{"title":"Rubidium isotopic evidence for sedimentary input to the mantle source of Martinique lavas from the Lesser Antilles arc","authors":"Baoliang Wang, Frédéric Moynier, Catherine Chauvel","doi":"10.1016/j.gca.2026.02.023","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.023","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"128 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146778174","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 : 2026-02-18DOI: 10.1016/j.gca.2026.02.019
Cyrena A. Goodrich, Victoria E. Hamilton, Michael E. Zolensky, Noriko Kita, Issaku Kohl, Lauren Tafla, Robert J. Macke, Takahiro Hiroi, Yoko Kebukawa, Wayne Buckley, Jacob B. Setera, Justin I. Simon, Allan H. Treiman, Jennifer S. Gorce, Harold C. Connolly Jr., Anna M. Fioretti, Edward Young, Qing-Zhu Yin, Audrey M. Miller, James Martinez, Guillaume Siron, William O. Nachlas, Takashi Tominaga, Michael Jercinovic, Peter Jenniskens, Muawia H. Shaddad
{"title":"Petrogenesis and Provenance of Unique Amphibole-Bearing Carbonaceous Chondrite Almahata Sitta 202: Further Evidence for a Ceres-Sized, Water-Rich Parent Body","authors":"Cyrena A. Goodrich, Victoria E. Hamilton, Michael E. Zolensky, Noriko Kita, Issaku Kohl, Lauren Tafla, Robert J. Macke, Takahiro Hiroi, Yoko Kebukawa, Wayne Buckley, Jacob B. Setera, Justin I. Simon, Allan H. Treiman, Jennifer S. Gorce, Harold C. Connolly Jr., Anna M. Fioretti, Edward Young, Qing-Zhu Yin, Audrey M. Miller, James Martinez, Guillaume Siron, William O. Nachlas, Takashi Tominaga, Michael Jercinovic, Peter Jenniskens, Muawia H. Shaddad","doi":"10.1016/j.gca.2026.02.019","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.019","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"46 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-02-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146778176","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 : 2026-02-16DOI: 10.1016/j.gca.2026.02.017
Si Athena Chen, Sabine M. Neumayer, Michael J. Zachman, Anton V. Ievlev, Jonathan D. Poplawsky, Tyler L. Spano, Peter J. Eng, Andrew G. Stack, Juliane Weber
Metal partitioning into calcite has important geochemical and environmental implications as its reactive surface structure exerts a strong impact on impurity mobility and distribution. Despite numerous observations that strontium (Sr) incorporation into calcite affects reaction rates, the mechanism driving enhancement/inhibition remains debated and is often described only qualitatively. To address this uncertainty, we quantified the chemical composition and lattice strain of the grown Sr-rich calcite using high-resolution chemical imaging techniques and nanoscale strain mapping. These observations were compared to in situ atomic force microscopy (AFM) measurements of the growth rate of single crystal calcite growth as a function of aqueous [Sr]/[Ca]aq ratio (0–1) with particular focus on hysteresis in growth rates after the solution composition was changed.
{"title":"Impurity incorporation and strain dynamics in calcite crystal growth: in situ analysis and multiscale chemical-strain mapping","authors":"Si Athena Chen, Sabine M. Neumayer, Michael J. Zachman, Anton V. Ievlev, Jonathan D. Poplawsky, Tyler L. Spano, Peter J. Eng, Andrew G. Stack, Juliane Weber","doi":"10.1016/j.gca.2026.02.017","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.017","url":null,"abstract":"Metal partitioning into calcite has important geochemical and environmental implications as its reactive surface structure exerts a strong impact on impurity mobility and distribution. Despite numerous observations that strontium (Sr) incorporation into calcite affects reaction rates, the mechanism driving enhancement/inhibition remains debated and is often described only qualitatively. To address this uncertainty, we quantified the chemical composition and lattice strain of the grown Sr-rich calcite using high-resolution chemical imaging techniques and nanoscale strain mapping. These observations were compared to <ce:italic>in situ</ce:italic> atomic force microscopy (AFM) measurements of the growth rate of single crystal calcite growth as a function of aqueous [Sr]/[Ca]<ce:italic><ce:inf loc=\"post\">aq</ce:inf></ce:italic> ratio (0–1) with particular focus on hysteresis in growth rates after the solution composition was changed.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"65 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146209412","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 : 2026-02-15Epub Date: 2026-01-08DOI: 10.1016/j.gca.2026.01.004
