SHRIMP U-Pb zircon dating of clastic sedimentary rocks of the Guandu Group, Zanhuang Complex, Hebei Province, and its geological significance

The Neoarchean-Paleoproterozoic supercrustal rocks as well as the Guandu Group from Zanhuang Complex have been widely reported in the whole North China Craton. The formation age and the environment of the Guandu Group are still controversial. Zircon SHRIMP U-Pb data of clastic sedimentary rocks of the Guandu Group, combined with previously available detrital zircon data, reveal that the majority of detrital ages are at~2.5Ga, with 2.0~2.2Ga peak for some samples. At least two metamorphic events were recorded, i.e., ~2.48Ga and 1.85~1.9Ga. Based on data obtained in this study as well as other studies of the Zanhuang Complex in recent years, some conclusions can be drawn as follows:① The well-preserved elongate prismatic morphology of some zircons implies that the source of depositional materials was not far away; ② The~2.48Ga metamorphic record is so close to the crystallization age of inner cores of zircons (~2.5Ga), probably suggests the existence of metamorphism that happened soon after the formation of the igneous rocks before the deposition of Guandu Group rocks, i.e., the deposition happened after~2.48Ga; ③ At least part of the Guandu Group was formed in Paleoproterozoic instead of late Archean; ④ The Guandu Group was probably not a continuous stratigraphic unit, but was composed of lithological units formed in different epochs and environments, and it thus should be disintegrated.