NW-SE Trending Research Articles

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

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

Hydrocarbon microseepages in the kerkennah islands, Eastern Tunisia: Integrated surface geochemical and geoelectrical prospecting approaches

Oil exploration is usually carried out using conventional techniques such as seismic reflection and exploratory drilling. However, these techniques are very costly with a high risk of dry holes or failure to find commercial quantities of hydrocarbons. Here we aim to evaluate surface geochemical prospection (SPG) methods which serve as preliminary step to derisk an area by exploring hydrocarbon micro-seeps. This approach helps to identify potential areas of interest when you have limited amount of money to explore a given area. This paper reports on surface gas micro-seepages in the Kerkennah archipelago, part of the Tunisian Pelagian Platform. 33 gas and soil samples were collected on a 1 × 1 km grid over Chergui Island. Both free gas and adsorbed soil gas techniques were used. Free hydrocarbon gas concentrations ranged from 0 to 21 ppm. Adsorbed gases showed concentrations up to 11 ppm. The presence of all light hydrocarbon gas components from methane to pentane, the values of the gas ratios C1/C2, C1/ΣC2+, (C3/C1) x 1000 and C1/(C2 + C3), and the Pixler and triangular diagrams together indicate that these gases are of thermogenic origin and have migrated from subsurface accumulations. Anomalous concentrations of hydrocarbon gases occurred in the middle and west of the study area. Both free and adsorbed gas anomalies have the same planar shape and form linear anomalies with a NW-SE trend. This orientation corresponds to that of the major fault system affecting the Kerkennah archipelago. Subsequent independent VES surveys and re-interpreted seismic lines confirmed the presence of a surface fault as suggested by the surface gas anomalies. In conclusion, our study has confirmed the presence of thermogenic hydrocarbon gas microseepage to the surface. The gases are interpreted to have migrated to the surface along faults. SPG methods were thus able to identify active hydrocarbon migration and can be considered as a useful low-cost approach to hydrocarbon exploration.

Structural inheritances, fault segmentation and seismogenic potential at the front of the eastern Southern Alps (central Carnic Prealps, NE Italy)

New geological and morphotectonic surface data coupled with the revision of the ENI-Exploration & Production seismic lines, made it possible to review the tectonic structure of the Pliocene-Quaternary front of the eastern Southern Alps in the area between the Cellina River and the Tagliamento River (central Carnic Prealps, NE Italy). The eastern Southern Alps are a SE-verging fold and thrust belt in activity from the middle Miocene to the Present. The presence of Paleogene structural inheritances influenced the current structural arrangement of the thrust-belt and the potential seismogenesis, supporting segmentation of the Neoalpine external front. In particular, the presence of the NW-SE trending Mt.Ciaurlec – Palmanova – Pozzuolo structural high, inherited from the W-ward propagation of the External Dinarides during Paleogene, generated lateral lithological facies change and influenced not only the undulation between the Neogene-Quaternary Maniago-Meduno and Toppo-Forgaria Thrusts, but also the segmentation of the outermost portion of the Neoalpine external front consisting into two segments with different geometric and structural characteristics: 1) the ENE-WSW striking Arba-Sequals segment that runs buried under the upper Pleistocene sequences of the piedmont Friuli plain; 2) the W-E Ragogna segment that shows widespread evidence of surface deformation of the Last Glacial Maximum (LGM) alluvial plain. In particular, the long-lasting activity of the Ragogna segment is testified by the late Miocene-Middle Pleistocene angular unconformities, forced drainage anomalies and tilted and uplifted Quaternary palaeosurfaces. A discussion on the seismogenic potential of the investigated structures is proposed.

