Chemical Geology最新文献

{"title":"Fe isotope systematics and their role in constraining front- and rear-arc processes in Iran Cenozoic magmatism: Beyond compositional and radiogenic isotopes evidence","authors":"Shahrouz Babazadeh ,&nbsp;Yajun An ,&nbsp;M. Santosh ,&nbsp;Tanya Furman ,&nbsp;Davood Raeisi ,&nbsp;Behnam Gholipour ,&nbsp;Massimo D'Antonio","doi":"10.1016/j.chemgeo.2025.122961","DOIUrl":"10.1016/j.chemgeo.2025.122961","url":null,"abstract":"<div><div>The Cenozoic arc of Iran preserves archetypal exposures of the continental arc developed during the north-eastward subduction of the Neo-Tethys oceanic slab and records the history of flare-up magmatism within the Zagros Orogen. Here we present a new dataset of high-precision Fe–Sr–Nd isotopic compositions of Eocene–Oligocene frontal- and rear-arc (<em>i.e.</em>, pre-collisional) magmatic products associated with subduction of the Neo-Tethys Ocean beneath Iran to provide new constraints on the fractionation of Fe isotopes and cycling of Fe within these tectonic settings. The δ⁵⁶Fe values range from +0.07 ‰ to +0.15 ‰, falling within the range of arc-related rocks worldwide. The rear arc samples display higher δ⁵⁶Fe (+0.135 ± 0.010 (2σ)) than samples from the coeval frontal arc (+0.090 ± 0.006 (2σ)). The low Fe³⁺/ƩFe values of all investigated samples in the range from 0.26 to 0.36 and the lack of negative correlation between δ⁵⁶Fe and Fe³⁺/ƩFe argue against incorporation of any significant sulfate- and/or carbonate-bearing fluids. Based on geochemical and isotopic data, we postulate that the high-flux magmatic events (<em>i.e.,</em> flare-ups) are related to partial melting of a garnet-free lherzolite mantle source and limited crustal assimilation. Our results also demonstrate that the Fe isotope fractionation in the Zagros orogen is primarily governed by fractional crystallization of Fe²⁺-rich phases (<em>e.g.</em>, olivine, clinopyroxene), particularly in rear-arc domains where deeper crystallization promotes heavier δ⁵⁶Fe signatures. Although changes in oxidation state can affect Fe isotope fractionation when iron is added or lost from the system, the relatively narrow range in Fe³⁺/ΣFe ratios and the absence of a systematic covariation with δ⁵⁶Fe suggest that redox-driven effects were likely secondary with respect to crystal–melt partitioning in this setting. This stands in marked contrast to global arc systems, particularly oceanic arcs, where slab-derived oxidizing fluids typically dominate over magmatic differentiation, underscoring the Zagros as a case where source composition and fractional crystallization outweigh subduction-related redox processes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122961"},"PeriodicalIF":3.6,"publicationDate":"2025-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144633017","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":"87Sr/86Sr of Ca-sulfates and water in Atacama Desert as tracer for Ca sources and hydrological distribution processes","authors":"Katharina Deußen, Carsten Münker, Michael Staubwasser","doi":"10.1016/j.chemgeo.2025.122956","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2025.122956","url":null,"abstract":"The Atacama Desert, known as the driest region on Earth, has accumulated substantial salt deposits owing to hyperarid conditions prevailing since the Miocene. These salt deposits mainly include Ca-sulfates and halite, but are also known for their large nitrate deposits. This study focuses on the sources of Ca-sulfates, which occurs in a great mineralogical and compositional diversity. Previous research argued that main sources contributing sulfate to the Atacama salt budget include secondary atmospheric sulfate and biologically recycled sulfate. Secondary atmospheric sulfate originates mostly from marine and atmospheric sources. Additionally, sources delivering Ca into the Atacama Desert include weathered material from the Andes, which is transported by rivers and groundwater flow into the Central depression and to a somewhat lesser extent also marine aerosols. However, there are still open issues, in particular with respect to the elemental mass balances of Ca and sulfur that are different because of contrasting relative abundances in seawater derived components and