A. Stephant, M. Anand, C. Carli, X. Zhao, J. Davidson, T. Cuppone, G. Pratesi, I.A. Franchi
Bulk rock chondrites and Earth’s reservoirs share a common chlorine isotopic value, while more differentiated bodies such as the Moon or Vesta record significant chlorine isotopic fractionation in their Ca phosphates. As such, an important but scarcely studied parameter is the effect of melting and differentiation processes on chlorine concentration and isotopic composition of a planetesimal. Here we report chlorine abundances and isotopic compositions for apatite in a range of primitive achondrites, acapulcoites and lodranites. These meteorites originated from a parent body that experienced some partial melting, allowing an assessment of chlorine behaviour during the early stages of planetary evolution in the inner Solar System. Overall, while bulk rock estimates of F and Cl abundances are indicative of degassing during the early stages of partial melting, no chlorine isotopic fractionation is recorded in apatite. Consequently, acapulcoites and lodranites retain their chondritic precursor isotopic signature for chlorine.
块状岩石软玉体和地球储层具有共同的氯同位素值，而月球或灶神星等分化程度较高的天体则在其钙磷酸盐中记录了显著的氯同位素分馏。因此，熔化和分化过程对行星的氯浓度和同位素组成的影响是一个重要但很少研究的参数。在这里，我们报告了一系列原始闪长岩、阿卡普尔科岩和洛德兰岩中磷灰石的氯丰度和同位素组成。这些陨石的母体曾经历过部分熔化，因此可以对太阳系内部行星演化早期阶段的氯行为进行评估。总体而言，虽然块状岩石中 F 和 Cl 丰度的估计值表明在部分熔化的早期阶段存在脱气现象，但磷灰石中没有氯同位素分馏的记录。因此，尖晶石和绿帘石保留了其金刚石前体的氯同位素特征。
{"title":"Chondritic chlorine isotope composition of acapulcoites and lodranites","authors":"A. Stephant, M. Anand, C. Carli, X. Zhao, J. Davidson, T. Cuppone, G. Pratesi, I.A. Franchi","doi":"10.7185/geochemlet.2406","DOIUrl":"https://doi.org/10.7185/geochemlet.2406","url":null,"abstract":"Bulk rock chondrites and Earth’s reservoirs share a common chlorine isotopic value, while more differentiated bodies such as the Moon or Vesta record significant chlorine isotopic fractionation in their Ca phosphates. As such, an important but scarcely studied parameter is the effect of melting and differentiation processes on chlorine concentration and isotopic composition of a planetesimal. Here we report chlorine abundances and isotopic compositions for apatite in a range of primitive achondrites, acapulcoites and lodranites. These meteorites originated from a parent body that experienced some partial melting, allowing an assessment of chlorine behaviour during the early stages of planetary evolution in the inner Solar System. Overall, while bulk rock estimates of F and Cl abundances are indicative of degassing during the early stages of partial melting, no chlorine isotopic fractionation is recorded in apatite. Consequently, acapulcoites and lodranites retain their chondritic precursor isotopic signature for chlorine.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139760978","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}
{"title":"Mantle depletion recorded by olivine and plagioclase megacrysts in oceanic basalts","authors":"K.W. Burton, I.J. Parkinson, D.A. Neave","doi":"10.7185/geochemlet.2405","DOIUrl":"https://doi.org/10.7185/geochemlet.2405","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139886755","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}
{"title":"Mantle depletion recorded by olivine and plagioclase megacrysts in oceanic basalts","authors":"K.W. Burton, I.J. Parkinson, D.A. Neave","doi":"10.7185/geochemlet.2405","DOIUrl":"https://doi.org/10.7185/geochemlet.2405","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139827047","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}
Interpreting signals of volcanic unrest requires knowledge of the architecture of the magmatic system, particularly the depths at which magmas are stored. Such information can be vital to help predict changes in eruptive style and vigour. However, popular petrological tools to assess magma storage depths (e.g., melt inclusions) are costly, present large uncertainties, and are too slow for real time monitoring. Here, we evaluate the reliability of Raman Spectroscopy measurements of CO2-dominated fluid inclusions as a geobarometer relative to microthermometry and melt inclusion barometry. We calculate storage pressures for 102 olivine-hosted fluid inclusions from the 2018 Lower East Rift Zone eruption of Kīlauea, which are statistically indistinguishable to those determined from melt inclusions. We show that calibrated Raman spectroscopy yields densities within 5–10 % of microthermometry for CO2-dominated fluid inclusions (<10 mol % H2O) but is a far more suitable method for systems like Kīlauea dominated by shallow magma storage. Overall, pressures determined from fluid inclusions by Raman spectroscopy are robust and require only a fraction of the time and resources of melt inclusion studies.
