Pub Date : 2026-03-10DOI: 10.1016/j.gca.2026.03.010
Ekaterina Rojas-Kolomiets, Michael Bizimis, Gene Yogodzinski, Ally Peccia, Terry Plank, Sune Nielsen
{"title":"Mo isotopes in Aleutian sediments: serpentinite-eclogite-sediment mixing and slab depth controls in arc magmas","authors":"Ekaterina Rojas-Kolomiets, Michael Bizimis, Gene Yogodzinski, Ally Peccia, Terry Plank, Sune Nielsen","doi":"10.1016/j.gca.2026.03.010","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.010","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"16 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147447945","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 : 2026-03-10DOI: 10.1016/j.gca.2026.03.012
Joshua Anadu, Nivedita Thiagarajan, Yanhua Shuai, Hao Xie, Oliver Warr, Barbara Sherwood Lollar, John Eiler
Non-methane hydrocarbons in the earth are predominantly sourced from the thermal degradation of organic matter (thermogenesis). Abiogenic polymerization has been proposed as an alternative mechanism of hydrocarbon creation in Precambrian shields, based on differences in carbon and hydrogen isotopic compositions between co-existing compounds. However, inverse isotopic signatures have been observed in thermogenic systems, suggesting this evidence is ambiguous. Prior work suggested low values of Δ13C2H6 (a measure of the departure from stochastic abundances of 13C13CH6) in ethane recovered from Kidd Creek formation waters are consistent with formation via abiotic polymerization (Taguchi et al., 2022). We have developed dual clumped isotopic measurements (Δ13C2H6 and Δ12C13CH5D) in ethane to investigate the sources and processes involved in the creation and destruction of terrestrial ethane from petroleum fields, fracture fluids from the Canadian Shield, and other sources. Our results suggest that ethanes created from all studied formation pathways and not subjected to subsequent intense heating are characterized by disequilibrated intermolecular and intramolecular isotope signatures. In low maturity thermogenic gases, both kinetic isotope effects and source inheritance can impart strongly disequilibrated Δ12C13CH5D signatures in product ethane, resulting in at least two distinct and recognizable thermogenic end members. Low Δ13C2H6 and Δ12C13CH5D signatures at Kidd Creek on the Canadian Shield are distinct from thermogenic ethanes and consistent with radical-mediated polymerization, favoring interpretation of abiotic origins. Δ12C13CH5D values for thermogenic ethanes approach equilibrium with increasing thermal maturity, consistent with suggestions from other intramolecular and intermolecular isotopic signatures in hydrocarbon systems that suggest partial equilibration through ‘metathetic’ chemical cycles (e.g., radical reaction networks) or interaction with solid catalysts.
地球上的非甲烷碳氢化合物主要来源于有机物的热降解（生热作用）。基于共存化合物之间碳、氢同位素组成的差异，非生物聚合被认为是前寒武纪盾构中另一种生烃机制。然而，在产热系统中观察到逆同位素特征，表明这一证据是不明确的。先前的工作表明，从Kidd Creek地层水中回收的乙烷中Δ13C2H6的低值（13C13CH6随机丰度偏离的测量值）与通过非生物聚合形成的地层相一致（Taguchi et al., 2022）。我们已经开发了乙烷的双团块同位素测量（Δ13C2H6和Δ12C13CH5D），以研究油田、加拿大地盾和其他来源的裂缝流体中陆生乙烷的产生和破坏的来源和过程。我们的研究结果表明，从所有研究的形成途径产生的乙烷，没有受到随后的强烈加热，具有不平衡的分子间和分子内同位素特征。在低成熟度热成因气体中，动力学同位素效应和源继承都可以在产物乙烷中赋予强烈的不平衡Δ12C13CH5D特征，导致至少两个不同且可识别的热成因端元。加拿大地盾基德溪的低Δ13C2H6和Δ12C13CH5D特征与产热乙烷不同，与自由基介导的聚合一致，有利于解释非生物起源。随着热成熟度的增加，产热乙烷的Δ12C13CH5D值接近平衡，这与碳氢化合物系统中其他分子内和分子间同位素特征的建议一致，这些特征表明通过“元合成”化学循环（例如自由基反应网络）或与固体催化剂的相互作用实现部分平衡。
{"title":"Investigating terrestrial ethane sources with molecular-average and clumped isotopes","authors":"Joshua Anadu, Nivedita Thiagarajan, Yanhua Shuai, Hao Xie, Oliver Warr, Barbara Sherwood Lollar, John Eiler","doi":"10.1016/j.gca.2026.03.012","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.012","url":null,"abstract":"Non-methane hydrocarbons in the earth are predominantly sourced from the thermal degradation of organic matter (thermogenesis). Abiogenic polymerization has been proposed as an alternative mechanism of hydrocarbon creation in Precambrian shields, based on differences in carbon and hydrogen isotopic compositions between co-existing compounds. However, inverse isotopic signatures have been observed in thermogenic systems, suggesting this evidence is ambiguous. Prior work suggested low values of Δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">2</ce:inf>H<ce:inf loc=\"post\">6</ce:inf> (a measure of the departure from stochastic abundances of <ce:sup loc=\"post\">13</ce:sup>C<ce:sup loc=\"post\">13</ce:sup>CH<ce:inf loc=\"post\">6</ce:inf>) in ethane recovered from Kidd Creek formation waters are consistent with formation via abiotic polymerization (Taguchi