Pub Date : 2026-03-17DOI: 10.1016/j.gca.2026.03.031
Bin Xiao, Hao Zou, Di Yang, Ye Wan, Jianghan Wu, Jinxiang Shen, Franco Pirajno, Huidong Yu, Nuru Said, Huawen Cao, Fang Liu, Zhiwu Li, Zhaofeng Zhang
Fluorite mineralization, an economically significant process, remains insufficiently understood because traditional geochemical tracers are limited in resolving Ca sources and depositional mechanisms within complex hydrothermal systems. In this study, we integrate calcium (Ca) isotopes with strontium–neodymium (Sr–Nd) isotopes, thermodynamic calculations, and in-situ optical observations to investigate the mineralization and precipitation mechanisms of diverse fluorite deposits, hosted in magmatic, volcanic, and carbonate rocks. Our results reveal considerable variations in δ44/40Ca values (0.90–1.89‰) among the deposits. These variations are governed primarily by fluid sources: elevated δ44/40Ca values (up to 1.89‰) reflect derivation from ancient evaporitic brines, whereas lower values indicate contributions from crustal or mantle sources. Additionally, equilibrium isotope fractionation during fluorite precipitation (0.21–0.44‰) further influences the δ44/40Ca values. Importantly, Ca isotopes demonstrate that Ca is derived predominantly from mineralization fluids rather than from host rocks, even in systems exhibiting strong hydrothermal alteration. To validate the model proposing both F and Ca derived from fluids, this study conducted thermodynamic calculations and in-situ optical observations. The results demonstrate that fluorite solubility exhibits temperature-dependence. Furthermore, specific ions in geological fluids (particularly Al3+ and H+) could significantly enhance fluorite dissolution through interactions with F− (via complexation and protonation). These findings indicate that Ca isotopes can serve as effective tracers for Ca sources in hydrothermal mineralization systems, and the coexistence mechanism of Ca and F can fully account for large-scale, highly efficient fluorite mineralization. This study provides the first evidence from Ca isotopes and thermodynamics for the cooling and decompression mineralization model.
{"title":"Calcium isotopes and thermodynamic calculations decipher fluorite mineralization in hydrothermal systems","authors":"Bin Xiao, Hao Zou, Di Yang, Ye Wan, Jianghan Wu, Jinxiang Shen, Franco Pirajno, Huidong Yu, Nuru Said, Huawen Cao, Fang Liu, Zhiwu Li, Zhaofeng Zhang","doi":"10.1016/j.gca.2026.03.031","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.031","url":null,"abstract":"Fluorite mineralization, an economically significant process, remains insufficiently understood because traditional geochemical tracers are limited in resolving Ca sources and depositional mechanisms within complex hydrothermal systems. In this study, we integrate calcium (Ca) isotopes with strontium–neodymium (Sr–Nd) isotopes, thermodynamic calculations, and in-situ optical observations to investigate the mineralization and precipitation mechanisms of diverse fluorite deposits, hosted in magmatic, volcanic, and carbonate rocks. Our results reveal considerable variations in <ce:italic>δ</ce:italic><ce:sup loc=\"post\">44/40</ce:sup>Ca values (0.90–1.89‰) among the deposits. These variations are governed primarily by fluid sources: elevated <ce:italic>δ</ce:italic><ce:sup loc=\"post\">44/40</ce:sup>Ca values (up to 1.89‰) reflect derivation from ancient evaporitic brines, whereas lower values indicate contributions from crustal or mantle sources. Additionally, equilibrium isotope fractionation during fluorite precipitation (0.21–0.44‰) further influences the <ce:italic>δ</ce:italic><ce:sup loc=\"post\">44/40</ce:sup>Ca values. Importantly, Ca isotopes demonstrate that Ca is derived predominantly from mineralization fluids rather than from host rocks, even in systems exhibiting strong hydrothermal alteration. To validate the model proposing both F and Ca derived from fluids, this study conducted thermodynamic calculations and in-situ optical observations. The results demonstrate that fluorite solubility exhibits temperature-dependence. Furthermore, specific ions in geological fluids (particularly Al<ce:sup loc=\"post\">3+</ce:sup> and H<ce:sup loc=\"post\">+</ce:sup>) could significantly enhance fluorite dissolution through interactions with F<ce:sup loc=\"post\">−</ce:sup> (via complexation and protonation). These findings indicate that Ca isotopes can serve as effective tracers for Ca sources in hydrothermal mineralization systems, and the coexistence mechanism of Ca and F can fully account for large-scale, highly efficient fluorite mineralization. This study provides the first evidence from Ca isotopes and thermodynamics for the cooling and decompression mineralization model.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"52 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465059","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 : 2026-03-16DOI: 10.1016/j.gca.2026.03.027
He Zhao, Thomas J. Algeo, Xiangdong Wang, Zhengyi Lyu, Xueqian Feng, Xinyang Yao, Zhenfeng Luo, Zhaochu Hu
The end-Permian mass extinction (EPME), the greatest biodiversity crisis since the Cambrian Explosion, was followed by a protracted and complex recovery. Intensified continental weathering and fluctuating primary productivity, under conditions of hyperwarming, characterized both the EPME and the subsequent protracted marine biotic recovery. However, detailed reconstructions of changes in weathering and productivity during the Permian-Triassic transition have not been achieved yet, leaving uncertainty regarding the nature of environmental controls during the extinction and recovery intervals. To address this issue, we apply a novel multi-proxy framework centered on the coupled use of carbonate zinc (δ<ce:sup loc="post">66</ce:sup>Zn<ce:inf loc="post">carb</ce:inf>) and conodont strontium (<ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr<ce:inf loc="post">conodont</ce:inf>) isotopes. We investigate the environmental sensitivity of this paired system using a high-resolution dataset from the Guryul Ravine section (Indian Kashmir), integrating δ<ce:sup loc="post">66</ce:sup>Zn<ce:inf