Najd Fault Research Articles

Deformation and fluid flow history of a fractured basement hydrocarbon reservoir below the Sab'atayn Basin, Habban Field, Yemen

Fractured crystalline basement reservoirs are of increasing economic interest for oil and gas exploration and subsurface fluid storage. The successful characterization of these reservoirs is commonly challenged by their structural heterogeneity, complexity in fracture distribution and flow properties at multiple scales, and the difficulty of imaging fractures in exploration seismic. We analyzed the fracture geometry and fracture diagenetic attributes in two oriented cores from the Habban Field in the Late Jurassic Sab'atayn Basin (Yemen) to evaluate the multi-phase deformation history and fracture flow pathway evolution for (hydrothermal) fluids and hydrocarbons. Analyses included petrographic and fluid inclusion analysis of fracture-filling cements, and stable sulfur isotope analyses of fracture-filling pyrite.The Paleoproterozoic basement consists of amphibolite-facies metamorphic ortho- and paragneiss cut by several phases of Neoproterozoic granitoid intrusions. The investigated lithologies in the drill cores comprise (1) epidote quartzite, (2) amphibolite, (3) monzogranite, (4) meta-arkose, and (5) quartz-feldspar porphyry. These lithologies show an inhomogeneous fracture network that is partially cemented. Ediacaran brittle-ductile deformation (D1) recognized only within a Pan-African monzogranite lead to cataclasis and porosity generating alteration. Late Jurassic – Early Cretaceous extension (D2) related to the break-up of Gondwanaland and the formation of the Sab'atayn Basin is found in all lithologies and likely resulted in pervasive quartz cementation. Late Jurassic fractures parallel to the NW-SE trending long axis of the Sab'atayn Basin are best recognized in a strongly foliated amphibolites. Cenozoic extensional fracturing (D3) reactivated older structures, which probably formed during activity of the Neoproterozoic Najd Fault System and caused multi-phased (pyrite-(saddle) dolomite-calcite) fracture cementations. The sulfur isotope compositions of pyrite with δ34S values ranging between −17.4 and + 26.4‰ vs. V-CDT reflects the variability of the fluid source during sulphide mineral formation from hydrocarbon-rich hydrothermal solutions. Fluid inclusions indicate that cementation reactions occurred in a relatively narrow temperature field between 120 °C and 140 °C, ideal for hydrocarbon maturation. Our results demonstrate the potentially complex charge history of basement reservoirs, involving multiple phases of fracture formation and cementation, and fluid charge episodes.

Mineralogy and Geochemistry of Titaniferous Iron Ores in El-Baroud Layered Gabbros: Fe-Ti Ore Genesis and Tectono-Metallogenetic Setting

The Neoproterozoic pyroxene gabbros and gabbronorites in the El-Baroud mafic intrusion in the Northern Eastern Desert (NED) of Egypt host Fe-Ti oxide ore deposits. This study discusses the major and trace elements of both titaniferous iron ores and their host rocks, along with the mineral chemistry (major and in situ trace elements) of interstitial clinopyroxene (Cpx), to gain a deeper understanding of the Fe-Ti oxide genesis. These ores occur as disseminated (55–60 vol.% of Fe-Ti oxides) and massive types (85–95 vol.%) in the form of the dyke, layer, and lens. They are composed of titanomagnetite (80–87 vol.%) with subordinate ilmenite (10–15 vol.%) and magnetite (3–5 vol.%), in accordance with their high Fe2O3 (75.66 wt.% on average) and TiO2 contents (16.30–17.60 wt.%). The Cpx in the investigated ores is diopside composition (Mg#; 0.72–0.83) and exhibits a nearly convex upward REE pattern, similar to Cpxs in the ferropicrite that originated from the primitive mantle. Melts in equilibrium with this Cpx resemble Greenstone ferropicrite melts; the parent melt of El-Baroud gabbros is possibly a ferropicritic melt that was derived from the lithospheric mantle during plume interaction. The El-Baroud gabbroic rocks were generated during the arc rifting and crystallized under a high oxygen fugacity at a temperature of 800–1000 °C and a pressure of 3 kbar with a depth of 12 km. The Fe-Ti oxide ores have been formed from ferropicritic parent melts by two processes, including in situ crystallization that leads to the formation of disseminated Fe-Ti oxides in the iron-rich gabbros at the bottom and liquid immiscibility that is responsible for the formation of thick Fe-Ti ore lenses and layers at the top of the gabbroic intrusion. Initially, titanomagnetite crystallized from the primary Ti-rich oxide melt. As cooling progressed, some of the excess titanium in this melt was exsolved in the form of the exsolution ilmenite lamellae within the titanomagnetite. The Fe-Ti oxide layers in the NED follow the trend of NW-SE (Najd trend), where their distribution is possibly controlled by the composition of parent melts (rich in Ti and Fe), high oxygen fugacity, and the structure related to the Najd fault system. The distribution of Fe-Ti oxide ores increases from the NED to the Southern Eastern Desert (SED), suggesting the dominant mantle plumes and/or shear zones in the SED relative to the NED.

