摘要
通过对北京密云地区沙厂铁矿条带状磁铁石英岩进行SHRIMP锆石U-Pb定年研究,主要获得两组锆石U-Pb年龄,分别为(1 806±13)、(2 464±18)Ma。结合其岩相学、阴极发光图像分析,这些锆石为变质成因锆石,因此,这两组年龄应代表条带状磁铁石英岩的两期变质作用时代,这与前人认为的华北克拉通东部陆块前寒武纪两期变质事件时间(约2.44Ga和约1.82Ga)相吻合。另外,在条带状磁铁石英岩中还发现了一颗年龄为(2 517±12)Ma的浑圆状锆石,代表了该磁铁石英岩中碎屑锆石的年龄,从而间接限定了该区条带状铁建造的形成时代为(2 464±18)^(2 517±12)Ma。结合前人研究资料,其可能形成于新太古代晚期。这些成果为该区乃至整个华北地区前寒武纪BIF型铁矿以及晚太古代至古元古代的构造演化提供了进一步详实的年代学资料。
SHRIMP zircon U-Pb ages for the banded magnetite quartzite from Shachang iron deposit in Miyun area of Beijing were reported. Zircon U-Pb ages of the magnetite quartzite are （1 806 ±13） Ma and （2 464 ± 18） Ma, respectively. Based on the CL images of zircons, together with the petrography of rocks, the ages should represent two stages of metamorphism of the banded magnetic quartzite, which are similar with the time of two large-scale metamorphic events （namely -2.44 Ga and -1.82 Ga） in the eastern block of North China Craton. Fortunately, a round zircon with the age of （2 517±12）Ma is found, representing the age of detrital zircon from the magnetite quartzite. It also indirectly constrains that the banded iron formation is formed at （2 46±418）-（2 517±12）Ma, most likely at the end of Neoarchean by combining previous data. The results also provide further detailed information for the study of Late Archean- Paleoproterozoic tectonic evolution and Precambrian BIF-type iron deposits in North China.
出处
《地球科学与环境学报》
CAS
2016年第4期547-557,共11页
Journal of Earth Sciences and Environment
基金
国土资源部公益性行业科研专项项目(201311116)
中国地质科学院地质研究所基本科研业务费项目(J1403)
