru are best interpreted to record interaction with groundwater that occurred post-mortem during flooding events. As reported in previous anthropological studies of a similar nature, the Pb isotope results reported here are particularly sensitive to monitoring post mortem diagenetic alteration given their extremely low abundances in non-altered tooth enamel. In contrast, the 87Sr/86Sr ratios have been minimally perturbed by post mortem alteration, and therefore most likely represent individuals with distinct Sr isotopic signatures inherited from different geographic regions.

Geochemistry and mineralogy of the Jebel Aja Igneous Intrusion and the associated exotic pegmatites, Arabian Shield, Saudi Arabia

We describe the Jebel Aja igneous intrusion (JAII), which sits at the farthest northeastern edge of the exposed Arabian Shield in Saudi Arabia. The JAII consists of late Neoproterozoic post-collisional A-type granites, and was emplaced during tectonic extension. It is a composite pluton consisting of a granitic core (monzogranite, syenogranite and alkali feldspar granite) surrounded by a later phase of alkaline and peralkaline granites. Pegmatites occur as pockets and dykes at the contact between the alkaline/peralkaline granites and syenogranite. The pegmatites have sharp contacts with their host granites and show variable colors (principally pink and white), grain sizes, textures, and mineral compositions. We report here that the white pegmatites host pockets with a unique mineralogy that includes the first observation of pyroxmangite, thortveitite and thalénite-(Y) in the whole Arabian Shield as well as a novel (Sc, Y, vacancy)-rich pyroxenoid and a vacancy-rich bustamite with excess octahedral Si. The pyroxmangite-dominated lithology also features accessory quartz, albite, spessartine, pyrochroite, muscovite, and fluorite. The presence of pyroxmangite rather than rhodonite, together with vacancy-rich and Si-excess pyroxenes, suggests an elevated pressure of emplacement. The granites of the JAII are highly evolved and have undergone extreme fractional crystallization of feldspars, leading to increases in the concentration of volatile and incompatible elements in the residual melt, which resulted eventually in injection of coeval pegmatites into the mostly solidified host granite. The syenogranite and alkaline/peralkaline granite of the JAII contain sodic amphibole and have geochemical characteristics common among within-plate rare-metal bearing A-type rocks. They have positive Nb-Ta anomalies that increase from syenogranite to alkaline/peralkaline granite. The pink pegmatite is highly mineralized and contains high concentrations of Nb (1540–1769 μg/g), Ta (103–136 μg/g), Y (1116–1616 μg/g), Zr (6362–9707 μg/g), Hf (215–264 μg/g), Th (278–384 μg/g), U (110–147 μg/g), and ∑REE (2334–3251 μg/g).

Age and hafnium isotope evolution of Sudanese Butana and Chad illuminates the Stenian to Ediacaran evolution of the south and east Sahara

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 largest plagiogranite on Earth formed by re-melting of juvenile proto-continental crust

The growth of continental crust through melt extraction from the mantle is a critical component of the chemical evolution of the Earth and the development of plate tectonics. However, the mechanisms involved remain debated. Here, we conduct petrological and geochemical analyses on a large (up to 5000 km2) granitoid body in the Arabian-Nubian shield near El-Shadli, Egypt. We identify these rocks as the largest known plagiogranitic complex on Earth, which shares characteristics such as low potassium, high sodium and flat rare earth element chondrite-normalized patterns with spatially associated gabbroic rocks. The hafnium isotopic compositions of zircon indicate a juvenile source for the magma. However, low zircon δ18O values suggest interaction with hydrothermal fluids. We propose that the El-Shadli plagiogranites were produced by extensive partial melting of juvenile, previously accreted oceanic crust and that this previously overlooked mechanism for the formation of plagiogranite is also responsible for the transformation of juvenile crust into a chemically stratified continental crust.

Mineral chemistry and petrology of mantle peridotites from the Qala En Nahal-Umm Saqata ophiolite, Gedarif State, Sudan

