Description of new shock-induced phases in the meteorites of Shergotty, Zagami, Nakhla and Chassigny
Résumé
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.
Domaines
Planétologie
Origine : Fichiers produits par l'(les) auteur(s)
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