Pub Date : 2026-03-05DOI: 10.1016/j.gca.2026.03.001
Tengfei Ma, Hang Deng, Puxuan Kang, Yuchao Feng, Xiaofan Yang, Liang Zhao, Xueying Li, Dexi Wang, Xingming Chen, Zhengmao Yang, Weisheng Qiu, Junfeng Ji, Yuanyuan Liu
CaCO3 precipitation plays a pivotal role in fracture evolution and permeability in subsurface reservoirs, directly impacting the efficiency and reliability of geological carbon sequestration. Yet, how flow-driven transport interacts with nucleation, polymorph deposition, mineral transitions, and fracture heterogeneity remains poorly constrained. Here, we combine micromodel experiments, in situ Raman spectroscopy, pore-scale fluid and solute transport simulations, and Darcy-scale advection–diffusion–nucleation simulations to unravel coupled dynamics of flow, mass transfer, and mineral precipitation. We show that flow-controlled mixing plays a critical role on early-stage nucleation, polymorph precipitation, and subsequent fracture structure evolution. In most regions, supersaturation develops progressively through solute mixing, triggering initial calcite nucleates, followed by the accumulation of metastable CaCO3 phases that fill pore space and enhance the total precipitation mass. However, at high flow rates, reactants advected from finer fractures into coarser, high-velocity preferential flow paths form confined supersaturation zones along streamlines. These zones promote rapid amorphous calcium carbonate (ACC) formation and delay its transformation to stable calcite. These early-stage processes—including stochastic nucleation, transient ACC persistence, and polymorph precipitation and transitions—do not alter the final mineralogy but strongly regulate fracture geometry, saturation fields, and the reproducibility of precipitation. As a result, divergent long-term outcomes emerge: high flow rates restrict precipitation to narrower zones, producing reproducible but clog-prone fracture sealing; whereas low flow rates broaden saturation zones, amplify the stochastic nature of nucleation, and increase variability in precipitation distribution and fracture geometry evolution. Our findings reveal an underexplored mechanism by which flow-controlled mixing governs early-stage nucleation and polymorph precipitation, thereby regulating long-term fracture structure evolution and precipitation variability. These insights provide a mechanistic framework for optimizing CO2 injection strategies, predicting reservoir heterogeneity, and improving models of mineral trapping in fractured subsurface systems.
{"title":"Flow-driven regulation of CaCO3 precipitation and fracture evolution in heterogeneous fractures","authors":"Tengfei Ma, Hang Deng, Puxuan Kang, Yuchao Feng, Xiaofan Yang, Liang Zhao, Xueying Li, Dexi Wang, Xingming Chen, Zhengmao Yang, Weisheng Qiu, Junfeng Ji, Yuanyuan Liu","doi":"10.1016/j.gca.2026.03.001","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.001","url":null,"abstract":"CaCO<ce:inf loc=\"post\">3</ce:inf> precipitation plays a pivotal role in fracture evolution and permeability in subsurface reservoirs, directly impacting the efficiency and reliability of geological carbon sequestration. Yet, how flow-driven transport interacts with nucleation, polymorph deposition, mineral transitions, and fracture heterogeneity remains poorly constrained. Here, we combine micromodel experiments, in situ Raman spectroscopy, pore-scale fluid and solute transport simulations, and Darcy-scale advection–diffusion–nucleation simulations to unravel coupled dynamics of flow, mass transfer, and mineral precipitation. We show that flow-controlled mixing plays a critical role on early-stage nucleation, polymorph precipitation, and subsequent fracture structure evolution. In most regions, supersaturation develops progressively through solute mixing, triggering initial calcite nucleates, followed by the accumulation of metastable CaCO<ce:inf loc=\"post\">3</ce:inf> phases that fill pore space and enhance the total precipitation mass. However, at high flow rates, reactants advected from finer fractures into coarser, high-velocity preferential flow paths form confined supersaturation zones along streamlines. These zones promote rapid amorphous calcium carbonate (ACC) formation and delay its transformation to stable calcite. These early-stage processes—including stochastic nucleation, transient ACC persistence, and polymorph precipitation and transitions—do not alter the final mineralogy but strongly regulate fracture geometry, saturation fields, and the reproducibility of precipitation. As a result, divergent long-term outcomes emerge: high flow rates restrict precipitation to narrower zones, producing reproducible but clog-prone fracture sealing; whereas low flow rates broaden saturation zones, amplify the stochastic nature of nucleation, and increase variability in precipitation distribution and fracture geometry evolution. Our findings reveal an underexplored mechanism by which flow-controlled mixing governs early-stage nucleation and polymorph precipitation, thereby regulating long-term fracture structure evolution and precipitation variability. These insights provide a mechanistic framework for optimizing CO<ce:inf loc=\"post\">2</ce:inf> injection strategies, predicting reservoir heterogeneity, and improving models of mineral trapping in fractured subsurface systems.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"188 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147393098","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 : 2026-03-02DOI: 10.1016/j.gca.2026.02.037
