Zircon trace element and isotopic analysis for an increasing number of isotopic systems provide valuable insights into magma crystallisation, and evolution of the continental crust. Zirconium stable isotopes have been measured recently and shown to vary by several per mille on Earth. Both positive and negative shifts of δ94/90Zr have been found in zircons and melts, and equilibrium isotopic fractionations are found to be small. We here employ and further develop a zircon crystallisation programme with two moving boundaries targeting zircon crystallisation in the presence of other minerals. We reproduce positive, negative, and inverse δ94/90Zr, Zr/Hf, and other compatible trace element variations in zircon and surrounding melt that can be entirely explained by the boundary layer processes during kinetics of zircon crystallisation in a realistic set of geologic conditions. Progressively lower δ94/90Zr values in zircon develop during rapid crystallisation, lower melt water contents, crystallisation in the lower temperature range, and whilst co-crystallising with the Zr-poor phase. Given large (multi-per mille) kinetic Zr isotope fractionations discovered, zircon may serve as a monitor of magmatic crystallisation conditions, but is unlikely to serve as a diagnostic tool for the bigger set of petrological problems (e.g., evolution of the continental crust) without proper context.
{"title":"The rises and falls of zirconium isotopes during zircon crystallisation","authors":"I.N. Bindeman, O.E. Melnik","doi":"10.7185/geochemlet.2241","DOIUrl":"https://doi.org/10.7185/geochemlet.2241","url":null,"abstract":"Zircon trace element and isotopic analysis for an increasing number of isotopic systems provide valuable insights into magma crystallisation, and evolution of the continental crust. Zirconium stable isotopes have been measured recently and shown to vary by several per mille on Earth. Both positive and negative shifts of δ<sup>94/90</sup>Zr have been found in zircons and melts, and equilibrium isotopic fractionations are found to be small. We here employ and further develop a zircon crystallisation programme with two moving boundaries targeting zircon crystallisation in the presence of other minerals. We reproduce positive, negative, and inverse δ<sup>94/90</sup>Zr, Zr/Hf, and other compatible trace element variations in zircon and surrounding melt that can be entirely explained by the boundary layer processes during kinetics of zircon crystallisation in a realistic set of geologic conditions. Progressively lower δ<sup>94/90</sup>Zr values in zircon develop during rapid crystallisation, lower melt water contents, crystallisation in the lower temperature range, and whilst co-crystallising with the Zr-poor phase. Given large (multi-per mille) kinetic Zr isotope fractionations discovered, zircon may serve as a monitor of magmatic crystallisation conditions, but is unlikely to serve as a diagnostic tool for the bigger set of petrological problems (<em>e.g.</em>, evolution of the continental crust) without proper context.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":"20 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138531304","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}
Y. Yu, R. Xie, M. Gutjahr, G. Laukert, Z. Cao, E. Hathorne, C. Siebert, G. Patton, M. Frank
{"title":"High latitude controls on dissolved barium isotope distributions in the global ocean","authors":"Y. Yu, R. Xie, M. Gutjahr, G. Laukert, Z. Cao, E. Hathorne, C. Siebert, G. Patton, M. Frank","doi":"10.7185/geochemlet.2242","DOIUrl":"https://doi.org/10.7185/geochemlet.2242","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42185216","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}
Phosphorus (P) concentrations in zircon have been used to discriminate their derivation from metaluminous versus strongly peraluminous granites (SPGs) based on the empirical observation of lower P concentrations in zircon from Phanerozoic metaluminous versus peraluminous granites. Higher P concentrations in zircon from Phanerozoic SPGs reflect enhanced apatite solubility in peraluminous melts and overall higher P concentrations in peraluminous granites. However, SPGs derived from partial melting of Precambrian sedimentary rocks have lower P concentrations compared to Phanerozoic metaluminous granites, reflecting lower P concentrations in Precambrian versus Phanerozoic sedimentary sources. We demonstrate that zircons from Precambrian SPGs also have lower P concentrations compared to Phanerozoic counterparts, likely reflecting lower P concentrations in their parental melts. Applying the P-in-zircon proxy to the detrital zircon record does not effectively discriminate between metaluminous and peraluminous sources and underestimates contributions from peraluminous granites. Although detrital zircons are an important early Earth archive, a uniformitarian perspective cannot always be applied when using trace element proxies developed on Phanerozoic samples.
