Two-phase intracontinental deformation mode in the context of India-Eurasia collision: insights from a structural analysis of the West Kunlun-Southern Junggar transect along the NW margin of the Tibetan Plateau

The convergence of India and Eurasia, which began in the early Cenozoic, established the Tibetan Plateau and the Circum-Tibetan Plateau Basin and Orogen System. When and how the convergence-driving strain propagated into this system is important in deciphering the growth processes of the Tibetan Plateau. We conducted a structural analysis of the West Kunlun-southern Junggar transect along the NW margin of the Tibetan Plateau to establish the propagation of deformation and, through this, to determine the plateau growth processes. Our results suggest a two-phase deformation mode. The first-stage features deformation confined to pre-existing weak zones (e.g. the West Kunlun orogen, the Buchu Uplift and the Tian Shan orogen) during the Paleogene, when the intracontinental strain is speculated to be mainly consumed by shortening of these weak zones. The second stage is characterized by deformation propagating into the foreland regions since the early Miocene, where shortening along the foreland fold-thrust belts on a scale of tens of kilometres and decreasing basinwards had a key role in absorbing intracontinental strain. We suggest that this two-phase deformation mode may reflect a shift in the governing mechanism of the expansion of the Tibetan Plateau from a rigid block to a critical wedge taper style.