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":null,"pages":null},"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}
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":null,"pages":null},"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}
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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}
Basaltic partial melts are produced in a range of tectonic settings, including fluid-assisted melting above subduction zones, decompression melting at ridges and thermally driven melting above mantle plumes. To examine the role of partial melting on Zn, isotope and abundance data are reported for modern large-degree partial melts of the mantle represented by 22 mid-ocean ridge basalts (MORB) from three ocean basins and the first data for boninites. Boninites have some of the lowest Zn abundances of all terrestrial basalts and Zn isotope compositions ( δ 66 Zn = þ 0.21 ± 0.06 ‰ ), generally lighter than for MORB ( δ 66 Zn = þ 0.28 ± 0.06 ‰ ). Accounting for partial melting, komatiites, boninites and MORB derive from mantle sources with δ 66 Zn of ∼ 0.16 ± 0.06 ‰ . Lower-degree partial melts, such as alkali basalts, can have higher δ 66 Zn, with up to ∼ 0.4 ‰ variation possible from partial melting of distinct peridotite mantle sources. Partial melting of fertile lherzolitic and depleted harzburgitic mantle sources can generate significant Zn isotope variability and should be evaluated prior to ascribing crustal, enriched or lithological components to mantle reservoirs from Zn compositions of planetary basalts.
{"title":"A partial melting control on the Zn isotope composition of basalts","authors":"J. Day, F. Moynier, O. Ishizuka","doi":"10.7185/geochemlet.2230","DOIUrl":"https://doi.org/10.7185/geochemlet.2230","url":null,"abstract":"Basaltic partial melts are produced in a range of tectonic settings, including fluid-assisted melting above subduction zones, decompression melting at ridges and thermally driven melting above mantle plumes. To examine the role of partial melting on Zn, isotope and abundance data are reported for modern large-degree partial melts of the mantle represented by 22 mid-ocean ridge basalts (MORB) from three ocean basins and the first data for boninites. Boninites have some of the lowest Zn abundances of all terrestrial basalts and Zn isotope compositions ( δ 66 Zn = þ 0.21 ± 0.06 ‰ ), generally lighter than for MORB ( δ 66 Zn = þ 0.28 ± 0.06 ‰ ). Accounting for partial melting, komatiites, boninites and MORB derive from mantle sources with δ 66 Zn of ∼ 0.16 ± 0.06 ‰ . Lower-degree partial melts, such as alkali basalts, can have higher δ 66 Zn, with up to ∼ 0.4 ‰ variation possible from partial melting of distinct peridotite mantle sources. Partial melting of fertile lherzolitic and depleted harzburgitic mantle sources can generate significant Zn isotope variability and should be evaluated prior to ascribing crustal, enriched or lithological components to mantle reservoirs from Zn compositions of planetary basalts.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46460824","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}
B. Laurent, L. Remusat, J. Viennet, R. Brunetto, L. Binet, M. Holin, M. Ciocco, C. Bouvier, A. Brunelle, S. Bernard
Mighei-type carbonaceous chondrites (CM) figure among the most primitive objects in the solar system. Yet, they all have experienced various degrees of aqueous alteration having modified their insoluble organic matter (IOM), in a sequence that remains to be accurately constrained. Here, we exposed the IOM of Paris, the least altered CM available, to hydrothermal conditions at 150 °C for 49 days and compared the experimental residue to the IOM of two altered CMs likely originating from the same parent body as Paris, namely Aguas Zarcas and Mukundpura. The experimental residue shows a chemical and isotopic composition similar to those of Aguas Zarcas and Mukundpura IOMs, confirming that these CMs can be seen as altered counterparts of Paris. The abundance of organic radicals also increases significantly during the experiment. Isotopic hotspots do not seem to have been lost during the experiment, suggesting that the hotspots generally observed within the CM IOMs may date back from pre-accretion era. Of note, the Raman signature of the residue differs from that of the CM IOMs, highlighting the need for further experiments better mimicking asteroidal-like conditions.
{"title":"reservation of the isotope signatures in chondritic IOM during aqueous alteration","authors":"B. Laurent, L. Remusat, J. Viennet, R. Brunetto, L. Binet, M. Holin, M. Ciocco, C. Bouvier, A. Brunelle, S. Bernard","doi":"10.7185/geochemlet.2233","DOIUrl":"https://doi.org/10.7185/geochemlet.2233","url":null,"abstract":"Mighei-type carbonaceous chondrites (CM) figure among the most primitive objects in the solar system. Yet, they all have experienced various degrees of aqueous alteration having modified their insoluble organic matter (IOM), in a sequence that remains to be accurately constrained. Here, we exposed the IOM of Paris, the least altered CM available, to hydrothermal conditions at 150 °C for 49 days and compared the experimental residue to the IOM of two altered CMs likely originating from the same parent body as Paris, namely Aguas Zarcas and Mukundpura. The experimental residue shows a chemical and isotopic composition similar to those of Aguas Zarcas and Mukundpura IOMs, confirming that these CMs can be seen as altered counterparts of Paris. The abundance of organic radicals also increases significantly during the experiment. Isotopic hotspots do not seem to have been lost during the experiment, suggesting that the hotspots generally observed within the CM IOMs may date back from pre-accretion era. Of note, the Raman signature of the residue differs from that of the CM IOMs, highlighting the need for further experiments better mimicking asteroidal-like conditions.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48969267","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. Nana Yobo, A. Brandon, L.M. Lauckner, J. Eldrett, S. Bergman, D. Minisini
The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2). Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear. In this study, a reconstruction of mid-Cenomanian seawater 187 Os/ 188 Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE. The absence of a prolonged unradiogenic Os isotope excursion (low 187 Os/ 188 Os) at the onset of the MCE interval argues against LIP involvement in the event ’ s initiation. Rather, more radiogenic 187 Os/ 188 Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering. The combination of decreasing 187 Os/ 188 Os from the middle of the MCE onward, coincident with a 40 Ar/ 39 Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE. These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.
