Pub Date : 2026-10-15Epub Date: 2026-08-24DOI: 10.1016/j.gca.2026.08.022
Ruifei Yu, Lidong Zhu, Ziyi Zhang, Jiabin Wu, Fengquan Li, Tianyang Wang, Wei Ye, Licheng Guo, Philip A.E. Pogge von Strandmann, Xiao Zhang, Ying Huang
Rare earth elements (REEs) are widely used as tracers of chemical weathering, yet their redistribution in intensely weathered subtropical systems remains poorly constrained. We investigate REE redistribution in loess-like Quaternary Red Clay (QRC) from mid-subtropical China using geochemical, statistical, and clay mineralogical approaches. Across intensely weathered conditions (CIA > 80), segmented regression and generalized additive models (GAMs) reveal a reproducible non-monotonic ΣREE trajectory with statistically supported breakpoints near CIA ≈ 86 and ≈ 89. Rather than following a simple monotonic depletion trend expected from progressive leaching alone, ΣREE shows a relative stabilization or slight recovery within the CIA 86–89 interval, followed by pronounced depletion under more extreme weathering conditions. Clay mineralogical observations indicate progressive shifts in mineral assemblages, including decreasing proportions of primary minerals and increasing abundance of secondary minerals, providing a plausible context for observed REE fractionation. The reproducibility of this non-monotonic pattern across multiple sections suggests that progressive weathering dominates, whereas variations in sediment input modulate its local expression. These findings demonstrate that REE redistribution in deeply weathered subtropical systems reflects coupled geochemical, mineralogical, and open-system sedimentary controls.
{"title":"Non-monotonic rare earth element redistribution under intense subtropical weathering","authors":"Ruifei Yu, Lidong Zhu, Ziyi Zhang, Jiabin Wu, Fengquan Li, Tianyang Wang, Wei Ye, Licheng Guo, Philip A.E. Pogge von Strandmann, Xiao Zhang, Ying Huang","doi":"10.1016/j.gca.2026.08.022","DOIUrl":"10.1016/j.gca.2026.08.022","url":null,"abstract":"<div><div>Rare earth elements (REEs) are widely used as tracers of chemical weathering, yet their redistribution in intensely weathered subtropical systems remains poorly constrained. We investigate REE redistribution in loess-like Quaternary Red Clay (QRC) from mid-subtropical China using geochemical, statistical, and clay mineralogical approaches. Across intensely weathered conditions (CIA > 80), segmented regression and generalized additive models (GAMs) reveal a reproducible non-monotonic ΣREE trajectory with statistically supported breakpoints near CIA ≈ 86 and ≈ 89. Rather than following a simple monotonic depletion trend expected from progressive leaching alone, ΣREE shows a relative stabilization or slight recovery within the CIA 86–89 interval, followed by pronounced depletion under more extreme weathering conditions. Clay mineralogical observations indicate progressive shifts in mineral assemblages, including decreasing proportions of primary minerals and increasing abundance of secondary minerals, providing a plausible context for observed REE fractionation. The reproducibility of this non-monotonic pattern across multiple sections suggests that progressive weathering dominates, whereas variations in sediment input modulate its local expression. These findings demonstrate that REE redistribution in deeply weathered subtropical systems reflects coupled geochemical, mineralogical, and open-system sedimentary controls.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 99-109"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148896065","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 : 2026-10-15Epub Date: 2026-09-01DOI: 10.1016/j.gca.2026.08.031
Bobo Bai, Youxue Zhang
Multicomponent diffusion in natural silicate melts controls many igneous processes such as magma mixing and crystal growth. In -component silicate melts, multicomponent diffusion is characterized by an diffusion matrix , whose eigenvectors define eigen-components that diffuse independently. Each eigenvalue is the diffusion coefficient for the corresponding eigen-component. Previous studies demonstrated that diffusion eigenvectors in 8-component SiO2-TiO2-Al2O3-FeO-MgO-CaO-Na2O-K2O basaltic melts are roughly invariant with temperature. In this work, we extend this investigation to andesitic compositions to test the temperature independence of diffusion eigenvectors in more evolved melts. Thirteen diffusion couple experiments were carried out at 1250, 1350, and 1500 °C: twelve andesite-andesite couples and one basalt-andesite couple. Diffusion profiles from the twelve andesite-andesite diffusion couple experiments can be fit simultaneously with a single eigenvector matrix, supporting the hypothesis that the eigenvectors are temperature invariant in andesitic melts.
The eigenvector matrix obtained from the andesitic melt is similar to that in basalt, indicating possible compositional invariance across the basaltic–andesitic range. To test compositional independence, we simultaneously fit andesitic diffusion couple profiles in this study and basaltic diffusion couple profiles from previous investigations using a single eigenvector matrix. All diffusion profiles can be well reproduced using a single eigenvector matrix, supporting the hypothesis that a common eigenvector/eigensubspace structure can characterize multicomponent diffusion in basaltic to andesitic melts over the investigated temperature and compositional range. The fitted eigenvector matrix was further tested using diffusion profiles from olivine dissolution experiments. The model reproduces the major features of the fitted profiles and can predict diffusion profiles at higher pressures that were not used in fitting. The results provide additional support for the broader applicability of the proposed multicomponent diffusion model. The extracted eigenvector matrix and eigenvalues are incorporated in an updated open-access diffusion calculator to compute multicomponent diffusion profiles in basaltic to andesitic melts.
