Stratigraphy and Zircon Provenance of a Late Paleoproterozoic Terrestrial Sequence underlying the Xiong'er Volcanics in the Southern North China Craton

The late Paleoproterozoic Dagushi Formation comprises a fluvial-lacustrine succession and represents the initial fill of the Xiong'er Basin in the southern North China Craton.Employing integrated outcrop surveys and detrital zircon UPb-Hf dating,this study examines the provenance and depositional setting of the Dagushi Formation.Five major depositional facies,including braided channel,distributary channel,subaqueous stream/mouth bar,pro-delta and shallow lake,were identified,based on lithofacies and associations.They were interpreted as representing a braided river deltalacustrine system.The ages of the last metamorphic event of the basement,covering volcanics and the youngest zircon together constrain a depositional age of ca.1.79 Ga for the Dagushi Formation.Zircon age distributions reveal a provenance change from ca.2.7–2.5 Ga rocks in the lower part,to ca.2.3–1.9 Ga sources in the middle-upper part of the Dagushi Formation.Considering the vertical sedimentology,this provenance change could be induced by the rising water-level caused by a tectonic subsidence.The ca.2.7–2.5 Ga zircons are suggested to be locally sourced from the late Neoarchean–Paleoproterozoic metamorphic basement.The northeast Zhongtiao Mts area(current co-ordinates)is supposed to have appeared as a paleo-uplift and served as a source area for the Paleoproterozoic grains.The Dagushi Formation records an early‘underfilled'stage of the Xiong'er Rift.