LA-ICP-MS zircon U-Pb geochronology and geochemistry of the porphyroclastic lava and rhyolite in west Taipusi Banner area of Inner Mongolia

LA-ICP-MS zircon U-Pb dating was carried out for two samples of porphyroclastic lava and rhyolite from the west Taipusi Banner, Inner Mongolia. As a result, their ages were obtained, which are 140.1±0.6Ma and 138.3±0.9Ma, respectively. The results show that all the rocks were produced by magmatic activities in Early Cretaceous. Porphyroclastic lava and rhyolite have the same geochemical features, characterized by high content of SiO₂, Na₂O+K₂O and low CaO, MgO, TiO₂ and P₂O₅, and belonging to the high-K calc-alkaline series. A/CNK values of the rocks are from 0.99 to 1.13, suggesting that they are peraluminous. The rocks are characterized by LILE enrichment (Rb, Th, U) and HFSE (Ti, Nb, Ta) strong depletion. They are characterized by enriched LREE patterns with strong negative Eu anomalies (δEu=0.06~0.24), with high TFeO/MgO(5.64~43.29) and 10⁴×Ga/Al(2.96~4.41) ratios, and strong depletion of Ba and Sr. All these geochemical data indicate that they are mainly aluminous A-type granite. Under the regional lithospheric extension, the asthenosphere upwelling and mafic magma underplating provided enhanced heat flux and triggered the partial melting of the overlying crust and then produced the porphyroclastic lava and rhyolite.