Arabian Shield Research Articles

Post–east African Orogen dilation and magmatism: development of a conjugate-style of dolerite dike swarm in the northwestern Arabian shield

The Al Madinah area bimodal dike swarms underwent detailed field mapping, measurements of dikes’ attitudes, structural analyses, remote sensing data interpretation, and petrology study. The oldest rock unit is a greenish intermediate dioritic unit that varies in its petrologic composition between microdiorite and andesite porphyry which is intruded by alkali granite. The dioritic and alkali granite units have been cut by intermediate to mafic dikes, ranging in texture and composition from micromonzodiorite and micromonzonite to microgabbro, microdolerite, and basalt or basaltic andesite, as revealed by thin-section work. A stereographic projection and rose diagrams of the mafic dikes formed a regional conjugate dike system, following probably a typical andersonian style, consisting of three major sets, namely, the WNW set which trends between N295 and N330, E-W set between N265 and N270, and finally the ENE (N065) set. The WNW set has its own local system, but it is considered as a set in the overall regional conjugate dike system. The WNW and E-W sets are the conjugate pair of the WNW Najd fault system maximum horizontal shearing, where the ENE set reflects the minimum regional horizontal shearing stress of the Najd system. The interpretation of this dike system is a WNW-ESE sinistral faulting and NE-SW dilation that formed Wadi Al-Hamd Ediacaran continental basin, bounded by two Najd faults and Thurwah-Bir Um suture. The study area underwent final thrust faulting that tilted the dikes towards the east. For the consequent magmatisms during the Neoproterozoic period, followed by Cenozoic volcanism, the Al Madinah area is considered a large igneous province.

Detrital zircon provenance of north Gondwana Palaeozoic sandstones from Saudi Arabia

AbstractWe present the first comprehensive detrital zircon U–Pb age dataset from Palaeozoic sandstones of Saudi Arabia, which provides new insights into the erosion history of the East African Orogen and sediment recycling in northern Gondwana. Five main age populations are present in varying amounts in the zircon age spectra, with age peaks at 625 Ma, 775 Ma, 980 Ma, 1840 Ma and 2480 Ma. Mainly igneous rocks of the Arabian–Nubian Shield are suggested to be the most prominent sources for the Ediacaran to middle Tonian zircon grains. Palaeoproterozoic and Archaean grains may be xenocrystic zircons or they have been recycled from older terrigenous sediment. A primary derivation from Palaeoproterozoic and Archaean basement is also possible, as rocks of such age occur in the vicinity. Approximately 4 % of the detrital zircons show Palaeozoic (340–541 Ma) ages. These grains are likely derived from Palaeozoic post-orogenic and anorogenic igneous rocks of NE Africa and Arabia. A few single grains gave up to Eoarchaean (3.6–4.0 Ga) ages, which are the oldest zircons yet described from Arabia and its vicinity. Their origin, however, is yet unknown. Detrital zircons with U–Pb ages of 1.0 Ga are present in varying amounts in all of the samples and are a feature of terrigenous sediment belonging to the Gondwana super-fan system with an East African – Arabian zircon province.

The Atud gabbro–diorite complex: glimpse of the Cryogenian mixing, assimilation, storage and homogenization zone beneath the Eastern Desert of Egypt

We analysed gabbroic and dioritic rocks from the Atud igneous complex in the Eastern Desert of Egypt to understand better the formation of juvenile continental crust of the Arabian–Nubian Shield. Our results show that the rocks are the same age (U–Pb zircon ages of 694.5 ± 2.1 Ma for two diorites and 695.3 ± 3.4 Ma for one gabbronorite). These are partial melts of the mantle and related fractionates (εNd 690 = +4.2 to +7.3, 87 Sr/ 86 Sr i = 0.70246–0.70268, zircon δ 18 O ∼ +5‰). Trace element patterns indicate that Atud magmas formed above a subduction zone as part of a large and long-lived ( c . 60 myr) convergent margin. Atud complex igneous rocks belong to a larger metagabbro–epidiorite–diorite complex that formed as a deep crustal mush into which new pulses of mafic magma were periodically emplaced, incorporated and evolved. The petrological evolution can be explained by fractional crystallization of mafic magma plus variable plagioclase accumulation in a mid- to lower crustal MASH zone. The Atud igneous complex shows that mantle partial melting and fractional crystallization and plagioclase accumulation were important for Cryogenian crust formation in this part of the Arabian–Nubian Shield. Supplementary material: Analytical methods and data, calculated equilibrium mineral temperatures, results of petrogenetic modeling, and cathodluminesence images of zircons can be found at https://doi.org/10.6084/m9.figshare.c.4958822

