Geological Journal最新文献

Narmada-Tapi dyke swarm is one of the two principal swarms within the Deccan Volcanic Province of India. This study presents new data on the field characters, geometry, and structure of mafic dykes of this giant swarm, housed in a mid-continental fault zone of Precambrian heritage mimicking horst-graben structure. We map 443 lineaments as dykes in an area of 7000 km² and validate 193 on ground. The braided map pattern in the swarm's densest parts indicates higher rates of fracture propagation and magma flow (movement) duly manifested by occasional incorporation of basement xenoliths and local contact-melting of host basalt lava flows. During dyke emplacement, the principal stress axes made a prolate ellipsoid (σ1 >> σ2 > σ3) and the 3D Mohr's stress circles related the magma pressure (P_m) to the paleo-stress regime as σ2 > P_m > σ3. The swarm induced ~5% crustal extension. We estimate magma overpressure that drove the dyke-melt upwards and laterally through the fractured granitic basement from ~10 to 12 km deep magma chamber, assisted by hydro-fracturing of older basaltic flows at shallow levels. We also review the significance of the regional fault-bounded dyke swarms in the emplacement of Deccan flood basalts.

The mantle beneath the Mariana subduction zone is commonly described as depleted, primarily composed of peridotite. This study aims to investigate whether subduction processes influence the lithologic characteristics of the mantle source beneath the Mariana subduction zone. We conducted a comprehensive analysis of olivine elemental compositions from basalts in different subduction settings in the Mariana region, including the island arc, back-arc and initial arc rifting stages. Analysis of major and trace elements in olivines, as well as key elemental ratios (e.g., 10,000 × Zn/Fe, Mn/Zn and 100 × Mn/Fe), reveals that olivines from different subduction settings exhibit characteristics consistent with a peridotite source. While Ca content varies significantly among samples, olivines with high Fo values (Fo > 87) and high Ca contents are consistent with peridotite characteristics. In contrast, olivines with low Fo values (Fo < 87) exhibit lower Ca contents, reflecting the characteristics of a pyroxenite mantle source. This discrepancy is attributed to slab subduction, which increases water content in the mantle wedge and facilitates greater incorporation of Ca into the melt. The compositional distributions of Mn in olivines indicate distinct partitioning behaviours under varying pressure and temperature conditions, with Mn concentrations being particularly sensitive to pressure variations. Therefore, the variation in Mn composition reflects the different pressure conditions experienced by peridotite during its evolution. In different tectonic settings, the variation in Ni contents is mainly controlled by magmatic evolution, with minimal influence from temperature and pressure. Despite the differences in elemental content, our results demonstrate that the mantle source region in the Mariana subduction zone, whether in the island arc, back-arc basin or initial arc rifting, consistently consists of peridotite, with no different results arising from variations in the subduction processes.

Attaining a firm slope stability analysis holds eminent importance in civil and geotechnical projects. This study is concerned with the indirect assessment of the stability of slopes using improved versions of artificial neural networks (ANN). Two novel metaheuristic techniques, namely the seeker optimization algorithm (SOA) and the electromagnetic field optimization (EFO) are employed for optimising the ANN that aims at predicting the factor of safety (FOS). Two hybrids of EFO-ANN and SOA-ANN, as well as a single conventional ANN, are trained and tested using a valid dataset collected from the earlier literature. First, examining the importance of the input factors showed that the unit weight of slope material (γ) is the most important one, followed by internal friction (ϕ), average angle of slope (β), cohesion (c), the height of slope (H), and pore water pressure coefficient (r _u ). Upon monitoring the performance of the ANN, this model stops training after some epochs because of the divergence in the solution, whereas this issue was resolved by the EFO and SOA in hybrid models. Consequently, significant improvements were achieved in both training and testing accuracies. By comparison, while the EFO-ANN was more successful in the training task, the SOA-ANN presented the most reliable prediction of the FOS. The prediction competency of these models is also verified through (a) comparison with earlier literature and (b) applying them to another real-world dataset for binary prediction of slope stability/failure. An explicit predictive formula is derived from the SOA-ANN, which is recommended as a convenient approximator of FOS in slope stability analysis.

