ENE-WSW Trending Research Articles

Structure of the Crust Beneath the South Western Cameroon, from Gravity Data Analysis

The study area is located in the south western Cameroon and includes part of the Cameroon Volcanic Line (CVL). Volcanic activity has been recorded in this area, precisely on the Mount Cameroon which recently erupted in 2002. In addition, deadly carbonic gas was emitted by crater lakes (Monoun and Nyos) in 1984 and 1986 respectively. Potential field model EGM2008 has been used to investigate the structure of the crust. A regional/residual separation is performed using upward continuation and polynomial separation methods. The results from this operation show a similarity between the regional anomalies resulting from both methods. The regional anomaly maps present an increasing gradient trending ENE-WSW above and below latitude 5?N. Moreover, six nearly parallel profiles were drawn on the CVL in addition to two other profiles at the northern edge of Congo craton. These profiles were used to estimate the depths of the Moho discontinuity and some shallow sources by the means of the Bouguer and the residual anomalies respectively. The results show that the Moho discontinuity depths vary from 19 - 25 km (under Mount Cameroon) to 28 - 34 km (in Kumbo), while the southern neighbouring zone presents a Moho discontinuity depth ranging between 23 - 31 km (in Ngambe) and 22 - 32 km (in Eseka). These findings agree with the previous seismic and gravity researches lead in the area. EGM2008 is therefore a reliable tool to investigate the subsurface structures.

The integration of gravity, magnetic and seismic data in delineating the sedimentary basins of northern Sinai and deducing their structural controls

Abstract The Sinai Peninsula is a part of the Sinai sub-plate that located between the southeast Nubian–Arabian shield and the southeastern Mediterranean northward. The main objectives of this investigation are to deduce the main sedimentary basin and its subdivisions, identify the subsurface structural framework that affects the study area and determine the thickness of sedimentary cover of the basement surface. The total intensity magnetic map, Bouguer gravity map and seismic data were used to achieve the study aims. Structural interpretation of the gravity and magnetic data were done by applying advanced processing techniques. These techniques include; Reduce to the pole (RTP), Power spectrum, Tile derivative and Analytical Signal techniques were applied on gravity and magnetic data. Two dimensional gravity and magnetic modeling and interpretation of seismic sections were done to determine the thickness of sedimentary cover of the study area. The integration of our interpretation suggests that, the northern Sinai area consists of elongated troughs that contain many high structural trends. Four major structural trends have been identified, that, reflecting the influence of district regional tectonic movements. These trends are: (1) NE–SW trend; (2) NNW–SSE trend; (3) ENE–WSW trend and (4) WNW–ESE trend. There are also many minor trends, E–W, NW–SE and N–S structural trends. The main sedimentary basin of North Sinai is divided into four sub-basins; (1) Northern Maghara; (2) Northeastern Sinai; (3) Northwestern Sinai and (4) Central Sinai basin. The sedimentary cover ranges between 2 km and 7 km in the northern part of the study area.

Impact of inversion tectonics on hydrocarbon entrapment in the Baggara Basin, western Sudan

Abstract The Baggara Basin of Sudan is an ENE-WSW trending basin located within the West and Central Africa Rift System (WCARS) and NW of the Muglad Basin. The trend of the Baggara Basin is similar to other basins in eastern Chad, where oil has been discovered. Since there are no published studies for the Baggara Basin, the present paper represents an addition to the geology of eastern extension of the WCARS in Sudan. The 2D seismic data interpretation sheds light on the development and evolution of key regional and local structures of the basin. The Baggara Basin is characterized by graben geometry with two boundary faults, characterized by dextral strike slip movement, and a depocenter at the central part. The interpretation reveals the presence of two types of structures within the Baggara Basin; inversion tectonics restricted to the larger basin-bounding faults in the western part and en-echelon faults in the central part. The timing of inversion tectonics is during the Eocene and it is related to a brief major compressional event due to the collision of the African and Eurasian plates. Although the inversion created a four-way dip closed anticline structure, this anticline postdated the initial migration from the source rock. Accordingly, the anticline structural is unsuccessful for hydrocarbon entrapment.

