Geochimica et Cosmochimica Acta最新文献

{"title":"Mineral-associated organic carbon dominance and persistence in coastal wetlands","authors":"Yanqi Xiao, Steven J. Hall, Aaron Thompson, Jialin Wang, Jingxuan Chen, Yilin Lan, Cong-Qiang Liu, Chunmei Chen","doi":"10.1016/j.gca.2026.04.011","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.011","url":null,"abstract":"Coastal wetlands are vital global carbon reservoirs, yet the mechanisms governing the accrual and persistence of organic carbon (OC) remain unresolved. Through a continental-scale survey of China’s coastal wetlands (including saltmarshes and mangroves) combined with a global data synthesis, we demonstrated that coastal wetlands were overwhelmingly dominated by mineral-associated OC (MAOC), which constituted ∼ 73% of total OC—significantly more than in forests and peatlands. This MAOC showed no evidence of mineral saturation, underscoring its potential as an important repository for additional carbon storage. The OC content of the high-density (&gt;1.6 <ce:hsp sp=\"0.25\"></ce:hsp>g<ce:hsp sp=\"0.25\"></ce:hsp>cm<ce:sup loc=\"post\">−3</ce:sup>) and fine-grained (silt + clay, &lt;53 <ce:hsp sp=\"0.25\"></ce:hsp>μm) soil fraction (g C kg<ce:sup loc=\"post\">−1</ce:sup> fraction), termed the dense/fine fraction, was driven by primary productivity, pH, and mineral specific surface area. Contrary to the prevailing assumption that both silt and clay promote MAOC, increasing silt content decreased specific surface area and diluted the OC content of the dense/fine fraction, while higher clay content provided greater surface area that enhanced OC accrual. MAOC persistence, measured by △<ce:sup loc=\"post\">14</ce:sup>C, was primarily predicted by OC content of the dense/fine fraction, outweighing the influence of mineral attributes. Mean annual temperature was the second strongest predictor of MAOC persistence, with warmer climate leading to a larger but faster-cycling MAOC pool, highlighting a climatological temperature-driven trade-off between its accumulation and vulnerability. Saltmarshes—with lower MAOC content yet greater persistence and more abundant high-reactivity phyllosilicates than mangroves—may represent ideal targets for boosting carbon storage through increased OC inputs. Our findings establish the dominance and persistence of mineral-associated carbon in coastal wetlands and underscore their potential for targeted efforts to accrue and store carbon.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"22 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681528","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":"Experimental determination of uranium isotope fractionations during early diagenesis of green rust","authors":"Loren Tessier, Morten B. Andersen, Franck Poitrasson, Armel Descamps-Mandine, Camille Duquenoy, Ludovic Menjot, Pauline Méjean, Jérôme Chmeleff, Carole Causserand, Mathieu Leisen, Romain Guilbaud","doi":"10.1016/j.gca.2026.04.013","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.013","url":null,"abstract":"Uranium (U) isotope compositions of ancient carbonates and shales are increasingly used as a redox proxy to reconstruct the extent of past ocean oxygenation. In euxinic (anoxic and sulphide-rich) settings, it is well known that the reduction of labile U(VI) into solid U(IV) as reduced U oxides (&lt;ce:italic&gt;e.g.&lt;/ce:italic&gt;, uraninite (UO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;)) is accompanied by a significant U isotope fractionation, with the heavy isotopes being preferentially incorporated into the reduced sediment. However, large uncertainty exists on the behaviour of U and its isotopes in ferruginous (anoxic and iron-rich) environments, which were prevalent for most of the Earth’s history, thus limiting our ability to interpret U isotope signatures in ancient sediments that deposited under those conditions. Here, we explore experimentally the fate of uranium during the diagenetic transformations of green rust, a predominant mineral in ferruginous environments. Sulphate and carbonate “Green Rust” minerals (GR(SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;) and GR(CO&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;), respectively), the most abundant green rust species in marine environments, were reacted with dissolved U(VI) at pH 8.4, and the effects of diagenesis were explored over a range of times and temperatures, from 1 h to 10 days at 25 °C and 90 °C. We find that the green rust species have different U reduction rates, and that U is immobilised in the sedimentary phase in the form of UO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; during early diagenesis, suggesting that sedimentary U enrichments are a robust redox tracer even for ferruginous settings. We also report for the first time U isotope fractionation occurring during its abiotic reduction by GR(SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;) and GR(CO&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;). We show that reduced U is enriched in &lt;ce:sup loc=\"post\"&gt;238&lt;/ce:sup&gt;U over &lt;ce:sup loc=\"post\"&gt;235&lt;/ce:sup&gt;U with &lt;mml:math altimg=\"si1.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msup&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"normal\"&gt;Δ&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mn&gt;238&lt;/mml:mn&gt;&lt;/mml:msup&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;U&lt;/mml:mi&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;UO&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mn&gt;2&lt;/mml:mn&gt;&lt;/mml:msub&gt;&lt;mml:mo&gt;-&lt;/mml:mo&gt;&lt;mml:mi&gt;U&lt;/mml:mi&gt;&lt;mml:mrow&gt;&lt;mml:mo stretchy=\"false\"&gt;(&lt;/mml:mo&gt;&lt;mml:mi&gt;V&lt;/mml:mi&gt;&lt;mml:mi&gt;I&lt;/mml:mi&gt;&lt;mml:mo stretchy=\"false\"&gt;)&lt;/mml:mo&gt;&lt;/mml:mrow&gt;&lt;mml:mi&gt;a&lt;/mml:mi&gt;&lt;mml:mi&gt;q&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;/mml:msub&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt; ranging from +0.92 to +1.68 ‰ for GR(SO&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;) and from +0.40 to + 0.84 ‰ for GR(CO&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;) at steady state. Our results imply that starting with modern seawater composition and under U removal at equilibrium between solid and fluid, sediments deposited under ferruginous conditions, and where GR(CO&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;) is the predominant U-reducing mineral, should yield δ&lt;ce:sup loc=\"post\"&gt;238&lt;/ce:sup&gt;U compositions ranging from ∼−0.2 to +0.4 ‰ (relative to CRM-145 standard), depending on the extent of ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"5 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681526","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":"Carbon and oxygen isotope compositions in calcite from the CM chondrites Aguas Zarcas and MIL 13005: Implications for O and C sources and alteration conditions","authors":"S.P. Goudy, M. Telus, K. Nagashima, G.R. Huss","doi":"10.1016/j.gca.2026.04.014","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.014","url":null,"abstract":"Here we present petrographic, O isotope, and C isotope data on calcite and petrographic and O isotope data on magnetite in Aguas Zarcas (CM2) and Miller Range (MIL) 13005 (CM1/2) in an effort to test CM aqueous alteration models. Our O and C isotope data for Aguas Zarcas and MIL 13005 are within the ranges reported in previous work for calcite in CMs. Using O isotope data from Δ<ce:sup loc=\"post\">17</ce:sup>O-matched calcite and magnetite grains in our samples, we calculated equilibrium-model formation temperatures for the analyzed calcites in each meteorite. Combining our isotopic and temperature data with literature data, we sort the data into less altered (CM2) and more altered (CM1/2 and CM1) categories, and examine that data for differences between the categories by analyzing the δ<ce:sup loc=\"post\">18</ce:sup>O-δ<ce:sup loc=\"post\">17</ce:sup>O, δ<ce:sup loc=\"post\">18</ce:sup>O-δ<ce:sup loc=\"post\">13</ce:sup>C, and model formation temperature data of the categories. We find potential differing cluster patterns between δ<ce:sup loc=\"post\">18</ce:sup>O and δ<ce:sup loc=\"post\">13</ce:sup>C in calcites between our two CM alteration categories, and find that sparse extant temperature data imply that more altered CMs (types 1 and 1/2) may have undergone alteration at a lower average temperature than CM2s. We also find that the O isotopic compositions between CM1s, CM2s, and CM1/2s do not differ significantly. Through use of a novel mass-balance model, we infer a pre-alteration ice Δ<ce:sup loc=\"post\">17</ce:sup>O within the range of 5.3–13.3‰. We find two generations of calcite formation in MIL 13005 with different proportions of their O being sourced from ices and anhydrous silicates, and one generation of calcites within Aguas Zarcas. We created concentration mixing models through an original machine-learning-based analytical approach, which show that the calcite data can be readily explained using three optimally determined C- and O-bearing sources.