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 δ18O 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.