Cenozoic Post-collisional Igneous Rocks in the Tibetan Plateau

The post-collisional igneous rocks (31–9 Ma) are widespread in the central and southern Lhasa subterranes and extend ~1500 km between 80°E and 91°E. They are associated with the N-S-striking normal faults, N-S elongated lakes, and Neogene basins or grabens. They mainly consist of three magmatic suites, namely, ultrapotassic volcanic rocks (UPVRs), potassic volcanic rocks (PVRs), and adakitic intrusions. The petrography, geochemistry, and petrogenesis are summarized in this chapter. The UPVRs were generated by the partial melting from a phlogopite-bearing peridotite upper mantle source region. The PVRs is proposed to be the combined results of the input of the UPVRs, partial melting of amphibole-bearing eclogite-facies lower crust, and fractional crystallization dominated by feldspar and clinopyroxene. The coeval adakitic rocks in the Lhasa terrane display high Sr/Y and La/Yb, low Y features, suggesting the source region is most probably thickened lower crust (garnet-bearing, hydrous amphibolite, or amphibole eclogite).