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.
The Jinniu Basin in southeast Hubei, located at the westernmost part of middle-lower valley of the Yangtze River, is one of the important vol- canic 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.
基金
Acknowledgements The authors would like to thank Southeast Hubei Geological Party and No.4 Geological Party of Hubei Province, and Hubei Geological Survey Institution for help during the field investigation. Chen Fukun, Li Sunrong, Feng Jiayi, Hu Jing, Qiu Yi, Tao Hua and Chen Zhenyu are thanked for their assistance during major and trace element and Sr-Nd isotope and SHRIMP analyses. Comments and discussion given by Wan Yusheng, Li Jianwei and Yang Zhusen were very helpful in improving and clarifying the manuscript. Two anonymous reviewers have provided detailed suggestions, critical comments, which led to considerable improvement and modification of this manuscript. This work was jointly supported by the National Natural Science Foundation of China （Grant Nos. 40434011 and 40402011）, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences （Grant Nos.GPM40504）, State Key Laboratory of 0re Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences （Grant Nos. 200402）, the Chinese Geological Survey Bureau （Grant Nos. 20031020081） and Postdoctoral Science Foundation.
