Exhumation history of eastern Ladakh revealed by 40 Ar/ 39 Ar and fission-track ages: the Indus River–Tso Morari transect, NW Himalaya

Abstract

Fission-track and 40 Ar/ 39 Ar ages place time constraints on the exhumation of the North Himalayan nappe stack, the Indus Suture Zone and Molasse, and the Transhimalayan Batholith in eastern Ladakh (NW India). Results from this and previous studies on a north–south transect passing near Tso Morari Lake suggest that the SW-directed North Himalayan nappe stack (comprising the Mata, Tetraogal and Tso Morari nappes) was emplaced and metamorphosed by c . 50–45 Ma, and exhumed to moderately shallow depths ( c . 10 km) by c . 45–40 Ma. From the mid-Eocene to the present, exhumation continued at a steady and slow rate except for the root zone of the Tso Morari nappe, which cooled faster than the rest of the nappe stack. Rapid cooling occurred at c . 20 Ma and is linked to brittle deformation along the normal Ribil–Zildat Fault concomitant with extrusion of the Crystalline nappe in the south. Data from the Indus Molasse suggest that sediments were still being deposited during the Miocene.