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鄂东南地区金牛盆地是长江中下游地区最西部的一个重要火山岩盆地.金牛盆地火山岩分布于马家山组、灵乡组和大寺组,岩性主要分别为流纹岩、玄武岩和玄武质安山岩及(粗面)玄武岩、玄武质粗面安山岩、(粗面)安山岩、(粗面)英安岩和流纹岩,其中大寺组火山岩是分布范围最广和规模最大的.选择大寺组火山岩为研究对象,应用SHRIMP锆石微区U-Pb测年技术对大寺组英安岩进行了精确测年,结果表明:火山岩存在大量的岩浆成因锆石,以高U和Th含量为特征,13个点SHRIMP谐和年龄为(128±1)Ma(MSWD=3.0).根据锆石形态和高的Th/U值,该年龄代表了火山岩的结晶年龄.马架山组、灵乡组与大寺组具有相似的富集大离子亲石元素和轻稀土特征,其同位素(87Sr/86Sr)i和(143Nd/144Nd)i分别为0.7063~0.7070,0.7065,0.7066~0.7072和0.5121~0.5123,0.5121,0.5121~0.5122.结合区域资料分析表明:鄂东南盆地火山岩主体形成于早白垩世,与长江中下游地区其他火山岩盆地形成时代类似,白垩纪长江中下游地区处于伸展构造背景.
The Jinniu Basin in southeastern Hubei is an important volcanic basin in the western part of the middle and lower reaches of the Yangtze River. The volcanic rocks in the Jinniu Basin are distributed in the Majiashan Formation, the Lingxiang Formation and the Dasi Formation. The lithologies are mainly rhyolite, basalts and basaltic andesite and ( Basaltic basalts, basaltic anorthosites, (rough) andesite, (rough surface) dacite and rhyolite, and the volcanic rocks in the Tiesi Formation are the most widely distributed and the largest in scale. , SHRIMP zircon U-Pb zircon dating was used to conduct an exact dating of the Dasidian dacite. The results show that there are a large number of magmatic zircons in the volcanic rocks, characterized by high U and Th content, 13 SHRIMP The harmonic age is (128 ± 1) Ma (MSWD = 3.0). According to the zircon morphology and high Th / U value, this age represents the crystallization age of volcanic rocks. (87Sr / 86Sr) i and (143Nd / 144Nd) i are 0.7063 ~ 0.7070,0.7065,0.7066 ~ 0.7072 and 0.5121 ~ 0.5123,0.5121,0.5121 ~ 0.5122, respectively, which are rich in large ion lithophile and light rare earth. The analysis of regional data shows that the main body of volcanic rocks in southeastern Hubei basin Formed in the Early Cretaceous and similar to the age of other volcanic basins in the middle and lower reaches of the Yangtze River. The Cretaceous middle and lower reaches of the Yangtze River are in an extensional tectonic setting.