Abstract:

The Beijige pluton is located in the Siziwangqi area, Inner Mongolia, tectonically belongs to the Xing-Meng orogenic belt, lying on the southern margin of the Erdaojing-Chaganwula-Honggeer suture zone. It is predominantly composed of syenogranite. LA-ICP-MS U-Pb zircon dating and petrochemical analysis have been carried out in order to understand the formation age and natures of the pluton. As a result, zircons from syenogranite give a LA-ICP-MS mean U-Pb age of (264.0±3.4)Ma(MSWD =1.5). Petrochemical data indicate that syenogranite belong to high-alkaline series (K₂O+Na₂O=8.0%-9.29 %, K₂O/Na₂O=1.20-2.59), low Rb/Sr ratios (2.4-4.2), rich in LILE((La/Yb)N =3.1-13.6), deplete in HFSE show an affinity to I-type granite. The main dark mineral and accessory mineral of syenogranite are biotite and sphere, with abundant mafic microgranular enclaves, a common feature of KCG, which formed in the transition stage of continental subduction and collision. In the discrimination diagrams, all samples fall into the syn-collision area. Geochronological and petrochemical data imply that the Beijige pluton is related to a syn-collisional regime, maybe triggered by an extensive underplating.

Key words: syn-collision; , granite; , zircon U-Pb dating, Beijige pluton, Siziwangqi, Inner Mongolia