Petrogenesis and tectonic significance of the Yari granites in the west-middle segment of the Lhasa Terrane Tibet Evidences from geochronology geochemistry and Hf isotope

More geological researchers are focusing on the Mesozoic magmatic activities of Lhasa terrane, which is significant for the evolution of the Lhasa terrane. But the petrogenesis and magmatic origin of the Late Jurassic Yari Granites(YRG) remain poorly constrained. This study presents petrology, zircon U-Pb ages, geochemistry, and Lu-Hf isotopic data of YRG. The zircon U-Pb age of the pluton is 152.1±1.5 Ma, indicating that it was formed in the Late Jurassic. The YRG are mainly adamellite characterized by high silicon (SiO₂=73.55%~74.19%), rich alkali, peraluminous and poor MgO, MnO and P₂O₅(0.12%~0.14%). It belongs to the series of high potassium calc-alkaline with high degree of differentiation. It is characterized by ΣREE of 104.12×10^-6~247.22×10^-6, (La/Yb) _N of 32.14~51.03, enrichment of light rare earth elements(ΣLREE), obvious negative Eu anomaly (δEu=0.54~0.68) and right-dipping distribution pattern of rare earth elements. It is enriched in Rb, Th, U and other large ion lithophile elements, and depleted in Nb, Ti. It belongs to highly differentiated S-type granite. Its petrology, geochronology and geochemistry indicate that the double subduction of the Neo-Tethys' northward subduction and Bangong-Nujiang Ocean' southward subduction led to the collision between the Gandese micro-continent and Chayu magmatic arc. The YRG were highly fractionated S-type adamellite and the source area might be related to the partial melting of mudstone with greywacke under the tectonic decompression settings. It is proposed that during the Late Jurassic, the Lhasa terrane area experienced a tectonic transformation from subduction to collision.