{"title":"Multicomponent diffusion in basaltic to andesitic melts: Toward a temperature- and composition-independent eigenvector matrix","authors":"Bobo Bai, Youxue Zhang","doi":"10.1016/j.gca.2026.08.031","DOIUrl":"10.1016/j.gca.2026.08.031","url":null,"abstract":"<div><div>Multicomponent diffusion in natural silicate melts controls many igneous processes such as magma mixing and crystal growth. In <span><math><mrow><mi>N</mi></mrow></math></span>-component silicate melts, multicomponent diffusion is characterized by an <span><math><mrow><mfenced><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></mfenced><mo>×</mo><mrow><mfenced><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></mfenced></mrow></mrow></math></span> diffusion matrix <span><math><mrow><mo>[</mo><mi>D</mi><mo>]</mo></mrow></math></span>, whose eigenvectors define <span><math><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></math></span> eigen-components that diffuse independently. Each eigenvalue is the diffusion coefficient for the corresponding eigen-component. Previous studies demonstrated that diffusion eigenvectors in 8-component SiO<sub>2</sub>-TiO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub>-FeO-MgO-CaO-Na<sub>2</sub>O-K<sub>2</sub>O basaltic melts are roughly invariant with temperature. In this work, we extend this investigation to andesitic compositions to test the temperature independence of diffusion eigenvectors in more evolved melts. Thirteen diffusion couple experiments were carried out at 1250, 1350, and 1500 °C: twelve andesite-andesite couples and one basalt-andesite couple. Diffusion profiles from the twelve andesite-andesite diffusion couple experiments can be fit simultaneously with a single eigenvector matrix, supporting the hypothesis that the eigenvectors are temperature invariant in andesitic melts.</div><div>The eigenvector matrix obtained from the andesitic melt is similar to that in basalt, indicating possible compositional invariance across the basaltic–andesitic range. To test compositional independence, we simultaneously fit andesitic diffusion couple profiles in this study and basaltic diffusion couple profiles from previous investigations using a single eigenvector matrix. All diffusion profiles can be well reproduced using a single eigenvector matrix, supporting the hypothesis that a common eigenvector/eigensubspace structure can characterize multicomponent diffusion in basaltic to andesitic melts over the investigated temperature and compositional range. The fitted eigenvector matrix was further tested using diffusion profiles from olivine dissolution experiments. The model reproduces the major features of the fitted profiles and can predict diffusion profiles at higher pressures that were not used in fitting. The results provide additional support for the broader applicability of the proposed multicomponent diffusion model. The extracted eigenvector matrix and eigenvalues are incorporated in an updated open-access diffusion calculator to compute multicomponent diffusion profiles in basaltic to andesitic melts.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 195-217"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148885182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
CO2-brine solubility controls CO2 partitioning and solubility trapping in saline subsurface systems. Mixed-ion composition, high salinity, and pressures around the critical pressure of pure CO2 increase thermodynamic nonlinearity and make equilibrium prediction more difficult. The objective of this study is to enable rapid and physically consistent early prediction of equilibrium CO2 solubility from partial experimental observations. Stepwise depressurization-to-equilibrium experiments were conducted for NaCl brines and mixed chloride brines prepared from NaCl, CaCl2, and MgCl2 at an approximate anhydrous salt mass ratio of 3:1:1, over 30/50/70 °C, 2–20 MPa, and 30/50/70 g L−1. CO2 solubility increased with pressure and decreased with temperature and salinity. At the same mass salinity, mixed brines showed lower solubility than NaCl brines. The first-order Setschenow relation adequately described the data (R2 ≈ 0.90–0.99), providing quantitative salting-out parameters and a salinity-dependent reference for the subsequent prediction framework. We then developed a two-stage time-series framework for dynamic tracking and early prediction of equilibrium solubility. The framework combines a feasible-domain constraint based on the thermodynamic upper bound C*(T, P, S) with a first-order relaxation residual used as a practical regularization term. These constraints helped reduce extrapolation drift and physically infeasible predictions in the tested cases, with complementary effects on prediction feasibility and trajectory stability. Overall, the experimental dataset and Setschenow-based salting-out analysis provide the data and physical basis for thermodynamically constrained early prediction of CO2 equilibrium solubility within the tested NaCl and mixed NaCl-CaCl2-MgCl2 brine systems. At this stage, the framework should be viewed primarily as a laboratory-scale tool for experimental acceleration and condition screening within the investigated range.
