Geochimica et Cosmochimica Acta最新文献

{"title":"Potential for formation of methylated thioarsenates in geothermal environments","authors":"Ketao Yan, Qinghai Guo, Luxia Wang, Yi Liu, Britta Planer-Friedrich","doi":"10.1016/j.gca.2024.10.012","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.012","url":null,"abstract":"Geothermal waters typically have elevated arsenic (As) concentrations. Various As species have been identified, including methylated thioarsenates, which present a high environmental and health risk due to high mobility and toxicity. Upon discharge from hot springs, temperature and geogenic sulfide excess decrease, while redox potential increases. The combined effects of those parameters on activities of sulfate-reducing bacteria and methanogens and thereby on extent of As methylation versus thiolation is currently unknown. Here, we incubated sediments from alkaline hot springs and outflow channels at the Tengchong geothermal region in southwestern China, where inorganic and methylated thioarsenates had been detected, at temperatures between 20 to 90 °C with different initial aqueous As and sulfur species. Results from field samples and incubation experiments showed methylated thioarsenates, but no methylated oxyarsenates, implying quantitative thiolation even at low sulfide concentrations. Enrichment cultures derived from one sediment with quantitative formation of dimethyl-dithioarsenate (DMDTA) at 55 °C, showed a dominance of inorganic trithioarsenate at 35 °C and monomethylated thioarsenates at 55 °C when incubated with two other sediments. The rate-limiting step was microbially mediated As methylation from arsenite, which was not observed at 20 °C or >= 75 °C, in contrast to thiolation of already methylated arsenates. Addition of free sulfide and thiosulfate to incubation experiments promoted formation of inorganic or monomethylated high-thiolated arsenates, while sulfate promoted full methylation and formation of DMDTA, probably due to continuous low supply of microbially produced sulfide. Since DMDTA is more mobile and toxic than inorganic and monomethylated thioarsenates, understanding constraints to its formation is especially important for future risk assessment.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"19 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673654","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":"Assessing the validity and limits of linear density models for predicting dissociation–association equilibria in supercritical water","authors":"Maximilian Schulze, Thomas Driesner, Sandro Jahn","doi":"10.1016/j.gca.2024.10.008","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.008","url":null,"abstract":"A linear relationship between the logarithms of solute dissociation constants, <mml:math altimg=\"si1.svg\" display=\"inline\"><mml:mrow><mml:mo>log</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mi>K</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math>, and the density of water, <mml:math altimg=\"si2.svg\" display=\"inline\"><mml:mo>log</mml:mo></mml:math> (<mml:math altimg=\"si274.svg\" display=\"inline\"><mml:msub><mml:mrow><mml:mi>ρ</mml:mi></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"normal\">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi></mml:mrow></mml:msub></mml:math>), has empirically been demonstrated for decades and raised hope for an universal formalism to describe solute thermodynamic properties over wide ranges of temperature and density at supercritical conditions. Yet, neither a theoretical foundation nor an assessment of the ranges of validity have been presented. Here, we use classical molecular dynamics (MD) simulations as a complementary tool to assess the validity of this linear relationship for the example of NaCl and reveal its limits at water densities below ca. 0.3<ce:hsp sp=\"0.16667\"></ce:hsp>g<ce:hsp sp=\"0.16667\"></ce:hsp>cm<ce:sup loc=\"post\">−3</ce:sup>. The derivative <mml:math altimg=\"si4.svg\" display=\"inline\"><mml:mrow><mml:mi>∂</mml:mi><mml:mo>log</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mi>K</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mo>/</mml:mo><mml:mi>∂</mml:mi><mml:mo>log</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mi>ρ</mml:mi></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"normal\">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> is