{"title":"Enhanced continental weathering activity at the onset of the mid-Cenomanian Event (MCE)","authors":"L. Nana Yobo, A. Brandon, L.M. Lauckner, J. Eldrett, S. Bergman, D. Minisini","doi":"10.7185/geochemlet.2231","DOIUrl":"https://doi.org/10.7185/geochemlet.2231","url":null,"abstract":"The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2). Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear. In this study, a reconstruction of mid-Cenomanian seawater 187 Os/ 188 Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE. The absence of a prolonged unradiogenic Os isotope excursion (low 187 Os/ 188 Os) at the onset of the MCE interval argues against LIP involvement in the event ’ s initiation. Rather, more radiogenic 187 Os/ 188 Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering. The combination of decreasing 187 Os/ 188 Os from the middle of the MCE onward, coincident with a 40 Ar/ 39 Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE. These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44299202","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}
New 87 Rb- 87 Sr data are reported for emeralds from Gravelotte, South Africa and Muzo, Colombia, the first such data in 30 years. The Gravelotte deposit is inferred to be the world ’ s oldest emerald deposit from the ∼ 2.97 Ga U-Pb age of the associated pegmatite. The majority of Gravelotte emeralds plot on an 87 Rb- 87 Sr errorchron with an age of 2883 ± 131 Ma, close to the pegmatite age, demonstrating that the emeralds are Mesoarchean in age. The Muzo emerald data, when combined with data from nearby Colombian emerald deposits, define an age of ∼ 48 Ma, younger than muscovite Ar-Ar ages (65 – 62 Ma), likely reflecting the resetting of 87 Rb- 87 Sr in some emeralds. The initial Sr isotopic composition for Gravelotte emeralds is radiogenic ( 87 Sr/ 86 Sr i = 0.841), and their trace element signatures support their formation from a mature, high Rb/Sr, felsic continental crustal protolith in the Mesoarchean. Direct 87 Rb- 87 Sr dating of emeralds holds promise for offering constraints on both mineralisation ages and source compositions.
报道了南非Gravelotte和哥伦比亚Muzo祖母绿的87 Rb- 87 Sr数据，这是30年来首次获得此类数据。根据其伴生伟晶岩的~ 2.97 Ga U-Pb年龄推断，该砾石矿床是世界上最古老的祖母绿矿床。砾石型祖母绿的锆石年龄为2883±131 Ma，与伟晶岩的锆石年龄接近，属于中太古代。Muzo祖母绿数据与附近哥伦比亚祖母绿矿床的数据相结合，确定了~ 48 Ma的年龄，比白云母Ar-Ar年龄(65 - 62 Ma)年轻，可能反映了一些祖母绿中87 Rb- 87 Sr的重置。砾石祖母绿的初始Sr同位素组成为放射性成因(87 Sr/ 86 Sr i = 0.841)，其微量元素特征支持其形成于中太古代成熟的高Rb/Sr长英质大陆地壳原岩。祖母绿的直接87 Rb- 87 Sr定年有望提供矿化年龄和来源成分的限制。
{"title":"Archean age and radiogenic source for the world’s oldest emeralds","authors":"R. Nicklas, J. Day, R. Alonso-Pérez","doi":"10.7185/geochemlet.2232","DOIUrl":"https://doi.org/10.7185/geochemlet.2232","url":null,"abstract":"New 87 Rb- 87 Sr data are reported for emeralds from Gravelotte, South Africa and Muzo, Colombia, the first such data in 30 years. The Gravelotte deposit is inferred to be the world ’ s oldest emerald deposit from the ∼ 2.97 Ga U-Pb age of the associated pegmatite. The majority of Gravelotte emeralds plot on an 87 Rb- 87 Sr errorchron with an age of 2883 ± 131 Ma, close to the pegmatite age, demonstrating that the emeralds are Mesoarchean in age. The Muzo emerald data, when combined with data from nearby Colombian emerald deposits, define an age of ∼ 48 Ma, younger than muscovite Ar-Ar ages (65 – 62 Ma), likely reflecting the resetting of 87 Rb- 87 Sr in some emeralds. The initial Sr isotopic composition for Gravelotte emeralds is radiogenic ( 87 Sr/ 86 Sr i = 0.841), and their trace element signatures support their formation from a mature, high Rb/Sr, felsic continental crustal protolith in the Mesoarchean. Direct 87 Rb- 87 Sr dating of emeralds holds promise for offering constraints on both mineralisation ages and source compositions.","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2022-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42208891","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 : 2022-08-01DOI: 10.7185/geochemlet.2226cor
X.-N. Liu, R. Hin, C. Coath, M. van Soest, E. Melekhova, T. Elliott
{"title":"Corrigendum to “Equilibrium olivine-melt Mg isotopic fractionation explains high δ26Mg values in arc lavas” by Liu et al., 2022","authors":"X.-N. Liu, R. Hin, C. Coath, M. van Soest, E. Melekhova, T. Elliott","doi":"10.7185/geochemlet.2226cor","DOIUrl":"https://doi.org/10.7185/geochemlet.2226cor","url":null,"abstract":"","PeriodicalId":12613,"journal":{"name":"Geochemical Perspectives Letters","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2022-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46266099","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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