Paleomagnetic Constraints And Implications For Late Mesozoic And Cenozoic Tectonic Events Of The Tibetan Plateau

The Tibetan Plateau, comprising several crustal terranes, has become thenatural geological laboratory for studying plate tectonics and continental dynamics.Convergence events related to a series of Gondwana-derived terranes (e.g., Lhasa andIndia) and Asian continent has produced the uplift of Tibetan Plateau and alsodeformed large parts of Asia. The process of the collision and the tectonic models bywhich the Tibetan Plateau was raised are of global concern for their effects onclimatical and continental dynamics. Tectonic events since Late Mesozoic such ashow and when India collided with Asia, the timing of collision for the Lhasa andQiangtang terranes, how and where convergence between India and Asia wasaccommodated since the collision etc., are still highly debated and hinder ourunderstanding of the dynamic processes governing the kinematic history andstructural development of Asia.In this thesis, I present new paleomagnetic and sedimentological data from theXigaze forearc basin, Nima basin (Lhasa terrane), and Shuanghu area (Qiangtangterrane). These data show that1) the Xigaze forearc basin was located at24.2±5.9°Nduring54-57Ma, providing for the first time a direct constraint on the position of thesouthernmost margin of Asia at this crucial stage. The age and locus of the initialIndia-Asia collision are at~50Ma and~24°N, respectively. Tibet resisted India’snorthward push during the first~16Ma of initial impactfrom the collision andexperienced little latitudinal displacement. Sometime a little after34Ma, GreaterIndia was consumed and thicker Indian Craton subsequently made contact with Asia,resulting in6°northward drift of Asia:2) Paleomagnetic results show that theQiangtang terrane was located at26.4±3.8°N during Late Cretaceous time.Lhasa-Qiangtang continental collision might finally terminate until the LateCretaceous:3) The paleolatitudes of the Xigaze forearc basin and Qiangtang terranesuggest approximately583km (since60Ma) and737km (since70Ma) of shorteningoccurred in Asian lithosphere. Most of post-50Ma India-Asia convergence partitionedinto Greater India consumed by underthrusting and shortening in the Himalaya:4)When compared with coeval age expected directions of Eurasia, the mean paleomagnetic directions indicate no Late Tertiary vertical-axis rotation of the NimaBasin and significant clockwise rotation (~55°) of the central Qiangtang terrane sinceLate Cretaceous. Rotations are highly variable in magnitude and time within localgeographic areas. The tectonic rotations can be explained as easily by deformationassociated with structures proximal to the sampling localities:5) The integratedsedimentology and magnetostratigraphy provide a maximum likelihood ofdepositional age of Abushan Formation and Dingqinghu Formation, which are LateCretaceous and Late Tertiary (~19-26Ma), respectively. The results from this thesisstudy suggest that the depositional environments (alluvial fan and lacustrine fan-delta)and arid features of the central Tibet have been well established by the LateCretaceous.