Geochimica et Cosmochimica Acta最新文献

{"title":"Weathering and recycling controls on rare earth element behavior: A comparative study on granitic, basaltic and aeolian red soil crusts","authors":"Long Han ,&nbsp;Bin Lü ,&nbsp;Chaoqiang Li ,&nbsp;Jiao Yang ,&nbsp;Wenjing Ge ,&nbsp;Jianlei Gao ,&nbsp;Xingxing Wang ,&nbsp;Yan Zheng","doi":"10.1016/j.gca.2025.06.033","DOIUrl":"10.1016/j.gca.2025.06.033","url":null,"abstract":"<div><div>Intense chemical weathering and sedimentary recycling have produced widespread REE-enriched red soil crusts in South China. This study compares REE fractionation and mobility across three representative regolith types: granitic (YQ), basaltic (ZJ), and aeolian lateritic (LZ). Total REE concentrations follow the order of YQ (512 ± 66 ppm) &gt; ZJ (153 ± 38 ppm) &gt; LZ (82 ± 35 ppm). The YQ profile is enriched in light REE (LREE), while heavy REE (HREE) are more readily leached during silicate decomposition. In contrast, the ZJ profile—rich in Fe–Mn (hydr)oxides—retains middle REE (MREE) due to redox-sensitive mineral transformations and surface complexation, but exhibits LREE depletion. The LZ profile shows the lowest total REE, but is relative enriched in HREE, reflecting the combined effects of quartz dilution and the accumulation of refractory detrital minerals such as zircon. Beyond lithology and climate, REE compositions are modulated by grain size, weathering intensity, and mineralogical variance, which jointly regulate REE adsorption and redistribution processes in regolith-hosted systems. Our results provide mechanistic insights into REE differentiation and establish a geochemical framework for REE exploration in tropical and subtropical environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"402 ","pages":"Pages 49-61"},"PeriodicalIF":4.5,"publicationDate":"2025-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144557681","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":"Temperature dependence of uranium and thorium partitioning in igneous zircons","authors":"Yuanyuan Liang ,&nbsp;Michael J. Krawczynski ,&nbsp;Noah M. McLean ,&nbsp;Paul K. Carpenter ,&nbsp;Jack P. Touran ,&nbsp;Ashley N. Cocciadiferro","doi":"10.1016/j.gca.2025.06.027","DOIUrl":"10.1016/j.gca.2025.06.027","url":null,"abstract":"<div><div>Zircon is a key mineral in geochronology because of its chemical and physical durability and tendency to incorporate radioactive trace elements such as U and Th. Quantifying the partitioning of the actinide elements is critical to constrain initial non-secular equilibrium amounts of ²³⁰Th in zircon. An excess or deficit of ²⁰⁶Pb will be produced from such an initial excess/deficit of ²³⁰Th from the secular equilibrium condition, which influences the calculated ²⁰⁶Pb/²³⁸U age (<span><span>Schärer, 1984</span></span>, <span><span>Mattinson, 1973</span></span>). However, there is no standard way to calculate Th/U partitioning ratios when applying age corrections to young igneous zircon, making uncertainties hard to estimate. To better understand U and Th partitioning of zircon/melt that is the cornerstone of the secular disequilibrium correction, zircon was synthesized in one-atmosphere experiments using basaltic andesite, andesite, and rhyolite starting materials, doped with Zr, U, and Th. Different experimental temperatures and oxygen fugacity conditions (ΔQFM−4 to ΔQFM+4) were explored to examine their effects on U and Th partitioning. In addition, we specifically quantify the effects of sector zoning, fractional crystallization, and melt composition on U and Th partitioning. By combining experimental and natural zircon data, we find that temperature has the primary control on the partitioning of U and Th in the zircon and calibrate an inverse relationship between these partition coefficients and crystallization temperatures. The calibrated equation can be applied to the ²³⁰Th correction for an improvement in the accuracy of Th-corrected ²⁰⁶Pb/²³⁸U dates when the zircon crystallization temperature is known.