loc="post">carb</ce:inf>, <ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr<ce:inf loc="post">conodont</ce:inf>, δ<ce:sup loc="post">13</ce:sup>C<ce:inf loc="post">org</ce:inf>, and bulk-rock geochemistry across the Permian-Triassic boundary. Elevated chemical index of alteration (CIA) and <ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr<ce:inf loc="post">conodont</ce:inf> values in the uppermost Permian record enhanced weathering that likely boosted marine productivity and caused anoxia. Elevated δ<ce:sup loc="post">66</ce:sup>Zn<ce:inf loc="post">carb</ce:inf> coupled with declining <ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr<ce:inf loc="post">conodont</ce:inf> in the lowermost Triassic (<ce:italic>H. parvus</ce:italic> Zone) suggests reduced weathering inputs following the EPME. A subsequent rapid <ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr rise (above <ce:italic>I. staeschei</ce:italic> Zone) marks renewed weathering and nutrient input, driving high productivity (high δ<ce:sup loc="post">66</ce:sup>Zn<ce:inf loc="post">carb</ce:inf>, positive δ<ce:sup loc="post">13</ce:sup>C<ce:inf loc="post">org</ce:inf>) and a second anoxic episode. A negative excursion in δ<ce:sup loc="post">66</ce:sup>Zn<ce:inf loc="post">carb</ce:inf> coupled with rising <ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr<ce:inf loc="post">conodont</ce:inf> at the Griesbachian-Dienerian boundary indicates strong weathering but low marine productivity. The amelioration of nutrient limitations during the Dienerian, indicated by a positive δ<ce:sup loc="post">66</ce:sup>Zn<ce:inf loc="post">carb</ce:inf> excursion, was potentially driven by declining seawater temperatures and weakened oceanic anoxia. This study establishes the Zn-Sr isotope pair as a robust tracer for deconvolving weathering-p
{"title":"Using carbonate Zn and conodont Sr isotopes to link marine productivity and chemical weathering intensity changes during the Permian-Triassic transition","authors":"He Zhao, Thomas J. Algeo, Xiangdong Wang, Zhengyi Lyu, Xueqian Feng, Xinyang Yao, Zhenfeng Luo, Zhaochu Hu","doi":"10.1016/j.gca.2026.03.027","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.027","url":null,"abstract":"The end-Permian mass extinction (EPME), the greatest biodiversity crisis since the Cambrian Explosion, was followed by a protracted and complex recovery. Intensified continental weathering and fluctuating primary productivity, under conditions of hyperwarming, characterized both the EPME and the subsequent protracted marine biotic recovery. However, detailed reconstructions of changes in weathering and productivity during the Permian-Triassic transition have not been achieved yet, leaving uncertainty regarding the nature of environmental controls during the extinction and recovery intervals. To address this issue, we apply a novel multi-proxy framework centered on the coupled use of carbonate zinc (δ<ce:sup loc=\"post\">66</ce:sup>Zn<ce:inf loc=\"post\">carb</ce:inf>) and conodont strontium (<ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr<ce:inf loc=\"post\">conodont</ce:inf>) isotopes. We investigate the environmental sensitivity of this paired system using a high-resolution dataset from the Guryul Ravine section (Indian Kashmir), integrating δ<ce:sup loc=\"post\">66</ce:sup>Zn<ce:inf loc=\"post\">carb</ce:inf>, <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr<ce:inf loc=\"post\">conodont</ce:inf>, δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">org</ce:inf>, and bulk-rock geochemistry across the Permian-Triassic boundary. Elevated chemical index of alteration (CIA) and <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr<ce:inf loc=\"post\">conodont</ce:inf> values in the uppermost Permian record enhanced weathering that likely boosted marine productivity and caused anoxia. Elevated δ<ce:sup loc=\"post\">66</ce:sup>Zn<ce:inf loc=\"post\">carb</ce:inf> coupled with declining <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr<ce:inf loc=\"post\">conodont</ce:inf> in the lowermost Triassic (<ce:italic>H. parvus</ce:italic> Zone) suggests reduced weathering inputs following the EPME. A subsequent rapid <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr rise (above <ce:italic>I. staeschei</ce:italic> Zone) marks renewed weathering and nutrient input, driving high productivity (high δ<ce:sup loc=\"post\">66</ce:sup>Zn<ce:inf loc=\"post\">carb</ce:inf>, positive δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">org</ce:inf>) and a second anoxic episode. A negative excursion in δ<ce:sup loc=\"post\">66</ce:sup>Zn<ce:inf loc=\"post\">carb</ce:inf> coupled with rising <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr<ce:inf loc=\"post\">conodont</ce:inf> at the Griesbachian-Dienerian boundary indicates strong weathering but low marine productivity. The amelioration of nutrient limitations during the Dienerian, indicated by a positive δ<ce:sup loc=\"post\">66</ce:sup>Zn<ce:inf loc=\"post\">carb</ce:inf> excursion, was potentially driven by declining seawater temperatures and weakened oceanic anoxia. This study establishes the Zn-Sr isotope pair as a robust tracer for deconvolving weathering-p","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"59 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465060","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 : 2026-03-16DOI: 10.1016/j.gca.2026.03.022
Mark Nestmeyer, Alex J. McCoy-West
The application of rare Earth element stable isotope compositions has become of increasing interest in geochemistry. Recently, studies have begun exploring variations in the stable 146Nd/144Nd isotope ratio in geological samples, with limited isotope fractionation observed in igneous rocks but significantly larger fractionations seen in low temperature systems. Experimental and theoretical studies on the equilibrium isotope fractionation of Nd are widely missing which can support understanding the fractionation of Nd isotopes among Earth’s major reservoirs. Here, we have modelled the isotope fractionation factors for 15 common rock forming and accessory minerals to help understand equilibrium stable isotope fractionation during medium to high temperature processes.