Shuai Kang , Zhihan Ji , Weiqiang Li , Jingjing Liu , Qian Wang , Na Wang , David French , Ian T. Graham , Victor P. Nechaev , James C. Hower , Jintian Zheng , Mengda Yao , Shifeng Dai
Coal, as an organic-rich sedimentary rock that records depositional, diagenetic, and hydrothermal processes, is highly susceptible to alteration by crustal fluids, resulting in significant elemental and mineralogical changes. Potassium (K), a fluid-mobile alkali element, is sensitive to hydrothermal processes. Despite growing interest in using stable K isotopes as a tracer of hydrothermal activity, studies comparing K isotope fractionation across different hydrothermal systems and evaluating their impact on K isotopic compositions in coal remain scarce. This study reports high-precision K isotope data for coals affected by two different hydrothermal events: i) magmatic hydrothermal alteration in the Daqingshan and Fengfeng coalfields (North China) and ii) submarine exhalative hydrothermal alteration in the Yishan Coalfield (South China). Coals intensely altered by magmatic hydrothermal fluids exhibit remarkably low δ41K values, ranging from − 1.92 ± 0.01 ‰ to − 0.63 ± 0.03 ‰, which are well below that of the Bulk Silicate Earth (BSE) (δ41KBSE = − 0.43 ± 0.17 ‰). In contrast, coals influenced by submarine exhalative hydrothermal fluids show markedly high δ41K values ranging from 0.18 ± 0.05 ‰ to 1.23 ± 0.04 ‰, well above modern seawater (δ41Kseawater ≈ 0.12 ‰). Such systematic difference in K isotopic composition of coals is ascribed to the formation of different ammonium-bearing secondary minerals (buddingtonite and ammonian illite) through interactions between distinct hydrothermal fluids and organic matter in coals. This study exemplifies that K isotopes can serve as a sensitive tracer for fingerprinting the history of hydrothermal activity in coal-bearing strata.
{"title":"Potassium isotopic variability in coals induced by magmatic and submarine exhalative hydrothermal activity","authors":"Shuai Kang , Zhihan Ji , Weiqiang Li , Jingjing Liu , Qian Wang , Na Wang , David French , Ian T. Graham , Victor P. Nechaev , James C. Hower , Jintian Zheng , Mengda Yao , Shifeng Dai","doi":"10.1016/j.gca.2026.01.004","DOIUrl":"10.1016/j.gca.2026.01.004","url":null,"abstract":"<div><div>Coal, as an organic-rich sedimentary rock that records depositional, diagenetic, and hydrothermal processes, is highly susceptible to alteration by crustal fluids, resulting in significant elemental and mineralogical changes. Potassium (K), a fluid-mobile alkali element, is sensitive to hydrothermal processes. Despite growing interest in using stable K isotopes as a tracer of hydrothermal activity, studies comparing K isotope fractionation across different hydrothermal systems and evaluating their impact on K isotopic compositions in coal remain scarce. This study reports high-precision K isotope data for coals affected by two different hydrothermal events: i) magmatic hydrothermal alteration in the Daqingshan and Fengfeng coalfields (North China) and ii) submarine exhalative hydrothermal alteration in the Yishan Coalfield (South China). Coals intensely altered by magmatic hydrothermal fluids exhibit remarkably low <em>δ</em><sup>41</sup>K values, ranging from − 1.92 ± 0.01 ‰ to − 0.63 ± 0.03 ‰, which are well below that of the Bulk Silicate Earth (BSE) (<em>δ</em><sup>41</sup>K<sub>BSE</sub> = − 0.43 ± 0.17 ‰). In contrast, coals influenced by submarine exhalative hydrothermal fluids show markedly high <em>δ</em><sup>41</sup>K values ranging from 0.18 ± 0.05 ‰ to 1.23 ± 0.04 ‰, well above modern seawater (<em>δ</em><sup>41</sup>K<sub>seawater</sub> ≈ 0.12 ‰). Such systematic difference in K isotopic composition of coals is ascribed to the formation of different ammonium-bearing secondary minerals (buddingtonite and ammonian illite) through interactions between distinct hydrothermal fluids and organic matter in coals. This study exemplifies that K isotopes can serve as a sensitive tracer for fingerprinting the history of hydrothermal activity in coal-bearing strata.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 25-39"},"PeriodicalIF":5.0,"publicationDate":"2026-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956572","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 : 2026-02-15Epub Date: 2025-12-28DOI: 10.1016/j.gca.2025.12.055
