Geochimica et Cosmochimica Acta最新文献

{"title":"Tin isotope systematics in subduction zones","authors":"Xueying Wang ,&nbsp;Oliver Nebel ,&nbsp;Alexandra Churchus ,&nbsp;Peter A. Cawood","doi":"10.1016/j.gca.2025.05.004","DOIUrl":"10.1016/j.gca.2025.05.004","url":null,"abstract":"<div><div>The origin of slab components in arc lavas remains controversial with proposed sources including direct sediment melts, sediment-mantle mélanges, or crustal fluids. Stable isotope distributions of fluid-borne metals and those immobile in subduction components have the potential to trace the respective contribution of these components if placed into the context of additional magmatic differentiation and in conjunction with radiogenic isotopes. Here, we present the first high-precision double-spike tin abundances and isotope compositions in twenty-six arc rocks sampled along the Indonesian Sunda arc, a subduction zone with the highest subducted sediment volume globally. <em>δ</em>^122/118Sn_3161a in these samples ranges from 0.13‰ to 0.46‰ and we find that Sn isotope compositions in Sunda arc rocks were affected by magmatic differentiation, superimposed on additional influences from components derived from the subducting slab. A step change in <em>δ</em>^122/118Sn_3161a at 4–5wt.% MgO suggests the removal of heavier Sn isotopes, likely due to higher compatibility of isotopically heavier Sn⁴⁺ in Fe-Ti oxides along the liquid line of descent. This change of ∼0.1‰, however, is dwarfed by Sn isotope variations consistent with sediment melt contribution coupled with fluid addition from altered oceanic crust, both of which introduce lighter Sn isotopes. Sediment melt contamination increases with depth (temperature), but some exceptions at shallow sub-arc sources (depth ≤ 130 km) indicate additional melting of a mélange-style source. Our findings suggest the coexistence of mélange contributions, and deep fluid-induced melting plus partial sediment melts in the Sunda arc. Mélanges contribute only at shallow depths (≤130 km), consistent with their diapiric nature, whereas deeper levels favor fluid-fluxed melting and, at higher temperatures and pressures, partial sediment melting. This study provides insights into the complex interactions between fluids, sediments, and mantle wedge in subduction zones, highlighting the depth-dependent nature of slab contributions to arc magmatism. It also demonstrates the utility of Sn isotopes for tracing these processes and advancing our understanding of subduction zone geochemistry.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"399 ","pages":"Pages 18-34"},"PeriodicalIF":4.5,"publicationDate":"2025-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143947247","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":"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, Ashis Biswas","doi":"10.1016/j.gca.2025.04.027","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.027","url":null,"abstract":"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;ce:sup loc=\"post\"&gt;3+&lt;/ce: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;ce:inf loc=\"post\"&gt;6&lt;/ce:inf&gt; octahedra (&lt;ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;1&lt;/ce:sup&gt;E&lt;/ce:italic&gt; and &lt;ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;C&lt;/ce:italic&gt; complexation), and therefore, the extent of association was dependent on the Fe&lt;ce:sup loc=\"post\"&gt;3+&lt;/ce:sup&gt; concentration in solution. At low Fe&lt;ce:sup loc=\"post\"&gt;3+&lt;/ce: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;ce:inf loc=\"post\"&gt;6&lt;/ce:inf&gt; octahedra, resulting in Fe(III)-bridged ternary complexation with DOM. At higher Fe&lt;ce:sup loc=\"post\"&gt;3+&lt;/ce:sup&gt; concentrations, it was complexed with polymeric Fe(O,OH)&lt;ce:inf loc=\"post\"&gt;6&lt;/ce:inf&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;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&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;ce:italic&gt;&lt;ce:sup loc=\"post\"&gt;2&lt;/ce:sup&gt;C&lt;/ce:italic&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;ce:sup loc=\"post\"&gt;3+&lt;/ce: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;ce:inf loc=\"post\"&gt;6&lt;/ce:inf&gt; octahedra st","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"1 1","pages":""},"PeriodicalIF":5.0,"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}