{"title":"Neodymium stable isotope fractionation in minerals: Implications for Earth’s differentiation, and planetary formation","authors":"Mark Nestmeyer, Alex J. McCoy-West","doi":"10.1016/j.gca.2026.03.022","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.022","url":null,"abstract":"The application of rare Earth element stable isotope compositions has become of increasing interest in geochemistry. Recently, studies have begun exploring variations in the stable <ce:sup loc=\"post\">146</ce:sup>Nd<ce:sup loc=\"post\">/144</ce:sup>Nd isotope ratio in geological samples, with limited isotope fractionation observed in igneous rocks but significantly larger fractionations seen in low temperature systems. Experimental and theoretical studies on the equilibrium isotope fractionation of Nd are widely missing which can support understanding the fractionation of Nd isotopes among Earth’s major reservoirs. Here, we have modelled the isotope fractionation factors for 15 common rock forming and accessory minerals to help understand equilibrium stable isotope fractionation during medium to high temperature processes.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"105 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465061","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 : 2026-03-15DOI: 10.1016/j.gca.2026.03.024
Fang Liu, Lei Li, Hongli Zhu, Xin Li, Yajun An, Zhaofeng Zhang
Plate subduction transports surface materials into the mantle, altering its chemical and isotopic composition. As an emerging geochemical proxy, stable neodymium (Nd) isotopes hold great potential for tracing recycled subducted materials; however, their isotopic fractionation behavior during subduction remains poorly constrained. Back-arc basin basalts (BABB), which range compositionally from MORB- to arc-like due to variable contributions of subducted fluids and sediments, provide an ideal natural laboratory to investigate the behavior of stable Nd isotopes in subduction zones. In this study, we present high-precision stable Nd isotopic composition (δ146/144Nd) of twenty-one fresh basaltic glasses from the Woodlark Basin, Vate Trough, and Lau Basin in the southwestern Pacific. Our results reveal that samples exhibit narrow variations in δ146/144Nd ranging from −0.048‰ to −0.005‰ with an average of −0.022 ± 0.018‰ (2SD, n = 21), similar to that of the Bulk Silicate Earth (BSE, −0.024 ± 0.031‰, 2SD) and global mid-ocean ridge basalts (MORB) reported in literature (−0.025 ± 0.013‰, 2SD). δ146/144Nd exhibited no correlation with indices of magma differentiation (MgO, CaO/Al2O3, Sr/Nd, Eu/Eu*) or partial melting (Nb/Yb, SmN/YbN), indicating that magmatic processes exert a negligible influence on Nd isotopic fractionation. Additionally, δ146/144Nd showed no resolvable correlations with subduction indicators (e.g., Ce/Pb, Nb/U, Ba/La, and Th/Yb). However, for BABB from the Lau Basin, weak but resolvable correlations were observed between δ146/144Nd and 87Sr/86Sr (r2 = 0.40) and 143Nd/144Nd (r2 = 0.41). The binary mixing model demonstrates that this relationship cannot be solely explained by the addition of recycled sediments. Instead, fluids derived from the altered oceanic crust (AOC) play a key role in generating the subtle Nd isotopic variations observed in the Lau Basin BABB. Our model suggests that less than 10% contribution of an AOC-sediment mixture (95–100% AOC) to the mantle source can explain the stable Nd isotopic variation of BABB. Therefore, we conclude that both AOC and sediments significantly influence the Nd isotopic composition of BABB, demonstrating that stable Nd isotopes have the potential to trace subduction components.
{"title":"Stable neodymium isotopic fractionation during plate subduction: insights from back-arc basin basalts","authors":"Fang Liu, Lei Li, Hongli Zhu, Xin Li, Yajun An, Zhaofeng Zhang","doi":"10.1016/j.gca.2026.03.024","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.024","url":null,"abstract":"Plate subduction transports surface materials into the mantle, altering its chemical and isotopic composition. As an emerging geochemical proxy, stable neodymium (Nd) isotopes hold great potential for tracing recycled subducted materials; however, their isotopic fractionation behavior during subduction remains poorly constrained. Back-arc basin basalts (BABB), which range compositionally from MORB- to arc-like due to variable contributions of subducted fluids and sediments, provide an ideal natural laboratory to investigate the behavior of stable Nd isotopes in subduction zones. In this study, we present high-precision stable Nd isotopic composition (<ce:italic>δ</ce:italic><ce:sup loc=\"post\">146/144</ce:sup>Nd) of twenty-one fresh basaltic glasses from the Woodlark Basin, Vate Trough, and Lau Basin in the southwestern Pacific. Our results reveal that samples exhibit narrow variations in <ce:italic>δ</ce:italic><ce:sup loc=\"post\">146/144</ce:sup>Nd ranging from −0.048‰ to −0.005‰ with an average of −0.022 ± 0.018‰ (2SD, n = 21), similar to that of the Bulk Silicate Earth (BSE, −0.024 ± 0.031‰, 2SD) and global mid-ocean ridge basalts (MORB) reported in literature (−0.025 ± 0.013‰, 2SD). <ce:italic>δ</ce:italic><ce:sup loc=\"post\">146/144</ce:sup>Nd exhibited no correlation with indices of magma differentiation (MgO, CaO/Al<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf>, Sr/Nd, Eu/Eu*) or partial melting (Nb/Yb, Sm<ce:inf loc=\"post\">N</ce:inf>/Yb<ce:inf loc=\"post\">N</ce:inf>), indicating that magmatic processes exert a negligible influence on Nd isotopic fractionation. Additionally, <ce:italic>δ</ce:italic><ce:sup loc=\"post\">146/144</ce:sup>Nd showed no resolvable correlations with subduction indicators (e.g., Ce/Pb, Nb/U, Ba/La, and Th/Yb). However, for BABB from the Lau Basin, weak but resolvable correlations were observed between <ce:italic>δ</ce:italic><ce:sup loc=\"post\">146/144</ce:sup>Nd and <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr (r<ce:sup loc=\"post\">2</ce:sup> = 0.40) and <ce:sup loc=\"post\">143</ce:sup>Nd/<ce:sup loc=\"post\">144</ce:sup>Nd (r<ce:sup loc=\"post\">2</ce:sup> = 0.41). The binary mixing model demonstrates that this relationship cannot be solely explained by the addition of recycled sediments. Instead, fluids derived from the altered oceanic crust (AOC) play a key role in generating the subtle Nd isotopic variations observed in the Lau Basin BABB. Our model suggests that less than 10% contribution of an AOC-sediment mixture (95–100% AOC) to the mantle source can explain the stable Nd isotopic variation of BABB. Therefore, we conclude that both AOC and sediments significantly influence the Nd isotopic composition of BABB, demonstrating that stable Nd isotopes have the potential to trace subduction components.