The increasing frequency and severity of climate-induced disruptions necessitate robust methodologies for assessing regional resilience. This study introduces a hybrid analytical framework integrating the Analytic Network Process (ANP), Artificial Neural Networks (ANN) and PROMETHEE-GAIA to systematically evaluate climate resilience across Chinese provinces. Resilience is assessed through three dimensions: exposure, sensitivity and adaptive capacity, each comprising multiple sub-criteria informed by expert inputs and literature review. ANP models the interdependencies among resilience factors, while ANN validates the assigned weights, ensuring methodological robustness. PROMETHEE-GAIA ranks provincial resilience levels, providing insightful visualisations of resilience trade-offs. The findings reveal substantial regional disparities: coastal provinces such as Jiangsu and Zhejiang exhibit higher resilience due to advanced infrastructure, economic robustness and effective governance, while inland regions like Qinghai and Gansu demonstrate heightened vulnerabilities due to limited adaptive capacity and economic dependencies on climate-sensitive sectors. The study provides a replicable framework for resilience assessments globally, offering actionable insights for policymakers to enhance climate adaptation strategies and equitable resource allocation.

In recent years, extensive oil and gas exploration in the Ordos Basin has led to the discovery of oil reservoirs within the Carboniferous Yanghugou Formation in the basin's southwestern margin. This study investigates the organic geochemical characteristics and oil-source correlations in the Yanghugou Formation, aiming to clarify the origin of crude oil in this formation by comparing samples from both the Yanghugou and Wulalike formations. Geochemical analyses reveal that the Yanghugou Formation source rocks exhibit high organic matter content, low maturity, and a freshwater-oxidising environment, with contributions from both land plants and aquatic organisms, suggesting significant potential for oil generation. Conversely, the Wulalike Formation source rocks exhibit lower organic matter content, higher maturity, and a brackish water-weakly reduced environment, reflecting a more moderate oil-generating potential. The study uses biomarkers and multivariate statistical methods, including cluster analysis and Q-factor analysis, to establish that the oil in the Yanghugou Formation is a mixed-source oil, originating from both the Yanghugou and Wulalike source rocks. The results highlight the importance of combining geochemical parameters and statistical techniques to improve oil-source correlations and aid exploration strategies in the southwestern Ordos Basin. This study provides new insights into the complex hydrocarbon accumulation mechanisms in the area and offers valuable information for future exploration efforts.

Bangladesh in the Bengal Delta faces complex environmental issues, including sea-level rise, coastal flooding, high population density, and widespread poverty. These factors lead to severe land loss, saltwater intrusion, water scarcity, and biodiversity decline, further exacerbated by climate change. These challenges significantly risk groundwater availability and increase the likelihood of natural hazards such as subsidence, landslides, and flooding. This study quantitatively maps the spatial distribution of subsidence in urban and agricultural settings by utilising Differential Interferometric Synthetic Aperture Radar (DInSAR) and Persistent Scatter Interferometric Synthetic Aperture Radar (PSI) techniques with ascending Sentinel-1 satellite data. We analysed 55 pairs of images with DInSAR and 142 pairs with PSI from March 2017 to October 2022, focusing on five target locations for DInSAR and urban Dhaka for PSI. Findings reveal consistent subsidence in urban Dhaka at an average rate of 16 mm/year, along with semi-seasonal subsidence variability in five agricultural locations. Specific rates are 7 mm/year in Dhaka, 8 mm/year in both Rajshahi and Mymensingh, and 9 mm/year in Rangpur. Sylhet subsides at a rate of 5 mm/year, potentially linked to the fold and thrust belt and the Dauki Fault. Our research highlights the significant environmental impacts of human activities like groundwater withdrawal and land-use changes, which contribute to subsidence and groundwater depletion via the Bengal Water Machine. While further study is required to comprehensively understand the relationship between LOS indicated subsidence rates, geological factors, and geomorphological changes, our findings offer crucial insights into the current impacts of climate change and ongoing environmental degradation in the region.

In the Garhwal–Kumaun Himalayas along the Alaknanda Valley, the Inner Lesser Himalayan (iLH) belt represents the late Paleoproterozoic magmatic arc setup for the active northern Indian margin. The Berinag Group of the iLH belt, representing the rifted back-arc basin, comprises the ubiquitously distributed volcano-sedimentary sequences of chlorite schist and quartzite intercalations. Previously published maximum depositional ages (MDAs) of the Berinag Group are based on various detrital U–Pb geochronology statistical methods. These ages vary over a broad time spectrum and do not represent the true depositional age (TDA) of the Berinag Group. In this study, we employ outcrop-to-microscopic scale observations, U–Pb magmatic and detrital zircon geochronology, and zircon grain shape analyses to characterise the penecontemporaneous volcano-sedimentary sequences. The TDA of the Berinag quartzite at 1879 ± 16 Ma is constrained from the crystallisation age of the mafic volcanic flows, represented by the interlayered meta-volcanic chlorite schist. The YGC2σ method accurately estimates the MDA of the same quartzite at 1871.3 ± 5.3 Ma, which closely approximates the TDA and is also consistent with the average crystallisation age of orthogneiss in the proximal northern magmatic arc at 1858 ± 15 Ma. Therefore, we argue that the active northern Indian margin witnessed a rapid and short-lived synchronous mafic volcanism, sedimentation, and felsic plutonism at ~1.87–1.86 Ga. Mafic volcanism constrained the sedimentation in the rifted back-arc basin. At the same time, the felsic plutonism in the nearby northern magmatic arc predominantly contributed to the detritus in the basin with minor input from the distant southern sources.