{"title":"Reliability of Raman analyses of CO2-rich fluid inclusions as a geobarometer at Kīlauea","authors":"C.L. DeVitre, P.E. Wieser","doi":"10.7185/geochemlet.2404","DOIUrl":"https://doi.org/10.7185/geochemlet.2404","url":null,"abstract":"Interpreting signals of volcanic unrest requires knowledge of the architecture of the magmatic system, particularly the depths at which magmas are stored. Such information can be vital to help predict changes in eruptive style and vigour. However, popular petrological tools to assess magma storage depths (<em>e.g.</em>, melt inclusions) are costly, present large uncertainties, and are too slow for real time monitoring. Here, we evaluate the reliability of Raman Spectroscopy measurements of CO<sub>2</sub>-dominated fluid inclusions as a geobarometer relative to microthermometry and melt inclusion barometry. We calculate storage pressures for 102 olivine-hosted fluid inclusions from the 2018 Lower East Rift Zone eruption of K&imacr;lauea, which are statistically indistinguishable to those determined from melt inclusions. We show that calibrated Raman spectroscopy yields densities within 5–10 % of microthermometry for CO<sub>2</sub>-dominated fluid inclusions (<10 mol % H<sub>2</sub>O) but is a far more suitable method for systems like K&imacr;lauea dominated by shallow magma storage. Overall, pressures determined from fluid inclusions by Raman spectroscopy are robust and require only a fraction of the time and resources of melt inclusion studies.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139663745","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}
C. Gil-Lozano, F. Baron, A. Gaudin, J.-P. Lorand, V. Fernandez, J. Hamon, N. Mangold
Martian carbonates are fundamental minerals for understanding the geochemical and climatic evolution of the planet and the search for potential life, representing one of the key objectives for the Perseverance rover at Jezero Crater. However, the scarcity of carbonate reservoirs on the surface compared to the extent of terrestrial carbonates questions whether these carbonates are indicators of past surface conditions or products from deeper processes unrelated to martian climate. We investigate the formation of carbonates by surface weathering under a CO2 atmosphere in a suite of individual minerals and martian simulants based on the early Mars crust composition. We identify the formation of magnesium carbonates in olivine-bearing samples, but not in the early martian crust simulants. These findings are consistent with the association of carbonates with olivine-rich substrate detected on Mars and highlight the role of the substratum composition in the distribution of carbonates formed by surface processes. Hence, we conclude that the limited surface reservoirs of carbonate are reconcilable with the existence of a CO2-rich atmosphere on early Mars.
