Reactivated Tibetan block in a Tethyan context

Abstract

The Tibetan block originated during the late Palaeozoic-early Mesozoic by separation from Gondwanic India and the opening of Neo-Tethys. The event, which was responsible for reactivating the Tibetan basement, closed Palaeo-Tethys, lying to the north of it, and created the Kun Lun fold system as a consequence of the collision of the north-moving Tibetan block with the Tarim—Tsaidam block. During the late Cretaceous, South Tibet developed into an Andean-type foldbelt (Nyenchen Thangla) by subduction of Neo-Tethyan lithosphere beneath Tibet which had begun in the late Triassic. Mesozoic sedimentary sequences in Tibet are the response to an extensional regime behind an active margin. A Neo-Tethys island arc system at this margin was crushed during the early Eocene with the development of the Transhimalayan ophiolite and plutonic belts. Final collision during mid-Eocene times between the Himalayan microcontinent, a fragment of India and reworked Tibet in the Mid-Eocene produced the Indus—Tsangpo suture zone. A large part of the microcontinent, with an unconsumed segment of Neo-Tethys oceanic crust attached to it, presumably underthrust Tibet prior to the Himalayan orogeny. This feature is responsible for the double thickness of Tibetan crust and its young volcanism.