Chemical Geology最新文献

{"title":"Extremely positive δ13C and subsurface CO2 phase separation isotope fractionation","authors":"Cheng Wang ,&nbsp;Wenxuan Hu ,&nbsp;Xun Kang ,&nbsp;Xiaolin Wang ,&nbsp;Bin Fu ,&nbsp;Suping Yao","doi":"10.1016/j.chemgeo.2025.122855","DOIUrl":"10.1016/j.chemgeo.2025.122855","url":null,"abstract":"<div><div>Extremely positive δ¹³C is found in calcite veins for the first time in the Huangqiao CO₂-gas reservoir, eastern China, with ¹³C-enriched values as high as +16.9 ‰. The calcite cannot be explained as a product of isotopic evaporation fractionation and/or microbial methanogenesis, given the high formation temperatures of 100–160 °C. Consequently, we propose a new model that attributes the extremely δ¹³C enrichment to subsurface vapor–liquid CO₂ phase separation. In the model, deep CO₂ was initially dissolved in the pore water, and then phase-separation occurred when CO₂ underwent supersaturation. Light ¹²CO₂ preferentially escaped, leading to the enrichment of heavier ¹³CO₂ in the pore water. During tectonic movements, the ¹³C-enriched pore water was injected into the gas reservoir strata and the high-δ¹³C calcite veins were precipitated along fractures. Numerical simulation supports this hypothesis, suggesting that phase separation can induce considerable C isotope fractionation. At temperatures below 140 °C, δ¹³C in fluid systems can rise to 17 ‰ through the phase separation of approximately 4.53 × 10¹¹ m³ CO₂, aligning with that of the current CO₂ reserves in the Huangqiao CO₂ gas field. Simultaneously, the δ¹³C values of the escaped CO₂ remain relatively stable and fall within the δ¹³C range of the current-day CO₂. Our results provide important insights into the isotopic fractionation in subsurface fluid systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"688 ","pages":"Article 122855"},"PeriodicalIF":3.6,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144089554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics and evolution of iron speciation during early diagenesis in the sand-mud transition zone of the East China Sea Shelf","authors":"Yumeng Zhu ,&nbsp;Daidu Fan ,&nbsp;Jianfeng Su ,&nbsp;Yijing Wu ,&nbsp;Xiang-Zhou Meng","doi":"10.1016/j.chemgeo.2025.122841","DOIUrl":"10.1016/j.chemgeo.2025.122841","url":null,"abstract":"<div><div>The early diagenesis of iron is a critical component of the biogeochemical cycling within shelf sediments; however, its variability across different sedimentary environments has been less known. This study analyzed two sediment cores (EH2-23 A and EH2-23B) from the sand-mud transition zone of the East China Sea (ECS) shelf, with a focus on sediment grain size, total organic carbon (TOC) content, ²¹⁰Pb and ¹³⁷Cs dating, iron speciation and porewater chemistry. The results reveal that the upper section of EH2-23 A and the lower section of EH2-23B comprise palimpsest sandy sediments, while the middle section of EH2-23 A consists of relict sandy sediments, all of which are characterized by low TOC%, older ages, and limited contents of highly reactive iron (Fe_HR), indicating minimal diagenetic activity. The lower section of EH2-23 A features interbedded sandy and muddy sediments, shaped by fluctuating hydrodynamic conditions and influenced by submarine groundwater discharge. In contrast, the upper section of EH2-23B comprises younger, TOC-rich muddy sediments, where early diagenesis is predominantly driven by sulfate reduction. Sandy sediments consistently exhibit higher degrees of pyritization (DOP) compared to muddy sediments, reflecting prolonged diagenetic processes. Depth-dependent patterns of the ratios of Fe_HR to total iron (Fe_HR/Fe_T) and pyrite to Fe_HR (Fe_py/Fe_HR) are classified into four distinct types. These findings contribute to a deeper understanding of early diagenesis and the C-S-Fe cycle in river-dominated shelf environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"687 ","pages":"Article 122841"},"PeriodicalIF":3.6,"publicationDate":"2025-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143943720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"High-resolution solid-state 7Li NMR study of