West Central Arabian Shield Research Articles

Structural mapping of the west central Arabian Shield (Saudi Arabia) using downward continued magnetic data

In this study, we have applied a stable downward continuation technique to magnetic anomalies from the global geomagnetic field model MAG2V3 to improve the resolution of magnetic data of the west central Arabian Shield, Saudi Arabia. Then, advanced interpretation methods such as the tilt angle of the horizontal gradient (TAHG), horizontal gradient of a modified tilt angle (HGSTDR), and enhanced horizontal gradient (EHGA) have been applied to downward continued magnetic dataset to highlight the main structural features in the region. The observed geologic structures from the magnetic analysis revealed NW-SE, NE-SW, and ENE-WSW orientations in the west central Arabian Shield. The depths of these structures were computed by the analytic signal (AS) technique and the obtained result shows depths varying from 1.2 to 9.2 km. This study provided a new map of the subsurface geological structures for a better understanding of the tectonic evolution of the west central Arabian Shield.

Dike swarms of the west-central Arabian Shield: a key to its tectono-magmatic evolution

Dike swarms of the west-central Arabian Shield: a key to its tectono-magmatic evolution

Mineral paragenesis and stratigraphic setting of the Neoproterozoic volcano-sedimentary succession of Samran Group, Jabal Farasan Area, West central Arabian Shield, Saudi Arabia

Jabal Farasan is located in the west central part of the Arabian Shield. The present study aims to reveal the stratigraphic setting and mineral paragenesis of the exposed volcano-sedimentary succession of the Samran Group in Jabal Farasan area. The succession of Samran Group is composed of three successive facies: the lower interbedded andesitic tuffs and tuffaceous andesites and trachyte’s (F1), the middle-altered quartz diorite/andesite (F2) and, an upper interbedded andesitic tuff, tuffaceous andesites and trachytes (F3). The vertical variations in the petrographic lithotypes depend mainly on the position of the depositional sites relative to the volcanic centers (proximal and distal). Both the volcanic rocks and the associated units are subjected to syn-and post-depositional diagenetic/metamorphic processes. These processes include the formation of the Fe2+-silicates: (i.e., chlorite instead of the volcanic ashes and the formation of plagioclase minerals). Post diagenetic recrystallization of the tuffaceous mudstones and the formation of microcrystalline quartz. The diagenetic oxidation of the Fe2+-silicates led to the formation of volcaniclastic red beds in certain stratigraphic horizons.

Stratigraphic setting, facies types, and mineral paragenesis of the carbonate-bearing succession of Jabal Farasan Area, West Central Arabian Shield, Saudi Arabia

Stratigraphic setting, facies types, and mineral paragenesis of the carbonate-bearing succession of Jabal Farasan Area, West Central Arabian Shield, Saudi Arabia

Landforms Evolution of Wadi Qudaid Area, West Central Arabian Shield, Saudi Arabia: An Example of the Role of the Geological Factors in the Urban Extensions

Wadi Qudaid is located in the west central part of Saudi Arabia. It about 135 km to the northeast of Jeddah city along Al Haramein highway and it represents the upstream of the very large alluvial plain along the Red Sea coast. It runs in NE direction parallel to many wadis of the west central part of Saudi Arabia i.e. Wadi Fatima, wadi Sitarah. The wadi floor is filled by Quaternary deposits which represent good groundwater aquifer. Geologically, the present-day residual landforms of Wadi Qudaid are composed mainly of Precambrian Arabia shield rocks overlained by Tertiary sedimentary rocks and finally harrat (Tertiary volcanic). The Precambrian rocks are represented by 1) a lower layered basic and intermediate volcanic and the intercalated volcaniclastics. This unit is correlatable with Samran Group, 2) an upper layered acidic volcanic and the intercalated acidic volcaniclastics. The Arabian shield rocks are intensively folded and dragged along the major NE faults. They are directly overlain by Tertiary basic volcanic (harrat) and the related volcanoclastic red beds). The main geomorphologic elements of the study area include plateau, scarps, and the wadi floor. The plateau is represented by the black basaltic sheet that contains some semi-rounded depressions filled with Quaternary eolian sands. The scarps of the main wadi and its tributaries are nearly steep and contain many asphaltic roads with some isolated cone hills detached from the scarps. Geomorphological, Wadi Qudaid represents the incomplete erosion cycle that begins with the formation of deep galleries and very steep and narrow wadies formed along the major NE faults and related fractures and folds. The progress of the erosion processes led to the formation of narrow interfluves as a result of pedimentation and sculpturing of the wadies sides by scarp retreat. The peniplanation stages of the erosion cycles are reached in the southwestern and the central part of the wadi where fast peniplained areas were formed. The results of this study revealed the role of the different geological processes (lithology, structural elements and climatic conditions) in the distribution of present-day human populations in urban extensions. Qudaid, Dhubaya-Jumah, Dabyah, Al Khamrah, Almansa and Al Massamah are the main villages of Wadi Qudaid area.

