Trachyandesitic volcanism in the early Solar System
Résumé
Volcanism is a substantial process during crustal growth on plane-tary bodies and well documented to have occurred in the early Solar System from the recognition of numerous basaltic meteorites. Considering the ureilite parent body (UPB), the compositions of magmas that formed a potential UPB crust and were complemen-tary to the ultramafic ureilite mantle rocks are poorly constrained. Among the Almahata Sitta meteorites, a unique trachyandesite lava (with an oxygen isotope composition identical to that of common ureilites) documents the presence of volatile-and SiO 2 -rich magmas on the UPB. The magma was extracted at low degrees of disequilib-rium partial melting of the UPB mantle. This trachyandesite extends the range of known ancient volcanic, crust-forming rocks and docu-ments that volcanic rocks, similar in composition to trachyandesites on Earth, also formed on small planetary bodies ∼4.56 billion years ago. It also extends the volcanic activity on the UPB by ∼1 million years (Ma) and thus constrains the time of disruption of the body to later than 6.5 Ma after the formation of Ca–Al-rich inclusions. differentiation | meteorite parent body | achondrites | differentiated
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