{"title":"The key role of bedrock composition in the formation of carbonates on Mars","authors":"C. Gil-Lozano, F. Baron, A. Gaudin, J.-P. Lorand, V. Fernandez, J. Hamon, N. Mangold","doi":"10.7185/geochemlet.2403","DOIUrl":"https://doi.org/10.7185/geochemlet.2403","url":null,"abstract":"Martian carbonates are fundamental minerals for understanding the geochemical and climatic evolution of the planet and the search for potential life, representing one of the key objectives for the Perseverance rover at Jezero Crater. However, the scarcity of carbonate reservoirs on the surface compared to the extent of terrestrial carbonates questions whether these carbonates are indicators of past surface conditions or products from deeper processes unrelated to martian climate. We investigate the formation of carbonates by surface weathering under a CO<sub>2</sub> atmosphere in a suite of individual minerals and martian simulants based on the early Mars crust composition. We identify the formation of magnesium carbonates in olivine-bearing samples, but not in the early martian crust simulants. These findings are consistent with the association of carbonates with olivine-rich substrate detected on Mars and highlight the role of the substratum composition in the distribution of carbonates formed by surface processes. Hence, we conclude that the limited surface reservoirs of carbonate are reconcilable with the existence of a CO<sub>2</sub>-rich atmosphere on early Mars.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139577823","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}
W. Wang, A.J. Dickson, M.A. Stow, M. Dellinger, K.W. Burton, P.S. Savage, R.G. Hilton, J. Prytulak
Recent analytical advances in the measurement of rhenium (Re) isotope ratios allow its potential as a palaeoredox and chemical weathering proxy to be explored. However, a successful isotopic proxy must be grounded by an understanding of its composition and behaviour in the solid Earth. Here, we present Re concentrations and Re isotopic (δ187Re) compositions for a well-characterised sequence of lavas from Hekla volcano, Iceland. The concentration of Re varies from 0.02 to 1.4 ng/g, decreasing from basalt to more evolved lavas. We show that the crystallisation and removal of magnetite is responsible for the Re decrease in this system. By contrast, δ187Re values for the same suite of samples show a relatively narrow range (−0.45 to −0.22 ‰), suggesting minimal resolvable Re isotope fractionation between magnetite and the silicate melt. Together with other samples, including mid-ocean ridge basalts, these first igneous data can be used to estimate a baseline for terrestrial materials (δ187Re = −0.33 ± 0.15 ‰, 2 s.d., n = 14), from which low-temperature Re isotope variations in Earth’s surficial environments can be assessed, alongside the global isotope mass balance of Re.
{"title":"Rhenium elemental and isotopic variations at magmatic temperatures","authors":"W. Wang, A.J. Dickson, M.A. Stow, M. Dellinger, K.W. Burton, P.S. Savage, R.G. Hilton, J. Prytulak","doi":"10.7185/geochemlet.2402","DOIUrl":"https://doi.org/10.7185/geochemlet.2402","url":null,"abstract":"Recent analytical advances in the measurement of rhenium (Re) isotope ratios allow its potential as a palaeoredox and chemical weathering proxy to be explored. However, a successful isotopic proxy must be grounded by an understanding of its composition and behaviour in the solid Earth. Here, we present Re concentrations and Re isotopic (δ<sup>187</sup>Re) compositions for a well-characterised sequence of lavas from Hekla volcano, Iceland. The concentration of Re varies from 0.02 to 1.4 ng/g, decreasing from basalt to more evolved lavas. We show that the crystallisation and removal of magnetite is responsible for the Re decrease in this system. By contrast, δ<sup>187</sup>Re values for the same suite of samples show a relatively narrow range (−0.45 to −0.22 ‰), suggesting minimal resolvable Re isotope fractionation between magnetite and the silicate melt. Together with other samples, including mid-ocean ridge basalts, these first igneous data can be used to estimate a baseline for terrestrial materials (δ<sup>187</sup>Re = −0.33 ± 0.15 ‰, 2 s.d., <em>n</em> = 14), from which low-temperature Re isotope variations in Earth’s surficial environments can be assessed, alongside the global isotope mass balance of Re.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139414518","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}
G. Rustioni, M. Wiedenbeck, N. Miyajima, A. Chanyshev, H. Keppler
Ferropericlase (Mg,Fe)O is after bridgmanite the most abundant phase in the lower mantle. The ultralow velocity zones above the core-mantle boundary may contain very Fe-rich magnesiowüstite (Fe,Mg)O, possibly as result of the fractional crystallisation of a basal magma ocean. We have experimentally studied the solubility of nitrogen in the ferropericlase-magnesiowüstite solid solution series as function of iron content. Multi-anvil experiments were performed at 20–33 GPa and 1600–1800 °C in equilibrium with Fe metal. Nitrogen solubility increases from a few tens ppm (μg/g) for Mg-rich ferropericlase to more than 10 wt. % for nearly pure wüstite. Such high solubilities appear to be due to solid solution with NiAs-type FeN. Our data suggest that during fractional crystallisation of a magma ocean, the core-mantle boundary would have become extremely enriched with nitrogen, such that the deep mantle today could be the largest nitrogen reservoir on Earth. The often discussed “subchondritic N/C” ratio of the bulk silicate Earth may be an artefact of insufficient sampling of this deep reservoir.