Geometric and tectonic analysis of Ad-Damm mega-scale fold: implication of Neoproterozoic Transpressive Regime in the west-central Arabian Shield

A mega-scale fold is exposed near Jeddah city in the western-central part of the Arabian Shield. This fold extends NE for about 35-km long and 12-km width and occupies the northwestern block of a distinct linear feature known as Ad-Damm Shear Zone. It is composed essentially of foliated, sheared, and mylonitized metamorphic and plutonic rocks. Para and ortho-gneisses were an amphibolite facies condition whereas greenschist facies units were represented by metasedimentary and metavolcanics. Image processing and field-based structural analysis, in addition to micro structural investigations of the mega-scale fold, indicating that the ductile dextral-sense of shear was overprinted by a brittle regime associated with the evolution of Ad-Damm shear zone. The Ad Dam mega-scale fold is a shear-related structure, north plunging overturned anticline. Mylonitization and dextral shear-related structures were developed during a transpressional regime. The Ad-Damm fold is a structural system that illustrates the evolution history of the Arabian Shield associated with the development of the NE-wrench fault. This fault started as an early plastic followed later by a brittle tectonic regime. The present study indicates that Ad-Damm shear zone and several sub-parallel dextral shears of NE-trends which located in the western side of the Arabian Shield represent a conjugate antithetic shear to the NW- trending sinistral shear of the Najd fault system.

Geochemical variation of the groundwater characters along Wadi Qudaid, northeast Jeddah, westcentral Arabian Shield, Saudi Arabia

Wadi Qudaid is present about 120 km northeast of Jeddah, Saudi Arabia. The area includes Precambrian Arabian Shield, Tertiary sedimentary rocks, Tertiary basic volcanics (harrat), and finally Quaternary wadi deposits which represent the main aquifer of Wadi Qudaid area. The present study indicates the presence of pronounced geochemical variations in the groundwater characters along the main channel of Wadi Qudaid from the southwestern part (downstream) to the northeastern (upstream) part. The groundwater-bearing horizon is thicker in the downstream part than the upstream part. The study also revealed that the groundwater is of good quality in the upstream (NE) part than the downstream (SW) part. This is related to the addition and depletion of many elements during the groundwater trip from NE to SW and the addition and depletion of some elements. The downstream part is of high hardness and TDS when compared with the upstream part. Also, the downstream part is of high bisnous element (As, Co, Ni) than the upstream part. The groundwater of the southwestern part of Wadi Qudaid are free from the following elements: i.e., Al, Mn, Fe, Ni, Cu, Zn, and Pb.

Thrust duplex deformation in the volcaniclastic sequence of the Fatima fold-and-thrust belt in the west-central Arabian Shield

