LA-ICP-MS zircon U-Pb dating of the Nuhete Early Cretaceous A-type granite in Xi Ujimqin Banner of Inner Mongolia and its geological significance

Located along the Hegenshan collisional orogenic suture zone in Xi Ujimqin Banner of Inner-Mongolia, the Nuhete Atype granite intruded into Late Carboniferous Meilaotewula ophiolite, Middle Permian Zhesi Formation and Late Carboniferous tonal-ite and consists mainly of syenogranites. The granite is geochemically characterized by high SiO₂(72.92%~76.18%), K₂O(4.1%~5.03%) and absolute alkali values (Na₂O+K₂O=8.01%~8.64%), low Al₂O₃, CaO, MgO, TiO₂, P₂O₅, Sr, Ba, Eu, Ti, P values, and relatively high Ga/Al, (Na₂O +K₂O)/CaO, K₂O/MgO, TFeO/MgO, Rb/Nb, Y/Nb, Sc/Nb ratios. It is characterized by a slightly right-inclined gull-wing shaped REE patterns with negative Eu anomalies (δEu=0.25~0.54). The Nuhete syenogranite exhibits the typical geochemi-cal characteristics of aluminous A-type granites, being significantly different from I, S and M type granites in geochemistry. According to the chemical subdivision diagrams of the A-type granitoids, the Nuhete A-type granite belongs to aluminous A₂-type granitoid formed and emplaced in a post-orogenic extension setting. The LA-ICP-MS zircon U-Pb dating shows that the age of the granite is 130.4 ±1.2 Ma and 130.4 ±1.4Ma, suggesting early Cretaceous. According to the temporal and spatial distribution and evolution charac-teristics of the ophiolites, subductional arc granitoids, collisional granites and post orogenic granitoids in the Hegenshan collisional oro-genic suture zone, the authors hold that the Hegenshan suture zone was in a post orogenic extension stage in the Early Cretaceous period.