Investigation of the clay minerals composition of soils derived from basalt parent materials in the Early Miocene to Early Pleistocene on the Arabian Shield using multiple techniques: implications for paleoclimatic conditions

Knowledge of clay minerals composition can be used to understand paleoenvironmental and/or paleoclimatic conditions, particularly for soils derived from volcanic parent materials that were subjected to diverse climatic conditions during pedogenesis. In this study, the clay minerals composition in soils developed from basaltic parent materials during the Cenozoic (mostly during the Early Miocene to Early Pleistocene) in the harrats region of the Arabian Shield in Saudi Arabia were investigated. Forty-seven clay samples were examined using selective dissolution analyses, X-ray diffraction (XRD), thermogravimetric analysis (TG), Fourier-transform infrared spectroscopy (ATR/FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to obtain a better understanding of the clay minerals developed in basaltic parent materials, particularly under a dry-hot environment. The XRD results revealed that the clay mineralogy was dominated by smectite, kaolin (kaolinite/halloysite), and interstratified vermiculite–chlorite (Vm–Ch), with mica, pseudo-chlorite, palygorskite, and Ca–zeolites as minor components. The TEM provided strong evidence for the presence of allophane and imogolite, which is in line with numerous previous studies on soils formed from basaltic parent materials. The existence of poorly-crystalline minerals in these soils was strongly supported by the selective dissolution analysis results. The combined influence of paleoclimates and parent material is evidenced in the clay minerals in the studied soils. The formation of smectite, Vm–Ch, and chlorite minerals in the harrats soils could be attributed to the simultaneous effect of temperate paleoclimates that dominated the Pliocene and the wet transition periods that occurred through the Pleistocene into the mid-Holocene, while the minor palygorskite and Ca–zeolites could be related to the dry conditions that started in the late-Holocene and persist to the present day. Additional studies regarding the clay mineral assemblages in similar geoenvironmental settings are highly recommend and should account for paleoclimatic conditions to provide a better understanding of the relationship between clay minerals and paleoclimates.

Major Tectonic Lineaments Influencing the Oilfields of the Zagros Fold-Thrust Belt, SW Iran: Insights from Integration of Surface and Subsurface Data

The Zagros fold-thrust belt (ZFTB) formed from the progressive collision between the African-Arabian and Eurasian plates. This study focuses on the major tectonic lineaments concerned with the distribution of oilfields in the southern Dezful Embayment as an extremely rich hydrocarbon province in the ZFTB, SW Iran. Integration of surface, near-surface and sub-surface data (e.g., remote sensing, overburden rocks, reservoir and aeromagnetic data) were used for locating major tectonic lineaments in the study area. The results show that the southern Dezful Embayment area was influenced by tectonic lineaments oriented in the NW-SE, NE-SW, E-W and N-S trends, which are possible fault indicators corresponding to surface, shallow subsurface and basement faults. The dominant N-S and E-W tectonic lineaments possibly highlight the stress regime inherited from old structures in the Arabian Shield basement while the NE-SW, NW-SE trends are interpreted as effects of the Zagros orogeny. Generally, these tectonic lineaments influenced both the basement and sedimentary rocks and are used here to divide the belt into several faulted blocks with different structural frameworks. A clear picture of the tectonic trends influencing the Zagros fold-thrust belt oilfields as well as guidance for delineating hydrocarbon reservoirs in the future are presented.

