Pub Date : 2024-09-04DOI: 10.1016/j.gca.2024.08.030
Guy N. Evans, Soisiri Charin, William E. Seyfried Jr., Xin-Yuan Zheng
The alkaline, H2-rich vent fluids of the Lost City Hydrothermal Field (LCHF) have generally been attributed to serpentinization of tectonically uplifted mantle peridotite. However, elevated concentrations of highly incompatible and fluid mobile trace alkali metals, Rb and Cs, indicate reaction with relatively unaltered mafic components (Seyfried et al., 2015). Here, we present high-precision stable-K isotope analyses of LCHF vent fluids, which provide new constraints on source-rock lithology and support more quantitative estimates of fluid:rock ratio, providing a new constraint on heat and mass transfer processes. We find that δ41K values of LCHF vent fluids (0.03–0.07 ‰) are distinct from local seawater (0.13 ± 0.02 ‰). In combination with near-seawater concentrations of K (10.4 ± 0.1 mmol/kg), these data are incompatible with hydrothermal alteration of peridotite alone, which is highly depleted in K. Instead, K-isotope and concentration data are consistent with hydrothermal alteration of mafic rocks (e.g., gabbro or diabase) at a fluid:rock ratio of 6–26, a range that agrees well with Rb, Cs, and 87Sr/86Sr-based estimates of fluid:rock ratio, updated here to reflect derivation from mafic source rocks.
Geochemical modeling of hydrothermal fluid-rock reactions indicates that LCHF vent fluids can be effectively reproduced by a two-stage reaction in which seawater initially reacts at 200–300 °C with mafic rocks at in a fluid:rock ratio of ∼ 10 —as constrained by the above isotopic and trace-element systematics— and subsequently reacts with peridotite at a fluid:rock ratio of ∼ 30 at roughly the same temperature, pressure conditions. We also note that LCHF vent fluids are ∼ 2 % depleted in Cl compared to seawater, which may reflect admixture of a vapor component derived from ongoing phase separation at higher (> 450 °C) temperatures. We thus propose that the LCHF represents waning-stage hydrothermal activity initiated by a discrete off-axis mafic intrusion that has subsequently cooled to intermediate temperatures conducive to olivine hydrolysis and production of alkaline vent fluids. In this interpretation, alkaline H2-rich vent fields occupy a narrow thermal window in the expected evolution of hydrothermal activity associated with episodic off-axis mafic intrusions into tectonically exposed ultramafic host rocks and are thus likely to be rare on the modern seafloor.
{"title":"The Role of Mafic Intrusions in Producing Alkaline Vent Fluids at the Lost City Hydrothermal Field: Evidence from Stable Potassium Isotopes","authors":"Guy N. Evans, Soisiri Charin, William E. Seyfried Jr., Xin-Yuan Zheng","doi":"10.1016/j.gca.2024.08.030","DOIUrl":"10.1016/j.gca.2024.08.030","url":null,"abstract":"<div><div>The alkaline, H<sub>2</sub>-rich vent fluids of the Lost City Hydrothermal Field (LCHF) have generally been attributed to serpentinization of tectonically uplifted mantle peridotite. However, elevated concentrations of highly incompatible and fluid mobile trace alkali metals, Rb and Cs, indicate reaction with relatively unaltered mafic components (<span><span>Seyfried et al., 2015</span></span>). Here, we present high-precision stable-K isotope analyses of LCHF vent fluids, which provide new constraints on source-rock lithology and support more quantitative estimates of fluid:rock ratio, providing a new constraint on heat and mass transfer processes. We find that δ<sup>41</sup>K values of LCHF vent fluids (0.03–0.07 ‰) are distinct from local seawater (0.13 ± 0.02 ‰). In combination with near-seawater concentrations of K (10.4 ± 0.1 mmol/kg), these data are incompatible with hydrothermal alteration of peridotite alone, which is highly depleted in K. Instead, K-isotope and concentration data are consistent with hydrothermal alteration of mafic rocks (e.g., gabbro or diabase) at a fluid:rock ratio of 6–26, a range that agrees well with Rb, Cs, and <sup>87</sup>Sr/<sup>86</sup>Sr-based estimates of fluid:rock ratio, updated here to reflect derivation from mafic source rocks.</div><div>Geochemical modeling of hydrothermal fluid-rock reactions indicates that LCHF vent fluids can be effectively reproduced by a two-stage reaction in which seawater initially reacts at 200–300 °C with mafic rocks at in a fluid:rock ratio of ∼ 10 —as constrained by the above isotopic and trace-element systematics— and subsequently reacts with peridotite at a fluid:rock ratio of ∼ 30 at roughly the same temperature, pressure conditions. We also note that LCHF vent fluids are ∼ 2 % depleted in Cl compared to seawater, which may reflect admixture of a vapor component derived from ongoing phase separation at higher (> 450 °C) temperatures. We thus propose that the LCHF represents waning-stage hydrothermal activity initiated by a discrete off-axis mafic intrusion that has subsequently cooled to intermediate temperatures conducive to olivine hydrolysis and production of alkaline vent fluids. In this interpretation, alkaline H<sub>2</sub>-rich vent fields occupy a narrow thermal window in the expected evolution of hydrothermal activity associated with episodic off-axis mafic intrusions into tectonically exposed ultramafic host rocks and are thus likely to be rare on the modern seafloor.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 84-95"},"PeriodicalIF":4.5,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662971","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}
Pub Date : 2024-09-04DOI: 10.1016/j.gca.2024.09.001
Jangmi Han , Kazuhide Nagashima , Changkun Park , Alexander N. Krot , Lindsay P. Keller
We report the results of coordinated mineralogical, microstructural, and oxygen isotopic analyses of grossite-bearing refractory inclusions from reduced CV (Vigarano type) chondrites to obtain a more complete picture of secondary parent body alteration processes and conditions. Grossite (CaAl4O7) occurs in cores of nodules in fine-grained Ca,Al-rich inclusions (CAIs) that likely represent aggregates of nebular condensates. In many occurrences, grossite has been partially replaced by hercynite [(Fe,Mg,Zn)Al2O4], which displays complex microstructures and compositions, and magnetite nanoparticles. The alteration of grossite was a crystallographically-controlled, fluid-driven process that occurred via partial dissolution of grossite and subsequent precipitation of hercynite and magnetite during short-lived and low-temperature metasomatic alteration on the CV chondrite parent body. The constituent phases of grossite-bearing CAIs show heterogeneous oxygen isotopic compositions, with grossite and perovskite displaying systematically 16O-depleted compositions (Δ17O= − 12 ‰ to − 1 ‰) relative to uniformly 16O-rich hibonite and spinel (Δ17O= − 25 ‰ to − 21 ‰). Melilite is variably 16O-depleted (Δ17O= − 25 ‰ to − 2 ‰). The observed oxygen isotopic distribution is interpreted as a result of mineralogically controlled oxygen isotopic exchange with an 16O-poor fluid on the CV chondrite parent body. Collectively, the presence of limited fluids played an important role in preferential alteration of grossite to hercynite and magnetite and various degrees of 16O depletion in grossite, perovskite, and melilite during thermal metamorphism. We conclude that, among refractory phases in the inclusions, grossite was the most susceptible to metasomatic reactions with Fe-rich fluids and the second most susceptible, after perovskite, to oxygen isotopic exchange with an 16O-poor fluid during the thermal history of the CV chondrite parent asteroid.