weathering products. This study uses <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr isotope compositions of both lacustrine as well as pedogenic Ca sulfates and water samples to further investigate sources and transport pathways of Ca within the Atacama Desert. Two case studies from the driest portion of the Atacama Desert, namely the Tiliviche basin (−19.5°S) and the Quillagua-Llamara-Basin (−21.5°S), are investigated in detail. The sulfate samples and their detrital impurities were dissolved utilizing a newly developed method for selective digestion of Ca-sulfates, using anion exchange resin. This method allows for rapid dissolution of Ca-sulfate samples without affecting inherent siliciclastic material. The water samples analyzed exhibit a moderately radiogenic range in <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr of ~0.7063 to ~0.7075. Fossil salar Ca-sulfates display less variation, ranging from ~0.7065 to ~0.7072, whereas pedogenic samples diverge toward higher values, spanning a range from ~0.7067 to ~0.7081. Siliciclastic particles, incorporated within the Ca-sulfates, span a wider <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr range from ~0.7058 to ~0.7095.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"13 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2025-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621777","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":"A general, microkinetic model for dissolution of simple silicate and aluminosilicate minerals and glasses as a function of pH and temperature","authors":"M.P. Andersson ,&nbsp;S.M. Ramsheh ,&nbsp;A.M. Schade ,&nbsp;J.D. Kubicki ,&nbsp;M. Turchi ,&nbsp;T.R. Walsh ,&nbsp;D. Okhrimenko ,&nbsp;M. Solvang ,&nbsp;S.L.S. Stipp","doi":"10.1016/j.chemgeo.2025.122960","DOIUrl":"10.1016/j.chemgeo.2025.122960","url":null,"abstract":"<div><div>Silicates and aluminosilicates form 95 % of Earth surface rocks and contribute substantially to building materials. Understanding their dissolution is essential for understanding the impact of mineral-H₂O-CO₂ equilibria and rock weathering on the carbon cycle and for optimising material performance and safety. Predicting dissolution rates is a key but traditional empirical models rely on non-integer reaction orders, which have little meaning, mechanistically and often must be determined for each system separately.</div><div>We present a microkinetic model for silicate dissolution, that describes behaviour of crystalline and amorphous silicates, with and without aluminium. The model, which builds on transition state theory for surface group hydrolysis, offers a general framework, that is applicable across a range of silicate materials. It considers factors, such as surface deprotonation and electrostatic interactions. The model predictions show excellent agreement with observed activation energies and dissolution rates, over a broad pH range, demonstrating the importance of electrostatic surface interactions and the role of aluminium in enhancing dissolution, particularly at low pH. The model predicts dissolution at high temperature and salinity so is robust for application in a variety of environmental scenarios. The advanced understanding of silicate dissolution offers promise for optimising material design, climate modelling and geochemical applications.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122960"},"PeriodicalIF":3.6,"publicationDate":"2025-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144613236","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":"Release and partitioning of neodymium and its radiogenic isotope during basaltic weathering","authors":"Anup Kumar Sharma ,&nbsp;Tarun Kumar Dalai ,&nbsp;Prem Chand Kisku ,&nbsp;Jitendra Kumar Pattanaik ,&nbsp;Sambuddha Misra ,&nbsp;Shivansh Verma ,&nbsp;Anil Dutt Shukla","doi":"10.1016/j.chemgeo.2025.122957","DOIUrl":"10.1016/j.chemgeo.2025.122957","url":null,"abstract":"<div><div>Studies on the chemical weathering of rocks on continents are essential for developing and refining elemental and isotopic compositions as robust tracers of weathering. In this study, we investigate chemical weathering in two basaltic weathering profiles from the Rajmahal Volcanic Province in India, after a