In this study, we present a field-based structural analysis of the unmetamorphosed Precambrian volcaniclastic sequences of the west-central Arabian Shield. The study area is known as the Fatima fold-and-thrust belt, which is an overturned synclinorium that developed during the Neoproterozoic era. This belt is composed primarily of green mudstone, green sandstone, an andesite flow, limestone, red mudstone and pyroclastic units. This stratigraphic succession, which presents different rheological multilayers, offers significant mesoscale folding and thrust-related structures. Mechanical anisotropy and thickness contrasts have played significant roles in controlling the style of the deformation. Deformed hinge zones, a simple duplex, a domino-style duplex, and imbricated and antiformal stacks are among the thrust-related structures presented and analyzed. The domino-style duplex observed on the backlimbs of the overturned anticlines formed a unique pattern that developed during thrust propagation. The results of this study indicate that the thrust duplex developed according to a thick-skinned model, and it represents a newly recognized tectonic regime in the Arabian Shield. Comprehensive field mapping and structural analyses revealed that the zone under study area was affected by four phases of deformation (D1–D4). The D1 and D2 phases present ductile deformation that developed during the final cratonization and assembly of the Arabian Shield, and they can be recognized at both the map and outcrop scales. The D1 phase represents a progressive regime and is indicated by a NW-SE stress orientation and the formation of a series of coaxial symmetrical NE-SW-plunging folds. NNW-directed thrust-related structures progressively developed during the D2 phase. An approximately fifty-three percent tectonic shortening can be calculated based on the restored structures. D3 and D4 have a brittle nature and are indicated by shearing and normal faulting, respectively.

Hydrogeology of Wadi Qudaid Area, Northeast Jeddah, West Central Arabian Shield, Saudi Arabia

The study area is a part of the Arabian Shield rocks of west central part of Saudi Arabia (150 km to the northeast of Jeddah). Geologically, the study area comprises five main geologic units i.e. 1) Layered basic volcanics and related volcaniclastics which are composed mainly from intercalated basalts and andesites and the related volcaniclastic derivatives, 2) Acidic volcanics and related volcaniclastics which are composed from layered and laminated dark and light acidic to intermediate igneous rocks, quartz and chert and marbles, 3) The Tertiary sedimentary succession which of volcaniclastic red beds and the intercalated clays; 5) Tertiary volcanics of Harrart, and 4) The Quaternary wadi fill deposits which are composed from friable pebble supported conglomerates, sandstones and clays. Hydrogeologically, the groundwater aquifer of Wadi Qudaid is present mainly in two main horizons i.e. i) unconfined shallow aquifer (13 - 37 m) within the well porous and permeable conglomerates of the Quaternary Wadi deposits, ii) The deep confined aquifer of the bedded tuffaceous sandstones and mudstone of the Tertiary sedimentary succession of Ash Shumaysi Formation. The water samples are analyzed for major elements i.e. Ca, Mg, Na, Cl, SO4, HCO3 and the results show the normal content of these elements. The study related the addition and depletion of many elements during the running trip of the groundwater from the northeast (recharge area) to the southwest (downstream) area.

Petrographic Characterization of the Different Types of Basalts of Harrat Al Fatih, Ablah Area, West Central Arabian Shield, Saudi Arabia

Harrat Al Fatih is located southwest of Ablah area, Assir terrain, southwestern Arabian Shield. It is present as black laterally extended horizontal basaltic sheet just overlying folded strata of the volcano-sedimentary succession of Ablah Formation (green mudstones, dolostones and green and red volcaniclastic red beds). These basalts are rift-related and represent part of the Oligo-Miocene basic volcanics of the western part of Saudi Arabia. The detailed field and microscopic description of these basalts enable the author to classify it into two main types: 1) Grey tuffaceous glassy basalts that present overlying the Ablah Formation. This basalt type is generally soft, bedded and intercalated with grey, green and red tuffaceous mudstones. Microscopically it composed of minute lath-like plagioclase and pyroxene crystals embedded in glassy groundmass. 2) Black olivine-rich basalts which are present in the topmost part of harrat Al Fatih are generally black, hard and contain remarkable reddish brown oxidized olivine spots and some calcite and amorphous quartz domains. Under the microscope, this basalt type is microcrystalline and composed mainly of lamellar twined Ca-plagioclase and colored olivines and pyroxenes. The olivines show different stages of oxidation and formation of amorphous blood red iron-oxyhydroxides and black hematite. The present study revealed the formation of the grey basalts at the initial stages of the volcanic eruption in ephemeral lakes and the second type of basalt was during the consolidation of proper basic magmas at the final stages of the volcanic eruption.

