The Cenozoic hyper-oblique collision zone of Indochina: A re-appraisal of escape tectonics.

Cenozoic strike-slip faults in Indochina were initially interpreted as related to SE expulsion of rigid blocks of continental crust between narrow, high-displacement strike-slip faults away from the Himalayan Orogen. Revision of this view indicates four main stages of development are present. The main 'rigid' block of Indochina actually underwent extensive, widespread Paleogene transpressional deformation during stage 1, involving pervasive strike-slip faulting, folding, structural inversion, sub-horizontal mid-lower crustal shearing, and widespread exhumation of several kilometres. This stage is associated with ∼ E -W oriented maximum horizontal stress (SHmax) (modern orientation). The three subsequent stages are: 2) 30–27 Ma transition, with retreat of transpressional deformation to the SE Tibetan Plateau, 3) 27–17 Ma onset of major sinistral displacement on ASRRSZ, 4) <17 Ma-present, diachronous reversal of motion on many faults, and cessation of extension in Thailand rifts. SHmax orientations evolved dominantly to between NE-SW and NW-SE orientations. Stage 4 is strongly linked with growth of the Tibetan Plateau, the modern GPS field, stress state, and geophysically-defined orientations of crustal and mantle flow. Five different strike-slip provinces have been identified for the post 30 Ma period, based on variations in structural style and kinematics caused by interacting factors including: 1) distance from the East Himalayan Syntaxis, 2) strength variations within SE Asian lithosphere, 3) pre-existing crustal fabrics 4) proximity to key regions contributing to the stress-state of SE Asia, 5) crustal and/or mantle flow. Whether the strike-slip faults are a product of a top- or bottom- driven system remains uncertain. Probably, the system is a hybrid. • A major Paleogene transpressional belt developed in Indochina. • Rigid block extrusion does not fit the Paleogene setting. • Five distinct Oligo-Neogene strike-slip provinces are described. • Cenozoic Strike-slip deformation developed in four key stages. • Ambiguous role of crustal and mantle flow as driving mechanisms. [ABSTRACT FROM AUTHOR]