Constraint from LA-MC-ICP-MS zircon U-Pb dating of mafic dyke swarms in Miyun County of Beijing and its geological implications

Archaean ultrabasic dyke swarms in Miyun District of Beijing are widely distributed and chronological researches on these swarms have attracted much attention and obtained many data. Nevertheless, the control of Archean metamorphic gneiss has been rarely discussed. In this study, U-Pb LA-MC-ICP-MS technology was used to obtain the age of 2497±15Ma. This shows that the diagenetic age of the metamorphic gneiss should be earlier than that of the mafic dyke swarms. The result obtained by the authors provides important reference data for the formation age of Archean gneiss in the study area.