{"title":"Secular variability in zircon phosphorus concentrations prevents simple petrogenetic classification","authors":"C.E. Bucholz, J. Liebmann, C.J. Spencer","doi":"10.7185/geochemlet.2240","DOIUrl":"https://doi.org/10.7185/geochemlet.2240","url":null,"abstract":"Phosphorus (P) concentrations in zircon have been used to discriminate their derivation from metaluminous <em>versus</em> strongly peraluminous granites (SPGs) based on the empirical observation of lower P concentrations in zircon from Phanerozoic metaluminous <em>versus</em> peraluminous granites. Higher P concentrations in zircon from Phanerozoic SPGs reflect enhanced apatite solubility in peraluminous melts and overall higher P concentrations in peraluminous granites. However, SPGs derived from partial melting of Precambrian sedimentary rocks have lower P concentrations compared to Phanerozoic metaluminous granites, reflecting lower P concentrations in Precambrian <em>versus</em> Phanerozoic sedimentary sources. We demonstrate that zircons from Precambrian SPGs also have lower P concentrations compared to Phanerozoic counterparts, likely reflecting lower P concentrations in their parental melts. Applying the P-in-zircon proxy to the detrital zircon record does not effectively discriminate between metaluminous and peraluminous sources and underestimates contributions from peraluminous granites. Although detrital zircons are an important early Earth archive, a uniformitarian perspective cannot always be applied when using trace element proxies developed on Phanerozoic samples.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":"1 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138531331","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}
Y. Sano, D. Pinti, T. Escobar-Nakajima, N. Takahata, M. Zhang, D. Goto, B. Marty
{"title":"Sun flare activity may solve unknown source of helium-3 in the atmosphere","authors":"Y. Sano, D. Pinti, T. Escobar-Nakajima, N. Takahata, M. Zhang, D. Goto, B. Marty","doi":"10.7185/geochemlet.2237","DOIUrl":"https://doi.org/10.7185/geochemlet.2237","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47777154","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}
A. Dickson, M. Davies, Marie-Laure Bagard, A. Cohen
The closure of seaways that connected the Arctic Ocean to the global ocean during the early Paleogene led to severe hydrographic restriction. We present new osmium isotope datafrom organic-rich sediments deposited in the central ArcticOcean during the Early – Middle Eocene. The new data show that the long term isotopic composition of osmium in Arctic seawater began to diverge from that of the global ocean at ∼ 54 Ma, after the Eocene Thermal Maximum 2 hyperthermal event. This divergence was prob-ablycausedbythegradualclosure of seaways connectingtheArcticOceantothe global ocean. The Os data are used to calculate water exchange rates between the Arctic and surrounding oceans and to calculate Arctic Ocean salinity during the Early Eocene. The results show that the development of severe, long term Arctic Basin restriction after ∼ 54 Ma occurred as open ocean seawater input decreased below ∼ 0.01 Sv, resulting in a mean basin salinity between 8 – 16 PSU, depending on model assumptions.
{"title":"Quantifying seawater exchange rates in the Eocene Arctic Basin using osmium isotopes","authors":"A. Dickson, M. Davies, Marie-Laure Bagard, A. Cohen","doi":"10.7185/geochemlet.2239","DOIUrl":"https://doi.org/10.7185/geochemlet.2239","url":null,"abstract":"The closure of seaways that connected the Arctic Ocean to the global ocean during the early Paleogene led to severe hydrographic restriction. We present new osmium isotope datafrom organic-rich sediments deposited in the central ArcticOcean during the Early – Middle Eocene. The new data show that the long term isotopic composition of osmium in Arctic seawater began to diverge from that of the global ocean at ∼ 54 Ma, after the Eocene Thermal Maximum 2 hyperthermal event. This divergence was prob-ablycausedbythegradualclosure of seaways connectingtheArcticOceantothe global ocean. The Os data are used to calculate water exchange rates between the Arctic and surrounding oceans and to calculate Arctic Ocean salinity during the Early Eocene. The results show that the development of severe, long term Arctic Basin restriction after ∼ 54 Ma occurred as open ocean seawater input decreased below ∼ 0.01 Sv, resulting in a mean basin salinity between 8 – 16 PSU, depending on model assumptions.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43927460","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}
Q. Ahmad, M. Wille, C. Rosca, Jabrane Labidi, T. Schmid, K. Mezger, S. König
Under modern oxidising Earth surface conditions, dehydrated subducted slabs show Mo isotope compositions as low as δ 98/95 Mo = − 1.5 ‰ , compared to the depleted mantle δ 98/95 Mo = − 0.2 ‰ . Such light Mo isotope compositions reflect the redox-dependent aqueous mobility of isotopically heavy Mo associated with slab dehydration. Here we analysed basaltic glasses from the South-Mid Atlantic Ridge, whose parental melts are influenced by the enriched Discovery and Shona mantle plumes. We report increasingly higher δ 98/95 Mo of up to − 0.1 ‰ from the most depleted samples towards those tapping more enriched mantle sources. δ 98/95 Mo values correlate with radiogenic Sr and Nd isotopes, which indicates the recycling of Proterozoic sediments with a Mo isotopic composition that was not affected by subduction-related, oxic dehydration. We propose that the Mo isotope signatures were retained during subduction and reflect anoxic conditions during deep sea sedimentation in the mid-Proterozoic. Finally, Mo isotope fractionation between different terrestrial reservoirs likely depends on the slab redox budget, and therefore on the timing of subduction with regard to Earth ’ s surface oxygenation.
