Geochimica et Cosmochimica Acta最新文献

{"title":"Disrupted magmatic evolution controls Nb and REE co-enrichment in alkaline-carbonatite systems","authors":"Chunwan Wei,&nbsp;Cheng Xu,&nbsp;John Mavrogenes,&nbsp;Jindrich Kynicky,&nbsp;Wenlei Song,&nbsp;Yuhan Ma","doi":"10.1016/j.gca.2026.09.012","DOIUrl":"10.1016/j.gca.2026.09.012","url":null,"abstract":"<div><div>Alkaline-carbonatite complexes host major Nb and rare earth element (REE) resources, but the two are rarely concentrated in the same lithological unit. Thus, the processes that allow their co-concentration despite their contrasting geochemical behavior remain unclear. Here we investigate the Khotgor complex, Mongolia, where Nb and REE mineralization is concentrated in calcite-rich syenite, whereas associated feldspar-dominated syenites and carbonatites are non-mineralized. Calcite and REE-bearing minerals from the mineralized syenite and carbonatites have uniform ⁸⁷Sr/⁸⁶Sr_(i) (∼0.70373) and εNd_(i) (∼+1.5), indicating a common mantle-sourced magmatic system. Pyrochlore records progressive Nb sequestration during evolution from silicate-dominated magmas to carbonate-rich liquid. Sparse, zoned Ta-Ti-Zr-rich grains associated with phenocrysts were followed by more abundant, unzoned Nb-dominant pyrochlore aggregate intergrowths of calcite and synchysite. Later hydrothermal modification produced Ba-Sr-rich domains while largely retaining Nb. Calcite grains in the mineralized unit record a shift from magmatic crystallization to REE precipitation, as shown by the decrease in La/Yb_CN from ∼19 in phenocryst cores to ∼6 in synchysite-bearing matrix calcite. Strong negative Ce anomalies (Ce*∼0.03) in matrix calcites and complementary positive anomalies (Ce*∼2.5) in phenocryst rims record subsequent oxidation. Low δ¹⁸O values (∼2.74 ‰) of fluid-related patchy apatite record involvement of an isotopically light meteoric fluid, whereas the increase in calcite δ¹⁸O from ∼8 ‰ in phenocryst cores to 10–25 ‰ in rims and matrix reflects calcite-fluid fractionation during cooling. Non-mineralized carbonatites (La/Yb_CN ∼ 0.06) represent carbonate-rich fractions formed after REE sequestration. We infer that magmatic differentiation co-concentrated Nb and REE in a carbonate-rich liquid, in which Nb precipitated as pyrochlore, while meteoric ingress triggered in situ REE precipitation without substantial Nb remobilization, thereby trapping both metals within the same mineralized unit.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 300-315"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148980599","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":"Magnitude of stable iron isotope fractionation limited by multiple stages of terrestrial core formation","authors":"Gabriel Nathan,&nbsp;Seth A. Jacobson","doi":"10.1016/j.gca.2026.08.006","DOIUrl":"10.1016/j.gca.2026.08.006","url":null,"abstract":"<div><div>One proposed mechanism for generating iron isotopic differences between planetary mantles and chondrites is metal-silicate equilibration during terrestrial core formation. Prior studies of this isotopic fractionation effect employ single-stage core formation models that are inconsistent with reproducing the siderophile element budget of the Earth’s mantle. Here, we model iron isotopic evolution of the Earth’s mantle in a multistage core formation scenario that is consistent with dynamic models of planet formation and reproduces the geochemistry of the bulk silicate Earth, specifically the refractory moderately siderophile elements. We find that multiple stages of core formation rebalance the fractionating effect of metal-silicate equilibration for the iron isotopic system, comparable to or smaller than typical analytical uncertainties in mantle rocks. Ultimately, this rebalancing effect — coupled with stochastic accretion and differentiation histories which further complicate planetary formation processes — makes it unlikely that isotopic fractionation during metal-silicate equilibration is the primary mechanism responsible for the iron isotopic composition of the Earth’s mantle.