{"title":"Rapid prediction of CO2 solubility in brines using segmented depressurization-steady-state experiments and physics-constrained time-series learning","authors":"Danqun Wang, Zhiping Li, Jingtao Lai, Yan Zhang, Jianping Guo, Qian Zhang","doi":"10.1016/j.gca.2026.08.027","DOIUrl":"10.1016/j.gca.2026.08.027","url":null,"abstract":"<div><div>CO<sub>2</sub>-brine solubility controls CO<sub>2</sub> partitioning and solubility trapping in saline subsurface systems. Mixed-ion composition, high salinity, and pressures around the critical pressure of pure CO<sub>2</sub> increase thermodynamic nonlinearity and make equilibrium prediction more difficult. The objective of this study is to enable rapid and physically consistent early prediction of equilibrium CO<sub>2</sub> solubility from partial experimental observations. Stepwise depressurization-to-equilibrium experiments were conducted for NaCl brines and mixed chloride brines prepared from NaCl, CaCl<sub>2</sub>, and MgCl<sub>2</sub> at an approximate anhydrous salt mass ratio of 3:1:1, over 30/50/70 °C, 2–20 MPa, and 30/50/70 g L<sup>−1</sup>. CO<sub>2</sub> solubility increased with pressure and decreased with temperature and salinity. At the same mass salinity, mixed brines showed lower solubility than NaCl brines. The first-order Setschenow relation adequately described the data (R<sup>2</sup> ≈ 0.90–0.99), providing quantitative salting-out parameters and a salinity-dependent reference for the subsequent prediction framework. We then developed a two-stage time-series framework for dynamic tracking and early prediction of equilibrium solubility. The framework combines a feasible-domain constraint based on the thermodynamic upper bound <em>C*</em>(<em>T</em>, <em>P</em>, <em>S</em>) with a first-order relaxation residual used as a practical regularization term. These constraints helped reduce extrapolation drift and physically infeasible predictions in the tested cases, with complementary effects on prediction feasibility and trajectory stability. Overall, the experimental dataset and Setschenow-based salting-out analysis provide the data and physical basis for thermodynamically constrained early prediction of CO<sub>2</sub> equilibrium solubility within the tested NaCl and mixed NaCl-CaCl<sub>2</sub>-MgCl<sub>2</sub> brine systems. At this stage, the framework should be viewed primarily as a laboratory-scale tool for experimental acceleration and condition screening within the investigated range.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 139-158"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148885246","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 : 2026-10-15Epub Date: 2026-08-11DOI: 10.1016/j.gca.2026.07.043
Toshihiro Yoshimura, Wenshuai Li, Xiao-Ming Liu
Coral skeletons have been increasingly utilized as geochemical archives for reconstructing past seawater temperature. The Li isotope composition of coral skeletons is a promising proxy, as it reflects both environmental conditions and physiological processes. In this study, we analyzed the Li isotope composition of massive Porites australiensis coral skeletons cultured under temperature-controlled conditions to evaluate the influence of seawater temperature and the vital effect. Our results show that Li isotope composition remains uniform, mostly ranging from 15 to 19‰ with a mean value of ∼ 17‰, and is similar to inorganic aragonite for samples with Li/Mg of > 1.5 mmol/mol. Conversely, the samples exhibiting higher growth rates both at 27 and 29°C show 7Li enrichment probably influenced by cellular processes. These results demonstrate that coral skeletal δ7Li is influenced by biologically mediated fractionation, which likely modifies equilibrium exchange with seawater especially at higher growth rates. The pronounced variability observed under controlled conditions highlights the important role of temperature-dependent cellular processes in regulating Li transport and incorporation during coral biomineralization.
{"title":"Experimental constraints on lithium isotope systematics in Porites corals: robustness of Li/Mg and δ7Li paleoceanographic proxies","authors":"Toshihiro Yoshimura, Wenshuai Li, Xiao-Ming Liu","doi":"10.1016/j.gca.2026.07.043","DOIUrl":"10.1016/j.gca.2026.07.043","url":null,"abstract":"<div><div>Coral skeletons have been increasingly utilized as geochemical archives for reconstructing past seawater temperature. The Li isotope composition of coral skeletons is a promising proxy, as it reflects both environmental conditions and physiological processes. In this study, we analyzed the Li isotope composition of massive <em>Porites australiensis</em> coral skeletons cultured under temperature-controlled conditions to evaluate the influence of seawater temperature and the vital effect. Our results show that Li isotope composition remains uniform, mostly ranging from 15 to 19‰ with a mean value of ∼ 17‰, and is similar to inorganic aragonite for samples with Li/Mg of > 1.5 mmol/mol. Conversely, the samples exhibiting higher growth rates both at 27 and 29°C show <sup>7</sup>Li enrichment probably influenced by cellular processes. These results demonstrate that coral skeletal δ<sup>7</sup>Li is influenced by biologically mediated fractionation, which likely modifies equilibrium exchange with seawater especially at higher growth rates. The pronounced variability observed under controlled conditions highlights the important role of temperature-dependent cellular processes in regulating Li transport and incorporation during coral biomineralization.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 56-66"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148716463","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 : 2026-10-15Epub Date: 2026-09-06DOI: 10.1016/j.gca.2026.09.003
Luke Bridgestock, Emily Stevenson, J.Jotautas Baronas, Alasdair Knight, Harold J. Bradbury, Alexandra V. Turchyn, Edward T. Tipper
Human activities have perturbed the balance between soil erosion and formation rates, driving declines in soil quality. Quantifying these soil imbalances remains challenging, especially at large scales. Here we present a novel isotope mass balance approach to quantify river catchment wide rates of change in cation exchange capacity (CEC), a key soil quality metric, in response to erosional perturbations. The approach uses differences in Ba isotope composition between river export fluxes and chemical weathering inputs to solve for rates of change of Ba storage within upstream soil exchange pools. Data for river water and suspended particulate material (SPM) samples from the Irrawaddy and Salween river demonstrate the utility of the approach. River dissolved loads and exchange pools of co-existing SPM loads feature a Ba isotope fractionation of Δ138/134Ba diss-sp = 0.23 ± 0.14 ‰. Variations in the Ba isotope composition of the sum of these two Ba pools in river outputs (δ138/134Baout) are predominantly controlled by SPM concentration. At low SPM concentrations δ138/134Baout are offset to higher values relative to average rocks. This is interpreted to reflect the accumulation of isotopically light Ba in upstream soil exchange pools due to CEC increases. Using a mass balance framework, catchment wide changes in CEC are quantified from the Ba isotopic data. During peak discharge conditions the Salween River basin is balanced within uncertainty of the data for its catchment wide CEC budget, while the Irrawaddy River basin features net CEC accumulation of at least 35 ± 5 meq/m2/year. Net CEC accumulation in the Irrawaddy River basin is interpreted to reflect SPM deposition in floodplains, while the CEC balance observed in the Salween River basin likely reflects the limited floodplain area of this catchment. These results demonstrate the utility of this approach to quantify river catchment wide soil quality (CEC) changes driven by human perturbations to terrestrial sediment transport.