Late Pleistocene Alberca de Guadalupe maar volcano (Zacapu basin, Michoacán): Stratigraphy, tectonic setting, and paleo-hydrogeological environment

Abstract The Late Pleistocene (~ 21,000 yr BP) Alberca de Guadalupe maar is one of the few phreatomagmatic volcanoes occurring within the scoria-cone dominated Plio-Quaternary Michoacan-Guanajuato Volcanic Field. The scarcity of this type of volcano implies that conditions favoring their formation are rarely met in this region. We identify these factors by implementing current methods of investigation with emphasis on hydrogeological conditions. We present the stratigraphy (including a set of 40 Ar/ 39 Ar and 14 C dates) of the SE margin of the Zacapu intermontane tectonic basin, where the maar just forms a hole (~ 1 km in diameter, ~ 150 m deep, bearing a ~ 9 m deep lake) in the otherwise planar topography of the underlying early Pleistocene lava flows of the Cerro Pelon scoria cone. The maar is composed of typical phreatomagmatic surge deposits that are poorly sorted and rich in accidental lithics (> 60 wt.% of the deposit) with few juveniles (basaltic andesite, SiO 2 = 54–58 wt.%). The entire structure is cut by an ENE–WSW trending normal fault and is underlain by andesite lavas and silicic ignimbrites (partly inferred from xenoliths encountered in the maar deposits) that are Miocene to Early Pleistocene in age. The crater is at the center of a N–S elongated drainage basin surrounded by topographic highlands that channel water with high hydraulic pressure from most directions towards the location of the maar. This geometric configuration was already in existence at the time of the maar-forming eruption, but the climate was different. Colder and more humid conditions during the Last Glacial Maximum (Cw2-climate type, annual precipitation of > 1000 mm) favored the saturation of the fractured shallow aquifer system (hydraulic conductivity of 10 − 8 to 10 − 7 m/s) that supplied sufficient groundwater at a high flow rate directed towards the center of the basin. Upon contact near surface ( 150 m deep crater with steep inner walls and an underlying shallow diatreme (

Geology, geochemistry, and paleomagnetism of rocks of the Utitsa Formation, north Sikhote Alin

The results of comprehensive geological, petrochemical, and paleomagnetic study of the Cenomanian–Turonian volcanic and sedimentary rocks of the Utitsa Formation are presented. The petrochemical characteristics indicate that the volcanic rocks were formed in a volcanic arc setting with supra-subduction geochemical sources. According to petro- and paleomagnetic study of the volcanic rocks, the paleolatitude of their formation is 53.7° ± 10.8° N and the coordinates of the paleomagnetic pole are Plat = 81.6°, Plong = 208.2°, dp = 10.8, dm = 12.5°. Comparison with the Mesozoic area of the trajectory of apparent migration of the pole of stable Siberia and Eurasia points to the autochtonous position of the Utitsa Formation relative to the Late Cretaceous continental margin. The data on the magnetic structure of the sedimentary rocks of the Utitsa Formation indicate the presence of an ENE–WSW-trending (50°–70°–230°–250°) bottom paleocurrent in the sedimentation basin.

