Early Himalayan exhumation: Isotopic constraints from the Indian foreland basin

Nd‐ and Sr‐isotopic compositions of Palaeogene foreland basin sediments are used to provide insights into early Himalayan evolution, particularly the timing of exposure of high87Sr/86Sr units, erosion of which may have caused the late Tertiary increase in oceanic Sr‐isotopic ratios. During the late Palaeocene–early Eocene, erosion was from mixed sources including suture zone rocks. Exhumation of the High Himalaya was occurring by the time of deposition of alluvial sediments after mid‐Oligocene times and this source has dominated Himalayan sediments from at least this time until the present day. The transition is interpreted to reflect exhumation of ‘basement rocks’ of the Indian plate, when the High Himalaya became a sufficient topographic barrier to separate suture zone rocks from the foreland basin. The marked rise in seawater87Sr/86Sr from 40 Ma is consistent with the erosion of a Himalayan source with a high87Sr/86Sr ratio.