Pressure-temperature Inversion Paths Obtained from Garnet in the Himalayan Collision Belt

Abstract

Prograde P-T paths were obtained by Gibbs method using zonings of garnet in the Annapurna area of central Nepal Himalaya. The results show different P-T paths in the uppermost and lower Lesser Himalayan Sequence (LHS), at the footwall of the Main Central Thrust (MCT). The uppermost LHS garnet shows paths with adiabatic compression (ΔP=90 MPa, ΔT=7°C) followed by heating (ΔT=20e), whereas the lower LHS garnet simply shows a sub-adiabatic compression (ΔP=350 MPa, ΔT=70°C) path. Tectonically, adiabatic compre-ssion is supposed to correspond with subduction, and subsequent heating with thrusting along the MCT. Heating by the MCT faulting seems to have occurred in a narrow zone of approx. 100 m in thickness.