et al., 2022). We have developed dual clumped isotopic measurements (Δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">2</ce:inf>H<ce:inf loc=\"post\">6</ce:inf> and Δ<ce:sup loc=\"post\">12</ce:sup>C<ce:sup loc=\"post\">13</ce:sup>CH<ce:inf loc=\"post\">5</ce:inf>D) in ethane to investigate the sources and processes involved in the creation and destruction of terrestrial ethane from petroleum fields, fracture fluids from the Canadian Shield, and other sources. Our results suggest that ethanes created from all studied formation pathways and not subjected to subsequent intense heating are characterized by disequilibrated intermolecular and intramolecular isotope signatures. In low maturity thermogenic gases, both kinetic isotope effects and source inheritance can impart strongly disequilibrated Δ<ce:sup loc=\"post\">12</ce:sup>C<ce:sup loc=\"post\">13</ce:sup>CH<ce:inf loc=\"post\">5</ce:inf>D signatures in product ethane, resulting in at least two distinct and recognizable thermogenic end members. Low Δ<ce:sup loc=\"post\">13</ce:sup>C<ce:inf loc=\"post\">2</ce:inf>H<ce:inf loc=\"post\">6</ce:inf> and Δ<ce:sup loc=\"post\">12</ce:sup>C<ce:sup loc=\"post\">13</ce:sup>CH<ce:inf loc=\"post\">5</ce:inf>D signatures at Kidd Creek on the Canadian Shield are distinct from thermogenic ethanes and consistent with radical-mediated polymerization, favoring interpretation of abiotic origins. Δ<ce:sup loc=\"post\">12</ce:sup>C<ce:sup loc=\"post\">13</ce:sup>CH<ce:inf loc=\"post\">5</ce:inf>D values for thermogenic ethanes approach equilibrium with increasing thermal maturity, consistent with suggestions from other intramolecular and intermolecular isotopic signatures in hydrocarbon systems that suggest partial equilibration through ‘metathetic’ chemical cycles (e.g., radical reaction networks) or interaction with solid catalysts.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"25 1 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147392970","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 : 2026-03-10DOI: 10.1016/j.gca.2026.03.006
Wei Wang, Chao Li, Matthew S. Dodd, Hao Xu, Meng Cheng, Zihu Zhang, Chunxia Yang, Jun Hu, Haiyang Wang, Xinyang Chen, Adrian Immenhauser
{"title":"Carbonate-associated fluorescent dissolved organic matter (CAFDOM): Establishing a new proxy for dissolved organic matter in ancient oceans","authors":"Wei Wang, Chao Li, Matthew S. Dodd, Hao Xu, Meng Cheng, Zihu Zhang, Chunxia Yang, Jun Hu, Haiyang Wang, Xinyang Chen, Adrian Immenhauser","doi":"10.1016/j.gca.2026.03.006","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.006","url":null,"abstract":"","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"9 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147447943","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 : 2026-03-07DOI: 10.1016/j.gca.2026.03.003
Philip A.E. Pogge von Strandmann, Silke Voigt, Ying Zhou, Denis Scholz, Wolfgang Müller, Anthony Dosseto, Frank Sirocko
Chemical weathering of silicate rocks is a fundamental control on the carbon cycle, although on timescales shorter than a few tens of kyr, transient carbon storage becomes more important. However, weathering can still act as an amplifier or inhibitor of the carbon cycle on these timescales. Further, weathering produces soils, a storage reservoir of carbon, although the rate at which soils can be produced is likely highly variable, and remains uncertain. Here, we use lithium isotopes in laminated maar sediments from western Germany to examine weathering and soil formation rates, principally across the rapid warming transitions of Greenland Interstadials (GI), also known as Dansgaard Oeschger (D/O) events, and rapid cooling of Greenland Stadials (GS). Our principal finding is that Li isotope ratios are higher during cooler periods, both on glacial-interglacial and GI-GS event scales. Thus, δ7Li values average −2.5 ± 1.6‰ during GI events, and −1.5 ± 1.5‰ in the intervening colder stadial events. Based on the evolution of Li isotopes with weathering, this suggests that there was more soil formation relative to primary mineral dissolution during cooler compared to warmer events. That is not to say that weathering rates were higher, but that clay formation was amplified relative to a given weathering rate when it was cooler, due to the combination of lower erosion rates, thermodynamically favoured conditions for clay formation, and enhanced water–rock contact times, promoting secondary mineral formation. Overall, the data show that soil formation responds even through rapid (∼100 years) climate change events.
