LA-ICP-MS zircon U-Pb geochronology and geochemical characteristics of the Early Permian granite in Chifeng area, Inner Mongolia

In this paper, the authors studied the geochronology and geochemistry of the Mingshan granitic complex and Jianshanzi granite in Chifeng area, with the purpose of providing constraints on the formation time, petrogenesis and tectonic background on the northern margin of the North China Block. The zircon U-Pb age data obtained by using laser ablation ICP-MS technique are 284.4±7.9Ma and 294.7±8.5Ma, indicating that the Mingshan granitic complex and Jianshanzi granite were formed in Early Permian. The major elements characteristics of the porphyritic biotite monzogranite are high in SiO 2 and (K₂O+Na₂O), with A/CNK lower than 1, belonging to high K calc-alkaline I-type granite. The syenogranite has Al₂O₃ 14.32%~15.14%, Na₂O/K₂O 0.71~0.99 and A/CNK 1.17~1.20, with corundum molecule in CIPW standard mineral calculation. The porphyritic biotite monzogranite and syenogranite are similar in trace elements, with enrichment of large ion lithophile elements, loss of high-field strong elements, and obvious negative Sr, P and Ti anomalies, thus having the characteristics of island-arc magma. In combination with the geochemistry and regional geological characteristics, it is suggested that the Early Permian granites in Chifeng area was generated in an island-arc/active continental margin tectonic setting.