Late Pleistocene Fault Slip Rate within the Bole Basin: Insights into deformation kinematics in the Central Tian Shan

Tian Shan is a vast and highly seismically active intracontinental mountain range. GPS measurements and field studies have shown that E-W and NW-SE trending thrusts and fault-related folds are distributed across central Tian Shan. However, few studies have determined the fault and fault-related-fold activity in the Bole Basin, the northernmost part of central Tian Shan. In this study, we focus on the Alashak Fold, which is situated along the southern margin of the Bole Basin. Using high-resolution uncrewed aerial vehicle-Digital Elevation Model data, field observations, and detailed mapping, we determined that the Alashak Fold is characterized by a trishear fault-propagation fold. Along the Alashak River, we identified five levels of fluvial surfaces, the T3 terrace was continuously preserved across the fold. Radiocarbon and surficial 10Be dating were used to determine the exposure age of the deformed T3 terrace. The folding characteristics of T3, trishear inversed modeling, and abandonment age indicate that the Alashak Fault has an uplift rate of 0.8 ± 0.3 mm/yr, a dip-slip rate of 4.2 ± 1.2 mm/yr, and a crustal shortening rate of 4.0 ± 1.2 mm/yr since the late Pleistocene, respectively. The Alashak and Latgan Faults intersect at a depth of 1.2 km, enclosing a wedge-shaped block. Our study emphasizes that tectonic activity along the southern margin of the Bole Basin has played a significant role in north-south shortening within central Tian Shan, as measured by geological measurements since the late Pleistocene. The Alashak Fault can potentially generate moderate–strong (Mw 5.0–7.0) earthquakes, while the Alashak and Latgan Faults can generate major (Mw 7.2) earthquakes.

Fluvial geomorphic parameters of the Shuiluo River Catchment and their tectonic implications, SE Tibetan Plateau

The Shuiluo River Catchment (SRC) is the front zone of the southeast compression and uplift of the Tibetan Plateau, with intense tectonic activity. In the basin, a series of regional large NW–SE trending active faults are developed. Studying clearly the geomorphic evolution of the SRC is conducive to further understanding the uplift and expansion mechanism of the SE edge of Tibetan Plateau. Our research was based on geographic information system, numerical analysis tool, and digital elevation model data, to extract six geomorpic parameters (hypsometric integral, asymmetry factor, basin shape ratio, valley floor width–valley height ratio, normalized channel steepness index and index of relative active tectonics) in SRC. After eliminating the impacts of climate, catchments area, and glacier, the geomorphic evolution of the SRC is mainly affected by geological structure and differential tectonic uplift movement; in the upstream and midstream (upper part), the shape of valleys and stream longitudinal profile shapes are affected by lithology; affected by geological structure and tectonic uplift, the tectonic activity in the midstream and downstream is relatively strong, and the intensity of activity in the downstream is stronger than that in the midstream, which may suggest that the faults’ activity in the downstream is stronger; the index of relative active tectonics values of the SRC are consistent with the regional seismic intensity, field-work and low-temperature thermochronology which indicates it is reasonable to use the fluvial geomorphic parameters to study the regional geomorphic evolution. The morphological parameters we extracted show different values in different regions of SRC, which may be the result of differential uplift in the southeastern of the Tibetan Plateau.

The 2013 Mw 6.2 Shonbeh (Kaki) earthquake (Zagros-Iran): seismo-tectonic implications for the Kazerun shear transition zone from high-resolution aftershock and InSAR data analysis

SUMMARY The aim of this study is to investigate the aftershock sequence data recorded by a dense temporary seismological network deployed in the epicentral area of the 2013 April 9 Shonbeh (Kaki) earthquake, located in the south of the Simply Folded Belt of the Zagros (Iran). For a comprehensive understanding, coseismic displacements of the Shonbeh earthquake have been investigated using Interferometric Synthetic Aperture Radar (InSAR) data. The epicentral distribution of high-resolution relocated aftershocks shows NW–SE and N–S trending of seismicity. The aftershocks are confined between ∼3 and ∼14 km depth, which implies that the rupture occurred mostly within the sedimentary cover beside the fault parameters retrieved from InSAR modelling. Projection of precisely located aftershocks on NE-oriented section and InSAR ground displacement data are consistent with both NW-trending NE- and SW-dipping fault segments. We observe a NNW–SSE right-lateral strike-slip motions that accommodate oblique convergence and differential motion between the North and Central Zagros. The spatial pattern and focal mechanisms of aftershocks are consistent with a distributed deformation between NW–SE trending reverse and N–S trending right-lateral strike-slip fault segments in the south of the Kazerun transition zone that accommodates a wide shear zone.

Evaluation of the environmental and structural impacts on urban expansion using airborne geophysical data at Hurghada city, Northern Eastern Desert, Egypt.

