Geochimica et Cosmochimica Acta最新文献

{"title":"Comparison of the earliest NC and CC planetesimals: Evidence from ungrouped iron meteorites","authors":"Fridolin Spitzer ,&nbsp;Christoph Burkhardt ,&nbsp;Thomas S. Kruijer ,&nbsp;Thorsten Kleine","doi":"10.1016/j.gca.2025.03.021","DOIUrl":"10.1016/j.gca.2025.03.021","url":null,"abstract":"<div><div>Isotope anomalies in meteorites reveal a fundamental dichotomy between <em>Non-Carbonaceous-</em> (NC) and <em>Carbonaceous-type</em> (CC) planetary bodies. Until now, this dichotomy is established for the major meteorite groups, representing about 36 distinct parent bodies. Ungrouped meteorites represent an even larger number of additional parent bodies, but whether they conform to the overall NC-CC dichotomy is unknown. Here, the genetics and chronology of 26 ungrouped iron meteorites are considered through nucleosynthetic Mo and radiogenic W isotopic compositions. Secondary cosmic ray-induced modifications of these isotope compositions are corrected using Pt isotope measurements on the same samples. We find that all of the ungrouped irons have Mo isotope anomalies within the range of the major meteorite groups and confirm the NC-CC dichotomy for Mo, where NC and CC meteorites define two distinct, subparallel <em>s</em>-process mixing lines. All ungrouped NC irons fall on the NC-line, which is now precisely defined for 41 distinct parent bodies. The ungrouped CC irons show scatter around the CC-line indicative of small <em>r</em>-process Mo heterogeneities among these samples. These <em>r</em>-process Mo isotope variations correlate with O isotope anomalies, most likely reflecting mixing of CI chondrite-like matrix, chondrule precursors, and Ca-Al-rich inclusions. This implies that CC iron meteorite parent bodies accreted the same nebular components as the later-formed carbonaceous chondrites. The Hf-W model ages of core formation for the ungrouped irons overlap with those of the iron meteorite groups from each reservoir and reveal a narrow age peak at ∼3.3 Ma after Ca-Al-rich inclusions for the CC irons. By contrast, the NC irons display more variable ages, including younger ages indicative of impact-induced melting events, which seem absent among the CC irons. This is attributed to the more fragile and porous nature of the CC bodies, making impact-induced melting on their surfaces difficult. The chemical characteristics of all iron meteorites together reveal slightly more oxidizing conditions during core formation for CC compared to NC irons. More strikingly, strong depletions in moderately volatile elements, typical of many iron meteorite parent bodies, predominantly occur among CC irons, for reasons that remain unclear at present.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 134-148"},"PeriodicalIF":4.5,"publicationDate":"2025-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824995","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":"Site-specific D-H exchange of amino acids under asteroidal hydrothermal conditions","authors":"Yuanyuan He ,&nbsp;Flavio Siro Brigiano ,&nbsp;Michel Sablier ,&nbsp;Nadezda Khodorova ,&nbsp;David Boulesteix ,&nbsp;Arnaud Buch ,&nbsp;Peter Reinhardt ,&nbsp;Sylvain Bernard ,&nbsp;Laurent Remusat","doi":"10.1016/j.gca.2025.03.017","DOIUrl":"10.1016/j.gca.2025.03.017","url":null,"abstract":"<div><div>Amino acids detected in carbonaceous chondrites are commonly enriched in heavy isotopes of hydrogen compared to terrestrial counterparts. This is interpreted as the consequence of synthesis processes happening in cold extraterrestrial environments. However, the magnitude of this enrichment is variable among classes of chondrites and among individual amino acid in a given chondrite. In this study, we investigated the evolution of the D/H isotope ratio of amino acids experimentally exposed to pure D₂O at 150 °C. We observed that not all the hydrogen-specific sites are prone to deuterium-hydrogen exchange under hydrothermal conditions. Ab-initio modeling pinpoints the higher acidity of the carbon in α position (C_α) leading to a site-specific preferential D-H exchange, affecting the hydrogen atoms bonded to C_α (α-H). This explains the low exchange rate of 2-aminoisobutyric acid and isovaline, these branched amino acids lacking α-H, and the rather high exchange rate of glycine, α-alanine and β-alanine, their α-H exchanging faster. By extrapolating these results, it can be assumed that chondritic amino acids lacking α-H and containing only primary hydrogen (i.e., –CH₃ group) have better retained their pre-accretional D/H values despite hydrothermal alteration on the parent body.