lithium incorporation in calcite and aragonite","authors":"A. Zhadan ,&nbsp;V. Montouillout ,&nbsp;J. Aufort ,&nbsp;V. Mavromatis ,&nbsp;E. Balan","doi":"10.1016/j.chemgeo.2025.122842","DOIUrl":"10.1016/j.chemgeo.2025.122842","url":null,"abstract":"<div><div>The concentration of Li and its isotope compositions in CaCO₃ minerals have been proposed as emerging paleo-environmental tools. Yet the bonding environment of Li in calcite and aragonite, a prerequisite for interpreting mechanisms controlling Li incorporation and isotope fractionation, is not known. In this study, the atomic-scale environment of lithium in two synthetic samples of calcite and aragonite, is determined for the first time using ⁷Li Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The spectra display several overlapping signals with ⁷Li chemical shift ranging between −2 and + 1 ppm in the calcite sample, and spanning a narrower range, from −1 to 0 ppm, in the aragonite sample. This attests to a diversity of Li atomic-scale environments, which are interpreted in the light of a theoretical study of Li-bearing calcite and aragonite models using the Density Functional Theory (DFT). In the aragonite sample, Li is dominantly located at neighbouring substitutional and interstitial sites, the interstitial Li atom ensuring the charge balance of the Li for Ca substitution. In the calcite sample, Li ions occur at substitutional and interstitial sites, but additional mechanisms could ensure the charge balance, notably involving the incorporation of H⁺ ions at nearby carbonate sites. This variability of Li solid-state environment could explain why it is challenging to identify the dominant factors controlling the Li incorporation in inorganic calcium carbonates from aqueous solutions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122842"},"PeriodicalIF":3.6,"publicationDate":"2025-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144098501","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 controls on Li, Sr and oxygen isotope composition of mixed CaMg carbonate phases with implications for sedimentary dolomites","authors":"Colton J. Vessey ,&nbsp;Yinuo Li ,&nbsp;Maija J. Raudsepp ,&nbsp;Jean-Michel Brazier ,&nbsp;Anna L. Harrison ,&nbsp;Sasha Wilson ,&nbsp;Sylvia Riechelmann ,&nbsp;Vasileios Mavromatis","doi":"10.1016/j.chemgeo.2025.122836","DOIUrl":"10.1016/j.chemgeo.2025.122836","url":null,"abstract":"<div><div>The formation of ordered dolomite is unlikely to occur under ambient Earth's surface conditions, yet “disordered dolomite,” has been shown to crystallize at temperatures as low as 40 °C. Such synthetic precipitates have a similar <em>d</em>(104) spacing as dolomite, and have been studied previously to determine their O isotope compositions as a function of temperature with the goal of using oxygen isotopes as a temperature proxy. However, laboratory synthesis yields mineralogical assemblages that transform to more stable phase assemblages over time. Previous studies however have not thoroughly addressed how this transformation proceeds and how it affects O isotope compositions of the precipitates. To better understand the relationship between temperature and δ¹⁸O values of Ca-Mg‑carbonates at temperatures &lt;100 °C, in this study, Ca<img>Mg carbonates were synthesized at 40, 60 and 80 °C and incubated up to 104 days. Mineralogical composition was quantified using Rietveld refinement of X-ray diffraction patterns, while concomitantly monitoring fluid and solid compositions to assess the utility of the δ¹⁸O_solid, Li, and Sr compositions as paleo-proxies in complex Ca-Mg‑carbonate assemblages. The results suggest a continuous transformation of the mineralogy of the samples throughout the duration of the experimental runs, although Mg/Ca of the bulk solids remained quasi-constant at ∼1, and between 40 and 104 days of reaction the bulk δ¹⁸O_solid values did not exhibit significant variations. These δ¹⁸O_solid values were used to estimate temperature-dependent oxygen isotope fractionation between bulk solid and fluid that can be expressed as:<span><span><span><math><msup><mn>10</mn><mn>3</mn></msup><mi>ln</mi><msub><mi>α</mi><mrow><mi>solid</mi><mo>−</mo><mi>fluid</mi></mrow></msub><mo>=</mo><mn>1.78</mn><mspace></mspace><mfenced><mrow><mo>±</mo><mn>0.13</mn></mrow></mfenced><mfrac><msup><mn>10</mn><mn>6</mn></msup><msup><mi>T</mi><mn>2</mn></msup></mfrac><mo>+</mo><mn>8.47</mn><mfenced><mrow><mo>±</mo><mn>1.20</mn></mrow></mfenced></math></span></span></span></div><div>where T is temperature in Kelvin.