NE-SW Trending Research Articles

Influence of multi-trend major fault reactivation during multiphase rifting: Beier Depression, Hailar Basin, NE China

AbstractComplex fault patterns associated with rift development in the Hailar Basin were largely influenced by the Mongolia–Okhotsk Ocean and Palaeo-Pacific tectonic regimes during the Late Jurassic to Early Cretaceous periods. Based on 3D seismic data from the Beier Depression in the Hailar Basin, we characterized the reactivation history of multi-trend major faults and examined the evolution of the Beier Depression during the Early Cretaceous period. NE–SW-, NW–SE- and ENE–WSW-oriented major faults originated from strike-slip-associated structures that were pre-existing fabrics and then were reactivated and propagated upward under extensional regimes in the Late Jurassic. During the syn-rift stage (K1t–K1n), the Hailar Basin was in a NNW–SSE- to NW–SE-oriented extensional setting, and major faults of all orientations were active. There was tectonic quiescence (K1n1L) between the syn-rift stages (a rifting transition stage). The short compression stage after the syn-rift stage caused regional compressional deformation. During the post-rift stage (K1d–K1y), the extension direction rotated to an E–W orientation, and a new population of N–S-trending faults formed together with the reactivation of NE–SW- and ENE–WSW-trending major faults. Structural analysis shows that the major ENE–WSW-trending major faults were polycyclic growth faults reactivated via an upward propagation mode and that the NE–SW-trending faults were dip linkage faults reactivated via a dip linkage mode. The reactivation intensity of the NE–SW-trending major faults was stronger than that of the ENE–WSW-trending major faults. These results demonstrate the differences in the evolution of the different trending faults in the same tectonic regime, and the complexity of the final fault patterns in the Beier Depression was produced by differences in the reactivation of major faults. The originate interpretation of the multi-trend major faults in the Hailar Basin provides new insights into fault generation, and the classification of fault growth also has useful implications for future research on multiphase rifts.

Integrated Landsat multispectral imagery and airborne geophysical data for enhanced litho-structural mapping: A case study of Adamawa Massif, north-eastern Nigeria

Landsat-7 ETM + satellite imagery integrated with corrected airborne geophysical data (radiometric, gravity, and aeromagnetic) anomalies maps, and field investigations were used to discriminate lithologies and related structures in Mayo-Belwa and Jada-Ganye-Toungo areas (Adamawa Massif), northeastern Nigeria. Field investigations portray the granite-gneisses as the oldest rock units, and have sequentially been invaded by the syn-, late-to post-collisional Older granites. Subsurface linear structures in the area display dominant NE-SW, NW-SE, NNE-SSW, and ENE-WSW trends, reflective of variations in pre-existing structural orientations, and near-surface expressions of reactivated zones of weakness in the basement crust. The geodynamic systems revealed that most elongated lineaments are expressed as axial part of valleys trending NE-SW, ENE and NNW, forming diagonal grid to the NW-SE stresses. Abnormally high total radioactivity gravitates to areas of deflection (alluvium), and late- and post-tectonic granites. The gravity intensity provides a spectrum of anomalous responses including abnormally high positive gravity (volcanic rocks), moderately high positive gravity (granite-gneisses and late-to post-tectonic and syn-tectonic granites), background gravity and low negative gravity (granite-gneisses, alluvium and proluvium). Aeromagnetic anomalies discriminate the Older granites (intense positive anomalies), granite-gneisses, sediments (moderate positive, near background, and moderate-intensive negative anomalies), syn-tectonic granites (moderate positive anomalies), banded-gneiss and amphibolite (intensive negative anomalies), volcanic rocks (intense negative anomaly), and alluvium/proluvium (low positive anomalies). This present study led to the development of up-to-date and accurate litho-structural and geophysical maps of the geologically-rugged and hardly accessible Adamawa Massif, north-eastern Nigeria and further constrain the geochemical (High-K calc-alkaline, peraluminous) and tectonic (syn-to post-collisional) characteristics of typical Pan-African granitoids.