{"title":"Soil formation and weathering over the past 60 kyr reconstructed using lithium isotopes from Maar records","authors":"Philip A.E. Pogge von Strandmann, Silke Voigt, Ying Zhou, Denis Scholz, Wolfgang Müller, Anthony Dosseto, Frank Sirocko","doi":"10.1016/j.gca.2026.03.003","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.003","url":null,"abstract":"Chemical weathering of silicate rocks is a fundamental control on the carbon cycle, although on timescales shorter than a few tens of kyr, transient carbon storage becomes more important. However, weathering can still act as an amplifier or inhibitor of the carbon cycle on these timescales. Further, weathering produces soils, a storage reservoir of carbon, although the rate at which soils can be produced is likely highly variable, and remains uncertain. Here, we use lithium isotopes in laminated maar sediments from western Germany to examine weathering and soil formation rates, principally across the rapid warming transitions of Greenland Interstadials (GI), also known as Dansgaard Oeschger (D/O) events, and rapid cooling of Greenland Stadials (GS). Our principal finding is that Li isotope ratios are higher during cooler periods, both on glacial-interglacial and GI-GS event scales. Thus, δ<ce:sup loc=\"post\">7</ce:sup>Li values average −2.5 ± 1.6‰ during GI events, and −1.5 ± 1.5‰ in the intervening colder stadial events. Based on the evolution of Li isotopes with weathering, this suggests that there was more soil formation relative to primary mineral dissolution during cooler compared to warmer events. That is not to say that weathering rates were higher, but that clay formation was amplified relative to a given weathering rate when it was cooler, due to the combination of lower erosion rates, thermodynamically favoured conditions for clay formation, and enhanced water–rock contact times, promoting secondary mineral formation. Overall, the data show that soil formation responds even through rapid (∼100 years) climate change events.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"52 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147393022","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}
Microfossil-bearing black cherts from the ca. 3.4 Ga Strelley Pool Formation in the Goldsworthy Greenstone Belt, Pilbara Craton, offer critical insights into early Archean microbial ecosystems. In this study, we analyzed concentric colloform pyrite grains in these cherts to investigate their formation mechanisms and potential microbial involvement. The examined chert samples contain abundant organic matter and microfossils. The colloform pyrite grains, typically less than 10 µm in diameter, exhibit high sphericity and concentric internal growth structures. Their spatial association with diagenetic silica veins suggests pyrite formation prior to lithification. In situ sulfur isotope analyses using nanoscale secondary ion mass spectrometry (NanoSIMS) revealed large intra-grain δ34S variations, up to 28.6‰. δ34S values reach as low as –20.1‰ (VCDT) in the innermost cores and progressively increase toward the outer layers, where they average approximately +4‰. These trends are consistent with Rayleigh-type isotope fractionation under sulfate-limited conditions, likely mediated by heterotrophic microbial sulfate reduction. Secondary ion mapping of 12C− and 12C14N− revealed alternating layers of organic matter and pyrite. The close spatial association between pyrite and organic matter with significant 12C-enriched carbon isotope signatures, further supports a biogenic origin. Collectively, these findings provide new microscale geochemical evidence for microbial sulfur metabolism in early Archean sedimentary environments
来自皮尔巴拉克拉通Goldsworthy绿岩带约3.4 Ga Strelley池组的含微化石黑色燧石，为研究早期太古代微生物生态系统提供了重要的见解。在这项研究中，我们分析了这些燧石中的同心胶状黄铁矿颗粒，以探讨它们的形成机制和潜在的微生物参与。燧石样品中含有丰富的有机质和微化石。胶状黄铁矿颗粒直径一般小于10 µm，具有较高的球形度和同心圆的内部生长结构。它们与成岩石英脉的空间关联表明黄铁矿形成于岩化作用之前。纳米二级离子质谱（NanoSIMS）原位硫同位素分析显示，颗粒内δ34S变化较大，最高可达28.6‰。δ34S值在最内层岩心低至-20.1‰（VCDT），向外层逐渐增大，平均约为+4‰。这些趋势与硫酸盐限制条件下的瑞利型同位素分馏一致，可能是由异养微生物硫酸盐还原介导的。12C -和12C14N -的二次离子映射显示有机质和黄铁矿的交替层。黄铁矿与有机质密切的空间联系，具有显著的富12c碳同位素特征，进一步支持其生物成因。这些发现为太古宙早期沉积环境中微生物硫代谢提供了新的微尺度地球化学证据
