Late Mesoproterozoic to early Neoproterozoic evolution of the Meghalaya gneissic complex, NE India: significance in Rodinia assembly

Abstract

ABSTRACT The Meghalaya Gneissic Complex (MGC) of northeast India is a little-studied high-grade metamorphic terrain, located close to the Late Palaeoproterozoic to early Neoproterozoic orogenic front. We include mapping, petrography, mineral chemistry, geochemistry, phase equilibria modelling, and U-Th-total Pb monazite geochronology to investigate the evolutionary history of deformed and metamorphosed ortho- and para-gneisses from the central MGC. The metapelite and metamafic rocks of the MGC are folded to E-W upright, antiforms-synforms; and intruded by charnockites during progressive deformations. Reconstructing the metamorphic history of pelite (garnet-cordierite granulite) and two pyroxene granulite, using a TiMnNCKFMASH and TiNCKFMASHO system, reveals a clockwise P–T path where the peak metamorphism was associated with mid crustal burial heating to granulite facies (~825°C and 5.5 to 6.5 kbar) and subsequent cooling with a minor decompression (~ 816°C and 5.3 kbar). Chemically zoned monazites were grown episodically during 1035 ± 13 Ma (n = 21), 976 ± 14 Ma (n = 16), and 494 ± 14 Ma (n = 26). The granulite metamorphism here initiated at 1035 ± 13 Ma and reached thermal peak at 976 ± 14 Ma. This contribution emphasizes the importance of late Mesoproterozoic to early Neoproterozoic metamorphic evolution of the MGC related to the collision of North and South Indian cratonic blocks. The studied P-T path differs from the previously reported Meso- to early Neoproterozoic paths of Central and Western India and close to Western Australia. This finding further explains the change in the early Neoproterozoic collisional pattern of the Central Indian Suture in extreme east (near MGC) and its significance in reconstructing the western Rodinia.