Different P-T-t paths and leucogranite occurrences along the High Himalayan Crystallines : Implications for subduction and collision along the northern Indian margin

Abstract

Different P-T-t paths and a heterogeneous distribution of Tertiary leucogranites are recorded along the High Himalayan Crystallines (HHC), in the collided Indian plate. Rapid subduction with eclogite formation during the early-Eocene is apparently restricted to part of the HHC of northern Pakistan, that is the zone of the first collision between the narrow NW Indian spur and the Kohistan island arc. In northern Pakistan rapid exhumation occurred along a cooling path and the crustally derived leucogranites of Tertiary age are rare or absent. East of the spur the delayed India-Eurasia collision occurred at lower rates of convergence and determined less rapid and deep continental subduction. Here exhumation of the HHC occurred at lower rates and at increasing T, giving a relatively warm thickened crust which underwent extensive anatexis during uplift in Oligocene-Miocene times. In eastern Himalayas, anatexis at medium- and low-P produced numerous cordierite-andalusite-bearing leucogranites which emplaced along extensional shear zones at high structural levels during the Miocene.