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 170-181"},"PeriodicalIF":4.5,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821318","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":"Heterogeneous enriched geochemical compositions in Hawaiian lavas: Contributions from recycled continental materials in the Loa source of the Hawaiian plume","authors":"Nicole M.B. Williamson ,&nbsp;Dominique Weis ,&nbsp;Elly Thistlethwaite ,&nbsp;Lauren N. Harrison ,&nbsp;Catherine Armstrong ,&nbsp;James S. Scoates ,&nbsp;Michael O. Garcia","doi":"10.1016/j.gca.2025.03.012","DOIUrl":"10.1016/j.gca.2025.03.012","url":null,"abstract":"<div><div>Several mantle plumes (Hawai‘i, Kerguelen, Pitcairn) produce ocean island basalt with enriched mantle I (EM-I) geochemical compositions. Hawai‘i is the most vigorous of these plumes, with the highest buoyancy flux. The isotopically enriched, EM-I-like compositions measured along the Hawaiian Island chain are limited to the Ko‘olau, Lāna‘i, and Kaho‘olawe volcanoes, which form the Enriched Loa geochemical group. A total of 37 new samples from seven locations across the Wai‘anae and Ko‘olau volcanoes (O‘ahu, Hawai‘i) were analysed for major element oxides, trace element concentrations, and Pb-Sr-Nd-Hf isotopic compositions to determine the composition and spatial distribution of Enriched Loa compositions along the Hawaiian chain. Combined with data from Lāna‘i and Kaho‘olawe, and a compilation of shield stage Hawaiian data spanning ∼6 Ma, this study shows that Enriched Loa compositions are chemically heterogeneous and that the Enriched Loa component was present intermittently along the Hawaiian chain over approximately 130 km and 1.4 Ma. The statistically distinct Pb-Sr-Nd-Hf isotopic means between the Makapu‘u stage of Ko‘olau, Lāna‘i, and Kaho‘olawe suggest that the Enriched Loa geochemical group consists of two different heterogeneities and implies that enriched components in the deep mantle source of the Hawaiian plume exist at multiple physical scales. The geochemical features of the Enriched Loa volcanoes require a distinct mantle component, with a source that likely contains recycled surface materials, possibly of continental origin, stored in the Pacific large low shear velocity province (LLSVP). Enriched Loa isotopic compositions share similarities with other EM-I ocean island basalt; however, they are not as radiogenic in ⁸⁷Sr/⁸⁶Sr as compositions from Kerguelen and Pitcairn. This suggests that the materials stored in the Pacific and African LLSVPs have slightly different sources and ages. Specifically, this work supports the hypothesis that the recycled surface materials from the Pacific LLSVP are younger than those from the African LLSVP.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 75-95"},"PeriodicalIF":4.5,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824996","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":"Cesium partitioning between granitic melts and aqueous fluids: Is Cs in hydrothermal fluids an accurate proxy of the degree of fractionation of parental magmas?","authors":"Chengming Wen ,&nbsp;Panlao Zhao ,&nbsp;Carter Grondahl ,&nbsp;Alexandra Tsay ,&nbsp;Zoltán Zajacz ,&nbsp;Shunda Yuan","doi":"10.1016/j.gca.2025.03.016","DOIUrl":"10.1016/j.gca.2025.03.016","url":null,"abstract":"<div><div>The concentration of Cesium in the aqueous magmatic fluid is widely used as an indicator for the degree of differentiation of the parental magma, which is fundamental for estimating the ore-forming potential of the fluid and characterizing the overall magmatic system. However, the fluid-melt partitioning behavior of Cs has not yet been well-characterized experimentally, posing some challenges in the quantitative use of measured Cs concentrations. In this study, we determined the fluid-melt partition coefficient of Cs (D_Cs^f/m) at 800 °C, 150 MPa and 250 MPa and the oxygen fugacity of the Ni-NiO buffer as a function of total Cl concentration (m_Cl^total) and HCl/total Cl (molar) ratios in the fluid. The results show that D_Cs ^f/m increases linearly from 0.21 ± 0.06 (1σ) to 6.31 ± 0.18 (1σ) as m_Cl^total increases from 1 to 16 m (5.5–48 wt% NaCl equivalent). At a constant m_Cl^total = 2 m, D_Cs^f/m broadly remains constant at 0.75 when HCl/total Cl ratios increase from 0.09 to 0.33. At a constant m_Cl^total = 1 m, D_Cs^f/m is identical within error (0.21 ± 0.01) at 150 and 250 MPa