Multi–Collision Tectonic Evolution of the Tibetan–Himalayan Orogenic Belt, and Its Significance for the Mesozoic–Cenozoic Geodynamics of Neotethys North of East Gondwana

The collision of India with Asia in the Cenozoic has been widely interpreted as the main collision event that led to the formation of the Tibetan–Himalayan orogenic belt, although the timing and the nature of this collision has been controversial. The most complete record of the orogenic belt evolution between India and Asia is presented by a terrestrial conglomerate deposit, the Liuqu Conglomerate (LQC), whose depositional and tectonic development encompassed at least two collisional events: an earlier collision between an intraoceanic arc–trench system (Trans–Tethyan arc–forearc system, now exposed in the Xigaze ophiolite) and India (arc–continent), and the later collision between India and Asia (continent–continent). We present in this talk structural, stratigraphic, and new U-Pb detrital zircon ages from the LQC to document its geological evolution as a critical archive and geochronometer for the complex collision tectonics of the Tibetan–Himalayan orogenic belt. The LQC within the central YZSZ represents an orogen–parallel fluvial depocenter in an intermontane valley that developed at the collision front between the rifted northern passive margin of India (or Tethyan Himalaya) and a latest Jurassic–early Cretaceous Trans–Tethyan arc–trench system within the Neotethyan oceanic realm to the north of East Gondwana. The arc–continent collision occurred near the tropical–subtropical latitudes in the late Cretaceous and the onset of the LQC deposition began shortly after this event in the latest Cretaceous–Paleocene. Transverse rivers and streams draining the orogenic hinterland in India to the south transported Archean, Proterozoic and Paleozoic zircons and clastic material northward into the Liuqu axial river basin. Southward flowing transverse streams from the northern part of the YZSZ transported ophiolitic clasts into the Liuqu fluvial depocenter. The lack of any detrital zircon grains, clastic material or felsic volcanic tuff originated from the Gangdese Magmatic Belt (GMB) or the Lhasa block further points to the distal position of the LQC depocenter away from the Andean–type Mesozoic active margin of Eurasia. Arrival at the active margin of Eurasia of the Indian subcontinent with the accreted arc ophiolites and the intra–suture LQC depocenter and the ensuing continent–continent collision marked the terminal closure of Neotethys in its easternmost domain and resulted in significant crustal uplift across the collision zone. Therefore, the onset of the India–Asia continental collision likely began in the late Oligocene (~23 Ma). The LQC depocenter started receiving clastic material and zircons for the first time from the GMB and the Xigaze forearc basin to the north by ~20 Ma.  Inversion of the fluvial basin and rapid exhumation of the LQC strata were nearly complete by the early–Middle Miocene. These discrete collision events during the evolution of the Tibetan–Himalayan orogenic system indicate an episodic lateral and vertical growth of the southern part of the Tibetan Plateau and a punctuated history of its crustal buildup.