Geochimica et Cosmochimica Acta最新文献

{"title":"Potassium isotopic variability in coals induced by magmatic and submarine exhalative hydrothermal activity","authors":"Shuai Kang ,&nbsp;Zhihan Ji ,&nbsp;Weiqiang Li ,&nbsp;Jingjing Liu ,&nbsp;Qian Wang ,&nbsp;Na Wang ,&nbsp;David French ,&nbsp;Ian T. Graham ,&nbsp;Victor P. Nechaev ,&nbsp;James C. Hower ,&nbsp;Jintian Zheng ,&nbsp;Mengda Yao ,&nbsp;Shifeng Dai","doi":"10.1016/j.gca.2026.01.004","DOIUrl":"10.1016/j.gca.2026.01.004","url":null,"abstract":"<div><div>Coal, as an organic-rich sedimentary rock that records depositional, diagenetic, and hydrothermal processes, is highly susceptible to alteration by crustal fluids, resulting in significant elemental and mineralogical changes. Potassium (K), a fluid-mobile alkali element, is sensitive to hydrothermal processes. Despite growing interest in using stable K isotopes as a tracer of hydrothermal activity, studies comparing K isotope fractionation across different hydrothermal systems and evaluating their impact on K isotopic compositions in coal remain scarce. This study reports high-precision K isotope data for coals affected by two different hydrothermal events: i) magmatic hydrothermal alteration in the Daqingshan and Fengfeng coalfields (North China) and ii) submarine exhalative hydrothermal alteration in the Yishan Coalfield (South China). Coals intensely altered by magmatic hydrothermal fluids exhibit remarkably low <em>δ</em>⁴¹K values, ranging from − 1.92 ± 0.01 ‰ to − 0.63 ± 0.03 ‰, which are well below that of the Bulk Silicate Earth (BSE) (<em>δ</em>⁴¹K_BSE =  − 0.43 ± 0.17 ‰). In contrast, coals influenced by submarine exhalative hydrothermal fluids show markedly high <em>δ</em>⁴¹K values ranging from 0.18 ± 0.05 ‰ to 1.23 ± 0.04 ‰, well above modern seawater (<em>δ</em>⁴¹K_seawater ≈ 0.12 ‰). Such systematic difference in K isotopic composition of coals is ascribed to the formation of different ammonium-bearing secondary minerals (buddingtonite and ammonian illite) through interactions between distinct hydrothermal fluids and organic matter in coals. This study exemplifies that K isotopes can serve as a sensitive tracer for fingerprinting the history of hydrothermal activity in coal-bearing strata.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 25-39"},"PeriodicalIF":5.0,"publicationDate":"2026-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956572","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":"The effect of iron sulfidation on the stability of the trisulfur radical ion S3•‾ in subduction zone fluids","authors":"Jianjiang Zhu ,&nbsp;Lu Zhang ,&nbsp;Huijuan Li ,&nbsp;Runze Jiang ,&nbsp;Lifei Zhang ,&nbsp;Renbiao Tao","doi":"10.1016/j.gca.2026.01.001","DOIUrl":"10.1016/j.gca.2026.01.001","url":null,"abstract":"<div><div>The sulfur cycle in subduction zones is crucial for modulating the redox evolution of the mantle wedge. The trisulfur radical ion (S₃•‾) has been proposed as a dominant carrier of ore–forming elements in subduction zone fluids. However, existing high P–T experiments have primarily focused on S₃•‾ stability in pure aqueous sulfide–sulfate systems. The role of iron sulfidation on S–rich fluids in subduction zone rocks, which may influence S₃•‾ stability, remains poorly understood. In this study, we systematically investigated the impact of iron/iron oxides on S₃•‾ stability in subduction-zone fluids using in situ high P–T experiments and thermodynamic simulations. Our results reveal that in pure aqueous systems containing both SO₄²⁻ and S²⁻, S₃•‾ is the dominant sulfur species at temperatures above 350 °C along typical subduction P–T paths. However, the introduction of Fe or FeO into these S₃•‾–rich fluids triggers sulfidation reactions that lead to the precipitation of sulfide minerals (e.g., pyrite, pyrrhotite), substantially reducing S₃•‾ stability in the fluid phase. In contrast, Fe₂O₃ has little effect on S₃•‾ stability due to the formation of a passivating pyrite layer, which inhibits further sulfidation. Additional thermodynamic modeling suggests that the mobility of S₃•‾ and associated metal ions in subduction zones is only feasible under high fluid/rock (F/R) ratios and may be tightly regulated by channelized fluid flow.