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大别山北缘中生代火山 -侵入岩的 14个全岩铅同位素组成表现为高的非放射性成因2 0 4 Pb ,较低的2 0 6 Pb/ 2 0 4 Pb比值和低且相对一致的2 0 7Pb/ 2 0 4 Pb比值 ,属于明显的低U/Pb体系 ,并暗示它们是由具低 μ值的源岩衍生的。同时其2 0 8Pb/ 2 0 4 Pb比值变化较大 ,显示源区具有不均一的Th/Pb比值。与区域铅同位素组成的比较研究表明 ,它们在很大程度上与大别 -胶南亚省中大别地块中生代花岗岩长石铅同位素组成相似 ,总体上具有华北板块的铅同位素特征。从岩石系列的角度来看 ,橄榄安粗岩系列岩石具有最高的2 0 4 Pb含量和最低的铅同位素比值 ,碱性系列岩石具有最低的2 0 4 Pb含量和最高的铅同位素比值 ,而高钾钙碱性系列岩石则介于两者之间 ,表明不同系列岩石的源区在形成时代和性质 (或成熟度 )上具有较明显的区别。河南商城的玄武安山岩具有低的2 0 4 Pb含量和偏高的2 0 8Pb/ 2 0 4 Pb比值 ,说明其源区具有明显富Th的特征。
The 14 Pb isotopic composition of the whole rock in the Mesozoic volcanic-intrusive rocks in the northern margin of the Dabie Mountains is characterized by a high non-radiogenic 204 Pb, a low 206 Pb / 204 Pb ratio and a low and relatively consistent 207 PCB / 2 0 4 Pb ratios, which are clearly low U / Pb systems and suggest that they are derived from source rocks with low μ values. At the same time, the 208Pb / 204B ratio changes greatly, which shows that the source region has a non-uniform Th / Pb ratio. Comparative studies with regional Pb isotopic composition indicate that they are largely similar to the Pb isotopic composition of the feldspar of the Mesozoic granites in the Dabie-Jiaonan area in the Dabie-Jiaonan Province and generally have the Pb isotopic characteristics of the North China plate. From the point of view of the series of rocks, the olivanam rock has the highest content of Pb2O4 and the lowest Pb isotopic ratio. The alkaline series rocks have the lowest content of 204 Pb and the highest Pb isotopic ratio, while the high K-Ca-Alkaline series rocks are in between, suggesting that the source regions of different series of rocks have obvious differences in formation age and property (or maturity). The basaltic andesite in Henan Shangcheng City has a low content of 204 Pb and a high 208Pb / 204B ratio, indicating that the source area has a significantly Th richness.