Airborne gamma-ray spectrometric and magnetic data were processed and interpreted aiming to evaluate the environmental and structural impacts on urban expansion, Hurghada City, Northern Eastern Desert, Egypt. The eastern (coastal area), northern, and southeastern parts of the study area possess the lowest level of absorbed dose rate (ADR) and annual effective dose equivalent (AEDE), which were estimated from the airborne gamma-ray spectral data of this area. Consequently, these parts are considered as suitable sites for urban expansion from the radioactivity point of view. The relatively high level of ADR and AEDE is associated with granitic rocks, some parts of Gabir formation and recent Wadi sediments, situated at southwestern, central, and eastern parts of the study area. The ADR and AEDE of these parts are considered harmful to individuals. Airborne magnetic data were also used to detect major structures that may affect various construction projects in the study area in the future. The NNW-SSE, NW-SE, N-S, and NE-SW trends represent the common structures in the study area. The obtained results of airborne gamma-ray spectrometric and magnetic data illustrated that the urban expansion should not be constructed to the west of the ring road. However, site investigations must be carried out on this part of the study area before starting any construction projects there. The present study proved the important role of airborne gamma-ray spectrometric and magnetic surveys as useful tools to delineate the environmental and structural impacts on urban expansion.

Estimation of surface deformation in Sikkim and Eastern Nepal Himalaya using PSInSAR technique

The region of the Himalayan arc covering Sikkim and eastern Nepal experiences dominant strike-slip deformation oblique to the convergence direction of the Indian plate. This region is also traversed by transverse structural and tectonic features. The present study is aimed at comprehending the horizontal and vertical deformation rates for this region using the PSInSAR technique. We utilized 70 and 78 Single Look Complex images in ascending and descending passes respectively, spanning from February 2017 to August 2023 for time-series displacement measurement along the radar line of sight (LOS). The results reveal the LOS velocity ranging from −15 to +10 mm/yr for the ascending data and ±20 mm/yr for the descending data. The mean line-of-sight velocities of ascending and descending passes were decomposed to estimate the horizontal (east-west) and vertical components of the deformation vector. These components range from ±15 mm/yr and −12 to +8 mm/yr, respectively, suggesting that the horizontal deformation predominates in the study area. A NW-SE trending boundary coinciding with the Tista lineament sub-divides the study region into the eastern Nepal and the Sikkim blocks based on the patterns of the deformation rates. The eastern Nepal block south of the Main Central Thrust exhibits locked portion of the arc with eastward motion, whereas the Sikkim block exhibits uplift (unlocked with creep) and westward motion. The amplitudes of these deformation rates support dominant strike-slip deformation with minor vertical deformation component. These results suggest that the Tista lineament is a prominent strike-slip fault and probably the most significant active tectonic feature in the region. Together with the seismicity data, we infer that probably the entire crustal block rather than the Himalayan wedge is contributing to the surface deformation, as mapped by the present PSInSAR study.

Lithospheric electrical structure of the Alxa Block, NW China, southern central Asian Orogenic Belt, revealed by 2D inversion of magnetotelluric data

The Alxa Block, situated between the Tarim and North China cratons, is essential to understand the tectonics of northwest China. It has undergone several tectonic cycles, including rifting from northern Gondwana in Neoproterozoic, subduction-accretion of the Paleo-Asian Ocean during Paleozoic, and intracontinental deformation in Mesozoic. Broadband magnetotelluric data covering a frequency range of 320 Hz to ∼ 10000 s was collected along two NW-SE trending lines across major tectonic units of the Alxa region to investigate the deep structures of the Alxa Block. By applying the nonlinear conjugate gradient (NLCG) inversion approach, two-dimensional (2D) electrical resistivity models were obtained at a 100 km depth. These findings indicate that the Zhusileng-Hangwula and Zongnaishan-Shalazhashan tectonic zones have high resistivity in their lower crust and upper mantle, with an overall layered high-low–high resistivity pattern. The upper crust of the Nuru-Langshan tectonic zone is primarily characterized by high resistivity values, whereas the lower crust and upper mantle contain a large-scale low-resistivity (or conductive) zone that is likely the result of partial melting. The large-scale Early–Middle Jurassic nappe structures may be connected to sub-horizontal low-resistivity anomalies in the shallow strata, which are located up to 20 km below the Yagan and Zhusileng–Hangwula tectonic zones. Below the Engger Us fault, two low-resistivity bands are interpreted as the product of bidirectional subduction and final closure of the Paleo-Asian Ocean. The Alxa Block may have subducted southwards beneath the Ordos Block, as suggested by a clear low-resistivity anomaly between the two blocks. Furthermore, partial melting may have happened for high-conductivity bodies in the upper mantle based on the modified Archie formula’s evaluation of their melting degree.