The Petrological and Geochemical Evolution of Ediacaran Rare‐Metal Bearing A‐type Granites from the Jabal Aja Complex, Northern Arabian Shield, Saudi Arabia

AbstractNew fieldwork, mineralogical and geochemical data and interpretations are presented for the rare‐metal bearing A‐type granites of the Aja intrusive complex (AIC) in the northern segment of the Arabian Shield. This complex is characterized by discontinuous ring‐shaped outcrops cut by later faulting. The A‐type rocks of the AIC are late Neoproterozoic post‐collisional granites, including alkali feldspar granite, alkaline granite and peralkaline granite. They represent the outer zones of the AIC, surrounding a core of older rocks including monzogranite, syenogranite and granophyre granite. The sharp contacts between A‐type granites of the outer zone and the different granitic rocks of the inner zone suggest that the AIC was emplaced as different phases over a time interval, following complete crystallization of earlier batches. The A‐type granites represent the late intrusive phases of the AIC, which were emplaced during tectonic extension, as shown by the emplacement of dykes synchronous with the granite emplacement and the presence of cataclastic features. The A‐type granites consist of K‐feldspars, quartz, albite, amphiboles and sodic pyroxene with a wide variety of accessory minerals, including Fe‐Ti oxides, zircon, allanite, fluorite, monazite, titanite, apatite, columbite, xenotime and epidote. They are highly evolved (71.3–75.8 wt% SiO2) and display the typical geochemical characteristics of post‐collisional, within‐plate granites. They are rare‐metal granites enriched in total alkalis, Nb, Zr, Y, Ga, Ta, REE with low CaO, MgO, Ba, and Sr. Eu‐negative anomalies (Eu/Eu* = 0.17–0.37) of the A‐type granites reflect extreme magmatic fractionation and perhaps the effects of late fluid‐rock interactions. The chemical characteristics indicate that the A‐type granites of the AIC represent products of extreme fractional crystallization involving alkali feldspar, quartz and, to a lesser extent, ferromagnesian minerals. The parent magma was derived from the partial melting of a juvenile crustal protolith with a mantle contribution. Accumulation of residual volatile‐rich melt and exsolved fluids in the late stage of the magma evolution produced pegmatite and quartz veins that cut the peripheries of the AIC. Post‐magmatic alteration related to the final stages of the evolution of the A‐type granitic magma, indicated by alterations of sodic amphibole and sodic pyroxene, hematitization and partial albitization.

Cadomian (ca. 550 Ma) magmatic and thermal imprint on the North Arabian-Nubian Shield (south and central Israel): New age and isotopic constraints

The Arabian-Nubian Shield (ANS) is a province of mostly juvenile Neoproterozoic continental crust in NE Africa and Arabia, forming the northern extension of the East-African orogen. Subsequent to widespread, mostly late- to post-orogenic early-Ediacaran calc-alkaline granitoid emplacement, the latest magmatic phase in the ANS saw the intrusion of alkaline shallow plutons alongside volcanic massifs and dikes of variable compositions. While some of these intrusions were dated to 550–530 Ma by Rb-Sr and Ar-Ar, U-Pb zircon data has mostly limited ANS magmatism to no younger than ca. 580 Ma. Here we report new age and isotopic data from latest Neoproterozoic intrusions along a N-S transect within the northern ANS and its periphery, substantiating the record of a ca. 550 Ma igneous-thermal event in the area. In the northern Negev of Israel, mafic igneous rocks intruded into the subsurface late Neoproterozoic clastic wedge of the Zenifim Formation produced apatite U-Pb isochron ages between 557 and 545 Ma. In the Amram alkaline massif, 150 km to the south, an alkali-granite was dated to 605 ± 2.5 Ma by zircon U-Pb, but apatite U-Pb ages from all rocks of the massif concentrate at ca. 550 Ma indicating thermal resetting. Apatites from the zircon dated 611 ± 5 Ma Roded quartz diorite in the Elat area, south of Amram, produced a 600 ± 4 Ma U-Pb age, demonstrating that southern segments were not thermally reset at ca. 550 Ma. Nd isotopes in apatite and whole rock show the ca. 550 Ma igneous rocks to be variable in their isotopic composition, ranging between εNd(t)=(-4) – (+2), far less juvenile than typical ANS magmas. The ca. 550 Ma intrusions resemble in their age and isotopic properties Cadomian granites and volcanic rocks that are known from southern Turkey, Iran and Europe. We interpret the ca. 550 Ma igneous overprint and thermal resetting documented in the northernmost ANS as related to the superposition of Cadomian orogeny on the ANS periphery. This can be related to the late Ediacaran subduction of proto-Tethys accompanying the accretion of the Cadomian basement of the Tauride block to NE Africa and Arabia, before the area was overstepped by Cambrian platform sedimentation.