</div><div>The use of this relation yields significantly different temperature dependence compared to that reported earlier by <span><span>Schmidt et al. (2005)</span></span> using the same synthesis procedure. The difference can be assigned to mineralogical changes occurring in the precipitates over the course of the 104-day runs that may not have occurred in the earlier study owing to a shorter experimental duration. Here we discuss in detail the role mineralogy has on the chemical and isotopic compositions of Ca<img>Mg carbonates, and the implications for using Ca<img>Mg carbonate minerals as paleoarchives.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122836"},"PeriodicalIF":3.6,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143942050","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluation of sample pretreatment methods for boron concentration analysis","authors":"Wei Wei ,&nbsp;Thomas Algeo ,&nbsp;Lin Chen ,&nbsp;Zhiquan Li ,&nbsp;Cody Lazowski ,&nbsp;Katherine Snihur ,&nbsp;Daniel Alessi ,&nbsp;Kurt Konhauser","doi":"10.1016/j.chemgeo.2025.122838","DOIUrl":"10.1016/j.chemgeo.2025.122838","url":null,"abstract":"<div><div>Elemental boron (B) concentrations have been shown to be useful in reconstruction of paleosalinity conditions. Accurate measurement of the B content of a sample is critical for this purpose, but B is a light and relatively volatile element, substantial amounts of which can be lost through sample preparation protocols that fail to take this property of B into consideration. Here, we evaluate the effects of four commonly used sample preparation protocols on measured B concentrations. The Conventional Acid Method uses concentrated HNO₃ and HF, but the latter acid can cause volatilization of B. A second method, the modified Conventional Acid Method, uses the same acids but with the addition of H₃PO₄ to reduce B volatility. Two further methods eliminate HF entirely: the Ammonium Digestion Method makes use of NH₄F/NH₄HF₂, and the Alkali Fusion Method fuses the sample with Na₂O₂. We tested 9 samples and 4 standards using these four pretreatment methods. Our results show that the Alkali Fusion Method consistently has the highest B yields, with an average recovery rate of ∼98 %, whereas the other methods have average yields ranging from 72 % to 92 %. Owing to the potential for incomplete B recovery using these other methods (especially the Conventional Acid Method, which has the lowest recovery rate), salinity values based on those methods are likely to be underestimated. Given the dominant use of the Conventional Acid Method in older studies reporting B concentrations, paleosalinity estimates based on those studies will require re-evaluation. In the future, we recommend that all studies measuring B concentrations make use of the Alkali Fusion Method in order to achieve near-quantitative recovery, and to provide for maximum robustness and comparability of paleosalinity estimates among studies.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"687 ","pages":"Article 122838"},"PeriodicalIF":3.6,"publicationDate":"2025-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143948997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Formation and biogeochemical potential of ferromanganese oxide deposited on dead sponges","authors":"Wenzhu Li ,&nbsp;Hengchao Xu ,&nbsp;Dominic Papineau ,&nbsp;Kaiwen Ta ,&nbsp;Shun Chen ,&nbsp;Shamik Dasgupta ,&nbsp;Shuangquan Liu ,&nbsp;Bohao Yin ,&nbsp;Xiaotong Peng","doi":"10.1016/j.chemgeo.2025.122840","DOIUrl":"10.1016/j.chemgeo.2025.122840","url":null,"abstract":"<div><div>Ferromanganese oxides that coat dead marine biological remains such as porous sponges, fish bones, and cold-water corals are widespread in deep-sea environments. However, their