Chemical Geology最新文献

{"title":"Zinc mineralisation in marine ooidal ironstones of Western Siberia: Origin and palaeoenvironmental significance","authors":"Maxim Rudmin , Edward J. Matheson , Andre Baldermann , Natalia Maximova , Evan Dasi , Sultan R. Tazhiev , Alexey Ruban","doi":"10.1016/j.chemgeo.2025.122755","DOIUrl":"10.1016/j.chemgeo.2025.122755","url":null,"abstract":"<div><div>The intricate nature and evolution of the zinc (Zn) biogeochemical cycle in modern and ancient sedimentary basins is a captivating scientific issue with regard to the complexity of Zn sources, diffusion paths and immobilisation processes. This article delves into assessing the sources, migration pathways, and concentration mechanisms of Zn in marine ooidal ironstone deposits of Western Siberia. The study focused on the Cretaceous-Paleogene ironstone strata of the ∼80 m thick Bakchar deposit. The study is based on SEM-EDS, XRF, ICP-MS, and Rock-Eval pyrolysis analyses. In this deposit, Zn minerals frequently form inclusions in the carbonate cement and clay matrix, including micro-impregnations at the contact between siderite spar and the clay matrix, or less common in the cortex of iron-rich ooids. Authigenic Zn mineralisation is predominantly represented by wurtzite ((Zn, Fe)S), while Zn nuggets, zincite (ZnO), tongxinite (Cu<sub>2</sub>Zn) and Zn-bearing sulphides occur less frequently. They are observed across all major ironstone-bearing Formations of the Bakchar deposit, which span from the Turonian-Coniacian to the Paleocene-Eocene. The inclusions in some layers form clusters that are more commonly associated with carbonate (siderite) cements. This is explained by intense seepage of hydrothermally sourced (reducing and acidic) fluids, likely linked to fault-controlled fluid migration within the bored rift zones of the West Siberian basin. Migration of Zn-bearing low-temperature hydrothermal fluids occurred into weakly lithified or well lithified marine sediments after the formation of iron-rich ooids and primary clay matrix, as reflected in the composition of wurtzite framboids and fracture forms with carbonate-filled ooids and quartz (epigenetic mineralisation). This epigenetic zinc mineralisation may have overprinted the earlier diagenetic phases, reflecting the complex multi-stage history of the deposit. At moderate or prolonged fluid diffusion rates (distal to the exhalation centre), wurtzite crystallised in a smectite matrix near siderite aggregates or immediately at the smectite-siderite grain boundary. Under such conditions, wurtzite often replaced pyrite framboids. During intense fluid-rock interactions, wurtzite and other Zn sulphides crystallised in siderite micro-veins, which altogether replaced and overprinted previously formed ooids and detrital quartz. A more enigmatic form of wurtzite is an ‘almond-shaped’ variety that grew within the pores of detrital organic matter. In rare cases, native Zn and tongxinite formed in micro-pores between clay microparticles. Within the deposits, Zn is positively correlated with hydrothermal and anoxic metals, such as Co, Pb, REE, Y, U, Sb, Mo, As, Th, Fe and Ni, but negatively or barely correlated with K, Si, Ba, Ge, Al and TOC. This distinct geochemical association suggests a hydrothermal origin of the Zn mineralisations. Based on the mineralogical and geochemical results obtained, we","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122755"},"PeriodicalIF":3.6,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143706469","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":"Spatial and temporal heterogeneity of the marine nitrogen cycle during the end-Triassic mass extinction","authors":"Jing Li ,&nbsp;Huyue Song ,&nbsp;Yong Du ,&nbsp;Paul B. Wignall ,&nbsp;David P.G. Bond ,&nbsp;Stephen E. Grasby ,&nbsp;Haijun Song ,&nbsp;Jacopo Dal Corso ,&nbsp;Li Tian ,&nbsp;Daoliang Chu","doi":"10.1016/j.chemgeo.2025.122752","DOIUrl":"10.1016/j.chemgeo.2025.122752","url":null,"abstract":"<div><div>The end-Triassic mass extinction (ETME) marks a pivotal event in Earth's history, characterized by major environmental changes in both marine and terrestrial settings and significant perturbations in the carbon and nitrogen biogeochemical cycles alongside extinction events. Here we employ high-resolution organic carbon isotopes (δ¹³C_org), nitrogen isotopes from bulk samples (δ¹⁵N_bulk), total organic carbon (TOC) and nitrogen content (TN), complemented by carbon (δ¹³C_kerogen) and nitrogen isotopes (δ¹⁵N_kerogen) of kerogen extracts from the Kuhjoch section in Austria in order to investigate the interplay between marine redox state, nitrogen cycling, and the biotic crisis across the Triassic–Jurassic boundary. Our