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 40-55"},"PeriodicalIF":5.0,"publicationDate":"2026-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956566","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":"Rubidium isotope fractionation during intense weathering of basaltic rocks: Implication for tracing weathering intensity in deep time","authors":"Ya-Qi Zhang, Wei Wei, Yingzeng Gong, Zhuoying Zhang, Xingchao Zhang, Xia Hu, Fang Huang","doi":"10.1016/j.gca.2026.01.005","DOIUrl":"https://doi.org/10.1016/j.gca.2026.01.005","url":null,"abstract":"Rubidium isotope system has been advocated as an emerging proxy for silicate weathering intensity, primarily based on systematical isotope fractionation during moderate granite weathering through adsorption–desorption processes by secondary clay minerals. However, the magnitude and mechanism of Rb isotope fractionation during chemical weathering of basaltic rocks (an alternatively important silicate rock in the Earth’s crust), especially under intense weathering conditions, are still poorly constrained, which hinders our understanding on the geochemical Rb isotope cycling at the Earth’s surface and the robust application of Rb isotopes as a paleo-weathering proxy. In this study, we present Rb isotope compositions (δ<ce:sup loc=\"post\">87</ce:sup>Rb) from a gabbro weathering profile in Leizhou Peninsula, which forms under tropical humid monsoon climate. The upper saprolites are characterized by a positive linear correlation between the Rb and Th (a least-mobile element that can indicate aeolian accretion) contents, and the consistency of the δ<ce:sup loc=\"post\">87</ce:sup>Rb values (–0.15 ± 0.09‰; 2SD, <ce:italic>n</ce:italic> = 30) with the Chinese loess (–0.11 ± 0.04‰) and the lower fresh gabbros (–0.11 ± 0.08‰; 2SD, <ce:italic>n</ce:italic> = 2), suggesting that the Rb in the saprolites is dominantly hosted in extraneous aeolian dusts while the geologic Rb derived from parent rocks has been completely removed during intense chemical weathering. The δ<ce:sup loc=\"post\">87</ce:sup>Rb values of the middle semi-weathered gabbros (from –0.07‰ to 0.83‰) are positively fractionated relative to the fresh gabbros, and show a decreasing trend with increasing weathering intensity, which are mainly caused by progressive desorption of previously adsorbed isotopically heavy Rb from secondary clay minerals. On this basis, we suggest to use detrital δ<ce:sup loc=\"post\">87</ce:sup>Rb record or seawater δ<ce:sup loc=\"post\">87</ce:sup>Rb record reconstructed from reliable marine archive to trace continental silicate weathering intensity on a regional or global scale, respectively. This study advances our understanding on the geochemical Rb isotope cycling at the Earth’s surface, especially under intense weathering conditions, and provides a fresh dimension to the toolbox for tracing weathering intensity in deep time.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"32 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956569","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":"Depositional settings and speciation control vanadium isotopic fractionation in black shales","authors":"Bojidar Mandjoukov, Anthony Chappaz, Ashley N. Martin, Kaarel Mänd, Johannes Vind, Kaarel Lumiste, Kalle Kirsimäe","doi":"10.1016/j.gca.2026.01.006","DOIUrl":"https://doi.org/10.1016/j.gca.2026.01.006","url":null,"abstract":"Vanadium (V) stands out as a relatively abundant and remarkably redox-sensitive metal that can be found in multiple oxidation states. In this study, we combine X-ray Absorption Near Edge Structure (XANES) speciation analyses and stable V isotope composition measurements with vanadium bulk concentration data. By applying this approach to samples from the extensively studied Cambrian-Ordovician Alum Shale Formation in Baltic Paleobasin, we refined our understanding of the V use as a paleo-redox proxy. Vanadium concentrations in the studied samples ranged from 798 to 2286 mg/kg, whilst bulk δ<ce:sup loc=\"post\">51</ce:sup>V values