Thermal and Chemical Evolution of an Archean Collision Zone: Insights from P–T–t History of Mafic Granulites from the Coorg Block, S. India.

This article investigates the pressure–temperature–time (P–T–t) evolution of Archean high-grade mafic granulites from the Mercara Shear Zone, a Mesoarchean suture between the Coorg Block and the Dharwar Craton in southern India, to elucidate early Earth tectonic processes. The study distinguishes low-Mg and high-Mg mafic granulites with differing metamorphic reaction histories, reconstructing a multi-stage metamorphic evolution involving granulite-facies metamorphism at ~3100–2700 Ma, a prolonged low-temperature residence, and a reheating event at ~2400 Ma, followed by cooling. Integrated petrological, geochronological (U–Pb zircon and Lu–Hf garnet dating), and diffusion chronometry data reveal slow cooling rates (25–50°C/Ma) and pulsed metamorphism consistent with peel-back style orogenesis, an early form of plate tectonics on a hotter Archean Earth. The findings also highlight how bulk rock composition influences intracrustal differentiation, potentially generating Mg-rich refractory lower crust through protracted, fluid/melt-assisted metamorphic processes.