{"title":"Potassium isotope composition in global loess: Origins and implications","authors":"Wenshuai Li, Xiao-Ming Liu, Kun Wang, Mohsen Shakouri, Catherine Chauvel","doi":"10.1016/j.gca.2025.04.023","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.023","url":null,"abstract":"Potassium (K) isotope compositions (δ<ce:sup loc=\"post\">41</ce:sup>K) in global loess deposits can provide valuable insights into the average upper continental crust (UCC). However, current knowledge of δ<ce:sup loc=\"post\">41</ce:sup>K in the UCC is limited due to the lithological complexity of the continental crust, which results in highly variable K isotope compositions. Accurately estimating the K isotope composition of the UCC remains a challenge. Here, we investigated the concentration, phase, and isotopic composition of K in loess samples from Asia, Europe, Oceania, North America, and South America to identify the dominant controls on loess δ<ce:sup loc=\"post\">41</ce:sup>K and better constrain the average composition of the UCC. Our results show that the δ<ce:sup loc=\"post\">41</ce:sup>K value in globally compiled loess ranges from −0.60 ± 0.08 ‰ to −0.33 ± 0.04 ‰, with an average of −0.46 ± 0.12 ‰ (2 S.D.). This loess-based δ<ce:sup loc=\"post\">41</ce:sup>K value of the average UCC is comparable to the average δ<ce:sup loc=\"post\">41</ce:sup>K value established from various crustal materials by Huang et al. (2020). Nonetheless, our new range is slightly narrower compared with the previous estimation. We infer the measured K isotope variation in loess reflects a result of eolian sorting rather than chemical weathering. The abundance of <ce:sup loc=\"post\">39</ce:sup>K-rich illite is the primary driver of the δ<ce:sup loc=\"post\">41</ce:sup>K variability in these loess samples. We suggest that the K isotope composition in bulk loess record provide more reliable information of the grain size sorting effect and thus inferring regional wind patterns (e.g., past monsoon variation).","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"33 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932403","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":"First-principles calculations of equilibrium isotope fractionation of Cl, Ca, and O in apatites and amphiboles","authors":"Shanqi Liu, Yongbing Li, Zhiming Yang, Huiquan Tian, Jianming Liu","doi":"10.1016/j.gca.2025.04.025","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.025","url":null,"abstract":"Apatites and amphiboles are common hydrous minerals in igneous and metamorphic rocks, which can be found from the crust to the lithospheric mantle. These minerals can incorporate chlorine (Cl) and fluorine (F) by substituting for hydroxyl groups (OH). The isotopic compositions of Cl, Ca, and O of apatites and amphiboles are valuable geochemical tools for understanding the terrestrial and extraterrestrial processes over a wide range of temperatures. In the present study, first-principles methods were used to investigate the equilibrium isotope fractionation of Cl, Ca, and O in apatites and amphiboles. Our results reveal that amphiboles are generally more enriched in <ce:sup loc=\"post\">37</ce:sup>Cl compared to apatites. In apatites, increasing the Cl/(Cl + F) and Cl/(Cl + OH) ratios reduces the <ce:italic>β</ce:italic><ce:inf loc=\"post\">Cl</ce:inf>-factors of Cl-F-apatites and Cl-OH-apatites, respectively, while substitution between F and OH has a small impact. In amphiboles, Cl contents have little effect on the <ce:italic>β</ce:italic><ce:inf loc=\"post\">Cl</ce:inf>-factors. For Ca isotopes, the <ce:italic>β</ce:italic><ce:inf loc=\"post\">Ca</ce:inf>-factors are largely unaffected by substitutions among Cl, F, and OH in either mineral. For O isotopes, the <ce:italic>β</ce:italic><ce:inf loc=\"post\">O</ce:inf>-factors vary depending on the type of oxygen atoms. In Cl-F-apatites and Cl-OH-apatites, the <ce:italic>β</ce:italic><ce:inf loc=\"post\">O</ce:inf>-factors for total oxygen atoms decrease with increasing Cl/(Cl + F) ratios but increase with Cl/(Cl + OH) ratios, respectively. Hydroxyl oxygen sites in amphiboles exhibit higher <ce:italic>β</ce:italic><ce:inf loc=\"post\">O</ce:inf>-factors than those in apatites, whereas silicate oxygen sites are more enriched in <ce:sup loc=\"post\">18</ce:sup>O than phosphate oxygen sites. Correlations between bond lengths and isotope fractionation properties are also observed: in both apatites and amphiboles, the <ce:italic>β</ce:italic><ce:inf loc=\"post\">Cl</ce:inf>-factor is negatively correlated with the Cl–Cation bond length, except in the cases of actinolite and richterite, while the <ce:italic>β</ce:italic><ce:inf loc=\"post\">O</ce:inf>-factors of phosphate oxygen and silicate oxygen correlate with the O–P and O–Si bond lengths, respectively. These results can enhance our understanding of Cl, Ca, and O isotope behavior in halogen-bearing phosphates and silicates, providing valuable insights into the role of apatites and amphiboles as indicators of evolutionary processes on Earth and in extraterrestrial bodies.