Dating of Early Jurassic volcanic rocks in the Mohe foreland basin of northern Greater Khingan Mountains, northeast China

Intermediate-basic volcanic rocks are largely distributed in Greater Khingan Mountains of Heilongjiang Province, and the determination of their ages is of great significance to understanding the regional tectonic evolution and petrogenesis of the Mesozoic volcanic belt in the Great Xing'an Range. Based on the 1:50000 regional geological and mineral resources survey in the study area, the LA-ICP-MS zircon U-Pb geochronology, petrology and petrogeochemistry of the intermediate-basic volcanic rocks previously attributed into the Middle-Late Jurassic Tamulangou Formation were systematically studied. Zircon U-Pb dating of the two trachyandesite samples and one basaltic andesite sample yields (185.8±8.1)Ma, (196.8±2.1)Ma and (196.3±2.7)Ma respectively, which indicates that there exists a set of early Jurassic intermediate-basic volcanic rocks in the Tamulangou Formation. These Early Jurassic volcanic rocks belong to metaluminous, mainly high-K calc-alkaline series generally enriched in large ion lithophile elements (such as Ba、K、La、Ce、Sr、Zr) and LREE, but depleted in high field strength elements (such as Th、Nb、P、Zr、Ti) and HREE. Combined with the regional tectonic evolution, it is conclude that the early Jurassic intermediate-basic volcanic rocks were formed in an active continental margin setting related to the southward subduction of the Mongol-Okhotsk oceanic plate beneath the Erguna Massif during the Early Jurassic.