calculated based on the volume of reaction and water compressibility derived from the simulations performed in the isothermal–isobaric ensemble at 673<ce:hsp sp=\"0.16667\"></ce:hsp>K. Our results corroborate the linear dependence of <mml:math altimg=\"si1.svg\" display=\"inline\"><mml:mrow><mml:mo>log</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mi>K</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> vs. <mml:math altimg=\"si6.svg\" display=\"inline\"><mml:mrow><mml:mo>log</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mi>ρ</mml:mi></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant=\"normal\">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mi mathvariant=\"normal\">O</mml:mi></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> in the experimentally studied density range and suggest that the linear dependence also extends to higher densities. However, towards lower densities, <mml:math altimg=\"si1.svg\" display=\"inline\"><mml:mrow><mml:mo>log</mml:mo><mml:mrow><mml:mo>(</mml:mo><mml:mi>K</mml:mi><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> decreases and takes on values that are lowe","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"15 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673655","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":"Quantifying mass-dependent isotope fractionation and nuclear field shift effects for the light rare Earth elements in hydrous systems","authors":"Mark Nestmeyer, Alex J. McCoy-West","doi":"10.1016/j.gca.2024.10.007","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.007","url":null,"abstract":"The improving sensitivity of mass-spectrometers has opened the potential of using stable isotope signatures of the rare Earth elements (REE) as geochemical tracers. However, thus far only limited studies have utilised REE stable isotopes, despite resolvable variations having been observed in a range of systems. An interesting but poorly explored area remains variations in aqueous environments across a range of temperatures including seawater, marine sediments, ion adsorption deposits or hydrothermal systems. Furthermore, the magnitudes and competing effects of mass-dependent isotope fractionation and mass-independent nuclear field shift effects, which can be significant factor for heavy elements especially at high temperatures, remain poorly understood.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"23 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673656","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":"Manganese oxidation states and availability in forest weathering profiles of contrasting climate","authors":"Zhuojun Zhang, Peng Yang, Ke Wen, Hai-Ruo Mao, Zhiqi Zhao, Congqiang Liu, Qing Zhu, Mengqiang Zhu","doi":"10.1016/j.gca.2024.10.006","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.006","url":null,"abstract":"The abundance and oxidation states (II, III and IV) of manganese (Mn) in a weathering profile encompassing both the soil layers (A and B horizons) and the underlaid saprolite (C horizons) determine the availability of Mn as a plant nutrient and regulate its role in cycles of other elements in Earth’s critical zone. However, it remains unclear how the abundance and oxidation states vary with depth under different climates, and how the soil forming processes and soil properties control the variations. We examined four forest granite weathering profiles developed under climates ranging from temperate to tropical climate. Regardless of climate types, all four profiles showed similar vertical variation patterns of Mn concentration and oxidation states. The major features of the patterns can be understood from the perspective of soil forming processes and soil properties. Climate affected the Mn oxidation states in the fine fraction (&lt; 2 mm; i.e., the soil fraction) of the poorly weathered saprolite by controlling the weathering degree of Mn-bearing primary minerals. The weathering released Mn(II) and Mn(III) in the primary minerals to the circumneutral environment where it was subsequently oxidized by O<ce:inf