Reactivation of Ramadi-Musaiyib Fault-Najd Faults System, Iraq

Nine earthquakes inside Mesopotamia Plain from 2016 to 2018 were analyzed. Three seismic networks have been relied on to relocate these events and know their responsible fault. These networks are; Mesopotamian Seismological Center, Al-Refaei Seismic Array and Iranian Seismological Center. The results showed that the root mean square (RMS) values for all relocated events ranged between 0.002-0.997. The results of the error ellipse ranged from 0.24 - 4.17 km with longitude and 0.76 - 8.24 km with latitude. The new locations of these events are on or near the Ramadi-Musaiyib Fault. This means that the Ramadi-Musaiyib Fault, which belongs to the Najd fault system, is currently in reactivation.

Structural and Stratigraphic Interpretations for Mishrif Formation in Kumait Oil Field, Using Seismic Reflection Data, Southern-Eastern Iraq

The Kumait oil field is located in the Maysan Governorate southeastern Iraq, which was studied and interpreted by using 2D and 3D seismic data provided by the Oil Exploration Company using Petrel software. The study concerned the Mishrif Formation belongs to the Cretaceous Age. The reflector was detected based on synthetic seismograms and well logs for Kt-1 well. Structural maps (two-way time, velocity, and depth) were derived from seismic reflection interpretations to show several structural features, such as four isolated irregular enclosures representing the Kumait structure plunging NW-SE and demonstrating that the Kumait oil field is influenced by the Najd fault system trending NW-SE. The stratigraphic interpretation used the variance attribute to delineate the edge of the fault, which extended from the Mishrif Formation with a depth of 3090m and used the Direct Hydrocarbon Indicators (DHI) to identify the stratigraphic features in the research region and the extraction of seismic attributes. The applied seismic attributes, such as the instantaneous phase, show dim spots, flat spots, and mounds and is followed by down-lap; the instantaneous frequency, which offers low-frequency areas indicating a high probability of hydrocarbon accumulation; and the RMS amplitude, which shows high amplitude in the seismic data that conforms to the structure and confirms the presence of hydrocarbon.

The Main Lineament Trends of Central Iraq, Depending on the THD of Residual Gravity and Magnetic Maps Obtained from Four Upward Continuation Levels

The upward continuation was used to obtain central Iraq's residual gravity and RTP magnetic maps at elevations 2, 12, 16, and 22 km. These maps are processed by the Total Horizontal Derivative (THD) technique to detect the main lineaments that represent the boundary of subsurface sources or faults. The obtained lineaments trends represented on the rose diagram and the main trends in the study area were found. The lineaments (faults) orders from the main trend descending, from gravity data, are N55W, N45W, N35W, N-S, and N65W, respectively, for the four considered upward elevations. The length of the faults obtained from gravity data ranges from 40-250km, while the length of faults obtained from magnetic data ranges from 20-100km. The lineament from the main trend descending, from magnetic data, are NS, N55W, N35W, N45W, N45E, N35E, N65W and N55E, respectively. The lineaments obtained from magnetic data indicate that the main trend in shallow sources is NW-SE, while for deep sources; the main trend is N-S. The NW-SE fault trends obtained from gravity data are related to the Najd faults system, while the N-S fault trends are related to the Nabitah system. Generally, it is indicated from the analysis of lineaments of gravity and magnetic data that the NW-SE is the main trend of shallow structures in most areas of central Iraq.

Lithological discrimination of the Fawakhir-Atalla belt in the Central Eastern Desert of Egypt based on Landsat-9 remote sensing data, airborne gamma-ray spectrometry, field and petrographic investigations with implications on the evolution of the Arabian Nubian Shield