{"title":"Magnesiowüstite as a major nitrogen reservoir in Earth’s lowermost mantle","authors":"G. Rustioni, M. Wiedenbeck, N. Miyajima, A. Chanyshev, H. Keppler","doi":"10.7185/geochemlet.2401","DOIUrl":"https://doi.org/10.7185/geochemlet.2401","url":null,"abstract":"Ferropericlase (Mg,Fe)O is after bridgmanite the most abundant phase in the lower mantle. The ultralow velocity zones above the core-mantle boundary may contain very Fe-rich magnesiowüstite (Fe,Mg)O, possibly as result of the fractional crystallisation of a basal magma ocean. We have experimentally studied the solubility of nitrogen in the ferropericlase-magnesiowüstite solid solution series as function of iron content. Multi-anvil experiments were performed at 20–33 GPa and 1600–1800 °C in equilibrium with Fe metal. Nitrogen solubility increases from a few tens ppm (μg/g) for Mg-rich ferropericlase to more than 10 wt. % for nearly pure wüstite. Such high solubilities appear to be due to solid solution with NiAs-type FeN. Our data suggest that during fractional crystallisation of a magma ocean, the core-mantle boundary would have become extremely enriched with nitrogen, such that the deep mantle today could be the largest nitrogen reservoir on Earth. The often discussed “subchondritic N/C” ratio of the bulk silicate Earth may be an artefact of insufficient sampling of this deep reservoir.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139105594","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}
L. Hoare, L.J.A. Rzehak, S. Kommescher, M. Jansen, M.T. Rosing, T. Nagel, M.-A. Millet, J.E. Hoffmann, R.O.C. Fonseca
The timing and formation of Earth’s first continents during the Archean are subjects of significant debate. By examining titanium isotope variations in Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks and using advanced thermodynamic modelling, we can narrow down the processes involved and emphasise the role of mafic precursor compositions. In our study of Eoarchean Isua metabasalts and Itsaq tonalites in southern West Greenland, we observed a pattern of increasing Ti isotope enrichment with higher SiO2 content, resembling the compositions found in modern subduction zone rocks. Our modelling suggests that the Ti isotope variations in TTGs can be best explained by a combination of partial melting of low TiO2 metabasalts and subsequent crystallisation of tonalitic magmas, resulting in heavier Ti isotopes. This means that Ti isotopes help us distinguish the contributions of various mafic sources and fractional crystallisation during TTG formation. In the case of Itsaq tonalites and many other Eoarchean TTGs, low TiO2 tholeiitic metabasalts with arc-like characteristics likely represent the mafic source rocks, suggesting the formation of some of Earth’s earliest continental crust within a proto-subduction zone setting.
关于地球上第一块大陆形成于阿基坦时期的时间和形成过程，一直是人们争论的焦点。通过研究安古宙辉长岩-钙钛矿-花岗闪长岩（TTG）岩石中的钛同位素变化，并利用先进的热力学模型，我们可以缩小相关过程的范围，并强调黑云母前驱体成分的作用。在对西格陵兰南部的始新世伊苏亚新玄武岩和Itsaq英安岩的研究中，我们观察到一种Ti同位素富集度随SiO2含量增加而增加的模式，与现代俯冲带岩石中的成分相似。我们的建模表明，TTGs 中 Ti 同位素变化的最佳解释是，低 TiO2 元青石部分熔化和随后的辉绿岩岩浆结晶相结合，导致了较重的 Ti 同位素。这意味着 Ti 同位素有助于我们区分 TTG 形成过程中各种岩浆源和部分结晶的贡献。在Itsaq tonalites和许多其他始新世TTG中，具有弧状特征的低TiO2透辉石变质岩可能代表了黑云母源岩，这表明地球最早的大陆地壳是在原俯冲带环境中形成的。
