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 ove...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.展开更多
The debate of assembly time between the Yangtze and Cathaysia blocks has aroused the disputation on the formation mechanism of Jiangnan orogen, South China. Therefore widespread magmatism of 830-750 Ma in South China ...The debate of assembly time between the Yangtze and Cathaysia blocks has aroused the disputation on the formation mechanism of Jiangnan orogen, South China. Therefore widespread magmatism of 830-750 Ma in South China is interpreted as the product of either plume or arc magmatism, which results in distinctive depositional background in the Neoproterozoic. Granite gravel located at the unconformity between the Banxi Group and Fanjingshan Group of the western Jiangnan orogen was collected, which gave a new age limit to the deposition of the Banxi Group and Nanhu rift. Zircons from the granite gravel crystallized yield a weighted mean 2~6pb/238U age of 789~11 Ma, which probably represents the end of the Jiangnan orogeny and marks the onset of Nanhua rift. These zircons have negative εHf（t） of -2.1 to -6.0, with TDM of 1.38-1.52 Ga and Tcrust of 1.81-1.98 Ga indicating an old continental crust origin for the granite.展开更多
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
文摘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.
基金supported by the SinoProbe-Deep Exploration in China (No. SinoProbe-08-01)the National Natural Science Foundation of China (No. 41202154)the China Geological Survey (Nos. 1212011120184, 1212011220261)
文摘The debate of assembly time between the Yangtze and Cathaysia blocks has aroused the disputation on the formation mechanism of Jiangnan orogen, South China. Therefore widespread magmatism of 830-750 Ma in South China is interpreted as the product of either plume or arc magmatism, which results in distinctive depositional background in the Neoproterozoic. Granite gravel located at the unconformity between the Banxi Group and Fanjingshan Group of the western Jiangnan orogen was collected, which gave a new age limit to the deposition of the Banxi Group and Nanhu rift. Zircons from the granite gravel crystallized yield a weighted mean 2~6pb/238U age of 789~11 Ma, which probably represents the end of the Jiangnan orogeny and marks the onset of Nanhua rift. These zircons have negative εHf（t） of -2.1 to -6.0, with TDM of 1.38-1.52 Ga and Tcrust of 1.81-1.98 Ga indicating an old continental crust origin for the granite.