The Central Eastern Desert (CED) is a key territory for understanding the evolution of the Arabian Nubian Shield (ANS) in Egypt as it contains Cryogenian-Tonian ensimatic supracrustal assemblages, such as ophiolitic and arc volcanic rocks, as well as gold deposits. So, it has been the subject of extensive studies over the last two decades. However, the lithological mapping of the Fawakhir-Atalla belt, located west of the Meatiq gneiss dome (infrastructure) of the CED, is still debated, as the magmatic texture of some rocks was partially obscured owing to the shearing and alteration related to the Najd Fault System, mantle CO2-bearing fluid, and igneous activity in the final stage of the Pan-African Orogeny. In this regard, integrated studies of airborne gamma-ray spectrometry and Landsat-9 satellite imagery processing techniques, as well as field and petrographic investigations, have been used for the lithological mapping of the belt. The results led to the following sequence; ophiolitic rocks > island arc assemblages > older granitoids (syn-tectonic subduction-related) > Hammamat Group (molasse-type origin) > post-Hammamat felsite > younger granite (post-tectonic suture-related). The applied color composite images, selective band ratios, and image transformation techniques show a clear distinction between rock units. Older granitoids are tonalite to quartz diorite, while younger granites are monzo-to syenogranite. They are well-discriminated from each other using band ratios, and younger granites have the highest K, eU, and eTh values coherent with the post-Hammamat felsite. The image enhancement and image transformation techniques show a clear discrepancy between the mélange rocks and Hammamat conglomerates. Mélange rocks are composed of fragments embedded in a foliated matrix, while Hammamat conglomerates are grain-supported with pebbles of volcanic source and have higher K, eU, and eTh values. Volcanic rocks in the belt are not a part of the Dokhan series as they are metamorphosed with a composition range from meta-basalts to meta-rhyolite, and show mainly aphanitic to infrequently porphyritic textures, which are typical of island arc metavolcanics.

Vase-shaped microfossils and possible trochamminid foraminifera from the Ediacaran Dhaiqa Formation of Saudi Arabia

We report the first discovery of vase-shaped microfossils (VSMs) and possible multichambered foraminifera from the Ediacaran rocks of Saudi Arabia. The Ediacaran successions of Saudi Arabia are well exposed in the northwestern and central part of the Arabian plate but are relatively understudied due to the lack of economic potential. The exposures can be found in different small sedimentary basins distributed along the flanks of Najd Fault system of the western Arabian Plate. The Dhaiqa sub-basin located near the historic city of Al-Ula contains some of the best exposures of Ediacaran Mattar and Dhaiqa Formations with collective exposure almost 400 m thick. These formations (especially the Dhaiqa Formation) were investigated to describe sedimentary facies, depositional environment, and possible microfossils. This study focuses on the identification of vase-shaped microfossils and possible trochamminid foraminifera of Ediacaran age that are herein recognized for the first time in Saudi Arabia. Outcrop samples were thin-sectioned and analyzed to reveal nine sedimentary facies belonging to four facies associations. The observed microfossils were found in a total of four samples from the cherty/siliceous carbonate and sandy microbialite facies. The microfossils are observed to be associated with diagenetic chert, which is abundant in these facies. The two facies contain a sparse microfossil assemblage with vase-shaped microfossils, which are single-chambered microfossils of uncertain taxonomic affinity, and possible multichambered agglutinated foraminifera that resemble trochamminids.

Petrogenesis and possible fingerprints of the Najd shear system on the evolution of deformed granitic rocks in the west Wadi Nugrus area, Egypt

In this paper, we present petrological constraints on the geodynamic evolution of deformed granitic rocks in the west Wadi Nugrus area, south Eastern Desert of Egypt. The deformation belt trends NW-SE forming the so-called “Nugrus Shear Zone (NSZ)” a major tectonic feature in the Arabian-Nubian Shield (ANS) at the junction between Wadi El Gemal and Wadi Hafafit areas, namely “Site I″ and “Site II”. The deformed granitic rocks comprise highly sheared arc granitoids and post-collisional to within-plate younger granites. Although the investigated granitic rocks are highly deformed, they show no signs of metamorphism and retain their primary igneous minerals. The melts from which the investigated granitic types originated experienced considerable degrees of partial melting in the transitional lower crust/upper lithospheric mantle as indicated by the contents of incompatible and rare-earth elements (REEs). Typical A-type granites developed before deformation and during emplacement in a continental environment. Zircon has ThO2/UO2 > 0.1, which is typical of igneous zircon, which sometimes experiences little recrystallization during the late magmatic deuteric stage, either pre-or syn-deformational due to circulation of fluids along the shear zone. It is believed that the deformation of all granitic rocks in the west Wadi Nugrus area is possibly synchronous and related to the Najd Fault System (NFS). The (NFS) extends from the western Arabian Peninsula to develop the NW-trending Nugrus Shear Zone (NSZ) in the south Eastern Desert. Sub-magmatic, solid-state, and sub-solidus deformational microstructures are evidence for the deformation related to the (NFS). Chessboard patterns in quartz and sub-magmatic fractures in plagioclase indicate deformation at high temperatures (T > 650 °C) in the presence of melt, which demonstrate the shearing during granitic cooling. On the other hand, quartz grain boundary migration and sub-grain recrystallization are two examples of solid state-related high-temperature deformation-related microstructures (T > 450 °C). Mica kinks along feldspar twinning and bending planes refer to low-temperature sub-solidus microstructures (T < 450 °C).