were highly variable, ranging from −0.01‰ to −0.95‰. XANES analyses revealed two main V species, V(+IV)-S and V(+III)-O, whereas ca. 26% of the latter is present in an early diagenetic V-rich illite-type clay mineral structure. In addition, we report the first direct V(+IV)-O-porphyrin detection in black shale using XANES analysis. Our results show a negative correlation between δ<ce:sup loc=\"post\">51</ce:sup>V values and V(+III)-O species, and a positive correlation between δ<ce:sup loc=\"post\">51</ce:sup>V values and V(+IV)-S species that also covaries positively with the increasing basinal restriction. This highlights the effects of depositional conditions and burial pathways on V isotope fractionation in shales. Additionally, our data imply the presence of two distinct environmental zones in the eastern facies of the Alum Shale formation in Estonia: in the west zone the sediments were initially formed under mild to weakly euxinic conditions, which later became more oxic; in the east zone, sedimentation was primarily controlled by the combination of increasing basinal restriction and temporal redox changes.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"32 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956588","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":"pH controlling boron isotope fractionation during chemical weathering of basalt","authors":"Rijing Wang, Jinlong Ma, Guipeng Mao, Guanhong Zhu, Kai Luo, Ti Zeng, Gangjian Wei","doi":"10.1016/j.gca.2026.01.003","DOIUrl":"https://doi.org/10.1016/j.gca.2026.01.003","url":null,"abstract":"Boron (B) isotopes serve as an effective tracer for the weathering of continental silicate rocks, but the mechanisms of B isotope fractionation remain controversial. This study quantifies B isotope fractionation through the mineralogical-geochemical and δ<ce:sup loc=\"post\">11</ce:sup>B coupling analysis of weathering profiles from basalt on Hainan Island. The δ<ce:sup loc=\"post\">11</ce:sup>B value of weathering products in profile ranges from −3.60 ‰ to 1.87 ‰, most of them are significantly higher than that of parent rock (−3.13 ‰), and its evolution may be controlled by three stages: 1) The decomposition of plagioclase releases B-rich fluid; 2) Smectite preferentially incorporates the light isotope (<ce:sup loc=\"post\">10</ce:sup>B) during its formation, and this isotopically light component may subsequently be released into the soil solution through partial dissolution and possible desorption as weathering progresses; 3) Kaolinite exhibits pH-dependent dual-mode adsorption, under weakly acid to neutral conditions (pH = 6–7), <ce:sup loc=\"post\">10</ce:sup>B is preferentially adsorbed during kaolinite formation, whereas under acidic conditions (pH &lt; 6), changes in surface hydroxyl group protonation on kaolinite enhance its affinity for <ce:sup loc=\"post\">11</ce:sup>B. Our study highlights that adsorption and desorption effects during weathering at different pH conditions reconfigure the δ<ce:sup loc=\"post\">11</ce:sup>B signature, which may result in a wide variability of δ<ce:sup loc=\"post\">11</ce:sup>B in global rivers (−11 ‰ to + 45 ‰). These results call for a reassessment of global B-cycle models, particularly under tropical acidic environments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"52 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956571","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":"Hydrogen in natural inclusions: geological legacy or laboratory artifact?","authors":"Haokun Lian, Xiaolin Wang, Matthew Steele-MacInnis, Dongquan Sun, Wenxuan Hu, I-Ming Chou","doi":"10.1016/j.gca.2026.01.002","DOIUrl":"https://doi.org/10.1016/j.gca.2026.01.002","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"29 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145902353","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":"Sustained recycling of anorthite-rich inclusions by outer-disk chondrule heating events","authors":"Mingming Zhang, Kohei Fukuda, Michael J. Tappa, William O. Nachlas, Bil Schneider, Makoto Kimura, Kouki Kitajima, Ann M. Bauer, Noriko