Nilanjana Sorcar

Partial melting of lower crustal rocks is an important mechanism for crustal differentiation and granulite genesis. Numerous natural and experimental data sets have firmly established the significance of dehydration melting (e.g. muscovite, biotite and hornblende melting) under varying physico-chemical conditions within the middle and lower crust. It is essential to develop quantitative mineral equilibria modelling of a partially molten rock system to constrain the P–T evolution which helps to better our understanding on crustal differentiation and the evolution of orogens. Precambrian HT/UHT terranes are important domains to understand the melting processes and scales of melt transfer. Regarded as exhumed root zones of ancient orogenic belts, these terranes provide an excellent window into middle–lower crust evolution. As for example, the evolution of garnet-cordierite gneiss of the Kerala Khondalite Belt (KKB) in Southern Granulite Terrane (SGT), India has been attempted to be characterized by constraining the phenomena of partial melting events through phase equilibria modelling as well as geochronological analyses of monazite and zircons. Pseudosection modeling with a melt-reintegration approach suggests that, with increasing pressure and temperature, a maximum of 35% granitic melt was produced. Integration of reaction histories constrained by textural evidence, kinetically constrained individual thermobarometry and pseudosection calculations establish a clockwise P–T path reflecting burial, heating and eventual exhumation of moderately-thickened crust. Further, the chemical ages from monazites and in-situ U–Pb isotopes from zircons point towards a complex tectonometamorphic evolution in the terrain with the clear indication of a Tonian metamorphic event subsequently overprinted by Cambrian tectonothermal episode.