Tibetan Plateau growth linked to crustal thermal transitions since the Miocene

The topographic transition of central-northern Tibet since the early Miocene has created a consistently high and flat plateau similar to that of today. However, to date, the associated deep crust and/or /mantle events are poorly understood, mainly due to an early Miocene metamorphic-magmatic lull within the Qiangtang Block. To address this issue, we undertook a study of crustal xenoliths and zircon xenocrysts in 6.0-2.3 Ma lavas in the Qiangtang Block. The occurrence of 22.6-12.9 Ma high-temperature-low-pressure granulite xenoliths implies that the middle crust of the block has been very hot since that time. Zircon xenocrysts and granitic xenoliths from 6.0-2.3 Ma lavas were studied and shown to have high delta O-18 values, which supports Miocene crustal melting and the formation of unexposed, coeval felsic plutons. Combined with paleoelevation data from the Tibetan Plateau, our results suggest that the early Miocene cold-hot thermal transition of the middle-lower crust was near-synchronous with topographic evolution from high-relief mountains to a flat plateau, which supports crustal flow as the main topographic smoothing mechanism for central-northern Tibet.