浙南龙泉地区晚侏罗世火山岩的厘定及成因探讨

浙江晚中生代大规模火山活动始于晚侏罗世还是早白垩世,长期以来存在争议。本文对浙南龙泉地区火山岩进行了锆石U-Pb定年,获得一批高精度的年代学数据,其SHRIMP锆石U-Pb和LA-ICP-MS锆石U-Pb年龄集中于163～145 Ma,确认浙江晚中生代火山活动始于晚侏罗世。地球化学特征和Sr-Nd同位素特征表明这套晚侏罗世火山岩具有高硅、高钾、低磷、贫铁镁的特征,属于过铝质高钾钙碱性岩石系列。由于晚中生代太平洋板块的俯冲作用,导致了下部地壳物质(基底变质岩)广泛熔融,形成了本区晚侏罗世火山岩浆活动。为了便于表达、对比,笔者建议新建"晚侏罗世黄茅尖群"地层单位。

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.