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 85-98"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148716457","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":"Biogeochemical controls on dissolved micronutrient (Ni, Cu, Zn, Cd) distributions in the Equatorial Pacific Ocean","authors":"Naman D. Singh,&nbsp;Zvi Steiner,&nbsp;Rena Czeschel,&nbsp;Peter Brandt,&nbsp;Yuping Guo,&nbsp;Xue-Gang Chen,&nbsp;Jana Blanke,&nbsp;Angèle Nicolas,&nbsp;Jinqiang Guo,&nbsp;Kathleen J. Gosnell,&nbsp;Edel M. O’Sullivan,&nbsp;Dominik Jasinski,&nbsp;André Mutzberg,&nbsp;Tim Steffens,&nbsp;Eric P. Achterberg","doi":"10.1016/j.gca.2026.08.026","DOIUrl":"10.1016/j.gca.2026.08.026","url":null,"abstract":"<div><div>The Equatorial Pacific Ocean (EPO) is one of the most productive regions in the ocean with upwelling of nutrient-rich subsurface waters and strong outgassing of CO₂, and thereby playing a prominent role in the global carbon cycle. We report distributions of dissolved (d) and particulate (p) trace metals (TM) including nickel (dNi), copper (dCu), zinc (dZn) and cadmium (dCd), along the GEOTRACES transect, GP11, in the EPO during a developing El Niño phase, associated with anomalous surface winds and currents. Using estimates of surface dTM fluxes and water mass mixing in deeper waters, we assessed biogeochemical controls on dTM distributions in the water column. Surface waters (depths &lt; 100 m) showed dTMs minima and significant correlations between pTM and particulate phosphorus, indicating phytoplankton uptake of TMs and low atmospheric input. A large proportion (64–99%) of dNi, dZn and dCd in the surface mixed layer (24–51 m) was supplied by vertical upwelling, which was strongly influenced by the west-east shoaling of the thermocline and transport of sub-surface waters by the Equatorial Undercurrent. Moreover, spatial variability in vertical fluxes controlled biological Cd uptake in the EPO. In mesopelagic and deep waters (depths &gt; 200 m), water mass mixing and organic matter (OM) remineralization largely governed the dCd distribution. The dNi, dCu and dZn distributions and their relationships with macronutrients were determined by particle scavenging of remineralized Ni, Cu and Zn and/or their retention (slower remineralization) to particles. Strong enrichments in dNi and dCu were observed in deep waters (depths &gt; 2500 m) of the eastern and central EPO, which could not be explained by water mass mixing and OM remineralization. Particulate data indicated a limited influence of reversible scavenging and deep-water remineralization, with the supply from sediments likely supporting the dNi and dCu increases in deep waters. Our results underscore the need to better quantify benthic trace metal fluxes across Pacific abyssal sediments, as sedimentary inputs may substantially influence deep ocean micronutrient reservoirs and their eventual redistribution to the upper ocean.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 122-138"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148893600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Synergistic interfacial and multi-omics regulation of La3+/Gd3+ biomineralization by Micromonospora auratinigra","authors":"Lili Wang,&nbsp;Chenyu Yin,&nbsp;Xinyu Chen,&nbsp;Chengliang Cao,&nbsp;Xiuming Liu,&nbsp;Wenping He,&nbsp;Rongpeng Li,&nbsp;Jihong Jiang,&nbsp;Jinjuan Liu","doi":"10.1016/j.gca.2026.02.015","DOIUrl":"10.1016/j.gca.2026.02.015","url":null,"abstract":"<div><div>Microorganisms play pivotal roles in the formation of weathering crust-type rare earth elements (REEs) deposits, yet the mechanisms underlying microbial-mediated REEs immobilization and secondary mineral formation remain insufficiently understood. This study systematically explores the synergistic biosorption and biomineralization mechanisms of La³⁺ and Gd³⁺ by the highly tolerant actinobacterium <em>Micromonospora auratinigra</em>. Under optimized conditions (biomass 1.5 g/L, pH 5, La/Gd ratio 2:1), the strain exhibited a preferential affinity for Gd³⁺ (135.9 mg/g) over La³⁺ (110.1 mg/g), with further enhanced uptake in mixed systems (143.1 mg/g). Kinetic and isotherm modeling indicated monolayer chemisorption behavior following pseudo-second-order kinetics and Langmuir adsorption patterns. Functional group masking experiments, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses revealed that carboxyl, phosphate, and amino groups on the cell surface were key contributors to REEs binding, with carboxyl groups playing the dominant role. Electron microscopy confirmed the formation of LaPO₄ and GdPO₄ nanocrystals on the bacterial surface, while HRTEM and SAED analyses revealed the formation of distinct monazite-type mineral phases. Multi-omics analysis demonstrated that the biosorption and mineralization processes were regulated by peptidoglycan functional groups, heavy metal resistance genes, oxidative stress response systems, and phosphate metabolism pathways. Notably, upregulation of phosphate transport and regulatory genes (<em>pstSCAB</em>, <em>phoR</em>/<em>phoU</em>) promoted phosphate acquisition and REEs-phosphate precipitation, while downregulation of organic acid biosynthesis genes prevented mineral dissolution. This work elucidates the molecular and interfacial mechanisms by which <em>M. auratinigra</em> immobilizes REEs, offering new insights into microbial mediation of REEs geochemical cycling. These findings provide a theoretical basis for the development of environmentally friendly technologies for REEs recovery and sustainable resource utilization.