Geochimica et Cosmochimica Acta最新文献

{"title":"Petit-spot hydrothermal systems simulated: Fluid evolution, chemical fluxes, and chemoautotrophic habitability","authors":"Keishiro Azami, Kanta Koyama, Takuya Saito, Takazo Shibuya, Syogo Kinoshita, Shiki Machida, Yasuhiro Kato, Etsuo Uchida","doi":"10.1016/j.gca.2025.09.008","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.008","url":null,"abstract":"Hydrothermal systems at petit-spot volcanoes are unique in that they induce hydrothermal activity around outer rises—i.e., oceanic plates prior to subduction. However, their biogeochemical significance remains poorly understood due to a lack of direct observation. In this study, hydrothermal experiments were conducted at 250°C and 350°C under 500 bar to simulate petit-spot hydrothermal systems. Petit-spot volcanism introduces volatile-rich magma into thick sediment layers. Accordingly, natural petit-spot lava and ambient pelagic sediment were used as initial solid materials, while a CO<ce:inf loc=\"post\">2</ce:inf>-rich NaCl solution served as the initial liquid to supplement CO<ce:inf loc=\"post\">2</ce:inf> degassed from the lava. The Nd-Sr-Pb isotope ratios of clastics in hydrothermal ferromanganese oxides collected from a petit-spot volcano indicated sediment involvement in water–rock interactions. This sediment involvement enhanced CH<ce:inf loc=\"post\">4</ce:inf> concentrations in the reacted fluid. Additionally, Ca, Fe, Mn, and Ba concentrations increased, likely due to a pH decrease associated with the production of organic acids. The decrease in Mo concentration due to sediment involvement, and the reduction in the Mn/Fe ratio resulting from lower reaction temperatures, observed in the experiments, do not contradict the geochemical characteristics of hydrothermal ferromanganese oxides collected from a petit-spot volcano. These findings suggest that the experiments successfully simulated petit-spot hydrothermal systems. Although the chemical fluxes from global petit-spot hydrothermal systems to the ocean may be negligible due to their limited fluid discharge, the potential metabolic energy available in the mixture of seawater and hydrothermal fluid near the seafloor is comparable to that of other hydrothermal systems where vent ecosystems have been confirmed. Therefore, petit-spot hydrothermal systems are likely habitable, at least for chemosynthetic microbes. Under certain conditions—such as high fluid flux during the early stages of hydrothermal activity, and the involvement of ultramafic xenoliths and SO<ce:inf loc=\"post\">2</ce:inf> gas in water–rock interactions—petit-spot hydrothermal systems may even serve as oases for higher organisms on old, cold oceanic plates.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"32 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145103524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Heterogeneous slab components impart diverse oxygen isotope of arc magmas in northwestern circum-Rodinia subduction system","authors":"Yu Zhu, Xiao-ping Xia, Xin Zhu, Chang-xin Yin, Zhuang Guo, Ren-zhi Zhu, Min Liu, Fang-yi Zhang, Hang Yang, Shao-cong Lai","doi":"10.1016/j.gca.2025.09.003","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.003","url":null,"abstract":"Oxygen isotopic diversity of arc magmas can be used to trace their distinct sources and, in turn, shed light on material recycling during crust-mantle interaction in the subduction zone. Herein, we present new zircon O isotopes for the Neoproterozoic (ca. 820–760 Ma) mafic to felsic igneous rocks in the western Yangtze Block (South China) to understand how slab subduction imparts diverse oxygen isotope in arc magmatic rocks from the northwestern circum-Rodinia subduction system. The ca. 807–802 Ma high zircon-δ<ce:sup loc=\"post\">18</ce:sup>O basaltic andesites to dacites display variable zircon εHf(t) (−0.37–+11.5) and high δ<ce:sup loc=\"post\">18</ce:sup>O values (up to 7.09 ‰). In combination with highly variable MgO (2.01–9.06 wt%), K<ce:inf loc=\"post\">2</ce:inf>O (2.43–4.70 wt%), Rb/Y (2.99–8.98), Th/Ce (0.15–0.31), Th/Sm (1.51–3.21), Th/La (0.30–0.64) and Th/Yb (3.20–10.1) as well as negative εNd(t) (−4.22 to −0.86) values, these basaltic andesites to dacites originated from a mantle wedge source metasomatized by subducted fluids and sediment melts. The ca. 820–760 Ma low zircon-δ<ce:sup loc=\"post\">18</ce:sup>O rhyolites and granites have elevated silicic contents (73.05–78.49 wt%), positive-dominantly εNd(t) (−0.69 to +1.99) and highly positive εHf(t) (+6.16∼+11.9) values as well as sub-mantle to mantle-like δ<ce:sup loc=\"post\">18</ce:sup>O values (3.82 ‰–5.58 ‰), which were formed by the partial melting of juvenile mafic arc lower crust that was originally supplemented by mantle wedge melts