Application of remote-sensing techniques in geological and structural mapping of Atalla Shear Zone and Environs, Central Eastern Desert, Egypt

The Atalla Shear Zone (ASZ) is one of the crucial megashears which are geometrically and kinematically akin to the Najd-Shear Corridor in the central Eastern Desert of Egypt. The Landsat-8 and ASTER-based mapping techniques integrated with extensive petrographic and structural-field investigations enhanced the geological and structural maps of the study area. The Neoproterozoic basement complex in the study area discriminated into ditinctive rock suites: Meatiq Group, ophiolitic melange, arc assemblage, syn- to late-tectonic granitoids, Dokhan Volcanics, Hammamat Sediments, post-Hammamat Felsites and post-tectonic granitoids. The true color composites (TCC) (4 3 2 for Landsat-8; 3 2 1 for ASTER), false color composites (FCC) (1 6 4, 1 6 7 and 7 5 1 for Landsat-8; 5 4 3 and 9 6 4 for ASTER), principal component analysis (PCA) (1 2 3, 3 2 1 and 6 4 2 for Landsat-8; 1 2 3 and 5 4 2 for ASTER), minimum noise fraction (MNF) (1 2 3 and 3 5 1 for Landsat-8; 1 2 4 and 3 2 1 for ASTER) and band ratios (BR) (6/2, 6/7, 6/5*4/3 and 7/6, 7/5, 5/3 for Landsat-8; 2/6, 7/5, 7/6 and 4/7, 3/4, 2/1 for ASTER besides the new created ratio 2/6, 7/5, 7/6) are the best combinations that demonstrate efficiency in discrimination of lithologic contacts and structural elements, using the spectral signature of different rock units. Moreover, the BR b7/b5, b5/b7 and b6/b4 of grey scale for Landsat-8 are used as a tool for mineral detection along with the spectral indices created to detect muscovite (b7/b6), ferrous silicates b5/b4 (biotite, chlorite and amphiboles) and ferrous iron b5/b3 (mafic minerals). The automatic lineament extraction utilizing the SRTM data advocated the role of NE- to NNE-trending lineaments in the tectonic framework of the study area. The structural fabric of the study area is evaluated in three main structural domains: Meatiq (MD), Atalla Shear Zone (ASZD) and Wadi Hammamat (WHD). The pronounced structural implication is the transposition of NE-oriented fabric in MD into NW-oriented penetrative shear-related fabric, fully in the ASZD and partly in WHD. The combination of transcurrent shearing with ENE-directed shortening along the ASZ that was resulted in noteworthy transpressive structures resemble in many respects those observed in the Ajjaj Shear Belt in Western Arabia. Among these structures are shear zone-related folds, imbricated thrust sheets, antiformal stacks and thrust duplexes. The deformation history of the investigated area proposed four phases of deformation (D1–D4). It depicts a long lasted deformational event covering the main accretion-collision phases concurrent with the E-W assembly of Gondwana, and the subsequent post-collision Najd-related transpressional phase which resulted in several major left-lateral transcurrent shear zones along with the exhumation of gneissic core complexes in the Arabian-Nubian Shield.