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"17 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465113","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 interplay between ferrous iron (Fe(II)) and salinity in regulating nitrate reduction pathways and nitrous oxide (N2O) emissions in lacustrine sediments remains a critical knowledge gap. This study investigated their coupled effects using sediments from Qinghai-Tibetan Plateau lakes spanning a salinity gradient (0.70–151.24 g/L), with treatments including 4 mM nitrate and 5 mM acetate (NrAc), nitrate and 5 mM Fe(II) (NrFe), and nitrate with both Fe(II) and acetate (NrFeAc). Through anoxic enrichments amended with nitrate, acetate, and/or Fe(II), the results showed that while salinity alone constrained denitrification rates, Fe(II) input (NrFe and NrFeAc) consistently retarded nitrate reduction (<13% removal in 20 days) and triggered incomplete denitrification, resulting in sustained accumulation of nitrite (∼1–4 μM) and N2O (20–60 μM). This was concurrent with Fe(II) oxidation and the formation of poorly crystalline iron minerals that extensively encrusted microbial cells. Without Fe(II) amendment (NrAc), denitrification was highly efficient (>95% nitrate removal in 72 h) with minimal accumulation of nitrite or N2O. Microbial community analysis revealed salinity as the primary factor, selecting for halotolerant genera (e.g., Halomonas and Marinobacter) at high salinity, while Fe(II) input further increased overall species richness but reduced the predicted abundance of key denitrification genes, indicating pathway incompletion. These findings indicate that Fe(II) overrides salinity constraints to promote incomplete denitrification and N2O production, with significant implications for nitrogen cycling in saline lakes.
{"title":"Ferrous iron input retards denitrification and drives N2O accumulation across salinity gradients","authors":"Jianrong Huang, Jingjing Zhao, Sayed Dildar Hussain, Mingxian Han, Jian Yang, Qing Liu, Andreas Kappler, Hongchen Jiang","doi":"10.1016/j.gca.2026.03.028","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.028","url":null,"abstract":"The interplay between ferrous iron (Fe(II)) and salinity in regulating nitrate reduction pathways and nitrous oxide (N<ce:inf loc=\"post\">2</ce:inf>O) emissions in lacustrine sediments remains a critical knowledge gap. This study investigated their coupled effects using sediments from Qinghai-Tibetan Plateau lakes spanning a salinity gradient (0.70–151.24 g/L), with treatments including 4 mM nitrate and 5 mM acetate (NrAc), nitrate and 5 mM Fe(II) (NrFe), and nitrate with both Fe(II) and acetate (NrFeAc). Through anoxic enrichments amended with nitrate, acetate, and/or Fe(II), the results showed that while salinity alone constrained denitrification rates, Fe(II) input (NrFe and NrFeAc) consistently retarded nitrate reduction (<13% removal in 20 days) and triggered incomplete denitrification, resulting in sustained accumulation of nitrite (∼1–4 μM) and N<ce:inf loc=\"post\">2</ce:inf>O (20–60 μM). This was concurrent with Fe(II) oxidation and the formation of poorly crystalline iron minerals that extensively encrusted microbial cells. Without Fe(II) amendment (NrAc), denitrification was highly efficient (>95% nitrate removal in 72 h) with minimal accumulation of nitrite or N<ce:inf loc=\"post\">2</ce:inf>O. Microbial community analysis revealed salinity as the primary factor, selecting for halotolerant genera (e.g., <ce:italic>Halomonas</ce:italic> and <ce:italic>Marinobacter</ce:italic>) at high salinity, while Fe(II) input further increased overall species richness but reduced the predicted abundance of key denitrification genes, indicating pathway incompletion. These findings indicate that Fe(II) overrides salinity constraints to promote incomplete denitrification and N<ce:inf loc=\"post\">2</ce:inf>O production, with significant implications for nitrogen cycling in saline lakes.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"52 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465063","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 : 2026-03-15DOI: 10.1016/j.gca.2026.03.021
Kun Chen, Yi-Xiang Chen, Tatsuki Tsujimori, Hans-Peter Schertl, Xin-Yue Qiao, Jia-Le Xu, Yu-Chen Liu, Naoko Takahashi, Fang Huang, Walter V. Maresch
Subduction-zone fluids play a critical role in mass transfer and crust-mantle evolution at convergent plate margins, yet their exact sources and fluid-rock interaction processes remain debated. Jadeitites in forearc serpentinite mélanges serve as unique archives for these fluids. Here, we present high-precision Mg–Fe isotopic data for jadeitites and jadeite-rich rocks from the Rio San Juan Complex (RSJC), Dominican Republic and integrate data from worldwide jadeitites to constrain fluid sources and geochemical evolution in the forearc mantle wedge. RSJC jadeitites exhibit low δ26Mg values (from −0.92‰ to −0.16‰, average = −0.48 ± 0.32‰, 2SD, n = 21) that lack correlations with carbonate indicators, precluding a significant carbonate contribution. Instead, the coupling of light Mg isotopes with enriched Ni and Cr contents, together with systematic negative correlations among δ26Mg, Na2O/TiO2, MgO and Ni, fingerprints a substantial contribution from serpentinizing fluids at forearc depths. In contrast to the light Fe isotope signatures of Myanmar jadeitites, RSJC jadeitites display relatively high δ56Fe values (−0.08‰ to 0.29‰, average = 0.15 ± 0.16‰, 2SD, n = 20). Systematic covariations between δ56Fe values, TFe2O3 contents and redox-sensitive proxies (V/Sc, U/Th, Ce anomalies and Sb/As) in jadeitites from the RSJC and Myanmar indicate that Fe isotope heterogeneity is primarily controlled by the redox state of the fluids. By integrating petrological and geochemical constraints, we propose that forearc serpentinization acts as a critical redox filter that governs the coupled Mg–Fe isotope heterogeneity of jadeitites. Olivine-dominated serpentinization generates reducing conditions and promotes Fe isotope fractionation, producing light Fe isotopic signatures as recorded by Myanmar jadeitites. In contrast, serpentinization involving orthopyroxene buffers the system under relatively oxidizing conditions, preserving high δ56Fe values in RSJC jadeitites. Jadeitite-forming fluids are best explained as mixtures of AOC-derived and serpentinizing fluid components, which either directly precipitate P-type jadeitites or metasomatize igneous protoliths to form R-type jadeitites. The subduction and melting of these rocks may transfer light Mg and heterogeneous Fe isotopic signatures to the mantle wedge and related arc magmas. Forearc serpentinization thus exerts critical control on the redox state and chemical evolution of subduction-zone fluids, with important implications for the chemical heterogeneity of the mantle wedge.
