ZIRCON U-Pb GEOCHRONOLOGY AND GEOCHEMISTRY OF THE DAHUANGHUA SYENOGRANITE IN AOHAN QI, INNER MONGOLIA

Based on the study of zircon U-Pb geochronology and geochemistry of the Dahuanghua syenogranite in Aohan Qi, Inner Mongolia, the formation time, petrogenesis and tectonic background are discussed. The result of the zircon U-Pb age by laser ablation ICP-MS technique is 162.6±1.9 Ma, indicating that the Dahuanghua syenogranite is formed in late Middle Jurassic. The major and rare elements are characterized by high Si, rich alkaline and obviously negative Eu, Ba, Sr, P and Ti anomalies. The rock, which experienced a high fractionate evolution(DI=95.1-95.88), is highly fractionated I-type granite. The low Sr/Yb ratio implies that it was formed in a melting environment with very low pressure. Combining the geochemical and regional geological characteristics, it is suggested that the Dahuanghua syenogranite should be generated in postcollisional extension tectonic setting with the evolution of Mongolian-Okhotsk suture zone.