Acta Geochimica最新文献

The Bainiuchang Ag-polymetallic ore deposit, located in southeastern Yunnan, China, is one of the region’s largest deposits. However, the hypabyssal granite porphyry within this mining area has yet to be comprehensively investigated. In this study, we conducted geochemical, geochronological, whole-rock Sr–Nd isotope, and zircon Hf isotope analyses on granite porphyry samples collected from the Bainiuchang deposit. The results indicate that the granite porphyry formed between 87.5 and 87.4 Ma in the Late Yanshanian period. Geochemically, the granite is strongly peraluminous, with high silica and alkali contents consistent with S-type granite characteristics. The granite porphyry is enriched in large-ion lithophile elements (Rb, Th, U, and K) and is relatively depleted in Ba and Sr. The initial ⁸⁷Sr/⁸⁶Sr ratios are high (0.71392–0.71585), accompanied by low ε_Nd(t) values (− 8.9 to − 8.2). The zircons exhibited similarly low ε_Hf(t) values (− 9.31 to − 3.6). These data suggest that the porphyry-forming magma originated from a continental crustal source. The two-stage Hf and Nd model ages are estimated at 1534–1216 Ma and 1615–1561 Ma, respectively. Thus, the granite porphyry likely formed under a strike-slip extensional setting in the Late Yanshanian period and resulted from the re-melting of Proterozoic basement metagreywackes. This porphyry shares a similar magmatic origin with concealed granite bodies within the deposit and is associated with structural reactivation during the Yanshanian. The findings of this study provide valuable insights into the tectonomagmatic mineralization processes in the Bainiuchang area.

The sedimentary geochemistry of St. Martin’s Island is important to determine the origin of the source rock, paleo weathering, tectonic setting, sediment recycling, maturity, sorting, redox condition, and paleo salinity of the sediments. Major oxides, trace elements, and rare earth elements (REEs) obtained from the INAA technique are presented by analyzing the sediment samples collected from the shoreline of St. Martin’s Island, Bangladesh. The elemental ratios, comparison with average upper continental crust (UCC), binary diagrams (Th/Sc vs. Sc, La/Th vs. Hf, Th/Co vs. La/Sc), and chondrite normalized REE patterns exhibit substantial LREE enrichment, relatively flat HREE fractionation, considerable negative Eu anomalies (average: 0.72), indicates the derivation from a source dominated by felsic rock, with contribution from intermediate source and mafic component. Sediments from St. Martin’s Island exhibit the deposition of sediments in transitional environments of active and passive continental margin settings. Weathering indices value of CIA, PIA, CIW, CIX, and K₂O/Rb ratio show moderate chemical weathering, indicating that the sediments are chemically mature. Sedimentary redox indicative proxies, such as U/Th, V/Cr, and V/Sc, show an oxic depositional environment during sediment deposition. The intermediate CIA and other weathering index values of the St. Martin’s sediments show that the area had semiarid and humid climatic conditions throughout the deposition. The Rb/K ratio of the St. Martin’s sediments suggests that the development and deposition of the sedimentary sequence of St. Martin’s Island mainly occurred in a brackish water environment during the geological past.

The Gabo lithium deposit represents a newly discovered pegmatite-type lithium deposit within the Himalayan metallogenic belt. The tourmaline-muscovite granite, the largest leucogranite in the mining area, displays a close spatial correlation with the Li-pegmatite veins. This study aims to examine the genesis of tourmaline and evaluate the significance and potential of pegmatite lithium deposits. Tourmaline is extensively distributed in tourmaline-muscovite granite at Gabo deposit in Luozha county (Xizang). Investigation of the compositional and in situ boron isotopes of the tourmaline revealed that the tourmalines mainly belong to the schorl group and exhibit uniform elevated Li–Sn contents and δ¹¹B values (− 11.6 ‰ to − 10.5‰). This indicates that the tourmaline mainly crystallized from a boron-rich granitic magma undergoing enrichment in elemental lithium during the tourmaline crystallization process. Compared with the principal rare metal leucogranite-pegmatites in the Himalayan orogen, it is proposed that the elevated lithium (Li) content of tourmaline serves as an effective mineral indicator for the highly evolved pegmatite-type rare metal deposits.

