Geochimica et Cosmochimica Acta最新文献

{"title":"Exploring the affinity and selectivity of sedimentary Mackinawite (FeS) towards natural organic matter","authors":"Kathryn Balind, Milad Ezzati, Aude Picard, Yves Gélinas","doi":"10.1016/j.gca.2025.07.009","DOIUrl":"https://doi.org/10.1016/j.gca.2025.07.009","url":null,"abstract":"While iron oxides have been thoroughly explored in terms of their ability to sorb and sequester organic carbon (OC) in sediments, the role of iron sulfide (Fe-S) minerals in the long-term sequestration of OC remains poorly defined. In this study, we assessed the affinity of different types of natural organic matter (NOM) towards synthetic Fe-S minerals using sorption isotherms. We found affinities and sorption capacities varying in the following order: plankton NOM > corn leaves NOM > aged terrestrial NOM. Scanning electron microscopy showed that NOM increases the size and surface area of Fe-S aggregates, likely also influencing their surface reactivity. High NOM contents in Fe-S minerals protected Fe(II) from oxidation after exposure to atmospheric oxygen. Analysis of the synthetically prepared Fe-S-NOM complexes by synchrotron scanning transmission X-ray microscopy (STXM) coupled to near-edge X-ray absorption fine-edge structure (NEXAFS) spectroscopy revealed strong interactions between Fe-S minerals and NOM extracted from plankton, specifically with amide and carboxylic functional groups. We also attempted to identify and characterize interactions between OC and Fe-S minerals in natural sulfidic sediments from the St. Lawrence Estuary and the Saguenay Fjord, hence linking our work on synthetic iron sulfides to what is occurring in natural environments, although this effort proved more challenging owing to the presence of Fe(III) minerals even at depth and the difficulty in distinguishing FeS from other Fe(II) minerals. We present depth concentration profiles of dissolved OC, iron, and sulfur in the liquid-phase (pore water) along with speciation data from sequential extractions of sulfur in the solid-phase collected from sediment cores. We found a clear association between mixed Fe(II)/Fe(III) minerals and OC in sediments, which, combined with the results of the synthetic FeS experiment, suggests that Fe-S minerals can promote OC sequestration in sediments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621780","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":"Uranium reduction in modern and ancient marine carbonate settings – insights from anaerobic U extractions and high-energy resolution X ray spectroscopy","authors":"Kasper Primdahl Olesen, Elvira Bura-Nakic, Ivan N. Pidchenko, Kristina O. Kvashnina, Tais W. Dahl","doi":"10.1016/j.gca.2025.07.006","DOIUrl":"https://doi.org/10.1016/j.gca.2025.07.006","url":null,"abstract":"In the marine environment, hexavalent uranium, U<ce:sup loc=\"post\">6+</ce:sup>, is incorporated into primary carbonate minerals with the same isotopic composition (δ<ce:sup loc=\"post\">238</ce:sup>U) as the seawater in which they are formed. Yet, modern marine carbonate sediments carry heavier U isotope compositions. This enrichment of heavy U isotopes has been linked to biogenic U reduction in and below the Fe-reducing zone inside the sediment. Still, the oxidation state(s) of uranium in marine carbonate sediments undergoing syndepositional diagenesis has never been measured before. Here, we 1) present an anaerobic ion chromatographic technique based on the TEVA® resin to chemically separate and quantify abundances of tetravalent U<ce:sup loc=\"post\">4+</ce:sup> and hexavalent U<ce:sup loc=\"post\">6+</ce:sup> fractions in the carbonate, and 2) compare the results from ion chromatography to U L3 edge HERFD-XANES spectroscopic measurements of the total U in sediments to 3) estimate U oxidation states of fresh carbonate sediments from a modern seawater-fed lake and ancient limestones. We find that our anaerobic extraction technique can provide credible evaluations of reduced U<ce:sup loc=\"post\">4+</ce:sup> and oxidized U<ce:sup loc=\"post\">6+</ce:sup> contents, applicable to carbonate sediments and rocks. Our results show that U resides both in reduced and oxidized states in modern carbonate sediments and ancient carbonate rocks. By comparing air-exposed, oven-dried samples to samples always kept under strictly anaerobic condition, we find that the majority of authigenic U in modern carbonate sediments resides in oxidation-sensitive phases that accumulate with sediment depth, instead of being