metasomatized by hydrothermally altered oceanic crust (AOC) melts. The heterogeneous zircon δ<ce:sup loc=\"post\">18</ce:sup>O values of igneous rocks, combined with available paleomagnetic data, indicate that the persistent peripheral subduction around Rodinia has introduced distinct metasomatized agents (i.e., subducted fluids, sediment melts, and AOC melts) into the sub-arc mantle source, which resulted in the mantle wedge heterogeneity and zircon δ<ce:sup loc=\"post\">18</ce:sup>O diversity of Neoproterozoic arc magmatism across the western Yangtze Block (South China) in northwestern circum-Rodinia subduction system. Slab subduction is thus significant for the geochemical diversification of arc magmas and mass exchange between the mantle and crust.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"86 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145059663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Copper and zinc isotopic variation in Apollo 17 double drive tube 73001/2 reveals space weathering history of lunar regolith","authors":"Megan Broussard ,&nbsp;Mason Neuman ,&nbsp;Piers Koefoed ,&nbsp;Frédéric Moynier ,&nbsp;Nicole X. Nie ,&nbsp;Richard V. Morris ,&nbsp;Bradley L. Jolliff ,&nbsp;Kun Wang","doi":"10.1016/j.gca.2025.09.004","DOIUrl":"10.1016/j.gca.2025.09.004","url":null,"abstract":"<div><div>As a part of the Apollo Next Generation Sample Analysis Program, we report the Cu and Zn isotopes in the Apollo 17 regolith core, double-drive tube 73001/2. The intervals in the upper core, which sampled the regolith closest to the lunar surface, are enriched in heavy Cu and Zn isotopes compared to the deeper intervals. The top 2 cm have a δ⁶⁵Cu value of 2.85 ± 0.01 ‰ and a δ⁶⁶Zn value of 5.54 ± 0.02 ‰. The intervals become lighter in isotopic composition to a depth of 8 cm. Below this depth, the average δ⁶⁵Cu is 1.02 ± 0.08 ‰, while the average δ⁶⁶Zn is 2.27 ± 0.24 ‰. We find strong correlations between the isotopic fractionations of Cu and Zn and the maturity index <em>I_S</em>/FeO. These correlations in the core result from a binary mixing between highly space-weathered soil at the lunar surface and deeper, shielded soil, with isotopic fractionation occurring at the surface due to space weathering and soil mixing occurring due to impact gardening. Using the K, Fe, Cu, and Zn isotopes measured in 73001/2, we find a strong correlation between the degree of isotope fractionation and volatility. We model the isotopic fractionation of K, Fe, Cu, and Zn by space weathering in lunar soils using mass balance equations between the lunar atmosphere and lunar soil and find agreement with the fractionation observed in 73001/2. Using the fractionation observed in 73001/2, we present a new exposure age model using Cu isotope fractionation in lunar soils.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 144-157"},"PeriodicalIF":5.0,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145045787","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Climate warming and strengthened hydrologic cycle accelerate CO2 release from rock weathering","authors":"Sen Xu ,&nbsp;Aaron Bufe ,&nbsp;Preston C. Kemeny ,&nbsp;Marcus Klaus ,&nbsp;Jun Zhong ,&nbsp;Tingting Ma ,&nbsp;Dongfeng Li ,&nbsp;Si-Liang Li","doi":"10.1016/j.gca.2025.09.006","DOIUrl":"10.1016/j.gca.2025.09.006","url":null,"abstract":"<div><div>Global climate is modulated by the balance between CO₂ release from coupled sulfide-carbonate weathering and CO₂ sequestration through silicate weathering, yet how this balance evolves under climate change remains poorly constrained. Here we investigate the temporal variability in dissolved chemistry and isotopic ratios from two major rivers on the Tibetan Plateau, the Jinsha River and the Yalong River, over two periods within a nine-year span (2013–2014 and 2018–2021). In the evaporite-rich, permafrost-dominated Jinsha River basin, we detected exceptional increases in evaporite-derived elemental concentrations and fluxes, both interannually and during the monsoon season, compared with other mineral sources. These shifts reflect enhanced evaporite exposure driven by warming-induced thermal processes such as permafrost thaw, altered subsurface flow paths, and enhanced hydrologic connectivity between saline lakes and rivers. By contrast, weathering fluxes in the evaporite-poor Yalong River basin exhibit relatively small temporal changes. Sulfide oxidation offsets all silicate weathering–driven alkalinity in the Jinsha River basin and 40–98% in the Yalong River basin, with the offset intensifying during monsoon-driven permafrost-thaw- and high-flow periods. Concurrently, accelerated gypsum/anhydrite weathering could prompt CO₂ release from soils and streams by inducing secondary carbonate precipitation. Interannually, the