The tectonic evolution of the Songpan-Garze (North Tibet) and adjacent areas from Proterozoic to Present: A synthesis

The Triassic orogeny in North Tibet results from interactions between the South China, North China and Qiangtang (North Tibet) blocks during the closure of the Paleotethys ocean. It is mainly composed, from west to east, by the Bayan Har, Songpan-Garze, and Yidun (or Litang-Batang) terranes. We focus here on the Triassic Songpan-Garze fold belt and the actual eastern margin of the Tibetan Plateau which is one of the key areas for understanding the tectonic evolution of the Asian continent and the Tibetan Plateau. At least three major deformation phases are recognized in eastern Tibet and south-east of the South China block: a Neoproterozoic phase (1-0.75 Ga) correlated to the assembly and break-up of the Rodinia Continent, a Late Triassic compression event and finally a Tertiary deformation related to the India-Asia collision. The tectonic and geodynamic history of this part of Asia is very complex and often vigorously debated. For example the Triassic compression event in Tibet is usually associated to the Indosinian Orogeny originally defined in Vietnam but this is probably an oversimplification. Our purpose is to review the various models proposed in the literature and to synthesize the tectonic and geodynamic history of this area. We show that the Songpan-Garze fold belt is not a typical collisional belt: the triangular shape of the closing oceanic basin as well as the huge volume of accreted sediments did not allow a complete continent-continent collision. Finally, the tectonic inheritance plays a major role in the evolution of the eastern margin of Tibet as most of the major Tertiary tectonic structures in the Longmen Shan are reactivated Paleozoic and Mesozoic faults. (C) 2010 Elsevier Ltd. All rights reserved.