LA-ICP-MS zircon U-Pb dating and geochemical characteristics of the pantellerite of Guanghua Formation from Longjiang basin in northern Da Hinggan Mountains and their geological implications

In this paper, geochemistry and zircon U-Pb isotope chronology of the pantellerite of Guanghua Formation from Longji-ang basin in northern Da Hinggan Mountains were studied and their petrogenesis and tectonic significance were discussed. The zir-cons from pantellerite of Longjiang basin show oscillatory growth zonation of typical magmatic origin and high Th/U ratios (0.71~2.12), indicating a magmatic origin for the zircons. LA-ICP-MS zircon U-Pb weighted average age is 122.4 ±1.7Ma (n=19, MSWD=0.77). The pantellerite is characterized by high SiO₂ content, high alkali content but low Mg, Ca content. The REE pat-terns are characterized by enrichment of LREEs relative to HREEs and distinct negative Eu anomalies in the chondrite-normalized REE patterns, characterized by right-inclined and "V" -shaped feature. These rocks are depleted in Sr and Ba but enriched in Rb, Th, U, Zr. All these characteristics are similar to features of A-type granites which originated from the partial melting of felsic crust under high temperature and low pressure conditions and the subsequent fractional crystallization of plagioclase and Ti and Fe oxides, thus representing an extensional tectonic environment.