Geochimica et Cosmochimica Acta最新文献

{"title":"Combined Ca, Sr isotope and trace element analyses of Late Cretaceous dinosaur teeth: assessing diet versus diagenesis","authors":"Mateusz M. Michailow ,&nbsp;Federico Lugli ,&nbsp;Anna Cipriani ,&nbsp;Francesco Della Giustina ,&nbsp;Annalisa Ferretti ,&nbsp;Daniele Malferrari ,&nbsp;Denver Fowler ,&nbsp;Elizabeth Freedman Fowler ,&nbsp;Michael Weber ,&nbsp;Thomas Tütken","doi":"10.1016/j.gca.2025.05.006","DOIUrl":"10.1016/j.gca.2025.05.006","url":null,"abstract":"<div><div>The Sr and Ca isotope composition, along with trace element content in fossil teeth, provides valuable insights into biogenic and diagenetic processes. Identifying pristine biological signals is crucial for reconstructing the diet and trophic levels of extinct taxa. We present novel geochemical data from Tyrannosauridae and Ceratopsidae teeth of the Late Cretaceous, using radiogenic Sr (⁸⁷Sr/⁸⁶Sr), stable Sr (<em>δ</em>^88/86Sr), and Ca (<em>δ</em>^44/42Ca) isotopes, along with trace elements abundances to differentiate biogenic signals from diagenetic alteration.</div><div>Our results reveal potential taxon-specific diagenetic effects, likely influenced by enamel microstructure. Tyrannosaurid enamel contains lower concentrations of rare earth elements (REE) and uranium (U) than dentine, whereas ceratopsid teeth typically exhibit higher REE and U compared to both the enamel and dentine of tyrannosaurids. Enamel <em>δ</em>^44/42Ca values differ significantly between herbivorous ceratopsids and carnivorous tyrannosaurids, reflecting trophic level effects seen in modern mammals and reptiles. A positive correlation between <em>δ</em>^44/42Ca and <em>δ</em>^88/86Sr suggests partial preservation of biological fractionation along the trophic chain. Yet, the lack of negative <em>δ</em>^88/86Sr values in our dataset – typically expected in biologic tissues – suggests alteration by diagenetic processes of both stable and radiogenic Sr. While <em>δ</em>^44/42Ca in enamel likely remains a reliable dietary proxy, Sr isotope composition of our samples appears then to be significantly altered. The presence of high <em>δ</em>^88/86Sr in terrestrial fossil teeth could serve as a novel diagenetic proxy to assess habitat related ⁸⁷Sr/⁸⁶Sr values, aiding provenance and mobility studies in fossil ecosystems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 172-189"},"PeriodicalIF":4.5,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133760","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":"Coprecipitation of phosphate with calcite: Molecular-scale evidence for incorporation and inclusion mechanisms","authors":"Chao Ren ,&nbsp;Yongfang Li ,&nbsp;Shaofeng Wang ,&nbsp;Jingzhao Wang ,&nbsp;Junfeng Ji ,&nbsp;Henry H. Teng ,&nbsp;Brian L. Phillips ,&nbsp;Kideok D. Kwon ,&nbsp;Wei Li","doi":"10.1016/j.gca.2025.04.032","DOIUrl":"10.1016/j.gca.2025.04.032","url":null,"abstract":"<div><div>Coprecipitation of phosphate in calcium carbonate minerals is a ubiquitous geochemical phenomenon in marine sedimentation and cave stalagmite formation, however, it is not clear whether phosphate is incorporated into the calcite structure. In this research, we applied solid-state nuclear magnetic resonance (NMR) spectroscopy to analyze P speciation during coprecipitation with calcite. The ³¹P NMR results show three peaks with chemical shifts of 3.9, 3.0 and −1.0 ppm, indicative of at least three phosphate species in the coprecipitates. Combined with advanced ³¹P{¹H} cross-polarization (CP)/MAS, ¹H DE/MAS, ³¹P{¹H} 2-d heteronuclear correlation (HetCor) and ³¹P{¹³C} cross-polarization rotational echo double resonance (CP-REDOR) NMR experiments, the 3.9 ppm peak can be tentatively assigned to calcite structural defects as amorphous calcium phosphate (ACP)-like environments while the 3.0 ppm peak arises from a carbonated hydroxyapatite (CHap). The ³¹P NMR peak at −1.0 ppm can be assigned to structurally incorporated phosphate in the calcite crystals in the form of HPO₄²⁻. Nano secondary ion mass spectrometry (NanoSIMS) and high-resolution scanning transmission electron microscopy (HR-STEM) analysis further suggests that the incorporated HPO₄²⁻ substitutes for the structural carbonate group (CO₃²⁻) of calcite. However, the local expansion stress field generated with HPO₄²⁻ incorporation in the calcite structure prevents PO₄/CO₃ isomorphous substitution and favors the precipitation of