俯冲带流体在趋同板块边缘的传质和壳幔演化中起着至关重要的作用，但其确切来源和流体-岩石相互作用过程仍存在争议。弧前蛇纹岩中的硬玉岩是这些流体的独特档案。本文利用来自多米尼加共和国里约热内卢圣胡安杂岩（RSJC）的翡翠岩和富翡翠岩的高精度Mg-Fe同位素数据，结合世界范围内的翡翠岩数据，对弧前地幔楔的流体来源和地球化学演化进行了研究。RSJC翡翠岩δ26Mg值低（−0.92‰~−0.16‰，平均值 =−0.48 ± 0.32‰，2SD, n = 21），与碳酸盐指标缺乏相关性，排除了显著的碳酸盐贡献。相反，轻Mg同位素与富集的Ni和Cr含量的耦合，以及δ26Mg、Na2O/TiO2、MgO和Ni之间的系统负相关，表明弧前深度的蛇纹石成矿流体有重要贡献。与缅甸翡翠石的轻铁同位素特征相比，RSJC翡翠石的δ56Fe值较高（- 0.08‰~ 0.29‰，平均值 = 0.15 ± 0.16‰，2SD, n = 20）。rssjc和缅甸翡翠岩中δ56Fe值、TFe2O3含量和氧化还原敏感指标（V/Sc、U/Th、Ce异常和Sb/As）的系统协变表明，铁同位素非均质性主要受流体氧化还原状态控制。通过综合岩石学和地球化学约束，我们提出弧前蛇纹岩化作用是控制翡翠岩Mg-Fe同位素耦合非均质性的关键氧化还原过滤器。以橄榄石为主的蛇纹岩作用产生还原条件，促进铁同位素分馏，产生缅甸翡翠岩记录的轻铁同位素特征。相反，含正辉石的蛇纹石化作用在相对氧化的条件下缓冲了体系，保留了RSJC翡翠岩中较高的δ56Fe值。翡翠岩形成流体最好的解释是aoc衍生流体和蛇纹石流体组分的混合物，它们要么直接沉淀p型翡翠岩，要么交代火成岩原岩形成r型翡翠岩。这些岩石的俯冲和熔融作用可能将轻Mg和非均质Fe同位素特征传递到地幔楔和相关弧岩浆中。弧前蛇纹石化对俯冲带流体的氧化还原状态和化学演化具有重要控制作用，对地幔楔的化学非均质性具有重要意义。
{"title":"The impact of forearc serpentinization on the composition of subduction-zone fluids revealed by Mg–Fe isotopes in jadeitites","authors":"Kun Chen, Yi-Xiang Chen, Tatsuki Tsujimori, Hans-Peter Schertl, Xin-Yue Qiao, Jia-Le Xu, Yu-Chen Liu, Naoko Takahashi, Fang Huang, Walter V. Maresch","doi":"10.1016/j.gca.2026.03.021","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.021","url":null,"abstract":"Subduction-zone fluids play a critical role in mass transfer and crust-mantle evolution at convergent plate margins, yet their exact sources and fluid-rock interaction processes remain debated. Jadeitites in forearc serpentinite mélanges serve as unique archives for these fluids. Here, we present high-precision Mg–Fe isotopic data for jadeitites and jadeite-rich rocks from the Rio San Juan Complex (RSJC), Dominican Republic and integrate data from worldwide jadeitites to constrain fluid sources and geochemical evolution in the forearc mantle wedge. RSJC jadeitites exhibit low δ<ce:sup loc=\"post\">26</ce:sup>Mg values (from −0.92‰ to −0.16‰, average = −0.48 ± 0.32‰, 2SD, n = 21) that lack correlations with carbonate indicators, precluding a significant carbonate contribution. Instead, the coupling of light Mg isotopes with enriched Ni and Cr contents, together with systematic negative correlations among δ<ce:sup loc=\"post\">26</ce:sup>Mg, Na<ce:inf loc=\"post\">2</ce:inf>O/TiO<ce:inf loc=\"post\">2</ce:inf>, MgO and Ni, fingerprints a substantial contribution from serpentinizing fluids at forearc depths. In contrast to the light Fe isotope signatures of Myanmar jadeitites, RSJC jadeitites display relatively high δ<ce:sup loc=\"post\">56</ce:sup>Fe values (−0.08‰ to 0.29‰, average = 0.15 ± 0.16‰, 2SD, n = 20). Systematic covariations between δ<ce:sup loc=\"post\">56</ce:sup>Fe values, TFe<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf> contents and redox-sensitive proxies (V/Sc, U/Th, Ce anomalies and Sb/As) in jadeitites from the RSJC and Myanmar indicate that Fe isotope heterogeneity is primarily controlled by the redox state of the fluids. By integrating petrological and geochemical constraints, we propose that forearc serpentinization acts as a critical redox filter that governs the coupled Mg–Fe isotope heterogeneity of jadeitites. Olivine-dominated serpentinization generates reducing conditions and promotes Fe isotope fractionation, producing light Fe isotopic signatures as recorded by Myanmar jadeitites. In contrast, serpentinization involving orthopyroxene buffers the system under relatively oxidizing conditions, preserving high δ<ce:sup loc=\"post\">56</ce:sup>Fe values in RSJC jadeitites. Jadeitite-forming fluids are best explained as mixtures of AOC-derived and serpentinizing fluid components, which either directly precipitate P-type jadeitites or metasomatize igneous protoliths to form R-type jadeitites. The subduction and melting of these rocks may transfer light Mg and heterogeneous Fe isotopic signatures to the mantle wedge and related arc magmas. Forearc serpentinization thus exerts critical control on the redox state and chemical evolution of subduction-zone fluids, with important implications for the chemical heterogeneity of the mantle wedge.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"47 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465732","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 : 2026-03-15DOI: 10.1016/j.gca.2026.03.026
Jessica C. Brown, Qiang Yu, Antonio Simonetti, Jeremy B. Fein
Sulfhydryl binding sites (R-SH) are ubiquitous on dissolved organic molecules in natural aqueous environments, within complex solid organic frameworks, and on microbial cell walls. Although their concentrations are typically lower than that of other ligands, sulfhydryl binding sites likely play an outsized role in metal binding due to their high affinity to bind chalcophile elements. Few studies have measured sulfhydryl concentrations in natural environmental samples due to the difficulty, until recently, of measuring total sulfhydryl concentrations on solids or in aqueous samples, and none have quantified the impact that these binding sites have on metal speciation. In this study, recent advances in measuring dissolved total sulfhydryl site concentrations were applied to a set of water samples from pristine and human-impacted lakes to determine the role of dissolved sulfhydryl binding sites in metal speciation in each lake. In addition to reporting sulfhydryl site concentrations in each sample, we also measured the pH, dissolved organic carbon concentration, the total dissolved concentrations of a wide range of elements and anions, and the total dissolved binding site concentrations. Chemical analyses were used in conjunction with Visual MINTEQ to model the speciation of the dissolved elements in each lake sample. Measurable sulfhydryl concentrations were recorded in all lake samples, with significantly