A study of geochronology and geochemistry of volcanic rocks from Meiletu Formation in Horqin Right Wing Front Banner, Inner Mongolia

Through LA-ICP-MS zircon U-Pb dating and elemental geochemical analysis of Meiletu Formation volcanic rock in Horqin Right Wing Front Banner, the authors obtained the eruption ages of 125.6±1.6Ma and 120.2±2.2Ma for andesite crystallinoclasitc welded tuff and andesite in Meiletu Formation, indicating that the forming ages of Meiletu Formation volcanic rock are between 120 and 126Ma in the Early Cretaceous. The rock has high SiO₂ (60.4%~65.3%) and total alkali content (7%~9.5%), with aluminum index A/CNK being 0.89~0.98, suggesting shoshonitic and high-K calc alkaline series; rare earths range from 124×10^-6 to 169×10^-6, and (La/Yb)_N values are in the range of 5.83~13.4, with weak negative Eu anomalies (δEu=0.84~1.05); on the primitive mantle normalized trace element spider diagram, there exist enrichment of Rb, Ba, Th, U, K, La and Nd and depletion of Nb, Ta, P and Ti, with Sr/Y ratio between 19.4 and 29.7. The rock source area should be enriched mantle, and the magma was contaminated by crustal material during the process of magma rising. The rock was formed in an intraplate extensional environment, and its geodynamic background might have been related to subduction of paleo-Pacific plate.