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 28-43"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146209471","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":"FTIR constraints on Martian mantle water from clinopyroxene in nakhlite and shergottite meteorites","authors":"Ioana-Bogdana Radu,&nbsp;Cécile Deligny,&nbsp;Henrik Skogby,&nbsp;Roland Stalder,&nbsp;Jeremy J. Bellucci,&nbsp;Martin J. Whitehouse","doi":"10.1016/j.gca.2026.06.002","DOIUrl":"10.1016/j.gca.2026.06.002","url":null,"abstract":"<div><div>Water on Mars has traditionally been estimated from hydrogen contents in melt inclusions and apatite, yet these may not account for magma degassing or post-crystallization dehydration. Pyroxenes offer an alternative approach, as they incorporate trace amounts of water during crystallisation via charge-balancing structural defects, that are retained after dehydration enabling experimentally reversing water loss and constraining magmatic water contents. Here we report the first hydrothermal rehydration experiments on pyroxene from both nakhlites and shergottites. The treated nakhlite augites contain 140‒185 ppm H₂O, consistent with previous values for Nakhla (130 ± 26 ppm) and within the range of terrestrial basaltic pyroxene. Using clinopyroxene-melt partition coefficients, this corresponds to 1.59 ± 0.03‒1.83 ± 0.10 wt% average H₂O in the nakhlite magma, slightly higher than previous estimates (0.69‒1.42 wt% H₂O). The complex hydrothermal history of nakhlites, including evidence for magmatic degassing and interaction with H₂O-poor, Cl-rich fluids, suggests these estimates may represent minimum values of the nakhlite magmatic water content. Assuming a low degree of partial melting, the nakhlite mantle source is expected to contain 80‒91 ppm H₂O, overlapping previous estimates (59‒184 ppm), and comparable to Earth’s MORB mantle (54‒330 ppm). This is consistent with a common magmatic source for all nakhlites, and broadly consistent with water estimates for the chassignite mantle source (39‒252 ppm), suggesting that any exogenous fluid assimilation had a negligible effect on the net water budget. In contrast, shergottite pigeonites show no detectable water by Fourier Transform Infrared Spectroscopy, consistent with expected water contents of ∼ 2‒11 ppm H₂O derived from published source compositions for depleted and enriched shergottites. Together, these results refine our understanding of martian magmatic water content, consistent with a common, more water-rich mantle source for nakhlites, distinct from the more heterogeneous and generally drier shergottite mantle reservoirs.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 44-55"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148289517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Redox overprinting and anthropogenic source shifts recorded by mercury isotope systematics in Eastern Mediterranean deep-sea sediments","authors":"Xiaowei Chen,&nbsp;Daniel Cossa,&nbsp;Jiawang Wu,&nbsp;Lars-Eric Heimbürger-Boavida,&nbsp;Songjing Li,&nbsp;Zhao Wang,&nbsp;Stéphane Guédron,&nbsp;Wang Zheng,&nbsp;Yi Liu,&nbsp;Jiubin Chen,&nbsp;Ruoyu Sun","doi":"10.1016/j.gca.2026.08.033","DOIUrl":"10.1016/j.gca.2026.08.033","url":null,"abstract":"<div><div>Deep-sea sediments constitute long-term archives of mercury (Hg) burial, yet the chronological record can be biased by post-depositional diagenetic processes, particularly in areas with high organic matter export and redox variations. We present Hg stable isotope data from Holocene deep-sea sediment cores of the Ionian Sea (Eastern Mediterranean) to quantify how depositional redox conditions, early diagenesis, and anthropogenic forcing shape sedimentary Hg systematics. The distinct organic-rich sapropel S1 developed during the early Holocene provides a natural redox perturbation experiment. During sapropel formation, Hg concentrations and accumulation rates increased markedly in concert with organic carbon burial, reflecting efficient scavenging of dissolved seawater Hg under enhanced productivity and stratified water-column conditions with reduced deep-water ventilation. Hg isotope signatures remained invariant and indistinguishable from background sediments, implying minimal isotopic fractionation during primary deposition and preservation of contemporaneous seawater isotope signatures. In contrast, post-depositional oxidation (“burn-down”) of the sapropel induced substantial Hg remobilization and redistribution across redox fronts, generating pronounced negative excursions in δ²⁰²Hg (up to ∼1.6‰, relative