Zircon U-Pb Dating and Geochemical Characteristics of Sihaiping Pluton from Southern Qinling Orogenic Belt in Shaanxi

Based on the geology, petrology and geochemistry studies, off whitemedium-granule-biotite-adamellite and porphyritic biotite-adamellite from the Sihaiping intrusion were identified. The Sihaipinggranitoid belongs to high-K calc-alkaline serieswith aluminous-peraluminous characteristics, which was enriched in Rb, Th, K and Nd,depleted in Ba, Nb, Ta, La, P and Eu, with significant loss of Nb, Ta and P. In addition, this intrusion has moderate-low REE concentration and right deviated distribution curve. It suggests that Sihaiping granite mass might be formed in aintra-plate setting.The magma came from the partial melting of earth crust. LA-ICP-MS zircon U-Pb analysis suggested that Sihaiping intrusion was formed at 168.2±1.1Ma, which is later than U-Pb age of Yanzhiba intrusion. Combining with previous researches, Sihaiping-Yanzhiba intrusions had experienced several magmation from late Triassic to middle Jurassic.