Zircon U-Pb age and geochemical characteristics of Ordovician pluton in Geleaobao, Inner Mongolia

The Geleaobao area of Inner Mongolia is located in the Xingmeng orogenic belt. By studying the Ordovician magmatic rocks in this area, researchers can further understand the structure and evolution of the Early Paleozoic strata in this orogenic belt. The ages of the LA-ICP-MS zircons of syenite and mottled monzogranite samples studied in this work are 441.6±3.7Ma to 454.9±4.6Ma. The age of formation is Ordovician. Geochemical analysis shows that the pluton has high-K calc-alkaline characteristics. Aluminum saturation index shows that it is peraluminous granite. The characteristics of trace elements in rocks indicate that they are enriched in large ionic lithophilic elements (LILEs) Rb, Th, U, K, depleted in Ba, Sr; enriched in high field strength elements (HFSEs) La, Ce, Nd, Zr, and depleted in Nb, P, Ti. The total amount of rare earths in the rocks is 38.7×10 -6 to 120.23×10 -6, and the light rare earths exhibit obvious differences in heavier rare earths, with higher fractionation and weaker negative Eu anomalies. Based on regional geological data, it is believed that the source region of the Ordovician magma in the Geleaobao area is partially melted upper crustal materials, and the formation environment was a back-arc basin. After the subduction of the ancient Asian Ocean to the north, it experienced an island-arc magmatic process cycle, being product of extension stage.