greater sulfhydryl concentrations in the pristine compared to the human-impacted lakes. Speciation modeling indicates that aqueous element-sulfhydryl complexes represent a significant proportion of the total dissolved element budget for a range of elements in both the natural and human-impacted lakes, with greater proportions observed in the pristine lake samples. For example, modeling results indicate that the pristine lake waters have an average of 47% of the total dissolved Zn present in solution as an aqueous Zn-sulfhydryl complex compared to a lower average of 29% for human-impacted lakes. Overall, the results of this study demonstrate that it is imperative to measure at least total aqueous sulfhydryl site concentrations in environmental aqueous samples in order to accurately model dissolved element speciation in those waters and thereby to assess and model contaminant mobility and bioavailability.
{"title":"The importance of dissolved sulfhydryl binding sites on the speciation of aqueous metals in lake waters: Results from pristine and human-impacted lakes","authors":"Jessica C. Brown, Qiang Yu, Antonio Simonetti, Jeremy B. Fein","doi":"10.1016/j.gca.2026.03.026","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.026","url":null,"abstract":"Sulfhydryl binding sites (R-SH) are ubiquitous on dissolved organic molecules in natural aqueous environments, within complex solid organic frameworks, and on microbial cell walls. Although their concentrations are typically lower than that of other ligands, sulfhydryl binding sites likely play an outsized role in metal binding due to their high affinity to bind chalcophile elements. Few studies have measured sulfhydryl concentrations in natural environmental samples due to the difficulty, until recently, of measuring total sulfhydryl concentrations on solids or in aqueous samples, and none have quantified the impact that these binding sites have on metal speciation. In this study, recent advances in measuring dissolved total sulfhydryl site concentrations were applied to a set of water samples from pristine and human-impacted lakes to determine the role of dissolved sulfhydryl binding sites in metal speciation in each lake. In addition to reporting sulfhydryl site concentrations in each sample, we also measured the pH, dissolved organic carbon concentration, the total dissolved concentrations of a wide range of elements and anions, and the total dissolved binding site concentrations. Chemical analyses were used in conjunction with Visual MINTEQ to model the speciation of the dissolved elements in each lake sample. Measurable sulfhydryl concentrations were recorded in all lake samples, with significantly greater sulfhydryl concentrations in the pristine compared to the human-impacted lakes. Speciation modeling indicates that aqueous element-sulfhydryl complexes represent a significant proportion of the total dissolved element budget for a range of elements in both the natural and human-impacted lakes, with greater proportions observed in the pristine lake samples. For example, modeling results indicate that the pristine lake waters have an average of 47% of the total dissolved Zn present in solution as an aqueous Zn-sulfhydryl complex compared to a lower average of 29% for human-impacted lakes. Overall, the results of this study demonstrate that it is imperative to measure at least total aqueous sulfhydryl site concentrations in environmental aqueous samples in order to accurately model dissolved element speciation in those waters and thereby to assess and model contaminant mobility and bioavailability.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"15 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147465062","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 : 2026-03-15Epub Date: 2026-02-01DOI: 10.1016/j.gca.2026.01.051
J. Douçot , J-B. Regnet , F. Bourdelle , J. Corvisier , P. Robion , D. Deldicque , C. David , S. Richoz , J. Fortin
Despite their geological significance, the thermochemical processes leading to the formation of early carbonate cements remain elusive. To bridge this knowledge gap, we carried out here laboratory-simulated diagenesis on aragonite ooids. They were placed in autoclaves, filled with distilled water, and subjected to varying temperatures and durations. Our results focus on the transformation from aragonite to calcite with temperature-dependent kinetics. At the grain scale, considered as a thermodynamic system on its own, two distinct stages of microstructural evolution were observed. In the first stage, diffusion processes predominate: the ooids experience progressive dissolution while a fringe of calcite cement forms around their periphery. In a second stage, radial diffusion stops and transformations are dominated by surface-controlled processes, characterized by calcite crystal growth within the ooids. The end-result is generally referred to as “neomorphism” in natural analogues. The transition from the diffusion-dominated to the surface-controlled stage is temperature-dependent and does not occur below 150°C. This behaviour can be explained by the progressive growth of the calcite fringe, which isolates the ooid from the surrounding pore water, while internal aragonite dissolution continues within the grain. These experiments show that early calcite cements, similar to those observed in meteoric phreatic environments, can grow without any external CaCO3 input. They also show that neomorphism in ooids requires the closure of the ooid system, a condition that can occur at any stage of diagenesis. Finally, our experiments support the presence of a diffusive boundary layer, offering a process-based refinement of the traditional ‘thin film’ concept.