The study area of this research some 70 km southwest of Gedarif city, Gedarif State, in eastern Sudan. With a geological position, it is located within two major lithological associations, representing two different crustal entities: Saharan Metacraton (SMC) in the west and the Arabian Nubian Shield (ANS) to the east. The main objective of the study is a petrological investigation of the mantle peridotites within Qala En Nahal-Umm Saqata area. The relatively large-scale exposed masses of mantle&rsquo;s peridotite, include mainly the Utash mass and the Umm Saqata mass in the south and the Qala en Nahal mass and the Fau mass in the north of the area. Petrographically, they are mostly serpentinite. They have low-contents of Al2O3, CaO, TiO2O, MgO, Na2O and K2O, all consistent with depleted mantle materials, and similar to the metamorphic peridotites. The analyzed serpentine minerals are mainly pseudomorphic serpentines with subordinate antigorite, which may suggest that the parent minerals were first retrogressed to form lizardite and chrysotile. Subsequently, progressive metamorphism has recrystallized these minerals into antigorite. The chromites from the study area have high Cr# (Cr# varies from 0.51 to 0.87), most probably representing the primary phase which is similar to chromian spinels in mantle-derived peridotites. The presence of podiform chromites in the studied serpentinites is e typical of supra-subduction ophiolites, with Cr# similar to those of forearc ophiolites and boninite-derived chromites. Qala En Nahal-Umm Saqata mantle peridotites were formed in a forearc setting, during the subduction initiation that developed as a result of southeastward-dipping subduction zone. They possibly represent ensimatic, thrusted material, after the collision of the Nubian-Arabian Shield with the older sialic continental Saharan Metacraton during the late Proterozoic, Pan-African tectono-thermal event. These investigations were carried out supported by the Peoples&rsquo; Friendship University of Russia (RUDN University), Moscow, Russia and the Faculty of Petroleum and Minerals, Al Neelain University, Sudan. The publication has been prepared with the support of the &laquo;RUDN University Program 5&ndash;100&raquo;. To all we express our thanks and appreciations.

Tourmaline and rutile geochemistry in the Early–Middle Devonian sandstones of the Padeha Formation, Alborz Range, Northern Iran

The provenance of Devonian sandstones of the Padeha Formation (Fm.), Eastern Alborz in Iran, has been investigated by standard heavy‐mineral analysis and tourmaline and rutile geochemistry. Heavy‐mineral assemblage is dominated by the ultra‐stable tourmaline, zircon, and rutile, while unstable species are completely absent. The Padeha Fm. sandstones show a very high value of zircon‐tourmaline‐rutile index signalizing either strong weathering in source area(s) or their recycled origin in older Early Palaeozoic formations. Detrital tourmaline shows predominantly dravitic, lesser Mg‐foititic, and uvitic compositions and metasedimentary origin. Metapelitic source is also indicated by rutile geochemistry. Temperature estimates according to Zr‐in‐rutile thermometry show a wide range from 519 to 872°C and indicate the presence of low‐ to upper‐amphibolite and granulite facies metapelitic rocks. Based on chemical composition of detrital tourmaline and rutile, we inferred that the crystalline basement rocks of the Arabian–Nubian Shield were potential primary sources for the Padeha Fm. deposits. Shape of tourmaline and rutile as well as their microtexture surface features indicate long‐distance transport, storage, and recycled history.

Evolution of the Al Amar-Idsas suture, eastern Arabian Shield: a strain analysis perspective

Evolution of the Al Amar-Idsas suture, eastern Arabian Shield: a strain analysis perspective

Metamorphic conditions and igneous activity in the Um Zariq area, East Sinai, Egypt: Mineralogical and petrological evidences for the transformation from collisional to an extensional regime in the Arabian-Nubian shield

The authors present new petrographic and mineralogical data for the Um Zariq Formation which belongs to Arabian–Nubian Shield metamorphic exposures in the Sinai Peninsula. The formation is believed to be a metasedimentary sequence whose protolith was deposited during the Sturtian Snowball Earth Event (SEE). Our new field data indicate the occurrence of metasomatised limestones/dolostones (calc-silicates) which is distinct from those reported from The Feiran-Solaf Metamorphic Complex. We highlight the presence of a lamprophyre body close to the Kid A-type granite; the Malhaq vogesite - a variety of hornblende-phyric lamprophyre with orthoclase feldspar-. Based on mineral assemblages, field observations and petrographic study, metapelites record an early greenschist/lower amphibolite facies regional metamorphism. Intrusion of the syn-collisional deformed granites (CA1) synchronised with the regional metamorphism at ca. 660±25 Ma. Both of the metamorphic events overprinted on the metapelites and calc-silicates. The contact metamorphism formed cordierite and andalusite in the metapelites and pyroxenes in the calc-silicates. Calc-silicates, on the other hand, record anisotropic fabrics, higher T metamorphic mineral assemblages with hornfelsic texture. The Um Zariq metapelites protoliths were deposited at a deeper stratigraphic level and thus, recorded the regional and contact metamorphism contrary to the shallower carbonates. The peak metamorphic conditions were followed by retrograde metamorphism marked by chlorite and prehnite from metapelites and prehnite, epidote and chlorite in calc-silicates. The Um Zariq igneous activity (Kid A-type Granite and the Malhaq Lamprophyre) marks the transformation from collisional to extensional regime in the Arabian–Nubian Shield at ca. 600 Ma.