James W. Dottin III, Alan Brandon, Erica Pitcavage, Steven B. Shirey, Michelle K. Jordan
{"title":"Isotopic constraints on the origin and nature of sulfur components within the ancient sub-continental lithospheric mantle","authors":"James W. Dottin III, Alan Brandon, Erica Pitcavage, Steven B. Shirey, Michelle K. Jordan","doi":"10.1016/j.gca.2026.02.037","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.037","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"251 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147360468","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 : 2026-03-01Epub Date: 2026-01-06DOI: 10.1016/j.gca.2026.01.003
Rijing Wang , Jinlong Ma , Guipeng Mao , Guanhong Zhu , Kai Luo , Ti Zeng , Gangjian Wei
Boron (B) isotopes serve as an effective tracer for the weathering of continental silicate rocks, but the mechanisms of B isotope fractionation remain controversial. This study quantifies B isotope fractionation through the mineralogical-geochemical and δ11B coupling analysis of weathering profile from basalt on Hainan Island. The δ11B values of weathering products in profile range from −3.60 ‰ to 1.87 ‰, most of them are significantly higher than that of the parent rock (−3.13 ‰). Their evolution may be controlled by three stages: (1) The decomposition of plagioclase releases B-rich fluid; (2) Smectite preferentially incorporates the light isotope (10B) during its formation, and this isotopically light component may subsequently be released into the soil solution through partial dissolution and/or possible desorption as weathering progresses; (3) Kaolinite exhibits pH-dependent dual-mode adsorption, under weakly acidic to neutral conditions (pH = 6–7), 10B is preferentially adsorbed during kaolinite formation, whereas under acidic conditions (pH < 6), changes in surface hydroxyl group protonation on kaolinite enhance its affinity for 11B. Our study highlights that adsorption and desorption effects during weathering at different pH conditions reconfigure the δ11B signature, which may contribute to the wide variability of δ11B observed in global rivers (−11 ‰ to + 45 ‰). These results call for a reassessment of global B-cycle models, particularly under tropical acidic weathering environments.
{"title":"pH controlling boron isotope fractionation during chemical weathering of basalt","authors":"Rijing Wang , Jinlong Ma , Guipeng Mao , Guanhong Zhu , Kai Luo , Ti Zeng , Gangjian Wei","doi":"10.1016/j.gca.2026.01.003","DOIUrl":"10.1016/j.gca.2026.01.003","url":null,"abstract":"<div><div>Boron (B) isotopes serve as an effective tracer for the weathering of continental silicate rocks, but the mechanisms of B isotope fractionation remain controversial. This study quantifies B isotope fractionation through the mineralogical-geochemical and δ<sup>11</sup>B coupling analysis of weathering profile from basalt on Hainan Island. The δ<sup>11</sup>B values of weathering products in profile range from −3.60 ‰ to 1.87 ‰, most of them are significantly higher than that of the parent rock (−3.13 ‰). Their evolution may be controlled by three stages: (1) The decomposition of plagioclase releases B-rich fluid; (2) Smectite preferentially incorporates the light isotope (<sup>10</sup>B) during its formation, and this isotopically light component may subsequently be released into the soil solution through partial dissolution and/or possible desorption as weathering progresses; (3) Kaolinite exhibits pH-dependent dual-mode adsorption, under weakly acidic to neutral conditions (pH = 6–7), <sup>10</sup>B is preferentially adsorbed during kaolinite formation, whereas under acidic conditions (pH < 6), changes in surface hydroxyl group protonation on kaolinite enhance its affinity for <sup>11</sup>B. Our study highlights that adsorption and desorption effects during weathering at different pH conditions reconfigure the δ<sup>11</sup>B signature, which may contribute to the wide variability of δ<sup>11</sup>B observed in global rivers (−11 ‰ to + 45 ‰). These results call for a reassessment of global B-cycle models, particularly under tropical acidic weathering environments.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 69-81"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956571","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 : 2026-03-01Epub Date: 2026-01-18DOI: 10.1016/j.gca.2026.01.018