Integration of satellite gravimetry, multispectral imagery and digital elevation model for investigating crustal deformation in the Niger Delta Basin

Remotely acquired gravity data from satellite gravimetry is integrated into the study to investigate crustal deformation in the Niger Delta Basin. The Niger Delta Basin is a well-documented example of a passive margin delta that has gravitationally deformed. The gravity-driven deformation has not been fully understood, and new trends may be emerging. In this study, we assess and delineate structural deformation and sediment accumulation of the Agbada and Akata stratigraphic sequences within the basin's prograding clastic wedge. This was done through the integration of data from the Gravity Recovery and Climate Experiment (GRACE) mission, Landsat 8 satellite imagery, and the Advanced Land Observation Satellite (ALOS) World 3D-30 m (AW3D) DEM. The methodology workflow incorporated gravity modelling from GRACE data, lineament extraction from Landsat imagery, and drainage network analysis from the AW3D DEM. The Niger Delta Basin as seen on the gravity models depicts large-scale block faults with a well-defined graben structural topography. This eventually shows that the basin is dominated by growth faulting with differential subsidence. The predominant directions of the mapped lineaments are in the N-S and W-E directions. With over 18,500 lineaments, the W-E direction is marginally the dominant direction of the two predominant directions. Many linear structures such as shear zones and fractures which have different orientations and directions characterise the study area. Also present are the minor N-S fractures which are attributed to brittle deformation and sets of NE-SW and NW-SE trends, produced by transcurrent movements as the structural framework of the Nigerian basement complex are dominated by the NE-SW lineaments. However, the complexity in the structural geometry and thrusting sequences in the Niger Delta shows the patterns of growth structure and imbricate thrusting. The structural pattern also exhibits outward radial gravity spreading of dip-orientated, extensional structures that include delta slope radial grabens and tear faults. Radial spreading has likely increased the segmentation of Niger Delta regional depo-belts in the N-S direction. It is observed that most of the structural deformations in the basin are syn-formational, evolving at the same time as sediment deposition.

Hydrothermal Uranium Mineralization in Umra, Udaipur District, Rajasthan, India: Inferences from Petrography, Mineral Chemistry and Sulfur Isotopic Studies

Abstract Uranium mineralization at Umra, Udaipur district, Rajasthan is hosted by carbon and siliceous phyllite (with minor calcareous components) of the Paleoproterozoic Aravalli Supergroup. The mineralized zone trends NE-SW to N-S, dipping 45-55° towards SE to E. Uraninite, coffinite and brannerite are the main uranium phases observed that occur in association with sulphides (pyrrhotite, pentlandite, gersdorffite, chalcopyrite and pyrite), magnetite and ilmenite. Uraninite is found to occur as veins and disseminated ultrafine grains. Colloform and botryoidal texture with shrinkage/ synaeresis cracks indicate the presence of pitchblende also, formed at relatively low-temperature. Textural features suggest remobilization of disseminated syngenetic and / or diagenetic uranium minerals during low-grade metamorphism and deformation. Textural features suggest multiple phases of sulphide mineralization also. Mineral chemical data indicate that uraninite and pitchblende are compositionally similar containing 80.09-87.17 wt.% UO2 (av. 84.45 wt.%) and 11.37-11.82 wt.% PbO (av. 11.58 wt.%) with negligible SiO2, CaO, TiO2, FeO, ThO2 and RE2O3. High U/Th ratio (>1000) in uraninite/ pitchblende indicates limited cationic substitution and therefore low temperature (<350°C) hydrothermal origin of mineralization. Chemical age, calculated on the basis of UO2, ThO2 and PbO concentration in uraninite, indicates the minimum age of mineralization is 956±12 Ma. S isotopic data of pyrite suggest syn-sedimentary or diagenetic origin by bacterial reduction of seawater or pore water sulphate under anoxic conditions (-24.7‰ to -16.2‰), as well as hydrothermal (-3.7‰ to +8.8‰) origin. Similarity of S isotopic composition of hydrothermal pyrite with that of pyrite (+5.2‰) from meta-basic rock indicates that a component of S has been derived from the associated basic/meta-basic rocks in the area. Signatures of multiple generations of uranium mineralization, and multiple episodes of deformation, metamorphism and hydrothermal alteration reveal a complex metallogenic history in Umra. Compositional details of uraninite and their occurrence in the form of veinlets in association with hydrothermal pyrite suggest dominantly epigenetic hydrothermal mineralization events coeval with deformations of the Aravalli sediments.

