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Silica minerals in cumulate eucrites: Insights into their thermal histories
Author(s) -
Ono Haruka,
Takenouchi Atsushi,
Mikouchi Takashi,
Yamaguchi Akira
Publication year - 2019
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.13384
Subject(s) - tridymite , monoclinic crystal system , cristobalite , quartz , mineral , geology , mineralogy , meteorite , orthorhombic crystal system , pyroxene , geochemistry , crystallography , materials science , olivine , chemistry , metallurgy , crystal structure , astrobiology , paleontology , physics
Some eucrites contain up to 10 vol% silica minerals; however, silica minerals have not been studied in detail so far. We performed a mineralogical study of silica minerals in three cumulate eucrites (Moore County, Moama, and Yamato [Y] 980433). Monoclinic tridymite was common in all three samples. Moama contained orthorhombic tridymite as lamellae within monoclinic tridymite grains. Y 980433 included quartz around an impact melt vein. The presence of orthorhombic tridymite in Moama indicates that Moama cooled more rapidly than the other two samples at low temperatures (<400 °C). This result is different from the slower cooling rates of Moama (≳0.0004 °C yr −1 ) than that of Moore County (>0.3 °C yr −1 , after the shock event) at high temperatures (>500 °C) estimated from compositional profiles of pyroxene exsolution lamellae. The difference of the cooling rates may reflect their geological settings. Y 980433 cooled slowly at low temperature, as did Moore County. Quartz in Y 980433 could be a local product transformed from monoclinic tridymite by a shock event. We suggest that silica minerals in meteorites record thermal histories at low temperatures and shock events.