{"title":"Erosion-driven changes in soil cation exchange capacity quantified using barium isotopes","authors":"Luke Bridgestock, Emily Stevenson, J.Jotautas Baronas, Alasdair Knight, Harold J. Bradbury, Alexandra V. Turchyn, Edward T. Tipper","doi":"10.1016/j.gca.2026.09.003","DOIUrl":"10.1016/j.gca.2026.09.003","url":null,"abstract":"<div><div>Human activities have perturbed the balance between soil erosion and formation rates, driving declines in soil quality. Quantifying these soil imbalances remains challenging, especially at large scales. Here we present a novel isotope mass balance approach to quantify river catchment wide rates of change in cation exchange capacity (CEC), a key soil quality metric, in response to erosional perturbations. The approach uses differences in Ba isotope composition between river export fluxes and chemical weathering inputs to solve for rates of change of Ba storage within upstream soil exchange pools. Data for river water and suspended particulate material (SPM) samples from the Irrawaddy and Salween river demonstrate the utility of the approach. River dissolved loads and exchange pools of co-existing SPM loads feature a Ba isotope fractionation of Δ<sup>138/134</sup>Ba <sub>diss-sp</sub> = 0.23 ± 0.14 ‰. Variations in the Ba isotope composition of the sum of these two Ba pools in river outputs (<em>δ</em><sup>138/134</sup>Ba<sub>out</sub>) are predominantly controlled by SPM concentration. At low SPM concentrations <em>δ</em><sup>138/134</sup>Ba<sub>out</sub> are offset to higher values relative to average rocks. This is interpreted to reflect the accumulation of isotopically light Ba in upstream soil exchange pools due to CEC increases. Using a mass balance framework, catchment wide changes in CEC are quantified from the Ba isotopic data. During peak discharge conditions the Salween River basin is balanced within uncertainty of the data for its catchment wide CEC budget, while the Irrawaddy River basin features net CEC accumulation of at least 35 ± 5 meq/m<sup>2</sup>/year. Net CEC accumulation in the Irrawaddy River basin is interpreted to reflect SPM deposition in floodplains, while the CEC balance observed in the Salween River basin likely reflects the limited floodplain area of this catchment. These results demonstrate the utility of this approach to quantify river catchment wide soil quality (CEC) changes driven by human perturbations to terrestrial sediment transport.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 260-274"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148933544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-10-15Epub Date: 2026-08-09DOI: 10.1016/j.gca.2026.08.001
Charles T. Kershaw, Nicole C. Hurtig, Alexander P. Gysi, Artas A. Migdisov, Laura E. Waters, Daniel Harlov
The rare earth elements (REE) are important metals used increasingly in advanced technologies. Within the crust, the elements Ce and Y are commonly more abundant compared to other lanthanides (La-Lu) and comprise important end-member constituents of REE-bearing minerals. Specifically, Ce is part of the light (L) REE which have larger ionic radii than the heavy (H) REE, which are grouped together with Y. These differences in ionic radius can lead to important physiochemical trends within the lanthanide group. Despite a recent increase in experimental and thermodynamic data for the REE at high temperature and pressure, there is still a significant lack of these data at supercritical conditions. In this study we conducted batch-type experiments to measure the solubility of REE phosphates (CePO4 and YPO4) at varying starting pH (1.5–10), and salinity (0.01–1.4 mol/kg NaCl) at 350 and Psat, and from 400 to 450 °C at 700 bar. Results show that the solubility of Ce (0.14 ± 0.01–33.0 ± 1.6 ppb) is generally higher than Y (0.16 ± 0.01–13.8 ± 0.7 ppb) and that Ce complexes more strongly with both chloride and hydroxyl ligands compared to Y. The solubilities of both REE phosphates are highly pH-dependent and, to a lesser extent, depend on salinity at the studied conditions. The solubility data from this study were implemented into the GEMSFITS program to optimize the thermodynamic properties of Ce and Y hydroxyl and chloride species. The updated standard partial molal Gibbs energies of formation (ΔfG0T,P) are used within the experimental temperature and pressure range to accurately predict the CePO4 and YPO4 solubility and Ce and Y speciation behavior. Based on the updated thermodynamic properties we also provide formation constants (log βnCl,OH) for Ce and Y hydroxyl and chloride species. Updated thermodynamic properties are applied to model REE-apatite dissolution and REE mobility based on the Pea Ridge iron oxide apatite deposit in Missouri, USA. The apatite dissolution model replicates natural observations including the replacement of monazite and xenotime after apatite and is an example of the utility of the application of new thermodynamic constants to supercritical crustal fluids. The findings of this study advance the predictive capabilities of geochemical models, our understanding of the behavior of individual REE, and permit modeling the overarching fractionation trends between LREE and HREE in supercritical crustal fluids.
