LA-ICP-MS zircon U-Pb dating of the biotite monzonitic granite from Shihahe area in Inner Mongolia and its geological significance

Zircon U-Pb chronology and geochemistry of the biotite monzonitic granite from Shihahe area of Urad Middle Banner were studied systematically to investigate its formation age and tectonic background. The weighted average age obtained by zircon LA-ICP-MS U-Pb method is(274.99±0.71)Ma, which represents its formation age. The biotite monzonitic granite belongs to subaluminous-weakly peraluminous I-type and calc-alkaline series, with its A/CNK being 0.93-1.10 and σ being 2.01-2.88. The total REE (ΣREE) is lower, LREE values are higher and HREE is lower, with LREE/HREE ratio varying from 9.86 to 15.63, indicating that LREE and HREE differentiated intensely. Eu has insignificant anomalies or weakly negative anomalies. In the primitive mantle normalized trace elements spider diagram, the biotite monzogranite is enriched in large ion lithophile elements Rb and K while depleted in high field strength element Nb, similar to features of normal arc granitic rock. According to tectonic setting as well as emplacement time and characteristics of geochemistry of the biotite monzogranite from Shihahe area, it is inferred that the rocks were formed in an active continental margin environment, and the upper limit of conversion from ocean crust subduction to continent collision was later than late Early Permian.