Abstract
The Tibetan Plateau was formed by the continued collision between the Indo-Australian plate and Eurasian plate over the past approximately 50 Ma. Any working hypothesis of the plateau evolution should be able to explain the post-collisional behaviors of the former plate. Since the opening of the Indian Ocean in the Neocomian, much of the Indo-Australian plate has remained tectonically quiet until mid-Miocene, when dramatically increased tectonic activity started across the entire plate. In the central Indian Ocean, North-South compression led to reverse faulting (5-10 km spaced) and long wave-length (100-300 km) folding starting at 15.4-13.9 Ma. Deformation sharply increased during the late Miocene and resulted in a regional unconformity at 8 Ma. This deformation continues today as manifested by abundant earthquakes. In the Carnarvon Basin and Perth Basin of western Australia, the passive margin remained truly passive after the Neocomian breakup and received continuous sedimentation with no apparent deformation before the Middle Miocene. During the Middle Miocene, ESE-WNW compression started and this led to nondeposition and widespread deformation. The majority of Tertiary hydrocarbon traps in western Australia were formed by folding and reverse faulting during this time and reactivation of older faults ubiquitous. The mid-Miocene starting age for the reactivation and its associated stress field, along with regional distributions of mid-Miocene deformation and changing deformation styles, allow us to strongly argue that the reactivation is an immediate response to the tectonic reorganization of the Tibetan Plateau (Yue and Liou, 1999; Ritts et al., 2008). During the Oligocene and Early Miocene, the Indo-Australian plate pushed the Tibetan lithosphere toward the Pacific subduction zone, a free tectonic boundary, and therefore, stress level in both Tibet and the Indo-Australian plate was low. At mid Miocene, weakened Tibetan lithosphere was locked down at northern Qilian Shan and was unable to extrude toward the Pacific margins. The continued push from Indo-Australian plate simultaneously led to the crustal thickening and uniform exhumation of the Tibet Plateau and tectonic reactivation observed in central Indian Ocean and Australia.