Orogenic lode-gold deposits and listvenization processes in the El-Barramiya area, Eastern Desert, Egypt

Gold mineralization in the El-Barramiya region of the Eastern Desert, Egypt, is connected to the post-accretionary stage throughout the Central Eastern Desert. It is represented by quartz, quartz-carbonate veins and disseminations in listvenite rocks. The thrust contact between rock units in El-Barramiya area played an imperative part in gold mineralization where the obduction of ophiolitic rocks over the metasediments and metavolcanics caused shear zones. Mineralization in the study area formed along shear zones and the gold mineralization prefers to precipitate along the transition zone between low-grade regional metamorphic area which is represented by metasediments and high grade which is represented by actinolite schist. The gold mineralization lode of El-Barramiya gold mine area is situated in E–W trending quartz and quartz-carbonate veins along a shear zone located in the intersections between faults trend in NE–SW (Najd fault), NW–SE and thrust faults trend in NEE–SWW in metavolcanic and metasedimentary host rocks. Porphyry granite in the mine area played an important role in hydrothermal alteration process where it represents the source of K, listvenite formed when fluids rich in CO2 and bearing-K permeate and alter the previously altered ultramafic rocks, usually serpentinites of the ophiolitic mélange rocks. The listvenitization process includes silicification and carbonatization metasomatic processes, tectonized serpentinites are altered to listvenite as the carbonatization becomes more intense close to dipping transpressive faults. Geochemical studies of listvenite and mineralized veins helped to determine the ultramafic genesis of listvenite and gold transformed as gold bisulfide. The whole rock geochemical data from El-Barramiya and elsewhere indicate that the transformation of serpentinite into listvenite involves profound metasomatic modification of the bulk-rock geochemistry. The chemical changes during alteration of serpentinite to listvenite are dominated by the addition of CO2, the removal of H2O, and the redistribution of SiO2, MgO and CaO as carbonate minerals and silica replace serpentine. All listvenites at El-Barramiya lode gold deposit are enriched in CaO, Fe2O3 and K2O, but depleted in MgO compared with associated serpentinite that is presumed to represent their protoliths. The chemical changes during alteration of serpentinite to listvenite are dominated by the addition of CO2, the removal of H2O, and the redistribution of SiO2, MgO and CaO as carbonate minerals and silica replace serpentine. Alteration also caused redistribution of trace elements, with some being locally remobilized within the rock, some being added from a fluid phase, and others being leached out of the rock. Petrographic investigation and geochemical studies show different types of alterations (carbonatization and silicification) and mineralization. Mineralizations are represented by gold and sulfides (pyrite, arsenopyrite and smaller quantities of chalcopyrite, sphalerite, galena, tetrahedrite and gersdorffite) found in auriferous quartz veins and disseminated in listvenite. The area exposed to brittle–ductile deformation in addition to different types of structures such as faults and fractures controlling on the formation of mineralization and act as hydrothermal channels ways for fluid flow. Fluid inclusions studies revealed that gold mineralization was formed from heterogeneous trapping of H2O–CO2 fluids at a temperature of 280–340 °C and pressure within the range of 1.5–1.9 kbar, which is consistent with the mesothermal conditions.

Tectono-stratigraphic framework and evolution of the northwestern Arabian plate, Central Jordan

The northwestern Arabian plate has been long influenced by various processes, including late Precambrian crustal extension, Paleozoic rifting and ice-sheet loading/unloading, and inversion during the Late Cretaceous–Late Eocene times. It has been experiencing extension in a N-S direction since the Oligocene, N-S-trending strike-slip faulting along the Dead Sea Transform Fault accompanied by the N-S extension of its surroundings, as well as shortening from E to W since the Miocene. The primary objective of this research is to examine the tectono-stratigraphic development of the Central Jordan Region (CJR), located in the northwestern Arabian plate, by employing data from seismic surveys and well logs. The CJR hosts five significant fault systems: Feinan-Zekimat AlHasa, Salwan, Karak-Wadi Al Fayha, Dana, and Hasa faults. Despite the surface expressions of these faults highlighting the tectonic impacts during the Late Cretaceous-recent period, there is a lack of comprehensive research investigating how previous tectonics influenced their structural evolution. Seismic data and well-log integration provide a unique opportunity to fill this knowledge gap. Here we identified six major stratigraphic units: upper Precambrian, Cambrian, Ordovician, Silurian, Lower Cretaceous, and Upper Cretaceous. Using time-structure maps, we also identified several phases of fault growth, with evidence suggesting that faulting primarily occurred during the late Precambrian as part of the Najd Fault System. The reactivation of these faults can be attributed to the combined effects of the Late Ordovician ice-sheet loading and the uplift during the late Paleozoic to Early Cretaceous periods. The growth of all pre-existing faults was contemporaneous with a change in the regional stress field from the Late Cretaceous to the recent. The vertical correlation between the latest Cretaceous faulting of the CJR and the previously published topographic lineaments map suggests a tectonic control on the evolution of the surface structures.