mineralization mechanisms and the intrinsic connections between ferromanganese oxides and biological remains are poorly understood. In this study, we examine ferromanganese oxide coatings (FMC) on five dead sponge specimens collected from seamounts in the Central Basin of the South China Sea (SCS) and in the West Mariana Ridge (WMR). Sponge FMC are friable and loosely attached precipitates grown onto the reticulate skeletal structure and they have a narrow range of thicknesses. High-resolution microscopic observations show that sponge FMC are composed of porous, spheroidal, and relatively compact sheath-like Mn oxides with variable oxidation state, which possibly imply a different formation pathway from general ferromanganese deposits (FMD). New observations further reveal the position of sponge FMC spatially overlapping with sponge collagen fibers, as well as reveal widespread presence of microbial cells, Nitrogen-enriched OM with abundant amide groups, and nanoscopic apatite in sponge FMC. The observations provide a new insight into the precipitation of sponge FMC that is related to the decomposition of skeleton-associated proteins of the sponge. The degradation of organic matter contributes to localized enrichment of metal cations and micro-scale oxic-suboxic transitions. Meanwhile, small-molecule carbon compounds derived from protein decomposition are favorable to the activity of heterotrophic microorganisms, which modulates localized physicochemical conditions. These redox variations in microenvironments are proposed to trigger the oxidation and reduction of metal cations and their precipitation into FMC around sponge remains. While the composition of sponge FMC resembles that of hydrogenic crusts, their rare element and yttrium (REY) patterns display notable discrepancies with hydrogenic processes, including weak negative or significantly positive Ce anomaly. The discrepancies reflect the unique geochemical characteristics of sponge FMC, possibly attributed to differences in the activity of oxic-suboxic transitions and in the redox behavior of Mn and Ce metals. Biological remains in the deep-sea have a widespread occurrence and most of them similarly serve also as FMC substrates, which may point to a broader implication for marine polymetallic cycling than previously considered.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"687 ","pages":"Article 122840"},"PeriodicalIF":3.6,"publicationDate":"2025-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143943719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"(UTh)/He Geochronology of Fe and FeAl Lateritic Duricrusts and Bauxites in Central-Northern Amazonia: Implications for Paleoclimate and Landscape Evolution","authors":"Márcio Fernando dos Santos Albuquerque ,&nbsp;Adriana Maria Coimbra Horbe ,&nbsp;Cécile Gautheron ,&nbsp;João Gabriel Cavalcante Vieira ,&nbsp;Pedro Val ,&nbsp;Rosella Pinna-Jamme ,&nbsp;Carlos Alejandro Salazar","doi":"10.1016/j.chemgeo.2025.122835","DOIUrl":"10.1016/j.chemgeo.2025.122835","url":null,"abstract":"<div><div>Over the past 100 million years, intense lateritization has resulted in the widespread development of Fe, Fe<img>Al, and bauxite lateritic duricrusts across Amazonia. In Central-Northern Amazonia, Fe-rich lateritic duricrusts formed around 44 Ma, with peaks at 11–10 Ma and 5–4 Ma, while bauxite formation occurred between 25 and 15 Ma. Expanding this interpretation to the Amazonian region, two main bauxitization episodes have been identified: (i) between 30 and 15 Ma and (ii) post-15 Ma, most pronounced at ∼3–4 Ma. These lateritic duricrusts suggest that lateritization persisted from the Eocene to the Pliocene. This indicates a predominantly humid, well-drained climate conducive to goethite (bauxite) formation, overprinted by drier ferruginization pulses associated with global climatic fluctuations.