U-Pb zircon geochronology and geochemical constraints on the Ediacaran continental arc and post-collision Granites of Wadi Hawashiya, North Eastern Desert, Egypt: Insights into the ~600 Ma crust-forming Event in the northernmost part of Arabian-Nubian Shield

The Wadi Hawashiya, North Eastern Desert of Egypt, is a mountainous granitic terrain exposing two Ediacaran granitoid suites, namely the Hawashiya Older Granites (HOG) and the Hawashiya Younger Granites (HYG). The HOG comprise normal to high-K, calc-alkaline, metaluminous granitoids (mainly quartz diorites), while the HYG are strongly high-K, calc-alkaline, slighty peraluminous syeno- and monzogranites. Zr is strikingly high (av. 335 ppm) in the HOG and is notably depleted (av. 108 ppm) in the more evolved HYG. The HYG have very low Nb contents almost matching those of the HOG (Nb ~ 6 ppm), which is typical of I-type granites generated at arc-type settings. Although the REE patterns of the HOG and HYG are comparably LREE-enriched with moderately steep slopes, the patterns of the HYG have significant deep negative Eu anomalies of variable magnitudes, whereas those of the HOG usually exhibit very shallow negative and occasional positive Eu anomalies. The assessed apatite crystallization temperatures for both granitoid suites are higher than those estimated from the zircon and monazite thermometers indicating that apatite crystallized before zircon and monazite from the melt. HOG evolved by assimilation-fractional crystallization processes from mantle-derived magmas, which subsequently interacted with crustal sources during ascent and residence in higher crustal levels. 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. The HYG were emplaced (586–601 Ma) after the collision between the juvenile crust of the Arabian-Nubian Shield (ANS) and the older pre-Neoproterozoic continental blocks of Saharan Metacraton. The emplacement of HOG (622-611 Ma) had occured earlier (ca. 10 Ma) in a normal mature continental arc. The geochemical signatures and age data suggest that the terminal collision between East and West Gondwanaland in the northern tip of the ANS occurred before ~620 Ma, most likely at ~630 Ma, and transitioned to an extensional setting at ~600 Ma.

Hydrogeologic assessment for groundwater prospects in Al-Abwa drainage basin, arid-terrain of Arabian Shield, Saudi Arabian Red Sea coastal belt

Hydrogeologic assessment for groundwater prospects in Al-Abwa drainage basin, arid-terrain of Arabian Shield, Saudi Arabian Red Sea coastal belt

Assessment of magmatic versus post-magmatic processes in the Mueilha rare-metal granite, Eastern Desert of Egypt, Arabian-Nubian Shield

The Mueilha rare-metal granite, exposed in the central Eastern Desert of Egypt, is a post-collisional intrusion that formed in the final magmatic stage of the evolution of the Arabian-Nubian Shield. The Mueilha intrusion was emplaced as a high-level magmatic cupola into metamorphic country rocks. It consists of two cogenetic intrusive bodies: an early phase emplaced at shallow depth and now penetratively altered to white albite granite and a later phase of red granites emplaced at greater depth that better preserve magmatic features. The albite granite is less common and represents the upper margin of the Mueilha intrusion, the apex of the magmatic cupola. The red granites are volumetrically dominant and appears to have crystallized from the margins inward, forming a composite pluton zoned from muscovite granite to alkali feldspar granite. All parts of the Mueilha pluton appear to have been emplaced within a short time interval, before complete crystallization of the earliest phase. The geochemistry of the Mueilha granites is typical of rare-metal granites, characterized by high SiO2, Na2O + K2O, Nb, Rb, Ta, Y, U, Th, Sn, and W with depletion in P, Mg, Ti, Sr and Ba. They are weakly peraluminous and highly fractionated with A-type character. The chondrite-normalized REE patterns have strongly negative Eu anomalies, typical of highly differentiated granites that evolved through a transitional magmatic–hydrothermal stage. The primary magma feeding the Mueilha intrusion was generated by partial melting of the juvenile crust of the Arabian-Nubian Shield; it subsequently underwent extensive fractional crystallization and metasomatism by late- to post-magmatic fluids. Separation of fluids from the oversaturated melt promoted both diffuse greisenization and focused segregation of pegmatite and fluorite and quartz veins. Alkalis liberated from feldspars consumed by greisenization were redeposited during albitization in the uppermost part of the magma chamber. Despite penetration of the intrusion boundary by discrete dikes, veins, and aphophyses, diffuse alteration of the metamorphic country rocks is not apparent. Primary columbite-series minerals crystallized from the melt and were later partly replaced by secondary Nb and Ta minerals (fluorcalciomicrolite and wodginite) during hydrothermal alteration.