confining pressure. The observed partitioning data suggest that Cs was dominantly present as CsCl in the Cl-rich aqueous fluids at the experimental conditions. The fluid-melt partition coefficients of alkali elements (M) increase in the order of Li &lt; K &lt; Rb &lt; Cs corresponding to decreasing ionic potential (except Na), which is controlled by the strength of M–O bonds and the structure of the silicate melts. Numerical modeling indicates that the Cs concentration in the evolving fluid decreases initially and then increases during fractional crystallization (a ‘U-type’ curve) when the initial melt has a high Cl/H₂O ratio or differentiates under higher pressure. In contrast, the Cs/Cl and Cs/Na ratios of the fluid exhibit a monotonous growth trend during crystallization at all modeled conditions. Therefore, we suggest that rather than the Cs concentration in fluid, the Cs/Cl and Cs/Na ratios of the fluid are more appropriate to be used as indicators for the degree of fractionation of the parental melt. In addition, the new partitioning data will facilitate direct estimation of the Cs concentration in the parental melt of observed ore-forming fluids, and thus the estimation of the residual melt fraction in the parental magma body at the time of fluid extraction, which can facilitate better understanding of the physical mechanism of fluid extraction from crustal magma reservoirs.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 159-169"},"PeriodicalIF":4.5,"publicationDate":"2025-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821317","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":"In Situ experimental study of talc carbonation in C-O-H fluid: Implications for the deep carbon cycle","authors":"Mengjun Xiong ,&nbsp;Zhi Zheng ,&nbsp;Jiangzhi Chen ,&nbsp;Xia Zhao ,&nbsp;Shenghua Mei","doi":"10.1016/j.gca.2025.03.015","DOIUrl":"10.1016/j.gca.2025.03.015","url":null,"abstract":"<div><div>The physical and chemical behavior of carbonate minerals during subduction is key to understanding the carbon cycle process in the deep Earth. Using diamond anvil cells combined with <em>in situ</em> Raman spectroscopy, we investigated talc stability at 200–550 ℃ and 0.5–3 GPa, corresponding to subduction zone conditions. Results demonstrate that talc readily reacts with C-O–H fluid to form magnesite at <em>T</em> &gt; 250 ℃ and <em>P</em> &gt; 1 GPa, highlighting the efficient CO₂ sequestration via a stepwise carbonation process, with talc carbonation rates positively correlated with both temperature and pressure. Consequently, C-O–H fluid-driven talc carbonation effectively sequesters CO₂ from the fluid into newly formed thermodynamically more stable magnesite, implying that it has great potential for transforming talc into magnesite in the deep Earth. We have also revealed the thermodynamic conditions of the talc carbonation process and demonstrated that the stability of talc in contact with the fluid is significantly lower than that under anhydrous conditions. Furthermore, enhanced CO₂ sequestration via talc carbonation at elevated pressures and temperatures may compensate for the relatively inefficient serpentinite carbonation under the subarc. Therefore, the findings provide critical insights into the thermodynamic conditions favoring talc carbonation and contribute to a deeper understanding of carbon cycling in the Earth’s interior.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 146-158"},"PeriodicalIF":4.5,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724027","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":"Symbiont regulation of nitrogen metabolism and excretion in tropical planktonic foraminifera","authors":"Ren-Yi Cai-Li ,&nbsp;Haojia Ren ,&nbsp;Wei-Ning Fang ,&nbsp;Er-Wen Yang ,&nbsp;Wen-Hui Chen ,&nbsp;Charlotte LeKieffre ,&nbsp;Oscar Branson ,&nbsp;Jennifer Fehrenbacher ,&nbsp;Lael Vetter ,&nbsp;Ming-Shiou Jeng ,&nbsp;Howard J. Spero","doi":"10.1016/j.gca.2025.03.009","DOIUrl":"10.1016/j.gca.2025.03.009","url":null,"abstract":"<div><div>Dissolved inorganic nitrogen (DIN) is one of the key major nutrients crucial for regulating marine productivity. Photosynthetic endosymbiosis, as seen in organisms like stony corals and foraminifera, appear to alleviate nutrient limitations in surface ocean waters through its symbiotic relationship with the host. Recent advancements in understanding the nitrogen isotopic compositions (¹⁵N/¹⁴N) of planktonic foraminifera reveal notably lower ¹⁵N/¹⁴N ratios in species harboring dinoflagellate