Geochronological and geochemical characteristics of the rhyolites in Taerqi of middle Da Hinggan Mountains and their geological significance

Taerqi area is located in the middle main ridge of Da Hinggan Mountains, where there is developed a suite of late Mesozo-ic volcanic rocks, which include basalt, andesite, dacite, rhyolite and tuff. In this paper, detailed LA-ICP-MS zircon U-Pb geochro-nological and element geochemical studies were carried out for the rhyolites. The zircon U-Pb dating yielded a weighted average age of 132±2Ma(MSWD=1.5, 2σ), indicating that the rhyolites were formed at the middle stage of the early Cretaceous. Rock geo-chemical characteristics show that the rocks are peraluminous cal-alkaline rhyolites, which are characterized by high SiO₂(71.6%~77%), high potassium and alkali content (K₂O=4.5%~5.46%, Na₂O+K₂O=7.94%~9.64%). Trace elements have a similar variation trend that systematic enrichment of LILE and depletion of HFSE as well as LREE fractionation are more obvious than that of HREE, and also show significant weak anomaly of Eu (δEu=0.22~0.7). In addition, there exist the depletion of Sr, Ba, P, Ti, Nb, Ta and en-richment of Rb, K, Th, U, Zr, Hf. The rocks belong genetically to A type with a high zirconium saturation temperature (T_Zr=842℃), and the magma source was probably similar to the metagrewacks. Accordingly, it is inferred that the A-type rhyolites were products of partial melting of the crust and formed in a post-collision environment and an extensional tectonic setting.