calcium phosphates. The findings of this study not only provide deep insights into carbonate crystal chemistry but also shed light on the application of carbonate materials as potent geochemical proxies in paleoenvironmental reconstructions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 1-17"},"PeriodicalIF":4.5,"publicationDate":"2025-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143922530","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":"238U/235U isotopic variations in angrites and their constituent minerals","authors":"Magdalena H. Huyskens ,&nbsp;Yuri Amelin ,&nbsp;Qing-Zhu Yin ,&nbsp;Tsuyoshi Iizuka","doi":"10.1016/j.gca.2025.04.030","DOIUrl":"10.1016/j.gca.2025.04.030","url":null,"abstract":"<div><div>Ages of angrites, a diverse and rapidly growing group of differentiated meteorites, are important for understanding the history of their parent body, which is proposed to be an archetypal first-generation planetesimal. Angrites also commonly serve as a time reference in the early Solar System chronology. Pb-isotopic ages of angrites can be determined with high precision, and the isotopic composition of uranium thus becomes a major contributor to the age accuracy and its total uncertainty budget. Two main groups of angrites, the rapidly cooled (volcanic and/or impact-generated) and plutonic angrites, were previously found to contain uranium with different ²³⁸U/²³⁵U ratios. The variations in isotopic compositions between mineral carriers of uranium within individual angrites, which are directly relevant to calculation of accurate Pb-isotopic ages, have not been studied yet. In this study, we determined the ²³⁸U/²³⁵U for whole rocks, leachate and residue of whole rocks and mineral separates for two rapidly cooled angrites D’Orbigny and Sahara 99555 and three plutonic angrites NWA 4801, NWA 4590 and Angra dos Reis. For the rapidly cooled angrites, all mineral separates as well as the whole rocks show consistent ²³⁸U/²³⁵U. Whole rock ²³⁸U/²³⁵U ratios for the plutonic angrites are distinctly lower than the ratios in the rapidly cooled angrites. In Angra dos Reis and NWA 4590, merrillite has higher ²³⁸U/²³⁵U than pyroxene, and both minerals have higher ²³⁸U/²³⁵U ratios than the respective whole rock, suggesting the presence of an unidentified mineral host of uranium with lower ²³⁸U/²³⁵U. These differences in U isotope composition could be possibly attributed to a combination of mass dependent and mass-independent isotope fractionation driven by the differences of oxidation state, and coordination in the crystals. We recalculated the existing Pb-isotopic dates when possible with the measured ²³⁸U/²³⁵U for the minerals that were used for the Pb-isotopic dating. The differences in U isotopic composition between cogenetic minerals point to the importance of ²³⁸U/²³⁵U determination in specific minerals that are used for Pb-isotopic dating for plutonic achondrites, rather than U isotopic data for bulk meteorites.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 205-220"},"PeriodicalIF":4.5,"publicationDate":"2025-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083379","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":"Thallium cycling and boundary exchange in a continental margin basin","authors":"Kasper P. Olesen ,&nbsp;Sune G. Nielsen ,&nbsp;Chadlin M. Ostrander ,&nbsp;Nicol Udy ,&nbsp;Donald E. Canfield","doi":"10.1016/j.gca.2025.04.005","DOIUrl":"10.1016/j.gca.2025.04.005","url":null,"abstract":"<div><div>Thallium (Tl) isotopes are a robust tracer of ancient ocean oxygenation through their link to the burial flux of deep-sea manganese oxide minerals. Yet, the details of Tl geochemistry at the continental margin remain largely unexplored, hindering quantitative application of the palaeoredox proxy. To develop our understanding of Tl diagenesis, phase dynamics, and mass transfer at the continent-ocean interface, we collected sediments from three sites in the perenially oxic Skagerrak sea as well as sediments and suspended particles from five adjacent rivers. The three Skagerrak sediment sites are biogeochemically diverse, with variable oxygen penetration (9–18 mm) and C-oxidation occurring predominantly through either sulfate, iron, or manganese reduction. Sequential extractions and porewater analyses reveal a highly homogeneous abundance and phase association pattern of Tl across all sample types and sites. Sediment and particle Tl resides almost exclusively in acid-leachable aluminous clays and residual crystalline phases. We interpret these phases to be terrigenous, except at the highly Mn-enriched site S9 where we find up to ∼45 % of Tl is authigenic. This claim is supported by Tl isotopic compositions of acid-leachable sediment (ε²⁰⁵Tl_HNO3), which average –2.5 ± 0.9‱, within uncertainty of the average upper crust value of –2.0 ± 0.5‱ and a regional riverine particle delivery value of –2.1 ± 1.2‱.