“High resolution seismic imaging of an active fault in the eastern Guadalquivir Basin (Betic Cordillera, Southern Spain)”

Abstract We calculated the high resolution seismic velocity, Poisson's ratio, crack density and saturation ratio structures in and around the source areas of the Torreperogil seismic series (October 2012–April 2013). This seismic series, characterized by a large number of low magnitude (below Mw 3.7 or Md 3.9) and very shallow microearthquakes, took place in the Guadalquivir Basin, a large flexural foreland basin with a linear ENE–WSW trending bounded to the north by the Iberian Massif and to the south by the Betic Cordillera and filled from a middle Miocene to Plio–Quaternary sedimentary sequence. In the upper layers of the crust, strong low-velocity anomalies are extensively distributed under the central zone, which together with high Poisson's ratio and crack density values may correspond to rocks which are less likely to fracture, perhaps due to the accumulation of tectonic and seismic stress. 93% of the earthquakes occurred at depths of up to 8 km, which could indicate that the base of the seismogenic zone lies at this depth. The seismic series was concentrated in layers of strong structural heterogeneities (in the boundary area between low and high anomalies), which were likely to generate earthquakes due to differential strain accumulation beneath the region. The high velocity areas are also considered to be strong yet brittle parts of the fault zone, which may generate earthquakes (at depths of between 5 km and 9 km). By contrast, low velocity areas are less prone to fracture, allowing seismic slippage to take place (from 2 to 4 km depth). The best estimate of the depth of the main shock (m bLg 3.9) is 7.6 km, which could tend to nucleate at the base of the seismogenic zone, at the “fault end” on the boundary between a low velocity zone to the east and a high velocity zone to the west, indicating the fault plane which separates both areas laterally. Assuming that this seismic contrast is one of the main Torreperogil faults it could imply that stress has accumulated in an existing fault zone with lateral heterogeneity in velocity.

Pan-African deformation markers in the migmatitic complexes of Parakou–Nikki (Northeast Benin)

The analysis of structural markers collected from the petrostrutural units of Parakou-Nikki, in Northeast Benin, indicates that the Pan-African remobilization or rejuvenation (600 ± 50 Ma) of the Benino-Nigerian Metacraton consits of a wide migmatization accompanied by five tectogenetic phases (Dn–Dn+4). The Dn phase is penecontemporaneous with the collision between the Benino-Nigerian shield and the oriental margin of the West-African Craton. This phase is associated with the granulitization or migmatization episode, and materialized by the Sn foliation on which the Dn+1 deformation markers (major Pan-African structuring phase in the Dahomeyide orogenic belt) are superimposed. Thus, the Sn+1 plane and the Ln+1 lineations indicate a perfect transposition of the Sn plane and a syn-Dn paragenesis remobilization in the syn-Dn+1 amphibolite facies retromorphosis. The strong resumption of the main foliation (Sn+1) corresponds to the Dn+2 deformation phase. The latter, associated with a second retromorphosis, is materialized by Pn+2 folds, with submeridian to NE–SW axes, and by a Sn+2 foliation or strain-slip cleavage. It is also the phase of emplacement of the Kandi mega-shear zone associated with the development of Cn+2 dextral shear plane very generalized over all the petrostructural units of Parakou–Nikki. At a large scale, the Dn+3 phase is expressed as Pn+3 kilometric synform and antiform structures with NE–SW to ENE–WSW trending axes. This Dn+3 phase can be considered as a transpression responsible for the development of the Cn+3 sinistral shear plane and flat shear structures displaying a westward overlapping. It ends with a fracturing episode materialized by strike-slip fault systems defining a main stress σ1 trending ESE–WNW to SE–NW. The late Dn+4 phase only corresponds to conjugated strike-slip faults which resulted from a major SE–NW to SSE–NNW compression.

Geological, seismological and geodetic evidence of active thrusting and folding south of Mt. Etna (eastern Sicily): Revaluation of “seismic efficiency” of the Sicilian Basal Thrust