results reveal a significant positive shift (∼3 ‰) in δ¹⁵N_bulk values, indicating a perturbed marine nitrogen cycle and expansion of the oxygen minimum zone prior to the ETME. The δ¹⁵N profiles suggest a transition from a nitrate-limited ocean dominated by nitrogen fixation to a post-extinction ocean with increased proportion of assimilation of NO₃⁻ undergoing non-quantitative denitrification. We also examine the spatial and temporal heterogeneity of the marine nitrogen cycle from different paleoenvironmental settings across the Triassic–Jurassic transition. Bioavailable nitrogen (NO₃⁻ and NH₄⁺) limitation prevailed at some localities before and during the ETME. However, the development of N limitation was not synchronous across different locations: it emerged before the ETME in some European basins and intensified after the ETME on Panthalassan shelves. The early Hettangian saw an expansion of euxinic waters into the photic zone and shoaling of the chemocline. Enhanced continental weathering and deep-water upwelling increased nutrient supply, thereby alleviating N limitation. Our new observations point to an unstable and stratified marine environment during the Triassic–Jurassic transition, and suggest that nitrogen bioavailability and redox conditions may be key factors for the devastation of marine ecosystems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122752"},"PeriodicalIF":3.6,"publicationDate":"2025-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143697922","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":"Utility of the B/Ga salinity proxy in carbonate and marly sediments","authors":"Wei Wei ,&nbsp;Thomas J. Algeo ,&nbsp;David Meyer ,&nbsp;Jiangsi Liu ,&nbsp;Katherine N. Snihur ,&nbsp;Cody Lazowski ,&nbsp;Zhiquan Li ,&nbsp;Daniel S. Alessi ,&nbsp;Kurt O. Konhauser ,&nbsp;Yuansheng Du ,&nbsp;Wenchao Yu","doi":"10.1016/j.chemgeo.2025.122751","DOIUrl":"10.1016/j.chemgeo.2025.122751","url":null,"abstract":"<div><div>Elemental proxies are widely used for analyzing watermass salinity in ancient shale and siliciclastic mudstone formations, but their application to limestones and marls has not yet been systematically tested. Unlike the Sr/Ba and S/TOC proxies, the B/Ga proxy offers considerable, albeit untested, potential for paleosalinity determinations in carbonate-bearing facies. To evaluate this potential, we analyzed the concentrations of B and Ga, as well as those of Al, Ca, and other lithology-associated elements, in a large suite of modern and ancient marine and marine-influenced carbonate samples, including both sediments and fossils. Our results show that B/Ga ratios tend to be elevated in carbonate-rich material due to low concentrations of Ga, which is primarily present in the detrital siliciclastic fraction. In marly sediments, robust salinity facies determinations are generally possible for samples with Ga concentrations as low as 3 ppm, compared to the typical range of 15–20 ppm in shales. For carbonate samples with Ga concentrations &lt;3 ppm, reliable salinity facies estimates may still be obtained using excess boron (B_xs) present in the sample, calculated as B_total – 6 × Ga. Excess boron content is typically ∼10–20 ppm for carbonates from fully marine facies. Deviations from this range may signal watermass salinities that are lower or higher than the normal marine salinity range of ∼33–38 psu (practical salinity units). This study establishes, for the first time, a robust framework for evaluating depositional salinities in ancient marine and marine-influenced carbonate and marl formations, providing a valuable tool for future paleoenvironmental research.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122751"},"PeriodicalIF":3.6,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679205","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":"Temperature effects on the reduction of Se(VI) by natural pyrite","authors":"Wujian Jin ,&nbsp;Mingliang Kang ,&nbsp;Danwen Qin ,&nbsp;Jingye She ,&nbsp;Zeyue Huang ,&nbsp;Lewen Sun ,&nbsp;Qiaoya Lin ,&nbsp;Hanyu Wu ,&nbsp;Andreas C. Scheinost ,&nbsp;Damien Prieur","doi":"10.1016/j.chemgeo.2025.122747","DOIUrl":"10.1016/j.chemgeo.2025.122747","url":null,"abstract":"<div><div>⁷⁹Se is a key radionuclide concerned in the geological disposal of high-level radioactive waste. Unlike lower valent Se(IV), previous studies have reported that the reduction of aqueous Se(VI) into insoluble Se⁰ or FeSe₂ by pyrite is challenging under ambient temperatures. Considering the thermal environment of radioactive waste repositories and the widespread presence of pyrite in the host rocks, this study investigated Se(VI) reduction by natural arsenic-scarce and arsenic-rich