{"title":"Grossite-bearing refractory inclusions from reduced CV chondrites: Mineralogical and oxygen isotopic constraints on the parent body alteration history","authors":"Jangmi Han , Kazuhide Nagashima , Changkun Park , Alexander N. Krot , Lindsay P. Keller","doi":"10.1016/j.gca.2024.09.001","DOIUrl":"10.1016/j.gca.2024.09.001","url":null,"abstract":"<div><div>We report the results of coordinated mineralogical, microstructural, and oxygen isotopic analyses of grossite-bearing refractory inclusions from reduced CV (Vigarano type) chondrites to obtain a more complete picture of secondary parent body alteration processes and conditions. Grossite (CaAl<sub>4</sub>O<sub>7</sub>) occurs in cores of nodules in fine-grained Ca,Al-rich inclusions (CAIs) that likely represent aggregates of nebular condensates. In many occurrences, grossite has been partially replaced by hercynite [(Fe,Mg,Zn)Al<sub>2</sub>O<sub>4</sub>], which displays complex microstructures and compositions, and magnetite nanoparticles. The alteration of grossite was a crystallographically-controlled, fluid-driven process that occurred via partial dissolution of grossite and subsequent precipitation of hercynite and magnetite during short-lived and low-temperature metasomatic alteration on the CV chondrite parent body. The constituent phases of grossite-bearing CAIs show heterogeneous oxygen isotopic compositions, with grossite and perovskite displaying systematically <sup>16</sup>O-depleted compositions (Δ<sup>17</sup>O= − 12 ‰ to − 1 ‰) relative to uniformly <sup>16</sup>O-rich hibonite and spinel (Δ<sup>17</sup>O= − 25 ‰ to − 21 ‰). Melilite is variably <sup>16</sup>O-depleted (Δ<sup>17</sup>O= − 25 ‰ to − 2 ‰). The observed oxygen isotopic distribution is interpreted as a result of mineralogically controlled oxygen isotopic exchange with an <sup>16</sup>O-poor fluid on the CV chondrite parent body. Collectively, the presence of limited fluids played an important role in preferential alteration of grossite to hercynite and magnetite and various degrees of <sup>16</sup>O depletion in grossite, perovskite, and melilite during thermal metamorphism. We conclude that, among refractory phases in the inclusions, grossite was the most susceptible to metasomatic reactions with Fe-rich fluids and the second most susceptible, after perovskite, to oxygen isotopic exchange with an <sup>16</sup>O-poor fluid during the thermal history of the CV chondrite parent asteroid.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 100-117"},"PeriodicalIF":4.5,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245894","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}
Pub Date : 2024-09-03DOI: 10.1016/j.gca.2024.08.025
William Nelson, Julia Hammer, Thomas Shea
Heterogeneities in the phosphorus (P) content of olivine are relatively resistant to diffusive homogenization when compared with other compositional heterogeneities. Thus, heterogeneities in the spatial distribution of P can preserve petrological information about olivine crystals from the earliest stages of crystallization which have been otherwise eliminated. However, compared to independent determinations of protracted cooling timescales in slowly cooled rocks, P enrichments are so sharp as to suggest a rate of diffusive mobility that is many orders of magnitude slower than previously suggested. Here, we heat single natural olivine crystals with sharply defined P heterogeneities (0.02–0.15 wt% P2O5 over 0.5 μm spatial scale) in a 1-atmosphere gas-mixing furnace for durations of 10–20 days at 1400°C, thus exposing them to conditions that should be sufficient for complete diffusive relaxation according to published P diffusivity values. However, high-precision chemical analysis of the same interior section before and after heating reveals no discernable difference in the sharpness of phosphorus concentration patterns. Therefore, diffusion chronometry applied to skeletal P enrichments in olivine currently provides erroneously short diffusive timescales. We discuss several possible causes for these discrepancies and the implications for diffusion chronometry as applied to phosphorus in olivine.
{"title":"Re-evaluating the diffusivity of phosphorus in olivine: Implications of low diffusive mobility for thermochronology","authors":"William Nelson, Julia Hammer, Thomas Shea","doi":"10.1016/j.gca.2024.08.025","DOIUrl":"10.1016/j.gca.2024.08.025","url":null,"abstract":"<div><div>Heterogeneities in the phosphorus (P) content of olivine are relatively resistant to diffusive homogenization when compared with other compositional heterogeneities. Thus, heterogeneities in the spatial distribution of P can preserve petrological information about olivine crystals from the earliest stages of crystallization which have been otherwise eliminated. However, compared to independent determinations of protracted cooling timescales in slowly cooled rocks, P enrichments are so sharp as to suggest a rate of diffusive mobility that is many orders of magnitude slower than previously suggested. Here, we heat single natural olivine crystals with sharply defined P heterogeneities (0.02–0.15 wt% P<sub>2</sub>O<sub>5</sub> over 0.5 μm spatial scale) in a 1-atmosphere gas-mixing furnace for durations of 10–20 days at 1400°C, thus exposing them to conditions that should be sufficient for complete diffusive relaxation according to published P diffusivity values. However, high-precision chemical analysis of the same interior section before and after heating reveals no discernable difference in the sharpness of phosphorus concentration patterns. Therefore, diffusion chronometry applied to skeletal P enrichments in olivine currently provides erroneously short diffusive timescales. We discuss several possible causes for these discrepancies and the implications for diffusion chronometry as applied to phosphorus in olivine.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 74-83"},"PeriodicalIF":4.5,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245896","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}
Pub Date : 2024-09-02DOI: 10.1016/j.gca.2024.08.026
Aindrila Pal, Rajdeep Dasgupta
<div><div>Nitrogen (N) is an essential element for life. Yet the processes of planet formation and early planetary evolution through which rocky planets like Earth obtained their atmospheric and surface nitrogen inventory are poorly understood. In order to understand the effect of early silicate differentiation of the rocky bodies on N inventory, here we study the elemental partitioning of N between the silicate minerals and melts. We conducted laboratory experiments using tholeiitic basalts and Fe + Si alloy mixtures at 1.5 – 4.0 GPa and 1300 to 1550 °C under graphite saturation at an oxygen fugacity range of IW–1.1 to IW–3.0. The experiments yielded an assemblage of Fe-rich alloy melt (am) + silicate melt (sm) + clinopyroxene (cpx) ± garnet (grt) ± orthopyroxene (opx) ± plagioclase (plag). Using electron microprobe, we determine that under the experimental conditions, N act as an incompatible element with <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>c</mi><mi>p</mi><mi>x</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> (0.11 – 