to background) coincident with manganese and molybdenum enrichments. These shifts suggest that early diagenesis imposed strong mass-dependent fractionation (MDF), most likely during oxidative mobilization and subsequent re-immobilization of Hg into authigenic phases. Throughout sapropel deposition and oxidation, mass-independent fractionation (MIF, Δ¹⁹⁹Hg and Δ²⁰⁰Hg) remained largely unaffected, indicating that Hg MIF signatures appear insensitive to these post-depositional processes and may preserve surface-derived signatures. The upper oxic sediments in the late Holocene show little impact of redox-driven diagenesis on Hg and record two isotopically distinct anthropogenic phases. A modest Hg enrichment during the late Iron Age–Roman period is characterized by elevated δ²⁰²Hg and near-zero Δ¹⁹⁹Hg values, consistent with lateral transport of local metallurgical residues. In contrast, Industrial Era sediments display sharply increased Hg enrichment accompanied by lower δ²⁰²Hg and slightly positive Δ¹⁹⁹Hg values, suggesting dominant inputs from industrial Hg emissions at a broader scale. Together, these results suggest that sedimentary Hg isotopes preserve both depositional and diagenetic information. When interpreted within a stratigraphically constrained redox framework, paired MDF–MIF systematics provide a robust approach for disentangling redox overprinting from source variability, thereby strengthening the reliability of marine sediments as archives of past Hg cycling and environmental change.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 234-246"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148885178","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":"Corrigendum to “Experimental characterization of multi-pathway diffusion of lithium in feldspar” [Geochim. Cosmochim. Acta 421 (2026) 252–268]","authors":"Brendan Garvey,&nbsp;Megan Holycross,&nbsp;Gabriel Larouche","doi":"10.1016/j.gca.2026.09.001","DOIUrl":"10.1016/j.gca.2026.09.001","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Page 316"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148933542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mg and Ca isotopes of phreatic groundwater on a carbonate island: implications for meteoric diagenesis of carbonates","authors":"Huiwen Huang,&nbsp;Gang Li,&nbsp;Yun Luo,&nbsp;Weihai Xu,&nbsp;Wen Yan","doi":"10.1016/j.gca.2026.09.005","DOIUrl":"10.1016/j.gca.2026.09.005","url":null,"abstract":"<div><div>Meteoric diagenesis can significantly overprint primary geochemical signatures of marine carbonates. Constraining the associated geochemical differentiation is therefore essential for distinguishing primary signals from alteration, but remains difficult based on altered-carbonate geochemistry alone. We investigated major ion concentrations and Ca<strong>–</strong>Mg isotopic compositions (<em>δ</em>^44/40Ca and δ²⁶Mg) of groundwater from Yongshu Island (southern South China Sea), a site marked by extensive freshwater–seawater mixing within its subsurface aquifers. By using Cl⁻ as a conservative seawater tracer in a binary mixing model, the freshwater δ²⁶Mg value of −2.1 ‰ was obtained, whereas the freshwater <em>δ</em>^44/40Ca value (∼0 ‰) was assumed to equal that of seawater, as it showed no correlation with Ca²⁺ concentration. The inferred δ²⁶Mg and <em>δ</em>^44/40Ca values of freshwater are markedly higher than those expected from carbonate dissolution. Together with box modeling of meteoric diagenetic water–rock reactions, these elevated isotopic values are inferred to arise from fluid isotopic evolution under sediment-buffered conditions within the vadose zone. The newly obtained δ²⁶Mg and <em>δ</em>^44/40Ca compositions of freshwater were used to model meteoric phreatic diagenesis of carbonate rocks. The modeled results can well reproduce the coupled Ca<strong>–</strong>Mg isotopic evolution observed in young meteoric water-altered carbonates from coral islands in the South China Sea and the Great Barrier Reef, Australia. These results are interpreted to reflect predominantly fluid-buffered meteoric diagenesis within the meteoric phreatic zone. Differentiating the sediment-buffered vadose zone from the fluid-buffered phreatic zone allows for a coherent interpretation of the Ca–Mg isotopic compositions in both meteoric limestones and reef-island freshwater. Elucidating Mg and Ca isotopic behavior in the vadose and phreatic zones during meteoric diagenesis will provide a robust framework for interpreting paleoenvironmental signals preserved in freshwater-altered carbonates.