Identification and genesis of the Late Jurassic volcanic rocks in Longquan area, southern Zhejiang Province

There has been controversy for a long time that the large-scale volcanic activity of Late Mesozioc in Zhejiang Province began with Late Jurassic or Early Cretaceous? Through zircon U-Pb geochronologic study of volcanic rocks in Longquan area of southern Zhejiang Province, a batch of high precision chronologic data were obtained. These zircon U-Pb ages are between 163 Ma to 145 Ma which were confirmed by SHRIMP and LA-ICP-MS. These data indicate that large-scale volcanic avtivity in Zhejiang Province began with Late Jurassic. According to geochemical characteristics and Sr-Nd isotope analysis, these Late Jurassic volcanic rocks belong to peraluminous and high potassium Ca-alkaline series characterized by high SiO₂, K₂O but low P₂O₅, FeOT and MgO. Due to the subduction of the Pacific plate in Late Mesozoic, the lower crust material (basement metamorphic rocks) was extensively melted and the late Jurassic volcanic-magmatic rocks in this area were formed. In addition, the authors propose defining a new rock-stratigraphic unit named" the Late Jurassic Huangmaojian Group"so as to better express and contrast.