Potential field survey of subsurface structures of the NW segment of the Zagros Fold‐Thrust Belt, Kurdistan Region

AbstractThis study reports results of gravity and magnetic surveys conducted for the first time in the western segment of the Zagros Fold‐and‐Thrust Belt in the Kurdistan Region. This study attempts to delineate deep structures in an area, which has not been surveyed before. CG‐5 Autograv gravimeter and G‐857 portable proton‐precession magnetometer were used to acquire gravity and magnetic data from 750 stations along over eleven traverses across and parallel to the Zagros trend (NW–SE). Six of these traverses are parallel to the Zagros trend, whereas the others are perpendicular to the trend of the other traverses and can be tied where they intersect. The total length of the traverses is about 1000 km. Tilt Angle of horizontal gradient method is used to detect regional gravity and magnetic lineaments. The mapped lineaments from regional gravity and magnetic surveys are divided into two categories: the NE–SW lineaments, which represent transversal faults in the study area, and the NW–SE lineaments, which represent the Zagros Thrust Faults, some of which may be linked to the inverted basement normal faults of Arabian passive margin (the NW–SE Najd Fault system). The results show that there is a relationship between the regional gravity and magnetic lineaments outlining the same deep geological features. The data presented here confirm the presence of regional longitudinal and transversal lineaments documented in other studies (e.g. Anah‐Qalat Dizeh Fault, Surdash‐Tikrit Fault, Sirwan Fault, Khanaqin Fault, Zagros Mountain Front Fault, Baranan Back Thrust Fault and High Zagros Reverse Fault) and outlines new lineaments not mapped before. Most of the detected regional lineaments in the current study coincide with the previously confirmed lineaments, which have played a significant role in the tectonic evolution of the Zagros Fold‐and‐Thrust Belt. As such, this study contributes to a better understanding of the subsurface structure of the Kurdistan segment of the Zagros Fold‐and‐Thrust Belt and probably the rest of the belt.

Remote sensing and geochemical investigations of sulfide-bearing metavolcanic and gabbroic rocks (Egypt): Constraints on host-rock petrogenesis and sulfide genesis

Field geology, geochemical analyses and multi-sensor remotely sensed data of Landsat-8, ASTER and Sentinel-2 were used to detect various types of hydrothermal alteration and sulfide-gold mineralization in Neoproterozoic metavolcanic and gabbroic rocks from Darhib and El-Beida areas in the South Eastern Desert (SED) of Egypt. We also used RADAR data of Sentinel-1 using PCI Geomatica software to decipher the structural lineaments that control this mineralization. Different styles of disseminated to massive sulfide deposits include: 1) undeformed magmatic disseminated ores in Darhib gabbros, metavolcanic rocks and metabasic dykes; 2) deformed (remobilized) massive ores mostly of a magmatic-hydrothermal origin in Darhib tremolite talc rocks along E-W shear zones; 3) hydrothermal sulfide ores along El-Beida NW–SE shear zones. Cu-Zn massive ores represent the main sulfides in the Darhib silicified tremolite-talc rocks and meta-andesites, and occur as bands, veins and patches along Darhib E-W shear zones. Discontinuous occurrences of sulfide ores-bearing tremolite-talc rocks indicate that major shear zones act as structural controls on mineralization. Sulfide ores consist chiefly of chalcopyrite, sphalerite, pyrite and galena as well as minor covellite and bornite. These ores are highly concentrated along E-W striking Darhib shear zones and resulted from granite-derived hydrothermal fluids that form/and or accumulate sulfide minerals from the sulfide-bearing metavolcanic rocks around shear zones. Two stages of hydrothermal alterations are recorded in the Darhib talc mine including pre- (talcification, amphibolitization and carbonatization) and syn- (silicification and chloritization) sulfide ore alterations. Disseminated sulfide mineralization hosted in Darhib gabbros, metavolcanic rocks and metabasic dykes is of a magmatic origin, similar to Cu-Ni sulfide deposits hosted in gabbroic varieties in worldwide mafic–ultramafic intrusions. On the other hand, El-Beida gold-sulfide-bearing quartz and quartz carbonate veins are hosted in ferruginated and silicified metavolcanics/ metavolcaniclastic rocks along NW–SE shear zones (Najd Fault System trend). These are spatially associated with regional convergent structures (high-angle convergent wrench structures), suggesting orogenic gold type mineralization. The E-W with minor WNW-ESE shear zones in Darhib and NW-SE trending shear zones in El- Beida structurally controlled sulfides and gold mineralization in the SED of Egypt. El-Beida sulfide mineralization occurs as disseminated ores that consist mainly of pyrite, chalcopyrite, covelite and chalcocite with occasional occurrence of gold. The spatial occurrence of native gold in ferrigenous alteration zones indicates the role of iron in gold precipitation through buffering of gold-bearing complexes. Mineralogical and geochemical data of Darhib and El-Beida sulfide-bearing rocks indicate that they crystallized from depleted mantle sources in a back-arc basin setting, starting with the generation of arc-like volcanic rocks in a nascent BAB stage followed by the emplacement of plutonic equivalent of MORB/OIB-like rocks such as gabbroic intrusions in a mature BAB.

