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

Abstract : The 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 in Shergotty, Zagami, Nakhla and Chassigny : 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 backtransformation products of post-stishovite silica polymorphs. Strong 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, consistently with previous descriptions. These observations evidence 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 interpret the preservation in martian meteorites of phases practically unaffected by shock being very close to strongly shock-metamorphized minerals.
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Valérie Malavergne, François Guyot, Karim Benzerara, Isabelle Martinez. Description of new shock-induced phases in the meteorites of Shergotty, Zagami, Nakhla and Chassigny. Journal of Maps, Taylor & Francis, 2001, pp.1297-1305. ⟨hal-01158610⟩

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