Transition to hot, wet crust and the flattening of the Tibetan Plateau

In the late Oligocene−Miocene, Tibet underwent a topographic transformation from high-relief mountains to its high but flat plateau of today. However, the associated deep crust−mantle evolution remains unknown. Here, we used a combination of geochemistry and thermodynamic and geodynamic modeling to address this issue. Our geochemical data reveal both high-temperature dehydration melting and low-temperature water-fluxed melting occurring within the Lhasa middle to lower crust at 30−15 Ma. This crustal state reflects a marked change from the prior magmatic gap associated with India’s flat-slab subduction and Lhasa’s cold-and-dry crust during the preceding interval from 45 to 30 Ma. Notably, this transition to hot-and-wet crust was synchronous with Tibet’s topographic transformation. Our modeling further validates crustal flow—due to the hot, wet, and weak crust—as the primary mechanism for the flattening of the Tibetan Plateau, as well as demonstrating that ongoing subduction of India has been able to maintain the elevation of the high, flat plateau since then.