The Shichuanhe River, a major tributary of the lower Weihe River, is situated in Xi’an, Shaanxi Province, China. It holds significant information regarding the evolution of the Northern Weihe River, making its study crucial for understanding environmental changes in the region. Despite its importance, research on the Shichuanhe River basin has thus far been primarily focused on riverbank construction, with limited exploration of its sediment characteristics. Although river sediments hold potential for guiding agricultural practices in the area, comprehensive studies on their composition and provenance remain scarce. To address this gap, a systematic sediment sampling campaign was conducted in the lower reaches of the Shichuanhe River, and detailed mineralogical analyses were performed. The results show that the sediment is predominantly composed of detrital quartz and feldspar (albite and orthoclase), with heavy minerals constituting approximately 10%–12% of the total sediment volume. The analysis of the heavy mineral assemblage reveals an absence of significant contributions from igneous rocks in the sedimentary profile. Furthermore, the distribution patterns of major, trace, and rare-earth elements in the Shichuanhe River’s argillaceous sediments exhibit similarities to those found in the Weihe River’s sediments. Elemental fractionation patterns suggest that the Shichuanhe River sediments are primarily derived from Loess Plateau sediments, aligning with findings from both the Weihe River and the middle reaches of the Yellow River.

Stable Sr isotopic composition (δ^88/86Sr) can be used to study magmatic processes, but their fractionation mechanism during magmatic evolution remains unclear. To understand the fractionation behaviors of the stable Sr isotopes during magmatism, we report the δ^88/86Sr values of the Huili granitic pluton, which was subjected to intensive crystal-melt separation. The Huili pluton consists of K-feldspar granite and more evolved albite granite, and the albite granite exhibits significantly higher δ^88/86Sr values (+ 0.36‰ to + 0.52‰) than that of K-feldspar granite (+ 0.11‰ to + 0.25‰). K-feldspar, which contributes most of the Sr budget of the K-feldspar granite, has slightly lower δ^88/86Sr values (− 0.01‰ to + 0.17‰) than the whole rock. The δ^88/86Sr variation of the Huili granites can be explained by separation of melt from K-feldspar-dominated crystals, because crystallization of K-feldspar can result in heavy Sr isotopic composition of the extracted interstitial melt. Stable Sr and Ba isotopic ratios in the Huili granites are highly coupled toward the heavy direction, reflecting their similar element partitioning and isotope fractionation behaviors between the crystalline K-feldspar and melt. This study indicates that melt extraction plays a key role in granitic magma evolution.

The lack of a comprehensive whole-rock geochemical and mineralogical dataset for the Archean granitoids of the Aravalli-Banded Gneissic Complex (BGC), northwest India, results in significant challenges for their correct characterization and assessment of their antiquity. The new field, mineralogical and geochemical data classify the Jaisamand granitoids into sanukitoids, TTGs, and transitional TTGs, which are most likely coeval in nature. The obtained results, in conjuncture with the previously published geochemical and geochronological results of the Aravalli–BGC granitoids, unveil the Neoarchean affinity of the Jaisamand pluton. The TTGs were generated by the melting of a subducting slab (metabasite) at shallow (high-HREE-Y TTGs) to moderate depths (medium-HREE-Y TTGs) above the garnet-in line but still within the plagioclase stability field, with garnet-poor residue. The ascending TTG melts were transformed into sanukitoids through differential interaction with the overlying mantle wedge peridotite. The TTG melts, generated at different pressures, interacted with older TTGs at lower and middle crustal levels to form the transitional TTGs. The coexistence of high-HREE-Y and medium-HREE-Y TTGs and sanukitoids suggests a subduction-related setting for the Jaisamand granitoids. The heat required for simultaneous melting at shallow and deeper depths during the Neoarchean was provided by the upwelling asthenosphere due to slab break-off. The study also revealed the occurrence of altered granitoids in the Jaisamand pluton, showing evidence of albitization and silicification. These rocks do not represent the pristine mineralogy and should be carefully examined to avoid misleading interpretations, particularly for the Archean granitoids.