{"title":"Microbial activity preserved in 3.4 Ga colloform pyrite: A micro–scale sulfur isotope analyses","authors":"Kohei Sasaki, Naoto Takahata, Akizumi Ishida, Takeshi Kakegawa, Kenichiro Sugitani","doi":"10.1016/j.gca.2026.03.005","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.005","url":null,"abstract":"Microfossil-bearing black cherts from the ca. 3.4 Ga Strelley Pool Formation in the Goldsworthy Greenstone Belt, Pilbara Craton, offer critical insights into early Archean microbial ecosystems. In this study, we analyzed concentric colloform pyrite grains in these cherts to investigate their formation mechanisms and potential microbial involvement. The examined chert samples contain abundant organic matter and microfossils. The colloform pyrite grains, typically less than 10 µm in diameter, exhibit high sphericity and concentric internal growth structures. Their spatial association with diagenetic silica veins suggests pyrite formation prior to lithification. In situ sulfur isotope analyses using nanoscale secondary ion mass spectrometry (NanoSIMS) revealed large intra-grain δ<ce:sup loc=\"post\">34</ce:sup>S variations, up to 28.6‰. δ<ce:sup loc=\"post\">34</ce:sup>S values reach as low as –20.1‰ (VCDT) in the innermost cores and progressively increase toward the outer layers, where they average approximately +4‰. These trends are consistent with Rayleigh-type isotope fractionation under sulfate-limited conditions, likely mediated by heterotrophic microbial sulfate reduction. Secondary ion mapping of <ce:sup loc=\"post\">12</ce:sup>C<ce:sup loc=\"post\">−</ce:sup> and <ce:sup loc=\"post\">12</ce:sup>C<ce:sup loc=\"post\">14</ce:sup>N<ce:sup loc=\"post\">−</ce:sup> revealed alternating layers of organic matter and pyrite. The close spatial association between pyrite and organic matter with significant <ce:sup loc=\"post\">12</ce:sup>C-enriched carbon isotope signatures, further supports a biogenic origin. Collectively, these findings provide new microscale geochemical evidence for microbial sulfur metabolism in early Archean sedimentary environments","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"7 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147393021","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 : 2026-03-06DOI: 10.1016/j.gca.2026.03.011
Brendan Garvey, Megan Holycross, Gabriel Larouche
The experimental calibration of Li diffusion in feldspar provides a method to quantify magmatic timescales in a ubiquitous mineral phase and ultimately aid in eruption forecasting. We ran Li-in-feldspar diffusion experiments with multiple feldspar compositions using powdered spodumene mixed with quartz as our dilute Li source. Li concentration gradients in our experiments show both simple error function-like profiles and more complex diffusion profiles. We fit the complex diffusion profiles using both concentration-dependent and multi-pathway forward numerical models. Lithium concentration gradients in our experiments are best explained by a multi-pathway diffusion mechanism where Li is simultaneously transported on two crystallographic sites in the feldspar, which we infer to be interstitial and vacant sites. The presence and relative contributions of the two diffusion pathways to the overall transport of Li in feldspar is dependent on the distribution of vacancies throughout the crystal. Lithium diffusion in Fe-free pure albite conforms to single-pathway error function solutions, while experiments with Fe-bearing An95, An60, and Or98 feldspar show two diffusion pathways for Li. Lithium diffusion in the Fe-bearing minerals show that the vacancy mechanism is slower than the interstitial mechanism by 1-3 orders of magnitude at the same temperature. Experiments in An60 run at oxygen fugacities buffered by the presence of nickel-nickel oxide display enhanced interstitial diffusion compared to those run in air, suggesting that reducing conditions limit the number of available vacant sites for Li diffusion in feldspar. There is no orientation dependence in endmember albite and anorthite, but there is diffusive anisotropy in the interstitial pathway for An60 plagioclase . Lithium transport in our experiments principally occurred via the interstitial mechanism, however, it is not entirely clear what diffusion mechanism may dominate in nature. If Li diffusion in magmatic feldspars operates via the vacancy mechanism, eruption timescales constrained by Li-in-feldspar diffusion chronometry may be 1-2 orders of magnitude longer than suggested by legacy experimental diffusion coefficients.