growing dominance of sulfide oxidation also shifts the CO₂ balance toward net CO₂ release. These processes demonstrate that mineral weathering associated with permafrost thaw can strengthen CO₂ sources to the atmosphere and amplify the permafrost carbon-climate feedback. Overall, global warming and the associated acceleration of the hydrologic cycle could result in CO₂ release rather than drawdown from rock weathering in permafrost landscapes underlain by sulfide- and evaporite-rich lithologies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 174-192"},"PeriodicalIF":5.0,"publicationDate":"2025-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145045901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"In-situ iron isotope analysis of pyrite from coals: Insights into iron isotope fractionation from dissimilatory iron reduction (DIR) and redox reactions","authors":"Mengda Yao, Shifeng Dai, David French, Ian T. Graham, Zhengfu Zhao, Yutang Zhang, Yang Liang, Shuai Kang, Jintian Zheng, Shaowei Zhang","doi":"10.1016/j.gca.2025.09.010","DOIUrl":"https://doi.org/10.1016/j.gca.2025.09.010","url":null,"abstract":"In-situ <ce:italic>δ</ce:italic><ce:sup loc=\"post\">56</ce:sup>Fe and <ce:italic>δ</ce:italic><ce:sup loc=\"post\">34</ce:sup>S compositions of pyrite from Late Paleozoic coals of the Qinshui Basin, China, were investigated using LA-MC-ICP-MS. The results demonstrate substantial micrometer-scale heterogeneity in Fe and S isotopes, reflecting spatially variable geochemical controls. The subduction of the Inner Mongolia Ocean and the uplift of the northern North China continent led to the formation of the Yinshan Oldland and surrounding highlands, intensifying the weathering of pre-Late Carboniferous rocks and providing the primary sediment source for the Qinshui Basin. While Rayleigh distillation partially explains observed Fe isotopic trends, deviations from theoretical predictions suggest additional fractionation during multi-stage Fe–S cycling. Dissimilatory iron reduction (DIR) mediated Fe(III) reduction leads to Fe(II) enrichment with negative <ce:italic>δ</ce:italic><ce:sup loc=\"post\">56</ce:sup>Fe values, which subsequently reacts with H<ce:inf loc=\"post\">2</ce:inf>S to form pyrite. In coal-rich settings, the extent of DIR is governed by organic matter availability and redox conditions. The organic matter in coal largely consists of structurally complex macromolecules such as humic substances and aromatic compounds, which are poorly bioavailable and restrict DIR. Moreover, sulfate reduction preferentially generates hydrogen sulfide (H<ce:inf loc=\"post\">2</ce:inf>S), which rapidly reacts with Fe(II) to form FeS and ultimately pyrite, further suppressing DIR. The <ce:italic>δ</ce:italic><ce:sup loc=\"post\">56</ce:sup>Fe values reflect the repeated Fe cycling process under the fluctuation of redox states, driven by processes such as incomplete reduction of Fe(III), partial reoxidation, and late-stage release of heavy Fe<ce:sup loc=\"post\">2+</ce:sup> via processes such as anaerobic oxidation of methane coupled to Fe reduction (AOM–FeR). This isotopic signature mirrors the persistent “hidden” Fe cycle observed in modern iron-rich basins, highlighting the combined influence of microbial activity, and diagenetic reworking, and SMTZ (sulfate-methane transition zone) dynamics in shaping Fe isotopic signatures in organic-rich sediments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"53 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145103522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Steroid acids with extended side chains and fumarate addition in reservoirs","authors":"Can Xie ,&nbsp;Gangtian Zhu ,&nbsp;Yuguang Hou ,&nbsp;Jochen J. Brocks","doi":"10.1016/j.gca.2025.08.043","DOIUrl":"10.1016/j.gca.2025.08.043","url":null,"abstract":"<div><div>Molecular markers that record microbial activity in oil reservoirs are still sparse. Here we report a series of novel steroid acids with extended side chains in in-reservoir biodegraded oils. Due to the lack of authentic standards, these steroid acids are tentatively identified based on ToF-MS spectra, chromatographic retention behavior, and comparisons with previously reported regular steroid acids and hopanoic acids. The correlation between significant consumption of steranes and generation of the steroid acids in oils suggests that these unique steroid acids originated from the biodegradation of regular steranes. The side chains of these steroid acids extended by up to three CH₂ units are consistent with the fumarate addition mechanism. Some co-occurring alkylsuccinates were also tentatively identified, supporting the occurrence of anaerobic biodegradation by fumarate addition. Furthermore, regular steroid acids with the same carbon numbers and configurations as those detected in the aerobically degraded samples from our previous laboratory study (Xie et al., 2024) were not detected in the oil samples in this study, indicating that the biodegradation pathway of steranes in oil reservoirs may differ from the pathway under aerobic conditions. If confirmed, these findings not only substantiate the existence of anaerobic biodegradation, but also provide the first direct evidence for the presence of hydrocarbon activation by fumarate addition in oil reservoirs.