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The U-Pb age and Hf isotope data on detrital zircons from Paleozoic metasedimentary rocks in the Lhasa terrane (Tibet) define a distinctive age population of ca. 1170 Ma with εHf (t) values identical to the coeval detrital zircons from Western Australia, but those from the western Qiangtang and Tethyan Himalaya terranes define an age population of ca. 950 Ma with a similar εHf (t) range. The ca. 1170 Ma detrital zircons in the Lhasa terrane were most likely derived from the Albany-Fraser belt in southwest Australia, whereas the ca. 950 Ma detrital zircons from both the western Qiangtang and Tethyan Himalaya terranes might have been sourced from the High Himalaya to the south. Such detrital zircon connections enable us to propose that the Lhasa terrane is exotic to the Tibetan Plateau system, and should no longer be considered as part of the Qiangtang-Greater India-Tethyan Himalaya continental margin system in the Paleozoic reconstruction of the Indian plate, as current models show; rather, it should be placed at the northwestern margin of Australia. These results provide new constraints on the paleogeographic reconstruction and tectonic evolution of southern Tibet, and indicate that the Lhasa terrane evolved as part of the late Precambrian-early Paleozoic evolution as part of Australia in a different paleogeographical setting than that of the Qiangtang-Greater India-Tethyan Himalaya system. [ABSTRACT FROM AUTHOR]

Uplift of the Tibetan Plateau and its influence on our global climate have been the focus of numerous studies. Miocene potassic to ultrapotassic volcanism is widespread in southern Tibet and has been generally attributed to convective removal of collision-thickened Asian lithosphere, which is also responsible for the uplift of the plateau. An implicit assumption of this model is the existence of a hydrous, metasomatized (i.e., phlogopite bearing) lithospheric mantle that remained after the convective thinning and was subsequently heated to form small-volume melts. If such a lithospheric mantle was present in the Miocene, it implies further change since that time, as seismic velocities indicate that cold and strong upper mantle occurs beneath the thick crust in southern Tibet. Here we describe peridotite xenoliths entrained in Middle Miocene ultrapotassic lavas from Sailipu, southern Tibet. The results suggest the existence of hot, highly metasomatized lithospheric mantle beneath southern Tibet during the Middle Miocene, and thus support the idea that convective thinning of the lithosphere was responsible for the uplift of the plateau. The relict mantle was later removed or squeezed northward by the underthrusting Indian continental lithosphere, which terminated magmatism in southern Tibet and played a role in creating the entire plateau. [ABSTRACT FROM AUTHOR]