The role of aeromagnetic data analysis (using 3D Euler deconvolution) in delineating active subsurface structures in the west central Arabian shield and the central Red Sea, Saudi Arabia

In this paper, we present a case study of structural mapping by applying the 3D Euler method to the high-resolution aeromagnetic data that was collected in the west central Arabian Shield region and the coastal region of the central Red Sea in Saudi Arabia. We show the 3D Euler deconvolution algorithm and apply it to magnetic potential field data from the west Central Arabian Shield and the Central Red Sea. The solution obtained with 3D Euler deconvolution gives better-focused depth estimates, which are closer to the real position of sources; the results presented here can be used to constrain depth to active crustal structures (volcanisms) for the study area. The results indicated that the area was affected by sets of fault systems, which primarily trended in the NNW–SSE, NW–SE, EW, and NE–SW directions. Moreover, estimated Euler solution map from aeromagnetic data delineated also the boundaries of shallow, small, and confined magnetic bodies on the offshore section of the study area. These nearly exposed basement intrusions are most likely related to the Red Sea Rift and may be associated with structures higher up in the sedimentary section. These volcanic bodies are extended to the continental part (onshore) of the west central Arabian Shield, particularly beneath both sides of the Ad Damm fault zone. This extension verifies that the fault was largely contemporaneous with a major period during the extension of the Red Sea Basin. Moreover, according to the distribution of circular magmatic-source bodies (circular-shaped ring dikes) that resulted from this study, we can state that the clustering of most earthquakes along this fault may most likely be attributed to the active mantle upwelling (volcanic earthquakes), which are ultimately related to volcanic processes. Furthermore, the oceanic crustal structures near and in the Red Sea offshore regions were also estimated and discussed according to the ophiolite occurrences and further opening of the Red Sea. Our results are largely comparable with studies of previous crustal sections, which were performed along the Red Sea Rift and the Arabian Shield. As a result, the areas above these anomalies are highly recommended for further geothermal study. This example illustrates that high-resolution aeromagnetic surveys can greatly help delineating the subsurface active structures in the west central Arabian Shield and the middle coastal region of the Red Sea of Saudi Arabia.

Mechanism of formation of Haddat Ash Sham ironstones (Oligo-Miocene), Makkah Al Mokaramah District, West Central Arabian Shield, Saudi Arabia

The present study aims to shed light on the mechanism of formation of the Oligo-Miocene oolitic ironstones of Haddat Ash Sham area, Saudi Arabia. These ironstones are enclosed within the middle part of the Oligo-Miocene siliciclastic succession of the western part of the Arabian Shield, western Saudi Arabia. The ironstone beds were formed during marine incursion and creation of short-lived starved time periods of high organic matter activities, ferrous iron, and low clastic input. The depositional and diagenetic processes involved in the formation of Haddat Ash Sham ironstones are summarized here as follows: (1) the deposition of detrital components (i.e., amorphous iron-bearing clays admixed with silt and sand-sized quartz grains) and their distribution by the waves and current actions in areas of different water depths (bars and inter-bar areas); (2) the deposition of the iron-bearing clays in slightly reducing transgressive conditions (dysaerobic zone) led to the authigenesis of green marine chamositic clays of variable mineralogical and chemical compositions according to the predominated depositional environments; and (3) in the upper parts of the depositional cycles, the iron-bearing clays become admixed with detrital quartz grains which resulted in the formation of silty and sandy ironstones of low iron content. The diagenetic processes led to the oxidation of the green chamositic clays and formation of amorphous Fe-oxyhydroxides, ferrihydrites, goethite, and hematite. These iron mineral phases are related to each other and show progressive steps of transformation during the diagenetic processes. The iron ooids represent in situ formed irregular domains formed during the diagenetic crystallization and dehydration of the amorphous iron oxyhdroxides resulted from the diagenetic oxidation of green chamositic clays. This is supported by the absence of detrital cores of the iron ooids, the gradational contact between the iron ooids and the enclosing matrix and also by the presence of many ooids of unclear and ill-defined internal structure.