Uranium and rare metal mineralization in the El Sela and Qash Amir granitic intrusions, south Eastern Desert, Egypt

The Gabal El Sela and Gabal Qash Amir younger granites in the Arabian Nubian Shield (ANS) occurred within the Onib- Sol Hamed suture zone in the southern Eastern Desert of Egypt. In the study area, a pluton composed of biotite granites, muscovite granites and two mica granites is crosscut by altered dibase, microgranitic and bostonite dykes with a distinctive distribution of mineralization with high concentrations of rare metals. Silicification, hematitization, kaolinitization, episyenitization and sericitization are the main hydrothermal alteration processes in these younger granites. Gabal El Sela fractured younger granite shows highly alteration, uranium enrichment and a strong enrichment in some rare elements (such as; Zr = 2287 ppm, Y = 1123 ppm and Nb = 269 ppm) whereas, the bostonite dyke (such as; Zr = 1604 ppm, Y = 709 ppm and Nb = 292 ppm). Gabal Qash Amir muscovite granite shows a favorable enrichment in some rare elements (such as; Zr = 1898 ppm, Y = 181 ppm and Nb = 966 ppm) while, the bostonite dyke (such as; Zr = 1500 ppm, Y = 711 ppm and Nb = 286 ppm).Mineral characterization of the highly radioactive zones shows enrichment in autunite, uranophane, uranothorite, zircon, xenotime, monazite, fergusonite, samarskite and columbite. Field radiometric measurements of the studied El Sela fractured granite revealed that eU reaches up to 459.5 ppm, bostonite dyke eU reaches up to 58 ppm and altered basic dyke eU reaches up to 1625 ppm, while Qash Amir muscovite granite eU reaches up to 51 ppm and the bostonite dyke eU reaches up to 34 ppm.Geological, mineralogical, radiometrical and geochemical studies indicated that Gabal El Sela fractured younger granite is the most promising area characterized by strong enrichment in both uranium and some rare metals mineralization than Gabal Qash Amir muscovite granite.

Metallogeny of a Pan-African oceanic arc: VHMS and gold deposits in the Ariab-Arbaat belt, Haya terrane, Red Sea Hills (Sudan)

Gold in the Ariab district (Red Sea Hills, Sudan) is mined in gossans developed over volcanogenic massive sulphide (VHMS) deposits formed in the context of a Tonian ensimatic arc of the Haiya terrane, in the Neoproterozoic Arabo-Nubian Shield. All the primary gold occurrences of the Ariab belt, whatever their style (VHMS-, quartz lode- or shear-zone-hosted), appear, however, to have been syn-to late-kinematic, i.e., formed in the context of the final Pan-African collision leading to the Arabian-Nubian Shield (D3 event), and therefore are post-VHMS. Gold is thus found associated with either galena or bismuth telluride in late syn- to post-metamorphic sets of (micro)cracks, mostly within earlier pyrite or arsenopyrite. Gold deposition as native gold or electrum occurred when an intense fluid circulation of metamorphic CO2-H2O rich fluids underwent significant decompression from lithostatic to hydrostatic pressures at temperatures decreasing from 400 to 430 °C at around 8 km depth down to 300 °C. Although no clear evidence of volatile unmixing was observed, the decompression, together with a temperature decrease due to dilution by aqueous rich fluids, favoured gold deposition.The late-D3 gold event in the Ariab belt has all the makings of an orogenic gold system, notably similar to the Late Carboniferous gold event in the West European Variscan belt. Thus, it is possible to propose that, at the end of the collision events, fluids released from the newly formed terrane root were channelled towards the upper crust through the major D3 shear zones such as the Oko shear zone. The fluids outpouring from these major drains were then conveyed through fault plays and damaged zones, up to specific chemical traps within massive sulphide ore bodies or quartz veins systems. Thus, the Ariab gold district could be classified as a representative of the class of orogenic gold deposits.

Structural Setting and Kinematic Analysis of the Halaban Region, Eastern Arabian Shield, Saudi Arabia

AbstractThe vorticity analysis technique was applied to measure the different lithological units, such as schist, metagranite and metavolcano‐sedimentary rocks, which are present in the Halaban region. This work aims to interpret the relationship between the different lithologies and the tectonic setting, in order to elucidate the nature of kinematic analysis in the Halaban region. The kinematic analyses were applied to feldspar porphyroclasts, quartz and hornblende for twenty‐six samples. The kinematic vorticity number (Wm) for deformed rocks in the study area ranged from ∼0.6 to 0.9. The direction of the long axes for finite strain data (X axes) revealed a WNW trend with shallow dipping. The direction of the short axes for finite strain data (Z axes) were represented by vertical with associated horizontal foliation. The results of the kinematic vorticity and strain analyses are characterized by simple shear with different degrees of deformation in the Halaban region. Furthermore, our finite strain data shows no significant volume change during deformation. The subhorizontal foliation was synchronized with thrusting and deformation. Furthermore, throughout the overlying nappes, the same attitudes of tectonic contacts are observable, the nappes in the orogens being formed from simple shear deformation.