Large-scale geological structures of the Egyptian Nubian Shield

Integration of potential field- and structural data make it possible to trace surface and subsurface large-scale geological structures of the Egyptian Nubian Shield (ENS). Obtained results indicate that the Northern Eastern Desert (NED) of the ENS is dominated by relatively younger (c. 580 Ma) E–W and NE–SW trending extensional structures that were controlled by the evolution and retreat of the Cadomian Arc. Density of such extensional structures increases with depth as displayed by the potential data. The prevailing structural trends in the Central Eastern Desert (CED) are NW–SE and WNW–ESE. Both trends are highly prompted by the timing of deformation upon the Najd Fault System, and are themselves dissected by a relatively younger NE–SW shearing trend. Lineament density in the CED is subordinate for both subsurface and near surface structures. The South Eastern Desert exhibits compressional and extrusion-related structures of two main prominent trends; WNW-to-NW (to the western part) and the N-, NNE- to NE (to the eastern part). The previously mentioned Neoproterozoic trends are remarkably influenced by the Oligocene–Miocene Red Sea-Gulf of Suez rift related fractures in the vicinity of the rift shoulder. The remarkable change in trends and densities of structural trends, especially in the NED, is interpreted in terms of concealing of the older structures by the younger extensional structures which in turns reflect an N-ward progressive deformation in the entire ENS. Gravity data are more appropriate in delineating the structural trends compared to the magnetic data which are largely affected by lithological variations and/or alteration zones and magnetic mineralogy.

Petrogenesis of the Wadi El-Faliq Gabbroic Intrusion in the Central Eastern Desert of Egypt: Implications for Neoproterozoic Post-Collisional Magmatism Associated with the Najd Fault System

The late Neoproterozoic gabbroic intrusion of the Wadi El-Faliq area in the central Eastern Desert of Egypt (north Arabian–Nubian Shield; henceforth, ANS) is a fresh, undeformed elliptical body elongated in a NW–SE trend following the main sinistral strike-slip faults of the Najd fault system. Mineralogical and geochemical evidence suggest that they were derived from hydrous tholeiitic mafic magmas with arc-like geochemical fingerprints resembling the post-collisional gabbroic intrusions in Saudi Arabia. Despite the arc-like signatures, their fresh and undeformed nature, together with the field relationships, indicates that the studied gabbroic intrusion post-dates the main collisional phase, supporting its emplacement after subduction ceased and during the post-collisional stage. As a result, the arc-like signatures were possibly transmitted from the earlier ANS subduction episode. Indeed, the high (La/Sm)N, and negative-Nb and positive-Pb anomalies suggest contributions from subduction components. Lithospheric delamination was possibly facilitated by the Najd faults and shear zones formed during the post-orogenic crustal extension associated with the Pan-African orogenic collapse. The delamination process could have generated a rapid upwelling and melting of the asthenosphere mantle. The melt-rock reaction process likely played an important role in the genesis of the studied rocks through the interaction of the asthenosphere melts with lithosphere mantle rocks during ascent. The HREE fractionation suggests a probable mixing between melts from both spinel- and garnet-bearing peridotites. We suggest that the Wadi El-Faliq gabbroic intrusion was likely emplaced due to the stretching and thinning of the lithosphere during the extensional tectonism following the Pan-African orogeny.

The Tectonic Map and Structural Provinces of the Late Neoproterozoic Egyptian Nubian Shield: Implications for Crustal Growth of the Arabian–Nubian Shield (East African Orogen)

