Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China
WANG Jian1, LI Xianhua2, DUAN Taizhong3, LIU Dunyi4, SONG Biao4, LI Zhongxiong1 & GAO Yonghua5 1. Chengdu Institute of Geology and Mineral Resources, China Geologi-cal Survey, Chengdu 610082, China; 2. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; 3. Colorado School of Mines, Golden, CO 80401-1887, USA (Present address: Marathon Oil Company, Houston, TX 77056-2725, USA); 4. Institute of Geology, Chinese Academy of Geological Sciences, Bei-jing 100037, China; 5. Graduate School of the Chinese Academy of Geological Sciences, Beijing 100037, China Correspondence should be addressed to Wang Jian (e-mail: jianwang@ mail.sc.cninfo.net)
The continental volcanic rocks and volcaniclas-tic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that over-lie with high-angle unconformity the flysch turbidites of the Lengjiaxi Group in the Upper Mesoproterozoic Eonothem. SHRIMP zircon U-Pb dating gives a weighted mean age of 814 12 Ma for the dacitic volcanic agglomerates from the lowest part of the volcanic rocks in the Cangshuipu Forma-tion. This age is younger than previously reported values of 921—933 Ma for the volcanic rocks from the Cangshuipu Formation. Our new dating represents the lower boundary age of the Neoproterozoic System in the studied area. The younger age for the Cangshuipu volcanic rocks is supported by the following observations: (1) Lower Neoproterozoic strata (814—1000 Ma) are missing in the studied area; (2) the Nanhua rift system was initiated at about 820 Ma; and (3) an age of ~820 Ma may be taken as the lower boundary tim-ing of the Nanhua System (even Neoproterozoic) in South China.
【CateGory Index】： P597