Abstract Geological studies and morphological analysis, compared with seismological and geodetic data, suggest that a compressive regime currently occurs at crustal depth in the western sector of Mt. Etna, accommodated by shallow thrusting and folding at the front of the chain, south of the volcanic edifice. In particular, a large WSW-ENE trending anticline, interpreted as detachment fold, is growing west and north of Catania city (the Catania anticline). Geological data suggest that during the last 6000 years the frontal fold has been characterized by uplift rates of ∼6 mm/yr along the hinge, consistent with the interferometric data (10 mm/yr) recorded in the last 20 years. Moreover, a NNW-SSE oriented axis of compression has been obtained by seismological data, consistent with GPS measurements over the last 20 years which have revealed a shortening rate of ∼5 mm/yr along the same direction. Besides the activity related to the volcanic feeding system, the seismic pattern under the Mt. Etna edifice can be certainly related to the regional tectonics. The compressive stress is converted into elastic accumulation and then in earthquakes along the ramps beneath the chain, whereas on the frontal area it is accommodated by aseismic deformation along an incipient detachment within the clayish foredeep deposits. The high rate of shortening at the aseismic front of the chain, suggests a greater “seismic efficiency” in correspondence of ramps at the rear.

The Main Shear Zone in Sør Rondane, East Antarctica: Implications for the late-Pan-African tectonic evolution of Dronning Maud Land

Structural investigations in western Sor Rondane, eastern Dronning Maud Land (DML), provide new insights into the tectonic evolution of East Antarctica. One of the main structural features is the approximately 120 km long and several hundred meters wide WSW-ENE trending Main Shear Zone (MSZ). It is characterized by dextral high-strain ductile deformation under peak amphibolite-facies conditions. Crosscutting relationships with dated magmatic rocks bracket the activity of the MSZ between late Ediacaran to Cambrian times (circa 560 to 530 Ma). The MSZ separates Pan-African greenschist- to granulite-facies metamorphic rocks with “East African” affinities in the north from a Rayner-age early Neoproterozoic gabbro-tonalite-trondhjemite-granodiorite complex with “Indo-Antarctic” affinities in the south. It is interpreted to represent an important lithotectonic strike-slip boundary at a position close to the eastern margin of the East African-Antarctic Orogen (EAAO), which is assumed to be located farther south in the ice-covered region. Together with the possibly coeval left-lateral South Orvin Shear Zone in central DML, the MSZ may be related to NE directed lateral escape of the EAAO, whereas the Heimefront Shear Zone and South Kirwanveggen Shear Zone of western DML are part of the south directed branch of this bilateral system.

The structure of the Temsamane fold-and-thrust stack (eastern Rif, Morocco): Evolution of a transpressional orogenic wedge

Abstract The structure of the Temsamane fold-and-thrust stack corresponds to four units limited by anastomosing ductile shear zones cutting a trend of south verging recumbent folds. This ductile stack was formed in an inclined left-handed transpressional zone at the North African paleomargin during Chattian to Langhian times producing two main deformational events. The first event (Dp) produced a Sp/Lp planar linear fabric generated in a non-coaxial deformation with a top-to-the-WSW sense of movement and was associated to metamorphic P–T conditions varying from late diagenesis in the southernmost Temsamane outcrops to epizone in the north. According to the 40Ar/39Ar ages, this deformation occurred at Chattian–Aquitanian times. The second deformational event (Dc event) generated ENE–WSW trending folds with SSE vergence and a set of anastomosing shear zones with Sm/Lm planar linear fabric. The latter units were generated at around 15 Ma (Langhian), and indicate a strong localization of the simple shear component of the transpression. Moreover, this orientation is compatible with the kinematics of the Temsamane detachment, which can explain most of the uplift of the Temsamane rocks from the middle to the uppermost crust. The described evolution indicates that collision between the western Mediterranean terranes and the North African paleomargin and the formation of the Rifean orogenic wedge occurred at Chattian to Langhian times.