The Late Neoproterozoic Egyptian Nubian Shield (ENS) has attracted increasing attention since the establishment of the Egyptian Geological Survey and Mining Authority (EGSMA (1896)), which conducted the first mapping. In the last three decades, rapid improvements in analytical techniques, along with field-oriented studies, have made it possible for the interpretation of the ENS as an integral part of the juvenile Arabian–Nubian Shield (ANS) as a portion of the East African Orogen (EAO). However, a consistent tectonic map of the ENS does not exist. Presentation of such a map is the main objective of the present work where Landsat-based lithological discrimination is combined with the systematic structural investigation and careful reassessment of previously published geological maps. Our interpretation of this map indicates that in accordance with previous work, the basement units of the Eastern Desert (ED) can be divided into three structural domains: Northern, Central, and South-Eastern Desert provinces. The proposed provinces are ascribed to three different plate tectonic far-field boundary conditions. The earliest magmatic, metamorphic, and tectonic history was set off by the approximate north–south convergence of the Gabgaba-Gebeit, Jiddah-Asir terranes, and Eastern Desert-Midyan terranes along the Yanbo-Onib-Sol-Hamid-Gerf-Allaqi-Heiani (YOSHGAH) suture between c. 800 and 620 Ma. The second event between c. 640 and 580 Ma was correlated with the Nabitah Orogeny when the Ad Dawadimi-Ar Rayn terranes in the eastern Arabian Shield accreted to the earlier consolidated arc terranes (Afif and Tathlith terranes). During this period, east–west convergence between northwestern Saudi Arabia and the Central Eastern Desert (CED) in Egypt caused a pronounced strike-slip deformation associated with the displacement along the wider Najd Fault system. The third orogenic phase, which was younger than c. 580 Ma, was controlled by the evolution and retreat of the Cadomian Arc. The northern portions of the ENS and the northern Arabian Shield experienced extension whereas extensive post-orogenic magmatism was related to mantle delamination and associated crustal thinning.

Nb-Zr enrichment in Jabal Al Bayda A-type granites, western Arabian Shield, Saudi Arabia: interplay of magmatic and hydrothermal processes

Al Bayda’s younger granitic pluton located within the western Arabian Shield, Al Madinah area, KSA, has been studied using collaborative techniques. The collected samples were studied petrographically using a polarizing microscope and geochemically using the XRF technique. Four suites of intrusions can be distinguished based on their mineralogical and geochemical characteristics. A muscovitized epidotize hornblende leucocratic altered granite is the earliest intrusion, followed by perthite alkali feldspar granite. Both are intruded by a chessboard-like texture, Arfvedsonite-aegirine nepheline peralkaline granite. These three types of younger granitoid rocks are intruded by pegmatite-aplite sheets. The metasomatically altered epidotized, muscovitized granite formed during a late magmatic phase that was probably followed by successive co-magmatic and hydrothermal alterations in a closed system. The metasomatic alteration produced enrichment in Zr (up to 699 ppm), Nb (up to 67 ppm), and REE (up to 261 ppm) contents. As a result, residual alkalis, fluoride complexes, and iron-rich mixing fluids contribute to these enrichments. The hypersolvus perthite alkali feldspar exhibited post-orogenic A-type geochemical characteristics, whereas the peralkaline exhibited an anorogenic affinity, and both have been generated within plate-related tectonic settings. An A-type signature is probably the result of melting in the lower crust, whereas tectonic mechanisms shifted from post-orogenic to anorogenic due to the Najd fault system. Utilizing Al Bayda granite placer deposit products in the ceramic industry requires removing zircon minerals. The recorded HFSE, Nb, and REE are also recommended for detailed exploration.

Highly evolved rare-metal bearing granite overprinted by alkali metasomatism in the Arabian Shield: A case study from the Jabal Tawlah granites

Jabal Tawlah granites represent a post-collisional composite stock of late Ediacaran age, exposed in the Midyan district of northwest Arabian Shield. The stock is extended in the northwest and tapers southeastward due to structural control by a NW-SE-striking fault, and a southern master fault exhibits dextral movement by an ENE-WSW fault trend. Two main phases of magmatic activity are recognized in the Jabal Tawlah stock. The early phase (rim) includes albite granite and quartz syenite, which was intruded by a late phase of microgranite. Most of the Tawlah granites are highly mineralized, which can be attributed to the Najd fault system and/or shear zones. The mineralization is represented by small fluorite veins and disseminated minerals such as columbite-tantalite, xenotime, thorite, cassiterite, fergusonite, pyrochlore, allanite, monazite, samarskite, zinnwaldite and bastnaesite. The Tawlah granites show some degree of alteration including silicification and albitization. Textural and geochemical data indicate that the Tawlah granites developed from a magmatic source, and were then overprinted by later sodic metasomatism. Ore minerals crystallized under both magmatic and hydrothermal conditions. The parent magma of Tawlah stock was generated through partial melting of a juvenile continental crust, followed by extensive fractional crystallization. The Tawlah granites should be considered as a potential resource to warrant exploration for REEs and other rare metals.