pyrites, namely Py@TL and Py@LY, respectively, under conditions of pH ∼2.0 to ∼9.0 and temperatures ranging from 25 °C to 85 °C. The results reveal that elevated temperatures and acidic conditions significantly enhance Se(VI) reduction via a Se(IV) intermediate to form insoluble nanoscale Se⁰ clusters along with Se-S compounds, following a pseudo-zero-order kinetic model. The apparent activation energy (<em>E</em>_<em>a</em>) values were determined to be 40.5 ± 2.4 and 59.1 ± 3.0 kJ⋅mol⁻¹ for Se(VI) reduction by the arsenic-scarce Py@TL, and 51.0 ± 1.8 and 63.2 ± 12.6 kJ⋅mol⁻¹ for the arsenic-rich Py@LY, at pH ∼2.0 and ∼2.5, respectively. These <em>E</em>_<em>a</em> values highlight surface chemical reactions as the rate-determining step, elucidating the inertness of Se(VI) on pyrite surfaces at ambient temperatures. Notably, arsenic impurities in Py@LY appear to enhance the reactivity by modifying the local structure of pyrite, but excessive Fe²⁺, As³⁺ competition, and solid layers of As⁰ and S⁰ impede the reduction process and elevate the apparent <em>E</em>_<em>a</em>. These findings provide novel insights into Se(VI) reduction mechanisms under complex geochemical conditions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122747"},"PeriodicalIF":3.6,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679204","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":"Isotopically heavy sulfur in nephelinite from Etinde, Cameroon Volcanic Line: Implications for the origin of intraplate magmatism","authors":"Sophie L. Baldwin ,&nbsp;Linda A. Kirstein ,&nbsp;J. Godfrey Fitton ,&nbsp;Adrian J. Boyce ,&nbsp;William Hutchison ,&nbsp;Michael A.W. Marks ,&nbsp;Eva E. Stüeken ,&nbsp;Chris Hayward","doi":"10.1016/j.chemgeo.2025.122748","DOIUrl":"10.1016/j.chemgeo.2025.122748","url":null,"abstract":"<div><div>Intraplate magmatism has traditionally been linked to anomalously hot mantle (hotspots) transported upwards from deep-sourced mantle plumes. However, many intraplate magmatic provinces lack convincing evidence for a mantle-plume origin, and the Cameroon Volcanic Line (CVL) located on the West African continental margin is one such province. Despite being active for ca. 65 million years, it lacks the time-progressive volcanic activity that would suggest the presence of a fixed mantle hotspot or plume; instead CVL magmatism has been linked to a shallow, enriched asthenospheric source. Etinde, a relatively young (&lt;1 Ma) volcano located at the centre of the CVL on the continent-ocean boundary, is the most silica-undersaturated and incompatible element-enriched volcano in the region and forms the focus of this study. It is constructed almost entirely of feldspar-free nephelinite lava flows, with compositions ranging from olivine nephelinite to felsic leucite nephelinite. We report new sulfide-, sulfate- and bulk-δ³⁴S data for a suite of Etinde rock samples; the first sulfur-isotope data for the CVL. Strong (∼8 ‰) S-isotope fractionation between sulfide and sulfate (haüyne, nosean) phases suggest equilibration temperatures of ∼600 °C, well below the magma solidus temperature and likely due to sub-solidus exsolution of nanoscale sulfide particles from the sulfate phenocryst phases. The most mafic samples from Etinde have been extensively degassed, containing less than 60 ppm sulfur, and therefore cannot be used to constrain the primary δ³⁴S. Instead, we use the intermediate and felsic volcanic rocks, where sulfur is locked in phenocrysts of haüyne and nosean, respectively. Bulk δ³⁴S of these rocks, which best represents the primary magmatic values, ranges from +3.7 ‰ to +6.3 ‰, a heavier signature than previously reported in alkaline igneous rocks. We propose that the heavy sulfur isotope values, together with the extreme silica undersaturation and incompatible element concentrations, reflect enrichment of the mantle source and fingerprint carbonate metasomatism in the mantle beneath the CVL. The heavy sulfur isotopic signature requires low-temperature fractionation and therefore implies the addition of sulfur through subduction processes. Our study has broad geochemical significance in contributing to a growing understanding of sulfur-isotope compositional variability in geochemically enriched mantle globally.