Portal de Periódicos da CAPES

Description of new shock‐induced phases in the Shergotty, Zagami, Nakhla and Chassigny meteorites

2001; Wiley; Volume: 36; Issue: 10 Linguagem: Inglês

10.1111/j.1945-5100.2001.tb01825.x

1945-5100

V. Malavergne, François Guyot, Karim Benzerara, Isabelle Martínez,

High-pressure geophysics and materials

Abstract— The Shergottite, Nakhlite and Chassignite (SNC) meteorites, Shergotty, Zagami, Nakhla and Chassigny, have been studied by analytical transmission electron microscopy. New phases, characteristic of strong shock conditions, have been discovered: calcium‐rich majorites in Shergottty, wadsleyite with anomalously elevated iron content in Chassigny, and impact melts in Shergotty, Zagami and Nakhla. Cristobalites (α and β polymorphs) observed in Shergotty and Zagami may also be related to shock and are interpreted as back transformation products of post‐stishovite silica polymorphs. Shocks corresponding to pressure and temperature conditions characteristic of the Earth's transition zone and lower mantle have occurred in those meteorites. Moreover, impact melts indicate high‐temperature conditions in localized areas. On the other hand, no massive impact melting is observed in those meteorites, consistent with previous descriptions. These observations provide evidence of highly heterogeneous shock conditions at the scale of few micrometers in these meteorites. Strongly heterogeneous conditions such as those suggested by the present study may help to explain the preservation in martian meteorites of phases practically unaffected by shock being very close to strongly shock‐metamorphized minerals.