loc=\"post\">2</ce:inf>. In contrast, climate affected the Mn oxidation states in the soil layers poor in parent materials largely by controlling soil redox conditions and pH because most of the Mn in soils was reactive. As the climate became warmer/wetter, the weathering intensified and soils became more reducing and acidic, resulting in more reduced Mn in the soil layers but more oxidized Mn in the fine fraction of saprolite. Moreover, relative to Mn(II) and Mn(IV), Mn(III) preferentially accumulated in the subsoil (B horizons), likely as Mn(III) oxyhydroxides in the colder and drier climates, and as a substitute ion in well-crystallized Fe(III) oxides in the warmer and wetter climates. These findings improve our understanding of Mn availability and cycling and its role in biogeochemical cycles of other elements in Earth’s critical zone.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"14 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673572","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":"Carbon Cycling in Marine Particles Based on Inorganic and Organic Stable Isotopes","authors":"Sijia Dong, Frank J. Pavia, Adam V. Subhas, William R. Gray, Jess F. Adkins, William M. Berelson","doi":"10.1016/j.gca.2024.10.005","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.005","url":null,"abstract":"The marine carbon cycle has a central role in biogeochemical cycling and a close interaction with the climate system. Here, we use the stable carbon isotope (<mml:math altimg=\"si2.svg\"><mml:mrow><mml:mi>δ</mml:mi></mml:mrow></mml:math><ce:sup loc=\"post\">13</ce:sup>C) of particulate inorganic carbon (PIC) and particulate organic carbon (POC) in marine particles to diagnose carbonate dissolution and organic matter respiration processes in the ocean water column. We show PIC dissolution both in the euphotic zone, potentially driven by POC remineralization, and a preferential dissolution of coccoliths compared to foraminifera below the saturation horizon in the water column. Within the oxygen deficient zone (ODZ), POC remineralization and consequent respiration-driven PIC dissolution are both significantly diminished. We also demonstrate that POC remineralization preferentially removes a <ce:sup loc=\"post\">13</ce:sup>C-enriched component compared to isotopically-light bulk POC in both the large size fraction (LSF, &gt; 51<mml:math altimg=\"si6.svg\"><mml:mrow><mml:mi mathvariant=\"normal\">μ</mml:mi></mml:mrow></mml:math> m) and small size fraction (SSF, 0.5 – 51<mml:math altimg=\"si6.svg\"><mml:mrow><mml:mi mathvariant=\"normal\">μ</mml:mi></mml:mrow></mml:math> m) of the pump particles, but exhibits a greater impact on the large particles because of its smaller inventory. Simultaneously, addition of a <ce:sup loc=\"post\">13</ce:sup>C-enriched heterotrophic or chemoautotrophic component to the SSF further increases the isotopic offset between SSF and LSF POC. Overall, this study uses <mml:math altimg=\"si2.svg\"><mml:mrow><mml:mi>δ</mml:mi></mml:mrow></mml:math><ce:sup loc=\"post\">13</ce:sup>C to provide novel evidence for different biogeochemical processes in marine particles, and demonstrates carbonate dissolution in the ocean water column, both driven by bulk seawater chemistry and organic matter respiration within particles. The absence of O<ce:inf loc=\"post\">2</ce:inf> in the ODZ likely protects carbonate from dissolving by severely limiting organic matter respiration, thus reducing shallow PIC dissolution within the ODZs.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"2 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673700","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":"Nitrogen in the Orgueil meteorite: Abundant ammonium among other reservoirs of variable isotopic compositions","authors":"Lucie Laize-Générat, Lison Soussaintjean, Olivier Poch, Lydie Bonal, Joël Savarino, Nicolas Caillon, Patrick Ginot, Anthony Vella, Alexis Lamothe, Rhabira Elazzouzi, Laurène Flandinet, Lionel Vacher, Matthieu Gounelle, Martin Bizzaro, Pierre Beck, Eric Quirico, Bernard Schmitt","doi":"10.1016/j.gca.2024.10.001","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.001","url":null,"abstract":"Nitrogen, because of its abundance and variety of carrier phases, is a unique