Monazite and cassiterite U[sbnd]Pb dating of the Abu Dabbab rare-metal granite, Egypt: Late Cryogenian metalliferous granite magmatism in the Arabian-Nubian Shield

The Abu Dabbab rare-metal granite in the Eastern Desert of Egypt is a highly-evolved alkali-feldspar granite with transitional magmatic-hydrothermal features. Extreme geochemical fractionation and the associated significant TaSn resource make the Abu Dabbab intrusion an important feature in the metallogenic evolution of the Arabian-Nubian Shield. UPb dating by laser ablation sector field (SF)-ICPMS analysis of igneous monazite yields a Concordia age of 644.7 ± 2.3 Ma, identical within uncertainty to a lower intercept Tera-Wasserburg isochron age of 644.2 ± 2.3 Ma obtained from hydrothermal cassiterite. Both ages place tight constraints on the timing of magmatic-hydrothermal processes in the Abu Dabbab granite which represents the oldest highly-evolved granite recognized so far in the Pan-African Arabian-Nubian Shield. Thus, the new ages also date the start of a period of late-orogenic metalliferous granite magmatism, when the basement of the Eastern Desert underwent a geodynamic transition from a compressive subduction-collision regime towards orogenic collapse in the late Cryogenian.

Geochemistry and Geotectonic Setting of the Post-orogenic granites at Qala En Nahal-Um Sagata Area, Gedarif State, Sudan

The survey area is located about 70 km southeast of Gedarif city, in Gedarif State east of Sudan, 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. This study aims to investigate the post-orogenic granites at Qala En Nahal-Um Sagata. Geologically, both the petrographic characteristics and rock geochemistry investigation have been conducted in order to determine the tectonic environment and original protolith of these granites rocks. The area is made up of predominantly low-grade volcano-sedimentary rocks, ophiolite complex and belt of high-grade metasediments and gneiss into which voluminous granitic rocks have been emplaced. The post-orogenic granites of Ban-Balos are non foliated, high K calc-alkaline, I-type, post-dating the main collisional event emplacement at shallow levels intrusions.

Seismic identification of geothermal prospecting in Harrat Rahat, Northern Arabian Shield

Harrat Rahat volcanic field lies along the Makkah-Madinah-Nafud active volcanic line. It has extensive linear weak zones of wrench faults that could provide ideal conduits for upwelling magma and hydrothermal fluids as well. Passive seismic data recorded by seismic stations installed within and around Harrat Rahat has been processed for the detection of microseismic events. Moreover, ambient noise was also gathered and analyzed to construct a subsurface velocity model. This model indicates low velocity zone in Harrat Rahat, and two areas with coincident basement faults and possibly with enhanced subsurface temperatures were identified. It is concluded that Harrat Rahat has high geothermal potential and promising for geothermal renewable power.

The Atbara porphyry gold–copper systems in the Red Sea Hills, Neoproterozoic Arabian–Nubian Shield, NE Sudan

Atbara city is located between the Nile and Atbara rivers, approximately 300 km northeast of Khartoum. The Atbara porphyry gold–copper system is situated at eastern part of Atbara about 70 km in the Red Sea Hills, Neoproterozoic Arabian–Nubian Shield, NE Sudan. The gold‑copper system is observed within different colored quartz veins that fill the tectonic zones in metasomically altered felsic-acidic igneous rocks Gold mineralization in the Atbara is observed in an area of 200 km2 and represented with pyrite, pyrrhotite, chalcopyrite, gold, galena, chalcocite-covellite, tetrahedrite-tennantite, hematite and goethite in the mineralized zone of the study area. The white and brown color quartz veins had E-W, NE-SW and NW-SE directions in these sectors and thickness between 5 and 300 cm. White color quartz samples had low concentration between 0.2 and 1.5 ppm and brown color quartz samples had high gold concentrations ranging from 1.0 to 26.63 ppm. Au does not have positive correlation with other elements, only except for Te and W. In contrast, there is no significant relationship between gold and copper in areas where copper is observed intensively. Cu has positive correlation with Bi, Cd, Pb, U, Hg and Ag. The average ΣREE contents in the hydrothermally altered wall rocks, copper mineralization and the quartz veins ranged from 10.2 ppm for Sector SA (SA, SB, SC, SD, SE and SF are the mining operation areas in the study area), to 14.27 ppm for Sector SB, 1.05 ppm for Sector SC, 20.89 ppm for Sector SD, 3.49 ppm for Sector SE, and 36.33 ppm for the Sector SF. The most of the studied samples have negative Ce and positive Eu anomalies with the LREE enrichment. This showed that it have low oxygen fugacity in the resource area of the hydrothermal solutions and an alkali magmatic source indicating an early stage of magmatic differentiation.

