Solid Earth Sciences最新文献

Electrically Conductive Olivine, ECO, is presented as a new reference model for the electrical conductivity of dry olivine. The model takes into account the prevailing redox state, temperature and pressure in the upper mantle, as well as their effects on the conductivity, and is based on conductivity analyses of dry single crystal olivine at high pressures. The model demonstrates higher conductivity of olivine than those previously proposed standard olivine models, which rely on the conductivity of olivine measured at room pressure. Accepting that the bulk electrical structure is in general dominated by olivine, the upper mantle is more conductive than the estimates of the previous models. The olivine conductivity is in fact high at the oxidizing conditions of the shallow mantle, but drops at greater depths where the mantle portion is reducing. The model provides a new reference basis for understanding the electrical structure of the upper mantle, and is important for invoking any other conductive candidates to explain enhanced mantle conductivity.

The composition of Nb, Sn, Ta, and W in rutile can serve as a highly sensitive indicator for the mineralization of these elements. This information could also be utilized to discriminate different stages of ore deposition or distinct types of deposits. Precise and accurate measurement of trace-level concentrations of these elements in rutile is imperative for such investigations, and can be effectively achieved using electron probe microanalysis (EPMA). In this study, we employed a CAMECA SX5 field emission EPMA to develop an optimal approach for precise and accurate analysis of trace-level Nb, Sn, Ta, and W in rutile. The analytical conditions include an accelerating voltage of 25 kV, a beam current of 200 nA, a beam diameter of 1 μm, optimized background positions for Nb Lα, Sn Lα, Ta Lα, and W Lα, and aggregate intensity counting with a peak counting time of 240 s for each element per spectrometer. The detection limits (3σ) for Nb, Sn, Ta, and W ranged from 22 to 53 ppm. The highest achievable spatial resolution was approximately 4.3 μm. Analytical results obtained from potential rutile standards R10 and R632 were consistent with previous studies within the errors. The precision of these results varied from 1% to 10% (1σ), excluding W in R10 and Nb and Ta in R632, which exceeds the precision achieved in previous EPMA studies. We recommend using R10 as a reference standard for analyses of trace-level Nb, Sn, and Ta, and R632 as an appropriate reference standard for Sn and W when quantifying rutile using EPMA.

Groundwater, a primary freshwater source for potable and agricultural uses, is increasingly threatened in southern coastal areas of Bangladesh because of rapid urbanization, industrialization, and climate change. Bagerhat, one of the coastal districts, faces not only frequent tropical cyclones, inundation of low-lying areas, and saline water intrusion but also rapid urbanization, population growth, and pollution from prawn culture and seafood processing industries. The study aims to assess the hydrogeochemistry and the suitability of groundwater based on its significance for potable and irrigation purposes in Bagerhat District. This research includes an integrated approach of hydrogeochemical, geospatial, and multivariate statistical methods to investigate the hydrogeochemical processes and groundwater quality using ninety groundwater samples from existing deep tube wells (around 350 m depth). The hydrogeochemical analysis determined the concentrations of major cations and anions were Na⁺>Mg²⁺> Ca²⁺> K⁺ and Cl⁻ > HCO₃^- > SO₄²⁻ > NO₃^-, correspondingly. Electrical Conductivity (EC) values ranged from 16,260 μS/cm in the southern Mongla Upazila to a minimum of 560 μS/cm in Chitalmari Upazila. The evaporation–crystallization processes were found to be the primary mechanism influencing groundwater chemistry in the study area. Multivariate statistics, including Pearson correlation matrix, principal component analysis (PCA), and cluster analysis, indicated that geogenic processes govern groundwater chemistry. The spatial distribution of the water quality index (WQI) map demonstrated that only 15% of groundwater samples are suitable for drinking in the central and eastern parts, while 85% are unsuitable in the study area. Furthermore, evaluation of irrigation water quality parameters, such as sodium percentage (Na%), sodium adsorption ratio (SAR), Kelly ratio (KR), permeability index (PI), magnesium hazard (MH), and salinity hazard, indicated that most wells are unsuitable for irrigation. The results provide insights into aquifer hydrogeochemistry, groundwater quality status, vulnerable areas of pollution, and sustainable, safe water options for groundwater management in the Bagerhat district.