Tectonic evolution of the northern Verkhoyansk Fold-and-Thrust Belt: insights from palaeostress analysis and U–Pb calcite dating

AbstractA combined structural and geochronological study was carried out to identify the tectonic evolution of the northern Verkhoyansk Fold-and-Thrust Belt, formed on the east margin of the Siberian Craton during late Mesozoic collision. Fault and fold geometries and kinematics were used for palaeostress reconstruction along the Danil and Neleger rivers cross-cutting the central and western parts of the Kharaulakh segment of the northern Verkhoyansk. Three different stress fields (thrust, normal and strike-slip faulting) were identified after separation from heterogeneous fault-slip data. Thrust and normal faulting stress fields were found in both areas, whereas a strike-slip faulting stress field was only found in Neoproterozoic rocks of the Neleger River area. U–Pb laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) dating of calcite slickenside samples reveals the following succession of major deformation events across the northern Verkhoyansk: (i) The oldest tectonic event corresponding to the strike-slip faulting stress field with NE–SW-trending compression axis is Early Permian (Cisuralian, 284 ± 7 Ma) and likely represents a far-field response to the late Palaeozoic collision of the Kara terrane with the northern margin of the Siberian Craton. (ii) A slickenfibrous calcite age of 125 ± 4 Ma is attributed to the Early Cretaceous compression event, when the fold-and-thrust structure was formed. (iii) U–Pb slickenfibre calcite ages of 76–60 Ma estimate the age of a Late Cretaceous – Palaeocene compression event, when thrusts were reactivated. Slickensides related to both (ii) and (iii) compressional tectonic events formed by similar stress fields with W–E-trending compression axes. (iv) From the Palaeocene onwards, extensional tectonics with approximately W–E extension predominated.

Geothermal System in Parang Wedang, Yogyakarta, Indonesia

Geothermal manifestations in Parangtritis, Indonesia, known as Parang Wedang Hot Spring, indicate a geothermal system in the subsurface. This circumstance motivated our research to model the Parang Wedang geothermal system in order to determine its subsurface conditions. Geological mapping, the geophysical method, and geochemical analysis were integrated to produce a conceptual model of the Parang Wedang geothermal system. The study area consists of structural hills, karst hills, and eolian plains with andesite breccias, limestone, andesite, and sand deposits as lithological variations. The results of magnetic modeling indicate that the research area is associated with the presence of an andesite intrusion and shows a NE-SW trending geological structure that is thought to be a path for hydrothermal fluid to the surface. Geochemical analysis was performed at two hot springs with temperatures of 47 °C and 49 °C. Geothermometer calculation showed that the geothermal reservoir in Parang Wedang has a temperature of 100 to 120 °C, a depth of about 180 to 285 m, and can be classified as a low enthalpy geothermal system.

Splitting a large pluton by Cretaceous crustal extension: Evolution of the Ziyuan Detachment and crustal thinning of the South China Block

The Cretaceous extensional province of the South China Block (SCB), and the decratonization-induced extension in the North China Block (NCB), were both controlled by the Late Mesozoic subduction of the Izanagi/Paleo-Pacific Plate. Different from the metamorphic core complexes exhuming deep crustal rocks of the NCB, extension of the SCB is expressed by numerous half-graben basins and detachment of upper-middle crustal rocks, but its mode and mechanism remain unclarified. At the westernmost of this extensional province, the Early Paleozoic Yuechengling-Miao'ershan Massif, composed of the ductilely deformed Yuechengling pluton and undeformed Miao'ershan pluton, records Late Mesozoic detachment and exhumation. Magnetic fabrics of the western Yuechengling pluton are consistent with structural fabrics, while the NE-SW trending magnetic lineation and NE-SW striking magnetic foliation of the Miao'ershan pluton and the undeformed Yuechengling pluton reflect a pre-existing magma flow structure. Integrating our structural observation, anisotropy of magnetic susceptibility (AMS) results with gravity modeling, we reveal the deep geometry of the extensional dome and restore the original structure before the Late Mesozoic Ziyuan detachment. The mode of extension argues for a single batholith split into two separate massifs, thinning the crust of the central SCB. The shallow-dipping Ziyuan detachment fault (10°-30°) may account for the large horizontal extension but low exhumation of mid-crustal rocks in the SCB, in contrast to the large exhumation of deep crustal rocks in the NCB.

