浙西北钟吕群流纹岩锆石U-Pb年龄及其年代地层学意义

 钟吕群出露于浙西北地区,为一套强变形、浅变质的碎屑岩-火山岩系,其下未见底,上被南华纪休宁组不整合覆盖。传统上将其对比于赣东北双桥山群。本文主要研究钟吕群流纹岩的锆石U-Pb 年龄。样品A120408-4 采自苏庄断层以北,层位上属钟吕群的中上部,岩性为灰白色致密块状流纹岩,强烈片理化。样品A120408-4 中获得大量锆石,完成LA-ICP-MS 锆石UPb定年测点38 个,获得年龄加权平均值为(777.1±3.6)Ma,结合地层特点及变质变形特征,得出钟吕群主体相当于河上镇群上墅组,应属扬子古陆新元古代晚期大陆裂谷的地质记录。

LA-ICP-MS zircon U-Pb dating of the rhyolite from the Zhonglü Group,northwestern Zhejiang Province,and its chronostratigraphic significance

The Zhonglü Group, outcropped in the northwestern part of Zhejiang Province, is a sequence of strongly-deformed, low-grade metamorphic clastic and volcanic rocks. It is overlaid unconformably by the Xiuning Formation, Nanhua period. Traditionally it is compared to the Shuangqiaoshan Group in the northeastern part of Jiangxi Province. This paper reports the LA-ICP-MS zircon U-Pb age of the rhyolite from the Zhonglü Group. The age of the Zhonglü Group is important to remodeling stratigraphic classification and correlation of Precambrian, and the mineralization geological background and conditions in the east part of South China are important as well. Sample A120408-4, collected from the north of Suzhuang fault, the middle-upper part of the Zhonglü Group, is massive rhyolite, which had been heavily foliated. Thirty-eight of the zircons were analyzed with LA-ICP-MS, and a weighed-mean U-Pb age of (777.1±3.6) Ma was obtained. Considering the stratum and metamorphic deformation characteristics, we draw the following conclusion: The main part of the Zhonglü Group is equivalent to the Shangshu Formation, Heshangzhen Group. Both of them belong to different facies of the same period, and they developed under the global tectonic background of Rodinia supercontinent cracking. The Zhonglü Group represents the cracking of the Yangtze ancient continent in the late neoproterozoic.