</div><div>Incubations of Skagerrak sediments with added bottom water Tl reveal a fractionation factor (α) of ∼1.0007, amounting to an isotope ratio difference of ∼7‱. A comparable fractionation of 2.4 to 4.5‱ is calculated for authigenic Tl removal in the Skagerrak sediments. However, this fractionation is lower than that observed in deep sea pelagic clays and hydrogenetic Mn crusts and nodules (α ∼1.0021), yet significantly higher than expected for mature diagenetic Mn oxides like triclinic birnessite and todorokite (α ∼1.00005). Thallium cycling is largely decoupled from Mn diagenesis at our marine sites and only associates weakly with the active sedimentary Mn recycling. Rather, effluxing of dissolved Tl is observed at all sites. We employ a diagenetic reaction-transport model to quantify dissolved Tl fluxes and compare these fluxes with independent assessments of Tl mass balance based on authigenic/terrigenous Tl proportions. We find that within the oxic Skagerrak basin, sediments may be both true sources and, if Mn-enriched, true sinks of Tl, with extrapolated flux magnitudes relevant to marine Tl mass balances. Our study presents a much-needed description of Tl diagenesis in diffusive margin sediments and suggests that hitherto unrecognized sources of originally terrigenous Tl to the marine environment may occur at the continent-ocean boundary, either via the release of labile clay-bound Tl directly from riverine particles or during sediment diagenesis.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 64-81"},"PeriodicalIF":4.5,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083381","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":"Strong depth-dependent chemical and structural characteristics of dissolved organic matter (DOM) in organic-rich sediment in a shallow temperate lake","authors":"Chenhui Wei ,&nbsp;Shu Tao ,&nbsp;Patrick G. Hatcher ,&nbsp;Dongqiang Zhu","doi":"10.1016/j.gca.2025.05.002","DOIUrl":"10.1016/j.gca.2025.05.002","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Porewater dissolved organic matter (DOM) in lake sediments is an important contributor to the global carbon cycle. The composition and structures of porewater DOM typically vary with depth, yet the variations in high-resolution depth intervals and the controlling biogeochemical processes are not well understood. Here we performed comprehensive, high-resolution (1 cm interval) characterization of sediment porewater DOM in Baiyangdian, a representative large shallow freshwater lake with abundant biomass deposition in northern China in the temperate zone, by employing chemical analysis, optical techniques, stable isotope analysis, ultra-high resolution mass spectrometry, and 16S rRNA gene sequencing. &lt;em&gt;Anaerolineaceae&lt;/em&gt; was the dominant microorganism in the sediment, reflecting fermentation as the key process involved in organic matter diagenesis. Contrasting &lt;sup&gt;13&lt;/sup&gt;C signatures between particulate organic matter (POM) and DOM suggest that selective degradation of organic matter with component-specific isotopic signatures at distinct depths is occurring. Corresponding to the concentration depth profile of POM, the composition and structures of DOM exhibited strong multilayered variations across the depths of 1–4 cm (surface layer), 5–13 cm (middle layer), and 14–19 cm (bottom layer). In the surface layer, intense fermentation of fresh POM rapidly released protein-like fluorescent components whose content decreased with depth, whereas humic-like fluorescent components gradually accumulated. Consistently, the aromaticity and molecular weight of chromophoric DOM analyzed by ultraviolet–visible spectroscopy increased with depth. Due to the exhaustion of labile POM and the decreased fermentation activity, the contents of protein-like and humic-like fluorescent components as well as the aromaticity and molecular weight of chromophoric DOM stayed relatively constant in the middle layer. In the bottom layer, the sharp increase in concentrations of dissolved organic carbon and volatile fatty acids (acetate, propionate, and butyrate) indicated re-enhanced fermentation activity, which was also supported by the prominent decrease in the protein-like and humic-like fluorescents as well as the decrease in aromaticity and molecular weight of chromophoric DOM. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis showed that the surface layer had the highest relative abundance of aliphatic compounds among the three layers, while aromatics and polycyclic aromatics accumulated only in the surface layer and middle layer, indicating their preferential production and consumption during POM deposition. However, lignin-like compounds accumulated gradually and consistently across the three layers, resulting from their refractory nature and continuous degradation of residual POM. Most of the N/S-containing molecules accumulating in the three layers were lignin-like, aromatic, and polycyclic aromatic compounds, which were appar","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 242-256"},"PeriodicalIF":4.5,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083380","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":"Corals feel the water chemistry: trace elements in coral skeletons reflect accurately their seawater chemistry, biological and geochemical implications","authors":"Sharon Ram,&nbsp;Jonathan Erez","doi":"10.1016/j.gca.2025.05.003","DOIUrl":"10.1016/j.gca.2025.05.003","url":null,"abstract":"<div><div>The incorporation of trace and minor elements into coral skeletons and the underlying chemical and biological processes that govern them, are highly relevant for understanding coral biomineralization and for accurate reconstructions of past ocean conditions. In the present experimental study, that follows our previous publications (Ram and Erez, 2021, 2023), we determined the partition of six cations (Li, Na, Mg, K, Sr and Ba) into corals skeletons by culturing nine hermatypic coral species in seawater with four different calcium concentrations (∼ 10,15, 20 and 25 mM). The cation to Ca ratios in the skeletons correlated linearly with their ratios in seawater, revealing consistent and species-specific partition coefficients (D_Coral). Consistent with our previous work, we find that the partition coefficients for Li, Mg, Na, and K were significantly lower than one but higher than the inorganic values (D_Inorg), while for Sr and Ba, D_Coral were higher than one but lower than D_Inorg values. In addition, D_Coral for the elements with D_El &lt; 1, showed significant inter-species systematic order, with the highest D_Coral for <em>A. lamarcki</em>, corresponding to its highest calcification rates, whereas <em>P. damicornis</em> showed the lowest D_Coral values, consistent with its lowest calcification rates. The opposite systematic trend was observed for the elements with D_El &gt; 1. We attribute these systematic relationships between elemental partitioning and calcification rates to species-specific physiological control, indicating precipitation of the skeleton from a semi-closed seawater reservoir. The modified seawater that comprises this extracellular calcifying fluid follows Rayleigh distillation with respect to all the measured trace and minor elements. The level of Ca utilization (1-f) and the degree of isolation of the calcifying fluid from external seawater, control the efficiency and rate of the calcification. Given the consistent D_Coral values observed across all Ca treatments (for all elements and all coral species) we conclude that kinetic effects on the partition coefficients were unlikely. The deviations from D_Inorg values (the so-called “vital effect”) are governed by the physiology of the calcification process, involving mainly pH and DIC elevation in the ECF that is well known for corals. In addition, the present study provides a strong basis for utilizing multi-elemental proxies in fossil corals for reconstructing past ocean chemistry and climate changes during the Cenozoic era and possibly beyond, well into the Mesozoic.