{"title":"Titanium isotope constraints on the mafic sources and geodynamic origins of Archean crust","authors":"L. Hoare, L.J.A. Rzehak, S. Kommescher, M. Jansen, M.T. Rosing, T. Nagel, M.-A. Millet, J.E. Hoffmann, R.O.C. Fonseca","doi":"10.7185/geochemlet.2342","DOIUrl":"https://doi.org/10.7185/geochemlet.2342","url":null,"abstract":"The timing and formation of Earth’s first continents during the Archean are subjects of significant debate. By examining titanium isotope variations in Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks and using advanced thermodynamic modelling, we can narrow down the processes involved and emphasise the role of mafic precursor compositions. In our study of Eoarchean Isua metabasalts and Itsaq tonalites in southern West Greenland, we observed a pattern of increasing Ti isotope enrichment with higher SiO<sub>2</sub> content, resembling the compositions found in modern subduction zone rocks. Our modelling suggests that the Ti isotope variations in TTGs can be best explained by a combination of partial melting of low TiO<sub>2</sub> metabasalts and subsequent crystallisation of tonalitic magmas, resulting in heavier Ti isotopes. This means that Ti isotopes help us distinguish the contributions of various mafic sources and fractional crystallisation during TTG formation. In the case of Itsaq tonalites and many other Eoarchean TTGs, low TiO<sub>2</sub> tholeiitic metabasalts with arc-like characteristics likely represent the mafic source rocks, suggesting the formation of some of Earth’s earliest continental crust within a proto-subduction zone setting.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2023-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139022542","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}
N. Nakanishi, T. Yokoyama, A. Ishikawa, R.J. Walker, Y. Abe, J. Aléon, C.M.O'D Alexander, S. Amari, Y. Amelin, K.-I. Bajo, M. Bizzarro, A. Bouvier, R.W. Carlson, M. Chaussidon, B.-G. Choi, N. Dauphas, A.M. Davis, T. Di Rocco, W. Fujiya, R. Fukai, I. Gautam, M.K. Haba, Y. Hibiya, H. Hidaka, H. Homma, P. Hoppe, G.R. Huss, K. Ichida, T. Iizuka, T.R. Ireland, S. Itoh, N. Kawasaki, N.T. Kita, K. Kitajima, T. Kleine, S. Komatani, A.N. Krot, M.-C. Liu, Y. Masuda, M. Morita, K. Motomura, F. Moynier, I. Nakai, K. Nagashima, A. Nguyen, L. Nittler, M. Onose, A. Pack, C. Park, L. Piani, L. Qin, S.S. Russell, N. Sakamoto, M. Schönbächler, L. Tafla, H. Tang, K. Terada, Y. Terada, T. Usui, S. Wada, M. Wadhwa, K. Yamashita, Q.-Z. Yin, S. Yoneda, E.D. Young, H. Yui, A.-C. Zhang, T. Nakamura, H. Naraoka, T. Noguchi, R. Okazaki, K. Sakamoto, H. Yabuta, M. Abe, A. Miyazaki, A. Nakato, M. Nishimura, T. Okada, T. Yada, K. Yogata, S. Nakazawa, T. Saiki, S. Tanaka, F. Terui, Y. Tsuda, S.-I. Watanabe, M. Yoshikawa, S. Tachibana, H. Yurimoto
Initial analyses of samples collected from two locations on the asteroid Ryugu indicated that the mineralogical, chemical, and isotopic characteristics of the Ryugu samples show similarities to carbonaceous chondrites, particularly the Ivuna-type (CI) group. In this study, we analysed a composite sample of four bulk Ryugu samples (A0106, A0106-A0107, C0107, and C0108) collected from both sampling locations that were combined in order to determine its mass independent Mo isotopic composition and reveal contributions from diverse nucleosynthetic sources. The ɛ94Mo and ɛ95Mo values for the Ryugu sample are characterised by the carbonaceous chondrite (CC)-type, which is consistent with the nucleosynthetic isotope compositions observed for other elements (Cr, Ti, Fe, and Zn). The Ryugu composite sample, however, is characterised by greater s-process depletion of Mo isotopes compared with any known bulk carbonaceous chondrite, even including CI chondrites. The observed Mo isotopic signature in the Ryugu composite was most likely caused by either incomplete digestion of s-process-rich presolar SiC, or biased sampling of materials enriched in aqueously-formed secondary minerals characterised by s-process-poor Mo isotopes, resulting from the physicochemical separation between s-process-rich presolar grains and a complementary s-process-poor aqueous fluid in the Ryugu parent body.