</div><div>These lateritic duricrusts have acted as effective erosion-resistant surfaces, forming three distinct geomorphic levels. Surface 1 (S1, &gt;240 m a.s.l.) and Surface 2 (S2, 100–240 m a.s.l.), characterized by extensive bauxite and Fe<img>Al lateritic duricrusts, developed at ∼20 Ma and between ∼17 and ∼ 11–5 Ma, respectively. Surface 3 (S3, &lt;100 m a.s.l.) formed under intense ferruginous lateritization at ∼4 Ma. A progressive decrease in goethite ages and Al content from S1 to S3 reflects increasing landscape dissection. Furthermore, (U<img>Th)/He data reveal a significant fluvial incision rate of 28 m/Ma, suggesting pronounced landscape rejuvenation, particularly between 10 and 3 Ma, which overprints older weathering phases preserved in southern Amazonia. Neotectonic activity facilitated the preservation of complete lateritic profiles on hilltops and plateaus, whereas truncated profiles with stone lines characterize valley slopes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"689 ","pages":"Article 122835"},"PeriodicalIF":3.6,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143948465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tracking the transition from magmatic to post-crystallization environment in the Sesia Magmatic System (Italy) by coupling quartz OH-defects and trace element analyses","authors":"G. Tumaini ,&nbsp;L. Tavazzani ,&nbsp;H. Skogby ,&nbsp;F. Bernardi ,&nbsp;S. Sinigoi ,&nbsp;D. Lenaz","doi":"10.1016/j.chemgeo.2025.122810","DOIUrl":"10.1016/j.chemgeo.2025.122810","url":null,"abstract":"<div><div>The production of a significant thermal and fluid anomaly during the assembly of large magmatic bodies inevitably leads to a prolonged, post-magmatic evolution of the system. To shed light on the transition between magmatic and post-crystallization environment, we investigated the variation of OH-defects and trace elements content in quartz from intrusive and eruptive products of the Sesia Magmatic System (SW Alps, Italy). Specifically, quartz crystals were sampled from a floor-to-roof section of the Valle Mosso Pluton and two rhyolitic units of the Sesia Caldera, which represents the crystallized remnants of a magmatic plumbing system beneath a large Permian caldera. A total of 120 quartz crystals were analysed using Fourier Transform InfraRed (FTIR) spectroscopy to investigate OH-defects both quantitatively and qualitatively and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) to assess trace element abundances. Results indicate systematic variations: (1) intrusive quartz shows gradual decrease in Ti and increase in total defect water content (1–25 ppm), following the differentiation degree; (2) volcanic quartz displays variable Ti and water contents (2–14 ppm) comparable to those of the intrusive lithologies; (3) in both intrusive and eruptive units, lattice-bound Al-specific defects dominate over non-lattice bound Li-specific defects, except in a porphyritic dike showing evidence of fast cooling. Our findings suggest that, in absence of fast cooling, slow-diffusing elements and lattice-bound OH-defects (e.g. Al, Ti, AlOH) preserve primary magmatic signals, while fast-diffusing elements (e.g. Li) and interstitial defects (e.g. LiOH) provide insights into post-crystallization histories. The combined analysis of these features offers a powerful tool for reconstructing the thermal and chemical evolution of magmatic systems, from magma chamber processes to post-eruptive alteration. Moreover, it provides insights on the robustness of quartz OH-defects and trace element inventory as a tool for provenance indicator.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"688 ","pages":"Article 122810"},"PeriodicalIF":3.6,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144138657","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Constraints on Fe-Ca metasomatism in mineralized mantle rocks: Insights from in-situ geochemistry and thermodynamic modeling","authors":"R. Coltat ,&nbsp;C.G.C. Patten ,&nbsp;J.A. Padrón-Navarta ,&nbsp;F. Hochscheid ,&nbsp;M. Ulrich ,&nbsp;Y. Branquet ,&nbsp;P. Boulvais ,&nbsp;C.J. Garrido","doi":"10.1016/j.chemgeo.2025.122826","DOIUrl":"10.1016/j.chemgeo.2025.122826","url":null,"abstract":"<div><div>Ultramafic-hosted seafloor massive sulfide deposits have been reported in present-day oceanic settings for nearly thirty years. However, the development of comprehensive genetic models that account for deep-seated hydrothermal processes