Xiulan Zong , Jingjing Guo , Wenru Yang , Jibao Dong , Niels J. de Winter , Hong Yan , Yougui Song , Youbin Sun , Francien Peterse , Martin Ziegler
Currently available reconstructions of past East Asian monsoon (EAM) variability achieve annual resolution at best, which limits their ability to resolve seasonal variations in precipitation and temperature. To address this gap, we present sub-annual scale reconstructions of temperature and precipitation variability based on carbonate clumped isotope (Δ47) and stable oxygen isotope (δ18Oshell) measurements from modern and fossil land snail shells collected from the western (Yuanbao, YB) and southeastern (Lingbao, LB) edge of the Chinese Loess Plateau (CLP). Whole-shell Δ47-derived temperatures (T47) from different modern snail species are consistent with land surface temperatures measured during their growing season (mid-April to September at YB and mid-March to October at LB), and show minimal inter-species differences, highlighting the ecological robustness of snail-based T47 reconstructions. Our intra-shell Δ47–δ18O–δ13C data show no obvious evidence of disequilibrium fractionation, supporting that land snail shell aragonite forms near isotopic equilibrium in natural settings. Notably, the reconstructed intra-shell T47 profiles show a sub-annual temperature variability of 7–10 °C and potential signs of short-term thermal stress. Reconstructed body water δ18O (δ18Obw) values from whole-shells are significantly enriched (by ∼ 3–6.5 ‰, p < 0.05) compared to local precipitation δ18O (δ18Op), due to evaporative effects and micro-environmental conditions. Intra-shell δ18Obw profiles reveal sub-annual fluctuations that follow seasonal δ18Op patterns, capturing dry-season evaporative isotopic enrichment and wet-season depletion masked in whole-shell averages.
The T47 from early Holocene and last glacial maximum (LGM)-aged shells provides geochemical evidence of a cooler growing season than today, perhaps caused by extended growing seasons during the early Holocene and climatically restricted ones during the LGM. Lower and more stable intra-shell T47 and more negative δ18Obw values during the wet seasons highlight seasonal hydroclimatic shifts under glacial boundary conditions. Together, our results demonstrate the sensitivity of snail shell geochemistry to hydroclimatic seasonality and support the use of combined intra-shell δ18O and Δ47 analyses to resolve climate seasonality beyond the resolution of traditional proxies.
{"title":"Unlocking sub-annual hydroclimate and temperature variability through land snail shell records","authors":"Xiulan Zong , Jingjing Guo , Wenru Yang , Jibao Dong , Niels J. de Winter , Hong Yan , Yougui Song , Youbin Sun , Francien Peterse , Martin Ziegler","doi":"10.1016/j.gca.2026.01.018","DOIUrl":"10.1016/j.gca.2026.01.018","url":null,"abstract":"<div><div>Currently available reconstructions of past East Asian monsoon (EAM) variability achieve annual resolution at best, which limits their ability to resolve seasonal variations in precipitation and temperature. To address this gap, we present sub-annual scale reconstructions of temperature and precipitation variability based on carbonate clumped isotope (Δ<sub>47</sub>) and stable oxygen isotope (δ<sup>18</sup>O<sub>shell</sub>) measurements from modern and fossil land snail shells collected from the western (Yuanbao, YB) and southeastern (Lingbao, LB) edge of the Chinese Loess Plateau (CLP). Whole-shell Δ<sub>47</sub>-derived temperatures (T<sub>47</sub>) from different modern snail species are consistent with land surface temperatures measured during their growing season (mid-April to September at YB and mid-March to October at LB), and show minimal inter-species differences, highlighting the ecological robustness of snail-based T<sub>47</sub> reconstructions. Our intra-shell Δ<sub>47</sub>–δ<sup>18</sup>O–δ<sup>13</sup>C data show no obvious evidence of disequilibrium fractionation, supporting that land snail shell aragonite forms near isotopic equilibrium in natural settings. Notably, the reconstructed intra-shell T<sub>47</sub> profiles show a sub-annual temperature variability of 7–10 °C and potential signs of short-term thermal stress. Reconstructed body water δ<sup>18</sup>O (δ<sup>18</sup>O<sub>bw</sub>) values from whole-shells are significantly enriched (by ∼ 3–6.5 ‰, <em>p</em> < 0.05) compared to local precipitation δ<sup>18</sup>O (δ<sup>18</sup>O<sub>p</sub>), due to evaporative effects and micro-environmental conditions. Intra-shell δ<sup>18</sup>O<sub>bw</sub> profiles reveal sub-annual fluctuations that follow seasonal δ<sup>18</sup>O<sub>p</sub> patterns, capturing dry-season evaporative isotopic enrichment and wet-season depletion masked in whole-shell averages.