Abstract: Mesozoic magmatic rocks are widely distributed in the Lhasa terrane, and the understanding of their petrogenesis and geodynamic setting may yield important information on the pre-Cenozoic geohistory of the Tibetan Plateau. In this paper, we carried out studies for the first time on the system zircon geochronology and major and trace elemental geochemistry of the Jiega Formation in the Sailipu area in western Lhasa block. The results show that the Jiega Formation has mainly andesite, basalt-andesite and basalt belonging to medium potassium calc alkaline series and is aged at 108.5±1.0 Ma by accurate LA-ICP-MS U-Pb dating. It is enriched in LILE Rb, Th, U and depleted in HFSE Nb, Ta, Ti, typical of island arc volcano rock. The REE patterns revealed enrichment of LREE with some flatness and weak negative Eu anomaly, indicating some low level magmatic differentiation. We conclude that the Jiega Formation volcano rocks were probably formed by partial melting of the metasomatic lithospheric mantle induced by upwelling of asthenosphere from the rotation of subducted slabs under the tectonic setting of the Bangong LakeNu River southward subduction of the Neo-Tethys.

Key words: island arc volcanic rocks, zircon LA-ICP-MS U-Pb dating, Jiega Formation, Sailipu, Lhasa block, Tibet