There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block (SCB) during the Early Mesozoic. One of the key points of contention is the tectonic–magmatic activity during the Triassic and its dynamic mechanisms. However, research on the detailed chronology and tectonic settings of granite plutons in key regions remains insufficient, limiting the understanding of the tectonic–magmatic dynamic mechanisms in the interior of SCB during the Triassic. In this contribution, we present whole-rock major and trace elemental data, Sr–Nd isotope data, LA-ICP-MS zircon U–Pb age dating, and Lu–Hf isotope data for granites of Dashenshan pluton in the Xiangzhong, northwest part of SCB. The results indicate that the Dashenshan granite has an emplacement age of 208.4–212.5 Ma, characterized by high SiO₂, Na₂O, and K₂O contents and low MgO and CaO. The Dashenshan granite is enriched in light rare-earth elements with a significant negative Eu anomaly (average δEu = 0.42). It is also enriched in Rb, K, and Th and shows pronounced depletion in Nb, Ta, and Ti, classifying it as peraluminous calc-alkaline granite, specifically of the I-type. The zircon ε_Hf(t) values range from − 8.39 to − 4.4, with an average of − 5.82, and the Sr–Nd isotopes are relatively enriched [ε_Nd(t) = − 9.31 to − 6.8]. Combining these geochemical characteristics, it is revealed that the Dashenshan granite was derived from the partial melting of middle to upper crustal metamorphic basement materials under medium- to low-temperature conditions, with possible minor contributions from mantle-derived materials. Furthermore, it underwent fractional crystallization, including plagioclase differentiation. By integrating the geochemical features and spatial distribution of Triassic granites in SCB, this study suggests that the regional tectonic evolution of SCB during the Triassic was primarily controlled by the collision of the SCB with the Indochina Block and the North China Block. In Xiangzhong, the tectonic setting transitioned from syn-collisional compression to post-collisional extension during the Late Triassic. The Dashenshan pluton formed in a post-collisional extensional setting, resulting from the decompression melting of middle-to-upper crustal rocks. The upwelling of the asthenosphere and upward heat transfer likely played a significant role in the formation of the Dashenshan granitic magma.

Permanently shadowed regions (PSRs) on the Moon are potential reservoirs for water ice, making them hot spots for future lunar exploration. The water ice in PSRs would cause distinctive changes in space weathering there, in particular reduction-oxidation processes that differ from those in illuminated regions. To determine the characteristics of products formed during space weathering in PSRs, the lunar meteorite NWA 10203 with artificially added water was irradiated with a nanosecond laser to simulate a micrometeorite bombardment of lunar soil containing water ice. The TEM results of the water-incorporated sample showed distinct amorphous rims that exhibited irregular thickness, poor stratification, the appearance of bubbles, and a reduced number of npFe⁰. Additionally, EELS analysis showed the presence of ferric iron at the rim of the nanophase metallic iron particles (npFe⁰) in the amorphous rim with the involvement of water. The results suggest that water ice is another possible factor contributing to oxidation during micrometeorite bombardment on the lunar surface. In addition, it offers a reference for a new space weathering model that incorporates water in PSRs, which could be widespread on asteroids with volatiles.

The concentrations of polycyclic aromatic hydrocarbons (PAHs), their sources and toxic equivalent (TEQ) in soil, suspended matter and bottom sediments in the Fatala River Basin ecosystem were obtained for the first time to our knowledge. Determination of 14 PAHs (ΣPAHs) was carried out using high-performance liquid chromatography. The ΣPAH content in soil ranged from 13 to 50,920 (Me = 820) ng/g. The composition of PAHs (high proportion of low-molecular-weight compounds and values of individual PAHs ratios) reflected the significant oil pollution of soil. Contaminated soil was localated in the central part of the Fatala River Basin. The median benzo(a)pyrene toxic equivalent of soil at the study site was 1.08 (range, 0.05 to 53.16) ngTEQ/g, showing generally low soil toxicity. The ΣPAH content in suspended matter was in the range of 33 to 1316 (Me = 309) ng/L. The ΣPAH content in bottom sediments ranged from 36 to 6943 (Me = 478) ng/L, corresponding to clean and moderately contaminated sediments. The ΣPAH content in bottom sediments depended on the anthropogenic impact on the Fatala River Basin territory and the bottom sediment features. Bottom sediments and suspended matter had a low toxic equivalent.