GEOCHRONOLOGY AND GEOCHEMISTRY OF THE JURASSIC GRANODIORITE IN JIANGJIATUN, TUQUAN COUNTY OF INNER MONGOLIA

Study on the isotopic chronology and lithogeochemistry of the Jiangjiatun granodiorite in Tuquan County, Inner Mongolia, indicates that the LA-ICP-MS zircon U-Pb weighted average age for the rock body is 154.8±1.8 Ma, which represents Late Jurassic. The petrological and geochemical data shows the granodiorite, belonging to high-K calc-alkaline series and A-type granite, is characterized by high SiO₂ (66.08%-67.80%), rich alkali (K₂O+Na₂O=7.35%-7.97%), rich Al₂O₃ (14.5-15.23), poor MgO (1.08%-1.62%), poor CaO (2.05%-3.04%) and low TiO₂ (0.56%-0.67%). The REE pattern curves are right-dipping with evident negative Eu anomalies and well LREE fractionation. The primitive mantle normalized trace element spidergrams show distinct negative Sr, Ba and Ti anomalies, depletion of Sr,Ba, Ta and Nb,and relative enrichment of Th,Zr,Hf and Pb. From the above, it is thought that the Jiangjiatun granodiorite is the product of post-orogenic lithosphere extension and shear thinning background affected by the subduction of Paleo-Pacific Plate.