Cenozoic Adakite‐type Volcanic Rocks in Qiangtang, Tibet and Its Significance

Abstract

Abstract Volcanic rocks in the study area, including dache, trachyandesite and mugearite, belong to the intermediate‐acid, high‐K calc‐alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that the rocks are characterized by SiO2>59%, enrichment in Al2O3 (15.09–15.64%) and Na2O (>3.6%), high Sr (649–885 μg/g) and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb)N>25, Sr/Y>40, MgO<3% (Mg#<0.35), weak Eu anomaly (Eu/Eu*=0.84‐0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd and Sr isotope data (87Sr/86Sr=0.7062‐0.7079, 143Nd/144Nd=0.51166‐0.51253, εNd = −18.61‐0.02), show that the magma resulted from partial melting (10%‐40%) of newly underplated basaltic lower crust under high pressure (1–4 GPa), and the pedogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will give an insight into the uplift mechanism of the Tibetan plateau.