</div><div>The T<sub>47</sub> from early Holocene and last glacial maximum (LGM)-aged shells provides geochemical evidence of a cooler growing season than today, perhaps caused by extended growing seasons during the early Holocene and climatically restricted ones during the LGM. Lower and more stable intra-shell T<sub>47</sub> and more negative δ<sup>18</sup>O<sub>bw</sub> values during the wet seasons highlight seasonal hydroclimatic shifts under glacial boundary conditions. Together, our results demonstrate the sensitivity of snail shell geochemistry to hydroclimatic seasonality and support the use of combined intra-shell δ<sup>18</sup>O and Δ<sub>47</sub> analyses to resolve climate seasonality beyond the resolution of traditional proxies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 168-182"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995743","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 : 2026-03-01Epub Date: 2026-01-16DOI: 10.1016/j.gca.2026.01.015
Mei Lu , Wei Tan , Jing Liu , Xiaoliang Liang , Stefanie M. Brueckner , Shoushu Wei , Yiping Yang , Hanliang Liu , Hongping He
<div><div>Cerium (Ce) exhibits distinctive geochemical behaviours in the group of chemically similar rare earth elements (REEs) due to its unique oxidability, making the Ce anomaly (Ce/Ce*) a powerful proxy for tracing variations in redox conditions and weathering processes. Though previous studies have investigated the genesis of Ce anomaly through simulation experiments and theoretical calculations, the detailed mineralogical characterization of field samples is still lacking, limiting the utilization of the Ce anomaly as a geochemical proxy. In this study, the geochemical and mineralogical evolution of Ce during chemical weathering was analysed through an approximately 90-meter-long drill core collected from the Huangshe ion-adsorption type REE (iREE) deposit in South China, which was further linked to the alteration of Fe and Mn (hydr)oxides. Based on the variation of chemical composition and rock texture, the whole weathering profile is divided into four layers displaying distinct Ce anomalies, i.e., topsoil (Ce/Ce* = 2.1–57.7), completely weathered horizon (Ce/Ce* = 0.03–2.88), semi-weathered horizon (Ce/Ce* = 0.90–1.34), and parent rock (Ce/Ce* = 0.90). In the parent rock, Ce-bearing minerals include allanite, titanite, apatite, bastnaesite-(Ce), synchysite-(Ce), monazite, and rhabdophane-(Ce), making up the majority of the accessory minerals. At the initial stage of weathering, the dissolution of these minerals gives rise to Ce mobility. Meanwhile, Fe-bearing minerals are dissolved, and then poorly crystalline goethite forms. The interaction between the goethite and the Ce ions immobilizes the latter to generate a slightly positive Ce anomaly. As the weathering proceed, Ce–Fe–Mn ternary-mixed (hydr)<span><span>oxide</span><svg><path></path></svg></span>s prevail in the lower completely weathered horizon. For Fe (hydr)<span><span>oxide</span><svg><path></path></svg></span>s, they are transformed from goethite into hematite, resulting in the decrease of surface hydroxyl density and specific surface area, and accordingly, the reduction of Ce uptake. As for Mn (hydr)<span><span>oxide</span><svg><path></path></svg></span>s, hausmannite promotes the oxidation of Ce<sup>3+</sup> to Ce<sup>4+</sup> via direct redox reaction, resulting in the formation of cerianite (CeO<sub>2</sub>) in the Fe–Mn–Ce composite and an increase of positive Ce anomaly. In the late weathering period, the well crystallized hematite and the cerianite eventually separate and become ubiquitous in the topsoil, resulting in the obvious Ce positive anomaly. Thus, Fe–Mn (hydr)oxides significantly constrain the migration of Ce through adsorption and oxidative scavenging. Consequently, unlike other REEs that are transported downward to the lower part of the weathering crust, Ce remains isolated in the surface zone, generating a positive Ce anomaly. Thus, the positive Ce anomaly can be utilized as a complementary geochemical exploration indicator to identify iREE deposits hosted i
{"title":"Cerium speciation and anomaly formation in mature regolith: implications for ion-adsorption type REE deposit prospecting","authors":"Mei Lu , Wei Tan , Jing Liu , Xiaoliang Liang , Stefanie M. Brueckner , Shoushu Wei , Yiping Yang , Hanliang Liu , Hongping He","doi":"10.1016/j.gca.2026.01.015","DOIUrl":"10.1016/j.gca.2026.01.015","url":null,"abstract":"<div><div>Cerium (Ce) exhibits distinctive geochemical behaviours in the group of chemically similar rare earth elements (REEs) due to its unique oxidability, making the Ce anomaly (Ce/Ce*) a powerful proxy for tracing variations in redox conditions and weathering processes. Though previous studies have investigated the genesis of Ce anomaly through simulation experiments and theoretical calculations, the detailed mineralogical characterization of