Overview Of Slope Stability, Earthquakes, Flash Floods And Expansive Soil Hazards In The Republic Of Yemen

Yemen has harsh natural conditions that increase certain geological processes more than other regions, leading to a variety of geological hazards. Yemen’s typical topography is distinguished by coastal plains of the Red Sea and cliff foothillls, followed by mountains of the Arabian Shield. These types of geological hazards can be classified into slope stability, earthquakes, flash floods and expansive soils. The current literature review presents a description backed with examples of the certain geological hazards in Yemen. The obtained results indicate that further consideration and thought are highly required for semi-arid regions. National and foreign organizations have to collaborate together with other individuals to maintain the adjusted environmental system and reduce the potential geological hazards. Therefore, mitigation measures should be implemented to avoid and minimize these geological hazards.

Geology, geochemistry, and petrogenesis of Jebal Ruro A-type granite, Blue Nile State, Sudan: implications for origin of HFSE mineralization

The Jebal Ruro granites occur west of the late Proterozoic Ingessana-Kurmuk suture of the Arabian-Nubian Shield located in the southeastern region of the Blue Nile State of the Sudan. A-type post-collisional granitoids from Jebal Ruro region were here studied through new field, petrographical and whole-rock data. These granitic intrusions comprise alkali granites consisting of aegirine granite, aegirine-arfvedsonite granite, and arfvedsonite granite. Geochemically, they are characterized by high Na2O, K2O, Fe/Mg, Ga/Al, Zr, Y, Nb, and REE (except Eu), and low abundances of CaO, MgO, TiO2, P2O5, and molar (Na2O+ K2O)/Al2O3 ratio ≥ 1 represent their peralkaline affinity. The Jebal Ruro granites show enrichment in Zr, Hf, Y, Nb, Ta, U, Th, Zn, and REE particularly in the aegirine granite and aegirine-arfvedsonite granite. Ruro granites show relatively high ratios of Nb/Ta and Zr/Hf close to that estimated for mantle magma source as well as Th/Ta, Th/U, Zr/Nb, La/Nb, and Rb/Nb. Furthermore, Ta+Yb vs. Gd/Yb, Sm/Yb, La/Yb, and Ta/Yb plots show that Ruro granites have distinguishable characteristics among arc and slab wedge-derived A-type magmas. In this study, we concluded that Jebal Ruro granites are A-type peralkaline to transitional metaluminous granites generated mainly by fractional crystallization from a mantle-derived OIB-like parent magma, emplaced in within-plate post-collisional tectonic environment.

Petrogenesis and geodynamic setting of high-Cr chromitites in fore-arc peridotites: A case study from the Halaban ophiolite, Eastern Arabian Shield, Saudi Arabia

The present study deals with chromitite pods and the associated mantle section of the Neoproterozoic Halaban ophiolite, Eastern Arabian shield, Saudi Arabia. The NNW–SSE-trending Halaban ophiolite represents a moderately dismembered Penrose-type ophiolite section that is tectonically emplaced over island arc assemblages. It comprises a mantle section below metagabbros upward to the pelagic sedimentary cover that overlies the mafic volcanics. The Halaban mantle section includes chromitite-bearing serpentinized ultramafics, as well as metaperidotites, listvenites and talc‑carbonates along shear zones and faults with variable degrees of alteration and metamorphism. Preserved textures include bastite and mesh indicating respectively harzburgite and dunite protoliths of the studied serpentinites. The chromitite pods are scarce being restricted to the uppermost mantle section and the overlying Moho transition zone (MTZ) dunite. They are commonly massive with interstitial serpentines, carbonates and Cr-rich chlorite (kämmererite). Cr-spinel of the chromitite pods hosts inclusions of isolated sulfides and silicates (serpentine, olivine and kämmererite). The Cr-spinel of the massive chromitites has higher Cr# (0.77–0.83) and Mg# (0.60–70) than the disseminated fresh Cr-spinel cores in the serpentinites (Cr# = 0.60–0.70 and Mg# = 0.43–0.60). High-Cr# combined with low-TiO2 character (<0.12 wt%) of the disseminated Cr-spinel consistent with residual mantle rocks that experienced high degrees of partial melt extraction. The mineralogical features of the Halaban serpentinites and the associated chromitite pods are similar to the mantle section that most probably formed in forearc peridotites of Supra-subduction zone (SSZ) environments. High-Cr# in Cr-spinel of chromitite pods suggesting possible boninitic parent magma. The parent magma had undergone melt–melt and melt–rock interactions with the precipitation of high-Cr chromitite from Al- and Ti-poor, and Cr-rich boninitic melts. Notably, the Cr# and Mg# of Cr-spinel increase from the harzburgite through the dunite to the chromitite due to increase intensity of melt-rock reaction during formation of the chromitite.