The exploration and extraction of deep salt lake resources are of great significance for alleviating potassium and lithium resource shortages. However, large-scale industrial extraction has not been achieved due to technical challenges and cost constraints. This study focuses on the Mihai Mining District in Qaida Basin, Qinghai Province, investigating the exploration and development of deep confined brine enriched with potassium and lithium. The Mihai Mining Area boasts vast reserves of deep confined brine, however, they are not well-utilised because of their heterogeneity, low water yields, and extremely low mining efficiency. Previous studies have revealed that the high-yield wells in mining areas are located within fault zones. Therefore, based on the theoretical models of ‘brine circulation and potassium formation in fault zones’ and ‘storage of brine in steeply inclined water-collecting corridors’, an efficient exploration technique is proposed, which focuses on identifying active fault zones within areas with well-developed high-quality brine reservoirs as key target areas. This study employed radar remote sensing interpretation of pre- and post-seismic deformation intensity to infer fault zone development areas. Integrated with radon gas measurements, the results confirm the presence of a NE-striking active fault within the key target zone. Functioning as the sedimentary centre, this zone exhibits highly concentrated brine with co-enrichment of K⁺ and Li⁺ (both elements showing anomalously high concentrations), indicating high potential for K-Li-rich brine discovery. Guided by the exploration theory, verification drilling revealed brine with elevated K-Li concentrations (approximately double those in adjacent areas) and high-yield water flows in most boreholes, demonstrating significant exploration success. The distribution pattern of the discovered high-yield, water-rich areas and the exploration prediction method are of great significance for the development of deep brine in the Mihai Mining Area and have considerable potential for promotion in the Qaida Basin.

The conjunction of the Qinling-Qilian Orogenic Belt is a critical area for understanding the tectonic relationship between the eastern and western sections of the Central China Orogenic Belt. It serves as an important region for studying the tectonic framework of the northern margin of the Proto-Tethys Ocean. This paper identifies a series of meta-volcanic rocks in the Fanjiaqu area of Fenggeling Town, situated in the eastern section of the North Qilian Orogenic Belt. To determine the formation age, petrogenesis, and tectonic environment of these volcanic rocks, we conducted systematic studies that include petrology, geochemistry, isotope geochronology, and zircon Lu-Hf isotope analysis. Petrographic analysis reveals that the protoliths of the meta-volcanic rocks comprise an assemblage of basalt, andesite, dacite, and rhyolite. LA-ICP-MS zircon U–Pb dating indicates that the protoliths of the meta-basaltic andesite and meta-dacite were formed at 441.9 ± 4.1 Ma and 443.9 ± 2.6 Ma, respectively. Geochemical characteristics show that the meta-basalt-andesite has medium SiO₂ contents (47.10% to 59.64%), higher TFe₂O₃ and TiO₂ contents, lower Cr and Ni concentrations, Mg^# values ranging from 43 to 53 and La/Nb ratios between 4.53 and 5.97. In contrast, the meta-dacite and meta-rhyolite exhibit high SiO₂ (67.62% to 75.18%) and Al₂O₃ contents, along with low TFe₂O₃, TiO₂ and P₂O₅ contents, as well as Mg^# values ranging from 42 to 55. Overall, the meta-volcanic rocks display notable negative Eu anomalies, with Eu/Eu* values varying from 0.76 to 0.83 for basic rocks and from 0.47 to 0.79 for acidic rocks. The meta-volcanic rocks are enriched in large-ion lithophile elements (LILE), such as Th and U, while being depleted in high-field-strength elements (HFSE) like Nb, Ta and Ti, indicating geochemical characteristics similar to those of arc magmatic rocks in subduction zones. The zircon ε _Hf (t) values of the meta-dacite range from +4.5 to +13.1, while the two-stage model ages (T_DM2) range from 1135 to 588 Ma. These characteristics suggest that the meta-basalt-andesite derived from partial melting of the mantle, metasomatised by subduction fluids, whereas the meta-dacite and meta-rhyolite are products of crust–mantle mixing. Integrating regional geological data, this study proposes that the meta-volcanic rocks in the Fenggeling area formed in a continental margin arc environment, while the eastern section of the North Qilian Orogenic Belt was in the subduction setting of back-arc oceanic crust during the Late Ordovician to Early Silurian.