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122748"},"PeriodicalIF":3.6,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143696012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Precise discrimination of basalt tectonic settings via dual-stream model with geochemical element matrix and series learning","authors":"Shuzhao Wu ,&nbsp;Changfeng Jing ,&nbsp;Sheng Yao ,&nbsp;Tianyi Zhang ,&nbsp;Gaoran Xu ,&nbsp;Shuhui Gong ,&nbsp;Sensen Wu ,&nbsp;Zhenhong Du ,&nbsp;KunFeng Qiu","doi":"10.1016/j.chemgeo.2025.122746","DOIUrl":"10.1016/j.chemgeo.2025.122746","url":null,"abstract":"<div><div>Precise discrimination of basalt tectonic settings serves as a crucial methodological approach for providing insights into Earth's history. To address the limitations of traditional discrimination methods, which include high subjectivity due to reliance on expert experience and restricted precision resulting from simplistic comparative analysis of geochemical elements, we developed an innovative discrimination model-the Element Matrix and Series Parallel Network (EMSPN). The model enhances the capacity of tectonic setting discrimination by integrating the correlation characteristics between geochemical elements and the sequential features of element reactivity, thereby obtaining more comprehensive lithogenetic information. Based on &gt;39,000 geochemical analyses of basalts from 9 typical tectonic settings after the Archaean period, we conducted application demonstrations through preprocessing operations, including feature engineering, missing value imputation, and category balancing. The proposed model demonstrated superior performance across multiple evaluation methods, achieving an overall discrimination accuracy of 88 %. This study compared the proposed model with four traditional machine learning models as baseline methods, and the results showed that the model outperformed other traditional machine learning models in overall discrimination accuracy across 9 tectonic settings. Additionally, in ablation experiments, by systematically removing key components of the EMSPN, the results validated the model design's rationality and confirmed each module's importance in information extraction and feature learning. Using the SHapley Additive exPlanations (SHAP) method, we analyzed and discussed the importance of different elements in discrimination results and the geochemical characteristics across various tectonic settings. When applied to controversial Archaean basalt samples, the results confirm the conclusions from traditional geochemical analysis methods, demonstrating the model's geological reliability and practical significance. This research provides a reliable technical approach for the field of lithogeochemistry and retrieves geodynamic information through tectonic setting discrimination, contributing to more accurate reconstruction of Earth's tectonic history.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122746"},"PeriodicalIF":3.6,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143679203","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":"Assessing the hydrothermal influence on natural waters in the Kirishima Volcanic Complex: Insights from rivers, springs and groundwater with varying residence time","authors":"Gibran Romero-Mujalli ,&nbsp;Jens Hartmann ,&nbsp;Takahiro Hosono ,&nbsp;Kiyoshi Ide ,&nbsp;Thorben Amann ,&nbsp;Pascale Louvat","doi":"10.1016/j.chemgeo.2025.122716","DOIUrl":"10.1016/j.chemgeo.2025.122716","url":null,"abstract":"<div><div>Rivers and groundwaters that drain active volcanic areas are characterized by relatively high nutrient concentrations and dissolved loads. The high dissolved load generally results from the fluid–rock interactions with high temperature fluids containing voclanic gases. In this study, the chemistry of spring and river waters from the Kirishima volcanic region (Kyushu, Japan) is analysed to determine the hydrothermal influence and how their chemical composition varies with respect to the groundwater transit time (residence time). The hydrothermal component is distinguished by combining spring water residence times with stable isotopic composition of <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>13</mn></mrow></msup><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi><mi>I</mi><mi>C</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>34</mn></mrow></msup><msub><mrow><mi>S</mi></mrow><mrow><mi>s</mi><mi>u</mi><mi>l</mi><mi>p</mi><mi>h</mi><mi>a</mi><mi>t</mi><mi>e</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>18</mn></mrow></msup><msub><mrow><mi>O</mi></mrow><mrow><mi>s</mi><mi>u</mi><mi>l</mi><mi>p</mi><mi>h</mi><mi>a</mi><mi>t</mi><mi>e</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>18</mn></mrow></msup><msub><mrow><mi>O</mi></mrow><mrow><mi>w</mi><mi>a</mi><mi>t</mi><mi>e</mi><mi>r</mi></mrow></msub></mrow></math></span>, <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mn>2</mn></mrow></msup><msub><mrow><mi>H</mi></mrow><mrow><mi>w</mi><mi>a</mi><mi>t</mi><mi>e</mi><mi>r</mi></mrow></msub></mrow></math></span> and the selenium to sulphate molar ratio. We found that the DIC and SO₄^2- in the waters draining the Kirishima volcanic complex arose for more than 50 % from volcanic CO₂ and SO₂. Consistently, the groundwaters flowing through longer and deeper flow paths accumulate more volcanic CO_2(g) and SO_2(g). The results from this study highlight the relevance of regional studies of active volcanic settings in understanding the chemical evolution of groundwaters and its implication for the carbon and sulphur budgets in a volcanic edifice.