{"title":"Experimental characterization of multi-pathway diffusion of lithium in feldspar","authors":"Brendan Garvey, Megan Holycross, Gabriel Larouche","doi":"10.1016/j.gca.2026.03.011","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.011","url":null,"abstract":"The experimental calibration of Li diffusion in feldspar provides a method to quantify magmatic timescales in a ubiquitous mineral phase and ultimately aid in eruption forecasting. We ran Li-in-feldspar diffusion experiments with multiple feldspar compositions using powdered spodumene mixed with quartz as our dilute Li source. Li concentration gradients in our experiments show both simple error function-like profiles and more complex diffusion profiles. We fit the complex diffusion profiles using both concentration-dependent and multi-pathway forward numerical models. Lithium concentration gradients in our experiments are best explained by a multi-pathway diffusion mechanism where Li is simultaneously transported on two crystallographic sites in the feldspar, which we infer to be interstitial and vacant sites. The presence and relative contributions of the two diffusion pathways to the overall transport of Li in feldspar is dependent on the distribution of vacancies throughout the crystal. Lithium diffusion in Fe-free pure albite conforms to single-pathway error function solutions, while experiments with Fe-bearing An<mml:math altimg=\"si1.svg\" display=\"inline\"><mml:msub><mml:mrow></mml:mrow><mml:mrow><mml:mn>95</mml:mn></mml:mrow></mml:msub></mml:math>, An<mml:math altimg=\"si2.svg\" display=\"inline\"><mml:msub><mml:mrow></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:math>, and Or<mml:math altimg=\"si3.svg\" display=\"inline\"><mml:msub><mml:mrow></mml:mrow><mml:mrow><mml:mn>98</mml:mn></mml:mrow></mml:msub></mml:math> feldspar show two diffusion pathways for Li. Lithium diffusion in the Fe-bearing minerals show that the vacancy mechanism is slower than the interstitial mechanism by 1-3 orders of magnitude at the same temperature. Experiments in An<mml:math altimg=\"si2.svg\" display=\"inline\"><mml:msub><mml:mrow></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:math> run at oxygen fugacities buffered by the presence of nickel-nickel oxide display enhanced interstitial diffusion compared to those run in air, suggesting that reducing conditions limit the number of available vacant sites for Li diffusion in feldspar. There is no orientation dependence in endmember albite and anorthite, but there is diffusive anisotropy in the interstitial pathway for An<mml:math altimg=\"si2.svg\" display=\"inline\"><mml:msub><mml:mrow></mml:mrow><mml:mrow><mml:mn>60</mml:mn></mml:mrow></mml:msub></mml:math> plagioclase . Lithium transport in our experiments principally occurred via the interstitial mechanism, however, it is not entirely clear what diffusion mechanism may dominate in nature. If Li diffusion in magmatic feldspars operates via the vacancy mechanism, eruption timescales constrained by Li-in-feldspar diffusion chronometry may be 1-2 orders of magnitude longer than suggested by legacy experimental diffusion coefficients.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"56 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147393024","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 : 2026-03-06DOI: 10.1016/j.gca.2026.02.031
Lei Zhang, Thomas J. Algeo, He Zhao, Zhengyi Lyu, Fang Hao
Conodont oxygen-isotope (δ<ce:sup loc="post">18</ce:sup>O) paleothermometry is widely used in paleoclimate studies, yet significant δ<ce:sup loc="post">18</ce:sup>O variability among conodont tissue types (i.e., albid crown vs. hyaline crown vs. basal body) implies a substantial diagenetic and/or ontogenetic influence, but the specifics of this relationship remain poorly constrained. Here, we conducted high-resolution secondary ion mass spectrometry analysis of various tissues and layers (i.e., outer surface vs. interior axial) on six coniform elements (108 total data points) of Early Ordovician paraconodonts. In addition, we undertook micro-laser Raman spectral analysis on interior layers of the Ordovician paraconodonts, and laser ablation multi-collector inductively coupled plasma mass spectrometric analysis of both Ordovician coniform elements, and pectiniform and ramiform elements of Early Triassic euconodonts as a supplement. Our results reveal variable degrees of post-depositional alteration for stratigraphically adjacent specimens as well as among the various tissues and layers of individual specimens. Raman spectral and petrographic studies reveal greater crystallinity of albid crown and hyaline crown relative to darker-colored basal body, which is characterized by more abundant skeletal microporosity and defects related to the presence of amorphous carbon, resulting in greater radiogenic Sr uptake during diagenesis. The more strongly recrystallized albid and hyaline crown tissues show lower and more scattered δ<ce:sup loc="post">18</ce:sup>O values (+13.5 ‰ to + 17.8 ‰, avg. + 15.9 ± 0.8 ‰) as well as lower G-band FWHM (i.e., full