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"402 ","pages":"Pages 62-75"},"PeriodicalIF":4.5,"publicationDate":"2025-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144557682","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":"Isotopic fractionation of Li and B in highly evolved granitic systems","authors":"Ruizhe Shi, Rolf L. Romer, Junxing Zhao, Johannes Glodny, Changtong He, Kezhang Qin","doi":"10.1016/j.gca.2025.06.026","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.026","url":null,"abstract":"The incompatible elements lithium (Li) and boron (B) generally show different degrees of isotopic fractionation during magmatic differentiation and fluid exsolution in highly evolved granitic pegmatite systems. We use the magmatic-hydrothermal evolution of the Qiongjiagang pegmatite-type Li deposit to demonstrate how fractionation and phase separation control the Li and B isotopic compositions of whole rock samples. The investigated samples include tourmaline-muscovite granites, unmineralized pegmatites, aplites, spodumene pegmatites and their associated wall rocks. Our data show systematic Li and B isotopic compositional variations among the studied rocks. The spodumene pegmatites have much higher Li concentrations, lower δ<ce:sup loc=\"post\">7</ce:sup>Li values, and lower B concentrations and δ<ce:sup loc=\"post\">11</ce:sup>B values than the tourmaline-muscovite granites, unmineralized pegmatites and aplites, which suggests phase separation into a fluid-rich melt and a fluid-poor melt. The fluid-rich melt experienced multi-stage magmatic differentiation with fluid exsolution, which eventually led to the formation of spodumene pegmatites. In contrast, the fluid-poor melt evolved through single-stage magmatic differentiation, eventually forming unmineralized pegmatites and aplites. Interactions with wall rocks modified the Li and B isotopic compositions of some aplite and unmineralized pegmatite samples. The Li and B isotopic compositions of minerals extracted from tourmaline-muscovite granite, unmineralized pegmatite, and spodumene pegmatite samples were also analyzed. The Li and B isotopic compositions of these minerals span a wide range, which is controlled by two primary factors: (i) coordination of Li and B and (ii) crystallization history. The crystallization of most magmatic minerals increases the δ<ce:sup loc=\"post\">7</ce:sup>Li and δ<ce:sup loc=\"post\">11</ce:sup>B values of the residual melt (except for tourmaline, whose crystallization seems not to change the δ<ce:sup loc=\"post\">11</ce:sup>B values of the residual melt significantly). For minerals with the same coordination of Li and B, the δ<ce:sup loc=\"post\">7</ce:sup>Li and δ<ce:sup loc=\"post\">11</ce:sup>B values are higher for later crystallized minerals. As the δ<ce:sup loc=\"post\">7</ce:sup>Li and δ<ce:sup loc=\"post\">11</ce:sup>B values of magmatic minerals are affected by the amount of Li and B that has been removed from the melt before these minerals crystallized, bulk-rock δ<ce:sup loc=\"post\">7</ce:sup>Li and δ<ce:sup loc=\"post\">11</ce:sup>B values are generally more reliable tracers of the source and evolution of melts than the δ<ce:sup loc=\"post\">7</ce:sup>Li and δ<ce:sup loc=\"post\">11</ce:sup>B values of minerals that crystallized from such a melt. Only if the budgets of Li or B are dominated by one single phase, δ<ce:sup loc=\"post\">7</ce:sup>Li and δ<ce:sup loc=\"post\">11</ce:sup>B values of minerals and bulk rocks are the same.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"17 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516006","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":"Atomic-level insights into nanoclay for prebiotic nucleoside phosphorylation","authors":"Yinyin Qian, Beibei Shi, Guangyao Li, Huaming Yang","doi":"10.1016/j.gca.2025.06.025","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.025","url":null,"abstract":"Kaolinite nanoclay has long been recognized as playing a key role in the origin of life. However, the interaction of kaolinite (Kaol) with biomolecules in prebiotic chemistry and its catalytic mechanism still remain a great challenge. Herein, we comprehensively investigate the nucleoside interactions and phosphorylation processes on Kaol surfaces by a combination of wet-dry cycle experiments and first-principles calculations. The experimental results show that Kaol is able to promote the phosphorylation reactions of four typical nucleosides, but there are differences in the catalytic ability for different nucleosides. In this study, we considered two physicochemically different Kaol end-surfaces—the aluminium-hydroxyl surface (Kaol(001)) and the silica-oxygen surface (Kaol(00 <mml:math altimg=\"si1.svg\"><mml:mover accent=\"true\"><mml:mrow><mml:mtext>1</mml:mtext></mml:mrow><mml:mrow><mml:mo stretchy=\"false\">¯</mml:mo></mml:mrow></mml:mover></mml:math>))—and find that Kaol(001) forms strong hydrogen bonds with the nucleoside, stabilizing the nucleoside that significantly reduces the kinetic barrier to phosphorylation. Moreover, <ce:italic>ab</ce:italic> initio molecular dynamics (AIMD) simulations showed that the Kaol(001)-nucleotide system is kinetically stable, highlighting its potential in protecting the reaction sites of prebiotic molecules and providing strong evidence for the role of Kaol in prebiotic chemistry.