Zircon SHRIMP U-Pb dating for the Cangshuipu volvanic rocks and its implications for the lower boundary age of the Nanhua strata in South China
Abstract 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 Dabie Orogen as the early Jurassic sedimentray provenanceConstraints from the detrital zircon SHRIMP U-Pb dating
Abstract The SHRIMP U-Pb ages of detrital zircon from the oldest Mesozoic strata, the Fanghushan Fomation, in the Hefei Basin range from 200 Ma to ca. 2500 Ma, which indicates that the Dabie Orogen as the early Jurassic sedimentary provenance was complex. The composition of the Dabie Orogen includes: the Triassic high pressure-ultrahigh pressure metamorphic rocks, of which the detrital zircon ages are from 234 Ma to 200 Ma; the rocks possibly related to the Qinling and Erlangping Groups representing the southern margin of the Sino-Korean craton in the Qinling and Dabie area, of which the detrital zircon has an age of 481±378 Ma; the Neoproterozoic rocks originated from the Yangtze croton, of which the detrital zircon ages are 799±721 Ma old; and the rocks with the detrital zircon ages of ca. 2000 Ma and ca. 2500 Ma, which could be the old basement of the Yangtze craton.
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