{"title":"Molybdenum isotopes in plume-influenced MORBs reveal recycling of ancient anoxic sediments","authors":"Q. Ahmad, M. Wille, C. Rosca, Jabrane Labidi, T. Schmid, K. Mezger, S. König","doi":"10.7185/geochemlet.2236","DOIUrl":"https://doi.org/10.7185/geochemlet.2236","url":null,"abstract":"Under modern oxidising Earth surface conditions, dehydrated subducted slabs show Mo isotope compositions as low as δ 98/95 Mo = − 1.5 ‰ , compared to the depleted mantle δ 98/95 Mo = − 0.2 ‰ . Such light Mo isotope compositions reflect the redox-dependent aqueous mobility of isotopically heavy Mo associated with slab dehydration. Here we analysed basaltic glasses from the South-Mid Atlantic Ridge, whose parental melts are influenced by the enriched Discovery and Shona mantle plumes. We report increasingly higher δ 98/95 Mo of up to − 0.1 ‰ from the most depleted samples towards those tapping more enriched mantle sources. δ 98/95 Mo values correlate with radiogenic Sr and Nd isotopes, which indicates the recycling of Proterozoic sediments with a Mo isotopic composition that was not affected by subduction-related, oxic dehydration. We propose that the Mo isotope signatures were retained during subduction and reflect anoxic conditions during deep sea sedimentation in the mid-Proterozoic. Finally, Mo isotope fractionation between different terrestrial reservoirs likely depends on the slab redox budget, and therefore on the timing of subduction with regard to Earth ’ s surface oxygenation.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44164007","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. Ma, W. Neumann, A. Néri, W. Schwarz, T. Ludwig, M. Trieloff, H. Klahr, A. Bouvier
We compare 13 Tafassasset-related meteorites and propose that they form the first meteorite group of carbonaceous primitive achondrites. We name this new group the Tafassites, which form a continuum from equilibrated petrological type 6 chondrites (termed T6) to partially molten type 7 primitive achondrites (T7) and bear carbonaceous meteorite-like (C) mass-independent isotopic signatures. We use SIMS Pb – Pb Ca phosphate ages to model the Tafassite parent body (TPB) accretion at 1.1 + 0.3 − 0.4 Myr before rapid cooling to below ∼ 720 K within ∼ 9.0 ± 5.0 Myr after CAI formation, respectively. This scenario is consistent with other primitive achondrites but incompatible with a commonly assumed CR chondrite parent body, which was constrained by Al – Mg, Hf – W, and Pb – Pb chondrule ages up to > 3.7 Myr after CAIs. Given their carbonaceous-like affinity, Tafassites therefore constitute the first early accreted chondritic meteorite group from an outer region of the protoplanetary disc, presumably close to the further CR feeding zone. Our findings support that planetary formation in the outer protoplanetary disc evolved nearly coevally with the inner part of the disc, with limited admixing of inward material during planetesimal formation over 4 million years after CAIs.