{"title":"Experimental insights into early cement development in carbonate aquifers: from diffusion to surface-controlled calcite growth","authors":"J. Douçot , J-B. Regnet , F. Bourdelle , J. Corvisier , P. Robion , D. Deldicque , C. David , S. Richoz , J. Fortin","doi":"10.1016/j.gca.2026.01.051","DOIUrl":"10.1016/j.gca.2026.01.051","url":null,"abstract":"<div><div>Despite their geological significance, the thermochemical processes leading to the formation of early carbonate cements remain elusive. To bridge this knowledge gap, we carried out here laboratory-simulated diagenesis on aragonite ooids. They were placed in autoclaves, filled with distilled water, and subjected to varying temperatures and durations. Our results focus on the transformation from aragonite to calcite with temperature-dependent kinetics. At the grain scale, considered as a thermodynamic system on its own, two distinct stages of microstructural evolution were observed. In the first stage, diffusion processes predominate: the ooids experience progressive dissolution while a fringe of calcite cement forms around their periphery. In a second stage, radial diffusion stops and transformations are dominated by surface-controlled processes, characterized by calcite crystal growth within the ooids. The end-result is generally referred to as “neomorphism” in natural analogues. The transition from the diffusion-dominated to the surface-controlled stage is temperature-dependent and does not occur below 150°C. This behaviour can be explained by the progressive growth of the calcite fringe, which isolates the ooid from the surrounding pore water, while internal aragonite dissolution continues within the grain. These experiments show that early calcite cements, similar to those observed in meteoric phreatic environments, can grow without any external CaCO<sub>3</sub> input. They also show that neomorphism in ooids requires the closure of the ooid system, a condition that can occur at any stage of diagenesis. Finally, our experiments support the presence of a diffusive boundary layer, offering a process-based refinement of the traditional ‘thin film’ concept.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"417 ","pages":"Pages 11-25"},"PeriodicalIF":5.0,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146110626","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 : 2026-03-15Epub Date: 2026-01-30DOI: 10.1016/j.gca.2026.01.044
Heng-Ci Tian , Wei Yang , Xinmiao Zhao , Jun Du , Liyu Shan , Wen-Jun Li , Jing Wang , Xuhang Zhang , Yangting Lin , Xian-Hua Li , Fu-Yuan Wu
The Moon possesses two distinct hemispheres, both of which have undergone space weathering, yet its role on the farside and differences from the nearside remain debated. Here, we present high-precision iron (Fe) and potassium (K) isotopic analyses of lunar soils returned by the Chang’e-6 (CE6) mission. The CE6 bulk and three sieved soils exhibit heavier Fe and K isotopic compositions than the lunar mantle (δ56Fe = 0.18 ± 0.02‰ to 0.30 ± 0.02‰; δ41K = 2.10 ± 0.04‰ to 4.67 ± 0.04‰). Such heavy isotopic signatures cannot be explained by the initial soil compositions, meteoritic input, or cosmic–ray effects. Instead, the observed positive correlations of Fe and K isotopes with both particle size and chemical composition indicate the dominant role of space weathering, particularly micrometeoroid impact processes. The heavy Fe and K isotopes indicate a mature nature for the CE6 samples. Based on Ne isotopes, the cosmic-ray exposure age of the CE6 soils is ∼ 146 Myr, longer than that of the Chang’e-5 (CE5) soils. Compared to CE5 soils from the nearside at similar latitudes, CE6 soils exhibit heavier Fe isotopic compositions, which can be best explained by their longer exposure history in conjunction with the presence of ancient regolith components formed between 2.8 and 2.0 Ga. Therefore, our results, combined with Si isotopes, suggest that the impact flux at the two landing sites have likely not differed since 2.8 Ga.
