Remnants of ≥3800 Ma crust in the Chinese part of the Sino-Korean craton

Ion microprobe U-Pb analyses of zircons from the Sino-Korean craton have identified remnants of ≥3800 Ma crust at two localities—near Caozhuang east of Beijing, and near Anshan, northeast China. Near Caozhuang, the detrital zircons in an Archean metaquartzite are 3550 Ma or older; about one-fourth have ages between 3800 and 3850 Ma. The ages for detrital zircons with concordant U-Pb ages form a polymodal distribution, interpreted to show that the detritus that formed the quartzite was derived from a terrane containing early Archean rocks of several ages. Near Anshan, sheared gneiss is present in a complex containing ca. 3300 and 3000 Ma granites. Some of the zircons in this gneiss are concordant with a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 3804 ±5 Ma (2 σ), interpreted to be the age of the protolith of the gneiss.