{"title":"Early formation of primitive achondrites in an outer region of the protoplanetary disc","authors":"N. Ma, W. Neumann, A. Néri, W. Schwarz, T. Ludwig, M. Trieloff, H. Klahr, A. Bouvier","doi":"10.7185/geochemlet.2234","DOIUrl":"https://doi.org/10.7185/geochemlet.2234","url":null,"abstract":"We compare 13 Tafassasset-related meteorites and propose that they form the first meteorite group of carbonaceous primitive achondrites. We name this new group the Tafassites, which form a continuum from equilibrated petrological type 6 chondrites (termed T6) to partially molten type 7 primitive achondrites (T7) and bear carbonaceous meteorite-like (C) mass-independent isotopic signatures. We use SIMS Pb – Pb Ca phosphate ages to model the Tafassite parent body (TPB) accretion at 1.1 + 0.3 − 0.4 Myr before rapid cooling to below ∼ 720 K within ∼ 9.0 ± 5.0 Myr after CAI formation, respectively. This scenario is consistent with other primitive achondrites but incompatible with a commonly assumed CR chondrite parent body, which was constrained by Al – Mg, Hf – W, and Pb – Pb chondrule ages up to > 3.7 Myr after CAIs. Given their carbonaceous-like affinity, Tafassites therefore constitute the first early accreted chondritic meteorite group from an outer region of the protoplanetary disc, presumably close to the further CR feeding zone. Our findings support that planetary formation in the outer protoplanetary disc evolved nearly coevally with the inner part of the disc, with limited admixing of inward material during planetesimal formation over 4 million years after CAIs.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45125987","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}
F. Moynier, W. Dai, T. Yokoyama, Y. Hu, M. Paquet, Y. Abe, J. Aléon, C. Alexander, S. Amari, Y. Amelin, K. Bajo, M. Bizzarro, A. Bouvier, R. Carlson, M. Chaussidon, B.-G. Choi, N. Dauphas, A. Davis, T. Di Rocco, W. Fujiya, R. Fukai, I. Gautam, M. Haba, Y. Hibiya, H. Hidaka, H. Homma, P. Hoppe, G. Huss, K. Ichida, T. Iizuka, T. Ireland, A. Ishikawa, M. Ito, S. Itoh, N. Kawasaki, N. Kita, K. Kitajima, T. Kleine, S. Komatani, A. Krot, M. Liu, Y. Masuda, K. McKeegan, M. Morita, K. Motomura, I. Nakai, K. Nagashima, D. Nesvorný, 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, R. Walker, K. Yamashita, Q. Yin, S. Yoneda, E. Young, H. Yui, Alvin 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. Watanabe, M. Yoshikawa, S.
The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as δ 44/40 Ca SRM915a ) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar δ 44/40 Ca SRM915a (0.58 ± 0.03 ‰ and 0.55 ± 0.08 ‰ , 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred ∼ 5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average δ 44/40 Ca SRM915a of the Solar System is defined to be 0.57 ± 0.04 ‰ (2
隼鸟2号宇宙飞船已将cb型小行星(162173)龙宫的样本带回地球。先前的岩石学和化学分析支持了Ryugu和CI球粒陨石之间的密切联系，它们被认为是化学上最原始的陨石，具有类似太阳的成分。然而，与典型的CI球粒陨石相比，Ryugu样品富含Ca。为了确定这种差异的原因，我们报告了从两个地点收集的龙宫样品的稳定Ca同位素数据(表示为δ 44/40 Ca SRM915a)。我们发现两个地点的样品具有相似的δ 44/40 Ca SRM915a(0.58±0.03‰和0.55±0.08‰，2 s.d)，属于ci定义的范围。这种同位素相似性表明，CIs和琉球样品的Ca收支以碳酸盐为主，琉球样品中Ca含量的变化是由于丰富的碳酸盐所致。龙宫上碳酸盐的沉淀很可能与太阳系形成后约5 Myr发生的一次主要的水活动相吻合。根据原始龙宫样品，确定了太阳系δ 44/40 Ca SRM915a平均值为0.57±0.04‰(2
{"title":"The Solar System calcium isotopic composition inferred from Ryugu samples","authors":"F. Moynier, W. Dai, T. Yokoyama, Y. Hu, M. Paquet, Y. Abe, J. Aléon, C. Alexander, S. Amari, Y. Amelin, K. Bajo, M. Bizzarro, A. Bouvier, R. Carlson, M. Chaussidon, B.-G. Choi, N. Dauphas, A. Davis, T. Di Rocco, W. Fujiya, R. Fukai, I. Gautam, M. Haba, Y. Hibiya, H. Hidaka, H. Homma, P. Hoppe, G. Huss, K. Ichida, T. Iizuka, T. Ireland, A. Ishikawa, M. Ito, S. Itoh, N. Kawasaki, N. Kita, K. Kitajima, T. Kleine, S. Komatani, A. Krot, M. Liu, Y. Masuda, K. McKeegan, M. Morita, K. Motomura, I. Nakai, K. Nagashima, D. Nesvorný, 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, R. Walker, K. Yamashita, Q. Yin, S. Yoneda, E. Young, H. Yui, Alvin 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. Watanabe, M. Yoshikawa, S.","doi":"10.7185/geochemlet.2238","DOIUrl":"https://doi.org/10.7185/geochemlet.2238","url":null,"abstract":"The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as δ 44/40 Ca SRM915a ) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar δ 44/40 Ca SRM915a (0.58 ± 0.03 ‰ and 0.55 ± 0.08 ‰ , 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred ∼ 5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average δ 44/40 Ca SRM915a of the Solar System is defined to be 0.57 ± 0.04 ‰ (2","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44847057","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}
J. W. Dottin III, J. Farquhar, S.‐T. Kim, C. Shearer, B. Wing, J. Sun, P. Ni
Lunar gardening results in volatile mobilisation and stable isotopic fractionations that are mass dependent. An unambiguous role for mass independent fractionation (MIF), such as that produced by photochemistry, has not been demonstrated on the Moon. We observe MIF for sulfur isotopes in lunar soil 75081, 690 while MIF is not observed in soil 74241, 204. The MIF is likely generated after sulfur is volatilised during soil maturation processes. The isotopic discrepancy between 75081, 690 and 74241, 204 may reflect differences in photochemistry, such as illumination or in generation of photochemically active volatile sulfur species, for instance, due to varying H contents from solar wind implantation.