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"26 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516072","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":"Process zone specific alteration of rare earth element (REE) patterns across the land–ocean transition of the southern North Sea","authors":"Corinna Mori ,&nbsp;Olaf Dellwig ,&nbsp;Jochen Wollschläger ,&nbsp;Michael Seidel","doi":"10.1016/j.gca.2025.06.017","DOIUrl":"10.1016/j.gca.2025.06.017","url":null,"abstract":"<div><div>Rare earth elements (REE) are powerful tracers in oceanography for tracking boundary exchange and internal biogeochemical processes. While extensive research has focused on REE cycling in marine environments, studies regarding the coastal ocean are limited. Coastal ecosystems are biogeochemically complex, because they are subject to intense organic matter cycling and shifts in redox gradients, driven by both <em>in situ</em> processes and benthic-pelagic interactions. The impact of these dynamics on REE cycling remains largely unclear, raising concern as certain potentially harmful REE, such as samarium (Sm) and gadolinium (Gd), increasingly enter coastal environments due to anthropogenic activities. To identify key drivers of REE cycling in these dynamic environments, we analyzed dissolved REE concentrations across the land–ocean continuum in the German Bight (southern North Sea). We assessed REE concentrations and respective shale-normalized patterns in relation to inorganic and organic parameters such as nutrients, manganese, suspended particulate matter, particulate organic matter, and dissolved organic matter (DOM), characterized both as bulk dissolved organic carbon (DOC) and at the molecular level using ultrahigh-resolution mass spectrometry. Natural and anthropogenic REE primarily originated from riverine input, with significant enrichments at riverine and estuarine stations. The magnitude of anthropogenic Sm and Gd anomalies and heavy-to-light ratio in shale-normalized REE patterns varied among the Elbe, Weser and Ems rivers, likely reflecting the characteristics of their respective catchment areas. The coastal interface was identified as a critical zone where interactions with the benthic environment through deposition and porewater flux led to significant alterations of REE patterns. Offshore, benthic-pelagic coupling diminished, allowing <em>in situ</em> processes to dominate. Changes in heavy-to-light ratio in shale-normalized REE patterns across the land–ocean continuum were attributed to shifts in complexing partners and changes in scavenger pool composition from terrestrial to more stable microbial-derived highly unsaturated DOM nearshore, followed by less stable marine metal-DOM complexes offshore. We highlight the crucial role of coastal interfaces for the cycling of anthropogenic Sm and Gd, acting as important alteration interfaces and reservoirs for anthropogenic REE, affecting their reactivity, environmental fate and affecting marine REE budgets.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"402 ","pages":"Pages 32-48"},"PeriodicalIF":4.5,"publicationDate":"2025-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516007","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":"Na, Ca carbonates in OSIRIS-REx samples: evidence for low-temperature, Na-bearing Brines on Bennu’s Parent Body","authors":"S.A. Singerling, F.E. Brenker, B. Tkalcec, S.S. Russell, T.J. Zega, T.J. McCoy, H.C. Connolly Jr., D.S. Lauretta","doi":"10.1016/j.gca.2025.06.028","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.028","url":null,"abstract":"We describe nanoscale observations obtained via transmission electron microscopy of Na,Ca carbonates in OSIRIS-REx samples of asteroid Bennu. Four Na,Ca carbonate grains were observed (including the one briefly described in McCoy and Russell et al., 2025), ranging in size from<ce:hsp sp=\"0.25\"></ce:hsp>140 nm to 2.36 µm. The stoichiometry of the grains and electron diffraction data best match gaylussite (Na<ce:inf loc=\"post\">2</ce:inf>Ca(CO<ce:inf loc=\"post\">3</ce:inf>)<ce:inf loc=\"post\">2</ce:inf>·5H<ce:inf loc=\"post\">2</ce:inf>O) or pirssonite (Na<ce:inf loc=\"post\">2</ce:inf>Ca(CO<ce:inf loc=\"post\">3</ce:inf>)<ce:inf loc=\"post\">2</ce:inf>·2H<ce:inf loc=\"post\">2</ce:inf>O). The grains