Cenozoic volcanism and tectonic evolution of the Tibetan plateau

Cenozoic volcanism on the Tibetan plateau, which shows systematic variations in space and time, is the volcanic response to the India-Asia continental collision. The volcanism gradually changed from Na-rich + K-rich to potassic-ultrapotassic + adakitic compositions along with the India-Asia collision shifting from contact-collision (i.e. "soft collision" or "syn-collision") to all-sided collision (i.e. "hard collision"). The sodium-rich and potasium-rich lavas with ages of 65-40 Ma distribute mainly in the Lhasa terrane of southern Tibet and subordinately in the Qiangtang terrane of central Tibet. The widespread potassic-ultrapotassic lavas and subordinate adakites were generated from similar to 45 to 26 Ma in the Qiangtang terrane of central Tibet. Subsequent post-collisional volcanism migrated southwards, producing ultrapotassic and adakitic lavas coevally between similar to 26 and 8 Ma in the Lhasa terrane. Then potassic and minor adakitic volcanism was renewed to the north and has become extensive and semicontinuous since similar to 20 Ma in the western Qiangtang and Songpan-Ganze terranes. Such spatial-temporal variations provide important constraints on the geodynamic processes that evolved at depth to form the Tibetan plateau. These processes involve roll-back and break-off of the subducted Neo-Tethyan slab followed by removal of the thickened Lhasa lithospheric root, and consequently northward underthrusting of the Indian lithosphere. The Tibetan plateau is suggested to have risen diachronously from south to north. Whereas the southern part of the plateau may have been created and maintained since the late-Oligocene, the northern plateau would have not attained its present-day elevation and size until the mid-Miocene when the lower part of the western Qiangtang and Songpan-Ganze lithospheres began to founder and detach owing to the persistently northward push of the underthrust Indian lithosphere. (C) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.