0.47) > <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>p</mi><mi>l</mi><mi>a</mi><mi>g</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> (0.41) ><span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>o</mi><mi>p</mi><mi>x</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> (0.25) ><span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>g</mi><mi>r</mi><mi>t</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span>(0.06 – 0.21). The <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi><mi>e</mi><mi>r</mi><mi>a</mi><mi>l</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> do not show any strong dependence on temperature, pressure, and melt composition. However, through comparison with previous estimates, it appears that with decreasing <em>f</em>O<sub>2</sub>, N becomes less incompatible. Under our experimental conditions of alloy melt-mineral equilibria, N behaves as a siderophile element (<span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>a</mi><mi>m</mi><mo>/</mo><mi>m</mi><mi>i</mi><mi>n</mi><mi>e</mi><mi>r</mi><mi>a</mi><mi>l</mi></mrow></msubsup></mrow></math></span> ranging from 4.1 to 60.6) with <em>f</em>O<sub>2</sub> playing the strongest control on <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>a</mi><mi>m</mi><mo>/</mo><mi>m</mi><mi>i</mi><mi>n</mi><mi>e</mi><mi>r</mi><mi>a</mi><mi>l</mi></mrow></msubsup></mrow></math></span>. Our data suggest that under reducing conditions, in the early stages of a magma ocean (MO) and/or deeper mantle, silicate minerals would hold a non-negligible fraction of N as N becomes less atmophile and siderophile. Therefore, reduced parent bodies could also retain substantial N in the residual mantle during partial
{"title":"The fate of nitrogen during early silicate differentiation of rocky bodies constrained by experimental mineral-melt partitioning","authors":"Aindrila Pal, Rajdeep Dasgupta","doi":"10.1016/j.gca.2024.08.026","DOIUrl":"10.1016/j.gca.2024.08.026","url":null,"abstract":"<div><div>Nitrogen (N) is an essential element for life. Yet the processes of planet formation and early planetary evolution through which rocky planets like Earth obtained their atmospheric and surface nitrogen inventory are poorly understood. In order to understand the effect of early silicate differentiation of the rocky bodies on N inventory, here we study the elemental partitioning of N between the silicate minerals and melts. We conducted laboratory experiments using tholeiitic basalts and Fe + Si alloy mixtures at 1.5 – 4.0 GPa and 1300 to 1550 °C under graphite saturation at an oxygen fugacity range of IW–1.1 to IW–3.0. The experiments yielded an assemblage of Fe-rich alloy melt (am) + silicate melt (sm) + clinopyroxene (cpx) ± garnet (grt) ± orthopyroxene (opx) ± plagioclase (plag). Using electron microprobe, we determine that under the experimental conditions, N act as an incompatible element with <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>c</mi><mi>p</mi><mi>x</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> (0.11 – 0.47) > <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>p</mi><mi>l</mi><mi>a</mi><mi>g</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> (0.41) ><span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>o</mi><mi>p</mi><mi>x</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> (0.25) ><span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>g</mi><mi>r</mi><mi>t</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span>(0.06 – 0.21). The <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>m</mi><mi>i</mi><mi>n</mi><mi>e</mi><mi>r</mi><mi>a</mi><mi>l</mi><mo>/</mo><mi>s</mi><mi>m</mi></mrow></msubsup></mrow></math></span> do not show any strong dependence on temperature, pressure, and melt composition. However, through comparison with previous estimates, it appears that with decreasing <em>f</em>O<sub>2</sub>, N becomes less incompatible. Under our experimental conditions of alloy melt-mineral equilibria, N behaves as a siderophile element (<span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>a</mi><mi>m</mi><mo>/</mo><mi>m</mi><mi>i</mi><mi>n</mi><mi>e</mi><mi>r</mi><mi>a</mi><mi>l</mi></mrow></msubsup></mrow></math></span> ranging from 4.1 to 60.6) with <em>f</em>O<sub>2</sub> playing the strongest control on <span><math><mrow><msubsup><mi>D</mi><mrow><mi>N</mi></mrow><mrow><mi>a</mi><mi>m</mi><mo>/</mo><mi>m</mi><mi>i</mi><mi>n</mi><mi>e</mi><mi>r</mi><mi>a</mi><mi>l</mi></mrow></msubsup></mrow></math></span>. Our data suggest that under reducing conditions, in the early stages of a magma ocean (MO) and/or deeper mantle, silicate minerals would hold a non-negligible fraction of N as N becomes less atmophile and siderophile. Therefore, reduced parent bodies could also retain substantial N in the residual mantle during partial ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 45-60"},"PeriodicalIF":4.5,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528489","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}
Pub Date : 2024-09-02DOI: 10.1016/j.gca.2024.08.020
Guy N. Evans , Shichao Ji , Betül Kaçar , Ariel D. Anbar , William E. Seyfried Jr.
Despite the importance of alkaline seafloor hydrothermal vents in broadening our understanding of deep-sea hydrothermal ecosystems, little is known about the mobility and concentrations of micronutrient transition metals in these environments. Here, we present new analyses of micronutrient transition metal concentrations in vent fluids from the iconic Lost City Hydrothermal Field (LCHF) and report concentrations of Fe = 2.9–18.3 µmol/kg, Zn = 1.30–5.86 µmol/kg, Cu = 0.43–5.06 µmol/kg, Ni = 86.4–556 nmol/kg, Mn = 8.3–274 nmol/kg, V = 25.9–127 nmol/kg, Mo = 24–94 nmol/kg, Co = 8.0–135 nmol/kg, W = 4.8–16 nmol/kg, and Cd = 1.7–4.5 nmol/kg. We additionally present results of a hydrothermal lherzolite alteration experiment conducted at 300 °C, 500 bar. Transition metal concentrations and major chemical parameters of experimental reaction fluids are broadly similar to LCHF vent fluids, indicating that transition metal concentrations in LCHF vent fluids, and alkaline hydrothermal fluids more generally, reflect metal solubility controlled by underlying rock-buffered hydrothermal reactions.
Concentrations of Ni and Mo are especially noteworthy because of their recognized importance for biological methanogenesis (Ni) and nitrogen fixation (Mo). When compared with known biological thresholds, our findings indicate that Ni concentrations in LCHF vent fluids are sufficient to support the robust methane-metabolizing microbial communities observed in the immediate vicinity of LCHF vents and suggest that Ni availability influences the spatial distribution of LCHF methanogens. Furthermore, our laboratory hydrothermal experiments demonstrate that Mo concentrations of similar magnitude to those observed in LCHF vent fluids (and also modern seawater) can be obtained by hydrothermal alteration of ultramafic rocks with Mo-free (Na, Ca) Cl aqueous solution. Thus, we conclude that alkaline hydrothermal fluids were likely similarly enriched in Mo prior to oxidation of the Earth’s atmosphere and ocean, providing localized Mo-rich geochemical environments capable of supporting Mo-dependent nitrogen fixation at currently recognized threshold concentrations.