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"407 ","pages":"Pages 105-120"},"PeriodicalIF":5.0,"publicationDate":"2025-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145045772","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mechanisms of cadmium isotopic fractionation during the substitution of cadmium for zinc in sphalerite (ZnS)","authors":"Chuanwei Zhu, Lisheng Gao, Xinran Yan, Hui Yin, Haifeng Fan, Yuxu Zhang, Guangshu Yang, Lei Zhang, Hanjie Wen","doi":"10.1016/j.gca.2025.08.042","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.042","url":null,"abstract":"The chalcophile character of Cd controls its hyper-enrichment in Zn–Pb ore deposits via substitution for Zn in sphalerite (up to 13.2 wt%) and, as such, these deposits form Earth’s richest Cd reservoirs. Cadmium isotopes can provide insights into the origins of these deposits and the behavior of Cd in hydrothermal systems. However, Cd isotopic variations in sulfides are affected by mineral precipitation and the initial composition of the fluid, which remain poorly constrained for sphalerite precipitation. This hinders the application of Cd isotopes to ore-forming systems. In this study, we investigated Cd isotopic fractionation during absorption into sphalerite under varying pH, ionic strength, initial Cd<ce:sup loc=\"post\">2+</ce:sup> content, and mineral crystallinity. Using extended X-ray absorption fine structure (EXAFS) spectroscopy and spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM), we demonstrate that Cd is incorporated into the ZnS lattice rather than being adsorbed onto its surface. Isotopic equilibrium is achieved after 18 h in pure water and 10 % NaCl at pH 5.5, with lighter Cd isotopes preferentially partitioning into the solid phase. The magnitude of isotopic fractionation (Δ<ce:sup loc=\"post\">114/110</ce:sup>Cd<ce:inf loc=\"post\">solid–solution</ce:inf> ≈ –0.5 ‰) is largely unaffected by the initial Cd<ce:sup loc=\"post\">2+</ce:sup> concentration, mineral crystallinity, and reaction pH in 10 % NaCl, but is higher than that in pure water (–0.7 ‰ to –0.9 ‰). This is probably due to Cl<ce:sup loc=\"post\">–</ce:sup> complexation favoring the lighter Cd isotopes, leaving isotopically heavier Cd<ce:sup loc=\"post\">2+</ce:sup> to be absorbed into the sphalerite. Monte Carlo simulations using the obtained fractionation factors indicate the composition of the ore-forming fluid is the primary control on the Cd isotopic variations in sphalerite. These results advance our understanding of Cd isotopic systematics in hydrothermal systems and during supergene sulfide weathering, and provide a framework for interpreting Cd isotopic data in natural environments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145009067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Zinc partitioning between minerals and melts: Implications for the origins of the iron-depletion trend in convergent-margin magmatism","authors":"Zhongxing Sun, Xiaolin Xiong, Hugh St.C. O’Neill, Li Li, Mingdi Gao, Wei Chen, Xingcheng Liu","doi":"10.1016/j.gca.2025.08.034","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.034","url":null,"abstract":"Zinc shows a marked preference for tetrahedral coordination in oxide and silicate minerals. The only phases among those suggested to be involved in the petrogenesis of basaltic-andesitic-dacitic magmas that has a tetrahedral site suitable for 2+ cations are the spinel group minerals, including magnetite. Zn therefore has the potential to be a geochemical indicator for magnetite in the same way that heavy rare earth elements are for garnet. In this capacity it has the advantage over vanadium in that it has only one oxidation state in silicate melts, namely 2+, making its mineral/melt partitioning dependent on oxygen fugacity only insofar as this variable affects the compositions of the minerals and melts. Here we report experiments on the partitioning of Zn between hydrous andesitic-dacitic melts and all the mineral phases hypothesized to be involved in their petrogenesis, including olivine, orthopyroxene, augitic clinopyroxene, amphibole (hornblende), garnet, ilmenite and magnetite-rich spinel. We combine these results with those available in the literature to show that Zn is indeed highly