{"title":"Space weathering on the lunar nearside and farside revealed by iron and potassium isotopes","authors":"Heng-Ci Tian , Wei Yang , Xinmiao Zhao , Jun Du , Liyu Shan , Wen-Jun Li , Jing Wang , Xuhang Zhang , Yangting Lin , Xian-Hua Li , Fu-Yuan Wu","doi":"10.1016/j.gca.2026.01.044","DOIUrl":"10.1016/j.gca.2026.01.044","url":null,"abstract":"<div><div>The Moon possesses two distinct hemispheres, both of which have undergone space weathering, yet its role on the farside and differences from the nearside remain debated. Here, we present high-precision iron (Fe) and potassium (K) isotopic analyses of lunar soils returned by the Chang’e-6 (CE6) mission. The CE6 bulk and three sieved soils exhibit heavier Fe and K isotopic compositions than the lunar mantle (δ<sup>56</sup>Fe = 0.18 ± 0.02‰ to 0.30 ± 0.02‰; δ<sup>41</sup>K = 2.10 ± 0.04‰ to 4.67 ± 0.04‰). Such heavy isotopic signatures cannot be explained by the initial soil compositions, meteoritic input, or cosmic–ray effects. Instead, the observed positive correlations of Fe and K isotopes with both particle size and chemical composition indicate the dominant role of space weathering, particularly micrometeoroid impact processes. The heavy Fe and K isotopes indicate a mature nature for the CE6 samples. Based on Ne isotopes, the cosmic-ray exposure age of the CE6 soils is ∼ 146 Myr, longer than that of the Chang’e-5 (CE5) soils. Compared to CE5 soils from the nearside at similar latitudes, CE6 soils exhibit heavier Fe isotopic compositions, which can be best explained by their longer exposure history in conjunction with the presence of ancient regolith components formed between 2.8 and 2.0 Ga. Therefore, our results, combined with Si isotopes, suggest that the impact flux at the two landing sites have likely not differed since 2.8 Ga.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"417 ","pages":"Pages 1-10"},"PeriodicalIF":5.0,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146089708","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 : 2026-03-15Epub Date: 2026-02-05DOI: 10.1016/j.gca.2026.01.054
Shuo Chen , Qiqi Xue , Yaoling Niu , Pu Sun , Pengyuan Guo , Joel B. Rodney , Tim Elliott
While there is growing interest in using Mo isotope systematics to understand subduction processes and crust-mantle recycling, how Mo isotopes may fractionate during seafloor alteration and the role of altered oceanic crust in these processes remains poorly understood. This study investigates Mo concentrations and isotope compositions (δ98/95Mo, relative to NIST SRM3134) in basalts from DSDP Sites 417A, 417D, and 418A in the Atlantic, which experienced varying extent of seafloor alteration. These samples display significant Mo concentration (28 to 738 ng/g) and Mo isotopic variability (δ98/95Mo = −2.33‰ to +0.99‰), resulting from distinct alteration conditions. Basalts from Site 417A, which generally underwent oxidative alteration at high water–rock ratios, exhibit low Mo concentrations and low δ98/95Mo values (−0.43 ± 0.26‰; 1σ). In these samples, the Mo mobilization ratios (RMo = [Mo]AOC/[Mo]fresh) show a positive correlation with δ98/95Mo and negative correlations with fluid–rock interaction proxies (e.g., K, Rb, 87Sr/86Sr), which is consistent with preferential leaching of isotopically heavy Mo from primary minerals during basalt dissolution. In contrast, samples from Site 417D generally exhibit Mo enrichment (RMo up to 3) and higher δ98/95Mo (up to +0.99‰), likely resulting from carbonate precipitation under relatively reducing conditions. Samples from Site 418A mostly show Mo uptake (RMo up to 4.5) but lower δ98/95Mo (−0.80 ± 0.53‰; 1σ), consistent with adsorption onto Fe-oxyhydroxides in sub-oxic environments. These findings indicate the dual role of altered ocean crust as both Mo sink and source on varying localized scales, which needs consideration in discussing global Mo cycling. The heterogeneity of Mo isotopes in altered ocean crust challenges its characterization as a uniform reservoir and supports the notion that deep, unaltered ocean crust may dominate slab-derived Mo fluxes in subduction zones. Our study highlights the need for mineral-scale isotopic analyses and experimental constraints to refine models of global Mo cycling and mantle heterogeneity.
{"title":"Molybdenum isotope fractionation during low-temperature alteration of the upper ocean crust at DSDP sites 417 and 418","authors":"Shuo Chen , Qiqi Xue , Yaoling Niu , Pu Sun , Pengyuan Guo , Joel B. Rodney , Tim Elliott","doi":"10.1016/j.gca.2026.01.054","DOIUrl":"10.1016/j.gca.2026.01.054","url":null,"abstract":"<div><div>While there is growing interest in using Mo isotope systematics to understand subduction processes and crust-mantle recycling, how Mo isotopes may fractionate during seafloor alteration and the role of altered oceanic crust in these processes remains poorly understood. This study investigates Mo concentrations and isotope compositions (<em>δ</em><sup>98/95</sup>Mo, relative to NIST SRM3134) in basalts from DSDP Sites 417A, 417D, and 418A in the Atlantic, which experienced varying extent of seafloor alteration. These samples display significant Mo concentration (28 to 738 ng/g) and Mo isotopic variability (<em>δ</em><sup>98/95</sup>Mo = −2.33‰ to +0.99‰), resulting from distinct alteration conditions. Basalts from Site 417A, which generally underwent oxidative alteration at high water–rock ratios, exhibit low Mo concentrations and low <em>δ</em><sup>98/95</sup>Mo values (−0.43 ± 0.26‰; 1σ). In these samples, the Mo mobilization ratios (R<sub>Mo</sub> = [Mo]<sub>AOC</sub>/[Mo]<sub>fresh</sub>) show a positive correlation with <em>δ</em><sup>98/95</sup>Mo and negative correlations with fluid–rock interaction proxies (e.g., K, Rb, <sup>87</sup>Sr/<sup>86</sup>Sr), which is consistent with preferential leaching of isotopically heavy Mo from primary minerals during basalt dissolution. In contrast, samples from Site 417D generally exhibit Mo enrichment (R<sub>Mo</sub> up to 3) and higher <em>δ</em><sup>98/95</sup>Mo (up to +0.99‰), likely resulting from carbonate precipitation under relatively reducing conditions. Samples from Site 418A mostly show Mo uptake (R<sub>Mo</sub> up to 4.5) but lower <em>δ</em><sup>98/95</sup>Mo (−0.80 ± 0.53‰; 1σ), consistent with adsorption onto Fe-oxyhydroxides in sub-oxic environments. These findings indicate the dual role of altered ocean crust as both Mo sink and source on varying localized scales, which needs consideration in discussing global Mo cycling. The heterogeneity of Mo isotopes in altered ocean crust challenges its characterization as a uniform reservoir and supports the notion that deep, unaltered ocean crust may dominate slab-derived Mo fluxes in subduction zones. Our study highlights the need for mineral-scale isotopic analyses and experimental constraints to refine models of global Mo cycling and mantle heterogeneity.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"417 ","pages":"Pages 26-36"},"PeriodicalIF":5.0,"publicationDate":"2026-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146135025","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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