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"400 ","pages":"Pages 142-157"},"PeriodicalIF":4.5,"publicationDate":"2025-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144133761","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":"Hydrogeochemical processes, reaction rates and effect of spatial scales in carbonate critical zone observatories: insights from the reactive-transport modeling of C-Q relations in four mountain watersheds","authors":"J. Ackerer ,&nbsp;C. Legout ,&nbsp;G. Nord ,&nbsp;C.Le Bouteiller ,&nbsp;L. Spadini ,&nbsp;N. Hachgenei ,&nbsp;B. Wild ,&nbsp;O. Fischer ,&nbsp;L. Jullien ,&nbsp;J. Martins ,&nbsp;C. Duwig ,&nbsp;J. Gaillardet ,&nbsp;I. Braud","doi":"10.1016/j.gca.2025.05.001","DOIUrl":"10.1016/j.gca.2025.05.001","url":null,"abstract":"<div><div>This study investigates hydrogeochemical processes, reaction rates and the effect of spatial scales in mountain carbonate watersheds. A reactive-transport model was deployed to capture the concentration-discharge relations (C-Q relations) of major solute species measured in the river waters of two critical zone observatories located in the south of France (southern Alps and Ardèche). The specific control of evaporite, carbonate and clay minerals on river water geochemistry is identified by the reactive-transport modeling. The dissolution of carbonate and evaporitic minerals strongly controls C-Q relations in Na⁺, Ca²⁺, Mg²⁺, SO4^2- and Cl^- solute species. The key role of evaporite dissolution cannot be neglected in the studied Alpine watersheds. The dissolution/precipitation of clay minerals and the surface remobilization is more important for shaping C-Q relations in H₄SiO₄ and K⁺. Concerning the coupling between hydrological and geochemical processes, the chemostatic behavior of rivers and the observation of overland flow events during high discharge periods can be reconciled by considering the evolved overland flow observed on hillslopes and characterized by high solute concentrations. Overland flow may lead to an overestimation of water transit time at high flow if elevated solute concentrations from overland flow sources are attributed to time-dependent weathering reactions. The C-Q relations in Ca²⁺ and Mg²⁺ are overestimated by our reactive-transport model, and the reactive surface area of calcite and dolomite must be reduced by 4–5 orders of magnitude in the input of the model to capture the measured data. We interpret this discrepancy as a result of probable subsurface heterogeneity in carbonate watersheds, since macroporosities and fractures can strongly decrease the apparent mineral reactive surfaces in the field. For the effect of spatial scales, shifting from elementary (&lt;5 km²) to mesoscale watersheds (20–50 km²) has little impact on the geochemical composition of river waters while differences in hydrological functioning are observed. This absence of geochemical contrast cannot be only explained by equilibrium concentrations, but must also imply a geomorphological control on water transit times. Finally, our work highlights the importance of multi-observatory investigations. It also demonstrates that a thorough knowledge of the regional geology is key to understand the critical zone architecture, its mineralogical composition and the main hydrogeochemical processes.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 221-241"},"PeriodicalIF":4.5,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083382","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":"Fluid systems captured by giant amethyst-hosted fluid inclusions from continental flood basalts","authors":"Marta Sośnicka ,&nbsp;Samuel Niedermann ,&nbsp;Rudolph Erasmus ,&nbsp;Sharad Master","doi":"10.1016/j.gca.2025.04.028","DOIUrl":"10.1016/j.gca.2025.04.028","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Continental flood basalt (CFB) provinces, defined by the rapid emplacement of large volumes of mafic lava, represent some of the most significant large-scale magmatic events in Earth’s geological record. Gaining insight into the origin and evolution of fluid systems within these settings is critical for understanding the geodynamic architecture of large igneous provinces (LIPs) and accompanying mineralisation processes. However, the provenance and reservoirs of hydrothermal fluid systems in CFB settings remain poorly constrained. This study provides new evidence on the origin and sources of fluids responsible for the formation of amethyst mineralisation within a CFB context. Unique, giant fluid inclusions entrapped in amethyst crystals enabled reconstruction of variations in fluid system dynamics during incremental crystal growth in the geodes, which developed in the LTZ.L series Goboboseb basalts in an active continental flood basalt volcanic setting of the Paraná-Etendeka CFB Province.