Reliability of using ASTER data in lithologic mapping and alteration mineral detection of the basement complex of West Berenice, Southeastern Desert, Egypt

The Neoproterozoic basement complex of Egypt outcrops in the Eastern Desert (ED) and southern Sinai, and is regarded to represent the northwestern continuation of the Arabian–Nubian Shield (ANS). The area west of Berenice has been given little attention, although it represents the key to understanding the geologic history of the South Eastern Desert and the entire ED. The present work is an integrated study using remote sensing (Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data imagery) and field-structural data to assess their utility in lithologic mapping and in detecting alteration mineral zones with considerable accuracy. A false-color-composite image, color-ratio composite image, decorrelation stretch, mafic index (MI), and quartz index (QI) were used to discriminate and map the various rock units. Correlation of False-color images of the ASTER band combination (7, 3, 1) with previous lithological mapping studies of the study area allow preliminary discrimination of different lithologies and drawing a base map. Subsequently, ASTER band ratios tested (4/1, 3/1, 12/14) and (4/7, 4/6, 4/10) with the ground truth data were used to refine the base map and construct the digital detailed geologic map. Petrographically, the investigated rock samples show kaolinite, chlorite, and epidote in alteration zones. The spectral angle mapper (SAM)-supervised classification using reference spectra of the USGS spectral library was used for detecting alteration zones. For verification, total accuracy assessment was carried out to evaluate the band combination and band ratios used in the lithologic mapping. That reached to 85.01% for band ratio 4/1, 3/1, 12/14 in RGB.

40Ar/39Ar and U-Pb SIMS zircon ages of Ediacaran dikes from the Arabian-Nubian Shield of south Jordan

A spectacular feature of the Arabian-Nubian Shield (ANS) is the abundance of well-exposed and extensive Neoproterozoic dike swarms of variable compositions. Most of these dikes are late to post-orogenic with respect to the East African Orogen (EAO) and are unmetamorphosed. We dated a composite dike with latite margins and a rhyolite core (607 ± 6 Ma, U-Pb), a biotite rhyolite dike (600 ± 4 Ma, 40Ar/39Ar age of biotite), an andesite dike (594 ± 3, 40Ar/39Ar age of amphibole) and a dolerite dike (~579 Ma, 40Ar/39Ar whole rock total gas age). We propose that the first three dikes represent one generation that was emplaced at different episodes extending between 607 and 590 Ma. Time and composition equivalent dikes are common in the northern ANS. The dikes crosscut late collisional granitoids and geochemically display a subduction-related character as evidenced by a negative Nb-Ta anomaly. These dikes are absent in the alkali feldspar A-type Humrat Syenogranite dated at 586 ± 5 Ma in Jordan and equivalent rocks in the northern ANS, which are crosscut only by the (~579 Ma) dolerite dikes. The within-plate character of the dolerite dikes is supported by the absence of the Nb-Ta anomaly and high field strength element geochemistry. We propose that the dolerite dikes are a generation, distinct from the ~607–590 Ma dikes, that reflects a change in tectonic regime and represents the last magmatic activity of the Neoproterozoic in the northern ANS. The ages of the dikes dated in this study agree with the published age range of the transitional stage from late orogenic calc-alkaline to extensional alkaline tectono-magmatic setting for the ANS. We propose that the magmatic activity was terminated ~50 m.y. before the age of the Cambrian unconformity at ~530 Ma. Correlation with ages of dikes and magmatic rocks in the northern ANS favors this supposition. The dike geochemistry and geochronology are compatible with a tectonic model that involves mantle lithosphere delamination from below the northern ANS after a significant crust-mantle thickening caused by the EAO, followed by thermal relaxation, subsidence and gradual denudation until the age of the unconformity at ~530 Ma.