对从小行星龙宫上的两个地点采集的样本进行的初步分析表明，龙宫样本的矿物学、化学和同位素特征显示出与碳质软玉，特别是伊武纳型（CI）组的相似性。在本研究中，我们分析了从两个取样地点采集的四个龙宫大块样本（A0106、A0106-A0107、C0107 和 C0108）的复合样本，以确定其质量无关的 Mo 同位素组成，并揭示来自不同核合成源的贡献。龙宫样本的ɛ94Mo和ɛ95Mo值具有碳质软玉（CC）类型的特征，这与其他元素（Cr、Ti、Fe和Zn）的核合成同位素组成一致。然而，与任何已知的大块碳质软玉体（甚至包括CI软玉体）相比，龙宫复合样本的特征是Mo同位素的s-过程损耗更大。在龙宫复合样本中观察到的 Mo 同位素特征很可能是由于对富含 s 过程的前极性 SiC 的不完全消化，或者是对富含水成二次矿物的材料进行了有偏差的取样，这些材料的特征是富含 s 过程的前极性晶粒与龙宫母体中富含 s 过程的补充性贫化水成流体之间的物理化学分离造成的贫化 Mo 同位素。
{"title":"Nucleosynthetic s-Process Depletion in Mo from Ryugu samples returned by Hayabusa2","authors":"N. Nakanishi, T. Yokoyama, A. Ishikawa, R.J. Walker, Y. Abe, J. Aléon, C.M.O'D Alexander, S. Amari, Y. Amelin, K.-I. Bajo, M. Bizzarro, A. Bouvier, R.W. Carlson, M. Chaussidon, B.-G. Choi, N. Dauphas, A.M. Davis, T. Di Rocco, W. Fujiya, R. Fukai, I. Gautam, M.K. Haba, Y. Hibiya, H. Hidaka, H. Homma, P. Hoppe, G.R. Huss, K. Ichida, T. Iizuka, T.R. Ireland, S. Itoh, N. Kawasaki, N.T. Kita, K. Kitajima, T. Kleine, S. Komatani, A.N. Krot, M.-C. Liu, Y. Masuda, M. Morita, K. Motomura, F. Moynier, I. Nakai, K. Nagashima, A. Nguyen, L. Nittler, M. Onose, A. Pack, C. Park, L. Piani, L. Qin, S.S. Russell, N. Sakamoto, M. Schönbächler, L. Tafla, H. Tang, K. Terada, Y. Terada, T. Usui, S. Wada, M. Wadhwa, K. Yamashita, Q.-Z. Yin, S. Yoneda, E.D. Young, H. Yui, A.-C. Zhang, T. Nakamura, H. Naraoka, T. Noguchi, R. Okazaki, K. Sakamoto, H. Yabuta, M. Abe, A. Miyazaki, A. Nakato, M. Nishimura, T. Okada, T. Yada, K. Yogata, S. Nakazawa, T. Saiki, S. Tanaka, F. Terui, Y. Tsuda, S.-I. Watanabe, M. Yoshikawa, S. Tachibana, H. Yurimoto","doi":"10.7185/geochemlet.2341","DOIUrl":"https://doi.org/10.7185/geochemlet.2341","url":null,"abstract":"Initial analyses of samples collected from two locations on the asteroid Ryugu indicated that the mineralogical, chemical, and isotopic characteristics of the Ryugu samples show similarities to carbonaceous chondrites, particularly the Ivuna-type (CI) group. In this study, we analysed a composite sample of four bulk Ryugu samples (A0106, A0106-A0107, C0107, and C0108) collected from both sampling locations that were combined in order to determine its mass independent Mo isotopic composition and reveal contributions from diverse nucleosynthetic sources. The ɛ<sup>94</sup>Mo and ɛ<sup>95</sup>Mo values for the Ryugu sample are characterised by the carbonaceous chondrite (CC)-type, which is consistent with the nucleosynthetic isotope compositions observed for other elements (Cr, Ti, Fe, and Zn). The Ryugu composite sample, however, is characterised by greater <em>s</em>-process depletion of Mo isotopes compared with any known bulk carbonaceous chondrite, even including CI chondrites. The observed Mo isotopic signature in the Ryugu composite was most likely caused by either incomplete digestion of <em>s</em>-process-rich presolar SiC, or biased sampling of materials enriched in aqueously-formed secondary minerals characterised by <em>s</em>-process-poor Mo isotopes, resulting from the physicochemical separation between <em>s</em>-process-rich presolar grains and a complementary <em>s</em>-process-poor aqueous fluid in the Ryugu parent body.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138824962","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}