structurally bound in carbonate minerals (aragonite and calcite) We propose a model to account for the observed trends in U oxidation state, U phase associations, and U isotope fractionation, where a substantial fraction of U in the sediments is likely delivered via microbial reduction and precipitated as a non-crystalline, reduced form near the sediment–water interface. We suggest these oxidation-sensitive reduced U species participate in redox cycling where some U is re-oxidized and perhaps bio-reduced again later, for example in the presence of Fe(III) mineral surfaces that undergo reductive dissolution with depth. Simultaneously, a continued incorporation of recalcitrant and isotopically light (i.e. <ce:sup loc=\"post\">238</ce:sup>U-depleted) U from the pore fluids into diagenetic carbonate may occur. The determination of U oxidation states in modern carbonates in this study helps to bridge a gap in our knowledge of how U isotope signals are affected by <ce:italic>syn</ce:italic>-sedimentary diagenetic U transformations, opening new avenues for understanding sedimentary U cycling and improving the δ<ce:sup loc=\"post\">238</ce:sup>U paleo redox proxy.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"13 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621781","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":"Coupled zinc and iron isotope fractionation in mantle xenoliths: records of carbonated melt–lithosphere interaction","authors":"Tian-Hao Wu, Sheng-Ao Liu","doi":"10.1016/j.gca.2025.07.007","DOIUrl":"https://doi.org/10.1016/j.gca.2025.07.007","url":null,"abstract":"Coupled zinc and iron isotopic variations in basaltic magmas are potential indices of recycled crustal materials that have modified their mantle sources. Nevertheless, how these isotopes fractionate in response to various types of mantle metasomatism is not well constrained as of yet. Here we present high-precision Zn (δ<ce:sup loc=\"post\">66</ce:sup>Zn<ce:inf loc=\"post\">JMC-Lyon</ce:inf>) and Fe (δ<ce:sup loc=\"post\">57</ce:sup>Fe<ce:inf loc=\"post\">IRMM-014</ce:inf>) isotope data and <ce:italic>in situ</ce:italic> chemistry for direct mantle samples (peridotites, pyroxenites, and their mineral separates), occurring as xenoliths within Cenozoic alkaline basalts from northeast China. Based on mineralogical and chemical compositions, these xenoliths are classified into four groups. Group I peridotites are almost non-metasomatized, whereas Group II peridotites exhibit typical characteristics of carbonated silicate melt metasomatism (e.g., high La/Yb, low Ti/Eu). Distinct from the normal mantle-like δ<ce:sup loc=\"post\">66</ce:sup>Zn (∼0.18 ‰) and δ<ce:sup loc=\"post\">57</ce:sup>Fe (∼0.03 ‰) values of Group I peridotites, Group II peridotites have highly variable and positively correlated δ<ce:sup loc=\"post\">66</ce:sup>Zn (−0.04 ‰ to 0.29 ‰) and δ<ce:sup loc=\"post\">57</ce:sup>Fe (−0.38 ‰ to 0.07 ‰; N = 6). The generally light Zn and Fe isotopic compositions of Group II peridotites are attributed to kinetic isotope fractionation during carbonated melt infiltration. Low-Mg# pyroxenites, characterized by Mg# (100 × atomic ratio of Mg/(Mg + Fe)) of &lt;89 and positive Eu anomalies in clinopyroxenes, have extremely high and positively correlated δ<ce:sup loc=\"post\">66</ce:sup>Zn (0.27 ‰–0.62 ‰) and δ<ce:sup loc=\"post\">57</ce:sup>Fe (0.19 ‰–0.84 ‰; N = 5). These pyroxenites are interpreted as cumulates from carbonated melts, akin to the host basalts originating from partial melting of the asthenospheric mantle containing recycled carbonate. By comparison, high-Mg# pyroxenites (Mg# &gt; 90) display gradual modal variations in the composite xenoliths, consistent with being the product of silicate melt-peridotite reaction. These pyroxenites have higher δ<ce:sup loc=\"post\">57</ce:sup>Fe (0.02 ‰–0.24 ‰) but lower δ<ce:sup loc=\"post\">66</ce:sup>Zn (−0.05 ‰ to 0.03 ‰; N = 5) than those of the normal mantle. The negatively correlated Zn and Fe isotopic ratios were caused by diffusion-induced fractionation during silicate melt metasomatism. Collectively, these observations demonstrate that asthenosphere-derived, carbonated and silicate melts could induce substantial and coupled Zn and Fe isotopic variations in the lithospheric mantle through reaction and diffusion during mantle metasomatism. Therefore, coupled variations of Zn and Fe isotopes in mantle-derived rocks or magmas provide valuable approaches for tracing carbonated melt–lithospheric mantle interaction.