Zhengliang Yu , Guangjian Wu , Wei Yang , Lun Luo , Fei Li , Deji , Haiying Qiu , Yifan Pan , Xiong Xiao
Glaciation-driven enhancement of chemical weathering plays a crucial role in the long-term carbon cycle and climate evolution. Temperate glacial environments generally exhibit intense chemical weathering; however, their carbon sink effect remains debated. This study investigated two representative temperate glacial catchments in the southeastern Tibetan Plateau, Zhuxigou (debris-covered Zhuxi Glacier) and Rinong Qu (debris-free Parlung No. 4 Glacier). Suomupu Qu, a non-glacial catchment with similar lithology and climate to the glacial catchments, was also included as a reference. High-frequency monitoring over 3 years provided comprehensive hydrochemical data (524 water samples). Isotopic evidence (δ34SSO4, δ18OSO4, and δ18OH2O) indicates that sulfate (SO42−) in all catchments is primarily derived from sulfide oxidation rather than evaporite dissolution. Based on Na/Ca/Sr ratios in river water and sediments, secondary calcite precipitation removed 93 % ± 2 %, 47 % ± 9 %, and 58 % ± 18 % of dissolved Ca2+ in the Zhuxigou, Rinong Qu, and Suomupu Qu catchments, respectively, leading to a 2- to 30-fold underestimation of carbonate weathering rates. In Zhuxigou, pronounced secondary calcite precipitation occurs mainly within subglacial drainage channels and is attributed to dominant carbonate weathering, which contributes 92.5 % ± 1.0 % of the riverine cation budget. Carbonate dissolution also prevails in Rinong Qu and Suomupu Qu, accounting for 70.8 % ± 5.4 % and 59.3 % ± 11.8 % of the riverine cation budget, respectively. In contrast, silicate weathering contributes only 1.5 % ± 0.4 % to 5.9 % ± 2.6 % in glacial catchments, but increases to 30.1 % ± 9.7 % in the non-glacial Suomupu Qu catchment. The net CO2 consumption rate was calculated by subtracting CO2 consumption due to silicate weathering from CO2 release from sulfide oxidation coupled with carbonate dissolution. It was found to be positive in the non-glacial Suomupu Qu catchment (0.99 × 105 mol/km2/yr) but negative in the glacial catchments (−5.30 × 105 and −2.15 × 105 mol/km2/yr in the Zhuxigou and Rinong Qu catchments, respectively). Enhanced sulfide oxidation, fueled by intense glacial abrasion, transforms temperate glacier catchments into net CO2 sources. Extrapolated to the entire Tibetan Plateau and surrounding mountains, glacial weathering may release 2.34 × 1010 mol of CO2 annually, counteracting ∼29 % of the CO2 consumption flux by silicate weathering in major river basins of this plateau. This highlights the role of temperate glaciers as active CO2 sources in the carbon cycle.
{"title":"Chemical weathering releases substantial CO2 in temperate glacial catchments of the southeastern Tibetan Plateau","authors":"Zhengliang Yu , Guangjian Wu , Wei Yang , Lun Luo , Fei Li , Deji , Haiying Qiu , Yifan Pan , Xiong Xiao","doi":"10.1016/j.gca.2025.12.055","DOIUrl":"10.1016/j.gca.2025.12.055","url":null,"abstract":"<div><div>Glaciation-driven enhancement of chemical weathering plays a crucial role in the long-term carbon cycle and climate evolution. Temperate glacial environments generally exhibit intense chemical weathering; however, their carbon sink effect remains debated. This study investigated two representative temperate glacial catchments in the southeastern Tibetan Plateau, Zhuxigou (debris-covered Zhuxi Glacier) and Rinong Qu (debris-free Parlung No. 4 Glacier). Suomupu Qu, a non-glacial catchment with similar lithology and climate to the glacial catchments, was also included as a reference. High-frequency monitoring over 3 years provided comprehensive hydrochemical data (524 water samples). Isotopic evidence (δ<sup>34</sup>S<sub>SO4</sub>, δ<sup>18</sup>O<sub>SO4</sub>, and δ<sup>18</sup>O<sub>H2O</sub>) indicates that sulfate (SO<sub>4</sub><sup>2−</sup>) in all catchments is primarily derived from sulfide oxidation rather than evaporite dissolution. Based on Na/Ca/Sr ratios in river water and sediments, secondary calcite precipitation removed 93 % ± 2 %, 47 % ± 9 %, and 58 % ± 18 % of dissolved Ca<sup>2+</sup> in the Zhuxigou, Rinong Qu, and Suomupu Qu catchments, respectively, leading to a 2- to 30-fold underestimation of carbonate weathering rates. In Zhuxigou, pronounced secondary calcite precipitation occurs mainly within subglacial drainage channels and is attributed