width at half maximum, mostly < 65 cm<ce:sup loc="post">−1</ce:sup>) and D1/G ratio (i.e., ratio of D1-band to G-band peak intensities; mostly < 0.7), exhibiting strong positive correlations of δ<ce:sup loc="post">18</ce:sup>O to D1/G as well as v<ce:inf loc="post">1</ce:inf>-PO3- 4FWHM. In contrast, the more coarsely crystalline basal body shows systematically higher and narrower δ<ce:sup loc="post">18</ce:sup>O ranges (∼+15.1 ‰ to ∼+17.5 ‰, avg. + 16.6 ± 0.5 ‰), and larger G-band FWHM (mostly > 65 cm<ce:sup loc="post">−1</ce:sup>) and D1/G ratios (mostly > 0.7) that are not correlated to δ<ce:sup loc="post">18</ce:sup>O. The axial versus outer layers of conodonts exhibit similar patterns to albid/hyaline crown versus basal body in weakly altered specimens. Our findings demonstrate that δ<ce:sup loc="post">18</ce:sup>O variation in conodonts is predominantly controlled by diagenesis, with ontogenetic effects playing a minor role. Consequently, conodont δ<ce:sup loc="post">18</ce:sup>O values, even from low thermal maturity specimens, should be interpreted with caution as a primary paleoenvironmental proxy. Due to widespread diagenetic alteration, published paleotemperature estimates derived from light-colored albid/hyaline crowns require a systematic correction on the order of ∼+0.8‰ to + 1.3‰, alt
{"title":"Diagenetic effects on conodont oxygen-isotopic compositions: implications for in-situ analysis and paleothermometry","authors":"Lei Zhang, Thomas J. Algeo, He Zhao, Zhengyi Lyu, Fang Hao","doi":"10.1016/j.gca.2026.02.031","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.031","url":null,"abstract":"Conodont oxygen-isotope (δ<ce:sup loc=\"post\">18</ce:sup>O) paleothermometry is widely used in paleoclimate studies, yet significant δ<ce:sup loc=\"post\">18</ce:sup>O variability among conodont tissue types (i.e., albid crown vs. hyaline crown vs. basal body) implies a substantial diagenetic and/or ontogenetic influence, but the specifics of this relationship remain poorly constrained. Here, we conducted high-resolution secondary ion mass spectrometry analysis of various tissues and layers (i.e., outer surface vs. interior axial) on six coniform elements (108 total data points) of Early Ordovician paraconodonts. In addition, we undertook micro-laser Raman spectral analysis on interior layers of the Ordovician paraconodonts, and laser ablation multi-collector inductively coupled plasma mass spectrometric analysis of both Ordovician coniform elements, and pectiniform and ramiform elements of Early Triassic euconodonts as a supplement. Our results reveal variable degrees of post-depositional alteration for stratigraphically adjacent specimens as well as among the various tissues and layers of individual specimens. Raman spectral and petrographic studies reveal greater crystallinity of albid crown and hyaline crown relative to darker-colored basal body, which is characterized by more abundant skeletal microporosity and defects related to the presence of amorphous carbon, resulting in greater radiogenic Sr uptake during diagenesis. The more strongly recrystallized albid and hyaline crown tissues show lower and more scattered δ<ce:sup loc=\"post\">18</ce:sup>O values (+13.5 ‰ to + 17.8 ‰, avg. + 15.9 ± 0.8 ‰) as well as lower G-band FWHM (i.e., full width at half maximum, mostly < 65 cm<ce:sup loc=\"post\">−1</ce:sup>) and D1/G ratio (i.e., ratio of D1-band to G-band peak intensities; mostly < 0.7), exhibiting strong positive correlations of δ<ce:sup loc=\"post\">18</ce:sup>O to D1/G as well as v<ce:inf loc=\"post\">1</ce:inf>-PO3- 4FWHM. In contrast, the more coarsely crystalline basal body shows systematically higher and narrower δ<ce:sup loc=\"post\">18</ce:sup>O ranges (∼+15.1 ‰ to ∼+17.5 ‰, avg. + 16.6 ± 0.5 ‰), and larger G-band FWHM (mostly > 65 cm<ce:sup loc=\"post\">−1</ce:sup>) and D1/G ratios (mostly > 0.7) that are not correlated to δ<ce:sup loc=\"post\">18</ce:sup>O. The axial versus outer layers of conodonts exhibit similar patterns to albid/hyaline crown versus basal body in weakly altered specimens. Our findings demonstrate that δ<ce:sup loc=\"post\">18</ce:sup>O variation in conodonts is predominantly controlled by diagenesis, with ontogenetic effects playing a minor role. Consequently, conodont δ<ce:sup loc=\"post\">18</ce:sup>O values, even from low thermal maturity specimens, should be interpreted with caution as a primary paleoenvironmental proxy. Due to widespread diagenetic alteration, published paleotemperature estimates derived from light-colored albid/hyaline crowns require a systematic correction on the order of ∼+0.8‰ to + 1.3‰, alt","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"19 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147393096","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 : 2026-03-06DOI: 10.1016/j.gca.2026.02.043
Alban Cheviet, Flavien Choulet, Martine Buatier, Christophe Galerne, Wolfgang Bach, Wolf-Achim Kahl, Armelle Riboulleau, Lucie Pastor