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 275-287"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148933539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Platinum occurs as α-PtO2 nanoparticles in deep-sea ferromanganese deposits","authors":"Jianlin Liao,&nbsp;Yan Li,&nbsp;Julien Léger,&nbsp;Andrea Koschinsky,&nbsp;Catherine Dejoie,&nbsp;Anne-Claire Gaillot,&nbsp;Irina Snigireva,&nbsp;Andrea Giacomelli,&nbsp;Stephan N. Steinmann,&nbsp;Olivier Mathon,&nbsp;Alain Manceau","doi":"10.1016/j.gca.2026.08.030","DOIUrl":"10.1016/j.gca.2026.08.030","url":null,"abstract":"<div><div>Understanding how critical metals such as platinum (Pt) are enriched in marine environments is essential for advancing knowledge of their geochemical cycles and the formation of oceanic mineral resources. Pt occurs in seawater at picomolar concentrations, yet deep-sea ferromanganese (FeMn) deposits contain up to eight orders of magnitude more Pt. The mechanism behind this enrichment remains unresolved. Although FeMn deposits exhibit high Pt partitioning, their low Pt levels and the co-occurrence of multiple elements pose challenges to investigating Pt oxidation state and uptake processes using traditional spectroscopic methods. In this study, high-energy-resolution X-ray absorption spectroscopy (XAS) was used to elucidate how Pt is sequestered at the atomic scale in FeMn crusts and nodules from the Pacific, Atlantic, and Indian oceans. Pt is present in the tetravalent form, resulting from the oxidation of dissolved divalent Pt in seawater upon interaction with Mn oxides. Tetravalent Pt is precipitated as α-PtO₂ nanoparticles with longer Pt-Pt distances than in well-crystallized α-PtO₂. Density functional theory calculations indicate that the local structure of Pt is best described by α-PtO₂ layers topotactically stacked on vernadite phyllomanganates, similar to (Co,Ni)-asbolane. The Pt content depth profiles are constant during spot analyses by laser ablation-inductively coupled plasma-mass spectrometry, suggesting that the Pt nanoparticles are uniformly dispersed within the ablated volume, rather than occurring as discrete metallic nuggets. These findings reveal a new pathway for Pt immobilization in marine environments and suggest that thermodynamically stable α-PtO₂ serves as a long-term sink for oceanic Pt. The advanced capabilities of high-energy-resolution XAS offer new opportunities to deepen understanding of how trace metals are sequestered in structurally disordered and chemically complex natural materials, with potential applications in georesource exploration.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 182-194"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148893595","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nickel and magnesium isotopic evidence for rapid melt-mantle interactions in supra-subduction zone settings","authors":"Zhuang Ma,&nbsp;Shui-Jiong Wang,&nbsp;Fahui Xiong,&nbsp;Wenzhong Wang,&nbsp;Kun-Feng Qiu,&nbsp;Long Zhang,&nbsp;Zhenyu Chen,&nbsp;Hanjie Wen,&nbsp;Li-Guang Wu","doi":"10.1016/j.gca.2026.09.006","DOIUrl":"10.1016/j.gca.2026.09.006","url":null,"abstract":"<div><div>Supra-subduction zone (SSZ) settings are characterized by extensive melt-mantle interactions that contribute substantially to the enrichment of economically critical metals. However, the rates and durations of these interactions are not well understood. In this study, we integrate nickel (Ni) and magnesium (Mg) isotopic analyses, first-principles calculations, and chromium-aluminum (Cr-Al) diffusion chronometry of chromite from SSZ-type ophiolites to elucidate the processes and timescales of melt-mantle interaction during chromite formation. Chromite and coexisting olivine from the Luobusa and Yushigou ophiolites exhibit systematically heavy Ni-Mg isotopic compositions (<em>δ</em>^60/58Ni = 0.63‰ to 0.96‰ for chromite and 0.09‰ to 0.36‰ for olivine; <em>δ</em>^26/24Mg = 0.16‰ to 0.61‰ for chromite and −0.26‰ to −0.13‰ for olivine) compared to mantle values, with significant inter-mineral isotope disequilibrium. These features cannot be attributed to subsolidus elemental exchange, but instead indicate that kinetic isotope fractionation during melt-mantle interaction was the dominant process. Diffusion modeling of both Ni-Mg isotopes and Cr-Al zoning in chromite yields consistently short timescales: Ni-Mg isotope diffusion constrains the duration to centennial scales, while Cr-Al diffusion modeling gives a median of decades to centuries (80% &lt; several thousand years). Our findings demonstrate that melt-mantle interactions in SSZ settings are transient but highly efficient, providing a temporal framework to constrain the rapid formation of podiform chromitites.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 288-299"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148933545","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}