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"38 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143932416","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":"Diffusion-driven zircon Zr isotopic fractionation during ultramafic–mafic magmatic differentiation","authors":"Li-Tao Ma, Li-Qun Dai, Shao-Bing Zhang, Ren-Xu Chen, Qiong-Xia Xia, Zi-Fu Zhao","doi":"10.1016/j.gca.2025.04.020","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.020","url":null,"abstract":"Previous studies of natural samples have documented marked variations in zircon Zr stable isotopes. However, the petrological mechanisms responsible for Zr stable isotopic fractionation during magmatic differentiation remain unclear. To address this, <ce:italic>in situ</ce:italic> Zr stable isotopic analyses of magmatic zircons were carried out on a suite of mafic plutonic rocks from the southwestern Tianshan, west China. Our results suggest that diffusion-driven Zr stable isotopic fractionation during zircon growth produces per mil-level, mass-dependent isotopic fractionation. Zircon Zr stable isotopic compositions range from –4.50 ‰ to +1.48 ‰, spanning a variation of 5.98 ‰. Some zircon grains exhibit internal Zr stable isotopic zoning, with lighter Zr isotopes in the core and heavier Zr isotope toward the rim, with intra-grain variations of up to 2.82 ‰. In addition, these zircons exhibit significant intra-grain variations in Zr/Hf ratios and Ti contents, which generally decrease with increasing <ce:italic>δ</ce:italic><ce:sup loc=\"post\">94/90</ce:sup>Zr values. While the Zr/Hf and Ti variations likely record fractional crystallization processes, the Zr stable isotopic variations cannot be attributed to mass-dependent, stable isotopic equilibrium fractionation, which would produce only ∼0.08 ‰ fractionation at 800 °C. As the temperature decreases and Zr supersaturation in the magma increases, the Zr stable isotopic fractionation becomes more pronounced. The <ce:italic>δ</ce:italic><ce:sup loc=\"post\">94/90</ce:sup>Zr values exhibit increasing variability toward both higher and lower values, rather than trending in a single direction. These variable Zr stable isotopic compositions can be explained by the diffusion-limited crystallization (DLC), which is primarily controlled by the zircon crystallization temperature and Zr supersaturation in the melt. As temperature decreases during magmatic differentiation, the diffusion-driven zircon Zr isotopic fractionation is enhanced. Therefore, diffusion during crystal accumulation provides a plausible explanation for the large Zr stable isotopic variability observed in zircons.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"139 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901850","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":"Cobalt-rich porphyry deposits derived from multiple mafic magma injections","authors":"Peng-Fei Shan, Ming-Jian Cao, Dong-Mei Tang, Zheng-Jie Qiu, Noreen J. Evans, Marina Lazarov, Da-Chuan Wang, Wei Hu, Ke-Zhang Qin, Ingo Horn, Stefan Weyer","doi":"10.1016/j.gca.2025.04.022","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.022","url":null,"abstract":"In addition to copper, gold, and molybdenum, porphyry deposits are important reservoirs of critical metals such as rhenium, selenium, tellurium, and platinum group elements (PGEs). However, enrichment of cobalt (Co) has received little attention. Several studies have shown that Co enrichment does occur in porphyry deposits, however, the source(s) of Co and the mechanism(s) responsible for its enrichment in the high-temperature hydrothermal systems that ultimately form Co-rich porphyry deposits, are poorly understood. In order to address this knowledge gap, we investigated the Jinchang porphyry deposit in Northeast China which is one of the most Co-enriched porphyry deposits worldwide. <ce:italic>In-situ</ce:italic> elemental and Fe-S isotopic analysis, as well as electron backscatter diffraction, have been conducted on two types of pyrite (Py1 and Py2). Py1 exhibits a core-mantle-rim structure, with Co enrichment in the core (Avg. 4.5 wt%) and rim (Avg. 7.5 wt%). Py2 displays a distinct core-rim structure, with Co enrichment only in the rim (Avg. 8.4 wt%). The early Co-rich fluid led to the formation of the Co-rich Py1 core. As pyrite continued to grow, Co in the fluid was depleted, leading to the formation of the Co-poor Py1 mantle and Py2 core. The most significant changes in δ<ce:sup loc=\"post\">56</ce:sup>Fe values and Co contents were observed between the Py2 core and Py2 rim (δ<ce:sup loc=\"post\">56</ce:sup>Fe: Δ0.94 ‰, Co: Δ10.67 wt%). This significant variation was generated by the re-injection of Co-rich fluids, which led to the coupled dissolution-reprecipitation of pyrite, leading to the formation of the Co-rich Py1 rim and Py2 rim. Each injection of Co-rich fluid not only formed a Co-rich zone in pyrite, but also precipitated Co-bearing minerals, such as siegenite and cobaltite. The magmatic δ<ce:sup loc=\"post\">34</ce:sup>S isotope signature of pyrite and chalcopyrite (1.5–5.3 ‰) rules out the possibility that Co originated from a sedimentary source. Due to the low Co content in felsic magmas, the repeated injections of Co-rich mafic magma are the only plausible source for the formation of such Co-rich fluids. Besides other possible causes, the heavy δ<ce:sup loc=\"post\">56</ce:sup>Fe<ce:inf loc=\"post\">fluid</ce:inf> values derived from mafic magmas suggest the addition of serpentinized oceanic crust slab during subduction, which directly contributed to the formation of mafic magmas.