field samples is still lacking, limiting the utilization of the Ce anomaly as a geochemical proxy. In this study, the geochemical and mineralogical evolution of Ce during chemical weathering was analysed through an approximately 90-meter-long drill core collected from the Huangshe ion-adsorption type REE (iREE) deposit in South China, which was further linked to the alteration of Fe and Mn (hydr)oxides. Based on the variation of chemical composition and rock texture, the whole weathering profile is divided into four layers displaying distinct Ce anomalies, i.e., topsoil (Ce/Ce* = 2.1–57.7), completely weathered horizon (Ce/Ce* = 0.03–2.88), semi-weathered horizon (Ce/Ce* = 0.90–1.34), and parent rock (Ce/Ce* = 0.90). In the parent rock, Ce-bearing minerals include allanite, titanite, apatite, bastnaesite-(Ce), synchysite-(Ce), monazite, and rhabdophane-(Ce), making up the majority of the accessory minerals. At the initial stage of weathering, the dissolution of these minerals gives rise to Ce mobility. Meanwhile, Fe-bearing minerals are dissolved, and then poorly crystalline goethite forms. The interaction between the goethite and the Ce ions immobilizes the latter to generate a slightly positive Ce anomaly. As the weathering proceed, Ce–Fe–Mn ternary-mixed (hydr)<span><span>oxide</span><svg><path></path></svg></span>s prevail in the lower completely weathered horizon. For Fe (hydr)<span><span>oxide</span><svg><path></path></svg></span>s, they are transformed from goethite into hematite, resulting in the decrease of surface hydroxyl density and specific surface area, and accordingly, the reduction of Ce uptake. As for Mn (hydr)<span><span>oxide</span><svg><path></path></svg></span>s, hausmannite promotes the oxidation of Ce<sup>3+</sup> to Ce<sup>4+</sup> via direct redox reaction, resulting in the formation of cerianite (CeO<sub>2</sub>) in the Fe–Mn–Ce composite and an increase of positive Ce anomaly. In the late weathering period, the well crystallized hematite and the cerianite eventually separate and become ubiquitous in the topsoil, resulting in the obvious Ce positive anomaly. Thus, Fe–Mn (hydr)oxides significantly constrain the migration of Ce through adsorption and oxidative scavenging. Consequently, unlike other REEs that are transported downward to the lower part of the weathering crust, Ce remains isolated in the surface zone, generating a positive Ce anomaly. Thus, the positive Ce anomaly can be utilized as a complementary geochemical exploration indicator to identify iREE deposits hosted i","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 139-153"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995730","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 : 2026-03-01Epub Date: 2026-01-20DOI: 10.1016/j.gca.2026.01.023
Yi Wang , Gabriela A. Farfan , Jeffrey E. Post , Huifang Xu , Colleen M. Hansel , Sune G. Nielsen
Manganese (Mn) oxides are important hosts of trace metals via adsorption and/or redox processes. Previous adsorption studies on synthesized Mn oxides have provided valuable insights on metal adsorption mechanisms, and yet a comparison of synthesized and natural minerals is still rare. Here we focus on thallium (Tl), a paleo-redox tracer with a major sink via Mn oxide burial, to investigate Tl adsorption and isotope fractionation on various natural minerals that have not been reported so far. We also compare our results on natural Mn oxide phases with previous adsorption experiments on synthetic phases. Adsorption experiments were performed on various natural Mn oxides with different structures and Mn oxidation states. Our results show that Mn2+ and Mn3+-rich oxides (hausmannite, feitknechtite, pyrolusite, and todorokite) have limited Tl affinity and isotopic fractionation upon adsorption. However, our data show unexpected Tl desorption and rapid isotope exchange on vernadite, leading to a much lower Tl affinity compared to synthesized structurally similar δ-MnO2. Using an isotope mass balance and X-ray absorption spectroscopy, we suggest that the observed Tl isotope exchange is likely to be non-oxidative with minor oxidative fractionation involved, which could be attributed to occupation of oxidative adsorption sites and competing adsorption by other trace metals (e.g., Co, Ni, Cu, etc). Our vernadite adsorption experiments thus suggest that Tl speciation changes may be prevalent in natural ferromanganese crusts. Should Tl desorption from vernadite occur periodically due to changes in ocean chemistry, the likely release of isotopically heavy 205Tl could complicate the use of Tl isotopes as an ocean oxygen proxy over geological history. As Mn oxides play an important role in metal biogeochemical cycles, our results highlight the necessity of additional research on desorption to better understand Tl cycling in nature and subsequent implications for interpreting paleo-redox conditions in the rock record.