Remote sensing-based mapping of the Wadi Sa’al-Wadi Zaghara basement rocks, southern Sinai, Egypt

The Wadi Sa'al-Wadi Zaghara area, southern Sinai, Egypt is a key geologic region within the framework of the Arabian-Nubian Shield (ANS). It almost documents the whole tectono-thermal evolution history of the Pan-African orogeny; hence it records the latest stages of Rodinia breakup (Late Mesoproterozoic) till the penultimate regional deformation event (D3) that impacted the northern tip of the ANS in the Late Neoproterozoic, i.e., before the Najd fault system. Since the metamorphosed volcano-sedimentary rock units in both Wadi Sa’al and Wadi Zaghara exhibit considerable differences in their geological evolution, they were dealt with as two distinct metamorphic belts. They cover a wide spectrum of basement rock varieties, which developed over a long period of time, from Late Mesoproterozoic (Wadi Sa’al metamorphosed volcano-sedimentary rocks) till Late Neoproterozoic Ediacaran period (post-collision granites). The different rock units of the study area were discriminated based on various image processing techniques such as Decorrelation Stretch (DS) Band Ratio (BR) and Principal Component (PC) of Sentinel-2, Landsat-8 and ASTER datasets. Remote sensing data analyses with the aid of petrography, previously published data and field verification enabled us to produce a new enhanced geological map of the study area. Advanced Land Observing Satellite (ALOS) digital elevation and enhanced Sentinel-2, Sobel directional filter images were successfully used for automatic lineaments extraction in the study area.

Petrogenesis of the late Tonian arc-related Um Balad gabbro-diorite complex (Egypt) and insight into its spatially related orogenic gold mineralization

ABSTRACT The gabbro-diorite complex of the Um Balad prospect hosts lode gold mineralization. The complex is dated at 723 ± 4 Ma using the LA-ICP-MS U-Pb zircon method and is correlated with the late Tonian-early Cryogenian subduction-related magmatic stage during the evolution of the Arabian-Nubian Shield. The gabbro-diorite complex evolved through the crystallization of a calc-alkaline magma and the subduction signature of this magma is verified by primitive mantle-normalized trace element patterns that show enrichment in large ion lithophile elements, U, and Th relative to high field strength elements as well as negative Nb and Ti anomalies. The high La/Ybcn (3.1–9.4) and Ta/Yb (0.12–0.41) ratios are consistent with a continental arc rather than an oceanic arc system. Amphibole chemistry indicates that this complex might have crystallized under a moderately oxidizing condition from a hydrous magma (>6 wt% water content) at temperature and pressure estimates of about 800°C and 3 kbar, respectively. Gold mineralization in the Um Balad prospect is confined to structurally controlled massive quartz±carbonate veins and surrounding alteration halos. Alteration in the prospect is represented by localized sericitization and carbonation as well as pervasive chlorite-sericite alteration. The alteration halos are characterized by enrichment in K and Rb and depletion in Ca and Sr compared to their host rocks. The veins of the prospect are related to lower order extensional fractures associated with the regional first order transpressional Najd Fault System. The high Fe contents of the gabbro-diorite complex represent a suitable chemical trap for gold through sulfidation of the host rocks. Supergene alteration resulted in the formation of goethite in association with atacamite and chrysocolla. Free mill gold is associated with these supergene phases, which were deposited in near neutral to slightly alkaline conditions.

Mapping Main Structures and Related Mineralization of the Arabian Shield (Saudi Arabia) Using Sharp Edge Detector of Transformed Gravity Data

Saudi Arabia covers most of the Arabian Peninsula and is characterized by tectonic regimes ranging from Precambrian to Recent. Using gravity data to produce the lateral boundaries of subsurface density bodies, and edge detection of potential field data, a new subsurface structural map was created to decipher the structural framework controls on the distribution of gold deposits in Saudi Arabia. Moreover, we detected the relationships between major structures and mineral accumulations, thereby simultaneously solving the problem of edge detectors over complex tectonic patterns for both deeper and shallower origins. Analytic signal (ASg), theta map (TM), TDX, and softsign function (SF) filters were applied to gravity data of Saudi Arabia. The results unveil low connectivity along the Najd fault system (NFS) with depth, except perhaps for the central zones along each segment. The central zones are the location of significant gold mineralization, i.e., Fawarah, Gariat Avala, Hamdah, and Ghadarah. Moreover, major fault zones parallel to the Red Sea extend northward from the south, and their connectivity increases with depth and controls numerous gold mines, i.e., Jadmah, Wadi Bidah, Mamilah, and Wadi Leif. These fault zones intersect the NFS in the Midyan Terrane at the northern part of the AS, and their conjugation is suggested to be favorable for gold mineralization. The SF maps revealed the boundary between the Arabian Shield and Arabian Shelf, which comprises major shear zones, implying that most known mineralization sites are linked to post-accretionary structures and are not limited to the Najd fault system (NFS).