Lithology and subsurface structures related to gold mineralisation in the Kibati prospect, Mozambique belt in eastern Tanzania, with implications for gold exploration

This paper provides an insight into the structures, lithologies, and potential zones and their relationships to gold mineralisation that were investigated to decipher the controls of gold mineralisation at the Kibati Gold Prospect within the Mozambique Belt. Although the Kibati area is located within the gold mineralised zone, lithology and subsurface geological structures associated with gold mineralisation are not well studied. The available high-resolution aeromagnetic data have not yet also been analysed and interpreted to derive geological features that are useful in mineral exploration. The investigation of the structures and lithologies was accomplished through integrated interpretation of high-resolution aeromagnetic data, ground magnetic data, geological mapping, and rock sampling. Aeromagnetic and ground magnetic results reveal the presence of two structural systems, which were previously not identified that trend in NW–SE and NE–SW, with the NW–SE being the dominant control of gold mineralisation. The subsurface structure with NW–SE trending controls the mineralised fluids as a consequence of gold mineralisation in the surface lithologies. Petrography and geological mapping show that granitic gneiss, garnet-biotite quartzo-feldspathic gneiss, dolerite, and amphibolite are the main exposed outcrops where the first two identified types of gneisses, based on their protolith, were previously not specified. Based on the gold assay results, which are persistent and collinear to the structural trend of NW–SE picked out by magnetic data, two (2) potential blocks (A and B) were identified. The trend of the structure in blocks A and B when overlaid with gold anomalies indicates that most of the gold concentrations are located in block B and the highest value of gold concentrations is located in block A where gold values range from 10.19 to 19.680 g/t in block A and 0.0623 to 4.419 g/t in block B. The difference in gold values between blocks A and B is due to the variation in the degree of alteration. The integration of the results indicates that the gold mineralisation in the Kibati area is structurally controlled and concentrated in shear zones. The findings therefore, indicate that the Mozambique Belt is potential for gold mineralisation and provide a warrant for future plan for gold exploration.

Petrology and Geochemistry of the Ultramafic Rocks of Yerrabali Schist Belt, Eastern Dharwar Craton, Telangana, India

Abstract The Yerrabali schist Belt (YSB) is a NW–SE trending 10 km long and 4 km wide belt located at the north eastern corner of Eastern Dharwar Craton (EDC) consisting of Banded Magnetite Quartzite (BMQ), ultramafic rocks, quartz–cordierite– gedrite ± garnet bearing schist, sillimanite–garnet–cordierite schist, metadolomite, amphibolite, ferruginous quartzite, tremolite schist and dolerite dyke. The ultramafic rocks consist of olivine, orthopyroxene, clinopyroxene and spinel. The Fe content of olivine varies from 88-91 and consists of high amount of NiO (0.3-0.511%). Orthopyroxone are enstatitic and clinopyroxene are Mg-augite in nature. The spinel grains are rich in Al2O3 (48.32-59.09%) and show very low Cr# values (0.08-0.29). Thermo-barometric analyses show equilibrium condition of 700°-1100°C temperature and 19-21 kb pressure. Oxygen fugacity of the ultramafic rocks range from -0.035 to -1.356 log units below FMQ buffer. Low Cr# values of spinel along with low oxygen fugacity suggest their formation by low degrees of partial melting from a less refractory Mid Oceanic Ridge (MOR) type mantle.

