Tectonic uplift in the northern Tibetan Plateau since 13.7 Ma ago inferred from molasse deposits along the Altyn Tagh Fault

In response to the collision of India with Asia, thick molasse deposits were shed off the high evolving edge of the northern Tibetan Plateau, providing great potential for understanding the relationships between mountain building, rock denudation, and sediment deposition. A precise knowledge of the initial accumulation of the molasse deposits is important for understanding uplift history along the northern margin of Tibet. Field investigations indicate that thick Neogene sediments in the piedmont depression zones of the Altun Mountains are strongly deformed in a fold and thrust system, indicating crustal shortening and thickening in the late Cenozoic. Detailed magnetostratigraphic studies of the molasse deposits along the Allyn Tagh Fault show that the accumulation of coarse conglomerate began ca. 13.7 Ma ago, the source material of the deposits changing at the same time. Together with the remarkable increase in the sedimentation rate after 13.7 Ma, we attribute the accumulation of the conglomerates to the tectonic uplift along the northern edge of the Tibetan Plateau, a process that continued until at least 9 Ma ago. (c) 2005 Elsevier B.V. All rights reserved.