Structural and geochronological constraints on the Mesozoic-Cenozoic tectonic evolution of the Longmen Shan thrust belt, eastern Tibetan Plateau

The Longmen Shan thrust belt in the eastern margin of the Tibetan Plateau underwent deformation of D-1 associated with the Late Triassic collision between the North and South China Blocks, followed by deformation of D-2 and D-3 related to the eastward growth of the Tibetan Plateau. The D-1 is marked by moderately tight folds (f(1)), spaced cleavage (S-1), mineral lineation (L-1), multistage reactivated faults, and top-to-the south thrusting. This deformation initiated before 237Ma and ended at 208Ma. The 193-159MaD(2) deformation is top-to-the-southeast directed and normal ductile in nature and was associated with the formation of half-graben basins. The Mesozoic deformation of the Longmen Shan belt was related to the subduction of the Paleo-Tethys oceanic lithosphere, followed by the South China Block underneath the Songpan-Ganze Terrane. The D-1 was produced in the pro-side of the overriding Songpan-Ganze plate, most probably driven by slab corner flow above the retreating South China Block. The D-2 and extensional Songpan-Ganze turbidite basin were produced by roll-back and migration of the overriding plate above the retreating subduction zone. This model for the deformation from D-1 to D-2 is similar to a Mediterranean-style model. The D-3 is characterized by SE-ward thrusting with stepwise migration of rapid denudation and dextral strike-slip faulting during the Late Cretaceous to present. Therefore, the Longmen Shan thrust belt involved Mesozoic compressional and extensional events that were overprinted by the Late Cretaceous to Cenozoic compressional event.