Stable isotopes reveal southward growth of the Himalayan-Tibetan Plateau since the Paleocene

Abstract

Original stable isotope compositions of carbonates representing conditions in the latest Oligocene-early Miocene Kailas and Qiabulin areas, both in southern Tibet, record Oligocene-Miocene paleoelevations of the Gangdese arc and the Himalayan orogen, and provide constraints on the formation of the Himalayan-Tibetan Plateau. Oxygen isotope compositions of bivalve shell, paleosol, and lacustrine carbonates indicate the preservation of unaltered isotopic signals of paleometeoric waters in the Kailas and Qiabulin areas, whereas the oxygen isotopic compositions of Liuqu Eocene paleosols were likely altered by paleometeoric waters. Paleoelevation estimates using oxygen isotopes indicate the Kailas area was at ~4.9km during ~20–19Ma and the Qiabulin Basin was at ~2.0km during 24–21Ma, but rose rapidly to ~4.1km between 21 and 19Ma. These results suggest a steep south-facing flank on the proto-Tibetan highland prior to the onset of the India-Asia collision. The Himalayan orogen began to be built against the pre-existed high (~4.5km) Gangdese Mountains in the early Eocene and obtained elevations close to those of the present by the early Miocene. We propose that the southernmost Tibetan Plateau and Himalayan orogen are the expression of an early Eocene to early Miocene southward migration of the locus of deformation. Early stage uplift is linked to the crustal thickening in the early Eocene, but the dramatic elevation gain in the early Miocene may have been caused by Indian slab rollback, break-off and coeval renewed underthrusting, behind which late Miocene to present east-west crustal extension took place.