symbionts compared to those without symbionts or with different types of symbionts. This species differentiation is hypothesized to arise from more efficient internal nitrogen cycling in dinoflagellate-bearing species, resulting in reduced nitrogen loss to the environment and thus diminished trophic enrichment. In our investigation, we monitored nitrogen excretion in incubation experiments involving several planktonic foraminifera species, including dinoflagellate-bearing <em>Globigerinoides ruber</em>, <em>Trilobatus sacculifer</em>, <em>Orbulina universa</em>, and chrysophyte-bearing <em>Globigerinella siphonifera</em>. <em>G. siphonifera</em> exhibited distinct diel cycles of ammonium production at night and uptake during the day, with its trophic enrichment in biomass ¹⁵N/¹⁴N increasing in tandem with ammonium loss. Conversely, no measurable excreted ammonium was detected from any of the three dinoflagellate-bearing species. These findings align with earlier observations indicating a tight interaction wherein hosts likely supply excess non-carbon nutrients to their symbionts via prey ingestion and digestion, in exchange for organic carbon. Our research underscores the pivotal role of symbiosis in shaping nutrient dynamics between planktonic foraminifera and the surrounding environment, with implications for using the species ¹⁵N/¹⁴N difference to reconstruct upper ocean nutrient conditions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 135-145"},"PeriodicalIF":4.5,"publicationDate":"2025-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143724029","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":"The effect of CO2 on the partitioning of H2O between clinopyroxene and melts and melting of volatile-bearing eclogites","authors":"Andrea Curtolo, Pierre Condamine, Federica Schiavi, Nathalie Bolfan-Casanova, Davide Novella","doi":"10.1016/j.gca.2025.03.013","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.013","url":null,"abstract":"H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O and CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; are critical components for the development and sustainment of life on Earth and affect a wide variety of geological processes. It has been suggested that the presence of CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; in the mantle could alter how H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O is stored and partitioned between minerals and melts, implying dramatic effects on both melting processes and H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O storage capacities of the Earth’s mantle. Eclogites, which are present as heterogeneities in the mantle, have been shown to participate in the production of oceanic island basalts such as the HIMU (High-µ, µ = &lt;ce:sup loc=\"post\"&gt;238&lt;/ce:sup&gt;U/&lt;ce:sup loc=\"post\"&gt;204&lt;/ce:sup&gt;Pb). They can host significant amounts of H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O in clinopyroxenes and their H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O storage capacity and melting temperature can be significantly influenced by the presence of CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;. Here, the effect of CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; on the partition coefficient of H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O between clinopyroxene and melt (&lt;mml:math altimg=\"si7.svg\"&gt;&lt;mml:mrow&gt;&lt;mml:msubsup&gt;&lt;mml:mi&gt;D&lt;/mml:mi&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;H&lt;/mml:mi&gt;&lt;mml:mn&gt;2&lt;/mml:mn&gt;&lt;/mml:msub&gt;&lt;mml:mi&gt;O&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;cpx&lt;/mml:mi&gt;&lt;mml:mo stretchy=\"true\"&gt;/&lt;/mml:mo&gt;&lt;mml:mi&gt;m&lt;/mml:mi&gt;&lt;mml:mi&gt;e&lt;/mml:mi&gt;&lt;mml:mi&gt;l&lt;/mml:mi&gt;&lt;mml:mi&gt;t&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;/mml:msubsup&gt;&lt;mml:mo linebreak=\"goodbreak\" linebreakstyle=\"after\"&gt;=&lt;/mml:mo&gt;&lt;mml:msubsup&gt;&lt;mml:mi&gt;C&lt;/mml:mi&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;H&lt;/mml:mi&gt;&lt;mml:mn&gt;2&lt;/mml:mn&gt;&lt;/mml:msub&gt;&lt;mml:mi&gt;O&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;cpx&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;/mml:msubsup&gt;&lt;mml:mo stretchy=\"true\"&gt;/&lt;/mml:mo&gt;&lt;mml:msubsup&gt;&lt;mml:mi&gt;C&lt;/mml:mi&gt;&lt;mml:mrow&gt;&lt;mml:msub&gt;&lt;mml:mi&gt;H&lt;/mml:mi&gt;&lt;mml:mn&gt;2&lt;/mml:mn&gt;&lt;/mml:msub&gt;&lt;mml:mi&gt;O&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;mml:mrow&gt;&lt;mml:mi