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"16 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901849","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":"Survivability and pathways of amino acids in oceanic hydrothermal systems: A mechanistic study of phenylalanine","authors":"Alexandria Aspin,&nbsp;Rhys Ellis,&nbsp;Megan Stull,&nbsp;Ziming Yang","doi":"10.1016/j.gca.2025.04.024","DOIUrl":"10.1016/j.gca.2025.04.024","url":null,"abstract":"<div><div>The survivability and pathways of amino acids in oceanic hydrothermal systems can be affected by fluid chemistry and composition including the presence of inorganic materials, however, their specific effects and underlying mechanisms remain largely unexplored. Using phenylalanine as a model compound, we find that decarboxylation is the primary degradation pathway for amino acids followed by deamination, via either substitution or elimination. Amino acid reactivity is influenced by solution pH, with degradation being strongly inhibited under highly acidic or alkaline conditions. The presence of dissolved metal salts not only changes the distribution of decarboxylation and deamination products but also plays a protective role, inhibiting the decomposition of amino acids. Overall, this study suggests that both relatively extreme pH and surrounding metal salts could enhance the survivability of amino acids, which may provide new insights into understanding the preservation and distribution of amino acids in oceanic hydrothermal systems on and outside Earth.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Pages 44-53"},"PeriodicalIF":4.5,"publicationDate":"2025-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143892260","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":"Experimental investigations of mineral-organic chondritic analogs under hydrothermal conditions: implications for carbonaceous asteroids","authors":"Coline Serra ,&nbsp;Olivier Grauby ,&nbsp;Daniel Ferry ,&nbsp;Fabrice Duvernay ,&nbsp;Grégoire Danger ,&nbsp;Johanna Marin-Carbonne ,&nbsp;Vassilissa Vinogradoff","doi":"10.1016/j.gca.2025.04.018","DOIUrl":"10.1016/j.gca.2025.04.018","url":null,"abstract":"<div><div>The occurrence of hydroxylated minerals in carbonaceous chondrites provides valuable insights of water –rocks interactions in hydrous asteroids. Yet, the evolution of water-organic-rock type experiments, applied to carbonaceous chondrites, remains understudied. Here, we present experimental studies of chondritic analogs containing a mixture of minerals and 4 wt% of OM under hydrothermal anoxic conditions at low temperature. The mineral composition is a mixture of anhydrous minerals (peridot, feldspar and troilite), combined with hexamethylenetetramine (C₆H₁₂N₄), a model organic molecule derived from interstellar grains. After being exposed to water at 80 °C for different duration time (up to 100 days) simulating early-stage alteration, a combination of analytical techniques (X-ray diffraction, transmission electron microscopy, infrared spectroscopy and elemental analyses) revealed significant changes in the mineral part of the chondritic analogs. The secondary minerals formed are diverse, consisting of hydroxylated phases such as phyllosilicates, but also iron oxides, which become more abundant with time. Amorphous silicate phases are also observed in abundance. The formation of these secondary minerals is strongly influenced by the presence of soluble organic matter, which can impact the nature of the formed hydroxylated phases and reduce the formation of iron oxides. The secondary phase assemblage obtained in our experiments exhibits similarities with carbonaceous chondrites that have undergone a low degree of aqueous alteration (CM-type). The results indicate that the presence of organic matter, even accounting for 4 wt%, is an important driver in the formation of secondary mineral phases during the initial stage of aqueous alteration. They highlight the importance of understanding the complex interactions between organic and inorganic materials in the context of hydrous asteroids.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"398 ","pages":"Pages 29-43"},"PeriodicalIF":4.5,"publicationDate":"2025-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143873278","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}