Fossilized lithospheric deformation revealed by teleseismic shear wave splitting in eastern China

Global mantle convection significantly impacts the processes at Earth’s surface and has been used to gain insights on plate driving forces, lithospheric deformation, and the thermal and compositional structure of the mantle. Upper-mantle seismic anisotropy has been widely employed to study both present and past deformation processes at lithospheric and asthenospheric depths. The eastern China region was affected by extreme mantle perturbation and crust-mantle interaction during the Mesozoic, leading to large-scale destruction of the cratonic lithosphere, accompanied by widespread magmatism and metallogeny. Here we use teleseismic shear wave splitting measurements to evaluate the lithosphere and upper mantle deformation beneath this region. Our results from some of the individual and station averages show WNW-ESEto NW-SE–trending fast polarization direction, similar to those observed in eastern Asia in some previous studies, consistent with the direction of Pacific plate subduction during the Cenozoic. This feature suggests that the asthenospheric flow beneath the eastern China region is influenced by the subduction of the western Pacific or Philippine plate. However, most of our data show E-Wor ENE-WSW–trending fast polarization direction, which is inconsistent with subduction from the east. The seismic stations in this study are located near the Qinling-DabieSulu orogenic belt, which formed through the collision between the North and South China blocks during the Late Paleozoic– Triassic, and the anisotropy with an E-Wor ENE-WSW–trending fast polarization direction parallel to the southern edge of the North China block suggests lithospheric compressional deformation due to the collision between the North and South China blocks. Although the deep root of the craton was largely destroyed by cratonic reactivation in the late Mesozoic, our results suggest that the “fossilized” anisotropic signature is still preserved in the remnant lithosphere beneath eastern China.

Uranium evaluation and its recovery from microgranite dike at G. El Sela area, South Eastern Desert, Egypt

The present work aims at integrating detailed field studies to prospect for uranium ores associated with microgranite dike. The investigated El Sela area is covered by two types of granitic intrusion comprising biotite granite and two-mica granite. They are cut by microgranite, dolerite, and bostonite dikes, and quartz and jasper veins. U mineralization is observed along an ENE–WSW shear zone where quartz and jasper veins bounded the microgranite dike which is affected by successive brecciation and fracturing. Ferrugination, silicification, kaolinization, illitization, and fluoritization affected microgranite dike having visible U mineralization. Different fractures in two-mica granite acted as good channels for the ascending hydrothermal fluids and the percolating meteoric water that leached uranium from its bearing minerals disseminated all over the host two-mica granite and redeposited them in microgranite dike along the main shear zone trending ENE–WSW. Uranium was determined in the collected samples spectrophotometrically using arzenaso III as complexing agent. Uranium concentrations measured by chemical analyses are higher than the “gamma radiometric” determinations of the same microgranite samples, which can be explained by a state of disequilibrium in the uranium decay series. Sulphuric acid was used, in the present work, for leaching uranium from a representative mineralized sample of highly ferruginated microgranite. Conditions were briefly studied to achieve uranium recovery under optimum conditions. The acid-leaching operating conditions allowed us to obtain a uranium recovery of about 90 %. Ion exchange resin was used for the concentration and purification of our pregnant solution. A 75 % dry uranium concentration in final yellow cake product has been achieved.

Oppositely dipping thrusts and transpressional imbricate zone in the Central Eastern Desert of Egypt

