华南扬子陆块成冰纪冰川作用的启动时限及其全球对比  

Onset time and global correlation of the Cryogenian glaciations in Yangtze Block,South China

作　　者：蔡娟娟[1] 崔晓庄[2,3] 兰中伍[4] 王剑[2] 江卓斐[2] 邓奇[2] 卓皆文[2] 陈风霖 江新胜[2] Cai Juan-Juan1, Cui Xiao-Zhuang2,3, Lan Zhong-Wu4 ,Wang Jian2, Jiang Zhuo-Fei2, Deng Qi2 ,Zhuo Jie-Wen2, Chen Feng-Lin3, Jiang Xin-Sheng2(1 Chinese Academy of Geological Science, Beijing 100037 ; 2 Chengdu Center, China Geological Survey, Chengdu 610081, Sichuan ; 3 Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, Sichuan ;4 State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 10002)

机构地区：[1]中国地质科学院,北京100037 [2]中国地质调查局成都地质调查中心,四川成都610081 [3]成都理工大学沉积地质研究院,四川成都610059 [4]岩石圈演化国家重点实验室,中国科学院地质与地球物理研究所,北京100029

出　　处：《古地理学报》2018年第1期65-86,共22页Journal of Palaeogeography：Chinese Edition

基　　金：国家自然科学基金项目(编号：41502114,41772115,41672112,41673016); 中国地质调查局项目(编号：DD20160017)共同资助

摘　　要：江口冰期和南沱冰期是华南地区引人注目的 2次成冰纪冰川事件,但其确切启动时间及其全球对比关系仍未有定论。为此,对桂北地区成冰系(南华系)长安组底部和南沱组底部冰成杂砾岩开展了碎屑锆石U-Pb年代学研究。长安组碎屑锆石U-Pb年龄集中分布于958—717 Ma,显著峰值为720、753、805及848 Ma,最年轻一组206Pb/238U年龄的加权平均值为719.6±6.1 Ma,可解释为长安组最大沉积年龄;南沱组碎屑锆石U-Pb年龄集中分布于987—649 Ma,显著峰值为650、720、753、779、803、823及848 Ma,最年轻一组206Pb/238U年龄的加权平均值为649.3±6.2 Ma,可解释为南沱组最大沉积年龄。结合已发表的相关年龄数据可知,江口冰期很可能启动于ca.715 Ma,与塔里木、阿拉伯—努比亚、劳伦等陆块的Sturtian冰川作用高度同步;南沱冰期的启动应晚于650 Ma,与西伯利亚、澳大利亚、劳伦等陆块的Marinoan冰川作用基本同步。另外,碎屑锆石U-Pb年龄谱与CL图像显示,长安组和南沱组的物质来源主要为下伏新元古界岩浆—沉积记录,揭示出冰川对下伏地层的强烈刨蚀作用和华南新元古代幕式构造岩浆热事件。扬子陆块成冰纪冰川刨蚀作用可能与Rodinia超大陆"裂离"有关的强烈伸展活动存在联系,并可能持续至Marinoan冰期结束。It＇s well known that the Jiangkou and Nantuo glaciations are two remarkable Cryogenian glaciations in South China. However,their precise onset time and global correlations remain undecided. In this study,detrital zircon LA-ICP-MS U-Pb dating was performed on the glacial diamictites from the basal part of the Chang＇an and Nantuo Formations in the southeastern Yangtze Block. The new results show that detrital zircon grains from the Chang＇an Formation give a concentrated ^206 Pb/^238 U age range of 958 to 717 Ma with distinct peaks at 720,753,805 and 848 Ma. The youngest age population yields a weighted mean of 719. 6±6. 1 Ma,representing the maximum depositional age of the Chang＇an Formation. Detrital zircon grains from the Nantuo Formation has a main ^206 Pb/^238 U age range between 987 and 649 Ma,with distinct peaks at 650,720,753,803,823 and 848 Ma. The youngest age population gives a weighted mean of 649. 3±6. 2 Ma,representing the maximum depositional age of the Nantuo Formation. Taking into account the available age data,it is suggested that the Jiangkou glaciation was most likely initiated at ca.715 Ma,which is synchronous with the Sturtian glaciation in other blocks such as Tarim,Arabia-Nubia and Laurentia; the Nantuo glaciation was probably initiated later than 650 Ma, synchronous with the Marinoan glaciation in other blocks such as Siberia,Australia and Laurentia. Furthermore,detrital zircon U-Pb age spectrums and CL images indicate that sediments of the Chang＇an and Nantuo Formations in the Yangtze Block were mainly derived from the underlying Neoproterozoic magmatic and sedimentary rocks,indicative of the intensive Neoproterozoic severe exaration and episodic tectonic-thermal events. The Cryogenian exaration in the Yangtze Block should be the response to the breakup of the Rodinia supercontinent prior to the termination of the global Marinoan glaciation.

关 键 词：成冰纪 冰成杂砾岩 碎屑锆石 江口冰期 南沱冰期 扬子陆块 

分 类 号：P512.4[天文地球—地质学] P534.3