Swarm seismicity illuminates stress transfer prior to the 2021 Fagradalsfjall eruption in Iceland

The 2021 Fagradalsfjall volcanic eruption in the Reykjanes Peninsula, Iceland, was followed by effusive lava outflow lasting six months. It was preceded by an intensive earthquake swarm lasting one month with the largest earthquake exceeding ML 5. We analyze seismic data recorded by the Reykjanet local seismic network to trace the processes leading to the eruption to understand the relation between seismic activity and magma accumulation.Precise relocations show two hypocenter clusters of the 2021 swarm in the depth range of 1-6 km; a NE-SW trending cluster that maps the dyke propagation, and a WSW-ENE trending cluster that follows the axis of the oblique plate boundary. Additionally, we relocated the preceding earthquake swarms of 2017, 2019 and 2020 and found that they form two branches along the oblique plate boundary, which coincide with the WSW-ENE trending cluster of the 2021 swarm. These branches form a stepover of ∼1 km offset, forming a pull-apart basin structure at the intersection with the dyke. This is the place where the eruption occurred, suggesting that magma erupted at the place of crustal weakening.The strong seismic activity started with a ML 5.3 earthquake of 24 February 2021, which triggered the aftershocks on the oblique plate boundary and in the area of magmatic dyke, both in an area of elevated Coulomb stress. The seismicity shows a complex propagation of the dyke, which started at its northern end, migrated southwestward and then jumped back to the central part where the effusive eruption took place. The observed N-S striking focal mechanisms are interpreted as right-lateral antithetic Riedel shears that accommodate the left lateral slip along the oblique plate boundary. The co-existence of seismic and magmatic activity suggests that the past seismic activity weakened the crust in the eruption site area, where magma accumulated. The following ML 5.3 earthquake of 24 February 2021 triggered the seismic swarm and likely perturbed the magma pocket which led to the six-months lasting eruption that started on 19 March.

Latest Triassic and Late Jurassic extensional tectonics of the Sulu UHP orogenic belt, East China: Evidence from geological and geophysical data

To understand the post-orogenic tectonics related to collision between the North China Craton (NCC) and the South China Block (SCB), the Northern Sulu massif is a representative area. It experienced a complex evolution marked by exhumation of ultra-high-pressure metamorphism rocks, migmatization, and alkaline magmatism in the Latest Triassic, and felsic magmatism in the Late Jurassic. In this contribution, we carried out a combined study including structural analysis, anisotropy of magnetic susceptibility (AMS), and gravity survey on the Northern Sulu massif. According to our structural analysis, it is interpreted as an extensional dome, exhibiting dominantly SE-dipping foliations in its east and center and NW-dipping ones closer to its northwestern margin, NW-SE mineral and stretching lineations, and top-to-the-NW kinematics. The Latest Triassic pyroxene syenite has dominantly SE-dipping mesoscopic/magnetic foliations, NW-SE magnetic lineations, and wedge shape at depth, and the Latest Triassic quartz syenite has variable magnetic fabric. Considering geometric relations of plutons and country rocks, the former is a “syn-kinematic” pluton, while the latter post-dates the regional tectonics, constraining the timing of the top-to-the-NW shearing at 220–210 Ma. Compared with the syn-orogenic tectonic events, the Latest Triassic ductile deformation points to a NW-SE extension related to lithospheric delamination. Late Jurassic isotropic monzogranite is characterized by “onion-skin” magnetic foliations with NE-SW trending magnetic lineations, and NE- or SW-ward decrease of thickness at depth. On the basis of regional understanding, we link its emplacement with the Late Jurassic NE-SW extensional tectonics attributed to the oblique subduction of the Paleo-Pacific plate. Such two episodes of crustal extensions with magmatism reformed the crustal architecture of the SE-margin of the NCC, which considerably facilitated stress-transmission from plate-boundary to intraplate during the development of subsequent Late Mesozoic intracontinental deformations.

New insights on the tectonic framework using EIGEN6C4 gravity data, seismicity, and finite element stress analysis: An attempt to map earthquake vulnerable zones in parts of North-East India and surroundings

