Unique igneous textures and shock metamorphism of the Northwest Africa 7203 angrite: Implications for crystallization processes and the evolutionary history of the angrite parent body
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Unique igneous textures and shock metamorphism of the Northwest Africa 7203 angrite : Implications for crystallization processes and the evolutionary history of the angrite parent body. / Hayashi, Hideyuki; Mikouchi, Takashi; Kim, Nak Kyu; Park, Changkun; Sano, Yuji; Takenouchi, Atsushi; Yamaguchi, Akira; Kagi, Hiroyuki; Bizzarro, Martin.
In: Meteoritics and Planetary Science, Vol. 57, No. 1, 2022, p. 105-121.Research output: Contribution to journal › Journal article › Research › peer-review
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TY - JOUR
T1 - Unique igneous textures and shock metamorphism of the Northwest Africa 7203 angrite
T2 - Implications for crystallization processes and the evolutionary history of the angrite parent body
AU - Hayashi, Hideyuki
AU - Mikouchi, Takashi
AU - Kim, Nak Kyu
AU - Park, Changkun
AU - Sano, Yuji
AU - Takenouchi, Atsushi
AU - Yamaguchi, Akira
AU - Kagi, Hiroyuki
AU - Bizzarro, Martin
N1 - Publisher Copyright: © 2021 The Meteoritical Society
PY - 2022
Y1 - 2022
N2 - Northwest Africa (NWA) 7203 is a quenched angrite, showing mineralogical features typically not present in other quenched angrites. NWA 7203 exhibits textures whose grain size varies from fine grains (<10 μm) to coarse grains (~3 mm), while other quenched angrites show only single-sized textures. Fine-grained and coarse-grained lithologies have nearly the same bulk compositions. Cooling rates were estimated to be ~80 °C h−1 for fine-grained lithologies and ~1 °C h−1 for coarse-grained lithologies. Mg-rich olivines (~Fo64) were found only in fine-grained lithologies. Crystallization of NWA 7203 started in the fine-grained lithologies with Mg-rich olivine grains acting as seeds for crystallization. Coarse-grained lithologies were subsequently formed under conditions of slower cooling. NWA 7203 shows clear shock metamorphic textures unlike other quenched angrites except for NWA 1670. We confirm that the oxygen isotopic ratios of NWA 7203 plot on the angrite fractionation line within uncertainty. However, the obtained Pb-Pb age of NWA 7203 is 4543 ± 19 Ma, younger than the ages of other quenched angrites, which might be a result of disturbance by shock metamorphism. The finding of shock metamorphism of NWA 7203 suggests that some angrites might be derived from asteroids that remained large (>10 km in diameter) during the late heavy bombardment.
AB - Northwest Africa (NWA) 7203 is a quenched angrite, showing mineralogical features typically not present in other quenched angrites. NWA 7203 exhibits textures whose grain size varies from fine grains (<10 μm) to coarse grains (~3 mm), while other quenched angrites show only single-sized textures. Fine-grained and coarse-grained lithologies have nearly the same bulk compositions. Cooling rates were estimated to be ~80 °C h−1 for fine-grained lithologies and ~1 °C h−1 for coarse-grained lithologies. Mg-rich olivines (~Fo64) were found only in fine-grained lithologies. Crystallization of NWA 7203 started in the fine-grained lithologies with Mg-rich olivine grains acting as seeds for crystallization. Coarse-grained lithologies were subsequently formed under conditions of slower cooling. NWA 7203 shows clear shock metamorphic textures unlike other quenched angrites except for NWA 1670. We confirm that the oxygen isotopic ratios of NWA 7203 plot on the angrite fractionation line within uncertainty. However, the obtained Pb-Pb age of NWA 7203 is 4543 ± 19 Ma, younger than the ages of other quenched angrites, which might be a result of disturbance by shock metamorphism. The finding of shock metamorphism of NWA 7203 suggests that some angrites might be derived from asteroids that remained large (>10 km in diameter) during the late heavy bombardment.
U2 - 10.1111/maps.13776
DO - 10.1111/maps.13776
M3 - Journal article
AN - SCOPUS:85121574502
VL - 57
SP - 105
EP - 121
JO - Meteoritics and Planetary Science
JF - Meteoritics and Planetary Science
SN - 1086-9379
IS - 1
ER -
ID: 288848074