Facies Analysis and Depositional Environments of Ash Shumaysi Formation (Oligocene–Miocene), Makkah Quadrangle, Wadi Ash Shumaysi, West Central Arabian Shield, Saudi Arabia

Ash Shumaysi Formation represents Oligo-Miocene fluvio-lacustrine succession consisting mainly of conglomerates, sandstones, siltstones, muddy, sandy and glauconitic ironstones, fresh water carbonates, tuffaceous mudstone and basalts in descending order. It shows the transition from proximal to distal parts of the depositional environments of braided streams into floodplain and finally into lacustrine facies. This succession comprises four main facies associations arranged according to their predominance from the lower to the upper parts of the succession of Ash Shumaysi Formation as follows: (1) proximal (conglomerates facies association I) braided streams which includes four facies of sandstones and conglomerates (F1, F2, F3 and F4), (2) distal (sandstones facies association II) braided streams which comprises three facies (F5, F6 and F7), (3) meandering streams (facies association III) which include the thinly bedded muddy, glauconitic and sandy ironstones–ferruginous sandstone facies (F8), (4) lacustrine delta (facies association IV) which includes three facies (F9, 10 and 11). The Oligo-Miocene siliciclastic sections of Ash Shumaysi represent deposition in mid to distal parts of alluvial fans formed as a result of interplay between climatic conditions, tectonic and sedimentation. In the extreme distal parts of these alluvial fans, river lakes were filled rapidly with conglomerates, sandstones, mudstones and finally fresh water carbonated were formed during arid periods of low siliciclastic input.

Major elements hydrochemistry and groundwater quality of Wadi Fatimah, West Central Arabian Shield, Saudi Arabia

Wadi Fatimah is the largest NE-SW trending low topographic area in the west central Arabian Shield, Saudi Arabia. It is bounded by in the NW side by the faulted and folded volcano-sedimentary succession of Fatima Formation and in the SE side by the metamorphic rocks of Jeddah Group. Some massive gabbros and granites and foliated amphibolites are also present along both sides and in the upstream of Wadi Fatimah. The groundwater of Wadi Fatimah is present in the shallow Quaternary alluvial deposits and also in the underlying fractured Precambrian bedrocks. The description of the chemical composition of the groundwater of Wadi Fatimah includes the variations of the groundwater salinity, the major and trace constituents as well as the groundwater character. According to the chemical analysis and the trilinear and durov diagrams, the prevalent chemical character is calcium chloride followed by sodium chloride water types. All the sub-basins of Wadi Fatimah are characterized by a relatively low to medium saline water. Highly mineralized water zone marked the lower part of the wadi, e.g., Al Jumum-Bahrah area, where the groundwater salinity reached up to 26,500 μS/cm with an average of about 9,500 μS/cm. Major and trace elements analyses of the groundwater samples from the different tributaries of Wadi Fatimah revealed its suitability for irrigation purposes.

Structural mapping from high resolution aeromagnetic data in west central Arabian Shield, Saudi Arabia using normalized derivatives

Aeromagnetic data covering an area of about 40,000 km2 at the west central Arabian Shield, Saudi Arabia has been collected and interpreted to provide structural map of the area. A number of normalized derivatives were used to help interpret the signature of magnetic data so that weak and small amplitude anomalies can be amplified relative to the stronger and larger amplitude anomalies. The interpretations obtained from these geophysical techniques of the field data demonstrated a strong correlation between magnetic anomalies and mapped subsurface geology. Based upon the variation in magnetic lineaments, shape amplitude, and trend structural map of the west central Arabian Shield on Saudi Arabia were obtained.

Geology and Lithostratigraphy of the Ultramafic-Mafic Rocks and Associated Mineralizations, Wadi Khamal Area, West-Central Arabian Shield

Field, petrography and major elements geochemistry of the ultramafic -mafic rocks of Wadi Khamal area led to the recognition of the following rock groups, namely: 1) ophiolitic suite, melagabbro- norite and cumulate gabbronorite to the south of Wadi Mahalah (southern ultramafic-mafic rocks) and 2) Wadi Khamal anorthosite- gabbro complex to the north. The ophiolitic rocks in the southern area include serpentinites, peridotites and pyroxenites. The serpentinites contain large blocks of amphibolites, schists, gneisses, and metagabbros. These rocks were in- truded by melagabbronorite and cumulate gabbronorite. On the AFM diagram, these rocks plot along the MgO-FeO* side in the tholeiitic field except those of the melagabbronorite which plot within the calc- alkaline field. The Wadi Khamal complex consists of four major units; mar- ginal gabbro unit, anorthosite unit, central gabbroic unit and northern gabbronorite unit. The marginal gabbro unit and anorthosite unit have a calc alkaline differentiation trend while those of the central gabbro unit (olivine gabbro, melagabbronorite and Fe-Ti oxides-apatite gab- bronorite) and the northern gabbronorite show a distinct different trend parallel to the FeO*-MgO side line and belong to the tholeiitic differentiation trend. Based on major element geochemistry, the southern ultramafic - mafic rocks were derived from a more mafic liquid source rather different from magma source(s) which formed the Khamal anorthosite-gabbro complex.