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122716"},"PeriodicalIF":3.6,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143643628","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Numerical study of the land-sourced iron precipitation and its effects on porewater flow at subterranean estuaries","authors":"Yajuan Yin ,&nbsp;Tao Wang ,&nbsp;Chenming Zhang","doi":"10.1016/j.chemgeo.2025.122744","DOIUrl":"10.1016/j.chemgeo.2025.122744","url":null,"abstract":"<div><div>During terrestrial freshwater discharge to the ocean, the freshwater containing high concentrations of dissolved ferrous iron (<em>Fe</em>²⁺) come into contact with the saltwater enriched in dissolved oxygen (<em>O</em>₂(<em>aq</em>)) within the coastal aquifer, resulting in the oxidation and precipitation of iron (Fe) as Fe oxy(hydr)oxides. The accumulated Fe precipitate forms a low-permeability zone, known as the “iron curtain” at subterranean estuaries (STEs), which influences the porewater flow. However, this process is not quantitatively well understood, and the underlying mechanisms remain unclear. Given the processes of variable density flow, Fe oxidation and oxidative precipitation, and the effects of Fe precipitation on porosity and permeability, the process of land-sourced Fe precipitation and its interactions with porewater flow at STEs have been numerically studied using the TOUGHREACT simulation program, which facilitates multiphase flow and reactive transport processes. Results indicate that Fe precipitates correspondingly reduce the porosity and permeability (by approximately 20 %–40 %) of the aquifer. These reductions subsequently decrease the porewater velocity (by approximately 6 % to 18 % seaward and 8 % to 32 % upward) over Fe-precipitated areas and increase the porewater velocity (by approximately 6 % to 12 % seaward and 4 % to 8 % upward) above and below Fe-precipitated areas. In turn, the porewater velocity changes decline the accumulation of Fe precipitates by approximately 0.001 to 0.003 in volume fraction or 3 % to 18 %. These findings highlight the interaction between groundwater-derived Fe and porewater flow at STEs, providing insights that enhance the understanding of the hydrochemical processes in coastal zones.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122744"},"PeriodicalIF":3.6,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666528","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":"Controls over cesium and rubidium contents of sedimentary rocks","authors":"Jan Środoń,&nbsp;Karol Jewuła","doi":"10.1016/j.chemgeo.2025.122745","DOIUrl":"10.1016/j.chemgeo.2025.122745","url":null,"abstract":"<div><div>In nature, Cs and Rb follow K, which is a much more abundant but chemically similar element. Data for these elements and their mineral carriers were acquired by the combined ICP-OES/ICP-MS (Inductively Coupled Plasma Optical Emission Spectroscopy/Inductively Coupled Plasma Mass Spectrometry) techniques and quantitative XRD (X-ray diffraction), supplemented by multivariate regression analysis, in order to detect controls over cesium and rubidium contents of clastic sedimentary rocks. The sample material comprised clay fractions of bentonites and paleosols, dominated by illite-smectite, and bulk mudstones, sandstones, paleosols, bentonites, basalts, and tuffs from several European basins, ranging from the Proterozoic to Miocene. Results indicate that Rb and Cs contents of clastic sedimentary rocks, and of mudstones in particular, are controlled by the relative concentrations of K-feldspar, micas, and illite-smectite, thus detrital and late diagenetic components of these rocks, and concentrations of Rb and Cs in these minerals. The concentrations of Cs in some illite-smectites, significantly higher than upper continental crust (UCC) averages, indicate hydrothermal alteration or, in case of paleosols and bentonites, can be inherited from anomalous parent rocks. K, Cs, and Rb contents of normal mudstones (unaffected by the hydrothermal fluids or anomalous parent rocks), whether marine or freshwater, are close to the UCC values. In normal mudstones of our collection, feldspars contain 0 to 22 % of Cs and 0 to 41 % Rb, micas 0 to 57 % Cs and 0 to 48 % Rb, and