尽管碱性海底热液喷口在拓宽我们对深海热液生态系统的认识方面非常重要，但我们对这些环境中微量营养过渡金属的流动性和浓度知之甚少。在这里，我们对标志性的失落之城热液田（LCHF）喷口流体中的微量过渡金属浓度进行了新的分析，并报告了Fe = 2.9-18.3 µmol/kg、Zn = 1.30-5.86 µmol/kg, Cu = 0.43-5.06 µmol/kg, Ni = 86.4-556 nmol/kg, Mn = 8.3-274 nmol/kg, V = 25.9-127 nmol/kg, Mo = 24-94 nmol/kg, Co = 8.0-135 nmol/kg, W = 4.8-16 nmol/kg, Cd = 1.7-4.5 nmol/kg。此外，我们还介绍了在 300 °C 和 500 bar 条件下进行的热液蛭石蚀变实验的结果。实验反应流体的过渡金属浓度和主要化学参数与LCHF喷口流体大致相似，这表明LCHF喷口流体以及更普遍的碱性热液中的过渡金属浓度反映了由底层岩石缓冲热液反应控制的金属溶解度。
{"title":"Transition metals in alkaline Lost City vent fluids are sufficient for early-life metabolisms","authors":"Guy N. Evans , Shichao Ji , Betül Kaçar , Ariel D. Anbar , William E. Seyfried Jr.","doi":"10.1016/j.gca.2024.08.020","DOIUrl":"10.1016/j.gca.2024.08.020","url":null,"abstract":"<div><div>Despite the importance of alkaline seafloor hydrothermal vents in broadening our understanding of deep-sea hydrothermal ecosystems, little is known about the mobility and concentrations of micronutrient transition metals in these environments. Here, we present new analyses of micronutrient transition metal concentrations in vent fluids from the iconic Lost City Hydrothermal Field (LCHF) and report concentrations of Fe = 2.9–18.3 µmol/kg, Zn = 1.30–5.86 µmol/kg, Cu = 0.43–5.06 µmol/kg, Ni = 86.4–556 nmol/kg, Mn = 8.3–274 nmol/kg, V = 25.9–127 nmol/kg, Mo = 24–94 nmol/kg, Co = 8.0–135 nmol/kg, W = 4.8–16 nmol/kg, and Cd = 1.7–4.5 nmol/kg. We additionally present results of a hydrothermal lherzolite alteration experiment conducted at 300 °C, 500 bar. Transition metal concentrations and major chemical parameters of experimental reaction fluids are broadly similar to LCHF vent fluids, indicating that transition metal concentrations in LCHF vent fluids, and alkaline hydrothermal fluids more generally, reflect metal solubility controlled by underlying rock-buffered hydrothermal reactions.</div><div>Concentrations of Ni and Mo are especially noteworthy because of their recognized importance for biological methanogenesis (Ni) and nitrogen fixation (Mo). When compared with known biological thresholds, our findings indicate that Ni concentrations in LCHF vent fluids are sufficient to support the robust methane-metabolizing microbial communities observed in the immediate vicinity of LCHF vents and suggest that Ni availability influences the spatial distribution of LCHF methanogens. Furthermore, our laboratory hydrothermal experiments demonstrate that Mo concentrations of similar magnitude to those observed in LCHF vent fluids (and also modern seawater) can be obtained by hydrothermal alteration of ultramafic rocks with Mo-free (Na, Ca) Cl aqueous solution. Thus, we conclude that alkaline hydrothermal fluids were likely similarly enriched in Mo prior to oxidation of the Earth’s atmosphere and ocean, providing localized Mo-rich geochemical environments capable of supporting Mo-dependent nitrogen fixation at currently recognized threshold concentrations.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"385 ","pages":"Pages 61-73"},"PeriodicalIF":4.5,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245685","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}
Pub Date : 2024-09-01DOI: 10.1016/j.gca.2024.08.024
Siddhartha Bharadwaj, Mukul Sharma
<div><p>Some young volcanic rocks have been found to possess intrasample Os-isotope heterogeneity. This has important implications for source tracing and dating. Here, we use a new procedure through which it is possible to sequentially extract, from a single aliquot, the <sup>187</sup>Os/<sup>188</sup>Os ratio of: i) the surface contaminant(s) (hydrobromic acid leachate); ii) the residual bulk rock powder (Step I) and iii) the Os-bearing phases entrapped within silicates (Step II). We applied this technique to two young basaltic reference materials (RMs), USGS BHVO-2 and EN026 10D-3. The former samples the 1919 lava from the Kīlauea summit crater (Hawaii) and the latter is a basalt sample dredged from Mohns Ridge (Greenland Sea). Both rock standards have previously been shown to display large intrasample Os isotope heterogeneity. In addition to analyzing these RMs, we also analyzed the RM USGS BHVO-1 for comparison, as well as another sample from the Kīlauea 1919 summit eruption (Kil 1919-6) along with a picritic tholeiite from the Kīlauea Iki 1959 eruption.</p><p>Our leaching results show that BHVO-2 is contaminated with a highly radiogenic and labile contaminant with <sup>187</sup>Os/<sup>188</sup>Os ratio of 0.525 ± 0.021. Without leaching, the Step I <sup>187</sup>Os/<sup>188</sup>Os ratios varied from 0.1399 ± 0.0013 to 0.1568 ± 0.0014 while those for Step II were uniform (average = 0.1286 ± 0.0006, N = 5). A comparison of Re, Mo concentrations and <sup>187</sup>Os/<sup>188</sup>Os ratio of the leachates of BHVO-2 and its predecessor (BHVO-1) indicates that BHVO-2 was contaminated during preparation. After leaching, the Step I and Step II <sup>187</sup>Os/<sup>188</sup>Os ratios of BHVO-1 and another sample (Kīlauea 1919-6) from the same lava flow are identical within error to that of the Step II ratio of BHVO-2. A picrite from the 1959 Kīlauea Iki eruption also analyzed using the new technique gives homogenous results for both the steps with an average <sup>187</sup>Os/<sup>188</sup>Os ratio of 0.1302 ± 0.0005. The <sup>187</sup>Os/<sup>188</sup>Os ratio of recent Kīlauea lavas is identical within error to that of the primitive upper mantle (=0.1296). The Kīlauea Os-isotope composition could represent a “common component” that occurs globally in many plumes. The Step I <sup>187</sup>Os/<sup>188</sup>Os ratio of EN026 10D-3 is 0.136 with Step II ratio being 0.131 (N = 2). The Step II <sup>187</sup>Os/<sup>188</sup>Os ratios are more radiogenic than the nearby Jan Mayen lavas (<sup>187</sup>Os/<sup>188</sup>Os = 0.124–0.129) that have been argued to influence the chemistry of the Western section of the Mohns Ridge basalt but fall within the range of the Primitive Upper Mantle. We also discovered that BHVO-1, KIL 1919-6, 1959 Kīlauea Iki picrite, and EN026 10D-3 show Os-isotope disequilibrium between the leachate and Step I, suggesting wall rock assimilation during magma ascent. The data set presented here indicates a need for re-evaluating th