to dominant carbonate weathering, which contributes 92.5 % ± 1.0 % of the riverine cation budget. Carbonate dissolution also prevails in Rinong Qu and Suomupu Qu, accounting for 70.8 % ± 5.4 % and 59.3 % ± 11.8 % of the riverine cation budget, respectively. In contrast, silicate weathering contributes only 1.5 % ± 0.4 % to 5.9 % ± 2.6 % in glacial catchments, but increases to 30.1 % ± 9.7 % in the non-glacial Suomupu Qu catchment. The net CO<sub>2</sub> consumption rate was calculated by subtracting CO<sub>2</sub> consumption due to silicate weathering from CO<sub>2</sub> release from sulfide oxidation coupled with carbonate dissolution. It was found to be positive in the non-glacial Suomupu Qu catchment (0.99 × 10<sup>5</sup> mol/km<sup>2</sup>/yr) but negative in the glacial catchments (−5.30 × 10<sup>5</sup> and −2.15 × 10<sup>5</sup> mol/km<sup>2</sup>/yr in the Zhuxigou and Rinong Qu catchments, respectively). Enhanced sulfide oxidation, fueled by intense glacial abrasion, transforms temperate glacier catchments into net CO<sub>2</sub> sources. Extrapolated to the entire Tibetan Plateau and surrounding mountains, glacial weathering may release 2.34 × 10<sup>10</sup> mol of CO<sub>2</sub> annually, counteracting ∼29 % of the CO<sub>2</sub> consumption flux by silicate weathering in major river basins of this plateau. This highlights the role of temperate glaciers as active CO<sub>2</sub> sources in the carbon cycle.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 266-282"},"PeriodicalIF":5.0,"publicationDate":"2026-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145895636","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}
Analysis of carbonate minerals in ungrouped carbonaceous chondrites offer valuable insights into the geological activity on a diverse range of early-formed, hydrated planetesimals in the outer Solar System. Essebi is a C2-ung chondrite, which originated from a water-rich asteroid with close affinities to the CM chondrites group. We performed a detailed geochemical, petrographic and isotopic study of Essebi. Modal mineralogy demonstrates that Essebi is dominated by a poorly crystalline, fine-grained phyllosilicate matrix (mostly a mix of saponite and serpentine ∼63 vol%) with a modest quantity of anhydrous silicates (20 vol%) and accessory magnetite (7.5 vol%), Fe-sulphides (5.5 vol%) and carbonates (2 vol%). Its bulk O-isotope composition (2.71 ‰ δ17O (± 0.018 1σ), 8.11 ‰ δ18O (± 0.002 1σ) and −1.53 ‰ Δ17O (± 0.017 1σ) and 2.56 ‰ δ17O (± 0.040 1σ), 7.65 ‰ δ18O (± 0.009 1σ) and −1.42 ‰ Δ17O (± 0.039 1σ)) places Essebi as part of the “CM field”, although overlapping with the “CR field”. Petrographic observations reveal multiple generations of carbonate that formed both before and after brecciation, exhibiting distinct characteristics that differ from the carbonates found in established groups (CMs). Essebi’s carbonate generations have distinct morphologies and C- and O- isotope compositions and, based on these data, are interpreted as two main generations and a series of other localised carbonate expressions.
The first generation (GA) carbonates formed prior to phyllosilicate growth, and have inferred maximum formation temperatures of +45 °C. They formed under high water-to-rock (W/R) ratios. The second generation (GB) carbonates show lower W/R ratios and at higher, although unquantified temperatures. They formed near the end of the alteration sequence from a residual fluid containing abundant dissolved cations. In addition to the two main generations, we identified a third population of vein carbonates (GC) that partially infilled fractures generated by brecciation. We also identified dolomite (GD) grains found exclusively within an xenolithic clast. This clast displays a more advanced stage of alteration (C1-ung) and shows evidence of fluid leaching after being embedded, resulting in the formation of a localized ring of calcites, referred to as GE, that remain distinct from all other carbonates in this sample.
Despite textural differences, the isotopic trends observed in these Essebi carbonates closely resemble the sequence described by T1 and T2 calcites in CM chondrites, suggesting that multiple distinct episodes of carbonate precipitation, aqueous alteration along a prograde metasomatic sequence, and isotopic evolution from 16O-poor to 16O-rich trajectories were common across several water-rich planetesimals that formed in the outer Solar System.