rapidly amorphized under the electron beam. We also found that the grains are reactive to the terrestrial atmosphere, with their compositions and textures changing over six months of storage in a standard desiccator. NaCl salts grew on the exteriors of the grains, and the compositions of the carbonates became richer in C, F, Cl, and Ca and poorer in O and Na","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"41 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516094","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":"Three-dimensional variations in carbon inputs to a subduction zone based on Mg–Zn isotopes","authors":"Shuai Xiong, Feng Wang, Yi-Ni Wang, Ke-Chun Hong, Si-Wen Zhang, Sheng-Ao Liu, Wen-Liang Xu","doi":"10.1016/j.gca.2025.06.023","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.023","url":null,"abstract":"Subduction zones are the main pathways for the transport of surficial carbon into the deep Earth. Heterogeneity of decarbonation was recognized in different subduction zones on a global scale. What is unclear yet is the small-scale along-strike variations in carbon released from slab in a subduction zone. In this paper, we present Mg–Zn isotope data for Miocene basalts distributed parallel to the Japan Trench that can be linked to different slab decarbonation efficiencies. The sampling sites can be divided into three groups based on the Mg–Zn isotope data: northern, central, and southern. The northern samples have high δ<ce:sup loc=\"post\">66</ce:sup>Zn (0.40 ‰ to 0.62 ‰) and low δ<ce:sup loc=\"post\">26</ce:sup>Mg (–0.48 ‰ to –0.37 ‰) values (i.e., there is coupling of the Mg–Zn isotopic compositions). The central samples have δ<ce:sup loc=\"post\">66</ce:sup>Zn values that overlap with those of global MORBs (0.25 ‰ to 0.31 ‰), and they have slightly lower δ<ce:sup loc=\"post\">26</ce:sup>Mg values (–0.35 ‰ to –0.19 ‰) than normal mantle (i.e., there is slight decoupling of the Mg–Zn isotopic compositions). In contrast, the southern samples have low δ<ce:sup loc=\"post\">26</ce:sup>Mg (–0.56 ‰ to –0.02 ‰) and normal δ<ce:sup loc=\"post\">66</ce:sup>Zn values (0.26 ‰ to 0.40 ‰) (i.e., there is decoupling of Mg–Zn isotopic compositions). The northern samples with coupled Mg–Zn isotopes indicate that dissolved carbonate sediment in slab-derived fluids contributes to arc/back-arc volcanism. In contrast, the southern samples have decoupled Mg–Zn isotopes, implying that carbonate sediment is retained in the slab and transported to great depths and long distances beneath the mantle wedge. This is consistent with the widespread occurrence of wehrlite xenoliths within associated intraplate volcanoes. These differences in carbon inputs correspond to the slab thermal structure caused by slab geometry and dynamics of mantle flow, which is hot in the north and cold in the south. Globally, the small-scale thermal structure of different subduction zones therefore affects the spatial variations in carbon input in short-distance along the trench, which are probably responsible for the elusive geophysical anomalies and redox heterogeneities of the deep mantle.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"50 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516107","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":"Self-induced differential stress and cascading reactions, fracturing, and permeability enhancement triggered by volatile-consuming reactions","authors":"Atsushi Okamoto ,&nbsp;Fukuma Sakashita ,&nbsp;Kazuki Yoshida ,&nbsp;Otgonbayar Dandar ,&nbsp;Masaoki Uno","doi":"10.1016/j.gca.2025.06.018","DOIUrl":"10.1016/j.gca.2025.06.018","url":null,"abstract":"<div><div>Reaction-induced fracturing is thought to be a key process controlling pervasive volatile-consuming reactions, including the serpentinization and carbonation of peridotites; however, the interactions between reactions, fluid flow, and fracturing remain poorly understood. We performed flow-through hydration experiments on sintered periclase aggregate [MgO + H₂O → Mg(OH)₂] samples with high and low porosities at temperatures of 180–200 °C, confining pressure of 20 MPa, and fluid pressures of 3–5 MPa. We monitored the solid volume, permeability, and axial stress simultaneously. For comparison, we also conducted batch experiments with the same samples. In the batch experiments, the high-porosity sample reacted uniformly with no macroscopic fracturing, whereas a sharp reaction front developed in the low-porosity sample. In the flow-through experiments with high-porosity samples, the reaction proceeded