Shillong Plateau and its surroundings experience frequent seismic activities characterised by the complex tectonic setup covering different parts of the Eastern Himalaya, Indo-Burma ranges and their conflux at the Assam syntaxis; which need further multivariate investigations. The present study deals with a combined analysis of EIGEN6C4 Bouguer gravity data, 56 years (1964–2020) seismicity data, 11 stations GPS velocity data (1996–2015) and focal mechanism of twelve earthquake events (1996–2017). We have enhanced Bouguer gravity data using the Theta derivative. Upward continuations of the Bouguer gravity were estimated at the heights of 5 km, 10 km, 20 km, 40 km, 60 km, and 100 km, which helped to infer the approximate persistent depth of the structures. Theta derivatives for the upward continued maps have also been estimated to enhance structures and fault zones at different approximated depths. Large numbers of smaller lineaments and shallow crustal smaller blocks are delineated at ∼2.5 km depth, whereas medium grade lineaments are mostly limited within the depth range of 2.5–25 km. However, relatively longer crustal-scale lineaments are highlighted at a greater depth of ∼30 km or more. Euler depth solutions of Bouguer gravity indicate a density heterogeneity interface in the depth range of 12–23 km that corroborates well with upward continuation results and past seismicity data. We have estimated Moho depth using the Parker-Oldenburg algorithm from the Bouguer gravity data. It delineates nine thin crustal structural features (S1–S9), twelve thick crustal structural features (D1-D12) and eleven crustal-scale lineaments (L1-L11) based on the distinct variations of Moho depths and their extensions. The b-value analysis indicates the highest order of b-value in the 15–30 km depth range, mainly in Mikir hill (∼1.7), the eastern part of Shillong Plateau (1.5) and the Indo-Burma ranges (2.3) that perhaps correlate well with the heterogeneity interface delineated by Euler depth solutions. The Eastern Himalaya generally exhibits characteristic low-Bouguer anomaly, high lineament density, low to moderate b-value, and deep-Moho/thick crust. The seismic stress model estimated using the finite element approach exhibits higher-order stress (∼34 MPa) around the central part of Shillong Plateau and at the northern part of Mikir hill with an SW-NE trend. Seismic stress correlates well with the regional lineament trend, GPS velocity/strain direction and low b-value, the joint analysis help to delineate a possible zone of future large earthquakes.

Digital geologic map, petrography and U-Pb geochronology of the Río Santiago Shear Zone, southernmost Sierra Madre Occidental, western Mexico

The boundary between the Sierra Madre Occidental (SMO) and the Trans-Mexican Volcanic Belt (TMVB) is well exposed along the Santiago River, on the border of the states of Nayarit and Jalisco. This region includes a polydeformed belt produced by the relative motion between the Jalisco Block and the SMO, here defined as the “Rio Santiago Shear Zone” (RSSZ). In this work, we present detailed geological cartography, petrographic descriptions, and new zircon U-Pb ages that allow us to establish the stratigraphy of the region surrounding the RSSZ, providing temporal constraints to its tectonic evolution. In the mapped area, the base of the SMO stratigraphic column consists of a succession of massive andesitic lava flows intruded by felsic dikes and a felsic subvolcanic body of 27.5 and 27.2 Ma, and it is covered by a series of ignimbrites of 26.8 and 25.3 Ma. A red beds succession separates a second package of ignimbrites of ∼20-19 Ma, in turn capped by rhyolitic lava domes of 19.7 and 18.6 Ma and a rhyodacitic lava flows of 15.6 Ma, this Miocene succession is also intruded by a felsic body of 18.3 Ma west of the La Yesca dam. The SMO succession is covered by rocks belonging to the bimodal volcanism of the TMVB, emplaced between the end of the Miocene and the Pleistocene. The RSSZ developed through several deformation phases that occurred since the end of the Oligocene. The Oligocene succession of the SMO is affected by NE-SW and WNW-ESE trending lateral faults, NW-SE open folds and WNW-ESE and E-W trending reverse oblique faults. Some of the reverse oblique faults were later reactivated as normal faults. WNW-ESE trending normal faults associated with the Tepic-Zacoalco Rift affected the area south of the Santiago River during the Pliocene and Pleistocene. Normal faulting produced an accumulated vertical offset up to 700 m between the northern and southern regions of the Santiago River.

Excess Lifetime Cancer Risk Associated with Granite Bearing Radioactive Minerals and Valuable Metals, Monqul Area, North Eastern Desert, Egypt.