Investigating Earth surface deformation with SAR interferometry and geomodeling in the transborder Meuse–Rhine region

Introduction: This study aims to differentiate local and regional ground uplift, as well as sub-regional subsidence induced by groundwater level drawdown, which are possibly enhanced across fault structures, as monitored by various synthetic aperture radar interferometry (InSAR) processing methods. A buoyant mantle plume under the Eifel may be responsible for the regional ground uplift, including the Weser–Geul (BE) and South Limburg regions (NL), which could negatively affect the area proposed for the future Einstein Telescope.Methods: Different InSAR processing techniques are compared to evaluate their limits in tracking fault structures on a time series of Copernicus Sentinel-1 images while detecting and measuring ground motion based on their phase signature. The results present an overall stable ground for the Euregio Meuse–Rhine region, especially at the Belgian–Dutch border, while tectonic activity is observed along the German side of the Rhine Graben.Results: As the current neotectonic activity in the target area was not well known, we performed a spatiotemporal analysis of ground deformation associated with the presence of NW–SE-trending normal faults where karst also develops, as well as along the Variscan NE–SW-trending thrust faults. This work demonstrates that the identification of deformation hazards using satellite remote sensing (and connected seismological) techniques is challenging mainly due to (very) small regional scale deformation, terrain conditions, and SAR properties.Discussion: Thus, the results mostly indicate ground stability over the area; however, also some agricultural activities were observed, as was deformation along some infrastructure such as railways. Displacements of millimetric order measured along the faults located near the Geul valley (BE) are probably related to old mining activities.

Salinity Fronts in the South Atlantic

Monthly climatology data for salinity fronts in the South Atlantic have been created from satellite SMOS sea surface salinity (SSS) measurements taken from 2011–2019, processed at the Barcelona Expert Center of Remote Sensing (BEC), and provided as high-resolution (1/20°) daily SSS data. The SSS fronts have been identified with narrow zones of enhanced horizontal gradient magnitude (GM) of SSS, computed using the Belkin–O’Reilly algorithm (BOA). The SSS gradient fields generated by the BOA have been log-transformed to facilitate feature recognition. The log-transformation of SSS gradients markedly improved the visual contrast of gradient maps, which in turn allowed new features to be revealed and previously known features to be documented with a monthly temporal resolution and a mesoscale (~100 km) spatial resolution. Monthly climatologies were generated and analyzed for large-scale open-ocean SSS fronts and for low-salinity regions maintained by the Rio de la Plata discharge, Magellan Strait outflow, Congo River discharge, and Benguela Upwelling. A 2000 km-long triangular area between Africa and Brazil was found to be filled with regular quasi-meridional mesoscale striations that form a giant ripple field with a 100 km wave length. South of the Tropical Front, within the subtropical high-salinity pool, a trans-ocean quasi-zonal narrow linear belt of meridional SSS maximum (Smax) was documented. The meridional Smax belt shifts north–south seasonally while retaining its well-defined linear morphology, which is suggestive of a yet unidentified mechanism that maintains this feature. The Subtropical Frontal Zone (STFZ) consists of two tenuously connected fronts, western and eastern. The Brazil Current Front (BCF) extends SE between 40 and 45°S to join the subantarctic front (SAF). The STFZ trends NW–SE across the South Atlantic, seemingly merging with the SAF/BCF south of Africa to form a single front between 40 and 45°S. In the SW Atlantic, the Rio de la Plata plume migrates seasonally, expanding northward in winter (June–July) from 39°S into the South Brazilian Bight, up to Cabo Frio (23°S) and beyond. The inner Plata front moves in and out seasonally. Farther south, the Magellan Strait outflow expands northward in winter (June–July) from 53°S up to 39–40°S to nearly join the Plata outflow. In the SE Atlantic, the Congo River plume spreads radially from the river mouth, with the spreading direction varying seasonally. The plume is often bordered from the south by a quasi-zonal front along 6°S. The diluted Congo River water spreads southward seasonally down to the Angola–Benguela Front at 16°S. The Benguela Upwelling is delineated by a meridional front, which extends north alongshore up to 20°S, where the low-salinity Benguela Upwelling water forms a salinity front, which is separate from the thermal Angola–Benguela Front at 16°S. The high-salinity tropical water (“Angola water”) forms a wedge between the low-salinity waters of the Congo River outflow and Benguela Upwelling. This high-salinity wedge is bordered by salinity fronts that migrate north–south seasonally.

