TY - JOUR
T1 - Three-dimensional microstructure and mineralogy of a cosmic symplectite in the Acfer 094 carbonaceous chondrite
T2 - Implication for its origin
AU - Matsumoto, Megumi
AU - Tsuchiyama, Akira
AU - Miyake, Akira
AU - Ito, Motoo
AU - Matsuno, Junya
AU - Uesugi, Kentaro
AU - Takeuchi, Akihisa
AU - Kodama, Yu
AU - Yasutake, Masahiro
AU - Vaccaro, Epifanio
N1 - Funding Information:
We thank S. S. Russell and Open University in Milton Keynes for providing Acfer 094 sample, A. Nakato for preliminary FE-SEM observation, T. Nakano and R. Stefano for supporting CT data processing, N. Tomioka, Y. Seto, T. Kim, and members of mineralogical laboratory in Kyoto University and early Solar System evolution research group in Tohoku University for helpful discussion, JEOL Ltd. for performing STEM-EDS analysis. We also thank anonymous reviewers and A. N. Krot, for their helpful reviews. The SR-XCT experiments at SPring-8 in this study were conducted under the proposals No. 2016A1245, 2016A1253, 2016B1350, 2016B1351, 2017A1442, 2017A1496, and 2017B1517. Funding: This study was supported by JSPS KAKENHI No. 15H05695 and No. 20H00205 for A. T., and No. 19K14776 for M. M. A. T. was also supported by Chinese Academy of Sciences President’s International Fellowship Initiative, Grant No.2019VCA0004.
Funding Information:
We thank S. S. Russell and Open University in Milton Keynes for providing Acfer 094 sample, A. Nakato for preliminary FE-SEM observation, T. Nakano and R. Stefano for supporting CT data processing, N. Tomioka, Y. Seto, T. Kim, and members of mineralogical laboratory in Kyoto University and early Solar System evolution research group in Tohoku University for helpful discussion, JEOL Ltd. for performing STEM-EDS analysis. We also thank anonymous reviewers and A. N. Krot, for their helpful reviews. The SR-XCT experiments at SPring-8 in this study were conducted under the proposals No. 2016A1245, 2016A1253, 2016B1350, 2016B1351, 2017A1442, 2017A1496, and 2017B1517. Funding: This study was supported by JSPS KAKENHI No. 15H05695 and No. 20H00205 for A. T. and No. 19K14776 for M. M. A. T. was also supported by Chinese Academy of Sciences President's International Fellowship Initiative, Grant No.2019VCA0004.
Publisher Copyright:
© 2022 Elsevier Ltd
PY - 2022/4/15
Y1 - 2022/4/15
N2 - Cosmic symplectites (COSes), consisting mainly of nanoscaled symplectic intergrowths of magnetite and Fe-Ni sulfides, have extremely heavy oxygen isotopic compositions and are considered tracers of 16O-poor primordial ice in the early solar system. We examined the three-dimensional microstructure and mineralogy of one COS particle, COS#1, in the Acfer 094 carbonaceous chondrite and investigated its origin. Synchrotron-radiation based X-ray computed nanotomography revealed a presence of micro-inclusions inside COS#1. The largest inclusion consists mainly of high-temperature phases of anhydrous sodium sulfate (Na2SO4) and elemental sulfur, which seem to have been formed from a Na2SO4-S eutectic melt. COS#1 showed a trilayered structure surrounding the large inclusion: the innermost coarse-grained layer consisting mainly of 100–200 nm-sized magnetite and Fe-sulfide, the symplectite layer consisting mainly of nanoscaled symplectic intergrowths of magnetite and Fe-Ni sulfides, and the outermost Fe-oxide layer. The symplectite layer comprises the major volume of COS#1 and shows the pseudomorphic structure of precursor Fe-Ni metal grains. The coarse-grained layer seems to have been formed via metal–salt interaction (hot corrosion) at high temperatures, where the precursor Fe-Ni metals contacted with the Na2SO4-S melt. The symplectite formed simultaneously with the coarse-grained layer due to high-speed diffusion of sulfur and oxygen inside the metal grains. The high-temperature metal–salt interactions should have occurred before the incorporation of COS#1 into the meteorite parent body. The precursor of COS#1 should have consisted of Fe-Ni metals and O-Na-S-rich material. The two reductive and oxidative components seem to have formed separately and got together by some mechanical mixing processes in nebula. The COS#1 precursor was heated in a short period and the O-Na-S-rich material melted. The melt induced the hot corrosion of the Fe-Ni metals and was subsequently cooled and solidified. Subsequently, it was incorporated into the meteorite parent body as COS#1. In the parent body, aqueous alteration occurred and formed the outermost Fe-oxide layer on the COS#1 surface.
AB - Cosmic symplectites (COSes), consisting mainly of nanoscaled symplectic intergrowths of magnetite and Fe-Ni sulfides, have extremely heavy oxygen isotopic compositions and are considered tracers of 16O-poor primordial ice in the early solar system. We examined the three-dimensional microstructure and mineralogy of one COS particle, COS#1, in the Acfer 094 carbonaceous chondrite and investigated its origin. Synchrotron-radiation based X-ray computed nanotomography revealed a presence of micro-inclusions inside COS#1. The largest inclusion consists mainly of high-temperature phases of anhydrous sodium sulfate (Na2SO4) and elemental sulfur, which seem to have been formed from a Na2SO4-S eutectic melt. COS#1 showed a trilayered structure surrounding the large inclusion: the innermost coarse-grained layer consisting mainly of 100–200 nm-sized magnetite and Fe-sulfide, the symplectite layer consisting mainly of nanoscaled symplectic intergrowths of magnetite and Fe-Ni sulfides, and the outermost Fe-oxide layer. The symplectite layer comprises the major volume of COS#1 and shows the pseudomorphic structure of precursor Fe-Ni metal grains. The coarse-grained layer seems to have been formed via metal–salt interaction (hot corrosion) at high temperatures, where the precursor Fe-Ni metals contacted with the Na2SO4-S melt. The symplectite formed simultaneously with the coarse-grained layer due to high-speed diffusion of sulfur and oxygen inside the metal grains. The high-temperature metal–salt interactions should have occurred before the incorporation of COS#1 into the meteorite parent body. The precursor of COS#1 should have consisted of Fe-Ni metals and O-Na-S-rich material. The two reductive and oxidative components seem to have formed separately and got together by some mechanical mixing processes in nebula. The COS#1 precursor was heated in a short period and the O-Na-S-rich material melted. The melt induced the hot corrosion of the Fe-Ni metals and was subsequently cooled and solidified. Subsequently, it was incorporated into the meteorite parent body as COS#1. In the parent body, aqueous alteration occurred and formed the outermost Fe-oxide layer on the COS#1 surface.
KW - Carbonaceous chondrite
KW - Cosmic symplectite
KW - Hot corrosion
KW - NanoSIMS
KW - TEM
KW - X-ray nanotomography
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U2 - 10.1016/j.gca.2022.02.024
DO - 10.1016/j.gca.2022.02.024
M3 - Article
AN - SCOPUS:85126307559
SN - 0016-7037
VL - 323
SP - 220
EP - 241
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
ER -