illite-smectite 32 to 100 % Cs and 17 to 100 % Rb, both mostly non-exchangeable and ‘fixed’ in the illite structure. The collected data do not support the use of Rb/K as a paleosalinity proxy and call for careful use of Rb and Cs in chemostratigraphy. The presented relationships indicate that Cs/K and Rb/K ratios in illite-smectite are controlled by the chemistry of fluids, which promote crystallization of illite during burial. Normal diagenetic fluids precipitate illite with, on average, 2.4 times more Cs and 70 % more Rb than the UCC values. In “abnormal” illites, the average Cs and Rb values are 18 and 2.5 times higher than the UCC, respectively. It is confirmed that thin illite crystals have higher Rb/K and Cs/K ratios, tentatively explained by the “supply and demand” mechanism: high ratio between the concentrations of Rb and Cs in pore fluids and the volume of neoformed illite at the beginning of illite crystallization. Major sources of Cs in diagenetic pore fluids in sedimentary basins are detrital micas or hydrothermal fluids invading those basins. The impact of Cs and Rb sorption at illite and mica wedges and/or frayed edges on the total budgets of these elements cannot be evaluated from our data.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"683 ","pages":"Article 122745"},"PeriodicalIF":3.6,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143735307","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":"Subducted sediment recycling and fractional crystallization of the Toba volcanic system constrained by plagioclase geochemistry","authors":"Meng-Hao Gao ,&nbsp;Ping-Ping Liu ,&nbsp;Dian-Bing Wang ,&nbsp;Xi-Jun Liu ,&nbsp;Gui-Bin Zhang ,&nbsp;Cheng Xu","doi":"10.1016/j.chemgeo.2025.122740","DOIUrl":"10.1016/j.chemgeo.2025.122740","url":null,"abstract":"<div><div>Understanding the processes and contributions of various sources to arc magmas, originating from the mantle wedge, is crucial for unraveling the complex interactions between crust and mantle in subduction zones. Plagioclase with a prolonged crystallization history serves as a key mineral in studying sources of magma and its evolution history. This study presents in-situ trace elements and Pb isotopes of plagioclase in basalts and rhyolites, and in-situ trace elements of clinopyroxene in basalts of the Toba volcanic system on the Sunda arc, Sumatra. The rhyolites from the ∼75 ka Youngest Toba tuff (YTT) and the basalts from the post-YTT Sipisupisu lave dome are cogenetic and share the same lower crustal magma reservoir. Some of the plagioclase crystals in rhyolites contain a sieved core with high Ca (An = 78 to 85 %) and high Fe contents (∼4800 ppm) that are not in equilibrium with the rhyolitic melts, but are compositionally similar to plagioclase in the cogenetic basalts. Since clinopyroxene in the basalts has negative Eu anomalies and crystallized at lower crustal depth (∼13 to 25 km deep), it can be inferred that plagioclase with positive Eu anomaly could have crystallized simultaneously with clinopyroxene at similar depth. Therefore, we infer that the high-Ca plagioclase cores were antecrysts crystallized from more primitive melts at lower crustal depth and then transported to the upper crust by more evolved melts. Lead isotopic compositions of the plagioclase cores are relatively homogeneous (²⁰⁶Pb/²⁰⁴Pb = 18.94–19.02, ²⁰⁷Pb/²⁰⁴Pb = 15.81–15.84, ²⁰⁸Pb/²⁰⁴Pb = 39.61–39.74) and plot between those of the depleted MORB mantle (DMM) and the upper crust/subducted sediments. The fact that plagioclase cores crystallized at lower crustal depth were endowed with an upper crustal Pb isotopic signature indicates that upper crustal materials were probably added to the mantle source of the Toba volcanic system via subduction. Considering that all the plagioclase crystals of the Toba volcanic system have similarly high ²⁰⁷Pb/²⁰⁴Pb ratios close to and slightly beyond that of the subducted Nicobar Fan sediments, the primary basaltic melts of the Toba volcanic system may have been enriched in radiogenic Pb isotopes by addition of the subducted sediments to the mantle wedge. The mantle-derived basaltic melts with highly radiogenic Sr and Pb isotopic compositions further evolve through assimilation and fractional crystallization (AFC) in the crust to form andesitic-rhyolitic melts. Using in-situ Pb isotopes of plagioclase, this study exemplifies a credible means to discern processes of sediment addition to the mantle wedge and crustal assimilation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"682 ","pages":"Article 122740"},"PeriodicalIF":3.6,"publicationDate":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143666527","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}