Characterization of partial melting events in garnet-cordierite gneiss from the Kerala Khondalite Belt, India

Abstract

Phase equilibria modelling coupled with U–Pb zircon and monazite ages of garnet–cordierite gneiss from Vallikodu Kottayam in the Kerala Khondalite Belt, southern India are presented here. The results suggest that the area attained peak P–T conditions of ~900 ​°C at 7.5–8 ​kbar, followed by decompression to 3.5–5 ​kbar and cooling to 450–480 ​°C, preserving signatures of the partial melting event in the field of high to ultra-high temperature metamorphism. Melt reintegration models suggest that up to 35% granitic melt could have been produced during metamorphism at ~950 ​°C. The U–Pb age data from zircons (~1.0 – ~0.7 ​Ga) and chemical ages from monazites (~540 ​Ma and ~941 ​Ma) reflect a complex tectonometamorphic evolution of the terrain. The ~941 ​Ma age reported from these monazites indicate a Tonian ultra-high temperature event, linked to juvenile magmatism/deformation episodes reported from the Southern Granulite Terrane and associated fragments in Rodinia, which were subsequently overprinted by the Cambrian (~540 ​Ma) tectonothermal episode. Keywords: Kerala khondalite belt (KKB), Garnet-cordierite gneiss, Partial melting, Pseudosection, Monazite-zircon geochronology