GEOCHRONOLOGY, PETROGEOCHEMISTRY AND GEOLOGIC IMPLICATION OF THE YUESHANDONG DIORITE PLUTON IN YANBIAN AREA, JILIN PROVINCE

The Yueshandong diorite pluton in Yanbian area, Jilin Province is tectonically located the boundary between the Longgang block and Ji-Hei orogenic zone. The LA-ICP-MS zircon U-Pb dating and geochemical data yield weighted mean ²⁰⁶Pb/²³⁸U ages of 178.4 ±1.2 Ma, indicating that the pluton was formed during the late of Early Jurassic. The petrogeochemistry is characterized by high Al and Na. The main oxides (Na₂O, K₂O, Al₂O₃, CaO, MgO, FeO_t, P₂O₅ and TiO₂) show a linear relation to SiO₂ from, which indicate that the magma experienced a fractional crystallization of pyroxene, apatite and magnetite. The rare earth contents of samples display similarly fractionated REE patterns, with enrichment in LREEs and depletion in HREEs. The ratios of δEu range from 0.67 to 1.04, with negative to slightly positive Eu anomalies. The trace element spider diagram shows that the rocks are enriched in large ion lithophile elements(LILEs, such as CS, Rb, Ba and K), whereas depleted in high field strength elements (HFSE, such as Nb, Ta, Ti and P). The ratios of Nb/Ta, La/Nb and Th/Nb are between the data of curst and mantle, showing that the magma is derived from crustmantle mixing source. From the geochemical charateristics and regional tectonic setting, the pluton is tectonically related to the subduction of the circum-Pacific tectonic system beneath the Eurasian continent and, at the same time, might be influenced by the collision between North China Plate and Siberia Plate.