Pub Date : 2024-10-18DOI: 10.1016/j.gca.2024.10.012
Ketao Yan, Qinghai Guo, Luxia Wang, Yi Liu, Britta Planer-Friedrich
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.
地热水域的砷（As）浓度通常较高。已确定的砷种类繁多，包括甲基化硫代砷酸盐，它们具有高流动性和毒性，对环境和健康构成高风险。温泉排放时，温度和地质硫化物过量会降低，而氧化还原电位会升高。目前还不清楚这些参数对硫酸盐还原菌和甲烷菌活动的综合影响，以及由此对砷甲基化与硫代化程度的综合影响。在此，我们将来自中国西南腾冲地热区碱性温泉和外流通道的沉积物（曾检测到无机硫代砷酸盐和甲基化硫代砷酸盐）在 20 至 90 ° C 的温度下与不同的初始水体砷和硫物种进行了培养。现场样本和培养实验的结果显示出甲基化硫代砷酸盐，但没有甲基化氧砷酸盐，这意味着即使在硫化物浓度较低的情况下也存在定量硫代砷化作用。来自一种沉积物的富集培养物在 55 °C时可定量形成二甲基二硫代砷酸盐（DMDTA），在 35 °C时显示出无机三硫代砷酸盐占主导地位，而在 55 °C时与另外两种沉积物一起培养则显示出单甲基硫代砷酸盐占主导地位。限速步骤是微生物介导的亚砷酸盐甲基化，在 20 °C 或 75 °C 时均未观察到，这与已甲基化砷酸盐的硫代化形成鲜明对比。在培养实验中加入游离硫化物和硫代硫酸盐可促进无机砷酸盐或单甲基化的高硫代砷酸盐的形成，而硫酸盐则可促进完全甲基化和 DMDTA 的形成，这可能是由于微生物产生的硫化物供应量持续偏低所致。由于 DMDTA 比无机硫代砷酸盐和单甲基化硫代砷酸盐更具流动性和毒性，因此了解其形成的制约因素对未来的风险评估尤为重要。
{"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}
Pub Date : 2024-10-16DOI: 10.1016/j.gca.2024.10.008
Maximilian Schulze, Thomas Driesner, Sandro Jahn
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
{"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}
Pub Date : 2024-10-15DOI: 10.1016/j.gca.2024.10.007
Mark Nestmeyer, Alex J. McCoy-West
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.
{"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}
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 (< 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 O2. 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.
{"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 (< 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}
Pub Date : 2024-10-14DOI: 10.1016/j.gca.2024.10.005
Sijia Dong, Frank J. Pavia, Adam V. Subhas, William R. Gray, Jess F. Adkins, William M. Berelson
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 (δ13C) 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 13C-enriched component compared to isotopically-light bulk POC in both the large size fraction (LSF, > 51μ m) and small size fraction (SSF, 0.5 – 51μ m) of the pump particles, but exhibits a greater impact on the large particles because of its smaller inventory. Simultaneously, addition of a 13C-enriched heterotrophic or chemoautotrophic component to the SSF further increases the isotopic offset between SSF and LSF POC. Overall, this study uses δ13C 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 O2 in the ODZ likely protects carbonate from dissolving by severely limiting organic matter respiration, thus reducing shallow PIC dissolution within the ODZs.
{"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, > 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}
Pub Date : 2024-10-09DOI: 10.1016/j.gca.2024.10.001
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
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 (NH4+) 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 NH4+ is present in Orgueil at a mean concentration of 0.07 ± 0.01 wt%, with a mean isotopic composition of δ15N = +72 ± 9 ‰ (14N/15N = 254 ± 2), confirming its extra-terrestrial origin. In the most terrestrially altered sample of Orgueil that we analysed, the isotopic composition is δ15N = +50 ± 12 ‰ (14N/15N = 259 ± 3). NH4+ 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.: < 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 δ15N (and 14N/15N) values of +32 ± 1 ‰ (264 ± 0.3) for IOM, +39 ± 16 ‰ (262 ± 4) for UOM, and +72 ± 9 ‰ (254 ± 2) for NH4+.
{"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.: < 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}
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., CH4, H2 – 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 CH4, H2 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 > 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., CO2), thus promoting the proliferation of subsurface microbial life at convergent margins.
{"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 > 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}
Pub Date : 2024-10-05DOI: 10.1016/j.gca.2024.10.002
Xu-Han Dong , Shui-Jiong Wang , Kwan-Nang Pang , Ji Shen , Yi-Xiang Chen , Mojtaba Rostami-Hossouri , Habibollah Ghasemi
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), FeT/Mn (58.2–77.4) and Zn/FeT ratios (11.9–16.4). The Ni isotopic compositions of the Sabzevar basalts (average δ60/58Ni = +0.15 ± 0.08 ‰; 2SD) are slightly heavier than the BSE value (average δ60/58Ni = +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 δ60/58Ni = +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 δ60/58Ni and Cu systematics in terrestrial basalts. In both models, the initial sulfide content (Sinitial) and oxygen fugacity (fO2) 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 Sinitial and fO2 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.
