长江中下游地区怀宁盆地火山岩锆石LA-ICPMS定年.docVIP

 长江中下游地区怀宁盆地火山岩锆石 LA-ICPMS 定年# * 5 10  摘要：怀宁盆地为长江中下游地区众多中生代火山岩盆地之一，自下而上发育彭家口组和江镇组火山岩， 岩性分别以安山质凝灰熔岩和玄武粗安岩为主。运用 LA-ICPMS 对彭家口组和江镇组火山岩进行了锆石 U-Pb 定年，获得了 206Pb/204Pb 加权平均谐和年龄分别为 130.0±1.7 Ma（MSWD=0.73）和 130.5±1.7 Ma （MSWD=0.78），指示怀宁盆地火山岩为早白垩纪的产物，喷发持续时间较短。该年龄和长江中下游地区 其他盆地火山岩的年龄一致，表明长江中下游地区中生代火山岩的喷发时代集中在 135—127 Ma 之间，是 在强烈拉张的背景下，岩石圈地幔部分熔融的产物。 关键词：火山岩；锆石 U-Pb；定年；怀宁盆地；长江中下游 中图分类号：P597+3 15 Zircon LA-ICPMS Dating of the Volcanic Rocks from Huaining Basin in the Middle and Lower Yangtze Valley 20 25 30 35 40 SHI Lei, YAN Jun, LI Quanzhong, LIU Jianmin, LIU Xiaoqiang, JIANG Zizhao (School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009) Abstract: Huaining basin is one of the many Mesozoic volcanic basins in the Middle and Lower Yangtze Valley, where from the bottom to up the volcanic rocks of Pengjiakou and Jiangzhen formations distributed. The rock types are dominantly andesitic tufflava and basaltic trachyandesit. Zircon LA-ICPMS U-Pb isotopic dating on the volcanic rocks from Pengjiakou and Jiangzhen formations gives weighted mean 206Pb/204Pb ages of 130.0±1.7 Ma (MSWD=0.73) and 130.5±1.7 Ma (MSWD=0.78), respectively. Indicating they erupted in the early Cretaceous and a briefly active duration. The ages of volcanic rocks in Huaining basin are consistent with that of other basin distributed in the Middle and Lower Yangtze Valley, suggesting that erupted ages of the Mesozoic volcanic rocks in the Middle and Lower Yangtze Valley concentrated in a period of 135 to 127 Ma and the volcanic rocks were derived from partial melting of lithospheric mantle under a intense extended setting. Key words: volcanic rocks; zircon U-Pb; dating; Huaining basin; the Middle and Lower Yangtze Valley 0 引言 长江中下游地区中生代发育强烈的岩浆活动，其中包括多个陆相火山盆地，自西向东分 别是金牛、怀宁、庐枞、繁昌、宁芜、溧水和溧阳火山盆地。由于与大型铁矿成因密切相关， 宁芜和庐枞盆地火山岩的研究程度较高，关于年代学和岩石成因取得了大量的研究成果[1~7]。 同时，关于金牛、繁昌、溧阳和溧水盆地火山岩也有一定程度的研究[7~10]。由于怀宁盆地中 火山岩分布面积较小，且保留不完整，目前尚无有关研究成果的报道。为此，本此工作在详 细的野外地质的基础上，采集了怀宁盆地彭家口组和江镇组火山岩的代表性样