Metamorphism and thrust tectonics in the Munsiari Group of Central Crystalline Zone of Garhwal Himalaya, India

Abstract

The Munsiari Group of the Central Crystalline Zone of Garhwal Himalaya comprises low to medium grade metamorphics of pelitic and psarnmitic rocks along with granitoids and gneisses. The textural and structural studies indicate that these rocks witnessed two strong tectonothermal metamorphic episodes (M₁ and M₂) The allochthonous rocks of the M₁ metamorphic episode are highly deformed and had undergone Tertiary intracontinental shortening and superposed metamorphism. The crystallisation, possibly initiated during the D₁ deformation phase, continued upto the D₂ deformation and biotite-chlorite (Bio-Chi), gamet-chlorite (Gt-Chi) and kyanite-staurolite (Ky-St) zones were developed. The porphyritic granitoids were emplaced at the end phase of the M₁ metamorphism. The M₂ phase of metamorphism occurred discordant to the M₁ episode and was mainly confined to the shears and are syntectonic to the movement of the Main Central Thrust. The P-T conditions inferred that metamorphism for M₁ episode took place at 400-600 °C/ 4-6 Kbar and at 300-500 °Cl 4-5 Kbar for the episode.