tracer of physico-chemical processes occurring throughout star and planet formations. The refractory organic matter is commonly considered as the main carrier of nitrogen in the most primitive objects of our Solar System. However, nitrogen in the form of ammonium (NH<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">+</ce:sup>) was observed in the Ivuna-type carbonaceous (CI) chondrites Alais in 1834, and Orgueil just after its fall in 1864, as well as more recently on Ceres, comet 67P/Churyumov-Gerasimenko, and possibly on some asteroids. In the present study, we have measured the nitrogen content and isotopic composition in various nitrogen-bearing phases of several samples of the Orgueil meteorite, with different degrees of terrestrial weathering. Water-soluble NH<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">+</ce:sup> is present in Orgueil at a mean concentration of 0.07 ± 0.01 wt%, with a mean isotopic composition of <ce:italic>δ</ce:italic><ce:sup loc=\"post\">15</ce:sup>N = +72 ± 9 ‰ (<ce:sup loc=\"post\">14</ce:sup>N/<ce:sup loc=\"post\">15</ce:sup>N = 254 ± 2), confirming its extra-terrestrial origin. In the most terrestrially altered sample of Orgueil that we analysed, the isotopic composition is <ce:italic>δ</ce:italic><ce:sup loc=\"post\">15</ce:sup>N = +50 ± 12 ‰ (<ce:sup loc=\"post\">14</ce:sup>N/<ce:sup loc=\"post\">15</ce:sup>N = 259 ± 3). NH<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">+</ce:sup> is in species that are thermally stable up to 383 K, possibly ammonium inorganic/organic salts and ammoniated phyllosilicates. We also show that the nitrogen in Orgueil is distributed among the insoluble organic matter (IOM) (35 ± 5 %), ammonium (27 ± 5 %), and other minor water-soluble species (e.g., nitrate, amines etc.: &lt; 6 %). The remaining nitrogen (34 ± 14 %) is mainly in an unidentified organic matter (UOM), which may be IOM lost during its extraction and/or acid hydrolysable functional groups bounded to the IOM and/or organic nitrogen trapped within minerals. The three main carriers of nitrogen in Orgueil have <ce:italic>δ</ce:italic><ce:sup loc=\"post\">15</ce:sup>N (and <ce:sup loc=\"post\">14</ce:sup>N/<ce:sup loc=\"post\">15</ce:sup>N) values of +32 ± 1 ‰ (264 ± 0.3) for IOM, +39 ± 16 ‰ (262 ± 4) for UOM, and +72 ± 9 ‰ (254 ± 2) for NH<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">+</ce:sup>.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"42 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673632","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":"Cold-subduction biogeodynamics boosts deep energy delivery to the forearc","authors":"Veronica Peverelli, Orlando Sébastien Olivieri, Tatsuki Tsujimori, Donato Giovannelli, Guanghai Shi, Enrico Cannaò, Francesca Piccoli, Alberto Vitale Brovarone","doi":"10.1016/j.gca.2024.10.004","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.004","url":null,"abstract":"Metamorphic fluids in subduction zones carry C–H–N–O–P–S species, which are crucial for sustaining subsurface microbial life at shallower crustal depths in the forearc region. Upwards migration of deeply released fluids to shallower levels, where temperatures permit the persistence of microbial life, is recorded by metasomatic rocks formed along the plate interface. Variations in the redox state and component speciation of metamorphic fluids – from local to secular, and highly dependent on thermal gradients and redox state of subduction inputs – may strongly control microbial pathways or even the possibility for metamorphic fluids to sustain microbial communities in the subsurface biosphere at convergent plate margins. We show that metamorphic fluids containing reduced energy sources for microbial life – e.g., CH<ce:inf loc=\"post\">4</ce:inf>, H<ce:inf loc=\"post\">2</ce:inf> – are common in Phanerozoic, high-pressure/low-temperature plate-interface metasomatic rocks such as jadeitites and albitites worldwide. Based on the stability fields of minerals hosting CH<ce:inf loc=\"post\">4</ce:inf>, H<ce:inf loc=\"post\">2</ce:inf> and graphite inclusions, we pinpoint the protracted, probably episodic migration of energy sources in the mantle wedge via fluid circulation being mediated by jadeitites from &gt; ca. 35 km