• The MBSB evolved during three post-collisional (740–540 Ma) deformation events. • Early top-to-the-northwest thrust due to NW–SE shortening (D 1 ). • NW-trending sinistral shear zones (D 2 ) strongly overprinted by (D 3 ). • NE-trending dextral transpressional imbricate zone (D 3 ). • These events formed during oblique convergence between East and West Gondwana . This paper documents the 40–60 km wide ENE–WSW trending Mubarak–Barramiya shear belt (MBSB) in the Central Eastern Desert of Egypt by examining its structural styles, kinematics and geometry. Our study revealed the existence of prevalent dextral and minor sinistral conjugate shear zones. The MBSB is metamorphic belt (greenschist–amphibolite) characterized by at least three post-collisional (740–540 Ma) ductile Neoproterozoic deformation events (D 1 , D 2 and D 3 ) followed by a brittle neotectonic deformation (D 4 ). D 1 event produced early top-to-the-northwest thrust displacements due to NW–SE shortening. D 2 produced discrete zones of NNW-trending upright folds and culminated in initiation of major NW-trending sinistral shear zones of the Najd Fault System (NFS, at c. 640–540 Ma ago) as well as steeply dipping S 2 foliation, and shallowly plunging L 2 lineation. NW-to NNW-trending F 2 folds are open to steep and vary in plunge from horizontal to vertical. D 2 deformational fabrics are strongly overprinted by D 3 penetrative structures. D 3 is characterized by a penetrative S 3 foliation, steeply SE- to NW-plunging and shallowly NE-plunging stretching lineations (L 3 ), asymmetric and sheath folds (F 3 ) consistent with dextral sense of movement exhibited by delta- and sigma-type porphyroclast systems and asymmetric boudinage fabrics. D 2 –D 3 represent a non-coaxial progressive event formed in a dextral NE- over NW-sinistral shear zone during a partitioned transpression in response to E–W-directed compression during oblique convergence between East and West Gondwana developed due to closure of the Mozambique Ocean and amalgamation of the Arabian–Nubian Shield in Cryogenian-early Ediacaran time.

Assessment of the geodynamical settings around the main active faults at Aswan area, Egypt

The proper evaluation of the level of crustal deformations in the Aswan region, especially around the main active faults, is crucial due to the existence of one major artificial structure: the Aswan High Dam. This construction created one of the major artificial lakes in the world: Lake Nasser. The Aswan area is considered as an active seismic area in Egypt due to the frequent recurrence of felted earthquakes. Two earthquakes occurred in the region (Kalabsha fault) after the construction of the Aswan High Dam: November 14, 1981 (ML = 5.6) and December 26, 2011 (ML = 4.1). The main goal of this study is to evaluate the active geological structures that can potentially affect the Aswan High Dam and that are being monitored in detail. For implementing such objective, several techniques (namely magnetic, seismic and GPS) have been utilized. A detailed land magnetic survey was carried out for the total component of the geomagnetic field using two proton magnetometers. The obtained magnetic results reveal that there are three major parallel faults affecting the area. The most dominant magnetic trend strikes those faults in the WNW-ESE direction. The seismicity and the fault plane solution associated with the December 26, 2011 earthquake have been also analyzed. The source mechanism of this event delineates two nodal planes. The trending ENE-WSW to E-W is consistent with the direction of the Kalabsha fault and its extension towards east. The trending NNW-SSE to N-S is consistent with the N-S fault trending. The movement along the ENE-WSW plane is right lateral, while left lateral along the NNW-SSE plane. Based on the estimated relative motions using GPS, dextral strike-slip motions at the Kalabsha and Seiyal fault systems are identified by the velocity gradient changes between the southern and northern stations. However, at the area between Kalabsha and Seiyal faults, other relative movements are also observed, which is consistent with other set of faults (N-S).

