U-Pb isotopic ages of zircon from Yuli Belt in Taiwan and its geological significance

Located in the east of Taiwan, the Yuli belt is composed of volcano-sedimentary rocks and metamorphic rocks characterized by high pressure and low temperature. The volcanic rocks belong to the calc alkaline series, with low Ba, Nb, Sr and high Pb; the total rare earth is generally low, with the patterns of less enrichment of light rare earth Eu and complete preservation of rare earth elements. LA-ICP-MS zircon U-Pb ages indicate that the apparent ²⁰⁶Pb/²³⁸U ages have 6 peaks:23.3Ma (Paleogene), the upper rock age; 96.7Ma (Late Cretaceous), 124.2Ma and 130.5Ma (Early Cretaceous), 214.1~228Ma (Late Triassic), 283.7Ma and 289Ma (Early Permian). Zircons with the sub-angular or sub-rounded shape represent the magmatic zircon and indicate magmatic source rock age. Zircons with apparent ²⁰⁷Pb/²⁰⁶Pb ages of 2 peaks 1769~1852Ma (Paleoproterozoic), 2506Ma and 2530Ma (Neoarchaean) are rounded or clastic metamorphic magmatic zircons, which represent Palaeoproterozoic ages of metamorphic basement. The metamorphic rocks in the Yuli belt might have been formed after 23.3Ma, with the expansion of the South China Sea, at the same time as the expansion of the South China Sea during the formation of the Eurasian continental block edge rift tectonics.