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"66 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681530","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":"Oceanic chlorine enrichment preceding end-Permian warming linked to volcanic degassing","authors":"Jing-Yi Wang, Yang Li, Hai-Jun Song, Ruo-Yu Bai, Xian-Hua Li","doi":"10.1016/j.gca.2026.04.008","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.008","url":null,"abstract":"Chlorine contents in bioapatite represent an emerging but largely untested geochemical proxy for reconstructing oceanic chlorinity variations in deep time. The Permian–Triassic mass extinction (PTME) represents the most severe biotic crisis in Earth’s history and is temporally associated with magmatism of the Siberian Traps Large Igneous Province (STLIP) and coeval felsic volcanism in South China. Although rapid warming, marine anoxia, and ocean acidification driven by volcanic degassing and sedimentary contact metamorphism have been widely invoked as primary kill mechanisms, the sequence and nature of environmental perturbations preceding the extinction remain incompletely resolved. Here we present in situ analyses of conodont δ<ce:sup loc=\"post\">18</ce:sup>O and chlorine (Cl) contents from the Jianzishan section, South China, to constrain short-term environmental changes across the Permian–Triassic transition. Sea-surface temperatures (SSTs) derived from conodont δ<ce:sup loc=\"post\">18</ce:sup>O rise from ∼18.5 to ∼27.5 °C, with peak warming lagging the extinction onset by &gt;0.04 Myr. In contrast, Cl contents from the same conodont exhibit an abrupt increase from ∼0.2 to &gt;0.5 wt% followed by a rapid return to background levels prior to the onset of the end-Permian extinction. From a mass balance perspective, such a Cl anomaly is unlikley to have occurred on a global scale. We therefore interpret this transient Cl spike as recording a short-lived increase in marine chlorine availability at the study section, although a decrease in oceanic F cannot be excluded. We consider halogen-rich volatile release during the sill-emplacement stage of STLIP magmatism and/or coeval felsic volcanism in South China is the most likely mechanism for this Cl anomaly. Our results suggest that short-lived halogen-rich volatile release may represent an early environmental perturbation preceding the end-Permian mass extinction, with subsequent warming amplifying stress on already vulnerable ecosystems. More broadly, this study demonstrates that in situ Cl analysis of conodont apatite can resolve short-lived oceanic chemical perturbations at high stratigraphic resolution, establishing bioapatite Cl as a promising proxy for paleo-ocean halogen cycling.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"91 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147681380","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":"Early diagenetic alteration of sediment porewater in Indian Ocean basins and its controls on rare earth elements enrichment","authors":"Fangyu Shen, Li Li, Xuefa Shi, Xiaojing Wang, Mu Huang, Hongna Liu, Miao Yu, Dongjie Bi, Jihua Liu","doi":"10.1016/j.gca.2026.04.006","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.006","url":null,"abstract":"Rare earth elements and Yttrium (REY) are widely found enriched in deep-sea sediment, yet the accumulation mechanisms remain debated. A lack of constraints on how early diagenesis overprints original seawater signals also limits the reliable application of REY proxies in the geological record. Here we present integrated geochemical analyses of sediments, porewater, and overlying seawater of two short sediment cores (24–36 cm) collected from the central Indian Ocean basins where REY-rich sediments developed. Despite generally oxic sedimentary conditions, early diagenetic alteration of porewater is characterized by elevated dissolved REY concentrations (18–103 nM) and pronounced middle REY enrichment, which is inferred to derive mainly from reductive or non-reductive dissolution of Fe-Mn (oxyhydr)oxides. Variations in porewater shale-normalized REY patterns reflect competitive partitioning of REY among various geochemical compositions in sediments, highlighting