is largely hindered by the limited availability of seafloor observations and their reliance on large-scale geophysical studies. The Platta nappe (Swiss Alps) preserves a Jurassic hydrothermal system (the Marmorera-Cotschen Hydrothermal System; MCHS), where Cu-Fe-Co-Zn-Ni mineralization is associated with Fe-Ca silicates (ilvaite, hydrogarnet, and diopside). Petrographic analyses and thermodynamic modeling indicate that Fe-Ca metasomatism occurred between 300 and 360 °C and at low <em>f</em>O₂ (from FMQ −6 to +1), likely coeval with early-stage serpentinization. The composition of Fe-Ca silicates (Co, Ni, and REE contents, measured by in-situ LA-ICP-MS) indicates fluid-rock interaction from an ultramafic-dominated system to an open-system, involving fluids derived from both mafic and ultramafic rocks. Mineralogical and geochemical signatures of Fe-Ca silicates in the MCHS do not support genetic relationships with common rodingitization. Our results highlight that Fe-Ca metasomatism may be a widespread deep-seated alteration along mafic–ultramafic rock contacts or in mantle rocks modified through melt-rock interaction accompanying mantle exhumation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"687 ","pages":"Article 122826"},"PeriodicalIF":3.6,"publicationDate":"2025-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143949054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Triple oxygen isotopes of rice (Oryza sativa L.) phytoliths as a quantitative proxy for relative humidity","authors":"Ritika Kaushal ,&nbsp;Prosenjit Ghosh ,&nbsp;Ilya N. Bindeman","doi":"10.1016/j.chemgeo.2025.122823","DOIUrl":"10.1016/j.chemgeo.2025.122823","url":null,"abstract":"<div><div>Relative humidity is a key climate parameter that varies with global temperature and the continentality of a location. It indicates the atmospheric moisture content, a significant component of the hydrological cycle. Notably, relative humidity has a strong potential to be recorded in the isotopic composition of silica precipitates within plant tissues, as the triple oxygen isotope compositions (δ¹⁷O, δ¹⁸O, and Δ¹⁷O) of evaporating plant waters vary systematically with relative humidity. Here, we investigated the triple oxygen isotope compositions of phytoliths, a biogenic silica mineral extracted from the grain husks of rice (<em>Oryza sativa</em> L.), to assess their utility as recorders of relative humidity during the growing season. We reconstructed triple oxygen isotopic values of equilibrium waters and compared them to isotopic compositions of environmental water at the sites and with the modeled plant waters. Results showed significant dependency of Δʹ¹⁷O of phytoliths and the Y intercept of the reconstructed meteoric waters on relative humidity, exhibiting lower and negative values for drier sites, which creates an application of the empirical relationship developed in the study as a quantitative recorder of relative humidity. Further, we measured the amount of structural water (3–5 wt%) in phytoliths and their hydrogen isotopic compositions (δ²H) (−165 to −119 ‰) to investigate their sensitivity to growing season ambient moisture levels and source water δ²H, and these lack correlations. While oxygen isotope composition (δ¹⁸O) of rice grain organic matter (expressed as ¹⁸O enrichment above source water) has already been established as a proxy for relative humidity, this new triple oxygen isotope approach on relatively environmentally resilient phytoliths will facilitate constraining hydroclimate estimates from the same rice grain specimen or from other environmental archives. As rice has been an important monsoonal cereal crop across tropical and subtropical Asia since the mid-Holocene, roughly 6000 years ago, while its wild progenitors date back to Cretaceous, further investigation is needed to establish the ability of phytoliths to preserve pristine signatures and be used as paleoenvironmental tool.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"687 ","pages":"Article 122823"},"PeriodicalIF":3.6,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144099328","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}