摘要
道县辉长岩包体的平衡深度为 1 9.2km ,来源于中下地壳。从块状辉长岩中选出锆石进行U Pb同位素测定 ,由四组锆石构成的不一致线产生的上交点年龄为 ( 787±30 )Ma,代表辉长质岩浆侵入的时代 ;下交点 2 98Ma±2 7Ma则是辉长岩的变质年龄 ,反映在海西期该区在下地壳范围内曾发生了变质作用 ,可能是区域构造热扰动的结果 ;另有一组锆石位于不一致线以外 ,其2 0 7Pb/ 2 0 6Pb表面年龄为 1 385Ma,应为岩浆上升过程中捕获的中元古代古壳残留的锆石。
Many middle to lower crustal gabbro xenoliths were entrained by volcano basalts in Daoxian County of Hunan Province. From individual samples ,three kinds of zircon crystals are distinguished, and their U-Pb isotope ages have been determined. The interception of the cordia and discordia gave ages of 787±30 Ma and 298±27 Ma. The two ages display two geological events, the former is the age of gabbroic magma formation and the latter age may display the metamorphic age of the lower crust. Another zircon age 1 385 Ma is far away from the cordia line. It may be of no geological significance, only showing the loss of Pb. From the result of Pb isotope dating, we can see that the Late Proterozoic mantle-derived basic magma had underplated to the lower crust, and crystallized as gabbro xenoliths, and the rocks underwent later metamorphism at 298±27 Ma .
出处
《矿物学报》
CAS
CSCD
北大核心
2002年第4期350-352,共3页
Acta Mineralogica Sinica
基金
国家自然科学基金 (批准号 :40 0 0 2 0 18)
原地质矿产部华南项目 ( 95 0 110 9)
中南工业大学青年科学基金