uniformly, with an initial decrease in permeability but no increase in volume. Axial stress then increased, and the sample subsequently yielded gradually. The reaction continued, causing circumferential expansion of the sample with no discrete failure while the permeability remained constant or increased. In the flow-through experiments with low-porosity samples, the reaction began slowly through surface layer spallation. After a prolonged initiation period, mechanical instability led to a sudden large failure. This failure triggered cascading reactions, with a build-up of reaction-induced stress followed by yielding and the formation of new fractures, resulting in the permeability increasing by two orders of magnitude and leading to reaction rates increasing by a factor of 18 compared with the batch experiments. The results suggest that (1) reaction-induced fracturing is strongly enhanced by self-induced differential stress related to the anisotropic elastic properties of the lithosphere, and (2) catastrophic failure can occur during the hydration and carbonation of impermeable mantle peridotite. These findings provide new links between microscopic failure at reaction interfaces and macroscopic fractures in a rock, and have implications for the pervasive serpentinization of the oceanic lithosphere, the formation of serpentine diapirs, and natural and anthropogenic CO₂ sequestration.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"402 ","pages":"Pages 1-15"},"PeriodicalIF":4.5,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516008","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":"Links between forearc decarbonation and generation of high δ26Mg fluids at subarc depths: constraints from carbonate-bearing forearc serpentinites","authors":"Kai Wu, Kan Li, Chang Zhang, Yuxiao Chen, Kaiyun Chen, Weidong Sun, Honglin Yuan","doi":"10.1016/j.gca.2025.06.024","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.024","url":null,"abstract":"Subduction zones play a critical role in carbon exchange between Earth’s surface and interior. While devolatilization of forearc serpentinites has been proposed as a contributor to arc magma genesis, its role in subduction-zone carbon (C) and magnesium (Mg) cycling, as well as its influence on the Mg isotopic variability in global arc lavas, remains poorly constrained. This study investigates Mg isotope fractionation during interactions between forearc peridotites and CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;-rich fluids in the Mianlue tectonic mélange, focusing on carbonate-bearing serpentinites from the Jianchaling and Liangyazi regions. Five Jianchaling lizardite-only serpentinites exhibit a narrow range of δ&lt;ce:sup loc=\"post\"&gt;26&lt;/ce:sup&gt;Mg values (−0.28 ± 0.02 ‰ to −0.13 ± 0.02 ‰), similar to those of four Jianchaling antigorite-lizardite serpentinites (−0.27 ± 0.03 ‰ to −0.17 ± 0.01 ‰). In contrast, seven Liangyazi antigorite-only serpentinites display a broader δ&lt;ce:sup loc=\"post\"&gt;26&lt;/ce:sup&gt;Mg range (−0.27 ± 0.03 ‰ to −0.01 ± 0.02 ‰). Magnesium isotopic compositions of mineral separates reveal temperature-dependent inter-mineral Mg isotope fractionations between carbonate and co-precipitated serpentine minerals. Thermodynamic modeling and mass balance calculations indicate minimal Mg loss from peridotites to fluids during their interaction with CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;-rich fluids. Instead, subsequent fluid infiltration and carbonate dissolution are responsible for the observed Mg isotopic variations. The concurrent precipitation of isotopically heavy silicate minerals and light carbonates in the forearc provides a plausible explanation for the elevated δ&lt;ce:sup loc=\"post\"&gt;26&lt;/ce:sup&gt;Mg values observed in some arc lavas. In subduction zones where the forearc slab-top temperatures can exceed the stability limit of antigorite (600 – 700 °C), significant forearc decarbonation produces CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;-rich fluids that interact with forearc peridotites at the bottom of the mantle wedge, forming abundant isotopically heavy silicate minerals. The subsequent breakdown of these silicates and limited release of slab-derived carbonates at subarc depths may be responsible for the high δ&lt;ce:sup loc=\"post\"&gt;26&lt;/ce:sup&gt;Mg values and low CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; outfluxes characteristic of these subduction zones. In contrast, subduction zones with cooler forearc slab-top temperatures, where