{"title":"The solubility and speciation of REE phosphate endmembers (CePO4 and YPO4) in Cl-rich aqueous fluids from 350 to 450 °C and implications for natural systems","authors":"Charles T. Kershaw, Nicole C. Hurtig, Alexander P. Gysi, Artas A. Migdisov, Laura E. Waters, Daniel Harlov","doi":"10.1016/j.gca.2026.08.001","DOIUrl":"10.1016/j.gca.2026.08.001","url":null,"abstract":"<div><div>The rare earth elements (REE) are important metals used increasingly in advanced technologies. Within the crust, the elements Ce and Y are commonly more abundant compared to other lanthanides (La-Lu) and comprise important end-member constituents of REE-bearing minerals. Specifically, Ce is part of the light (L) REE which have larger ionic radii than the heavy (H) REE, which are grouped together with Y. These differences in ionic radius can lead to important physiochemical trends within the lanthanide group. Despite a recent increase in experimental and thermodynamic data for the REE at high temperature and pressure, there is still a significant lack of these data at supercritical conditions. In this study we conducted batch-type experiments to measure the solubility of REE phosphates (CePO<sub>4</sub> and YPO<sub>4</sub>) at varying starting pH (1.5–10), and salinity (0.01–1.4 mol/kg NaCl) at 350 and <em>P</em><sub>sat</sub>, and from 400 to 450 °C at 700 bar. Results show that the solubility of Ce (0.14 ± 0.01–33.0 ± 1.6 ppb) is generally higher than Y (0.16 ± 0.01–13.8 ± 0.7 ppb) and that Ce complexes more strongly with both chloride and hydroxyl ligands compared to Y. The solubilities of both REE phosphates are highly pH-dependent and, to a lesser extent, depend on salinity at the studied conditions. The solubility data from this study were implemented into the GEMSFITS program to optimize the thermodynamic properties of Ce and Y hydroxyl and chloride species. The updated standard partial molal Gibbs energies of formation (Δ<em><sub>f</sub></em>G<sup>0</sup><em><sub>T,P</sub></em>) are used within the experimental temperature and pressure range to accurately predict the CePO<sub>4</sub> and YPO<sub>4</sub> solubility and Ce and Y speciation behavior. Based on the updated thermodynamic properties we also provide formation constants (log <em>β</em><sub>n</sub><sup>Cl,OH</sup>) for Ce and Y hydroxyl and chloride species. Updated thermodynamic properties are applied to model REE-apatite dissolution and REE mobility based on the Pea Ridge iron oxide apatite deposit in Missouri, USA. The apatite dissolution model replicates natural observations including the replacement of monazite and xenotime after apatite and is an example of the utility of the application of new thermodynamic constants to supercritical crustal fluids. The findings of this study advance the predictive capabilities of geochemical models, our understanding of the behavior of individual REE, and permit modeling the overarching fractionation trends between LREE and HREE in supercritical crustal fluids.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 67-84"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148716472","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 : 2026-10-15Epub Date: 2026-08-29DOI: 10.1016/j.gca.2026.08.028
Kang Liu, Li Zhang, Hesan Wu, Wan-Cai Li, Huaiwei Ni
Lunar volcanic glass beads preserve records of sulfur evolution in primitive lunar magmas and provide important constraints on the sulfur inventory of the lunar interior. Reconstruction of their pre-eruptive sulfur contents requires sulfur diffusivity data for lunar melts, which have remained largely unavailable. Here we experimentally determined sulfur diffusivities in three synthetic lunar basaltic melts, spanning compositions from Apollo green (low TiO2, 0.52 wt%) and orange (intermediate TiO2, 8.58 wt%) to red (high TiO2, 13.93 wt%), with SiO2 decreasing from 45.35 to 35.92 wt% and MgO from 16.00 to 11.00 wt%, using diffusion-couple experiments at 0.5 GPa and 1674–1876 K in a piston cylinder apparatus. Sulfur diffusivity increases systematically from green to orange to red glass compositions, with NBO/T rising from 1.76 to 2.49 to 2.82, respectively. At 1673 K, sulfur diffusivity in lunar melts is 6–13 times higher than that in terrestrial basaltic melts (NBO/T = 0.61–0.79), primarily owing to the more depolymerized structure of lunar melts. Combining these results with published experimental data, we develop a general parameterization for sulfur diffusivity in anhydrous lunar and terrestrial silicate melts under reduced conditions as a function of temperature (T) and melt composition (XSi+Al, expressed by the combined mole fraction of Si + Al), which reproduces nearly all available experimental data within a factor of 2. Applying our new sulfur diffusivity data to Apollo green and orange glass beads yields revised pre-eruptive sulfur concentrations of 282–311 and 331 μg/g, corresponding to mantle source sulfur abundances of 9–28 and 27–63 μg/g, respectively. These estimates differ substantially from values previously inferred for Apollo and Chang’e mare basalts, indicating significant sulfur heterogeneity within the lunar interior, likely inherited from lunar magma ocean differentiation and subsequent mantle overturn.