{"title":"Intrasample osmium isotope disequilibrium in young volcanic rocks: Insights from a new progressive digestion procedure","authors":"Siddhartha Bharadwaj, Mukul Sharma","doi":"10.1016/j.gca.2024.08.024","DOIUrl":"10.1016/j.gca.2024.08.024","url":null,"abstract":"<div><p>Some young volcanic rocks have been found to possess intrasample Os-isotope heterogeneity. This has important implications for source tracing and dating. Here, we use a new procedure through which it is possible to sequentially extract, from a single aliquot, the <sup>187</sup>Os/<sup>188</sup>Os ratio of: i) the surface contaminant(s) (hydrobromic acid leachate); ii) the residual bulk rock powder (Step I) and iii) the Os-bearing phases entrapped within silicates (Step II). We applied this technique to two young basaltic reference materials (RMs), USGS BHVO-2 and EN026 10D-3. The former samples the 1919 lava from the Kīlauea summit crater (Hawaii) and the latter is a basalt sample dredged from Mohns Ridge (Greenland Sea). Both rock standards have previously been shown to display large intrasample Os isotope heterogeneity. In addition to analyzing these RMs, we also analyzed the RM USGS BHVO-1 for comparison, as well as another sample from the Kīlauea 1919 summit eruption (Kil 1919-6) along with a picritic tholeiite from the Kīlauea Iki 1959 eruption.</p><p>Our leaching results show that BHVO-2 is contaminated with a highly radiogenic and labile contaminant with <sup>187</sup>Os/<sup>188</sup>Os ratio of 0.525 ± 0.021. Without leaching, the Step I <sup>187</sup>Os/<sup>188</sup>Os ratios varied from 0.1399 ± 0.0013 to 0.1568 ± 0.0014 while those for Step II were uniform (average = 0.1286 ± 0.0006, N = 5). A comparison of Re, Mo concentrations and <sup>187</sup>Os/<sup>188</sup>Os ratio of the leachates of BHVO-2 and its predecessor (BHVO-1) indicates that BHVO-2 was contaminated during preparation. After leaching, the Step I and Step II <sup>187</sup>Os/<sup>188</sup>Os ratios of BHVO-1 and another sample (Kīlauea 1919-6) from the same lava flow are identical within error to that of the Step II ratio of BHVO-2. A picrite from the 1959 Kīlauea Iki eruption also analyzed using the new technique gives homogenous results for both the steps with an average <sup>187</sup>Os/<sup>188</sup>Os ratio of 0.1302 ± 0.0005. The <sup>187</sup>Os/<sup>188</sup>Os ratio of recent Kīlauea lavas is identical within error to that of the primitive upper mantle (=0.1296). The Kīlauea Os-isotope composition could represent a “common component” that occurs globally in many plumes. The Step I <sup>187</sup>Os/<sup>188</sup>Os ratio of EN026 10D-3 is 0.136 with Step II ratio being 0.131 (N = 2). The Step II <sup>187</sup>Os/<sup>188</sup>Os ratios are more radiogenic than the nearby Jan Mayen lavas (<sup>187</sup>Os/<sup>188</sup>Os = 0.124–0.129) that have been argued to influence the chemistry of the Western section of the Mohns Ridge basalt but fall within the range of the Primitive Upper Mantle. We also discovered that BHVO-1, KIL 1919-6, 1959 Kīlauea Iki picrite, and EN026 10D-3 show Os-isotope disequilibrium between the leachate and Step I, suggesting wall rock assimilation during magma ascent. The data set presented here indicates a need for re-evaluating th","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 14-26"},"PeriodicalIF":4.5,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0016703724004307/pdfft?md5=0418a7c24df8c80605e3cbf44179cfbd&pid=1-s2.0-S0016703724004307-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142164643","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}
Pub Date : 2024-09-01DOI: 10.1016/j.gca.2024.08.028
Olga M. Żygadłowska , Jessica Venetz , Wytze K. Lenstra , Niels A.G.M. van Helmond , Robin Klomp , Thomas Röckmann , Annelies J. Veraart , Mike S.M. Jetten , Caroline P. Slomp
The production of methane in coastal sediments and its release to the water column is intensified by anthropogenic eutrophication and bottom water hypoxia, and it is still uncertain whether methane emissions to the atmosphere will be enhanced. Here, we assess seasonal variations in methane dynamics in a eutrophic, seasonally euxinic coastal basin (Scharendijke, Lake Grevelingen). In-situ benthic chamber incubations reveal high rates of methane release from the sediment to the water column (74–163 mmol m−2 d−1) during monthly measurements between March and October 2021. Comparison of these in-situ total benthic methane fluxes and calculated diffusive fluxes point towards a major role for ebullition. In spring and fall, when the water column was oxic, microbial removal of dissolved methane occurred aerobically in the bottom water. In summer, in contrast, dissolved methane accumulated to concentrations of up to 67 μmol L−1 below the oxycline. Shifts in δ13C–CH4 and δD-CH4 towards higher values and the abundant presence of methane oxidizing bacteria point towards removal of methane around the oxycline, likely through both aerobic and anaerobic pathways, with the latter possibly linked to iron oxide reduction. Shifts in δ13C–CH4 and δD-CH4 to lower values above the oxycline indicate that bubble dissolution contributed to dissolved methane. Methane emissions to the atmosphere were observed in all seasons with the highest, in-situ measured diffusive fluxes (1.2 mmol m−2 d−1) upon the onset of water column mixing at the end of summer. Methane release events during the measurement of in-situ water-air fluxes and model calculations point towards a flux of methane to the atmosphere in the form of bubbles, which bypass the microbial methane filter. The model calculations suggest a potential year-round ebullitive methane flux between 30 and 120 mmol m−2 d−1. We conclude that methane emissions from eutrophic coastal systems may be much higher than previously thought because of ebullition.