Sedimentary basins are at the interface between deep (lithosphere) and superficial (hydrosphere, atmosphere and biosphere) reservoirs, with the capacity to trap large quantities of volatile elements (e.g. S, C, H, Cl, F) over time through sedimentation and diagenesis. These volatiles can be released abruptly due to contact metamorphism associated to the emplacement of magmatic intrusions in the sediments, further disturbing the geochemical cycles in the atmosphere and biosphere. The interactions between magma and sediments during sill emplacement are complex and include contact metamorphism and contamination processes, but also the assimilation of sediments into the sill. In this study, we examine the impact of magma-sediment interactions on the sulphur cycle. The Ringvent sill in the Guaymas Basin drilled during Expedition IODP 385, is a funnel-shaped sill that emplaced in soft sediments at the subseafloor, representing an exceptional in-situ natural laboratory for studying magma-sediment interactions. The petrological and geochemical study of the sediments, magmatic rocks and magma-sediment mixtures reveals a high concentration of pyrite at the magma-sediment interfaces. Multiple types of pyrite indicate different sulphur-trapping processes occurring during the emplacement of the sill. Trace elements and isotopic (δ34S) analyses were used to identify the different sources of sulphur and to better constrain the processes. We demonstrate that the assimilation of sediment and the contamination of porewater in the Ringvent sill enables the formation of these different pyrite types from the time of sill emplacement until to late hydrothermal circulations, which remain still active. Such processes enable the storage of a minimum of 700,000 tonnes of sulphur within the sill, while there is minimal evidence of the release of volatiles in the surrounding area, indicating that, under certain conditions, these systems can function as a significant sulphur sink.
{"title":"Do magmatic sill intrusions simply liberate the sulphur of the sedimentary reservoirs?","authors":"Alban Cheviet, Flavien Choulet, Martine Buatier, Christophe Galerne, Wolfgang Bach, Wolf-Achim Kahl, Armelle Riboulleau, Lucie Pastor","doi":"10.1016/j.gca.2026.02.043","DOIUrl":"https://doi.org/10.1016/j.gca.2026.02.043","url":null,"abstract":"Sedimentary basins are at the interface between deep (lithosphere) and superficial (hydrosphere, atmosphere and biosphere) reservoirs, with the capacity to trap large quantities of volatile elements (e.g. S, C, H, Cl, F) over time through sedimentation and diagenesis. These volatiles can be released abruptly due to contact metamorphism associated to the emplacement of magmatic intrusions in the sediments, further disturbing the geochemical cycles in the atmosphere and biosphere. The interactions between magma and sediments during sill emplacement are complex and include contact metamorphism and contamination processes, but also the assimilation of sediments into the sill. In this study, we examine the impact of magma-sediment interactions on the sulphur cycle. The Ringvent sill in the Guaymas Basin drilled during Expedition IODP 385, is a funnel-shaped sill that emplaced in soft sediments at the subseafloor, representing an exceptional in-situ natural laboratory for studying magma-sediment interactions. The petrological and geochemical study of the sediments, magmatic rocks and magma-sediment mixtures reveals a high concentration of pyrite at the magma-sediment interfaces. Multiple types of pyrite indicate different sulphur-trapping processes occurring during the emplacement of the sill. Trace elements and isotopic (δ<ce:sup loc=\"post\">34</ce:sup>S) analyses were used to identify the different sources of sulphur and to better constrain the processes. We demonstrate that the assimilation of sediment and the contamination of porewater in the Ringvent sill enables the formation of these different pyrite types from the time of sill emplacement until to late hydrothermal circulations, which remain still active. Such processes enable the storage of a minimum of 700,000 tonnes of sulphur within the sill, while there is minimal evidence of the release of volatiles in the surrounding area, indicating that, under certain conditions, these systems can function as a significant sulphur sink.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"31 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147393097","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 : 2026-03-06DOI: 10.1016/j.gca.2026.03.002
M. Koike, Y. Sumiya, R. Kanemaru, B.G. Rider-Stokes, R. Sakai, N. Takahata, K. Sasaki, H. Asanuma, Y. Sano
