Journal
METEORITICS & PLANETARY SCIENCE
Volume 54, Issue 11, Pages 2744-2757Publisher
WILEY
DOI: 10.1111/maps.13384
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Funding
- Sasagawa Scientific Research Grant from The Japan Science Society
- NIPR Project [KP307]
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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 degrees C). This result is different from the slower cooling rates of Moama (greater than or similar to 0.0004 degrees C yr(-1)) than that of Moore County (>0.3 degrees C yr(-1), after the shock event) at high temperatures (>500 degrees 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.
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