In this study, we report for the first time a new gabbro diorite, forming in an intraplate extensional environment during the Early Devonian, in the Shimian of the western margin of the Yangtze Block. Zircon SIMS U–Pb dating indicates that the gabbro diorite formed at ca. 406 Ma. This gabbro diorite belongs to low-K tholeiite and has enriched in Rb, Ba, K, Pb, negative anomalies of Nb, Ta, depletion of flat LREE patterns, negative ε_Hf(t) (−1.1 to −11.7), and high δ¹⁸O (8.83 ± 0.21‰) ratios, showing that the magma formed by partial melting of N-MROB-type mantle and indicating that the magma underwent crustal contamination during emplacement. The magma is formed in the extensional environment, which provides evidence for the extensional environment in the western margin of the Yangtze. The geochemical characteristics and emplacement time of the rocks are similar to those in the early Paleozoic post-orogenic mafic rocks in South China, suggesting that the gabbro diorite may be influenced by the early Paleozoic orogeny in South China.

The geochemical and tectonic characteristics of volcanic formations in Central Java, specifically the Sumbing-Slamet volcanics, were investigated to understand the processes associated with slab failure in the region. Through comprehensive geochemical analysis and comparison with other volcanic formations, insights into the magmatic evolution and tectonic settings of the Sumbing-Slamet volcanics were gained. The findings support the hypothesis of slab tearing beneath Central Java, as evidenced by distinct geochemical signatures and magmatic interactions observed in the Sumbing-Slamet volcanics. Geochemical data reveal medium to high potassium content (K₂O = 0.77–2.32%), low Nb/Y (<0.6561), low TiO₂ relative to Al₂O₃ [TiO₂ < (−1.1610 + 0.1935 × Al₂O₃)], Th/La >0.2, as well as a wide range of Nb/La and Nb/Zr (0.14–0.89 and 0.0304–0.0744, respectively), notable depletions in high-field strength elements (HFSE; such as Nb, Ti), low to high Ta-anomaly (δTa = 0.21–1.03), and whole-rock isotopes of ⁸⁷Sr/⁸⁶Sr (0.704458–0.705800) and ¹⁴³Nd/¹⁴⁴Nd (0.513059–0.512766) demonstrate that they were formed from active continental margin (ACM) tectonics involving subducted sediment input. These magmatic processes likely resulted from the mixing of lithospheric and asthenospheric mantle sources due to slab failure in the northern part of Central Java. The research contributes to strengthening the geophysical view regarding the existence of slab tearing in Central Java, understanding the dynamic geological processes occurring in subduction zones, and emphasizing the importance of interdisciplinary approaches in studying such phenomena.

Water utilization for different human activities is universally crucial, but it is not readily available for consumption in some areas, such as the central parts of Lagos State, Nigeria. Moreover, there are many groundwater controlling factors (GWCFs) spanning geological, geophysical, and hydrological factors that contribute to this scenario, coupled with uncertainties that necessitate their careful selection using appropriate modelling techniques. In this study, the Dempster–Shafer Theory of Evidential Belief Function (DST-EBF) model (a coupling approach) was deployed to produce a groundwater prospectivity zonation (GWPZ) map for the study areas. The choice of the selected locations was informed by the continued dearth of water supplies, necessitating the need to discover new locations or re-appraise the existing ones for groundwater resource development. Furthermore, remote sensing, geological, field geophysical, and hydrological datasets that constituted GWCFs were integrated into a Geographic Information System (GIS) environment. Next, the computed values for the evidence of the mass functions (i.e., belief, disbelief, uncertainty, and plausibility) were combined using the Dempster–Shafer combination rule and then interpolated using the Inverse Distance Weighted (IDW) method. Subsequently, the GWPZ map was generated and classified into five zones, ranging from very low to high prospectivity zones. The GWPZ map was validated using cross-validation to estimate statistical errors, the receiver operating characteristic (ROC) curve, and the use of inverted resistivity models from the 2D electrical resistivity imaging surveys. All the metrics used for the validation provided good account for the classified GWPZ map. The north-eastern and the south-central parts are the most promising regions for groundwater, which could be harnessed for sustainable development through borehole drilling. Thus, the integration of the DST-EBF model and GIS for effective groundwater resources and uncertainty mapping was quite successful and impressively reliable.