{"title":"Fluid history in the ungrouped C2 Essebi meteorite parent body","authors":"L.J. Riches , M.D. Suttle , I.A. Franchi , X. Zhao , M.M. Grady","doi":"10.1016/j.gca.2025.12.035","DOIUrl":"10.1016/j.gca.2025.12.035","url":null,"abstract":"<div><div>Analysis of carbonate minerals in ungrouped carbonaceous chondrites offer valuable insights into the geological activity on a diverse range of early-formed, hydrated planetesimals in the outer Solar System. Essebi is a C2-ung chondrite, which originated from a water-rich asteroid with close affinities to the CM chondrites group. We performed a detailed geochemical, petrographic and isotopic study of Essebi. Modal mineralogy demonstrates that Essebi is dominated by a poorly crystalline, fine-grained phyllosilicate matrix (mostly a mix of saponite and serpentine ∼63 vol%) with a modest quantity of anhydrous silicates (20 vol%) and accessory magnetite (7.5 vol%), Fe-sulphides (5.5 vol%) and carbonates (2 vol%). Its bulk O-isotope composition (2.71 ‰ δ<sup>17</sup>O (± 0.018 1σ), 8.11 ‰ δ<sup>18</sup>O (± 0.002 1σ) and −1.53 ‰ Δ<sup>17</sup>O (± 0.017 1σ) and 2.56 ‰ δ<sup>17</sup>O (± 0.040 1σ), 7.65 ‰ δ<sup>18</sup>O (± 0.009 1σ) and −1.42 ‰ Δ<sup>17</sup>O (± 0.039 1σ)) places Essebi as part of the “CM field”, although overlapping with the “CR field”. Petrographic observations reveal multiple generations of carbonate that formed both before and after brecciation, exhibiting distinct characteristics that differ from the carbonates found in established groups (CMs). Essebi’s carbonate generations have distinct morphologies and C- and O- isotope compositions and, based on these data, are interpreted as two main generations and a series of other localised carbonate expressions.</div><div>The first generation (GA) carbonates formed prior to phyllosilicate growth, and have inferred maximum formation temperatures of +45 °C. They formed under high water-to-rock (W/R) ratios. The second generation (GB) carbonates show lower W/R ratios and at higher, although unquantified temperatures. They formed near the end of the alteration sequence from a residual fluid containing abundant dissolved cations. In addition to the two main generations, we identified a third population of vein carbonates (GC) that partially infilled fractures generated by brecciation. We also identified dolomite (GD) grains found exclusively within an xenolithic clast. This clast displays a more advanced stage of alteration (C1-ung) and shows evidence of fluid leaching after being embedded, resulting in the formation of a localized ring of calcites, referred to as GE, that remain distinct from all other carbonates in this sample.</div><div>Despite textural differences, the isotopic trends observed in these Essebi carbonates closely resemble the sequence described by T1 and T2 calcites in CM chondrites, suggesting that multiple distinct episodes of carbonate precipitation, aqueous alteration along a prograde metasomatic sequence, and isotopic evolution from <sup>16</sup>O-poor to <sup>16</sup>O-rich trajectories were common across several water-rich planetesimals that formed in the outer Solar System.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 146-165"},"PeriodicalIF":5.0,"publicationDate":"2026-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785265","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 : 2026-02-15Epub Date: 2025-12-23DOI: 10.1016/j.gca.2025.12.051
Martin R. Lee , Sammy Griffin , Ross Findlay , Xuchao Zhao , Ian A. Franchi
The CM2 meteorites Grove Mountains (GRV) 021536, Murchison, and Shidian, contain anhydrous lithic clasts that have been interpreted as fragments of a planetesimal linked to CM or CV group carbonaceous chondrites. Here we describe 57 lithic clasts in Cold Bokkeveld (CM2) that are strikingly similar to those in the other three CMs in their petrography, mineralogy, and chemical and isotopic compositions. The Cold Bokkeveld clasts are dominated by equilibrated olivine, with subordinate plagioclase feldspar (andesine), clinopyroxene (diopside), nepheline, a spinel-group oxide (ferrian chromite), pentlandite, pyrrhotite, troilite and merrillite. Their bulk chemical composition is chondritic, and olivine oxygen isotope values span a wide range, from δ18O 3.6 ‰ Δ17O −3.9 ‰ to δ18O 20.3 ‰ Δ17O 1.1 ‰. Two clusters of clasts can potentially be distinguished from the chemical composition of their olivine: Fa38 and Fa41. The Fa38 cluster includes most of Cold Bokkeveld’s clasts and is close in chemical composition to those described from GRV 021526 and Murchison. The Fa41 cluster is represented by the largest Cold Bokkeveld clast, and its olivine is compositionally comparable to that in Shidian. Anhydrous lithic clasts that occur in all four of the CM meteorites are likely to have been derived from a large planetesimal with CM and CY affinities that had undergone thermal metamorphism and metasomatism. The CV3 breccias Mokoia and Yamato 86009 contain anhydrous lithic clasts that are close in mineralogy and oxygen isotopic composition to those in the four CMs and so are likely to have been sourced from the same carbonaceous planetesimal or one with a similar geological history. The oxygen isotopic compositions of olivine in clasts from GRV 021536, Murchison, Shidian, Cold Bokkeveld, Mokoia and Yamato 86009 plot on a shared trendline in 3-oxygen isotope space that connects the CV-CK-CO, CM, and CY fields thus suggesting genetic or evolutionary links between the five carbonaceous chondrite groups. The occurrence of these distinctive clasts in four CM2 meteorites could indicate that their parent body was the same rubble pile asteroid that had been built from aqueously altered and thermally metamorphosed lithologies.