thorough evaluation of their preservation state and potential external contamination. This investigation included measurements of major and trace elements concentrations, and ¹⁴³Nd/¹⁴⁴Nd ratios (expressed as <span><math><msub><mi>ε</mi><mi>Nd</mi></msub></math></span>) in bulk samples and chemically extracted exchangeable and oxyhydroxide phases. The major element compositions clearly indicate progressive chemical weathering in both profiles. Based on variations in [Sm], [Nd] and <span><math><msub><mi>ε</mi><mi>Nd</mi></msub></math></span> as a function of the chemical index of alteration (CIA), we infer that the preferential release of radiogenic neodymium (¹⁴³Nd) results from differential chemical weathering of minerals such as pyroxene. Using Th as a reference immobile element, we estimate that up to 40 % of Nd is lost from the parent basalts during weathering. The <span><math><msub><mi>ε</mi><mi>Nd</mi></msub></math></span> values of the weathering solutions, calculated based on mass balance considerations, are ∼5.0 units higher than that of the parent basalts. Our results also unequivocally demonstrate that the degree of radiogenic Nd release is correlated with CIA. Our results of incongruent release of radiogenic Nd, in conjunction with published reports of extensive Nd adsorption onto river sediments and their <span><math><msub><mi>ε</mi><mi>Nd</mi></msub></math></span> difference between the leachate and residual phases, allow us to posit that riverine particulate <span><math><msub><mi>ε</mi><mi>Nd</mi></msub></math></span> would be modulated during fluvial transport.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122957"},"PeriodicalIF":3.6,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144613186","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":"The antimony isotope composition of Earth's mantle and crust","authors":"A.B. Kaufmann ,&nbsp;S. Weyer ,&nbsp;S. Viehmann ,&nbsp;F. Marxer ,&nbsp;I. Horn ,&nbsp;R.L. Rudnick ,&nbsp;A. Vymazalová ,&nbsp;S. Kiefer ,&nbsp;J. Majzlan ,&nbsp;M. Lazarov","doi":"10.1016/j.chemgeo.2025.122959","DOIUrl":"10.1016/j.chemgeo.2025.122959","url":null,"abstract":"<div><div>A new ion-exchange chromatography method was developed for the separation of Sb from different matrices to determine the δ¹²³Sb values of the bulk silicate Earth (BSE) and upper continental crust (UCC) relative to NIST SRM 3102a (δ¹²³Sb = [((¹²³Sb/¹²¹Sb)_sample/(¹²³Sb/¹²¹Sb)_{NIST SRM 3102}) - 1] × 1000). Using this method, we analyzed a wide variety of ultramafic to felsic igneous rocks, metamorphic, and sedimentary rocks. Ultramafic and mafic rocks, most closely representing the composition of the depleted upper mantle, display small variations in δ¹²³Sb from −0.11 to 0.11 ‰, yielding a rather homogenous Sb isotopic composition of 0.00 ± 0.04 ‰ (average, 2SE, <em>n</em> = 16). The average δ¹²³Sb value of intermediate and felsic igneous rocks (<em>n</em> = 10) and magmatic sulfides (<em>n</em> = 2) is nearly indistinguishable from that of the depleted upper mantle, indicating insignificant Sb isotope fractionation during formation of the continental crust. The depleted upper mantle may, thus, be considered to represent the BSE. By contrast, greater variability in δ¹²³Sb (−0.28 to 0.52 ‰) is observed for Mesoarchean to Paleozoic glacial diamictite composites, potentially recording the compositional evolution of the UCC. Mesoarchean diamictites tend to have slightly heavier Sb isotopic composition (average δ¹²³Sb = 0.31 ± 0.38 ‰, 2SD, <em>n</em> = 4), though they are within uncertainty of the average values of Paleoproterozoic (0.07 ± 0.46 ‰, 2SD, <em>n</em> = 7), Neoproterozoic (0.01 ± 0.29 ‰, 2SD, <em>n</em> = 9) and Phanerozoic (average 0.00 ± 0.14 ‰, 2SD, <em>n</em> = 3) diamictites. The reason for the large variability of δ¹²³Sb of the Precambrian UCC, as indicated by the diamictites, is uncertain, but may reflect weathering effects, an isotopically heterogeneous early UCC, changing behavior of Sb during crustal differentiation, or a sampling bias (e.g., all of the Archean diamictites are from the Kaapvaal craton). Combining data obtained for the diamictites with those of felsic and intermediate magmatic samples yields a δ¹²³Sb value of 0.07 ± 0.07 ‰ (2SE, <em>n</em> = 33), which provides an estimate for the average UCC. These results provide a framework for investigating the formation of Sb ore deposits, and deep- or near-surface bio-geochemical Sb cycling.