Redox conditions in past oceans have attracted significant interest and many proxies have been used to probe redox changes through time. For example, the redox dependent behaviour of Ce, resulting in negative or positive elemental Ce anomalies, has been widely used. More recently, mass dependent Ce isotopic variations have been proposed as a powerful tool to study Ce oxidation in natural environments. In this study, we demonstrate, for the first time, that Ce isotopes are fractionated during oxidation reaction, confirming the utility of Ce isotopes to study redox reactions. This result suggests that seawater Ce isotopic composition should be fractionated toward heavy values relative to the continental crust. Measured natural rock samples (carbonates, banded iron formations and Mn nodules) have variable Ce isotopic compositions, ranging from −0.055 ± 0.045 ‰ to +0.280 ± 0.045 ‰. The relation between Ce elemental anomalies and Ce isotopic composition in carbonate rocks suggest that mass dependent Ce isotopes can be used to distinguish elemental anomalies produced by oxidation reactions from those produced by other processes. Coupled with La-Ce chronology, mass dependent Ce isotope analysis is a very powerful tool to study redox reactions in past oceans.
过去海洋中的氧化还原条件引起了人们的极大兴趣，许多代用指标被用来探测不同时期的氧化还原变化。例如，Ce 的氧化还原行为导致负或正的元素 Ce 异常，已被广泛使用。最近，质量依赖性铈同位素变化被认为是研究自然环境中铈氧化的有力工具。在这项研究中，我们首次证明了铈同位素在氧化反应过程中会发生分馏，从而证实了铈同位素在研究氧化还原反应方面的实用性。这一结果表明，相对于大陆地壳，海水中的Ce同位素组成应向重值方向分馏。测量到的天然岩石样本（碳酸盐岩、带状铁地层和锰结核）的Ce同位素组成各不相同，从-0.055 ± 0.045 ‰到+0.280 ± 0.045 ‰不等。碳酸盐岩中的Ce元素异常与Ce同位素组成之间的关系表明，与质量相关的Ce同位素可用于区分氧化反应产生的元素异常与其他过程产生的元素异常。质量依赖性Ce同位素分析与La-Ce年代学相结合，是研究过去海洋氧化还原反应的有力工具。
{"title":"Stable cerium isotopes as a tracer of oxidation reactions","authors":"P. Bonnand, M. Boyet, C. Bosq","doi":"10.7185/geochemlet.2340","DOIUrl":"https://doi.org/10.7185/geochemlet.2340","url":null,"abstract":"Redox conditions in past oceans have attracted significant interest and many proxies have been used to probe redox changes through time. For example, the redox dependent behaviour of Ce, resulting in negative or positive elemental Ce anomalies, has been widely used. More recently, mass dependent Ce isotopic variations have been proposed as a powerful tool to study Ce oxidation in natural environments. In this study, we demonstrate, for the first time, that Ce isotopes are fractionated during oxidation reaction, confirming the utility of Ce isotopes to study redox reactions. This result suggests that seawater Ce isotopic composition should be fractionated toward heavy values relative to the continental crust. Measured natural rock samples (carbonates, banded iron formations and Mn nodules) have variable Ce isotopic compositions, ranging from −0.055 ± 0.045 ‰ to +0.280 ± 0.045 ‰. The relation between Ce elemental anomalies and Ce isotopic composition in carbonate rocks suggest that mass dependent Ce isotopes can be used to distinguish elemental anomalies produced by oxidation reactions from those produced by other processes. Coupled with La-Ce chronology, mass dependent Ce isotope analysis is a very powerful tool to study redox reactions in past oceans.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138743596","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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