ZIRCON U-Pb CHRONOLOGY AND GEOCHEMISTRY OF THE PILLOW BASALTS FROM RAOHE COMPLEX: Geological Implications

As one of the most reliable geological records of paleo-Pacific Plate subduction in eastern China, the Nadanhada accretionary complex is of great importance to define the westward subduction of paleo-oceanic plate. The Raohe Complex is located in the core of the complex, developed with typical accretionary complex association, among which the basaltoids, mostly in structural lenticles, are occurred in the ultramafic-mafic complex zone with slight deformation but no metamorphism. Study on the isotopic chronology and geochemistry of the pillow basalt samples from Raohe Complex shows that the LA-ICP-MS zircon U-Pb age is Middle Jurassic(168±2 Ma), with depletion of LILEs (Rb and Sr), enrichment of HFSEs(Nb and Ta) and high-abundant Th, which was formed in the ocean island environment (OIB). Its formation age and genetic environment is significant to study the tectonic dynamic background of the area during the Jurassic period.