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  

作　　者：WANGJian LIXianhua DUANTaizhong LIUDunyi SONGBiao LIZhongxiong GAOYonghua 

机构地区：[1]ChengduInstituteofGeologyandMineralResources,ChinaGeologicalSurvey,Chengdu610082,China [2]GuangzhouInstituteofGeochemistry,ChineseAcademyofSciences,Guangzhou510640,China [3]ColoradoSchoolofMines,Golden,CO80401-1887.USA(Presentaddress:MarathonOilCompany,Houston,TX77056-2725,USA) [4]InstituteofGeology,ChineseAcademyofGeologicalSciences,Beijing100037,China [5]GraduateSchooloftheChineseAcademyofGeologicalSciences,Beijing100037,China

出　　处：《Chinese Science Bulletin》2003年第16期1663-1669,共7页

基　　金：supported both by the National Natural Science Foundation of China(Grand Nos.40032010-B.40072083 and 49972046);“100 Young Geologists”grant from both Chinese Ministry of Geology and Minera1 Resources and Sichuan Province

摘　　要：The continental volcanic rocks and volcaniclastic sedimentary conglomerates of the Cangshuipu Formation occur well in Yiyang of Hunan Province, consisting of a wedge-shaped succession of Neoproterozoic strata that overlie 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 Formation. 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 timing of the Nanhua System (even Neoproterozoic) in South China.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.

关 键 词：地质年代 锆 年代测定 火山岩 中国 湖南 楔形 原生代 复理层 元古代 

分 类 号：P534[天文地球—古生物学与地层学] P588.14[天文地球—地质学]