{"title":"Thallium isotopic fractionation during adsorption onto natural manganese oxides: a comparison with synthesized analogs","authors":"Yi Wang , Gabriela A. Farfan , Jeffrey E. Post , Huifang Xu , Colleen M. Hansel , Sune G. Nielsen","doi":"10.1016/j.gca.2026.01.023","DOIUrl":"10.1016/j.gca.2026.01.023","url":null,"abstract":"<div><div>Manganese (Mn) oxides are important hosts of trace metals via adsorption and/or redox processes. Previous adsorption studies on synthesized Mn oxides have provided valuable insights on metal adsorption mechanisms, and yet a comparison of synthesized and natural minerals is still rare. Here we focus on thallium (Tl), a paleo-redox tracer with a major sink via Mn oxide burial, to investigate Tl adsorption and isotope fractionation on various natural minerals that have not been reported so far. We also compare our results on natural Mn oxide phases with previous adsorption experiments on synthetic phases. Adsorption experiments were performed on various natural Mn oxides with different structures and Mn oxidation states. Our results show that Mn<sup>2+</sup> and Mn<sup>3+</sup>-rich oxides (hausmannite, feitknechtite, pyrolusite, and todorokite) have limited Tl affinity and isotopic fractionation upon adsorption. However, our data show unexpected Tl desorption and rapid isotope exchange on vernadite, leading to a much lower Tl affinity compared to synthesized structurally similar δ-MnO<sub>2</sub>. Using an isotope mass balance and X-ray absorption spectroscopy, we suggest that the observed Tl isotope exchange is likely to be non-oxidative with minor oxidative fractionation involved, which could be attributed to occupation of oxidative adsorption sites and competing adsorption by other trace metals (e.g., Co, Ni, Cu, etc). Our vernadite adsorption experiments thus suggest that Tl speciation changes may be prevalent in natural ferromanganese crusts. Should Tl desorption from vernadite occur periodically due to changes in ocean chemistry, the likely release of isotopically heavy <sup>205</sup>Tl could complicate the use of Tl isotopes as an ocean oxygen proxy over geological history. As Mn oxides play an important role in metal biogeochemical cycles, our results highlight the necessity of additional research on desorption to better understand Tl cycling in nature and subsequent implications for interpreting paleo-redox conditions in the rock record.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 238-251"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146015033","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 : 2026-03-01Epub Date: 2026-01-18DOI: 10.1016/j.gca.2026.01.019
Antao Xu , Ed Hathorne , Florian Scholz , Chen Ling , Andrea Koschinsky , Martin Frank
The Amazon shelf and slope are key components of the tropical ocean margin systems, representing large reservoirs of terrestrial minerals and organic matter and important sources of trace elements to seawater. Radiogenic neodymium (Nd) and hafnium (Hf) isotopes trace continental weathering regimes and lithogenic inputs and are also used for the investigation of water mass mixing and the reconstruction of past changes in ocean circulation. However, the global oceanic Nd budget is not balanced and a substantial global Nd input component is missing. Boundary exchange along continental margins has been proposed as the dominant Nd source to the ocean, controlling its isotopic compositions of seawater. Yet, the detailed processes and magnitude of these inputs are not well constrained. By analyzing combined Nd and Hf isotope compositions and concentrations of rare earth elements and Hf along the Amazon margin, we demonstrate that the dissolution of terrigenous riverine iron-manganese (Fe-Mn) oxyhydroxides in resuspended sediments and porewaters together supply a shelf area weighted-mean net Nd flux of 8.3 × 108 g yr−1 to the near-bottom shelf waters. Our study underscores the dominant role of interactions between resuspended sediments and seawater, in particular via Fe and Mn cycling, and porewater-seawater mixing, in controlling the geochemical behavior of rare earth elements and Hf, and by inference other trace elements on the Amazon shelf. Terrigenous riverine Fe-Mn oxyhydroxide fractions of sediments on the shelves are shown to be an important source in the global oceanic Nd and Hf budgets.
