江南造山带东段新元古代登山群年代学及大地构造意义  

Geochronology of the Dengshan Group in the Eastern Jiangnan Orogen,and Its Tectonic Significance

作　　者：张继彪 刘燕学[1] 丁孝忠[1] 张恒[1] 石成龙 Zhang Jibiao;Liu Yanxue;Ding Xiaozhong;Zhang Heng;Shi Chenglong(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《地球科学》2020年第6期2011-2029,共19页Earth Science

基　　金：中国地质调查局地质调查项目(Nos.DD20190370,121201111120117)。

摘　　要：为探讨江南造山带东段新元古代构造演化机制,对江南造山带东段登山群砂岩及火山岩进行锆石U-Pb年代学及地球化学研究.SHRIMP锆石U-Pb定年显示登山群高山组凝灰岩年龄为855.5±8.2 Ma,叶家组流纹岩年龄为798.1±7.8 Ma.地球化学数据显示高山组砂岩物源区为大陆岛弧,形成于弧后盆地;叶家组火山岩为双峰式火山岩,流纹岩轻稀土富集,重稀土亏损;高FeOt/(FeOt+MgO)和Ga/Al值、低CaO、MgO,εHf(t)值为7.9~10.9,富集Ba、Th、U等大离子亲石元素和高场强元素,强烈亏损Sr、P、Ti的特征显示其为典型的A型花岗岩,来自初生地壳的部分熔融;玄武岩属拉斑玄武岩系列,具有OIB特征,富集轻稀土及大离子亲石元素,来自软流圈地幔的部分熔融.双峰式火山岩形成于板内伸展背景.年代学及地球化学结果表明新元古代江南造山带东段扬子与华夏板块拼贴时限为855~800 Ma之间.造山结束之后地幔物质上涌,华南板块进入裂谷期.Detailed researches on Zircon U-Pb chronology and geochemistry of the Dengshan Group in the eastern Jiangnan orogen have been undertaken in this paper in order to figure out the tectonic setting of the eastern Jiangnan orogen in the Neoproterozoic.SHRIMP zircon U-Pb dating of two samples yielded weighted mean ages of 855.5±8.2 Ma and 798±7.8 Ma, respectively. The sandstone rocks are mostly affiliated with a continental arc, in good agreement with the proposed back-arc basin scenario. These rhyolites display LREE enriched REE patterns, with positive εHf(t) values, and has high values of FeOt/(FeOt+MgO) and Ga/Al, low contents of CaO and MgO, and it is enriched in Ba, Th, U and HFSEs, and depleted in Sr, P, and Ti, thus resembling A-type granitoids. These basalts are of tholeiitic basalt, and display ocean island basalt(OIB)-like geochemical signatures, with the enrichment of LREE and large-ion lithophile element relative to HREE. The bimodal volcanic rocks are suggested to be formed during post-collisional extension setting. Combined with the previously data from the Jiangnan orogen, we propose that the Jiangnan orogen leading to the assembly of the Yangtze and Cathaysia Blocks took place during 855-800 Ma. This was followed by breakup after the orogenesis which was triggered by mantle upwelling.

关 键 词：新元古代 登山群 锆石U-PB年龄 地球化学 江南造山带 

分 类 号：P548[天文地球—构造地质学] P597[天文地球—地质学]