{"title":"The behavior of nickel isotopes during mantle melting","authors":"Xu-Han Dong , Shui-Jiong Wang , Kwan-Nang Pang , Ji Shen , Yi-Xiang Chen , Mojtaba Rostami-Hossouri , 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<sub>T</sub>/Mn (58.2–77.4) and Zn/Fe<sub>T</sub> ratios (11.9–16.4). The Ni isotopic compositions of the Sabzevar basalts (average <em>δ</em><sup>60/58</sup>Ni = +0.15 ± 0.08 ‰; 2SD) are slightly heavier than the BSE value (average <em>δ</em><sup>60/58</sup>Ni = +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><sup>60/58</sup>Ni = +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><sup>60/58</sup>Ni and Cu systematics in terrestrial basalts. In both models, the initial sulfide content (<em>S<sub>initial</sub></em>) and oxygen fugacity (<em>f</em>O<sub>2</sub>) 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<sub>initial</sub></em> and <em>f</em>O<sub>2</sub> 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}
Pub Date : 2024-10-05DOI: 10.1016/j.gca.2024.10.003
Zvi Steiner, Alexandra V. Turchyn, Patrizia Ziveri, Alan M. Shiller, Phoebe J. Lam, Adina Paytan, Eric P. Achterberg
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 (SrSO4) 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 (BaSO4) precipitation and/or dissolution on the marine Sr cycle is negligible, accounting for <1 % of the water column concentration structure for Sr and ∼3 % of the sedimentary Sr burial. The Sr-Ba-PO4 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.
我们沿着从夏威夷到阿拉斯加的一条横断面研究了碱土金属锶（Sr）和钡（Ba）在水体中的分布。尽管锶和钡的化学性质相似，但我们发现它们在横断面上的浓度变化受不同的化学和生物过程的控制，这意味着这些元素在现代和古代环境中可被视为独立变量。阿拉斯加边缘沉积物是北太平洋溶解钡的一个特别重要的来源，可能是通过含盐海底地下水排放和锰（Mn）氧化物的还原溶解共同作用产生的。我们发现，超过 90% 的水体 Sr 浓度变化是由 Acantharia 的天青石（SrSO4）骨架的沉淀和溶解引起的。然而，在全球海洋水体中钡浓度的变化中，刺芹中的高钡含量仅占5-8%。同样，重晶石（BaSO4）的沉淀和/或溶解对海洋锶循环的影响微乎其微，只占水柱锶浓度结构的1%和沉积锶埋藏量的∼3%。北太平洋的 Sr-Ba-PO4 浓度分布与重晶石大量出口到深海和沉积物的情况不符。这表明在中间深度形成的重晶石大多溶解在与其形成相似的地层中。浮游植物有机物中的钡含量太低，不足以构成中层北太平洋微粒钡的主要来源，这表明钡被异养微生物浓缩在海洋聚集体中。
{"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 <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}
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, δ44/40Ca, 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 (δ18Ool = +5.33 ± 0.13‰; 1σ; n = 12) overlap average mantle values. Clinopyroxene and garnet δ18O values (δ18Ocpx = +5.31 ± 0.10‰; δ18Ogrt = +5.37 ± 0.23‰; 1σ) extend below those reported in most mantle peridotites and are strongly correlated with clinopyroxene δ44/40Ca (avg. = +1.00 ± 0.10‰; 1σ) and garnet δ44/40Ca (avg. = +1.18 ± 0.19‰; 1σ) respectively, extending from typical mantle values to low δ18O and high δ44/40Ca values. In general, Δ18Ocpx-ol and Δ18Ogrt-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 δ18Ogrt and Δ18Ogrt-ol and garnet major and trace element composition (Na2O, H2O, La/YbN). 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 δ44/40Ca 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.
{"title":"Tracking subduction-related metasomatism of the subcontinental lithospheric mantle using Ca-, O-, and H-isotopes","authors":"S.E. Brooker , J.D. Barnes , J.C. Lassiter , A. Satkoski , 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 δ<sup>18</sup>O, δ<sup>44/40</sup>Ca, and δD values for twelve kimberlite-hosted mantle xenoliths from the Slave Craton (NWT, Canada), which show varying degrees of metasomatism. The δ<sup>18</sup>O values of olivine (δ<sup>18</sup>O<sub>ol</sub> = +5.33 ± 0.13‰; 1σ; n = 12) overlap average mantle values. Clinopyroxene and garnet δ<sup>18</sup>O values (δ<sup>18</sup>O<sub>cpx</sub> = +5.31 ± 0.10‰; δ<sup>18</sup>O<sub>grt</sub> = +5.37 ± 0.23‰; 1σ) extend below those reported in most mantle peridotites and are strongly correlated with clinopyroxene δ<sup>44/40</sup>Ca (avg. = +1.00 ± 0.10‰; 1σ) and garnet δ<sup>44/40</sup>Ca (avg. = +1.18 ± 0.19‰; 1σ) respectively, extending from typical mantle values to low δ<sup>18</sup>O and high δ<sup>44/40</sup>Ca values. In general, Δ<sup>18</sup>O<sub>cpx-ol</sub> and Δ<sup>18</sup>O<sub>grt-ol</sub> (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 δ<sup>18</sup>O<sub>grt</sub> and Δ<sup>18</sup>O<sub>grt-ol</sub> and garnet major and trace element composition (Na<sub>2</sub>O, H<sub>2</sub>O, La/Yb<sub>N</sub>). 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 δ<sup>18</sup>O, δD, and high δ<sup>44/40</sup>Ca 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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：