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122959"},"PeriodicalIF":3.6,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144613281","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":"Refertilized Neoproterozoic sub-arc Tongbai Orogen lithospheric mantle preserved between the North China and Yangtze cratons","authors":"Tingting Wang ,&nbsp;Jianping Zheng ,&nbsp;James M. Scott ,&nbsp;Ilya Bindeman ,&nbsp;Xianquan Ping ,&nbsp;Jingao Liu","doi":"10.1016/j.chemgeo.2025.122958","DOIUrl":"10.1016/j.chemgeo.2025.122958","url":null,"abstract":"<div><div>Cratons form the nuclei of continents, and their margins are key locations for lithospheric mantle construction, modification and destruction. Here, we present bulk-rock major and trace element data, oxygen isotope compositions, platinum group element (PGE) concentrations, and <em>Re</em><img>Os isotopic data for the Liushuzhuang orogenic peridotites from the Paleozoic Tongbai Orogen in central China. These peridotites represent the only known mantle fragments within the Tongbai orogen, which is situated between the North China and Yangtze cratons along the former Shangdan Ocean. Building on our published petrographic and mineralogical data, which identify these rocks as phlogopite-amphibole-rich harzburgites and dunites, our new geochemical results confirm significant refertilization–as indicated by linear correlations between bulk rock MgO and Al₂O₃ and TiO₂ and, elevated (La/Yb)_N (4.2 to 14.2), enrichment in large ion lithophile elements (e.g., K, Rb, Ba, Th and U), and positive Pb anomalies. A subtle 0.24 ‰ increase of olivine δ¹⁸O (5.05 to 5.29 ‰) from the harzburgites to the dunites, translating into ∼0.17 ‰ increase (5.23 to 5.40 ‰) in reconstructed bulk compositions, indicates that the melt-rock reactions required high-δ¹⁸O slab-derived fluids. Although petrographic and geochemical evidence suggests that the dunites formed via melt-rock interaction, the most depleted dunites exhibit low Re concentrations (0.02–0.07 ppb) and unradiogenic ¹⁸⁷Os/¹⁸⁸Os ratios (0.12350–0.12464), indicating minimal disturbance of their <em>Re</em><img>Os isotope systematics. They yield Neoproterozoic T_RD model ages (0.68–0.84 Ga), representing a minimum timing of melt extraction. On the basis of the Re<img>Os isotopic data, the Liushuzhuang peridotites are unlikely to have been from the adjacent Archean-Proterozoic cratonic mantle. Instead, they can be interpreted as fragments of sub-Tongbai arc mantle lithosphere that were assembled, depleted and refertilized during the Paleozoic. Combined with sulfide petrology and positive Ru<img>Pd anomalies, we interpret that slab-derived high-<em>f</em>O₂, Ti-rich fluids/melts, along with S-undersaturated boninitic melts and S-saturated basaltic melts, penetrated the sub-arc Tongbai mantle. Our findings provide new geochemical and isotopic evidence for the existence of Neoproterozoic sub-arc lithospheric mantle in the Tongbai Orogen and offer rare insights into how ultra-refractory mantle domains are generated and preserved outside Archean cratons.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122958"},"PeriodicalIF":3.6,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144604923","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":"Emplacement and formation of archean anorthosites in the lower crust via hydrous magma underplating and differentiation: Evidence from a new pressure estimator","authors":"Hua Huang ,&nbsp;Yuanming Pan ,&nbsp;Biji Luo ,&nbsp;Yuanbao Wu","doi":"10.1016/j.chemgeo.2025.122955","DOIUrl":"10.1016/j.chemgeo.2025.122955","url":null,"abstract":"<div><div>Understanding the emplacement depth of Archean anorthosites is crucial for deciphering the mechanisms governing Earth's continental crust formation. Traditionally, Archean anorthosites were thought to crystallize in shallow, low-pressure environments, favoring high anorthite plagioclase formation. However, recent research, including hydrous experimental studies and investigations of Phanerozoic arc root complexes, suggests that anorthosites may have formed in