The raising and westward expansion of central Tibet.

Understanding the Cenozoic growth history of the Himalaya-Tibetan Plateau (HTP) is essential for elucidating the underlying geodynamic mechanism and interactions among topography, biosphere and atmosphere. However, the spatial-temporal evolution of the HTP, especially that of the Paleogene Central Tibetan Valley (CTV), remains hotly debated. In this study, through radiometric geochronology, plant assemblages, oxygen and clumped isotope paleoaltimetries, we reconstruct the uplift history of the east-west-oriented Luolong Basin in eastern Tibet. Results show that the Luolong Basin was at 0.6 (+0.2/-0.4) km at ca. 54-46 Ma, then rose to 2.9 ± 0.9 km at ca. 44 Ma. The newly discovered Luolong Flora indicates the Eocene CTV extending into eastern Tibet, and that the valley was higher in the east, sloping to the west, inferring a westward progressive rise of the valley floor. Integrated evidence from paleomagnetism, magmatism and seismic tomography suggests that the birth of the near modern plateau is attributed to the stepwise delamination (drip) of the subducted Lhasa lithosphere from east to west.