Geology and ore fluids geochemistry of the Hamzeh–Gharanin orogenic gold deposit, NW Iran

The Hamzeh–Gharanin gold deposit (HGD) is located in the Qolqoleh–Kasnazan shear zone in the northwest of Sanandaj–Sirjan Zone (SSZ) and 40 km SW of Saqez. The main rock units are an assemblage of the Precambrian metasedimentary (pelitic) rocks and the Cretaceous phyllite associated with marble interlayers. The post–Cretaceous intrusive granitoids with NW–SE trends intruded within these two units. Mineralization occurs mainly within the NE–SW extensional veines and veinlets in proto–mylonitic, mylonitic and ultra–mylonitic rocks. Hydrothermal alterations consist of sericitization, carbonatization, silicification and chloritization. The main ore minerals include pyrite, chalcopyrite, arsenopyrite, pyrrhotite, sphalerite, galena, gold, magnetite and hematite. The fluid inclusions study from quartz minerals associated with the mineralization shows four different phases: single vapor phase (V; type I), single liquid phase (L; type II), liquid–vapor biphasic (LV; type III) and three phases (LLV; type IV). Microthermometric studies were performed on types III and IV of fluid inclusions. Homogenization temperatures (Th) for Types III and IV inclusions vary between 138 and 310 °C (mean 230 °C) and 250–335 °C (mean 300 °C) and their salinity varies between 0.52 and 13.87 and 4.79 to 9.58 (wt% NaCl), respectively. Moreover, the density of Types III and IV inclusions vary from 0.71 to 0.927 g/cm3 and 0.700–0.870 g/cm3, respectively. The oxygen (in quartz: 4.58–7.80 ‰; mean 5.82 ‰) and δ34S (in pyrite: 5.54–6.28 ‰; mean 5.91‰) isotope compositions of the mineralizing fluids indicate an insignificant meteoric water input during hydrothermal evolution and a magmatic origin of sulfur in the deposit which is broadly similar to those of orogenic gold deposits worldwide.

Subsurface linear structures and potential zones of mineralisation of the Iramba-Sekenke greenstone belt, central Tanzania with implications for the structural-controlled mineralisation

This study aims to delineate concealed subsurface linear structures and their relationship with mineralisation in the Iramba-Sekenke greenstone belt. Results reveal three different types of linear structures and their concealed continuations, which were previously not identified. These structures include dykes trending in NE-SW and NS; shear zones with NW-SE trending and faults that trend in NE-SW, NW-SE and N–S. The faults and shear zones, which were previously shown to terminate at the northwestern end of the Iramba Plateau due to sediment cover, have been revealed to continue into Wembere depression. Moreover, the aeromagnetic and gravity results show that some faults are intruded by dykes in the same trends, which were not previously identified. The geological relationship between these linear structures shows that the youngest structures are the western dolerite dyke trending N–S and the oldest is the NE-SW Wembere-Iramba Plateau fault. The delineation of geological structures from magnetic and gravity data using different analysis techniques reveals that the mining pits are located close to geological structures trending in NW-SE, NE-SW and N–S directions. The integration of the findings from CET grid analysis techniques, together with magnetic maps and geological information reveals a good correlation between known occurrences of minerals and promising exploration target areas. The good correlation between the artisanal mining pits with the location of the potential exploration targets is consistent with the location of lineaments and provides future promising prospects for mineral exploration. The correlation suggests that mineralisation and ore deposits in the study area are respectively structurally controlled and hosted in deformed rocks. This study is potentially useful as a guide for the delineation of concealed subsurface linear structures and integration of structural geometry and geophysical methods for exploration of hidden mineral deposits in the Iramba-Sekenke greenstone belt.

Ultrapotassic plutons as a source of uranium of vein-type U-deposits (Moldanubian Zone, Bohemian Massif): insights from SIMS uraninite U–Pb dating and trace element geochemistry

