Petrology of an Inverted Metamorphic Sequence from the Western Arunachal Himalaya

Abstract

In this study, an inverted metamorphic sequence in the western Arunachal Himalaya (WAH) is reconstructed using combined structural and metamorphic analyses of rocks of the Lesser and Greater Himalyan Sequences (LHS and GHS respectively), which are exposed along the transect, Sessa-Rupa-Bomdila-Dirang-Se La. Five metamorphic zones from garnet through kyanite, kyanite migmatite, kyanitesillimanite migmatite to K-feldspar-kyanite-sillimanite migmatites are sequentially developed in the metamorphosed low-alumina pelites with increasing structural heights. In the garnet-zone, peak metamorphism is marked by post-D2 garnet growth through biotite+plagioclase→garnet+muscovite reaction. An even earlier phase of syn-D1 garnet growth occurred in the chlorite stability field with or without epidote.