Abstract

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Title:: SHRIMP U-Pb Ages of Zircons from Banded Magnetite Quartzite of Shachang Formation in Miyun Area of Beijing and Their Significance

Author(s):: SHI Zhi-qiang; SHI Yu-ruo; 1. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;2. Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

Keywords:: banded iron formation; U-Pb age; zircon; Precambrian; metamorphic event; formation age; North China Craton

Abstract:: 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 (2 464±18)-(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.