{"title":"Anhydrous lithic clasts in four CM2 carbonaceous chondrites derived from a thermally metamorphosed planetesimal with CM and CY affinities","authors":"Martin R. Lee , Sammy Griffin , Ross Findlay , Xuchao Zhao , Ian A. Franchi","doi":"10.1016/j.gca.2025.12.051","DOIUrl":"10.1016/j.gca.2025.12.051","url":null,"abstract":"<div><div>The CM2 meteorites Grove Mountains (GRV) 021536, Murchison, and Shidian, contain anhydrous lithic clasts that have been interpreted as fragments of a planetesimal linked to CM or CV group carbonaceous chondrites. Here we describe 57 lithic clasts in Cold Bokkeveld (CM2) that are strikingly similar to those in the other three CMs in their petrography, mineralogy, and chemical and isotopic compositions. The Cold Bokkeveld clasts are dominated by equilibrated olivine, with subordinate plagioclase feldspar (andesine), clinopyroxene (diopside), nepheline, a spinel-group oxide (ferrian chromite), pentlandite, pyrrhotite, troilite and merrillite. Their bulk chemical composition is chondritic, and olivine oxygen isotope values span a wide range, from δ<sup>18</sup>O 3.6 ‰ Δ<sup>17</sup>O −3.9 ‰ to δ<sup>18</sup>O 20.3 ‰ Δ<sup>17</sup>O 1.1 ‰. Two clusters of clasts can potentially be distinguished from the chemical composition of their olivine: Fa<sub>38</sub> and Fa<sub>41</sub>. The Fa<sub>38</sub> cluster includes most of Cold Bokkeveld’s clasts and is close in chemical composition to those described from GRV 021526 and Murchison. The Fa<sub>41</sub> cluster is represented by the largest Cold Bokkeveld clast, and its olivine is compositionally comparable to that in Shidian. Anhydrous lithic clasts that occur in all four of the CM meteorites are likely to have been derived from a large planetesimal with CM and CY affinities that had undergone thermal metamorphism and metasomatism. The CV3 breccias Mokoia and Yamato 86009 contain anhydrous lithic clasts that are close in mineralogy and oxygen isotopic composition to those in the four CMs and so are likely to have been sourced from the same carbonaceous planetesimal or one with a similar geological history. The oxygen isotopic compositions of olivine in clasts from GRV 021536, Murchison, Shidian, Cold Bokkeveld, Mokoia and Yamato 86009 plot on a shared trendline in 3-oxygen isotope space that connects the CV-CK-CO, CM, and CY fields thus suggesting genetic or evolutionary links between the five carbonaceous chondrite groups. The occurrence of these distinctive clasts in four CM2 meteorites could indicate that their parent body was the same rubble pile asteroid that had been built from aqueously altered and thermally metamorphosed lithologies.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 235-251"},"PeriodicalIF":5.0,"publicationDate":"2026-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145823788","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 : 2026-02-15Epub Date: 2025-12-17DOI: 10.1016/j.gca.2025.12.033
Katherine L. French , Paul C. Hackley , Erik A. Sperling
Green sulfur bacteria biomarkers that indicate euxinia within the photic zone sometimes co-occur with evidence of contradictory depositional redox conditions, such as oxygen-requiring fossils or bioturbation. Intermittent euxinia may explain this apparent contradiction, and recent studies of modern environments show that green sulfur bacteria dwell in transiently euxinic settings. As a result, new approaches are needed to distinguish green sulfur bacteria biomarkers indicative of persistent versus intermittent euxina in ancient sedimentary samples, which this study addresses by investigating how the distribution of isorenieratene derivatives relates to depositional redox conditions. To accomplish this objective, this study focuses on two drill cores through the Upper Cretaceous Mowry Shale and the Eagle Ford Group. These drill cores are comparably thermally immature according to vitrinite reflectance data, and these formations in these cores capture a spectrum of depositional redox conditions according to multiple organic and inorganic proxies, including newly acquired iron speciation and kerogen organic sulfur data. The results presented here reveal that higher molecular weight diagenetic products of isorenieratene are preferentially preserved under persistent euxinia compared to intermittently euxinic intervals that contain isorenieratene derivatives that are shifted to lower molecular weights. Further, the total inventory of aromatic carotenoid diagenetic products contains features that can be used to identify green sulfur bacteria biomarkers from reworked petrogenic sources. Accordingly, the diagenetic fate of isorenieratene and the distribution of its diagenetic products distinguish persistent versus intermittent euxinia, which can be used to sharpen our evaluation of euxinia in the geologic record.
