The Yarlung Zangbo suture zone (YZSZ) in southern Tibet is divided by the Zhongba terrane into two subparallel belts in its western end. The northern belt (NB) is tectonically juxtaposed against an accretionary prism complex and the Gangdese magmatic arc of Eurasia along dextral oblique-slip faults. Peridotite massifs in this belt are intruded by mafic dikes, providing critical geochemical, geochronological, and isotopic information about the melting-melt extraction history of the Tethyan mantle. Peridotites consist of harzburgite and clinopyroxene harzburgite with minor Iherzolite and dunite-chromitite. Dolerite and microgabbro dikes crosscutting these peridotites display U-Pb zircon ages of 128-122 Ma, and show normal mid-oceanic ridge basalt (N-MORB) like rare earth element patterns with negative Nb, Ta, and Ti anomalies, high ε Nd (t) Pb of 37.724-37.845, suggesting that their N-MORB-like mantle source was modified by island arc melts. Slab rollback-induced extension in an arc-trench system along the Eurasian continental margin led to ~7%-12% partial melting of subduction-influenced, spinel lherzolite peridotites, producing dike magmas. The NB peridotite massifs and ophiolites thus represent a suprasubduction zone oceanic lithosphere formed in close proximity to the late Mesozoic active continental margin of Eurasia.

No abstract

No abstract

No abstract

No abstract

No abstract

No abstract

<p>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 <em>Liuqu Conglomerate</em> (LQC), whose depositional and tectonic development encompassed at least two collisional events: an earlier collision between an intraoceanic arc–trench system (Trans<strong>–</strong>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<strong>–</strong>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.</p>