mathvariant=\"italic\"&gt;melt&lt;/mml:mi&gt;&lt;/mml:mrow&gt;&lt;/mml:msubsup&gt;&lt;/mml:mrow&gt;&lt;/mml:math&gt;) was explored at high-pressure and high-temperature by conducting piston cylinder experiments at 1200 °C and 2 GPa. The experiments employed a basaltic starting mixture with different concentrations of H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O and CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; and produced an assemblage consisting of more than 60 wt% basaltic-andesitic melt in equilibrium with high-Al (Al&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt; = 7.83–11.18 wt%) clinopyroxene crystals. The H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O concentration in clinopyroxene, measured by Fourier Transform Infrared spectroscopy, ranges from 869 ± 71 to 1950 ± 134 ppm wt, and shows a negative correlation with the concentration of CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; in the system and a positive correlation with tetrahedrally-coordinated Al&lt;ce:sup loc=\"post\"&gt;3+&lt;/ce:sup&gt; in the clinopyroxene. The quenched melts have H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O and CO&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt; concentratio","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"130 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824997","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":"Gold solubility enhanced by H2O in sulfur-bearing magma: Implications for gold partitioning and mineralization","authors":"Xingcheng Liu ,&nbsp;Lanqin Li ,&nbsp;Ting Xu ,&nbsp;Xiaolin Xiong ,&nbsp;Jintuan Wang ,&nbsp;Zaicong Wang ,&nbsp;Hugh St.C. O’Neill","doi":"10.1016/j.gca.2025.01.017","DOIUrl":"10.1016/j.gca.2025.01.017","url":null,"abstract":"<div><div>Most endogenic gold deposits are associated with H₂O-rich magmatism or their associated hydrothermal systems. However, the role that H₂O plays in the transfer and enrichment of gold remains elusive. Here we conducted piston cylinder experiments at 1 GPa and 850 or 950 °C on sulfur-bearing dacitic compositions with variable H₂O contents and under different controlled oxygen fugacity. Our results show that increasing the H₂O contents of the melts from 2 to 15 wt% enhances gold solubilities by up to 37-fold at moderate oxidizing conditions (approximately 2 log units above the fayalite-magnetite-quartz buffer). This dramatic increase results from H₂O-induced elevation of melt FeO content, which increases reduced sulfur concentrations, thereby promoting Au-S complexation in the melt. Under these conditions, H₂O-rich, near fluid-saturated melts exhibit gold partition coefficients between sulfide and silicate melt that are one order of magnitude lower than in H₂O-poor melts. Thus, H₂O content, combined with moderate oxygen fugacity, exerts substantial control on the gold fertility of primary magmas. These findings indicate that both partial melting of H₂O-rich sources and crystallization of H₂O-rich magmas can effectively mobilize and concentrate gold. The process is further enhanced when fluid exsolution occurs before gold sequestration into sulfides. In contrast, copper partitioning shows stronger dependence on oxygen fugacity than H₂O content, explaining the differing behavior of gold and copper during magmatic-hydrothermal evolution. These results provide new insights into the formation of gold-rich magmatic-hydrothermal ore deposits.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 170-181"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055250","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":"Earth’s early differentiation recorded by halogen abundance ratios in Hawaiian lavas","authors":"Mark A. Kendrick ,&nbsp;Oliver Nebel ,&nbsp;Takeshi Hanyu ,&nbsp;Bryden L. Maunder ,&nbsp;Roland Maas","doi":"10.1016/j.gca.2025.01.019","DOIUrl":"10.1016/j.gca.2025.01.019","url":null,"abstract":"<div><div>Halogens (F, Cl, Br, I) and radiogenic isotopes were investigated in a suite of submarine basalt glasses from across the Hawaiian archipelago in order to better understand the origin of xenon isotope anomalies related to extinct ¹²⁹I and the nature of metasomatic agents involved in peripheral Arch magmatism. We found that Lō’ihi tholeiites with high ³He/⁴He of up to 26 Ra (where Ra denotes the atmospheric ³He/⁴He) are characterised by unusually low I/Cl of (27 ± 3) × 10⁻⁶, whereas peripheral alkaline lavas from the