{"title":"Differentiating persistent and intermittent euxinia from the molecular derivatives of green sulfur bacteria carotenoids","authors":"Katherine L. French , Paul C. Hackley , Erik A. Sperling","doi":"10.1016/j.gca.2025.12.033","DOIUrl":"10.1016/j.gca.2025.12.033","url":null,"abstract":"<div><div>Green sulfur bacteria biomarkers that indicate euxinia within the photic zone sometimes co-occur with evidence of contradictory depositional redox conditions, such as oxygen-requiring fossils or bioturbation. Intermittent euxinia may explain this apparent contradiction, and recent studies of modern environments show that green sulfur bacteria dwell in transiently euxinic settings. As a result, new approaches are needed to distinguish green sulfur bacteria biomarkers indicative of persistent versus intermittent euxina in ancient sedimentary samples, which this study addresses by investigating how the distribution of isorenieratene derivatives relates to depositional redox conditions. To accomplish this objective, this study focuses on two drill cores through the Upper Cretaceous Mowry Shale and the Eagle Ford Group. These drill cores are comparably thermally immature according to vitrinite reflectance data, and these formations in these cores capture a spectrum of depositional redox conditions according to multiple organic and inorganic proxies, including newly acquired iron speciation and kerogen organic sulfur data. The results presented here reveal that higher molecular weight diagenetic products of isorenieratene are preferentially preserved under persistent euxinia compared to intermittently euxinic intervals that contain isorenieratene derivatives that are shifted to lower molecular weights. Further, the total inventory of aromatic carotenoid diagenetic products contains features that can be used to identify green sulfur bacteria biomarkers from reworked petrogenic sources. Accordingly, the diagenetic fate of isorenieratene and the distribution of its diagenetic products distinguish persistent versus intermittent euxinia, which can be used to sharpen our evaluation of euxinia in the geologic record.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 130-145"},"PeriodicalIF":5.0,"publicationDate":"2026-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785266","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 : 2026-02-15Epub Date: 2025-12-06DOI: 10.1016/j.gca.2025.12.003
Zhaojie Yu , Zehua Song , Xiaojie Tang , David J. Wilson , Germain Bayon , Yi Huang , Xiaoying Kang , Hualong Jin , Shiming Wan , Christophe Colin
Continental weathering of silicate rocks has long been proposed as an important regulator of Earth’s climate over geological timescales. However, whether silicate weathering fluxes have increased, decreased, or remained unchanged during the Cenozoic, and across glacial-interglacial cycles, remains under debate. A major source of uncertainty stems from the multiple controls on weathering proxies and a lack of consistency between existing records. Seawater neodymium (Nd) isotopes have been extensively used to trace the mixing and evolution of water masses in the open ocean. Here, an emerging application of seawater Nd isotopes to trace continental weathering inputs based on marine sediment records from marginal settings is reviewed and applied to the northern Indian Ocean. Seawater Nd isotope observations and reconstructions in the Bay of Bengal spanning a range of timescales (modern – millennial – orbital – tectonic) reveal a strong influence of South Asian continental weathering inputs, which may be related to drivers such as Himalayan tectonic uplift and monsoon precipitation. The long-term evolution of seawater Nd isotopes in the Bay of Bengal has the potential to trace the evolving Himalayan weathering inputs since the Oligocene, and to reveal the links between tectonics, climate, and weathering, while there were also weathering changes on orbital timescales in the Pleistocene. While demonstrating the strong potential of marginal seawater Nd isotopes in tracing past continental weathering inputs, more research on particle-seawater interaction processes and on the quantitative relationship between Nd isotopes and weathering inputs is still needed.