strong coupling between porewater and reactive sediment components. The high porewater REY concentrations may be attributed to relatively low phosphate contents in sediments, and to the stabilization of dissolved REY in colloidal phases, as indicated by the flat patterns when normalizing leachable REY fractions by porewater. Sequential extraction results reveal contrasting REY-hosting phases between the two cores, and further support that porewater plays an important role in REY accumulation in sediments, either by promoting authigenic apatite formation or by enhancing REY adsorption onto Fe-Mn (oxyhydr)oxides. Combining the data obtained in this study and previous studies, substantial REY enrichment in deep-sea sediments requires a combination of specific conditions, including limited carbonate dilution, oxic bottom water, low sedimentation rate, sufficient REY-bearing phases and moderate hydrothermal inputs. Overall, porewater acts as a dynamic reservoir and transfer medium during early diagenesis, facilitating REY redistribution and eventual fixation into REY-hosting minerals. These findings provide crucial insights into the mechanisms of REY enrichment in deep-sea sediments and demonstrate that porewater REY serve as sensitive recorders of early diagenetic processes, with important implications for interpreting REY signals preserved in sedimentary archives","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"116 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147629818","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":"Geochemical Insights into Planetary Evolution: from Core to Surface","authors":"Fang-Zhen Teng, Ricardo Arevalo, Xiao-Ming Liu, Ming Tang","doi":"10.1016/j.gca.2026.04.001","DOIUrl":"https://doi.org/10.1016/j.gca.2026.04.001","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"130 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147598308","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":"Radiogenic 182W and 142Nd anomalies in a 2.7 Ga old basaltic lava flow indicate long-term preservation of early mantle heterogeneities","authors":"Jan L. Hellmann, Igor S. Puchtel, Vinciane Debaille, Janne Blichert-Toft, Richard J. Walker","doi":"10.1016/j.gca.2026.03.044","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.044","url":null,"abstract":"Understanding the origin and preservation of early mantle heterogeneities is essential for reconstructing Earth’s accretion and early differentiation history. This can be investigated using the short-lived <ce:sup loc=\"post\">146</ce:sup>Sm–<ce:sup loc=\"post\">142</ce:sup>Nd and <ce:sup loc=\"post\">182</ce:sup>Hf–<ce:sup loc=\"post\">182</ce:sup>W isotope systems, which provide insights into large-scale differentiation processes through <ce:sup loc=\"post\">142</ce:sup>Nd and <ce:sup loc=\"post\">182</ce:sup>W anomalies in Earth’s oldest rocks. In this study, we present <ce:sup loc=\"post\">182</ce:sup>W data for Theo’s Flow, a thick, differentiated, mafic–ultramafic flow of tholeiitic affinity, as well as <ce:sup loc=\"post\">147</ce:sup>Sm–<ce:sup loc=\"post\">143</ce:sup>Nd, <ce:sup loc=\"post\">176</ce:sup>Lu–<ce:sup loc=\"post\">176</ce:sup>Hf, and <ce:sup loc=\"post\">187</ce:sup>Re–<ce:sup loc=\"post\">187</ce:sup>Os isotope data and trace element concentrations, including highly siderophile elements, for Theo’s Flow and closely spatially and temporally associated Pyke Hill komatiites, both from the ∼ 2.7 Ga old Kidd-Munro Assemblage of the Abitibi greenstone belt, Ontario, Canada. Theo’s Flow samples are characterized by an average µ<ce:sup loc=\"post\">182</ce:sup>W value of + 6.7 ± 2.7, which, together with the previously reported positive µ<ce:sup loc=\"post\">142</ce:sup>Nd anomaly of + 6.8 ± 2.5, indicate long-term survival of mantle domains resulting from magmatic differentiation early in Earth’s history. If it is assumed that the bulk silicate Earth evolved with a suprachondritic Sm/Nd ratio, anomalies for both elements can be explained by a single silicate differentiation event at ∼ 4.54 Ga. Alternatively, if the bulk silicate Earth evolved with a chondritic Sm/Nd ratio, a model fractionation age of ∼ 4.45 Ga is obtained. In this case, due to extinction of <ce:sup loc=\"post\">182</ce:sup>Hf by that time, the <ce:sup loc=\"post\">182</ce:sup>W anomaly would have to have been generated by another process, such as derivation from a mantle source characterized by a deficit in late accreted