The present work is concerned with assessing the cancer risk contributed by the studied granite types including valuable metals, such as Cu, Au, and Ba mineralization, as well as radioactive-bearing mineralization, such as monazite and zircon, in south Monqul at Wadi Makhrag El Ebel, north Eastern Desert, Egypt. The mineralization analyses illustrated that copper mineralization containing chrysocolla and tenorite minerals were restricted to the alteration zone, especially (argillic, phyllic, and propylitic) in monzogranite. However, barite veinlets had an ENE–WSW trend, while gold mineralization was confined to quartz veins having NE–SW trends. Monazite and zircon are radioactive-bearing minerals recorded in monzogranite causing high radioactive zones in south Monqul. The radionuclide activity concentrations were detected in the studied monzogranites. The mean values of AU (103 ± 91 Bq kg−1), ATh (78 ± 19 Bq kg−1), and AK (1484 ± 334 Bq kg−1) in the monzogranite samples were higher than the recommended worldwide average. The change in radioactive-transporting minerals found inside granite faults caused the high amounts of radioactivity seen in the samples. Due to the monzogranites being applied in building materials, the radiological hazards were assessed by calculating risk indices such as annual effective dose (AED) and excess lifetime cancer risk (ELCR). The acceptable limit for the ELCR readings was surpassed. As a result, the investigated monzogranite samples are not suitable for use in infrastructure materials.

Comparative analysis of the structural pattern over the Indian Ocean basins using EIGEN6C4 Bouguer gravity data

The Indian Ocean witnessed numerous seismic and tectonic activities, making the region an intricate seismotectonic and seismo-genesis potential zone. The high-resolution global satellite-derived Bouguer Gravity Anomaly (BGA) data was used for comparative analysis of the structural patterns of six Indian Ocean basins. THETA (TA) edge enhancement and upward continuation techniques were used to study the Indian Ocean crustal structure by mapping both short and longwave lineaments. Rayleigh wave group velocity (RWGV) tomography at different time periods indicates pseudo depths of ∼30 km and ∼50 km are suitable for the upward continuation (UC) of BGA that perhaps lead to understanding different contrasting boundaries in their TA map. The UC of the BGA was generated at 60 km and 100 km for highlighting different lineaments/structures/contrasting geological boundaries at the depths of about 30 km and 50 km. The orientation of TA lineaments shows NNE-SSW, NE-SW, and EES-WWN structural trends. The statistical analysis of the lineaments shows that the Mid-Indian Basin constitutes the highest values of lineament number, lineament density (LD), circular variance (CV) and circular standard deviation (CSD), indicating a slow tectonic deformation over a long period. The Somalian Basin shows the minimum lineament number and lowest LD with high values of CV and CSD, indicating a relatively stable tectonic set-up compared to other Indian Ocean basins. The Arabian and Bay of Bengal basins offer relatively low lineament statistics than the Mid-Indian, Wharton and Madagascar basins, indicating frequent tectonic activity.

Stress distribution in the western India-Eurasia collision zone, its kinematics and seismotectonic implications

In this study, we use iterative joint stress inversion technique on a declustered catalogue of 324 focal mechanisms to evaluate the stress distribution in the western India-Eurasia collision zone (IECZ). The stress field has been obtained for different tectonic settings, such as the Himalayan Seismic belt, Karakoram-Tibet region and the individual zones identified based on geology, tectonics and available focal mechanism solutions. The results reveal NE-SW trending principal stress (σ1) with compression for Himalayan seismic belt and strike-slip stress regime for Karakoram-Tibet. We observe that even within the Himalayan region, the western region (75°-77° E latitudes) exhibits arc-oblique compression (NE-SW) in contrast to the arc-normal compression (NNE-SSW) in central Himalaya beyond 77°E; consistent with GPS vectors. The Stress field for the aftershock sequence of 2005 Kashmir earthquake in the Hazara Syntaxis region displays dissimilarity with its adjoining regions (Pamir, Nanga Parbat, Hindukush, etc.), but exhibits similarity with the Central Himalaya. Within the Karakoram-Tibet region, the Karakoram fault exhibits NNE-SSW oriented principal stress with transpressional fault motion, while the Kaurik Chango rift shows N-S oriented principal stress with transtensional motion. The stress ratio in the western IECZ broadly varies between 0.07 and 0.9, suggesting the prominent role of the intermediate stress axis (σ2) in the areas of low-stress ratios. The inferences drawn suggest that the stress distribution in the western IECZ is heterogeneous with variable seismic hazard.

The buried Variscan granites and associated structures in the High Moulouya basin from gravity data and their role during the Triassic-Liassic extensional tectonics (Moroccan Meseta-Atlas domain).