depth, and by their retrogressed counterparts forming from between 35–15 km depth. These fluids can cross the so-called biotic fringe – whose limit is the depth corresponding to ca. 122–135 °C (as deep as ca. 13 km depth depending on geothermal gradients) – as suggested by previous documentation of slab-derived fluids reaching subsurface microbial communities. Thermodynamic modeling indicates that cool thermal gradients, possibly combined with increased inputs of organic matter-rich sediments into subduction, favor the abundance of reduced energy sources relative to more oxidized species (e.g., CO<ce:inf loc=\"post\">2</ce:inf>), thus promoting the proliferation of subsurface microbial life at convergent margins.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"74 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673776","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 behavior of nickel isotopes during mantle melting","authors":"Xu-Han Dong ,&nbsp;Shui-Jiong Wang ,&nbsp;Kwan-Nang Pang ,&nbsp;Ji Shen ,&nbsp;Yi-Xiang Chen ,&nbsp;Mojtaba Rostami-Hossouri ,&nbsp;Habibollah Ghasemi","doi":"10.1016/j.gca.2024.10.002","DOIUrl":"10.1016/j.gca.2024.10.002","url":null,"abstract":"<div><div>Mantle-derived mafic rocks show relatively large variations in nickel (Ni) isotopes and mostly isotopically light compared to the bulk silicate Earth (BSE). Whether this signature is due to the source heterogeneity or controlled by melting processes has been a debatable issue. Here, we analyzed Ni isotopic compositions of 18 intraplate basalts from the Sabzevar region, northern Iran and 16 serpentinized peridotites from Cyprus and South China. The Sabzevar basalts were likely sourced from a sulfur-free/barren mantle domain with recycled pyroxenites involved, manifested by their high Cu contents (127–265 ppm), Fe_T/Mn (58.2–77.4) and Zn/Fe_T ratios (11.9–16.4). The Ni isotopic compositions of the Sabzevar basalts (average <em>δ</em>^60/58Ni = +0.15 ± 0.08 ‰; 2SD) are slightly heavier than the BSE value (average <em>δ</em>^60/58Ni = +0.11 ± 0.06 ‰; 2SD), consistent with equilibrium Ni isotope fractionation during mantle silicate melting as predicted by ionic model calculations. Our new data of serpentinized peridotites (average <em>δ</em>^60/58Ni = +0.16 ± 0.06 ‰; 2SD), together with previously reported data for oceanic sediments and metabasalts, suggest that recycled lithologies have mantle-like or relatively heavy Ni isotopic compositions. Thus, the isotopically light Ni in mafic rocks is unlikely to be caused by crustal recycling-induced mantle heterogeneity. Rather, the light Ni isotopic signature is caused by the dissolution of recycled sulfides into the mantle melts. We suggest two sulfide dissolution models (“dissolve and go” and “dissolve and equilibrium”) to describe the <em>δ</em>^60/58Ni and Cu systematics in terrestrial basalts. In both models, the initial sulfide content (<em>S_initial</em>) and oxygen fugacity (<em>f</em>O₂) exert a major control on Ni isotopic compositions of resulting melts. These two parameters vary among different geological settings. Basalts derived from mantle sources with high <em>S_initial</em> and <em>f</em>O₂ are characterized by light Ni isotopic compositions, whereas basalts sourced from sulfur-free/barren and reduced mantle domains are likely characterized by heavy Ni isotopic compositions, aligning with the characteristic observed in natural samples.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 34-44"},"PeriodicalIF":4.5,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142421791","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 roles of celestine and barite in modulating strontium and barium water column concentrations in the northeast Pacific Ocean","authors":"Zvi Steiner, Alexandra V. Turchyn, Patrizia Ziveri, Alan M. Shiller, Phoebe J. Lam, Adina Paytan, Eric P. Achterberg","doi":"10.1016/j.gca.2024.10.003","DOIUrl":"https://doi.org/10.1016/j.gca.2024.10.003","url":null,"abstract":"The water column distributions of the alkaline earth metals strontium (Sr) and barium (Ba) were studied along a transect from Hawaii to Alaska. Despite similarity in the chemical properties of Sr and Ba, we find that changes in their concentrations along the