亚马逊陆架和斜坡是热带海洋边缘系统的重要组成部分，是陆相矿物和有机物的大型储存库，也是海水微量元素的重要来源。放射性成因钕（Nd）和铪（Hf）同位素追踪大陆风化机制和岩石成因输入，也用于调查水团混合和重建过去海洋环流的变化。然而，全球海洋Nd收支不平衡，大量的全球Nd输入成分缺失。沿大陆边缘的边界交换被认为是海洋的主要Nd来源，控制了海水的同位素组成。然而，这些投入的详细过程和规模并没有得到很好的限制。通过分析亚马逊河边缘的Nd和Hf同位素组合以及稀土元素和Hf的浓度，我们发现陆源河流铁锰（Fe-Mn）氧溶蚀在重悬浮沉积物和孔隙水中的溶解共同为近底部陆架水域提供了8.3 × 108 g yr−1的陆架面积加权平均净Nd通量。我们的研究强调了再悬浮沉积物与海水之间的相互作用，特别是通过Fe和Mn循环以及孔隙水-海水混合，在控制亚马逊陆架上稀土元素和Hf的地球化学行为中起主导作用，并由此推断出其他微量元素。陆架沉积物的陆源河流铁锰氢氧化物组分是全球海洋Nd和Hf收支的重要来源。
{"title":"Sediment resuspension and reductive dissolution of terrigenous Fe-Mn oxides control dissolved neodymium and hafnium inputs from the Amazon shelf","authors":"Antao Xu , Ed Hathorne , Florian Scholz , Chen Ling , Andrea Koschinsky , Martin Frank","doi":"10.1016/j.gca.2026.01.019","DOIUrl":"10.1016/j.gca.2026.01.019","url":null,"abstract":"<div><div>The Amazon shelf and slope are key components of the tropical ocean margin systems, representing large reservoirs of terrestrial minerals and organic matter and important sources of trace elements to seawater. Radiogenic neodymium (Nd) and hafnium (Hf) isotopes trace continental weathering regimes and lithogenic inputs and are also used for the investigation of water mass mixing and the reconstruction of past changes in ocean circulation. However, the global oceanic Nd budget is not balanced and a substantial global Nd input component is missing. Boundary exchange along continental margins has been proposed as the dominant Nd source to the ocean, controlling its isotopic compositions of seawater. Yet, the detailed processes and magnitude of these inputs are not well constrained. By analyzing combined Nd and Hf isotope compositions and concentrations of rare earth elements and Hf along the Amazon margin, we demonstrate that the dissolution of terrigenous riverine iron-manganese (Fe-Mn) oxyhydroxides in resuspended sediments and porewaters together supply a shelf area weighted-mean net Nd flux of 8.3 × 10<sup>8</sup> g yr<sup>−1</sup> to the near-bottom shelf waters. Our study underscores the dominant role of interactions between resuspended sediments and seawater, in particular via Fe and Mn cycling, and porewater-seawater mixing, in controlling the geochemical behavior of rare earth elements and Hf, and by inference other trace elements on the Amazon shelf. Terrigenous riverine Fe-Mn oxyhydroxide fractions of sediments on the shelves are shown to be an important source in the global oceanic Nd and Hf budgets.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 1-16"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995733","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 : 2026-03-01Epub Date: 2026-01-14DOI: 10.1016/j.gca.2026.01.013
Jesse T. Gu, Rebecca A. Fischer, Lucy Jacobsen, Michail I. Petaev
Moderately volatile elements are depleted in the Earth relative to chondrites, but it remains uncertain to what extent these depletions of siderophile volatile elements are controlled by volatility versus core formation. Here, we report new metal–silicate partitioning experiments on Pb at pressures and temperatures up to 65 GPa and 5520 K, respectively. Combined with other moderately volatile elements, we use core formation models to show that homogeneous volatile accretion results in an overabundance of volatile siderophile elements relative to lithophile elements in the bulk Earth. Late volatile addition with metal–silicate equilibration at higher pressures and temperatures could potentially resolve this discrepancy by lowering bulk Earth abundances of volatile siderophile elements to be within uncertainty of the lithophile volatility trend. However, uncertainties in core formation parameters, element volatilities, volatile loss mechanisms, and the lithophile volatility trend complicate this interpretation. Our data support a relatively larger role for volatile depletion than for core formation in establishing the Pb content of the bulk silicate Earth.
