METAMORPHIC EVOLUTION OF BHILWARA SUPRACRUSTAL ROCKS FROM RAJASTHAN, NW INDIA

Abstract

1-ugh-grade metamorphic terrains have proved to be the key areas to study the plate-tectonic processes on Earths. Metamorphic terrains have been classified broadly into three types on the basis of the mineral assemblages and facies: (I) low temperature high pressure-ultrahigh pressure terrains (eclogite and blueschist facies, characterized by geothermal gradients 4-10°C/km), (ii) medium-temperature eclogite to granulite facies terrains (characterized by geothermal gradients (10-20°C/km) and (iii) ultrahigh temperature granulite facies terrains (>20°C/km; Brown, 2010). Geothermal gradients recorded from the peak metamorphic conditions throughout the high grade metamorphic terrains of the world, as summarized by Brown (2007a) indicate that during the beginning of plate tectonics in the Proterozoic, the geothermal gradients of the metamorphic terrains mostly varied from 25-40°C/km and 10-20°C/km in the Grenvillian period (1.0 Ga). The Proterozoic Era was marked by duality of thermal regimes i.e. simultaneous occurrence of low temperature ultra-high pressure regimes with low pressure granulite to ultrahigh temperature regimes. 1-lence one-sided subduction zone processes, which is the hallmark of Phanerozoic tectonic processes was initiated in the Proterozoic