South Arch that have ³He/⁴He of up to 18 Ra are characterised by unusually high I/Cl of (120 ± 20) × 10⁻⁶. In comparison, rejuvenated lavas with ³He/⁴He of ∼ 8 Ra have I/Cl in the range of (60 ± 30) × 10⁻⁶ that is typical of mid-ocean ridge and ocean island basalt lavas elsewhere. The variations in I/Cl, ³He/⁴He and radiogenic isotopes are consistent with mixing between three mantle end-members. The most primitive end-member with high ³He/⁴He and low ¹²⁹Xe_I/¹³⁶Xe_Pu has low I/Cl but normal Br/Cl, H₂O/Cl and F/Cl ratios. Compared to the primitive mantle it is strongly depleted in I and weakly depleted in the other volatiles F, Cl, Br and H₂O. The depletion of I (and ¹²⁹Xe derived from extinct ¹²⁹I) probably results from a combination of Earth’s heterogenous accretion and preferential partitioning of I into the Earth’s core. The high I/Cl of the South Arch lavas can be explained by input of low degree carbonatitic melts derived from carbonated eclogite in the plume source. This is implied because carbonated ocean crust is uniquely enriched in I. The involvement of carbonatitic melts is consistent with previously reported H₂O, Ba and light rare earth element enrichments of South Arch lavas. Taken together the halogen abundance ratios in lavas sourced from around Hawaii record Earth’s early accretion and differentiation, the subsequent subduction of carbonated ocean crust into the mantle and its mobilisation in minor carbonatitic components enriching the periphery of the plume.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 196-207"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143462869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Quantifying the impacts of exogenous dust inputs to the critical zone using reactive transport modeling","authors":"Celia Aranda Reina ,&nbsp;Julien Bouchez ,&nbsp;Jennifer L. Druhan","doi":"10.1016/j.gca.2025.01.023","DOIUrl":"10.1016/j.gca.2025.01.023","url":null,"abstract":"<div><div>In upland watersheds, depletion of essential nutrients due to physical erosion and chemical weathering can be compensated by exogenous inputs such as aeolian dust deposition. However, it remains an outstanding challenge to describe the impacts of dust on the reaction rates that produce weathering profiles and how this cascades into ecosystem function and water chemistry. As increasingly intense and episodic periods of drought and aridity are promoted by a warming climate, the role of dust production and deposition in Critical Zone structure and function requires improved modeling techniques to facilitate rigorous quantification and prediction. Here we present a newly developed process-based reactive transport framework by modifying the open-source CrunchTope software in order to quantitatively interpret the impacts of dust deposition and solubilization in stream water chemistry, regolith weathering rates, and ecosystem nutrient availability. We describe two simulations: (1) a generic model demonstrating a simplified system in which bedrock uplift and soil erosion occur in tandem with solid phase dust deposition at the land surface; (2) a case study based on a small (0.54 km<span><math><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup></math></span>) upland Mediterranean watershed located on Mont Lozère in the National Park of Les Cévennes, France. In the absence of an exogenous dust input, long-term field observations of calcium in stream water, rain, soil, and plant samples cannot be produced by reactive transport simulations of the weathering profile. By adding a carbonate-bearing depositional input consistent with the composition of Saharan dust, both stream water chemistry and elemental mass-transfer coefficients in the soil profile better align with field observations, suggesting that dust has become a significant input to this field site in the last <span><math><mo>∼</mo></math></span>10 ka. Over this period, the deposition of exogenous carbonates has introduced far more calcium into the system than what could be supplied by the Ca-poor granitic bedrock. This highly soluble carbonate also limits the reactive potential of infiltrating precipitation, ultimately inhibiting chemical weathering rates and hence the component of elemental export fluxes derived from local bedrock.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"393 ","pages":"Pages 254-267"},"PeriodicalIF":4.5,"publicationDate":"2025-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143684050","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}