{"title":"Metal–silicate partitioning of Pb and implications for the accretion of moderately volatile elements to Earth","authors":"Jesse T. Gu, Rebecca A. Fischer, Lucy Jacobsen, Michail I. Petaev","doi":"10.1016/j.gca.2026.01.013","DOIUrl":"10.1016/j.gca.2026.01.013","url":null,"abstract":"<div><div>Moderately volatile elements are depleted in the Earth relative to chondrites, but it remains uncertain to what extent these depletions of siderophile volatile elements are controlled by volatility versus core formation. Here, we report new metal–silicate partitioning experiments on Pb at pressures and temperatures up to 65 GPa and 5520 K, respectively. Combined with other moderately volatile elements, we use core formation models to show that homogeneous volatile accretion results in an overabundance of volatile siderophile elements relative to lithophile elements in the bulk Earth. Late volatile addition with metal–silicate equilibration at higher pressures and temperatures could potentially resolve this discrepancy by lowering bulk Earth abundances of volatile siderophile elements to be within uncertainty of the lithophile volatility trend. However, uncertainties in core formation parameters, element volatilities, volatile loss mechanisms, and the lithophile volatility trend complicate this interpretation. Our data support a relatively larger role for volatile depletion than for core formation in establishing the Pb content of the bulk silicate Earth.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 110-121"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995734","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 : 2026-03-01Epub Date: 2026-01-14DOI: 10.1016/j.gca.2026.01.014
Wei Wu , Yigang Xu , Zhaofeng Zhang
To constrain calcium isotopic fractionation during magma differentiation and its significance for planetary geochemistry, this study analyzed δ44/40Ca compositions of whole rocks, clinopyroxene, and plagioclase in mafic–ultramafic intrusions from two major large igneous provinces: the Tarim Large Igneous Province (Xiaohaizi intrusion) and the Emeishan Large Igneous Province (Panzhihua intrusion). Whole-rock δ44/40Ca ranges from 0.75 to 1.00 ‰ for Xiaohaizi and 0.82 to 0.97 ‰ for Panzhihua, while Pl δ44/40Ca varies from 0.69 to 1.07 ‰ (Xiaohaizi) and 0.78 to 0.99 ‰ (Panzhihua). Disequilibrium in selected samples is attributed to distinct geological processes: magma replenishment (Panzhihua) and crustal material assimilation (Xiaohaizi). For equilibrium samples, the Ca isotopic fractionation factor between Pl and melt (1000lnαPl-melt) exhibits no correlation with Pl An content and remains stable under specific temperature–pressure conditions for mafic to ultramafic plagioclase. By integrating this new dataset with published Δ44/40CaCpx-Pl data (including ab initio predictions and magmatic evolution model results), we determined 1000lnαPl-melt at 1273 K is −0.07 ± 0.10 ‰ (2SD, N = 28). This study clarifies the role of Pl in magmatic Ca isotopic fractionation, providing a reliable framework for tracing magma evolution and reconstructing early crust formation processes of terrestrial planets.
{"title":"Calcium isotopic fractionation in plagioclase from mafic-ultramafic rocks: implications for magmatic processes and planetary differentiation","authors":"Wei Wu , Yigang Xu , Zhaofeng Zhang","doi":"10.1016/j.gca.2026.01.014","DOIUrl":"10.1016/j.gca.2026.01.014","url":null,"abstract":"<div><div>To constrain calcium isotopic fractionation during magma differentiation and its significance for planetary geochemistry, this study analyzed δ<sup>44/40</sup>Ca compositions of whole rocks, clinopyroxene, and plagioclase in mafic–ultramafic intrusions from two major large igneous provinces: the Tarim Large Igneous Province (Xiaohaizi intrusion) and the Emeishan Large Igneous Province (Panzhihua intrusion). Whole-rock δ<sup>44/40</sup>Ca ranges from 0.75 to 1.00 ‰ for Xiaohaizi and 0.82 to 0.97 ‰ for Panzhihua, while Pl δ<sup>44/40</sup>Ca varies from 0.69 to 1.07 ‰ (Xiaohaizi) and 0.78 to 0.99 ‰ (Panzhihua). Disequilibrium in selected samples is attributed to distinct geological processes: magma replenishment (Panzhihua) and crustal material assimilation (Xiaohaizi). For equilibrium samples, the Ca isotopic fractionation factor between Pl and melt (1000lnα<sub>Pl-melt</sub>) exhibits no correlation with Pl An content and remains stable under specific temperature–pressure conditions for mafic to ultramafic plagioclase. By integrating this new dataset with published Δ<sup>44/40</sup>Ca<sub>Cpx-Pl</sub> data (including ab initio predictions and magmatic evolution model results), we determined 1000lnα<sub>Pl-melt</sub> at 1273 K is −0.07 ± 0.10 ‰ (2SD, N = 28). This study clarifies the role of Pl in magmatic Ca isotopic fractionation, providing a reliable framework for tracing magma evolution and reconstructing early crust formation processes of terrestrial planets.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"416 ","pages":"Pages 122-138"},"PeriodicalIF":5.0,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145995738","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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