ABSTRACT

A swarm of quartzofeldspathic dykes extensively intruded the Permian-Triassic Yeongdeok pluton and xenoliths therein in southeastern Korea. Zircons from the dyke intruding a diorite xenolith yield sensitive high resolution ion microprobe ²⁰⁶Pb/²³⁸U dates ranging from Middle Permian (ca. 260 Ma) in the crystal cores to Late Cretaceous (ca. 82 Ma) in the outermost rim, with a negative correlation between U contents and dates. Such systematic variations can be explained by an initial mixing between inherited zircons from the host Permian diorite and overgrowth rims with various U/Pb ratios crystallized during intrusion of the dyke in the Cretaceous. This study shows that zircon U-Pb data from dyke rocks need to be treated with caution for geochronological interpretation.