{"title":"Ebullition drives high methane emissions from a eutrophic coastal basin","authors":"Olga M. Żygadłowska , Jessica Venetz , Wytze K. Lenstra , Niels A.G.M. van Helmond , Robin Klomp , Thomas Röckmann , Annelies J. Veraart , Mike S.M. Jetten , Caroline P. Slomp","doi":"10.1016/j.gca.2024.08.028","DOIUrl":"10.1016/j.gca.2024.08.028","url":null,"abstract":"<div><p>The production of methane in coastal sediments and its release to the water column is intensified by anthropogenic eutrophication and bottom water hypoxia, and it is still uncertain whether methane emissions to the atmosphere will be enhanced. Here, we assess seasonal variations in methane dynamics in a eutrophic, seasonally euxinic coastal basin (Scharendijke, Lake Grevelingen). In-situ benthic chamber incubations reveal high rates of methane release from the sediment to the water column (74–163 mmol m<sup>−2</sup> d<sup>−1</sup>) during monthly measurements between March and October 2021. Comparison of these in-situ total benthic methane fluxes and calculated diffusive fluxes point towards a major role for ebullition. In spring and fall, when the water column was oxic, microbial removal of dissolved methane occurred aerobically in the bottom water. In summer, in contrast, dissolved methane accumulated to concentrations of up to 67 μmol L<sup>−1</sup> below the oxycline. Shifts in <em>δ</em><sup>13</sup>C–CH<sub>4</sub> and <em>δ</em>D-CH<sub>4</sub> towards higher values and the abundant presence of methane oxidizing bacteria point towards removal of methane around the oxycline, likely through both aerobic and anaerobic pathways, with the latter possibly linked to iron oxide reduction. Shifts in <em>δ</em><sup>13</sup>C–CH<sub>4</sub> and <em>δ</em>D-CH<sub>4</sub> to lower values above the oxycline indicate that bubble dissolution contributed to dissolved methane. Methane emissions to the atmosphere were observed in all seasons with the highest, in-situ measured diffusive fluxes (1.2 mmol m<sup>−2</sup> d<sup>−1</sup>) upon the onset of water column mixing at the end of summer. Methane release events during the measurement of in-situ water-air fluxes and model calculations point towards a flux of methane to the atmosphere in the form of bubbles, which bypass the microbial methane filter. The model calculations suggest a potential year-round ebullitive methane flux between 30 and 120 mmol m<sup>−2</sup> d<sup>−1</sup>. We conclude that methane emissions from eutrophic coastal systems may be much higher than previously thought because of ebullition.</p></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 1-13"},"PeriodicalIF":4.5,"publicationDate":"2024-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0016703724004319/pdfft?md5=384b051ee7c3246e364c144f2e32ec84&pid=1-s2.0-S0016703724004319-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142164642","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}
Pub Date : 2024-08-31DOI: 10.1016/j.gca.2024.08.023
Hao Xie , Michael J. Formolo , Alex L. Sessions , John M. Eiler
<div><div>Stable isotope ratios of C<sub>1</sub>–C<sub>5</sub> alkanes, the major constituents of subsurface gaseous hydrocarbons, can provide valuable insights on their origins, transport, and fates. Equilibrium isotope effects are fundamental to interpreting stable isotope signatures, as recognition of them in natural materials indicates reversible processes and constrains the temperatures of equilibrated systems. Hydrogen isotope equilibrium of C<sub>1</sub>–C<sub>5</sub> alkanes is of particular interest because evidence shows that alkyl H can undergo isotopic exchange with coexisting compounds under subsurface conditions. We present the results of a combined experimental and theoretical effort to determine equilibrium hydrogen isotope distributions in mixtures of these hydrocarbon compounds. We created two mixtures: one with C<sub>1</sub>, C<sub>2</sub> and C<sub>3</sub> (where C1 indicates methane, C<sub>2</sub> ethane, etc., hereinafter called ‘C<sub>1</sub>–C<sub>3</sub> mixture’) and another one with C<sub>2</sub>, C<sub>3</sub>, <em>i</em>C<sub>4</sub>, <em>n</em>C<sub>4</sub>, <em>i</em>C<sub>5</sub> and <em>n</em>C<sub>5</sub> (hereinafter called ‘C<sub>2</sub>–C<sub>5</sub> mixture’); in both cases, the mixtures were created to start out of hydrogen isotope equilibrium. We tested the performance of several metal catalysts as aids to H isotopic exchange by exposing these mixtures to different metal catalysts at 100 or 200 °C and analyzing the compound-specific hydrogen isotope ratios of the product gases. The C<sub>1</sub>–C<sub>3</sub> mixture exchanged hydrogen isotopes among the starting gas components rapidly in the presence of Ru/Al<sub>2</sub>O<sub>3</sub> at 200 °C. The isotope ratios reach a steady-state (presumably equilibrium) after 72 h of heating (up to 120 h). The hydrogen isotopic ratios of alkanes in the C<sub>2</sub>–C<sub>5</sub> mixture shifted significantly in the presence of Rh/Al<sub>2</sub>O<sub>3</sub> at 100 °C and C<sub>3</sub>-C<sub>5</sub> compounds approached steady state after 70 h, whereas C<sub>2</sub> had not yet reached a steady state D/H ratio after 216 h of heating. We evaluated the reaction progress of isotope exchange for each compound as a function of time with a reaction-network model informed by constraints on chemical kinetics. The model indicates that C<sub>3</sub>, <em>i</em>C<sub>4</sub>, <em>n</em>C<sub>4</sub>, <em>i</em>C<sub>5</sub> and <em>n</em>C<sub>5</sub> in the C<sub>2</sub>-C<sub>5</sub> mixture reached internal isotope equilibrium after 70 h, hence we used their values to calculate experimental equilibrium results. We also calculated equilibrium isotope fractionations with the Bigeleisen-Mayer theorem using vibrational frequencies computed from the density functional theory (B3LYP/aug-cc-pVTZ). We included torsional conformers and explicit H positions in the calculations. We found that the experimental results from both the 200 ˚C C<sub>1</sub>–C<sub>3</sub> experiment and 100 ˚C
{"title":"Theoretical and experimental constraints on hydrogen isotope equilibrium in C1-C5 alkanes","authors":"Hao Xie , Michael J. Formolo , Alex L. Sessions , John M. Eiler","doi":"10.1016/j.gca.2024.08.023","DOIUrl":"10.1016/j.gca.2024.08.023","url":null,"abstract":"<div><div>Stable isotope ratios of C<sub>1</sub>–C<sub>5</sub> alkanes, the major constituents of subsurface gaseous hydrocarbons, can provide valuable insights on their origins, transport, and fates. Equilibrium isotope effects are fundamental to interpreting stable isotope signatures, as recognition of them in natural materials indicates reversible processes and constrains the temperatures of equilibrated systems. Hydrogen isotope equilibrium of C<sub>1</sub>–C<sub>5</sub> alkanes is of particular interest because evidence shows that alkyl H can undergo isotopic exchange with coexisting compounds under subsurface conditions. We present the results of a combined experimental and theoretical effort to determine equilibrium hydrogen isotope distributions in mixtures of these hydrocarbon compounds. We created two mixtures: one with C<sub>1</sub>, C<sub>2</sub> and C<sub>3</sub> (where C1 indicates