ZIRCON U-Pb DATING, GEOCHEMISTRY AND THEIR SIGNIFICANCE OF THE EARLY CRETACEOUS CHAOYANGGOU GRANITES IN LINXI, INNER MONGOLIA

The Chaoyanggou pluton in Linxi area, Inner Mongolia, is tectonically located in the east of Xingan-Mongolia orogenic belt between the North China plate and Siberian plate. The LA-ICP-MS zircon U-Pb dating for the Chaoyanggou rock body indicates that the granite was emplaced in Early Cretaceous (126.2±2.5 Ma). The intrusive rock is geochemically characterized by high SiO₂(68.5%-72.1%), Al₂O₃(14.05%-14.95%), alkali(K₂O+Na₂O=8.34%-10.03%) and Fe₂O₃ (2.2 7%-4.15%), belonging to quasi aluminum and calc-alkaline granite, with A/CNK=0.97-1.09 and high Mg^# values (12.66-15.02). The pluton shows relatively more enriched LREE(124×10^-6-199×10^-6) in comparison with HREE(15×10^-6-21×10^-6). It has evident negative Eu anomaly, with distinct negative Ba, Ta, Nb, Sr, P and Ti anomalies and enrichment of LILE such as Rb, Th, U and K. Based on the (Yb+Nb)-Y and R1-R2 diagrams, all samples fall in postcollisional granite area and late orogenic granite area. Considering the regional geological setting, it is concluded that the Chaoyanggou granite pluton is the product of extensive background after collision.