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SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications
摘    要:The Jinniu Basin in southeast Hubei,located at the westernmost part of middle-lower val-ley of the Yangtze River,is one of the important vol-canic basins in East China. Volcanic rocks in the Jin-niu Basin are distributed mainly in the Majiashan Formation,the Lingxiang Formation and the Dasi Formation,consisting of rhyolite,basalt and basaltic andesite,(trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively,in which the Dasi volcanism is volumet-rically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indi-cate that there exist a large amount of magmatic zir-cons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128 ± 1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios,this age is considered to represent the crystallization time of the Dasi volcan-ism. The volcanic rocks in the Dasi,Majiashan and Lingxiang Formations share similar trace elementand REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geol-ogy,it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Creta-ceous,just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also sug-gested for tectonic regime in this region in the Cre-taceous Period.

关 键 词:火山岩  SHRIMP锆石U-Pb测年  湖北东南部  地质构造  年代学  长江中下游地区
收稿时间:2006-01-04
修稿时间:2006-04-28

SHRIMP zircon U-Pb dating for volcanic rocks of the Dasi Formation in southeast Hubei Province, middle-lower reaches of the Yangtze River and its implications
Authors:Guiqing Xie  Jingwen Mao  Ruiling Li  Shaodong Zhou  Huishou Ye  Quanren Yan  Zusong Zhang
Institution:(1) State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, 100083, China;(2) Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China;(3) Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China;(4) No. 4 Geological Party of Hubei Province, Xianning, 437100, China;(5) Institute of Geology, Chinese Academy of Geosciences, Beijing, 100037, China;(6) Southeast Hubei Geological Party of Hubei Province, Daye, 435100, China
Abstract:The Jinniu Basin in southeast Hubei, located at the westernmost part of middle-lower valley of the Yangtze River, is one of the important volcanic basins in East China. Volcanic rocks in the Jinniu Basin are distributed mainly in the Majiashan Formation, the Lingxiang Formation and the Dasi Formation, consisting of rhyolite, basalt and basaltic andesite, (trachy)-basalt and basaltic trachy-andesite and (trachy)-andesite and (trachy)-dacite and rhyolite respectively, in which the Dasi volcanism is volumetrically dominant and widespread. The Dasi volcanic rocks were selected for SHRIMP zircon U-Pb dating to confirm the timing of volcanism. The results indicate that there exist a large amount of magmatic zircons characterized by high U and Th contents in the volcanic rocks. The concordia ages for 13 points are 128 ± 1Ma (MSWD = 3.0). On account of the shape of zircons and Th/U ratios, this age is considered to represent the crystallization time of the Dasi volcanism. The volcanic rocks in the Dasi, Majiashan and Lingxiang Formations share similar trace element and REE partition patterns as well as Sr-Nd isotopic compositions. In combination with the regional geology, it is proposed that the southeast Hubei volcanic rocks were formed mainly during the Early Cretaceous, just like other volcanic basins in middle-lower Yangtze valley. A lithospheric extension is also suggested for tectonic regime in this region in the Cretaceous Period.
Keywords:zircon SHRIMP dating  Dasi Formation volcanic rocks  Jinniu Basin  Yangtze River  
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