{"title":"Sulfur diffusion in lunar melts and its implications for lunar mantle sulfur abundance","authors":"Kang Liu, Li Zhang, Hesan Wu, Wan-Cai Li, Huaiwei Ni","doi":"10.1016/j.gca.2026.08.028","DOIUrl":"10.1016/j.gca.2026.08.028","url":null,"abstract":"<div><div>Lunar volcanic glass beads preserve records of sulfur evolution in primitive lunar magmas and provide important constraints on the sulfur inventory of the lunar interior. Reconstruction of their pre-eruptive sulfur contents requires sulfur diffusivity data for lunar melts, which have remained largely unavailable. Here we experimentally determined sulfur diffusivities in three synthetic lunar basaltic melts, spanning compositions from Apollo green (low TiO<sub>2</sub>, 0.52 wt%) and orange (intermediate TiO<sub>2</sub>, 8.58 wt%) to red (high TiO<sub>2</sub>, 13.93 wt%), with SiO<sub>2</sub> decreasing from 45.35 to 35.92 wt% and MgO from 16.00 to 11.00 wt%, using diffusion-couple experiments at 0.5 GPa and 1674–1876 K in a piston cylinder apparatus. Sulfur diffusivity increases systematically from green to orange to red glass compositions, with NBO/T rising from 1.76 to 2.49 to 2.82, respectively. At 1673 K, sulfur diffusivity in lunar melts is 6–13 times higher than that in terrestrial basaltic melts (NBO/T = 0.61–0.79), primarily owing to the more depolymerized structure of lunar melts. Combining these results with published experimental data, we develop a general parameterization for sulfur diffusivity in anhydrous lunar and terrestrial silicate melts under reduced conditions as a function of temperature (<em>T</em>) and melt composition (<em>X</em><sub>Si+Al</sub>, expressed by the combined mole fraction of Si + Al), which reproduces nearly all available experimental data within a factor of 2. Applying our new sulfur diffusivity data to Apollo green and orange glass beads yields revised pre-eruptive sulfur concentrations of 282–311 and 331 μg/g, corresponding to mantle source sulfur abundances of 9–28 and 27–63 μg/g, respectively. These estimates differ substantially from values previously inferred for Apollo and Chang’e mare basalts, indicating significant sulfur heterogeneity within the lunar interior, likely inherited from lunar magma ocean differentiation and subsequent mantle overturn.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 159-170"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148885245","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 : 2026-10-15Epub Date: 2026-09-01DOI: 10.1016/j.gca.2026.08.032
Xinchu Wang, Xu Zhang, Wei Guo, Hu Ding, Jiarui Liu, Rob M. Ellam, Si-Liang Li, Cong-Qiang Liu
Methane is a potent greenhouse gas that plays an important role in Earth’s climate change. The aquatic methane emissions are dynamic hotspots, while the cause of high variability of methane fluxes is uncertain given the complexity of multiple, overlapping microbial processes in methane cycling. Here, we investigated methane cycling across a salinity gradient in a coastal aquatic system (CAS) by integrating the relative abundances of doubly substituted “clumped” methane isotopologues (13CH3D and 12CH2D2) with field surveys, bulk isotopes and metagenomic sequencing. We found that methane production involved mixed methanogenic pathways, while spatially variable methane oxidation overprinted these primary signals. Two contrasting clumped isotope patterns were observed: (1) In saline zones, methane has high Δ13CH3D but low Δ12CH2D2 values, consistent with strong kinetic and/or combinatorial isotope effects. (2) In freshwater zones, clumped isotope signatures shift from depleted toward more enriched value. Yet, despite Δ13CH3D and Δ12CH2D2 moving partly toward thermodynamic equilibrium, kinetic isotope effects remain expressed. Taken together, the observed clumped isotope patterns reflect a combination of mixing, kinetic effects, and partial isotope exchange. Metagenomic and functional gene data further supported the coexistence of methane production and oxidation potential across the CAS, providing independent biological evidence for the processes inferred from the isotope systematics. We interpret the partial isotope exchange as low reaction reversibility linked to rate-limiting enzyme, methyl coenzyme M reductase (MCR) complex, which catalyzes the last step of methanogenesis and the first step of methanotrophy. Thus, clumped isotope data improve our understanding of methane biogeochemical cycling and hence provide new insights into methane estimation in Earth system models.