FEATURES CONTROLLING RADIOELEMENTS DISTRIBUTION IN AL AGLAB REGION, NORTH EASTERN DESERT, EGYPT

This work is an approach to integrate multi-discipline set of data including geological and remote sensingas well as airborne, ground radiometry and aeromagnetic geophysical data aiming to establish the controllingfeatures of the radioelement potential distribution within Al Aglab area. The investigated area of Al Aglabregion is located within the Northern Eastern Desert litho-structural domain where the outcropping rock typescomprise: metavolcanics (oldest), quartz diorites, Dokhan volcanics, Hammamat sediments and gabbrogranophyreassociations intruded by monzogranite, syenogranite and post granitic dykes (youngest). Thegranitic rocks display sharp contact with the older pre-existing rock. The radioactive anomalies lay at theintersections between NNW-SSE to N-S and NE-SW to ENE-WSW trending structure lineaments (joints,faults and shear zones) within the syenogranites pluton of G. Al Aglab and along the NE-SW to ENE-WSWtrending felsitic dykes, jasperoid veines and pegmatite bodies.Landsat Thematic Mapper (TM) remote sensing map in great concordance with airborn gamma rayspectrometric data delineate most of the surface geology over the compiled geological map. The extractedstructural lineaments are coherent to those inferred from the analytical signal magnetic maps in completeharmony with the NNW-SSE to N-S and NE-SW to ENE-WSW trending fault systems obtained from theground geological and radiometric investigation. Moreover, different types of alterations such as hematitization,Kaolinitization, chloritization and silicification are recorded within the synogranite, where their distributionis mainly controlled by the intersections between the NNW-SSE to N-S and NE-SW to ENE-WSW trendingstructural lineaments.The studied structural lineaments are arranged according to three main trend clusters around NNW-SSEto N-S, NE-SW to ENE-WSW and NW-SE to WNW-ESE directions representing the main factor controllingthe emplacement of the different granitic intrusions in Al Aglab area. Moreover, most of these lineaments, asobtained from field measurements, show strike-slip movement criteria within an extensional context. All therecorded mineralized occurrences are related to extensional events that create the necessary space either formineral entrapment and/or the percolation of the hydrothermal carrying solutions along these structural trendsespecially at their intersections.Spectrometric data (K, U and Th) shows a very high consistency between the radioelement distributionsand the differentiated outlines of different rock types. Results from integrated field studies, Landsat ThematicMapper (TM) remote sensing data and geophysical data analyses provide important constraints on the tectonicevolution of Al Aglab area and importantly, demonstrate the strength of combining remote sensing data withgeophysical data and geological observations in resolving the surface geometry of major fault systems andtheir impact on the radioelement potential distribution within Al Aglab area.

Application of remote sensing in exploration for uranium mineralization in Gabal El Sela area, South Eastern Desert, Egypt

Abstract This research aims at integrating remote sensing data and field studies to prospect for radioactive materials at Gabal El Sela area, South Eastern Desert of Egypt. This area is a part of the Arabo-Nubian shield, which is constituted by Late Precambrian basement rocks and developed during the Pan African tectono-thermal event. Geological interpretation of Landsat ETM+ image and field studies revealed that the study area is mainly covered by ophiolitic ultramafic rocks, intermediate metavolocanics, granodiorites, biotite granites and garnetiferous muscovite granites. These rocks are injected by pegmatitic and quartz veins and cut by acidic and basic dykes. The processed Landsat ETM+ data enable also to identify uraniferous alteration zones hosted in the granitic rocks (using band ratio 5/7, 4/5, 3/1 in RGB, density slicing and supervised classification techniques). The measured reflectance values (DNs) of six spectral bands of Landsat ETM+ for all exposed rock types in the study area show that the alteration zones have the highest reflectance values. The study recorded the presence of uranium mineralizations in alteration zones associating with the granitic rocks occurring along ENE–WSW trending shear zones. Three uranium-bearing alteration zones hosted in granitic rocks were detected. These zones are characterized by ferrugination, silicification, grizenization and kaolinitization. The most promising alteration zones (Site 1) occurs at the northeastern part of Gabal El Sela and is characterized by very high radioactive anomalies (up to 5000 ppm eU). Microprobe analyses of samples collected from these alteration zones reveal the presence of uraninite crystals. It seems that the high fractures density of the granitic rocks acted as good channels for the ascending hydrothermal fluids and the percolating meteoric water, that leached the uranium minerals disseminated all over the rocks and redeposited them along the fractures of the shear zones. This study demonstrates the utility of orbital remote sensing data for finding unknown mineralized zones in the Eastern Desert of Egypt and similar arid regions.

