Tibetan Plateau insights into >1100 degrees C crustal melting in the Quaternary

Partial melting during high-temperature to ultrahigh-temperature (UHT) metamorphism facilitates crustal differentiation, element transfer, and the evolution of topography in orogens, however the mechanisms that drive heating of Earth's crust remain controversial. We provide new evidence from ca. 2.3 Ma dacites in the Tibetan Plateau, representing the youngest known UHT metamorphic event. Our results show that these dacites were mainly generated by fluid-absent melting of metasedimentary rocks and minor mafic rocks at peak temperatures of 1100-1150 degrees C and pressures of 0.8-0.9 GPa. The dacites represent mixtures of UHT melts and granulite residues and are geochemically similar to A-type granites with extremely high heat-production values (5.33-5.99 mu W m(-3)). Compared with the geological and geophysical observations, numerical modeling indicates that the key factor determining the thermal evolution of Tibet is the thickness of the radioactive layer. Orogens dominated by rocks of felsic composition, like Tibet, could easily reach UHT conditions within a short period of time (20-40 m.y.) after crustal thickening by radioactive heating, without the need for an additional tectonic mechanism.