&lt;/div&gt;&lt;div&gt;Three compositionally different types of fluid inclusions, namely H&lt;sub&gt;2&lt;/sub&gt;O-NaCl-N&lt;sub&gt;2&lt;/sub&gt;-CH&lt;sub&gt;4&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;-CH&lt;sub&gt;4&lt;/sub&gt;-CO&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;-CH&lt;sub&gt;4&lt;/sub&gt;, preserved in individual amethyst and quartz crystals have archived an intricate fluid evolution history. Amethyst crystallisation commenced at moderate temperatures (281–327 °C) from low salinity (0.3–8.7 wt% NaCl equiv.) aqueous H&lt;sub&gt;2&lt;/sub&gt;O-NaCl-N&lt;sub&gt;2&lt;/sub&gt;-CH&lt;sub&gt;4&lt;/sub&gt; fluid. As crystal growth rates decreased and the fluid system cooled to 160–211 °C, some crystals captured fluid boiling/phase separation in the environment of ongoing magmatic CO&lt;sub&gt;2&lt;/sub&gt; degassing. Fluid properties and fluid-host rock thermal equilibrium, coupled with high SiO&lt;sub&gt;2&lt;/sub&gt; and H&lt;sub&gt;2&lt;/sub&gt;O contents of the low Ti/Zr LTZ.L series basalts, support a magmatic-hydrothermal origin of the aqueous fluid. For the first time, fluid inclusion noble gas data reveal unequivocal evidence of deep primordial mantle contributions (&lt;sup&gt;3&lt;/sup&gt;He) to magmatic-hydrothermal fluids involved in amethyst formation. The results provide convincing evidence for the Tristan da Cunha plume-related magmatism in the Paraná-Etendeka CFB Province and confirm that deep-sourced volatiles can migrate into shallow crustal levels via magmatic degassing. Strongly elevated &lt;sup&gt;40&lt;/sup&gt;Ar*/&lt;sup&gt;4&lt;/sup&gt;He, nucleogenic &lt;sup&gt;21&lt;/sup&gt;Ne/&lt;sup&gt;22&lt;/sup&gt;Ne isotope ratios and crustal δ&lt;sup&gt;15&lt;/sup&gt;N signatures of fluids indicate significant assimilation of continental crust and entrainment of old crustal fluids during magma fractionation in feeder chambers at different crustal levels above the Tristan da Cunha mantle plume, supporting models of lithospheric recycling and magma-crust interaction. The engagement of multi-source fluid systems, predominantly mantle and crust-derived, across different evolution stages shows the complexity of fluid systems in CFB volcanic settings. Moreover, the findings of th","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 171-190"},"PeriodicalIF":4.5,"publicationDate":"2025-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083383","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":"Chromite as a key player on highly siderophile elements and osmium isotope compositions of the refractory mantle","authors":"Ben-Xun Su, Ibrahim Uysal, Recep Melih Akmaz, Qi-Qi Pan, Yılmaz Demir, Lukáš Ackerman, Paul T. Robinson","doi":"10.1016/j.gca.2025.04.026","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.026","url":null,"abstract":"Chromitites in ophiolites are recognized for their high concentrations of highly siderophile elements (HSE), notably IPGE (Os, Ir and Ru). However, the effects of this enrichment on ophiolitic rocks and mantle heterogeneity remain poorly understood and to address this issue, we investigated chromitites from the Pozantı-Karsantı and Kızıldağ ophiolites in Türkiye. The results reveal HSE enrichment, particularly IPGE, in chromite separates compared to matrix, with indistinguishable Os isotope compositions between the two phases. This observation aligns with the presence of platinum-group minerals (PGM) occurring as inclusions within chromite grains. The IPGE enrichment and similar Os isotope compositions are also present in chromitites relative to dunites, suggesting close affinity of HSE with chromite fractions relative to silicate melts during chromite crystallization and aggregation. A global compilation of data on chromitites in ophiolites demonstrates covariations of HSE and their ratios with chromite Cr# values, indicating that chromite composition modulates its capacity to retain HSE. Peridotites containing chromite with low-Cr# (&lt;45) exhibit consistent HSE concentrations and a decrease in <ce:sup loc=\"post\">187</ce:sup>Os/<ce:sup loc=\"post\">188</ce:sup>Os<ce:inf loc=\"post\">t</ce:inf> ratios as chromite Cr# values increase, reflecting different partial melting degrees. In contrast, the refractory peridotites (with chromite Cr# &gt; 45) show more scattered HSE variations and distinct trends with chromite Cr#, generally trending towards the chromitite field. This variability likely reflects the compositional effects of chromite on HSE variations, suggesting significant metasomatism and interaction with parental melts of chromitites or evolved melts. Therefore, chromite plays a critical role in the variations of HSE contents and <ce:sup loc=\"post\">187</ce:sup>Os/<ce:sup loc=\"post\">188</ce:sup>Os within the refractory mantle.