T. Kita","doi":"10.1016/j.gca.2025.12.056","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.056","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"33 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145893633","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":"Transport of Pt and Pd in hydrous sodium silicate melt: A study from X-ray absorption spectroscopy","authors":"Qi Chen, Jacob Huffaker, Matt Newville, Antonio Lanzirotti, Craig C. Lundstrom","doi":"10.1016/j.gca.2025.12.061","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.061","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"13 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145893634","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":"Earth’s composition: Origin, energy budget, and insights from geoneutrinos","authors":"William F. McDonough","doi":"10.1016/j.gca.2025.12.060","DOIUrl":"https://doi.org/10.1016/j.gca.2025.12.060","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"48 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145895532","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 distribution of moderately volatile elements in the Moon determined from Apollo 15 and 17 pyroclastic glass beads","authors":"Eleanor C. McIntosh,&nbsp;James M.D. Day","doi":"10.1016/j.gca.2025.12.059","DOIUrl":"10.1016/j.gca.2025.12.059","url":null,"abstract":"<div><div>The Apollo 17 high-Ti orange (74220) and Apollo 15 low-Ti green (15426) lunar pyroclastic glasses are some of the most primitive igneous samples from the Moon and are considered critical for understanding the volatile content of the lunar interior. The orange and green glass deposits are petrologically distinct, containing both holohyaline (glassy) and crystallized beads. In this study, edge and center analyses on holohyaline beads representative of the deposits were conducted by laser ablation inductively coupled plasma mass spectrometry to constrain the distribution of moderately volatile elements (MVE: K, Cu, Zn, Cs, Ga, Ge, Rb, Cd, and Pb), and trace element images were produced of the beads in 74220. Bead edges have elevated MVE abundances compared to centers in the larger (107 µm average diameter) low-Ti Apollo 15 green glasses, likely resulting from <em>syn</em>-eruptive processes. Leaching experiments of 15426 bulk beads support a large fraction of Na, K, Zn, Cu, Cd and Pb on their outer surfaces. The smaller (42 µm average diameter) high-Ti Apollo 17 orange glasses have a greater extent of overlap in MVE contents between bead edges and centers. Orange and green glass bead centers offer approximations of melt MVE abundances, indicating ∼500 µg/g K, ≤20 µg/g Zn, ∼6 µg/g Cu, &lt;4 µg/g Ga, ≤ 1 µg/g Rb, &lt;0.1 µg/g Pb and ≤ 100 µg/g K, ≤1 µg/g Zn, ≤2.5 µg/g Cu, &lt;2 µg/g Ga, ≤ 0.5 µg/g Rb and Pb, respectively. These estimates are as much as ten times lower than bulk bead MVE abundances within the pyroclastic glass deposits, are depleted compared to terrestrial mid-ocean ridge basalts, and are similar to, or lower than, bulk silicate Earth (BSE) concentration estimates. Partial melting estimates for the source of the pyroclastic glass beads indicate similarities with tholeiitic and komatiite lavas on Earth and between ∼10 and 30 % melting of their mantle source, consistent with high mantle potential temperatures at ∼3.5 billion years ago in the Moon. The estimated MVE composition of the orange glass bead mantle source is marginally higher than the green glass mantle source, and both are within or lower than bulk silicate Moon estimates. More shallowly derived mare basalts have been shown to be yet more MVE depleted, indicating that the lunar interior had a heterogeneous distribution of volatile elements, with a deep interior with volatile abundances ∼10 times lower than BSE sampled by the pyroclastic glass beads, volatile-poor upper magma ocean cumulates, and an incompatible volatile-enriched KREEP reservoir.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 297-312"},"PeriodicalIF":5.0,"publicationDate":"2025-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145895533","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}