high-pressure environments within the lower crust. Our study contributes to this understanding by systematically comparing amphibole and plagioclase datasets from Phanerozoic arc root complexes with independent geothermobarometric results. These results validate the use of early amphibole and late plagioclase crystallization as a robust proxy for high-pressure conditions. Building upon these insights, we conduct a comprehensive re-examination of the emplacement and formation of the Archean Fiskenæsset Anorthosite Complex (FAC). Our multifaceted approach combines field investigations, petrographic analysis, and geochemical methods to unravel the processes involved in underplating hydrous magma and its subsequent differentiation. The pressure estimated for the FAC from a new approach based on amphibole-plagioclase crystallization sequences and supported by independent geothermobarometers suggests an emplacement depth of approximately 25–28 km, placing it in the lower crust. The formation of extremely calcic plagioclase (An 94–99) in Suite B gabbros likely requires crystallization from hydrous basalts with anomalously high CaO/Na₂O values (&gt;8) because normal-ratio basalts lack sufficient calcium enrichment. This detailed study advances our understanding of the formation mechanisms of Archean anorthosites and associated rocks, including gabbronorites and hornblendites, highlighting their important role in shaping early continental crust.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122955"},"PeriodicalIF":3.6,"publicationDate":"2025-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144580552","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":"Magnesium isotope compositions of seep carbonates fingerprint dolomite formation pathways","authors":"Tingting Chen ,&nbsp;Yang Lu ,&nbsp;Zhiyong Lin ,&nbsp;Wei Wei ,&nbsp;Xiaoming Sun ,&nbsp;Fang Huang","doi":"10.1016/j.chemgeo.2025.122954","DOIUrl":"10.1016/j.chemgeo.2025.122954","url":null,"abstract":"<div><div>Dolomite is a common yet poorly understood constituent of modern seep carbonates. To decipher the fundamental controls governing its formation, we investigate authigenic carbonates from Dongsha and Shenhu areas of the South China Sea using magnesium isotopes (δ²⁶Mg) combined with mineralogy, rare earth elements, δ¹³C, and δ¹⁸O. Dongsha samples mainly comprise Mg calcite precipitating under dynamic redox conditions and exhibit broad δ²⁶Mg variability (−3.77 ‰ to −1.46 ‰). The δ²⁶Mg values are positively correlated with δ¹³C values and negatively correlated with δ¹⁸O, Ce anomalies, and Mg/Ca ratios, reflecting kinetic Mg isotope fractionation during rapid incorporation of seawater-derived Mg enhanced by intense sulfate-driven anaerobic oxidation of methane (SD-AOM). In contrast, Shenhu samples are dominated by ordered dolomite formed under persistently reducing conditions. The low δ²⁶Mg values with narrow range (−3.60 ‰ ∼ −3.16 ‰) are close to high-Mg calcite containing weakly ordered dolomite, implying a deeper, closed-system porewater Mg source and near-equilibrium precipitation during ordering. The contrasting δ²⁶Mg signatures coupled with a paragenetic sequence of Mg calcite and dolomite support a two-step formation pathway for seep dolomite: (1) precipitation of initial Mg calcite precursors, followed by (2) cation ordering development. Sustained SD-AOM activity in locally restricted environments maintains sulfide-rich, supersaturation conditions that favoring ordered dolomite formation at seeps.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122954"},"PeriodicalIF":3.6,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144580555","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":"Quantifying the contribution of biogenic iron sulfides to magnesite formation in the Basque Lakes, British Columbia, Canada","authors":"Colton J. Vessey ,&nbsp;Maija J. Raudsepp ,&nbsp;Maria L. Arizaleta ,&nbsp;Sasha Wilson ,&nbsp;Anna L. Harrison ,&nbsp;Kelly J. Rozanitis ,&nbsp;Helen E.A. Brand ,&nbsp;Kurt O. Konhauser ,&nbsp;Kwon Rausis ,&nbsp;Ian M. Power","doi":"10.1016/j.chemgeo.2025.122952","DOIUrl":"10.1016/j.chemgeo.2025.122952","url":null,"abstract":"<div><div>Understanding terrestrial carbon cycling is important to develop carbon dioxide removal (CDR) technologies. Neutralization of carbonic acid (H₂CO₃) to make carbonate minerals provides a secure, long-term sink for CO₂ in natural and anthropogenic systems. In the sediment, dissimilarly sulfate reduction has the potential to generate alkalinity and induce biogenic precipitation of carbonate minerals, however, the proportion of Fe-sulfides to carbonate minerals is rarely quantified. Saline and hypersaline lakes containing carbonate minerals are excellent environments to examine closed system geochemical cycles of carbon, sulfur and iron. Here, we quantified the contribution of biogenic Fe-sulfide minerals and buried organic carbon to magnesite (MgCO₃) formation in the sediment of Basque Lake #2, a Mg-Na-SO₄ hypersaline lake near Ashcroft, British Columbia, Canada. While the overlying surface water contains over 2 M SO₄²⁻, the total solid iron sulfide content of the sediment was &lt;0.4 wt%. The Basque Lake #2 sediment core had much more abundant carbonate minerals than sulfide minerals, suggesting the biogenic processes that form Fe-sulfides have a minimal role in magnesite formation (&lt;1.0 wt%). Laboratory experiments were also conducted to study the relative influence of microbial sulfate and iron reduction on alkalinity generation and biogenic mineral formation with different organic carbon amendments. Filter-sterilized sulfate-rich waters (∼800 mM SO₄²⁻) from Basque Lake #1 were inoculated with anoxic Basque Lake sediment and microbial communities with or without the addition of ferrihydrite [Fe₁₀^IIIO₁₄(OH)₂]. Biogenic magnetite (Fe^III₂Fe^IIO₄) and mackinawite (Fe^IIS) formed when ferrihydrite was added to microbial experiments and siderite (Fe^IICO₃) precipitated in the lactate-amended experiment. The bulk analysis techniques used in these laboratory experiments suggest there is minimal to no additional magnesite precipitation. This study highlights that in closed systems, such as Basque Lake #2, the role of dissimilatory sulfate reduction in net carbonate precipitation will be limited by ferric iron input into lakes, which therefore inhibits biogenic Fe-sulfide formation, even with extremely high aqueous sulfate concentrations. Ultimately, it is unlikely that sulfate and iron reduction play important roles in Mg‑carbonate formation within Fe-limited environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122952"},"PeriodicalIF":3.6,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144580554","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":"Isotopic evidence for dew uptake by land snails from Bayesian modeling of body water δD and δ18O","authors":"Jiawei Da","doi":"10.1016/j.chemgeo.2025.122953","DOIUrl":"10.1016/j.chemgeo.2025.122953","url":null,"abstract":"<div><div>Land snail shells serve as valuable paleoclimate archives, with their isotopic compositions recording past changes in regional ecology and hydrology. To quantitatively reconstruct paleoclimate parameters such as the oxygen isotopic composition of precipitation (δ¹⁸O_p), a flux balance model targeting snail body fluid was developed by <span><span>Balakrishnan and Yapp (2004)</span></span>. However, previous applications of the flux balance model based on modern observations have consistently reported offsets between modeled and observed δ¹⁸O_p values. In this study, I re-evaluated the model input parameters using a published high-resolution dataset and Bayesian inversion to refine estimates of the isotopic compositions of the snail's drinking water (δ¹⁸O_in, δD_in). The modeled δ¹⁸O_in and δD_in plot above the local meteoric water line, indicating substantial contributions of atmospheric vapor to the snail body water via dew uptake. Assuming that the ambient water vapor forms through evaporation of meteoric water, the updated flux balance model suggested that dew accounts for up to ∼50 % of snail's water intake in the study site. This finding highlights a critical oversight in previous paleoclimate reconstructions that ignored dew uptake, potentially leading to underestimation of δ¹⁸O_p.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122953"},"PeriodicalIF":3.6,"publicationDate":"2025-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144580553","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}