{"title":"Clumped isotope evidence for methane cycling in coastal aquatic system","authors":"Xinchu Wang, Xu Zhang, Wei Guo, Hu Ding, Jiarui Liu, Rob M. Ellam, Si-Liang Li, Cong-Qiang Liu","doi":"10.1016/j.gca.2026.08.032","DOIUrl":"10.1016/j.gca.2026.08.032","url":null,"abstract":"<div><div>Methane is a potent greenhouse gas that plays an important role in Earth’s climate change. The aquatic methane emissions are dynamic hotspots, while the cause of high variability of methane fluxes is uncertain given the complexity of multiple, overlapping microbial processes in methane cycling. Here, we investigated methane cycling across a salinity gradient in a coastal aquatic system (CAS) by integrating the relative abundances of doubly substituted “clumped” methane isotopologues (<sup>13</sup>CH<sub>3</sub>D and <sup>12</sup>CH<sub>2</sub>D<sub>2</sub>) with field surveys, bulk isotopes and metagenomic sequencing. We found that methane production involved mixed methanogenic pathways, while spatially variable methane oxidation overprinted these primary signals. Two contrasting clumped isotope patterns were observed: (1) In saline zones, methane has high Δ<sup>13</sup>CH<sub>3</sub>D but low Δ<sup>12</sup>CH<sub>2</sub>D<sub>2</sub> values, consistent with strong kinetic and/or combinatorial isotope effects. (2) In freshwater zones, clumped isotope signatures shift from depleted toward more enriched value. Yet, despite Δ<sup>13</sup>CH<sub>3</sub>D and Δ<sup>12</sup>CH<sub>2</sub>D<sub>2</sub> moving partly toward thermodynamic equilibrium, kinetic isotope effects remain expressed. Taken together, the observed clumped isotope patterns reflect a combination of mixing, kinetic effects, and partial isotope exchange. Metagenomic and functional gene data further supported the coexistence of methane production and oxidation potential across the CAS, providing independent biological evidence for the processes inferred from the isotope systematics. We interpret the partial isotope exchange as low reaction reversibility linked to rate-limiting enzyme, methyl coenzyme M reductase (MCR) complex, which catalyzes the last step of methanogenesis and the first step of methanotrophy. Thus, clumped isotope data improve our understanding of methane biogeochemical cycling and hence provide new insights into methane estimation in Earth system models.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 218-233"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148885350","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 : 2026-10-15Epub Date: 2026-08-27DOI: 10.1016/j.gca.2026.08.029
Angel Mojarro, Adam B. Jost, Benjamin T. Uveges, Kristin D. Bergmann, Tyler Mackey, Diana Dumit, Mark L. Roberts, Jakob Vinther, Kristian Svennevig, Lisbeth L. Pedersen, Lis Allaart, Ole Bennike, Roger E. Summons
Concretions are lithified bodies found in sedimentary rocks often formed as a result of microbial decay of an organic carbon source thereby promoting carbonate authigenesis. Prior studies have demonstrated that this process can enhance the preservation of biological and geochemical signals relative to the unconsolidated host sediment. What remains uncertain is why certain locations or geologic time periods appear to be particularly conducive toward concretion formation. Here we present an integrated radiocarbon, carbonate clumped isotope, and stable carbon isotope analysis of concretions from three Late Quaternary-age deposits across West Greenland and Canada which have encapsulated fish remains. These concretions contain capelin, Mallotus villosus, a small forage fish whose spawning leads to mass mortalities of males. Microbial decay of the resultant carrion generates alkalinity that can stimulate concretion formation. However, despite the periodic nature of the capelin lifecycle, concretion assemblages do not occur after every post-spawning mortality event. Carbon isotope values (–19.8 to –14.0‰) indicate that alkalinity was derived from capelin carrion via bacterial sulfate reduction rather than methanogenesis. Radiocarbon ages of concretion carbonate date the fish-derived carbon and variable contributions of 14C-depleted (old) carbon from the marine reservoir and therefore provide maximum age constraints on formation timing. After applying appropriate site-specific marine reservoir corrections, ages subsequently converge with independent stratigraphic chronologies at each location. Clumped isotope analysis and reconstructed precipitation temperatures from West Greenland reflect regional oxygen isotope and temperature trends associated with cooling, increasing aridity/evaporation, and glacier stillstands during the 8.2-kyr climate anomaly. Results from Canada reveal a record of glacial freshening and retreat of the Champlain Sea coinciding with a ∼60 m decrease in sea level together with anomalously cool and arid periods. We propose a two-factor model in which cryogenic and/or evaporative concentration of dissolved inorganic carbon during cold-climate intervals, coupled with transient microbial alkalinity pulses from capelin mass mortalities, mediated rapid syn-sedimentary concretion formation. Our work further suggests that geochemical records preserved within carbonate concretions may be utilized to supplement and possibly reconstruct past climate events.