{"title":"Neodymium isotopes in marginal seawater trace continental weathering inputs","authors":"Zhaojie Yu , Zehua Song , Xiaojie Tang , David J. Wilson , Germain Bayon , Yi Huang , Xiaoying Kang , Hualong Jin , Shiming Wan , Christophe Colin","doi":"10.1016/j.gca.2025.12.003","DOIUrl":"10.1016/j.gca.2025.12.003","url":null,"abstract":"<div><div>Continental weathering of silicate rocks has long been proposed as an important regulator of Earth’s climate over geological timescales. However, whether silicate weathering fluxes have increased, decreased, or remained unchanged during the Cenozoic, and across glacial-interglacial cycles, remains under debate. A major source of uncertainty stems from the multiple controls on weathering proxies and a lack of consistency between existing records. Seawater neodymium (Nd) isotopes have been extensively used to trace the mixing and evolution of water masses in the open ocean. Here, an emerging application of seawater Nd isotopes to trace continental weathering inputs based on marine sediment records from marginal settings is reviewed and applied to the northern Indian Ocean. Seawater Nd isotope observations and reconstructions in the Bay of Bengal spanning a range of timescales (modern – millennial – orbital – tectonic) reveal a strong influence of South Asian continental weathering inputs, which may be related to drivers such as Himalayan tectonic uplift and monsoon precipitation. The long-term evolution of seawater Nd isotopes in the Bay of Bengal has the potential to trace the evolving Himalayan weathering inputs since the Oligocene, and to reveal the links between tectonics, climate, and weathering, while there were also weathering changes on orbital timescales in the Pleistocene. While demonstrating the strong potential of marginal seawater Nd isotopes in tracing past continental weathering inputs, more research on particle-seawater interaction processes and on the quantitative relationship between Nd isotopes and weathering inputs is still needed.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 313-326"},"PeriodicalIF":5.0,"publicationDate":"2026-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145689930","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 : 2026-02-15Epub Date: 2026-01-08DOI: 10.1016/j.gca.2026.01.001
Jianjiang Zhu , Lu Zhang , Huijuan Li , Runze Jiang , Lifei Zhang , Renbiao Tao
The sulfur cycle in subduction zones is crucial for modulating the redox evolution of the mantle wedge. The trisulfur radical ion (S3•‾) has been proposed as a dominant carrier of ore–forming elements in subduction zone fluids. However, existing high P–T experiments have primarily focused on S3•‾ stability in pure aqueous sulfide–sulfate systems. The role of iron sulfidation on S–rich fluids in subduction zone rocks, which may influence S3•‾ stability, remains poorly understood. In this study, we systematically investigated the impact of iron/iron oxides on S3•‾ stability in subduction-zone fluids using in situ high P–T experiments and thermodynamic simulations. Our results reveal that in pure aqueous systems containing both SO42− and S2−, S3•‾ is the dominant sulfur species at temperatures above 350 °C along typical subduction P–T paths. However, the introduction of Fe or FeO into these S3•‾–rich fluids triggers sulfidation reactions that lead to the precipitation of sulfide minerals (e.g., pyrite, pyrrhotite), substantially reducing S3•‾ stability in the fluid phase. In contrast, Fe2O3 has little effect on S3•‾ stability due to the formation of a passivating pyrite layer, which inhibits further sulfidation. Additional thermodynamic modeling suggests that the mobility of S3•‾ and associated metal ions in subduction zones is only feasible under high fluid/rock (F/R) ratios and may be tightly regulated by channelized fluid flow.
{"title":"The effect of iron sulfidation on the stability of the trisulfur radical ion S3•‾ in subduction zone fluids","authors":"Jianjiang Zhu , Lu Zhang , Huijuan Li , Runze Jiang , Lifei Zhang , Renbiao Tao","doi":"10.1016/j.gca.2026.01.001","DOIUrl":"10.1016/j.gca.2026.01.001","url":null,"abstract":"<div><div>The sulfur cycle in subduction zones is crucial for modulating the redox evolution of the mantle wedge. The trisulfur radical ion (S<sub>3</sub>•‾) has been proposed as a dominant carrier of ore–forming elements in subduction zone fluids. However, existing high P–T experiments have primarily focused on S<sub>3</sub>•‾ stability in pure aqueous sulfide–sulfate systems. The role of iron sulfidation on S–rich fluids in subduction zone rocks, which may influence S<sub>3</sub>•‾ stability, remains poorly understood. In this study, we systematically investigated the impact of iron/iron oxides on S<sub>3</sub>•‾ stability in subduction-zone fluids using in situ high P–T experiments and thermodynamic simulations. Our results reveal that in pure aqueous systems containing both SO<sub>4</sub><sup>2−</sup> and S<sup>2−</sup>, S<sub>3</sub>•‾ is the dominant sulfur species at temperatures above 350 °C along typical subduction P–T paths. However, the introduction of Fe or FeO into these S<sub>3</sub>•‾–rich fluids triggers sulfidation reactions that lead to the precipitation of sulfide minerals (e.g., pyrite, pyrrhotite), substantially reducing S<sub>3</sub>•‾ stability in the fluid phase. In contrast, Fe<sub>2</sub>O<sub>3</sub> has little effect on S<sub>3</sub>•‾ stability due to the formation of a passivating pyrite layer, which inhibits further sulfidation. Additional thermodynamic modeling suggests that the mobility of S<sub>3</sub>•‾ and associated metal ions in subduction zones is only feasible under high fluid/rock (F/R) ratios and may be tightly regulated by channelized fluid flow.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"415 ","pages":"Pages 40-55"},"PeriodicalIF":5.0,"publicationDate":"2026-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145956566","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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