Asteroid 4 Vesta is an ancient, differentiated rocky body, whose lithologies are represented on Earth as howardite–eucrite–diogenite meteorites (HEDs). Chronological studies of HEDs provide key constraints on the formation and evolution process of Vesta and offer insights into early Solar System history. Here, we present new U–Pb dataset for Ca-phosphate minerals (apatite and merrillite) and zircon in four eucrite-melt breccias, Northwest Africa (NWA) 13,166, NWA 10,602, NWA 10,603, and NWA 11,576. Zircon grains from the four samples yield a weighted mean 207Pb/206Pb age of 4556 ± 13 Ma (all uncertainties are reported at 2-sigma level), consistent with previously reported ages of old zircons in eucrites (a weighted mean 207Pb/206Pb age of 4552.6 ± 0.9 Ma; n = 25). Total U–Pb discordia are obtained from co-existing phosphate grains in NWA 13,166 (upper intercept at 4169 + 82/-83 Ma and lower intercept of 72 ± 26 Ma) and NWA 10,603 (4234 + 62/-63 Ma and 46 ± 74 Ma). Model 207Pb/206Pb ages of individual phosphate grains range from ∼ 4370 to ∼ 4110 Ma across the four studied samples. When considered with published data, phosphate 207Pb/206Pb ages in basaltic eucrites define two distinct populations: an older population with a weighted mean age of 4520.6 ± 5.0 Ma (n = 7), and a younger population with a weighted mean age of 4206 ± 27 Ma (n = 9). The older phosphates likely record prolonged cooling of Vesta’s crust and/or impact-related reheating at ∼ 4520 Ma. In contrast, the younger phosphates reflect multiple bombardment events at ∼ 4200 Ma. Microstructural observations of phosphate crystals reveal extensive deformation and recrystallization, consistent with impact-resetting of their U–Pb systems. Reported 40Ar/39Ar ages of HEDs span a broader range, clustering at ∼ 4490 Ma for unbrecciated eucrites, varying between ∼ 3900–2500 Ma for brecciated eucrites and howardites, and ≤ 2400 Ma for diogenites. These chronological constraints suggest that Vesta experienced an extended period of bombardment from ∼ 4200 Ma to ∼ 2500 Ma. As suggested by previous studies, the meteoritic record is more consistent with a prolonged and monotonic decline in impact rates beginning in the early stages of Solar System formation, rather than a discrete collisional spike envisioned in the Late Heavy Bombardment hypothesis.
{"title":"A prolonged bombardment history of asteroid 4 Vesta: insights from U–Pb chronology of eucrite phosphates and zircons","authors":"M. Koike, Y. Sumiya, R. Kanemaru, B.G. Rider-Stokes, R. Sakai, N. Takahata, K. Sasaki, H. Asanuma, Y. Sano","doi":"10.1016/j.gca.2026.03.002","DOIUrl":"https://doi.org/10.1016/j.gca.2026.03.002","url":null,"abstract":"Asteroid 4 Vesta is an ancient, differentiated rocky body, whose lithologies are represented on Earth as howardite–eucrite–diogenite meteorites (HEDs). Chronological studies of HEDs provide key constraints on the formation and evolution process of Vesta and offer insights into early Solar System history. Here, we present new U–Pb dataset for Ca-phosphate minerals (apatite and merrillite) and zircon in four eucrite-melt breccias, Northwest Africa (NWA) 13,166, NWA 10,602, NWA 10,603, and NWA 11,576. Zircon grains from the four samples yield a weighted mean <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">206</ce:sup>Pb age of 4556 ± 13 Ma (all uncertainties are reported at 2-sigma level), consistent with previously reported ages of old zircons in eucrites (a weighted mean <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">206</ce:sup>Pb age of 4552.6 ± 0.9 Ma; n = 25). Total U–Pb discordia are obtained from co-existing phosphate grains in NWA 13,166 (upper intercept at 4169 + 82/-83 Ma and lower intercept of 72 ± 26 Ma) and NWA 10,603 (4234 + 62/-63 Ma and 46 ± 74 Ma). Model <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">206</ce:sup>Pb ages of individual phosphate grains range from ∼ 4370 to ∼ 4110 Ma across the four studied samples. When considered with published data, phosphate <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">206</ce:sup>Pb ages in basaltic eucrites define two distinct populations: an older population with a weighted mean age of 4520.6 ± 5.0 Ma (n = 7), and a younger population with a weighted mean age of 4206 ± 27 Ma (n = 9). The older phosphates likely record prolonged cooling of Vesta’s crust and/or impact-related reheating at ∼ 4520 Ma. In contrast, the younger phosphates reflect multiple bombardment events at ∼ 4200 Ma. Microstructural observations of phosphate crystals reveal extensive deformation and recrystallization, consistent with impact-resetting of their U–Pb systems. Reported <ce:sup loc=\"post\">40</ce:sup>Ar/<ce:sup loc=\"post\">39</ce:sup>Ar ages of HEDs span a broader range, clustering at ∼ 4490 Ma for unbrecciated eucrites, varying between ∼ 3900–2500 Ma for brecciated eucrites and howardites, and ≤ 2400 Ma for diogenites. These chronological constraints suggest that Vesta experienced an extended period of bombardment from ∼ 4200 Ma to ∼ 2500 Ma. As suggested by previous studies, the meteoritic record is more consistent with a prolonged and monotonic decline in impact rates beginning in the early stages of Solar System formation, rather than a discrete collisional spike envisioned in the Late Heavy Bombardment hypothesis.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"74 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2026-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147393025","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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