Diversity and Evolution of the Tibetan Plateau Lithosphere

In this chapter, we discuss the nature of the upper mantle beneath the southern Tibetan Plateau on the basis of mantle xenolith hosted in the Sailipu ultrapotassic volcanic rocks (trachyandesite, ~17Ma). Sailipu mantle xenolith differs from cratonic lithosphere in having high temperature (990~1140°C) and highly metasomatized composition as illustrated by the magmatism associated with well-developed N-S normal fault systems on the plateau surface. Three geochemical components (reservoirs) are readily identified in terms of Sr-Nd-Pb-O isotopes, i.e., (A) the North Tibet geochemical province, (B) the Neo-Tethyan mantle reservoir, and (C) the Himalayan continental crust component. These three reservoirs control the composition of the magmatism in the Lhasa terrane as shown by the geochemical mixing relationships recorded in the magmatic rocks.