Mantle flow: The deep mechanism of large-scale growth in Tibetan Plateau

The origin and growth of the Tibetan Plateau, located in the back lands of the Himalayan orogenic belt, have always been considered controversial. Based on data from previous studies and our own comprehensive research, we found that a giant high-heat flow zone thousands of kilometres long developed, spanning different tectonic units of the Qinghai-Tibet Plateau, encompassing the Kunlun, Qiangtang, Mangkang-Dali and Honghe-Ailao Mountain ranges. All these tectonic units show a tendency to have migrated from the inner plateau towards the northeast edge. Several rock groups are distributed along this giant high-heat flow zone in a continuous pattern: The potassic mafic rock-lamprophyre group (42–32 Ma) and potassic alkaline rock-carbonate rock (27–7 Ma) from partial melting of lithosphere and mantle, the ocean island basalt (16–1 Ma) from decompression melting of the asthenosphere, and the potassic feldspathic rock (40–0.3 Ma) from the melting of the middle-lower crust. The high temperature deep metamorphic zone, characterized by granulite facies metamorphism in the peak period, was accompanied by a large strike-slip fault zone (40–17 Ma). The metamorphic temperatures of the lower crust granulite xenoliths rose to 800°C. However, the mantle peridotite xenoliths show characteristics of vertical mantle flow. The six large low-speed anomalous bodies revealed by geophysical exploration are clustered, equidistant, and intermittently distributed. Our research proposes that the Indian continental lithospheric-mantle subduction triggered the Asian continental asthenosphere surge, which caused vertical upwelling along a number of mantle channels in the posterior continental region, thermally corroding and engulfing the mantle-lithosphere and reaching as far as the bottom of the crust. These “mantle flow channels” came from depths around 400 km. They began forming after the late (hard) collision 40 Ma, and not only provided deep heat to sustain the Tibetan Plateau uplift but also prepared new mantle source material for the plateau’s crustal growth. At the same time, this high-heat flow zone caused the plastic and lateral flow of the middle-lower crust, driving the lateral growth of the Tibetan Plateau to the northeast.