{"title":"Geochemical data links Late Quaternary-age concretion formation to North Atlantic cold climate episodes","authors":"Angel Mojarro, Adam B. Jost, Benjamin T. Uveges, Kristin D. Bergmann, Tyler Mackey, Diana Dumit, Mark L. Roberts, Jakob Vinther, Kristian Svennevig, Lisbeth L. Pedersen, Lis Allaart, Ole Bennike, Roger E. Summons","doi":"10.1016/j.gca.2026.08.029","DOIUrl":"10.1016/j.gca.2026.08.029","url":null,"abstract":"<div><div>Concretions are lithified bodies found in sedimentary rocks often formed as a result of microbial decay of an organic carbon source thereby promoting carbonate authigenesis. Prior studies have demonstrated that this process can enhance the preservation of biological and geochemical signals relative to the unconsolidated host sediment. What remains uncertain is why certain locations or geologic time periods appear to be particularly conducive toward concretion formation. Here we present an integrated radiocarbon, carbonate clumped isotope, and stable carbon isotope analysis of concretions from three Late Quaternary-age deposits across West Greenland and Canada which have encapsulated fish remains. These concretions contain capelin, <em>Mallotus villosus</em>, a small forage fish whose spawning leads to mass mortalities of males. Microbial decay of the resultant carrion generates alkalinity that can stimulate concretion formation. However, despite the periodic nature of the capelin lifecycle, concretion assemblages do not occur after every post-spawning mortality event. Carbon isotope values (–19.8 to –14.0‰) indicate that alkalinity was derived from capelin carrion via bacterial sulfate reduction rather than methanogenesis. Radiocarbon ages of concretion carbonate date the fish-derived carbon and variable contributions of <sup>14</sup>C-depleted (old) carbon from the marine reservoir and therefore provide maximum age constraints on formation timing. After applying appropriate site-specific marine reservoir corrections, ages subsequently converge with independent stratigraphic chronologies at each location. Clumped isotope analysis and reconstructed precipitation temperatures from West Greenland reflect regional oxygen isotope and temperature trends associated with cooling, increasing aridity/evaporation, and glacier stillstands during the 8.2-kyr climate anomaly. Results from Canada reveal a record of glacial freshening and retreat of the Champlain Sea coinciding with a ∼60 m decrease in sea level together with anomalously cool and arid periods. We propose a two-factor model in which cryogenic and/or evaporative concentration of dissolved inorganic carbon during cold-climate intervals, coupled with transient microbial alkalinity pulses from capelin mass mortalities, mediated rapid <em>syn</em>-sedimentary concretion formation. Our work further suggests that geochemical records preserved within carbonate concretions may be utilized to supplement and possibly reconstruct past climate events.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 171-181"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148885247","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 : 2026-10-15Epub Date: 2026-09-01DOI: 10.1016/j.gca.2026.08.025
N. Meunier-Mili, M.-A. Kaczmarek, M. Bystricky
Chassignite meteorites are martian achondrites that display a magmatic cumulate texture and are mainly composed of olivine with a small amount of poikilitic pyroxene. This study presents a detailed petrological and microstructural analysis using electron backscatter diffraction of all chassignite meteorites documented up to now, Chassigny, NWA 2737 and NWA 8694, in order to decipher early magmatic, deformation and shock processes. The new results reveal that olivine crystals in chassignite meteorites initially formed through synneusis, a magmatic process where individual crystals accumulate and aggregate together in specific orientations in the earlier stages of consolidation. Many olivine crystals stick together along (100) crystalline faces as evidenced by the significant concentration of misorientation [100] axes at grain boundaries for all three samples. Synneusis was probably interrupted and progressively replaced by crystal settling until complete crystallisation was achieved. Olivine crystallographic preferred orientations indicate slip on [100](010) and olivine subgrain boundaries reveal high densities of geometrically necessary dislocations of the [100](010) type. The [100](010) slip system is active at high temperatures and low stresses in the Earth’s upper mantle and is often observed in plastically deformed peridotites, though it is not necessarily dominant in terrestrial olivine cumulative rocks. Furthermore, pyroxene crystallographic preferred orientations are consistent with those of olivine ([100] olivine axes parallel to pyroxene [001] axes), supporting the hypothesis of minor plastic deformation of olivine and pyroxene at high temperatures and low stresses. These observations are consistent with possible crystallization and emplacement of the chassignite-type magma in the shallow martian crust. Finally the strong shock events recorded by these meteorites are supported by significant internal deformation of olivine grains, concentration of misorientation axes along their [100] axes, and the activation of the [001](010) slip system leading to formation of olivine subgrain boundaries. Altogether these results are good indicators to decipher primary planetary processes.
{"title":"Textures of Chassignite meteorites: Clues to cumulate formation and early deformation processes on Mars","authors":"N. Meunier-Mili, M.-A. Kaczmarek, M. Bystricky","doi":"10.1016/j.gca.2026.08.025","DOIUrl":"10.1016/j.gca.2026.08.025","url":null,"abstract":"<div><div>Chassignite meteorites are martian achondrites that display a magmatic cumulate texture and are mainly composed of olivine with a small amount of poikilitic pyroxene. This study presents a detailed petrological and microstructural analysis using electron backscatter diffraction of all chassignite meteorites documented up to now, Chassigny, NWA 2737 and NWA 8694, in order to decipher early magmatic, deformation and shock processes. The new results reveal that olivine crystals in chassignite meteorites initially formed through synneusis, a magmatic process where individual crystals accumulate and aggregate together in specific orientations in the earlier stages of consolidation. Many olivine crystals stick together along (100) crystalline faces as evidenced by the significant concentration of misorientation [100] axes at grain boundaries for all three samples. Synneusis was probably interrupted and progressively replaced by crystal settling until complete crystallisation was achieved. Olivine crystallographic preferred orientations indicate slip on [100](010) and olivine subgrain boundaries reveal high densities of geometrically necessary dislocations of the [100](010) type. The [100](010) slip system is active at high temperatures and low stresses in the Earth’s upper mantle and is often observed in plastically deformed peridotites, though it is not necessarily dominant in terrestrial olivine cumulative rocks. Furthermore, pyroxene crystallographic preferred orientations are consistent with those of olivine ([100] olivine axes parallel to pyroxene [001] axes), supporting the hypothesis of minor plastic deformation of olivine and pyroxene at high temperatures and low stresses. These observations are consistent with possible crystallization and emplacement of the chassignite-type magma in the shallow martian crust. Finally the strong shock events recorded by these meteorites are supported by significant internal deformation of olivine grains, concentration of misorientation axes along their [100] axes, and the activation of the [001](010) slip system leading to formation of olivine subgrain boundaries. Altogether these results are good indicators to decipher primary planetary processes.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"431 ","pages":"Pages 110-121"},"PeriodicalIF":5.2,"publicationDate":"2026-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148885181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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