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"57 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621782","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":"Gallium isotope fractionation during granite weathering: Insights from two profiles in contrasting climatic conditions","authors":"Wei Yuan, Ting Gao, Zhengrong Wang, Jiubin Chen, Hongming Cai, Tong Zhang, Guanghui Yu, Nana Feng, Chengshuai Liu, Congqiang Liu, Jacques Schott","doi":"10.1016/j.gca.2025.07.004","DOIUrl":"https://doi.org/10.1016/j.gca.2025.07.004","url":null,"abstract":"The recently developed gallium (Ga) isotope systematics provides valuable insights into continental weathering, particularly under conditions of intense chemical weathering. However, the relationship between Ga isotope fractionation and the factors influencing the intensity of silicate weathering has yet to be systematically explored. In this study, we report Ga isotope compositions from two granite weathering profiles developed under contrasting climates: a temperate semiarid climate in the Beijing profile and a tropical moist monsoon climate in the Guangdong profile. Our study shows that the majority of Ga in these weathering profiles is retained within the crystal-lattice of Al-bearing minerals, followed by Fe-bearing minerals, with minimal surface adsorption. Mössbauer spectra and sequential extraction results show that the influence of Fe on Ga concentrations and isotope compositions becomes more significant as weathering intensity increases, driven by the transformation of dissolved ferrous Fe into ferric Fe at advanced weathering stages. Both granite weathering profiles exhibit a similar trend of slightly decreasing δ<ce:sup loc=\"post\">71</ce:sup>Ga values from bedrock to surface (Beijing profile: from 0.71 ‰ to 0.61 ‰; Guangdong profile: from 0.70 ‰ to 0.54 ‰). This suggests that the lighter Ga isotope, <ce:sup loc=\"post\">69</ce:sup>Ga, is preferentially enriched in regolith relative to the coexisting aqueous solution in the pore spaces of weathered rocks, consistent with observations from a basalt weathering profile. In the Beijing profile, a strong correlation between τ<ce:italic><ce:inf loc=\"post\">Ga,Th</ce:inf></ce:italic> (a weathering index) and δ<ce:sup loc=\"post\">71</ce:sup>Ga values suggests that Ga isotope compositions are mainly controlled by the dissolution of primary minerals. This correlation indicates that variations in δ<ce:sup loc=\"post\">71</ce:sup>Ga values can serve as effective tracers of weathering intensity during early stages of chemical weathering. However, this pattern is absent in the Guangdong profile, where Ga isotope compositions appear to be influenced not only by mineral dissolution but also by processes such as mineral adsorption and coprecipitation. A broader comparison of our results with previously published Ga isotope composition suggests the lithology of bedrock provides the major control on the extent of Ga isotope fractionation. Other factors, including the composition of secondary minerals and the climatic conditions, also play significant roles in influencing Ga mobility and Ga isotope fractionation during chemical weathering.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"69 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144622047","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":"Multiple fluid-rock interactions in the subduction channel evidenced by magnesium isotopes","authors":"Yongxiang Yao ,&nbsp;Yuanyuan Xiao ,&nbsp;Yaoling Niu ,&nbsp;Weidong Sun","doi":"10.1016/j.gca.2025.07.003","DOIUrl":"10.1016/j.gca.2025.07.003","url":null,"abstract":"<div><div>Fluids from the subducted oceanic slab are closely associated with mass transfer in subduction zones, which significantly affect the composition of arc magmas and deep mantle. Previous studies have shown that magnesium isotopes can be used to identify the source of fluids and to trace carbonate cycling. However, the Mg isotope variation as a function of fluids in the subduction channel remains obscure. As large-scale fluid flows and strong fluid-rock interactions can significantly enhance elemental mobility, Mg isotope variations may be recorded in metabasaltic rocks with large-scale veins (which represent original fluid pathways). Here we present Mg isotope data for different parts of a metabasaltic block from Tianshan (ultra)high pressure metamorphic belt, southwest of China to reveal the Mg isotope composition of fluids and their effects in the subduction channel. All the samples have been