{"title":"Isotopic evidence of sulfur photochemistry during lunar regolith formation","authors":"J. W. Dottin III, J. Farquhar, S.‐T. Kim, C. Shearer, B. Wing, J. Sun, P. Ni","doi":"10.7185/geochemlet.2235","DOIUrl":"https://doi.org/10.7185/geochemlet.2235","url":null,"abstract":"Lunar gardening results in volatile mobilisation and stable isotopic fractionations that are mass dependent. An unambiguous role for mass independent fractionation (MIF), such as that produced by photochemistry, has not been demonstrated on the Moon. We observe MIF for sulfur isotopes in lunar soil 75081, 690 while MIF is not observed in soil 74241, 204. The MIF is likely generated after sulfur is volatilised during soil maturation processes. The isotopic discrepancy between 75081, 690 and 74241, 204 may reflect differences in photochemistry, such as illumination or in generation of photochemically active volatile sulfur species, for instance, due to varying H contents from solar wind implantation.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44658632","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.R. Bennett, C.K. Sio, E. Schauble, C.E. Lesher, J. Wimpenny, A. Shahar
Despite decades of work, the origin of pallasite meteorites has remained enigmatic. Long thought to be samples of the core-mantle boundary of differentiated asteroids, more recent studies have suggested a range of mechanisms for pallasite formation. These include olivine-metal mixing during a planetesimal collision and the intrusion of over-pressured core liquids into a planetesimal mantle. Establishing if the olivine and metal that comprise pallasites were once equilibrated at high temperature remains key to discriminating between these hypotheses. To this end, we determined the iron isotope compositions of olivine and metal in eleven main-group pallasites and found, in all cases, that olivine is isotopically lighter than metal. To interpret these data, we constrained the olivine-metal equilibrium Fe isotope fractionation with ab initio calculations and high temperature experiments. These independent approaches show that olivine preferentially incorporates the heavy isotopes of iron relative to metal. Our results demonstrate that pallasitic olivine and metal never achieved isotopic equilibrium with respect to iron. This precludes extended cooling at high temperature and is best reconciled with an impact origin for the main-group pallasites.
{"title":"Iron isotope evidence of an impact origin for main-group pallasites","authors":"N.R. Bennett, C.K. Sio, E. Schauble, C.E. Lesher, J. Wimpenny, A. Shahar","doi":"10.7185/geochemlet.2229","DOIUrl":"https://doi.org/10.7185/geochemlet.2229","url":null,"abstract":"Despite decades of work, the origin of pallasite meteorites has remained enigmatic. Long thought to be samples of the core-mantle boundary of differentiated asteroids, more recent studies have suggested a range of mechanisms for pallasite formation. These include olivine-metal mixing during a planetesimal collision and the intrusion of over-pressured core liquids into a planetesimal mantle. Establishing if the olivine and metal that comprise pallasites were once equilibrated at high temperature remains key to discriminating between these hypotheses. To this end, we determined the iron isotope compositions of olivine and metal in eleven main-group pallasites and found, in all cases, that olivine is isotopically lighter than metal. To interpret these data, we constrained the olivine-metal equilibrium Fe isotope fractionation with <em>ab initio</em> calculations and high temperature experiments. These independent approaches show that olivine preferentially incorporates the heavy isotopes of iron relative to metal. Our results demonstrate that pallasitic olivine and metal never achieved isotopic equilibrium with respect to iron. This precludes extended cooling at high temperature and is best reconciled with an impact origin for the main-group pallasites.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":"6 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2022-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138543171","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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