Heavy minerals as provenance indicator in glaciogenic successions: An example from the Palaeozoic of Ethiopia

We use heavy minerals and rutile and garnet chemical compositions to constrain the provenance of two glaciogenic sandstone formations that build up the Palaeozoic succession in Ethiopia. The heavy mineral assemblage of the Upper Ordovician–Lower Silurian Enticho Sandstone is dominated by ultra-stable minerals, implying high maturity of the sediment. Variable amounts of garnet are present as well. The Carboniferous–Permian Edaga Arbi Glacials contain mainly less stable heavy minerals, such as garnet and apatite, suggesting little chemical alteration. A combination of magmatic and metamorphic source rocks is likely for both formations. Rutile and garnet chemistry point to mainly amphibolite-facies and to a lesser extent granulite-facies metamorphic source rocks with generally slightly higher metamorphic temperatures for detrital heavy minerals in the Enticho Sandstone. We conclude that the Enticho Sandstone is mainly the product of reworked mature Cambrian–Ordovician sediment, which may have been supplied via the Gondwana super-fan system. Locally, glaciers of the Late Ordovician glaciation eroded fresh basement material, delivering the garnet. For the Edaga Arbi Glacials, a rather proximal provenance is likely. The potential source area is the southern hinterland, where Precambrian low-to higher grade metamorphic rocks of the Arabian–Nubian Shield occur at the transition to the Mozambique Belt.

An analysis of a moderate earthquake, eastern flank of the Red Sea, Saudi Arabia

The present study presents the analysis of a moderate earthquake (Mw 4.0) and its largest aftershocks located along the Red Sea coast, southwestern Saudi Arabia, with the aim to understand the enigma of peculiar seismicity in the Arabian Shield. We analyzed a high-quality waveform dataset collected from ten well-recorded earthquakes of moment magnitude ranging from 2.0 to 4.0 in order to determine the hypocenter locations and focal mechanisms. The focal mechanisms were retrieved from the regional moment-tensor inversion for the mainshock and using the P-wave polarities for the corresponding aftershocks of Mw ≥ 2.0, respectively. The focal mechanism solutions were inverted to retrieve the seismogenic stress using the stress tensor inversion. The combination of the nearby fault trends and the obtained results from hypocentral relocations, focal mechanism solutions, and stress tensor inversion emphasizes that the NE fault trend is likely to be the causative fault resulting in the 2017 Namas earthquake sequence, implying that the local tectonic setting is incompatible with the large-scale regional tectonics of the Red Sea opening. On the contrary, estimates of low-stress drops exhibit typical values compatible with those reported for the shallow plate-boundary earthquakes that occurred in the Red Sea, suggesting that the existing weak zones in the southernmost part of the Arabian Shield may be attributed to the large-scale regional tectonics of the Red Sea opening.

Subvertical, linear and progressive deformation related to gold mineralization at the Galat Sufar South deposit, Nubian Shield, NE Sudan

The Galat Sufar South (GSS) gold deposit (Block 14, NE Sudan) is located within a complexly deformed zone at the junction between the Keraf Shear Zone and the Atmur-Delgo Suture, within the western portion of the Arabian-Nubian Shield (ANS). The combination of a petrographic and structural study of the gold mineralization at the GSS deposit, carried out at the μm-to tens of km-scale, allows the deciphering of the deformation history of this poorly documented area and provides insights on the geodynamic context favorable for gold mineralization in the northwesternmost Nubian Shield.Our study highlights that the GSS gold deposit recorded a polyphase deformation history dominated by an early, ductile-dominated, progressive deformation episode associated with the economic gold mineralization at GSS. It displays an atypical structural control by subvertical simple shearing evidenced by subvertical linear features (stretching lineation and potential sheath folding). The proposed multi-scale approach helps to correlate this subvertical, linear, progressive deformation event and the coeval economic gold mineralization with the early N-trending compressive tectonics related to the Atmur-Delgo suturing.