Zircon U-Pb Geochronology of Granulites in Panzhihua-Xichang Area:New Evidence for the Neoproterozoic Geological Evolution in the Western Margin of Yangtze Block

The Panxi (Panzhihua-Xichang) granulites have long been recognized as the oldest rock of the crystalline basement with the highest metamorphic grade on the western margin of the Yangtze Block. The TIMS zircon U-Pb dating results of the Panxi granulites in this paper indicate that the protoliths of these granulites were formed in the late Paleoproterozoic (1870±24 Ma). Seventeen zircon U-Pb concordant ages (from 858 to 778 Ma) show the time of amphibolite-facies retrogressive metamorphism of the Panxi granulites. Amphibolite-facies retrograde metamorphism took place during rapid cooling and uplift of the Panxi granulite, which was probably correlated with the Neoproterozoic mantle plume activities. This is the key period during which the geodynamic system of the global Rodinia Supercontinent was transited from amalgamation to break-up in the Neoproterozoic.