Geochemistry and Depositional Environments of the Tertiary Clays in Makkah and Rabigh Quadrangles, West Central Arabian Shield, Saudi Arabia

The present work deals with a detailed chemical study on the clay mineral assemblages characterizing some clay deposits, shales and mudstones, which differ in their texture, colour, lithology, and depositional environments. Samples selected from seven Tertiary formations located in Makkah and Rabigh quadrangles are chemically analyzed; some are used as environmental discriminators. The distribution of major and some trace elements in 77 samples has been investigated and the results obtained were tabulated and graphically illustrated. A wide range of variation is shown in the results of both major and trace constituents. This is due to their variable content of clay mineral constituents and the abundance or paucity of other admixtures, e.g. quartz, feldspar and minor heavy mineral grains. The local occurrence of minor gypsum and carbonate veinlets in some formations and ferrugination in others are also effective. A positive correlation exists in some formations between Fe2O3 and each of MnO, Cr, Ni, Cu & Zn; between each of Sr & Cu versus CaO; and in most cases between Ga and Al2O3. Whereas SiO2 shows a negative correlation with each of Al2O3 and L.O.I . Most of trace elements entered the depositional basin in close association with clay minerals and Ca-Fe-bearing detritus. The examined clay minerals and their trace elements are mainly source controlled (e.g. granitic and some pelitic rocks) and, an environmental illustration using Ga, B & Rb in a ternary diagram would 98 R.J. Taj et al. indicate transitional to marine depositional environments for the studied clay deposits.

Mineralogy of the Tertiary Clay Deposits in Makkah and Rabigh Quadrangles, West Central Arabian Shield, Saudi Arabia

The mineralogy of the Tertiary clay deposits in Makkah and Rabigh quadrangles was thoroughly investigated by X-ray diffraction and differential thermal and thermogravimetric analyses in addition to other techniques. Results show that the investigated samples are predominantly composed of montmorillonite (Ca++ and/or Mg++ rich variety) and kaolinite, associated with subordinate illite and minor chlorite. Mixed layer montmorillonite-illite is recorded only in two samples. The relative abundance of these minerals by X-ray diffraction analysis showed that the studied clay deposits are of three types. The first, which is the most common, is highly montmorillonitic, the second is made up of a mixture of montmorillonite followed by kaolinite and illite and the third is highly kaolinitic with some montmorillonite. Generally, kaolinite shows a southward increase in Makkah quadrangle while chlorite, as a minor component, shows a northward increase in Rabigh quadrangle.

Regional rock quality designation (RRQD) of the west central Arabian Shield : B.H. Sadagah & M.Y.H.T. Qari Bulletin-Association of Engineering Geologists, 30(4), 1993, pp 455–467

Regional rock quality designation (RRQD) of the west central Arabian Shield : B.H. Sadagah & M.Y.H.T. Qari Bulletin-Association of Engineering Geologists, 30(4), 1993, pp 455–467

Regional Rock Quality Designation (RRQD) of the West Central Arabian Shield

Engineering and hydrogeological behaviors of rock masses are intimately related to the intensity, extension and orientation of discontinuities hosted by the rock. Qualitative descriptions of such discontinuities provides general base information about any type of engineering structure such as dams, highways, pressure tunnels, airports, etc. However, more significantly, their quantitative descriptions are of prime importance especially concerning design variables. One of the most used indices in this regard is the Rock Quality Designation (RQD). So far in the literature only one-dimensional assessments of RQD are available along scanlines such as tunnel axis or along highway rock cuttings. This paper extends the concept of RQD into two dimensions which helps to assess the rock quality on a regional basis. The technique proposed herein is based on lying a regular mesh over the study area and calculating the regional RRQD values at nodal points by considering two orthogonal directions along which conventional RQD9s are obtained. Based on these nodal points contour maps or three-dimensional appearances of RQD within the region are presented.