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
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
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DOI：
10.1360/03wd0168
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发表时间：
2003-08
影响因子：
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通讯作者：
Jian Wang;Xian‐Hua Li;T. Duan;Dunyi Liu;B. Song;Zhongxiong Li;Yonghua Gao
中科院分区：
文献类型：
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作者：
Jian Wang;Xian‐Hua Li;T. Duan;Dunyi Liu;B. Song;Zhongxiong Li;Yonghua Gao
湖南益阳地区广泛产出的沧水铺组陆相火山岩和火山碎屑沉积砾岩，是一套以高角度不整合面覆盖于上中元古代冷家溪群复理石浊积岩之上的新元古代楔形地层。沧水铺组火山岩底部英安质火山团块的SHRIMP锆石U-Pb年龄为814 ±12 Ma。这一年龄比以前报道的沧水铺组火山岩的年龄值921-933 Ma要小。新的测年结果代表了本区新元古代的下限年龄。沧水铺火山岩年龄较年轻的观点得到以下几点的支持：（1）研究区缺少新元古代早期地层（814-1000 Ma）;（2）南华裂谷系形成于820 Ma左右;（3）华南南华系（甚至新元古代）的下限年龄可定为820 Ma左右。
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.