Thermal evolution and exhumation of the Ladakh Batholith, northwest Himalaya, India

Abstract

High elevation, low relief regions are recognised across the northwest Himalaya, including the Ladakh and Kohistan areas. A homogeneity of uplift and cooling histories across these large spatial (> 360 km) and temporal (> 35 Ma) scales would be remarkable. Here we examine the thermal evolution of the Ladakh Batholith, northwest India since the early Tertiary using a combination of amphibole geobarometry and apatite and zircon low temperature thermochronometry data to investigate the spatio-temporal progression of emplacement, uplift and exhumation. The emplacement depth varies with distance north of the Indus River and suggests that the southern part of the batholith (< 10 km from the Indus River) had more overlying rocks removed (~ 3–5 km more) compared to the northern edge. Compiled low temperature thermochronometry data from elevations > 3200 m above mean sea level indicate significant exhumation of the southern margin of the Ladakh Batholith in the Oligocene (> 26 Ma) while exhumation of the northern margin occurred later in the Mid to Late Miocene (< 17 Ma). Topography across the batholith was asymmetric throughout the Oligocene and Miocene and potentially only since the Pliocene has the current amplitude and wavelength been established. This extensive dataset from across the Ladakh Batholith does not support a generalised regional model of early rapid exhumation post India–Eurasia collision followed by steady and slow denudation to the present.