Solid Earth Sciences最新文献

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.

The formation of continental red beds is generally considered to be related to an arid climate. Heating experiments (performed by L.J. and G.C.) using dried black mud sediment also demonstrate that the reddening may be caused by the transformation of goethite to haematite that begins at approximately 150 °C under anhydrous conditions, and increasing the temperature to 450 °C is positively correlated with the red colour and peak value of haematite. If this process applies to continental red beds, it implies a thermal origin of red beds as a result of high diagenetic temperatures rather than as the cause of their deposition under an arid climate. Namely, subsiding red-bed basins are heated from below rather than warmed from above. Here, we further strengthen this idea by new evidence from borehole cores drilled from red beds in SE China, showing a clear geological section from the surface soil to red beds to bottom granite. The data reveal that the continental red beds formed at least at a temperature within 150–400 °C, and the underlying granite usually formed at temperatures greater than 600 °C. Our results imply a possible relationship between continental red bed events and Earth's thermal cycles.

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 polyphase deformation features and detachment faults on the northern (Gumusler) and southern (Camardı) borders of the Nigde Massif rocks, as well as the structures developed as a result of these faults, are investigated in this paper. The Nigde Massif in the studied areas is basement Palaeozoic–Mesozoic metamorphic units. The Late Cretaceous Uckapılı granodiorite and Sineksizyayla meta-gabbro introduced the Nigde massif. These units are overlain unconformably by Late Cretaceous-Quaternary rocks. The metamorphic rocks on the massif's southern edge underwent 5-phase ductile deformation, whereas the metamorphic rocks on the northern margin underwent 3-phase folding. Both the northern and southern edges include post-Middle Eocene extensional detachment features. These are most likely extensional detachment faults related to the massif's uplift. Central Anatolia is still under an extensional tectonic regime today. Therefore, detachment fault activity and occurrence continue. A large portion of the low-angle normal faults shows an extensional detachment feature. The detachment faults identified north and south of the study area are also active today.

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.