transect are governed by different chemical and biological processes, meaning that these elements can be treated as independent variables in modern and ancient environments. Alaskan margin sediments are a particularly important source of dissolved Ba to the North Pacific, likely through a combination of saline submarine groundwater discharge and reductive dissolution of manganese (Mn) oxides. Abyssal North Pacific sediments are also a source of Ba to the bottom waters but a sink for Sr. We find that over 90 % of the water column variability in Sr concentrations is driven by precipitation and dissolution of the celestine (SrSO<ce:inf loc=\"post\">4</ce:inf>) skeletons of Acantharia. However, the high Ba content of Acantharia celestine accounts for only 5–8 % of the global ocean variability in Ba concentrations in the water column. Similarly, the effects of barite (BaSO<ce:inf loc=\"post\">4</ce:inf>) precipitation and/or dissolution on the marine Sr cycle is negligible, accounting for &lt;1 % of the water column concentration structure for Sr and ∼3 % of the sedimentary Sr burial. The Sr-Ba-PO<ce:inf loc=\"post\">4</ce:inf> concentration distributions in the North Pacific are inconsistent with significant export of barite to the deep ocean and sediment. This suggests most of the barite formed at intermediate depths dissolves at similar horizons to its formation. The Ba content of phytoplankton organic matter is too low to constitute a major source for particulate Ba in the mesopelagic North Pacific, which suggests Ba is concentrated in marine aggregates by heterotrophic micro-organisms.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"33 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673569","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":"Tracking subduction-related metasomatism of the subcontinental lithospheric mantle using Ca-, O-, and H-isotopes","authors":"S.E. Brooker ,&nbsp;J.D. Barnes ,&nbsp;J.C. Lassiter ,&nbsp;A. Satkoski ,&nbsp;D.G. Pearson","doi":"10.1016/j.gca.2024.09.036","DOIUrl":"10.1016/j.gca.2024.09.036","url":null,"abstract":"<div><div>Mantle xenoliths provide effective records of the metasomatic processes that affect continental lithosphere evolution, such as interaction with subducted components or modification via small-degree melts. Correlations between major/trace element geochemistry with stable and radiogenic isotope compositions can help constrain the source and timing of this metasomatism. We report new δ¹⁸O, δ^44/40Ca, and δD values for twelve kimberlite-hosted mantle xenoliths from the Slave Craton (NWT, Canada), which show varying degrees of metasomatism. The δ¹⁸O values of olivine (δ¹⁸O_ol = +5.33 ± 0.13‰; 1σ; n = 12) overlap average mantle values. Clinopyroxene and garnet δ¹⁸O values (δ¹⁸O_cpx = +5.31 ± 0.10‰; δ¹⁸O_grt = +5.37 ± 0.23‰; 1σ) extend below those reported in most mantle peridotites and are strongly correlated with clinopyroxene δ^44/40Ca (avg. = +1.00 ± 0.10‰; 1σ) and garnet δ^44/40Ca (avg. = +1.18 ± 0.19‰; 1σ) respectively, extending from typical mantle values to low δ¹⁸O and high δ^44/40Ca values. In general, Δ¹⁸O_cpx-ol and Δ¹⁸O_grt-ol (ranging from −0.19‰ to +0.19‰ and from −0.56‰ to +0.35‰, respectively) are lower than expected equilibrium values at mantle temperatures. Strong negative correlations are found between δ¹⁸O_grt and Δ¹⁸O_grt-ol and garnet major and trace element composition (Na₂O, H₂O, La/Yb_N). Furthermore, phlogopite-bearing kelyphitic rims have δD values (avg. = −126 ± 13‰; 1σ) lower than typical mantle values. Whole rock Sm-Nd model ages and oxygen isotope diffusion modeling suggest that metasomatism occurred during the Mesozoic, shortly before kimberlite entrainment, consistent with indications from diamond-forming fluids from the Slave craton. The combined low δ¹⁸O, δD, and high δ^44/40Ca signature of the mantle peridotite xenoliths, along with the age constraints, suggest the metasomatic fluid/melt is sourced from a recycled oceanic crust component related to Mesozoic subduction in western North America.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 16-33"},"PeriodicalIF":4.5,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142421785","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}