The High Moulouya Basin (HMB) occupies a key location between the Southern Middle Atlas and the Central High Atlas. Gravity data from the HMB show the presence of three gravity lows. Borehole data show a thin Meso-Cenozoic cover in the HMB that eliminates the possibility that these lows are due to sedimentary rocks. The gravity anomalies may therefore be related to hidden granitic bodies within the Paleozoic basement. In order to map these granite bodies and associated structures, gravity data sets were processed and enhanced using various mathematical techniques, transformations, and 2D gravity modeling. The following were either better defined or revealed: i) The High Moulouya Batholith is a large NE-SW trending batholith that crops out partially in the Aouli-Mibladen and Boumia Paleozoic inliers. Our study shows the continuity of this batholith with a 90 km long and 30 km wide granitic structure. ii) The Hidden Engil granite is a subcircular, relatively small granite body (20 × 18 km) located at the Middle Atlas's eastern boundary. The hidden granite of Zebzat (30 × 10 km) represents a narrow E-W trending pluton bounded by the High Atlas tectonic structures on its southern boundary. The tectonic influence of these granite bodies may explain, to some extent, the stability of the HMB throughout the development of the Atlasic subsiding basins. The two Atlas basins are separated by the High Moulouya granite-cored intrabasinal high. As shown by the horizontal gradient and Euler deconvolution methods, during Triassic-Liassic NW-SE extensional events, the formation of the Middle and High Atlas basins was guided by Variscan inherited faults bounding the granitic bodies of the HMB. The main factors responsible for the formation of the High Moulouya granite-cored intrabasinal high are the isostatic compensation that follows the granite emplacement during the Variscan orogeny, the distribution of strain and deformation around the granite bodies during the Triassic-Liassic extensional tectonics and their concomitant buoyancy forces.

Mapping the possible origin of anomalous saline water occurrence in Agbabu, Eastern Dahomey Basin, Nigeria: insights from geophysical and hydrochemical methods

Many researchers have suspected saltwater occurrence in Agbabu in the eastern Dahomey Basin. However, there is a need to get an insight to the possible origin of saltwater in the area. The aim of this study is to determine the source of saltwater in the inland aquifers of Agbabu, southwestern Nigeria for proper management of scarcely available freshwater resource in the area. 23 vertical electrical sounding, 2D electrical resistivity tomography (ERT), aeromagnetic and hydrochemical data (11 subsurface water samples) analyses were utilized in this study. The results from the magnetic analysis revealed the inland extension of the Chain Fracture Zone (CFZ). This NE-SW trending fracture zone cuts across the entire eastern Dahomey Basin, including Agbabu and its environs. Four (4) geoelectric layers were delineated across Agbabu namely, the topsoil (4 - 2806 Ωm), clayey sand (3 - 1280 Ωm), clayey (3 - 161 Ωm) and bituminous sand (1 - 10390 Ωm) layers. Anomalously low resistivity (1 - 20 Ωm) zones suspected within the bituminous sand correspond to the saltwater intrusion zones. The bituminous sand unit harbouring freshwater exhibits characteristic resistivity values of 33 – 160 Ωm. The interface between the freshwater and saltwater intruded zones in the area was suspected at 10 m depth with resistivity values ranging between 21 Ωm and 33 Ωm. The results from the hydrochemical water analysis also confirmed the presence of saltwater intrusion in the area. The salinity extent chart which was generated from the VES results indicated the mobility of the saltwater into the groundwater system. The fracture connectivity between the complex aquifers of Agbabu and the Atlantic Ocean (CFZ), that was mapped from the aeromagnetic and electrical resistivity results, is suspected to be primarily controlling the localization of saltwater in the study area.

Structural and mineral exploration study at the transition zone between the North and the Central Eastern Desert, Egypt, using airborne magnetic and gamma-ray spectrometric data

The transition zone between the North and the Central Eastern Desert of Egypt has been investigated using airborne magnetic and radiometric data to better characterize the subsurface structures, the tectonic framework, and mineral occurrences in the area. The magnetic data were subjected to several filtering and depth estimation techniques including edge detectors, Euler deconvolution, 2D forward modeling and 3D inversion. Statistical trend analysis of the lineaments obtained from geological and filtered magnetic maps shows that the major tectonic trends are NNE–SSW, NE–SW, and NW–SE, in addition to less predominant ENE–WSW and N–S trends. Two parallel shear zones trending NE–SW were detected. The causative magnetic structures were imaged at depths varying from the surface down to 2200 m. A number of strong uranium anomalies associated with Younger Granites and Dakhla, Duwi, and Quseir formations were identified which are worth being considered for further ground investigations.