The Bohemian Massif hosts significant hydrothermal U-deposits associated with shear zones in the high-grade metamorphic basement. But there is a lack of evidence of a genetic link between mineralization and U-fertile igneous rocks. This contribution provides constraints on the major U source of the vein-type U-deposits, the timing of ore formation and the metallogenetic model. The anomalous trace element signatures of the low-temperature hydrothermal deposits (high Zr, Y, Nb, Ti, ∑REE) and their close spatial relation with ultrapotassic rocks of the durbachite series point to a HFSE and REE enriched source rock. The durbachites have high U content (13.4–21.5 ppm) mainly stored in magmatic uraninite and other refractory minerals (e.g., thorite, zircon, allanite) that became metamict over a time interval sufficient to release U from their crystal structure, as suggested by the time gap between emplacement of the durbachites (EMP uraninite U–Pb age ~ 338 Ma) and hydrothermal activity (SIMS uranium ore U–Pb age ~ 270 Ma). Airborne radiometric data show highly variable Th/U ratios (1.5–6.0), likely reflecting a combination between (1) crystallization of magmatic uraninite, (2) hydrothermal alteration, and (3) leaching and mobilization of U along NW–SE-trending fault zones, manifested by elevated Th/U values in the radiometric map. The presence of rare magmatic uraninite in durbachites suggests almost complete uraninite dissolution; EMP imaging coupled with LA-ICP-MS analyses of refractory accessory phases revealed extensive mobilization of U together with HFSE and REE, providing direct evidence for metal leaching via fluid-driven alteration of radiation-damaged U-rich minerals. The large-scale HFSE and REE mobilization, demonstrated by the unusual trace element signatures of the U-deposits, was likely caused by low-temperature (270–300 °C), highly alkaline aqueous solutions containing F-, P-, and K-dominated complexing ligands. The first SIMS U–Pb age of 270.8 ± 7.5 Ma obtained so far for U-mineralization from the Bohemian Massif revealed a main Permian U mineralizing event, related to crustal extension, exhumation of the crystalline basement, and basin formation, as recorded by U–Pb apatite dates (280–290 Ma) and AFT thermal history models of the durbachites. The Permo-Carboniferous sedimentary cover probably represented a source of oxidized basinal brines infiltrating the basement-hosted durbachite plutons and triggering massive metal leaching. The interaction between basin-derived brines and durbachites resulted in significant modification of the chemical composition of the hydrothermal system (K and F release during biotite chloritization, P liberation through monazite alteration), leading to the formation of ore-bearing fluids responsible for the metallogenesis of the basement-hosted unconformity-related U-deposits in shear zones in the Bohemian Massif.

Remote Sensing-based Morphometry on the Petroliferous Cambay Rift Basin (Gujarat, Western India)

Abstract The Cambay Rift Basin (CRB) is a product of rifting in western India that formed during India’s drift following the breakup of Gondwanaland during the Early Jurassic and Tertiary Periods. Being petroliferous, the basin has attained paramount attention. Seismicity in CRB proves its present-day tectonic sensitivity. Several NNW-SSE, NW-SE and NE-SW trending faults regulate the channel morphology within a portion of the basin. Drainage network systems are proxies of active faulting. Geomorphic indices e.g., long profile analysis, basin-scale parameters, stream length gradient index and sinuosity index along the main channels in the five watersheds have been evaluated in this work. The Index of Active Tectonics (IAT) is derived from the basin-scale parameters and is clubbed into three classes: class 1 (IAT = 1.4 - 1.9), class 2 (IAT = 1.91 - 2.4) and class 3 (IAT = 2.41 - 2.9). IAT Class 1 indicates a higher present-day tectonic activity than the other watersheds such as 1, 2 and 5. Watersheds in the northern and eastern Cambay region (watersheds 3 and 4, and portions of 1 and 5) exhibit higher tectonic activity. Slope breaks and low sinuosity index near the crossing-points in these northern and eastern portions indicate active / weak zones. Along these zones, channels incise vertically and more efficiently than laterally in watersheds 3 and 4. These weak zones may indicate older structures such as lineaments and faults. The Ahmedabad-Mehsana block in watershed 3 and partly in watershed 1 within the CRB with several oil fields are tectonically highly active. Therefore, well-bore stability studies need to be carried out in this block.

