Petrography, mineral chemistry, metamorphism and Raman spectroscopic studies of Mahadevpur fall meteorite, India

Abstract

The Mahadevpur (27°39′48″ N, 95°51′32″ E; Arunachal Pradesh, India) meteorite is a fall‐type, coarse‐grained rock consisting of a heterogeneous mixture of chondrules of varying types occurring in a matrix comprising mostly chondrule fragments. It was earlier classified as poorly shocked (S1, unshocked) ordinary chondrite (H4/5). The minerals observed in the Mahadevpur meteorite include olivine, orthopyroxene, clinopyroxene, albitic‐plagioclase, Fe‐Ni alloy and troilite with minor amounts of chromite and phosphate. Olivine and orthopyroxene are almost equilibrated. The textures and compositional features of minerals and chondrule margins indicate a limited degree of recrystallization. The equilibration temperature (700–800°C) for the Mahadevpur chondrite is consistent with the computed temperature (752–902°C) derived from the coexisting orthopyroxene‐clinopyroxene pairs. In the light of new evidences observed during the present study, such as olivine exhibiting undulose extinction and planar to sub‐planar fractures, olivine and orthopyroxene showing strong mosaicism, the shock‐melted plagioclase glasses, the presence of high‐pressure mineral phases and silicate darkening, the earlier proposed shock stage pronouncement has been modified to S4–S5 with supporting petrographic, sub‐microscopic and Raman spectroscopic data. This is the first comprehensive account of the Mahadevpur chondrite with an upgraded shock stage classification.