divided into three groups depending on their position in each “pillow” of the metamorphic block, i.e., those from the omphacite-rich interior, glaucophane-rich vein and transitional part. The omphacite-rich interior is mainly composed of omphacite and phengite, with minor garnet, while the glaucophane-rich vein mainly consists of garnet, glaucophane and epidote. The transitional part between the omphacite-rich interior and glaucophane-rich vein is dominated by epidote and carbonate, and aragonite has been widely replaced by dolomite. Together with our previous study, we think that the metabasaltic block has experienced two stages of rehydration overprinting after eclogitization: the first stage rehydration led to the common enrichment of LILEs in the whole block compared to its protolith E-MORB; the second stage rehydration resulted in the carbonate reprecipitation at the transitional part and the redistribution of garnet component.</div><div>The δ²⁶Mg values of the omphacite-rich interior are lower (−0.42 ‰ to −0.34 ‰) than those of MORBs (−0.25 ± 0.06 ‰), which probably indicates that subduction dehydration can lead to lighter Mg isotope composition of the residual eclogite and heavier Mg isotope composition of the released fluids. Furthermore, the lighter Mg isotope composition of the transitional part (δ²⁶Mg = −0.67 ‰ ∼ −0.63 ‰) and glaucophane-rich vein (δ²⁶Mg = −0.71 ‰ ∼ −0.54 ‰) may be caused by the reprecipitation of dolomite and garnet through Ca-Mg exchange as the result of interaction with externally derived carbonate rich fluids. The residual fluid after the reprecipitation of carbonate minerals is also expected to show a heavier Mg isotope composition. In addition, the recrystallization of dolomite in the subduction channel could not only hamper the influence of subducted carbonate-derived fluids on the heavier Mg isotope composition of arc magmas compared to MORBs, but also facilitate the transfer of carbonate with lighter Mg isotope compositions into the deep mantle.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 67-78"},"PeriodicalIF":4.5,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621783","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":"Limited mercury (Hg) partitioning into bitumen and efficient gaseous Hg reabsorption during early thermal maturation of organic-rich mudrocks","authors":"Asri O. Indraswari ,&nbsp;Joost Frieling ,&nbsp;Erdem Idiz ,&nbsp;Tamsin A. Mather ,&nbsp;Hugh C. Jenkyns ,&nbsp;Stuart A. Robinson ,&nbsp;Alexander J. Dickson","doi":"10.1016/j.gca.2025.07.001","DOIUrl":"10.1016/j.gca.2025.07.001","url":null,"abstract":"<div><div>Recent studies have looked into the impact of exposure to extremely high temperature, such as typifies contact metamorphism, on mercury (Hg) distributions in sediments, and observed significant Hg loss with increasing temperature. By contrast, sediment cores of Lower Jurassic organic-rich Posidonienschiefer (also known as Posidonia Shale) from the Lower Saxony Basin, Germany seemingly showed Hg enrichment after maturation related to basin subsidence and burial under more typical geothermal gradients. To investigate the apparent differences in Hg behaviour, we conducted a series of artificial maturation experiments on immature Posidonienschiefer samples, analysing Hg concentrations within rock residues and bitumen generated during early maturation stages. Thermal desorption profiles were used to track Hg speciation changes in the matured sediment. Our results show a progressive decrease in Hg concentrations in sediments with increasing thermal maturity throughout the experiments, which dominantly relates to released gaseous Hg with only a fraction of the Hg being partitioned into the bitumen (≤1% of the total initial Hg). Further experiments showed that gaseous Hg in closed vessels was rapidly (≤1 h) and efficiently (≥95 %) reabsorbed into the sediment during cooling. We speculate that our experiments may simulate some of the processes that drive Hg mobilisation and recapture occurring in contact aureoles, such as the rapid release and recapture of gaseous Hg. However, the Hg speciation changes that occur in our experiments and during natural burial maturation clearly differ. Specifically, the changes in Hg speciation in the natural system with burial-related maturation suggest that under those conditions organic matter associated Hg may instead transition into more thermally stable phases.