subarc slab-top temperatures approach the stability limit of antigorite, experience less significant forearc decarbonation. In such settings, limited formation of isotopically heavy silicate phases and enhanced release of slab carbonates at subarc depths due to infiltrations of slab-derived fluids can potentially result in arc magmas with δ&lt;ce:sup loc=\"post\"&gt;26&lt;/ce:sup&gt;Mg values close to or slightly below the normal mantle. These findings underscore the critical role of fluid-rock interactions in the forearc region in regulating deep carbon cycling a","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"639 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516005","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":"Distinct patterns and drivers of total and refractory terrestrial organic carbon burial in river-dominated continental margins: From climatic control to anthropogenic perturbations","authors":"Xueshi Sun, Dejiang Fan, Xilin Zhang, Peng Cheng, Zuosheng Yang, Zhigang Guo","doi":"10.1016/j.gca.2025.06.020","DOIUrl":"https://doi.org/10.1016/j.gca.2025.06.020","url":null,"abstract":"The burial of terrestrial organic carbon (OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt;) in marine sediments is a major geological CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; sink. The largest sink for OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; burial in present-day oceans lies in river-dominated continental margins, which are key components of the global carbon cycle. Climate change and anthropogenic forcing have disrupted the cycling of OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; at the land–ocean interface, impacting its storage at these margins. Despite this recognition, the fate of OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; in marine sediments and the potential feedback mechanisms of these changes remain unclear, primarily because of the lack of reliable sedimentary records from 1850 to the present that capture the substantial internal spatial and temporal heterogeneity. Here, we present a high-resolution OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; record covering the past two centuries from a well-preserved sediment core in the mud depocenter of the East China Sea, using sedimentological, mineralogical, and geochemical techniques. By integrating our new results with literature data, we quantitatively evaluate the modern patterns and drivers of changes in OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; burial. During the climate-controlled period (pre-1950s), despite high precipitation and sediment influx driven by the East Asian summer monsoon, the observed lower and fluctuating OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; loadings suggest that the OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; accumulation rate was not directly proportional to the lithogenic sediment flux. Analyses of X-radiographs and sediment composition indicated that energetic marine processes—such as tides, waves, and typhoon events that are intensified by the East Asian winter monsoon—promoted sediment resuspension, dispersion, and redeposition. These dynamic physical processes regulate hydrodynamic particle sorting, resulting in the high variability and suppression of OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; burial during this interval. In contrast, the post-1950s era, marked by intensive human impact, saw a persistent decline in the overall OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; burial. This trend is primarily attributed to the reduced delivery of fine mineral sediments and altered sediment sources to marine environments due to large-scale dam construction. Although the preservation of sedimentary OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; has diminished, our study provides new evidence of increased mobilization and burial of refractory OC&lt;ce:inf loc=\"post\"&gt;terr&lt;/ce:inf&gt; in marine sediments. Using a chemical oxidation method, we quantified the proportions of refractory organic carbon (OC) and found that, on average, 60 ± 11 % of the refractory OC exported by the Yangtze River is delivered to the adjacent continental margin. Coinciding with periods of intensive human impact (post-1950s), anthropogenic disturbances, notably inputs of fossil-derived OC, have reintroduced grea","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"18 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144516024","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}