methane, C<sub>2</sub> ethane, etc., hereinafter called ‘C<sub>1</sub>–C<sub>3</sub> mixture’) and another one with C<sub>2</sub>, C<sub>3</sub>, <em>i</em>C<sub>4</sub>, <em>n</em>C<sub>4</sub>, <em>i</em>C<sub>5</sub> and <em>n</em>C<sub>5</sub> (hereinafter called ‘C<sub>2</sub>–C<sub>5</sub> mixture’); in both cases, the mixtures were created to start out of hydrogen isotope equilibrium. We tested the performance of several metal catalysts as aids to H isotopic exchange by exposing these mixtures to different metal catalysts at 100 or 200 °C and analyzing the compound-specific hydrogen isotope ratios of the product gases. The C<sub>1</sub>–C<sub>3</sub> mixture exchanged hydrogen isotopes among the starting gas components rapidly in the presence of Ru/Al<sub>2</sub>O<sub>3</sub> at 200 °C. The isotope ratios reach a steady-state (presumably equilibrium) after 72 h of heating (up to 120 h). The hydrogen isotopic ratios of alkanes in the C<sub>2</sub>–C<sub>5</sub> mixture shifted significantly in the presence of Rh/Al<sub>2</sub>O<sub>3</sub> at 100 °C and C<sub>3</sub>-C<sub>5</sub> compounds approached steady state after 70 h, whereas C<sub>2</sub> had not yet reached a steady state D/H ratio after 216 h of heating. We evaluated the reaction progress of isotope exchange for each compound as a function of time with a reaction-network model informed by constraints on chemical kinetics. The model indicates that C<sub>3</sub>, <em>i</em>C<sub>4</sub>, <em>n</em>C<sub>4</sub>, <em>i</em>C<sub>5</sub> and <em>n</em>C<sub>5</sub> in the C<sub>2</sub>-C<sub>5</sub> mixture reached internal isotope equilibrium after 70 h, hence we used their values to calculate experimental equilibrium results. We also calculated equilibrium isotope fractionations with the Bigeleisen-Mayer theorem using vibrational frequencies computed from the density functional theory (B3LYP/aug-cc-pVTZ). We included torsional conformers and explicit H positions in the calculations. We found that the experimental results from both the 200 ˚C C<sub>1</sub>–C<sub>3</sub> experiment and 100 ˚C","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"386 ","pages":"Pages 63-73"},"PeriodicalIF":4.5,"publicationDate":"2024-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245686","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}
Pub Date : 2024-08-31DOI: 10.1016/j.gca.2024.08.021
E.S. Steenstra , C.J. Renggli , J. Berndt , S. Klemme
The processes responsible for the isotopic compositions and abundances of volatile elements in the early solar system remain highly debated. Orders of magnitude variation of (highly) volatile elements exist between different magmatic iron meteorite groups, but it is unclear to what extent their depletions can be explained by evaporation from metal melts during parent body accretion and/or subsequent break up. To this end, we present 86 new evaporation experiments with the aim of constraining the volatility of most volatile metals from metallic melts. The results confirm the previously proposed important effects of S in metal melt on the volatility of the elements of interest governed by their S-loving or S-phobic behavior. Nominally S-loving elements In, Sn, Te, Pb and Bi are significantly more volatile in Fe melt relative to FeS liquid, whereas nominally S-avoiding elements Ga and Sb are more volatile in FeS liquid relative to Fe melt, at a given pressure and temperature. The newly derived volatility sequences for S-free/poor and S-rich metallic melts were also compared with commonly used volatility models based on condensation temperatures. The results indicate significant differences between the latter, including the much more volatile behavior of Te, relative to Se, in both explored bulk compositions, which are traditionally assumed to be equally volatile. The (minimum) degree of volatile element depletion due to evaporation was quantified using the new experimental results and models. A comparison between the volatile element depletions in magmatic iron meteorites and the predicted depletions appropriate for evaporation from Fe melts shows that the latter depletions can be easily reconciled with (an) evaporation event(s). Altogether, the new data and models will provide an important framework when more accurate and precise estimates of magmatic iron meteorite bulk volatile element contents are available.
对于早期太阳系中挥发性元素的同位素组成和丰度的形成过程仍存在很大争议。在不同的岩浆铁陨石群之间，（高）挥发性元素存在数量级的差异，但目前还不清楚它们的损耗在多大程度上可以通过母体吸积和/或随后的碎裂过程中金属熔体的蒸发来解释。为此，我们展示了 86 项新的蒸发实验，目的是限制金属熔体中大多数挥发性金属的挥发。实验结果证实了之前提出的金属熔体中的 S 对相关元素挥发性的重要影响，这种影响受其亲 S 或疏 S 行为的支配。在给定的压力和温度下，名义上喜 S 的元素 In、Sn、Te、Pb 和 Bi 在铁熔体中的挥发性要明显高于铁溶液，而名义上厌 S 的元素 Ga 和 Sb 在铁溶液中的挥发性要高于铁熔体。新得出的无 S/贫 S 和富 S 金属熔体的挥发性序列还与常用的基于凝结温度的挥发性模型进行了比较。结果表明，后者与传统上被认为具有同等挥发性的前者之间存在显著差异，包括在两种已探索的体成分中，Te 的挥发性要比 Se 高得多。利用新的实验结果和模型，对蒸发导致的挥发性元素损耗（最小）程度进行了量化。岩浆铁陨石中的挥发性元素损耗与铁熔体蒸发的预测损耗之间的比较表明，后者的损耗很容易与（一次）蒸发事件相协调。总之，当对岩浆铁陨石块体挥发性元素含量有了更准确和精确的估计时，新的数据和模型将提供一个重要的框架。
{"title":"Quantification of evaporative loss of volatile metals from planetary cores and metal-rich planetesimals","authors":"E.S. Steenstra , C.J. Renggli , J. Berndt , S. Klemme","doi":"10.1016/j.gca.2024.08.021","DOIUrl":"10.1016/j.gca.2024.08.021","url":null,"abstract":"<div><p>The processes responsible for the isotopic compositions and abundances of volatile elements in the early solar system remain highly debated. Orders of magnitude variation of (highly) volatile elements exist between different magmatic iron meteorite groups, but it is unclear to what extent their depletions can be explained by evaporation from metal melts during parent body accretion and/or subsequent break up. To this end, we present 86 new evaporation experiments with the aim of constraining the volatility of most volatile metals from metallic melts. The results confirm the previously proposed important effects of S in metal melt on the volatility of the elements of interest governed by their S-loving or S-phobic behavior. Nominally S-loving elements In, Sn, Te, Pb and Bi are significantly more volatile in Fe melt relative to FeS liquid, whereas nominally S-avoiding elements Ga and Sb are more volatile in FeS liquid relative to Fe melt, at a given pressure and temperature. The newly derived volatility sequences for S-free/poor and S-rich metallic melts were also compared with commonly used volatility models based on condensation temperatures. The results indicate significant differences between the latter, including the much more volatile behavior of Te, relative to Se, in both explored bulk compositions, which are traditionally assumed to be equally volatile. The (minimum) degree of volatile element depletion due to evaporation was quantified using the new experimental results and models. A comparison between the volatile element depletions in magmatic iron meteorites and the predicted depletions appropriate for evaporation from Fe melts shows that the latter depletions can be easily reconciled with (an) evaporation event(s). Altogether, the new data and models will provide an important framework when more accurate and precise estimates of magmatic iron meteorite bulk volatile element contents are available.</p></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"384 ","pages":"Pages 93-110"},"PeriodicalIF":4.5,"publicationDate":"2024-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0016703724004253/pdfft?md5=69f6e1afe9c52631d186a677b23b1e57&pid=1-s2.0-S0016703724004253-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142274545","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}