Characteristic Analysis of the MS6.0 Ma'erkang Earthquake Sequence on Jun. 10, 2022

On June 10, 2022, the MS6.0 Ma'erkang earthquake sequence occurred in the Bayan Har block. In this paper, the temporal and spatial distribution and attenuation characteristics of earthquake sequence is analyzed based on the regional structure, the temporal and spatial distribution of earthquake sequence, the focal mechanism solution, and the parameters of earthquake sequence, using the data of Sichuan Seismic Network and the temporary stations incorporated into the network. The results show that: (1) The MS6.0 Ma'erkang earthquake sequence is generally distributed in NW-SE direction, and the long axis of this series is basically consistent with the nearby Songgang fault. (2) As the earthquake sequence is formed by three large events with MS ≥5.0, the frequency of small earthquakes in the earthquake sequence area generally attenuates relatively slowly, while the activity level (magnitude) of aftershocks attenuates rapidly. (3) After the MS5.2 earthquake, the sequence parameters obtained show that the h-value is 1.09 and the p-value is stable at 1.02, indicating that the intensity and frequency attenuation of the earthquake sequence are gradually stable and tend to be normal. The b-value is 0.95, indicating that the maximum aftershock magnitude of the series is estimated to be ML5.1, and the b-value gradually tended to be stable, indicating that the stress in the region gradually tended to be balanced after the MS5.2 earthquake. The MS4.4 (ML5.0) earthquake that occurred at 4:37 on June 10 (local time) is the largest aftershock after the MS5.2 earthquake in the sequence. (4) The Songgang fault with NW-SE trend is presumed to be the main seismogenic tectonics, but the migration of three earthquakes with MS≥5.0 may also indicate that the Songgang fault is not a single seismogenic tectonics, which requires further field scientific investigation and analysis.

Deformational History Reconstruction of Basement Complex Rocks in Okomita, Ojirami and Environs, South Western Nigeria

Deformation histories aid in remodeling the forces related to rock formation. Hence, the objectiveof this paper as to examine the deformational history of the Basement Complex rocks in Okomita, Ojirami and Environs, South Western Nigeria using appropriate standard methods. Results of the field work embarked upon revealed that the major rocks encountered include older granite and metasediments like mica schist, quartzite and gneiss. The analysis of the structures contained in the rocks was achieved by plotting the orientation of the structures on rose diagrams and stereonet. The results show that the rocks were subjected to polyphase deformation, comprising of pre-Pan African and the Pan-African orogeny. While the Pan African orogeny left imprint of NE-SW trend as observed in all the rocks, the pre-Pan African orogeny generally has a NW-SE trend which was observed to be associated more commonly with only the metasediments.

Active Faults, Kinematics, and Seismotectonic Evolution during Tajogaite Eruption 2021 (La Palma, Canary Islands, Spain)

During the 2021 La Palma strombolian and fissure eruption, two faults were identified that controlled the spatial distribution of earthquake hypocenters and effusive eruptive vents. One of these faults has a NW-SE trend (Tazacorte Fault: TZF) and the other one shows an ENE-WSW trend (Mazo Fault: MZF). Previous works on fault structural analysis in La Palma indicated that the eruption zone was compatible with an extensional tectonic strain ellipsoid which activated normal-strike-slip directional faults at the confluence of TZF and MZF. These fractures were activated during the 2021 Tajogaite eruption, determining the NW-SE and WSW-ENE spatial distribution of vents. Both faults were mapped in real time during the volcanic eruption from fieldwork and remote sensing imagery (aerial drone images). We have collected more than 300 fracture data associated with the effusive vents and post-eruption seismic creep. Since the affected area was densely inhabited, most of these fractures affect houses and infrastructures. Some of the houses affected by the TZF were damaged 9 months after the eruption, although they were not damaged during the eruption. Surprisingly, these houses already had repairs made to the same fractures since 1980, giving information of previous fault creep movement. During the 2021 Tajogaite eruption, shallow seismicity was spatially related to both faults, suggesting a seismic behavior instead of the precedent creep movement. However, the lack of seismicity after the eruption indicates that the faults went back to creep aseismic behavior, similarly to 1980. The mapping and monitoring of these faults (TZF and MZF) is relevant bearing in mind that they have been active since 1980 and the post-eruptive phase of the 2021 volcanic eruption, which has to be included in the land use planning in areas affected by the volcanic eruption and creep movement. Furthermore, both faults could act as seismogenic sources triggering volcanic earthquakes with potential high macroseismic intensities and mass movements. The data presented here show the importance of having this type of study before the onset of the eruption, thus allowing a better interpretation of seismic data during volcanic unrest.