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"2 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-05-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932529","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":"Colloidal association of selenite and selenate in water containing dissolved organic matter and ferric iron: implication for selenium mobility in the aquatic environments","authors":"Subhashree Dalai,&nbsp;Ashis Biswas","doi":"10.1016/j.gca.2025.04.027","DOIUrl":"10.1016/j.gca.2025.04.027","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Dissolved organic matter (DOM)-modified organic and inorganic colloids are known to enhance the mobilization and transport of different trace elements in aquatic environments. Occurrences of selenium (Se) in natural waters often positively correlate with DOM under diverse environmental conditions, suggesting that DOM may enhance Se mobilization at the soil/sediment–water interface. Despite its importance, however, the extent and mechanism of the association of Se species with DOM-modified colloids in water is poorly understood. Therefore, the size distribution of selenite and selenate in water containing Suwannee River aquatic DOM (SRNOM) was determined in the absence and presence of Fe&lt;sup&gt;3+&lt;/sup&gt; under different environmentally relevant conditions by batch incubation followed by filtration (0.2 µm) and ultrafiltration (50 and 3 kDa). The mechanism of the association of Se species with SRNOM-modified colloids was determined by Fe and Se K-edge X-ray absorption spectroscopy (XAS). Results suggest that Se species can be considerably associated with DOM-modified colloids in water, and therefore, their mobilization and transport can be enhanced in aquatic environments. The colloidal association of selenite occurred predominantly due to its inner-sphere complexation with the Fe(O,OH)&lt;sub&gt;6&lt;/sub&gt; octahedra (&lt;em&gt;&lt;sup&gt;1&lt;/sup&gt;E&lt;/em&gt; and &lt;em&gt;&lt;sup&gt;2&lt;/sup&gt;C&lt;/em&gt; complexation), and therefore, the extent of association was dependent on the Fe&lt;sup&gt;3+&lt;/sup&gt; concentration in solution. At low Fe&lt;sup&gt;3+&lt;/sup&gt; concentrations (&lt;200 µmol/L, C/(C + Fe) molar ratio &gt; 0.91), selenite was complexed with organically bound monomeric Fe(O,OH)&lt;sub&gt;6&lt;/sub&gt; octahedra, resulting in Fe(III)-bridged ternary complexation with DOM. At higher Fe&lt;sup&gt;3+&lt;/sup&gt; concentrations, it was complexed with polymeric Fe(O,OH)&lt;sub&gt;6&lt;/sub&gt; octahedra, resulting in its sorption onto the neo-formed Fe oxyhydroxides. In addition, selenite could also be directly complexed with N-containing functional groups (e.g., –NH&lt;sub&gt;2&lt;/sub&gt;) of the SRNOM. Selenate formed the colloidal association predominantly due to its direct binary complexation with O-containing functional groups (e.g., –COOH and –OH) of the SRNOM. In addition, Fe(III)-bridged ternary complexation (&lt;em&gt;&lt;sup&gt;2&lt;/sup&gt;C&lt;/em&gt; complexation), binary complexation with S-containing functional groups (e.g., –SH) of the SRNOM, and outer-sphere complexation could contribute to its colloidal association with DOM. Therefore, the extent of the colloidal association of selenate was not strongly dependent on the Fe&lt;sup&gt;3+&lt;/sup&gt; concentration in the solution. Selenate generally had a greater tendency to form colloids with SRNOM than selenite. Only when polymeric Fe(O,OH)&lt;sub&gt;6&lt;/sub&gt; octahedra started to form in solution (at Fe&lt;sup&gt;3+&lt;/sup&gt; concentration ≥ 200 µmol/L) did the colloidal association of selenite exceed that of selenate initially and then decreased again when the cluster size of the polymeric Fe(O,OH)&lt;sub&gt;6&lt;/sub&gt; octahedra was big ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 156-170"},"PeriodicalIF":4.5,"publicationDate":"2025-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932415","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}