materials. Regardless of the timing of the early silicate differentiation, the preservation of both <ce:sup loc=\"post\">182</ce:sup>W and <ce:sup loc=\"post\">142</ce:sup>Nd anomalies in the 2.7 Ga old rocks highlights the survival of early-formed mantle domains for nearly 1.8 Gyr after Earth’s formation. Comparison of isotopic and chemical data for Theo’s Flow with those for the Pyke Hill and Boston Creek komatiites, which were argued to have all been derived from melting in a single mantle plume, provides evidence for the survival of early mantle heterogeneities on a plume scale","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"14 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147587147","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":"Tin isotope fractionation in arc magmas controlled by degassing and slab input","authors":"Wei-Cheng Jiang, Jia-Xin She, Alexandra Davidson, Chun-Fei Chen, Chris Firth, Simon Turner, Wei-Qiang Li, Trevor Ireland, Paolo A. Sossi, Jing-Hua Wu, Shane Cronin","doi":"10.1016/j.gca.2026.03.047","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.047","url":null,"abstract":"As a redox-sensitive and volatile-chalcophile tracer, Sn isotopes provide unique insights into the origin and transport mechanisms of Sn at convergent margins, yet the drivers of their fractionation remains poorly understood due to a lack of integrated spatial and process-oriented studies. We present high-precision Sn isotopic compositions of lavas (pumices) and hydrothermal products and clinopyroxene-inferred H<ce:inf loc=\"post\">2</ce:inf>O concentrations from Whakaari (arc-front) and Taranaki (rear-arc) in the Kermadec- Hikurangi subduction system.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"477 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147587131","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":"Trace element partitioning during water-saturated eclogite melting at 3 GPa under variable oxygen fugacity – Implications for subduction zone magmatism","authors":"Alexandre Corgne, Gaëlle Plissart, Julien Siebert, Jessica Langlade, Christèle Guivel, José Joaquín Figueroa Ruíz, Joaquín Catalan, Manuel Schilling","doi":"10.1016/j.gca.2026.03.046","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.046","url":null,"abstract":"To shed light on the composition of partial melts of subducted oceanic crust potentially produced at subarc depths and constrain the contribution of this particular melting process to arc magmatism, we performed melting experiments of an eclogite source at relevant conditions (3 GPa, 800–950 °C and oxygen fugacity from ∼FMQ + 3 to FMQ-3) and produced new partition coefficients (D) for many trace elements between eclogite minerals and hydrous rhyolitic melts. Our results show that lattice strain control on partitioning is significant, as evidenced by a near-parabolic dependence of log D to the ionic radius for trivalent cations entering the large sites of both garnet and clinopyroxene. The partition coefficients of some trace elements also display significant dependences on temperature and oxygen fugacity. D&lt;ce:inf loc=\"post\"&gt;Sc&lt;/ce:inf&gt;, D&lt;ce:inf loc=\"post\"&gt;Y&lt;/ce:inf&gt;, D&lt;ce:inf loc=\"post\"&gt;Hf&lt;/ce:inf&gt;, D&lt;ce:inf loc=\"post\"&gt;Zr&lt;/ce:inf&gt;, D&lt;ce:inf loc=\"post\"&gt;Th&lt;/ce:inf&gt; and D&lt;ce:inf loc=\"post\"&gt;Ce&lt;/ce:inf&gt; decrease with increasing temperature for both garnet-melt and clinopyroxene-melt partitioning. With increasing temperature, D&lt;ce:sup loc=\"post\"&gt;Grt-Liq&lt;/ce:sup&gt;&lt;ce:inf loc=\"post\"&gt;REE&lt;/ce:inf&gt; tends to decrease, while D&lt;ce:sup loc=\"post\"&gt;Cpx-Liq&lt;/ce:sup&gt;&lt;ce:inf loc=\"post\"&gt;Ba&lt;/ce:inf&gt; and D&lt;ce:sup loc=\"post\"&gt;Cpx-Liq&lt;/ce:sup&gt;&lt;ce:inf loc=\"post\"&gt;Sr&lt;/ce:inf&gt; increase. We also observed a strong increase in D&lt;ce:inf loc=\"post\"&gt;V&lt;/ce:inf&gt; with decreasing fO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; for garnet-, clinopyroxene- and rutile-melt partitioning, while D&lt;ce:inf loc=\"post\"&gt;Eu&lt;/ce:inf&gt; shows the opposite trend. With increasing fO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; from FMQ-3 to FMQ + 3, D&lt;ce:sup loc=\"post\"&gt;Grt-Liq&lt;/ce:sup&gt;&lt;ce:inf loc=\"post\"&gt;Eu&lt;/ce:inf&gt; increases by more than an order of magnitude and D&lt;ce:sup loc=\"post\"&gt;Cpx-Liq&lt;/ce:sup&gt;&lt;ce:inf loc=\"post\"&gt;Eu&lt;/ce:inf&gt; increases