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 240-251"},"PeriodicalIF":4.5,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144622048","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":"Sequestration of carbon in the forearc mantle wedge","authors":"Guoji Wu, Yongsheng Huang, Michihiko Nakamura, Tatsuki Tsujimori, Yuan Li","doi":"10.1016/j.gca.2025.07.002","DOIUrl":"https://doi.org/10.1016/j.gca.2025.07.002","url":null,"abstract":"Subduction zones are crucial in governing the global carbon (C) cycle. Recent geochemical and geophysical observations have revealed extensive serpentinite carbonation in the forearc mantle wedges, hinting at a potentially vast C reservoir within these serpentinized areas. In this study, we conducted experimental investigations on serpentinite carbonation in multicomponent (H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O–CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;–NaCl) fluids under various pressure–temperature (P-T) conditions that mimic the mantle wedge. Our aim was to precisely determine the reaction extent (RE, RE = &lt;ce:italic&gt;V&lt;ce:inf loc=\"post\"&gt;mgs&lt;/ce:inf&gt;&lt;/ce:italic&gt; / &lt;ce:italic&gt;V&lt;ce:sup loc=\"post\"&gt;0&lt;/ce:sup&gt;&lt;ce:inf loc=\"post\"&gt;mgs&lt;/ce:inf&gt;,&lt;/ce:italic&gt; where &lt;ce:italic&gt;V&lt;ce:inf loc=\"post\"&gt;mgs&lt;/ce:inf&gt;&lt;/ce:italic&gt; represents the actual magnesite volume in the run product and &lt;ce:italic&gt;V&lt;ce:sup loc=\"post\"&gt;0&lt;/ce:sup&gt;&lt;ce:inf loc=\"post\"&gt;mgs&lt;/ce:inf&gt;&lt;/ce:italic&gt; denotes the theoretical magnesite volume through the complete reaction of CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;.) of serpentinite carbonation in the multicomponent fluids and, subsequently, estimate C storage in the forearc mantle wedge. Our findings indicate that serpentinite reacts with CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; to form magnesite and talc. Time-series experiments demonstrated that reaction equilibrium is attained within 48 h. The results revealed that RE increases with rising P-T and CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; concentration in fluids. However, a notable decrease in RE was observed with increasing salinity, particularly at low salinities (&lt; 10 wt%). This decrease can be attributed to the reduced fluid pH, decreased CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; and H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O activities (a&lt;ce:inf loc=\"post\"&gt;CO2&lt;/ce:inf&gt; and a&lt;ce:inf loc=\"post\"&gt;H2O&lt;/ce:inf&gt;), and increased magnesite solubility in salt-bearing fluids. Based on previous and our experimental data, we derived an empirical equation to describe the RE of serpentinite carbonation in H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O–CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;–NaCl fluids. We extrapolated the potential RE regarding P-T conditions and fluid compositions within the mantle wedge to estimate C inventory in forearc mantle wedges. Our calculations indicated that even a minimal degree of serpentinization (&lt; 10 vol%) in the mantle wedge could result in the sequestration of 49–76 % of C from slab-derived fluids originating from depths of 15–80 km through serpentinite carbonation, leading to the formation of magnesium-rich carbonates. On a global scale, this carbonation process has the capacity to sequester 0.02–4.17 million tons of C per year (Mt C/yr) within forearc mantle wedges. Consequently, a portion of the C stored in carbonated serpentinite may persist in the cold, stagnant regions of the wedge, potentially contributing to long-term C storage and seismic activity. Furthermore, due to processes such as down-dragging and subduction erosion, some of the C","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"38 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621824","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":"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":"Mineralogical and chronological records of strong shock metamorphism in pigeonite cumulate eucrite Northwest Africa 8326","authors":"Lang Zhang ,&nbsp;Ai-Cheng Zhang ,&nbsp;Xiao-Wen Liu ,&nbsp;Yan-Jun Guo ,&nbsp;Jia-Ni Chen ,&nbsp;Yuan-Yun Wen ,&nbsp;Qiu-Li Li ,&nbsp;Yu Liu ,&nbsp;Xiao-Xiao Ling ,&nbsp;Jin S. Zhang","doi":"10.1016/j.gca.2025.06.032","DOIUrl":"10.1016/j.gca.2025.06.032","url":null,"abstract":"<div><div>Mineralogical records of strong shock metamorphism (around or above 20 GPa) are common in L-group chondrites, Martian meteorites, and lunar meteorites, but