compatible in the spinels, including magnetite, but incompatible in amphibole and garnet, confirming its usefulness for detecting magnetite fractionation. The behaviour of Zn in a number of convergent-margin magmatic suites shows that magnetite entered the cotectic assemblage when the suites had differentiated to 5 ± 1 wt% MgO. It is magnetite + amphibole crystallization that causes the depletion of Fe and concomitant enrichment of SiO<ce:inf loc=\"post\">2</ce:inf> of the calc-alkaline trend. The correlated depletion of V with Zn suggests that this happened under moderately oxidizing conditions, at approximately FMQ +2 (±1), where FMQ is the fayalite-magnetite-quartz equilibrium. Thermodynamic analysis of the Zn partitioning data shows that Zn behaves similarly to Mg, and is thus a member of a group of mid-sized divalent cations comprising Mg, Fe<ce:sup loc=\"post\">2+</ce:sup>, Mn, Co, Ni, and Cr<ce:sup loc=\"post\">2+</ce:sup>, whose oxide activity coefficients in silicate melts all vary with melt composition in a remarkably similar manner, despite the differences in their electronic configurations and chemical bonding characteristics, which are so obvious in their crystal chemistry in ferromagnesian silicates and spinels.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"36 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145059703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Calibrating olivine Forsterite content as a measure of melting degree in residual peridotites","authors":"Jia-Le Mou, Cin-Ty Lee, Jackson Borchardt","doi":"10.1016/j.gca.2025.08.021","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.021","url":null,"abstract":"The extent to which the mantle can melt depends on temperature, pressure, and its bulk composition. Reconstructing the extent of mantle melting from ancient primitive magmas or residual mantle peridotites can thus provide insights into the thermal and dynamic state of the Earth’s interior. Here, we show using compiled experimental data that olivine Forsterite (Fo = molar Mg/(Mg + Fe)) content in residual peridotites can be used to estimate melting degree:","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"14 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145009045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microbial transformation and mineral adsorption control chemical evolution of soil organic matter during semi-arid ecosystem development","authors":"Hai-Ruo Mao, Stephen C. Hart, Derek Peak, Amy M. McKenna, Mengqiang Zhu","doi":"10.1016/j.gca.2025.08.041","DOIUrl":"https://doi.org/10.1016/j.gca.2025.08.041","url":null,"abstract":"The chemical composition and diversity of soil organic matter influence soil organic carbon (SOC) persistence and climate responses, yet their evolution during soil development in drylands remains unclear. We characterized the chemical composition and diversity of bulk SOC and water-extractable organic matter (WEOM) across a 3-million-year-old semi-arid volcanic soil chronosequence, spanning a steep silt and clay concentration gradient. Soils were sampled from beneath pine or juniper tree canopies and inter-canopy spaces covered by grasses and/or shrubs. As soil developed, those beneath pine or juniper canopies became enriched in aromatic C due to a synergistic effect of intensified microbial decomposition of non-aromatic plant material and preferential adsorption of aromatics from WEOM onto minerals in the silt and clay fraction. Consequently, WEOM was depleted in aromatics with soil development. Both bulk SOC and WEOM also showed increasing proportions of microbial carbon, facilitated by higher silt and clay concentrations that mitigated water scarcity and provided suitable pore spaces for microbial proliferation. Inter-canopy soils showed minimal trends with soil development, ascribed to the higher litter quality than tree litter. The WEOM molecular α-diversity remained stable as the influences from microbial transformation and mineral adsorption counteracted each other. However, β-diversity, reflecting compositional dissimilarity of bulk SOC or WEOM across samples at each soil developmental stage, declined as soil developed. This chemical convergence resulted from dominant microbial and mineral interactions overriding vegetation and other influences. Our findings suggest the dual role of silt and clay in controlling SOM chemistry in dryland soils, enhancing accrual of both microbial C and the aromatic portion of the plant-derived C. These new insights can inform process-based models to better describe soil organic C dynamics and persistence in drylands.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"25 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145059704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}