Oligocene Orogen-Parallel Extension in Southern Tibet During Indian Continental Subduction

The controversial history of Indian subduction beneath Asia is crucial to understand the Himalayan orogeny and more in general the geodynamic process of continental subduction. New key information is here presented from the Oligocene-Pliocene Shiquanhe Basin located in the southwestern Tibetan Plateau. The alluvial-fan, lacustrine, and braided-river sediments of the Oligocene Rigongla Formation were non-conformably deposited onto the Upper Cretaceous Gangdese granitoid rocks and fed from erosion of the batholith itself and of associated Paleogene Linzizong volcanic rocks. Stratigraphic evidence testifies to the development of an orogen-parallel intracontinental rift along the retro-side of the Gangdese arc in the Oligocene, at the same time as the Kailas basin formed along the pro-side of the Gangdese arc. The subsidence of these twin basins may have been caused by steepening of the subducting Indian continental slab or by the passage of a wave of dynamic topography during continuing subduction.