by a factor of 3. Our new data allow us to model the trace element composition of primary adakitic melts produced by melting of subducted oceanic crust at typical subarc depths of about 100 km. These melts are characterized by (i) a progressive enrichment in the most incompatible elements from about 0.1 (Sc) to 10 (Rb) times MORB values, (ii) strong Nb-Ta negative anomalies, (iii) Sr positive anomalies and (iv) a significant depletion in HREE and Y. Stronger Nb-Ta anomaly and lowers Ti, Hf and Zr contents are observed if more rutile is present in the source. Meanwhile, the contents of the most incompatible elements (Rb, Ba, U, Th), the positive Sr anomaly and Sr/Y and La/Yb ratios decrease with increasing degree of melting. We show that the calculated primary adakitic melts can evolve to form high-silica adakites following assimilation-fractional crystallization processes in the mantle wedge and crust. However, to preserve the positive Sr anomaly of high-silica adakites, plagioclase fractionation and sediment melting should remain moderate. Oxybarometry based on V/M ratios (M = Eu, Sc, Yb, Ti) indic","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"14 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147587132","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":"Labile Fe(III) species control arsenic adsorption and oxidation during magnetite-solution interactions under anoxic conditions","authors":"Xinyue Yu, Di Wu, Wan Cheng, Yuefei Ding, Xiaoxu Li, Jing Chen, Xiaohui Wu, Xin Zhang, Juan Liu, Linling Wang, Anxu Sheng, Kevin M. Rosso","doi":"10.1016/j.gca.2026.03.041","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.041","url":null,"abstract":"Interfacial electron transfer (IET) between aqueous Fe(II) (Fe(II)<ce:inf loc=\"post\">aq</ce:inf>) and iron (oxyhydr)oxides is a widespread process that generates highly reactive Fe(III) species (Fe(III)<ce:inf loc=\"post\">labile</ce:inf>), facilitating rapid mineral recrystallization into stable crystalline phases. These systems are known to be more reducing towards a wide variety of electron accepting species. However, these same systems show anomalous redox reactivity toward arsenic, in that they favor oxidation of As(III) rather than reduction of As(V). We hypothesized this reactivity arises from a direct quantitative connection between Fe(III)<ce:inf loc=\"post\">labile</ce:inf> production and As(III) oxidation. Here we tested this hypothesis by employing magnetite nanoparticles with varying stoichiometries (Fe(II)/Fe(III) ratios), denoted Mt<ce:inf loc=\"post\">0.48</ce:inf>, Mt<ce:inf loc=\"post\">0.37</ce:inf>, and Mt<ce:inf loc=\"post\">0.24</ce:inf>, as representative minerals that, along with varying Fe(II)<ce:inf loc=\"post\">aq</ce:inf> amendment, were used to manipulate Fe(III)<ce:inf loc=\"post\">labile</ce:inf> generation and establish its role in reactions with As(III) and As(V). Magnetite could generate Fe(III)<ce:inf loc=\"post\">labile</ce:inf> through dual pathways of Fe(II)<ce:inf loc=\"post\">aq</ce:inf> release and adsorption, driven by reversible electron redistribution across the magnetite-solution interface. At pH 7.0 and 20–100 µM arsenic, the adsorption rates and capacities for both As(III) and As(V), as well as As(III) oxidation extents, followed the order Mt<ce:inf loc=\"post\">0.48</ce:inf> &gt; Mt<ce:inf loc=\"post\">0.37</ce:inf> &gt; Mt<ce:inf loc=\"post\">0.24</ce:inf>, despite the lower apparent redox potentials of more stoichiometric particles. These reactions were accompanied by extensive depletion of Fe(III)<ce:inf loc=\"post\">labile</ce:inf>, showing a strong global linear correlation between Fe(III)<ce:inf loc=\"post\">labile</ce:inf> consumption and As(III) oxidation across all systems. DFT calculations further revealed the strong electronic interactions and substantial Bader charge transfer (1.943 − 2.212 <ce:italic>e</ce:italic>) from As(III) to Fe(III)<ce:inf loc=\"post\">labile</ce:inf>. Our results identify Fe(III)<ce:inf loc=\"post\">labile</ce:inf> as the critical redox-active species controlling arsenic adsorption and As(III) oxidation on magnetite nanoparticles, providing new mechanistic insights into the role of this important species and coupled arsenic-iron cycling in subsurface environments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"20 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147587133","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}