CONSTRAINING THE METAMORPHIC AND KINEMATIC EVOLUTION OF THE LEO PARGIL DOME, NORTHWEST INDIAN HIMALAYA, THROUGH INTEGRATED PRESSURE-TEMPERATURE-TIME-DEFORMATION DATA
Rocks within the dome contain garnet, kyanite, and staurolite porphyroblasts that record prograde Barrovian metamorphism during crustal thickening that reached ~530-630 °C and ~7-8 kbar, ending by ~30 Ma. Cordierite and sillimanite overgrowths on Barrovian assemblages within the dome record dominantly top-down-to-the-west shearing during near-isothermal decompression of the footwall rocks to ~4 kbar by 23 Ma. Quartz microstructures combined with EBSD analyses show that top-down-to-the-west ductile deformation is recorded at temperatures from >650 °C at the deepest levels within the dome and from 400-500 °C through 400-280 °C at the shallowest structural levels within the dome. These data suggest that the rocks within the shear zone were exhumed from mid-crustal depths by west-directed deformation following Barrovian metamorphism.
Contemporaneous onset of near-isothermal decompression and top-down-to-the-west shearing following Barrovian metamorphism, combined with ages from leucogranites within the dome from other studies, suggests that early Barrovian metamorphism and crustal melting may have created a weakened crust that was proceeded by localization of strain and shear zone development. Exhumation along the shear zone accommodated decompression by 23 Ma in a kinematic setting that favored orogen-parallel extension.