摘要
怀宁盆地是长江中下游地区晚中生代发育的一系列断陷型火山岩盆地中的一个,盆地内的火山岩主体以高钾和相对富碱为特征,属典型的橄榄玄粗岩系列。但晚期出现玄武质—流纹质双峰式火山岩组合。盆地内的火山岩均表现出明显富集Rb、Th、U、K等强不相容元素和轻稀土元素,亏损高场强元素Nb和Ta的地球化学特征。本文分别测得怀宁盆地早期彭家口组粗安岩的SHRIMP和LA–ICP–MS锆石U–Pb年龄分别为(129.4±1.6)Ma和(131.6±0.6)Ma,晚期江镇组双峰式火山岩的酸性端元——流纹岩的LA–ICP–MS锆石U–Pb年龄为(122.3±0.7)Ma。区域对比表明,怀宁盆地内火山作用的时间总体与庐枞盆地等长江中下游地区其他火山岩盆地中岩浆活动的时代类似,但火山活动结束的时间要晚于其他盆地约6 Ma。怀宁盆地内的火山岩与长江中下游地区其他橄榄玄粗岩系列火山岩盆地相比具有更宽广的εNd(t)值变化范围和相对更低的εNd(t)值,这与其所处的构造位置紧邻大别造山带,有更多地壳物质的参与有关,显示怀宁火山岩盆地内的岩浆主要来自富集型地幔的部分熔融,但不同程度地混染了古老的下地壳物质。
The volcanic rocks in Huaining basin, one of a series of late Mesozoic volcanic basins developed in the Middle-lower Yangtze region, are characterized by high K and rich alkali and mainly belong to typical shoshonitic series. However, bimodal volcanic association appeared at the late stage of volcanism in Huaining basin. The volcanic rocks in the basin are all depleted in high-field-strong-elements （HFSE） such as Nb and Ta, and enriched in strong incompatible elements such as Rb, Th, U and K as well as light rare earth elements （LREE）. In this study, the authors used SHRIMP and LA-ICP-MS zircon U-Pb technique to date the samples from Pengjiakou Formation and early volcanism respectively in Huaining basin, and obtained emplacement ages of 129.4±1.6 Ma and 131.6±0.6 Ma respectively. The age of 122.3±0.7 Ma was also obtained by LA-ICP-MS zircon U-Pb technique for rhyolite from J on a comparison with other volcanic basins of volcanism in Huaining basin are similar iangzhen Formation, which is late volcanism in Huaining basin. Based in the Middle-lower Yangtze region, the authors found that the ages to those of such other volcanic basins in the Middle-lower Yangtze region as Luzong basin and Ningwu basin; nevertheless, the end of volcanism in Huaining basin occurred about 6 Ma later than other volcanic basins. The volcanic rocks in Huaining basin have wider variation range and lower εNd（t） values than other shoshonite volcanic basins in the Middle-lower Yangtze region, which may be related to the fact that their tectonic setting was near the Dabie orogen, and hence more crust materials were added to the magma. The proto magma of Huaining volcanic basin mainly came from partial melting of the enriched mantle, with different degrees of mixture of lower crust materials during the magmatic evolution.
出处
《中国地质》
CAS
CSCD
北大核心
2013年第3期694-714,共21页
Geology in China
基金
深部探测技术与实验研究专项(SinoProbe-05-05)
中国地质调查局地质调查项目(1212010711814)
地质矿产调查评价专项(1212011121116)共同资助