rarely reported in Howardite-Eucrite-Diogenite (HED) meteorites. Here, we report detailed mineralogical observations of shock-induced features and ion-microprobe merrillite U-Pb ages from the pigeonite cumulate eucrite Northwest Africa (NWA) 8326. Shock-induced mineralogical features in NWA 8326 contain: (i) planar fractures in pyroxene and partial maskelynitization of plagioclase; (ii) presence of high-pressure minerals such as tissintite, stishovite, vacancy-rich augite, super-silicic garnets within melt veins, and xieite, tuite, and reidite in the host rock outside melt veins. We also observed fine-grained clinoenstatite and pigeonite at the edges of shock melt and propose they formed through metastable crystallization. Our study indicates that NWA 8326 experienced shock metamorphism of at least 20 GPa, comparable to those observed in L-group chondrites, Martian meteorites, and lunar meteorites. We propose that the relatively low shock pressures inferred for shocked eucrites in previous investigations could be due to the absence of suitable high-pressure mineralogical indicators. The ion-microprobe ²⁰⁷Pb/²⁰⁶Pb age of merrillite in NWA 8326 is 4238 ± 32 Ma (95 % confidence) and represents the timing of the shock metamorphism. The similarity of the impact ages across NWA 8326, some eucrites, lunar samples/meteorites, and chondrites suggests that there were probably widespread impact events at ∼4.2 Ga in the Solar System.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 1-19"},"PeriodicalIF":4.5,"publicationDate":"2025-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144571699","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":"Zirconium isotope considerations of carbonatite genesis and implications for carbonatite metasomatism of the Earth’s mantle","authors":"Tomáš Magna ,&nbsp;Vladislav Rapprich ,&nbsp;Shengyu Tian ,&nbsp;Frédéric Moynier ,&nbsp;R.Johannes Giebel ,&nbsp;Ondřej Pour ,&nbsp;František Laufek","doi":"10.1016/j.gca.2025.06.029","DOIUrl":"10.1016/j.gca.2025.06.029","url":null,"abstract":"<div><div>We present the first comprehensive survey of stable zirconium (Zr) isotope systematics in carbonatites of various ages from distinctive tectonic settings and with different mineralogy, chemistry, and the presence or absence of significant post-emplacement overprint. All these parameters are plausibly linked with extreme variability in abundances of Zr in carbonatites spanning over five orders of magnitude although Zr typically is considered as an immobile element. No temporal variation in δ^94/90Zr values (per mil deviation from IPGP-Zr reference solution) is observed, indicating a global scale homogeneity of Zr isotope composition of the ultimate mantle sources of carbonatites over time, in accord with homogeneous δ^94/90Zr (per mil deviation from IPGP-Zr solution) value of mantle and crust. Carbonatites devoid of significant post-magmatic mineral assemblages (hydrothermal baryte, goethite, chalcedony and fluorite) define a δ^94/90Zr of +0.31 ± 0.08 ‰, which is ∼0.3 ‰ above the currently accepted mantle value. This difference likely is owing to Zr isotope fractionation during low-degree partial melting at mantle conditions and fractionation of carbonatite melts, although exact isotope fractionation factors between carbonate melt and silicate mantle have not yet been experimentally constrained, and alternative scenarios (diffusion, liquid immiscibility, different coordination of Zr in carbonate and silicate melts) should also be considered. This value also is ∼0.2 ‰ above mean crustal δ^94/90Zr value and contamination by common crustal materials can thus be considered negligible. Most of the δ^94/90Zr variation, in total reaching ∼0.5 ‰, is restricted to carbonatites with clear evidence of post-emplacement processes, resulting in ⁹⁴Zr-depleted signature with δ^94/90Zr as low as −0.10 ‰. This decrease is paralleled by broadly colinear increases in Zr/Hf and Nb/Ta. These observations collectively underscore the enhanced mobility of expectedly immobile Zr and Nb during overprint by F- and OH-rich liquids, paralleled by notable Zr isotope fractionation. Mantle lithologies metasomatized by carbonate-rich liquids may thus potentially acquire a wide range of Zr/Hf and Nb/Ta ratios, and δ^94/90Zr values.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"403 ","pages":"Pages 37-51"},"PeriodicalIF":4.5,"publicationDate":"2025-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144587408","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}