The Tibetan Plateau formed through the collision of India with Eurasia. K-rich volcanic activity in the Tibetan Plateau has been occurring since 50 million years ago. After 8 million years ago, this volcanism occurred mainly in northwestern Tibet. It is not clear why volcanism occurs in the Tibetan plateau considering that the area is dominated by the collision between continents rather than subduction, which happens in other volcanically active areas. Southward subduction of the Asian Plate and the northward one of the Indian Plate have been found. Mélange from these subducting plates forms the source material of the magmas of the volcanic fields in northwestern Tibet, although isotope data suggest that the Ashikule magma may not derive from subduction. Magma generation in Ashikule could have been affected by garnet or garnet-containing crustal layers. More generally, the crust beneath northern and central Tibet is suspected to be partially molten between of depth.