Pub Date : 2024-08-31DOI: 10.1016/j.gca.2024.08.022
Boris R. Tagirov, Nikolay N. Akinfiev, Mariia E. Tarnopolskaia, Irina Yu. Nikolaeva, Irina Yu. Zlivko, Valentina A. Volchenkova, Luydmila A. Koroleva, Alexander V. Zotov
Gold solubility was measured at temperatures of 350, 400, 450, and 490 °C and pressures of 500 and 1000 bar in an ’oxidized sulfide’ system, as a function of pH<ce:inf loc="post">T</ce:inf> (2 – 10) and sulfur concentration (<ce:italic>m</ce:italic>(S<ce:inf loc="post">total</ce:inf>) = 0.03 – 1.2 [mol·(kg H<ce:inf loc="post">2</ce:inf>O)<ce:sup loc="post">-1</ce:sup>]). In this system, sulfur primarily exists as H<ce:inf loc="post">2</ce:inf>S, H<ce:inf loc="post">2</ce:inf>SO<ce:inf loc="post">3</ce:inf>, H<ce:inf loc="post">2</ce:inf>SO<ce:inf loc="post">4</ce:inf>, their dissociation products, and radical species such as S<ce:inf loc="post">2</ce:inf><ce:sup loc="post">-</ce:sup> and S<ce:inf loc="post">3</ce:inf><ce:sup loc="post">-</ce:sup>. The complexes Au(HS)<ce:inf loc="post">2</ce:inf><ce:sup loc="post">-</ce:sup>, Au<ce:inf loc="post">2</ce:inf>S<ce:inf loc="post">2</ce:inf><ce:sup loc="post">2-</ce:sup>, AuHS<ce:inf loc="post">(aq)</ce:inf>, AuHS(H<ce:inf loc="post">2</ce:inf>S)<ce:inf loc="post">3(aq)</ce:inf>, and AuOH<ce:inf loc="post">(aq)</ce:inf> were identified as the primary gold species in the experimental fluids, varying with pH and <ce:italic>m</ce:italic>(S<ce:inf loc="post">total</ce:inf>). The solubility constants for Au(HS)<ce:inf loc="post">2</ce:inf><ce:sup loc="post">-</ce:sup>, a critical (hydro)sulfide complex, align excellently with literature for ’reduced sulfide’ fluids, where sulfur predominantly exists in the 2- oxidation state. New experimental data from the ’oxidized sulfide’ system were regressed along with reliable literature data from ’reduced sulfide’ systems to calculate standard thermodynamic properties and parameters of the Helgeson-Kirkham-Flowers (HKF) model. The solubility constants for charged complexes, Au(HS)<ce:inf loc="post">2</ce:inf><ce:sup loc="post">-</ce:sup> and Au<ce:inf loc="post">2</ce:inf>S<ce:inf loc="post">2</ce:inf><ce:sup loc="post">2-</ce:sup>, increase sharply with temperature, whereas those for neutral species, AuHS<ce:inf loc="post">(aq)</ce:inf> and AuHS(H<ce:inf loc="post">2</ce:inf>S)<ce:inf loc="post">3(aq)</ce:inf>, show a pronounced peak near 300 °C. These (hydro)sulfide complexes account for gold solubility ranging from a few tens of ppb to a few tens of ppm in natural sulfide fluids, depending on the fluid pH. Thermodynamic calculations also indicate that, in addition to (hydro)sulfide species and the hydroxide complex, AuCl<ce:inf loc="post">2</ce:inf><ce:sup loc="post">-</ce:sup> significantly contributes to Au mobility in high-temperature acidic chloride fluids. Based on new experimental data and prior studies using solubility and X-ray absorption spectroscopy methods, other gold complexes including mixed Au-HS-Cl, Au-HS-S<ce:inf loc="post">3</ce:inf><ce:sup loc="post">-</ce:sup> species, and complexes with alkali metal cations, are deemed redundant. Above 250 °C, the influence of chloride salts on gold solubility can be accurately modeled using a simple extended
{"title":"Gold in sulfide fluids revisited","authors":"Boris R. Tagirov, Nikolay N. Akinfiev, Mariia E. Tarnopolskaia, Irina Yu. Nikolaeva, Irina Yu. Zlivko, Valentina A. Volchenkova, Luydmila A. Koroleva, Alexander V. Zotov","doi":"10.1016/j.gca.2024.08.022","DOIUrl":"https://doi.org/10.1016/j.gca.2024.08.022","url":null,"abstract":"Gold solubility was measured at temperatures of 350, 400, 450, and 490 °C and pressures of 500 and 1000 bar in an ’oxidized sulfide’ system, as a function of pH<ce:inf loc=\"post\">T</ce:inf> (2 – 10) and sulfur concentration (<ce:italic>m</ce:italic>(S<ce:inf loc=\"post\">total</ce:inf>) = 0.03 – 1.2 [mol·(kg H<ce:inf loc=\"post\">2</ce:inf>O)<ce:sup loc=\"post\">-1</ce:sup>]). In this system, sulfur primarily exists as H<ce:inf loc=\"post\">2</ce:inf>S, H<ce:inf loc=\"post\">2</ce:inf>SO<ce:inf loc=\"post\">3</ce:inf>, H<ce:inf loc=\"post\">2</ce:inf>SO<ce:inf loc=\"post\">4</ce:inf>, their dissociation products, and radical species such as S<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">-</ce:sup> and S<ce:inf loc=\"post\">3</ce:inf><ce:sup loc=\"post\">-</ce:sup>. The complexes Au(HS)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">-</ce:sup>, Au<ce:inf loc=\"post\">2</ce:inf>S<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">2-</ce:sup>, AuHS<ce:inf loc=\"post\">(aq)</ce:inf>, AuHS(H<ce:inf loc=\"post\">2</ce:inf>S)<ce:inf loc=\"post\">3(aq)</ce:inf>, and AuOH<ce:inf loc=\"post\">(aq)</ce:inf> were identified as the primary gold species in the experimental fluids, varying with pH and <ce:italic>m</ce:italic>(S<ce:inf loc=\"post\">total</ce:inf>). The solubility constants for Au(HS)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">-</ce:sup>, a critical (hydro)sulfide complex, align excellently with literature for ’reduced sulfide’ fluids, where sulfur predominantly exists in the 2- oxidation state. New experimental data from the ’oxidized sulfide’ system were regressed along with reliable literature data from ’reduced sulfide’ systems to calculate standard thermodynamic properties and parameters of the Helgeson-Kirkham-Flowers (HKF) model. The solubility constants for charged complexes, Au(HS)<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">-</ce:sup> and Au<ce:inf loc=\"post\">2</ce:inf>S<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">2-</ce:sup>, increase sharply with temperature, whereas those for neutral species, AuHS<ce:inf loc=\"post\">(aq)</ce:inf> and AuHS(H<ce:inf loc=\"post\">2</ce:inf>S)<ce:inf loc=\"post\">3(aq)</ce:inf>, show a pronounced peak near 300 °C. These (hydro)sulfide complexes account for gold solubility ranging from a few tens of ppb to a few tens of ppm in natural sulfide fluids, depending on the fluid pH. Thermodynamic calculations also indicate that, in addition to (hydro)sulfide species and the hydroxide complex, AuCl<ce:inf loc=\"post\">2</ce:inf><ce:sup loc=\"post\">-</ce:sup> significantly contributes to Au mobility in high-temperature acidic chloride fluids. Based on new experimental data and prior studies using solubility and X-ray absorption spectroscopy methods, other gold complexes including mixed Au-HS-Cl, Au-HS-S<ce:inf loc=\"post\">3</ce:inf><ce:sup loc=\"post\">-</ce:sup> species, and complexes with alkali metal cations, are deemed redundant. Above 250 °C, the influence of chloride salts on gold solubility can be accurately modeled using a simple extended ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"46 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2024-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142245687","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}
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