Mechanism and timing of tectonic inversion in Cyrenaica (Libya): Integration in the geodynamics of the East Mediterranean

Abstract In the eastern Mediterranean, the South-Tethys paleo-margin experienced poly-phased rifting episodes during Paleozoic and Mesozoic times. This domain has been subsequently inverted by discontinuous events occurring since the Late Cretaceous as a consequence of the Africa–Eurasia convergence. The Cyrenaica promontory (northeast Libya), including the Jabal Al Akhdar antiformal ridge, is not yet involved in the Africa–Eurasia collision zone. It thus gives an opportunity to analyze tectonic inversions occurring early in the development of the system and their possible causal links with events occurring along the plate boundary (i.e., within the Hellenic subduction). For this purpose, we present new geological cross-sections supported by offshore industrial 2D seismic profiles imaging the northeast prolongation of the antiformal ridge indenting the Mediterranean Ridge accretionary prism. The onshore part of this ENE–WSW trending structure exposes Upper Cretaceous to recent sedimentary rocks. Well calibrations allow us to be precise about the geometry of the structure, inherited from a Lower Cretaceous rift basin, and the timing of the main tectonic events. Oligocene sediments seal unconformably the main episodes of contractional deformation. Just below, growth strata of Late Ypresian to Priabonian age indicate a protracted folding episode during the Middle–Late Eocene, post-dating an older Late Cretaceous inversion. This evolution contrasts with what is observed in the adjacent Sirt Basin, characterized at the same time by extensional deformation and subsidence. Finally, we appraise how far these tectonic scenarios match the geodynamic evolution of the Hellenic domain.

Study of the 26 December 2011 Aswan earthquake, Aswan area, South of Egypt

The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies fo for P-wave spectra show a value of 6.6 Hz; the seismic moment (Mo) is 4.2 × 1022 Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (Mw) is 4.4.

The Aledjo Quartzitic Ruins in Northern Togo: Genesis and Structural Geomorphology

In northern Togo, the Aledjo Mountains represent a NE-SW to ENE-WSW trending segment of the Pan-African Dahomeyide orogen. This mainly quartzitic topography belongs to the external zone of the belt and, more precisely, to the eastern assemblage of the Atacora Structural Unit. It corresponds to a ruiniform landscape which resulted from an erosive sculpturing that started at the end of the Pan-African tectogenesis within the Dahomeyide Belt, at about 550 Ma. A first interpretation of these spectacular sculptures attributed their great variety to predisposition factors related to the petrographic heterogeneity of the quartzites and to the Pan-African tectogenesis. With reference to these genetic factors, the Aledjo quartzitic ruins are subdivided into two morphostructural groups related either to a combination of folding and erosion or fracturing and erosion. Moreover, the Aledjo ruiniform landscape may be considered as an attractive touristic target which can contribute to regional economic development in northern Togo. Keywords: Quartzitic Ruins, Aledjo Montains, Dahomeyide, Northern Togo, Morphogenesis

Relationship between geological structures and groundwater flow and groundwater salinity in Al Jaaw Plain, United Arab Emirates; mapping and analysis by means of remote sensing and GIS

Geological structures can be of great influence groundwater movement and accumulation in the surface and subsurface, and should therefore be taken into consideration in studies related to groundwater contamination impact. This study attempts to investigate the influence of geological structures on groundwater flow and groundwater salinity in Al Jaaw Plain, United Arab Emirates. A set of thematic maps derived from digital elevation model (DEM), LANDSAT, and Spaceborn Imagine Radar-C/X-Band Synthetic Aperture Radar were enhanced by applying Soble filter with 10 % threshold and equalization enhancement to reveal and map geological structures crosscut the entire region. Drainage pattern was derived from DEM automatically using D8 algorithm. The algorithm determines in which neighboring pixel any water in a central pixel will flow naturally. The trends of geological structures and drainage pattern extracted from remote sensing data were correlated with the spatial variation of hydraulic head, thickness aquifer, and groundwater salinity in the region. The results of the study reveal that the wadi courses, thickness of the aquifer, and topography are structural controlled by NNW–SSE, NE–SW, and ENE–WSW trending fault zones, significantly influencing the groundwater flow and groundwater contamination in Al Jaaw Plain.