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Multiple Phases of Mountain Building on the Northern Tibetan Margin


 The history of mountain building along the northern Tibetan margin since its initiation remains unclear. The exhumation evolutionary history of the Kunlun Belt, the first-order mountain range of northern Tibet, is resolved by using 40Ar/39Ar thermochronological analyses of Paleozoic and Mesozoic granitic intrusions. Four rapid exhumation events are identified from analyses employing multiple domain diffusion theories in the Carboniferous (~355-295 Ma), Triassic (~245-205 Ma), Cretaceous (~120-95 Ma), and Eocene (~40-35 Ma). The cooling rates and the therefrom deduced denudation rates are estimated for these stages. The events are interpreted to reflect the closure of the Prototethys Ocean in the early Paleozoic, closure of the Paleotethys ocean in the late Paleozoic, far-field effects from the closure of the Mesotethys Ocean, and far-field effects from the Paleogene convergence of India and Eurasia, respectively. These events collectively built up the present northern Tibetan margin.