An integrated evaluation approach on dry hole analysis: A case study of Ballat anticline, Naccowlah Block, Eromanga Basin, Queensland, Australia

This study is based on an integrated investigation of seismic, well log, geological and geochemical data, the detailed analysis of source, reservoir, and structures were conducted in the Naccowlah Block, Eromanga Basin, Queensland, Australia. The Naccowlah Block is one of the most important hydrocarbons producing areas centered in Eromanga Basin, with several producing wells, except Ballat‐01 and Chilla‐01. This study pertains specifically to the Ballat structure, which was declared dry. The purpose of this research is to evaluate and identify specific ‘Dry Hole’ failure, based on analysis of several factors: reservoir deliverability, source maturity, migration, and structural presence. 3D seismic data revealed NE–SW trending series of reverse faulting mainly conquered by four‐way dip closure due to compressional tectonics in the study area. The burial history and event chart depict the preservation and maturation of potential source rock, which is furthermore affirmed by the vitrinite reflectance curve. Interpreted regional migration model and structural analysis of Naccowlah Block stated the presence of a suitable structure for hydrocarbon generation and migration pathways. Despite all favourable aspects for the accumulation of hydrocarbon in Hutton sandstone, the structural restoration analysis proves the absence of trap at the time of migration and accumulation. However, geophysical, geological, and geochemical shreds of evidence suggest that the spatial distribution of the events provides valuable guidance for the development of the area.

Tectonic and oceanographic controls on the slope-confined dendritic canyon system in the Dongsha Slope, South China Sea

Dendritic canyon system is the most widespread type of submarine canyons along continental margins and plays important roles in sediment delivery and deep-water ecosystem. Based on high-resolution multibeam bathymetric and seismic reflection data, this study investigates a slope-confined dendritic canyon system in the Dongsha Slope, South China Sea. The dendritic canyon system between water depths of 550–2200 m consists of one main canyon (C2) and three V-shaped tributaries (C1, C3, and C4), in association with clearly visible tectonic deformation (uplifting and faulting) at the upper segment. The main canyon is characterized by a concave-up longitudinal profile, while the tributaries show convex-up and/or linear profiles, probably indicating that they are affected by tectonic deformation to variable degrees. The alignments and locations of tributaries C3 and C4 are determined by the NE-SW trending faults, while the distribution of the tributary C1 and the upper segment of C2 is less affected by faults, which also indicates that tectonic controls on the dendritic canyon system vary spatially among tributaries. Widespread NE-SW oriented sediment waves and southeast-facing scarps and isolated scour depressions at canyon banks highlight the significant influence of northwestward-propagating internal tide/wave on the morpho-sedimentary processes. The internal tides/waves within canyons not only flushed canyon floor, but also contributed to the asymmetric distribution of sidewall gullies and failures. The obliquely shoaling internal waves, combined with other hydrodynamics (e.g., Kuroshio Current and mesoscale eddies), could significantly intensify along-slope bottom currents and erode the NE-SW-oriented trough and tributaries. Under the significant erosion of ocean currents, some of the sidewall gullies, troughs and sub-tributaries may finally evolve into new tributaries. This study reveals the coupling relationship between slope-confined dendritic canyon system and tectonic/oceanographic processes, which can shed light on the slope/canyon evolution of similar settings worldwide.

Aeromagnetic investigation of crustal stability of Osi, north central Nigeri

High-resolution aeromagnetic data of Osi north central Nigeria has been processed with a view to establish the earthquake-prone fault zones in the area. The analytical signal amplitude, shaded relief total horizontal derivative, first vertical derivative and 3D Euler deconvolution maps produced from the residual magnetic intensity anomalies of the study area identified the structural features in the area. The locations and the orientations of the extracted magnetic lineaments were revealed by the structural map of the area and the associated rose diagram. The lineaments were observed to strike NE-SW, ENE-WSW, E-W, NW-SE, WNW-ESE, NNE-SSW and NNW-SSE. The upward continuation maps showed evidence of deep-lying faults while the source parameter imaging and spectral analysis revealed depth to magnetic sources ranging from 81 m to 402 m and 103 m to 460 m respectively. The predominant NE-SW and NNE-SSW trending faults in the study area depicted stress history related to Ifewara faults; which is an indication of possible impending earthquake occurrence in the area.