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.

Late Paleoproterozoic Paleogeography of Baltica and Laurentia: New Paleomagnetic Data from 1.80–1.75 Ga Mafic Intrusions of Fennoscandia and Sarmatia

Tectonic evolution and paleogeography of the two major continental blocks Fennoscandia and VolgoSarmatia during their docking to form the East European Craton(Baltica)at 1.8–1.7 Ga represent important‘puzzle

Tectonothermal Records in Migmatite-Like Rocks of the Guandi Complex in Zhoukoudian, Beijing: Implications for Late Neoarchean to Proterozoic Tectonics of the North China Craton

Migmatite-like rocks transformed from strongly metamorphosed and deformed enclave- bearing felsic plutons usually make people confuse with the true migmatites and mistake in interpreta- tion of their petrogenesis and tectonic implications. Here we report a suite of rocks that have long been called as migmatites from the Guandi complex in Zhoukoudian region, southwest of Beijing. The rocks are dominated by felsic gneisses with garnet-free amphibolites. Field occurrence, petrography and geochemistry indicate that the felsic gneisses and amphibolites were metamorphosed from protoliths of intermediate-acid and basic igneous rocks, respectively. New LA-ICP-MS zircon U-Pb dating and geothermobarometry study further reveal that precursor magmas of the two types of rocks were emplaced at 2.54-2.56 Ga and the rocks subsequently underwent medium P/T-type metamorphism with upper amphibolite facies conditions of 0.55-0.90 GPa and 670-730℃ at -2.48-2.50 Ga. Geochemically, precursor magmas of the amphibolites were suggested to be derived from an enriched lithospheric mantle source in continental arc setting, and those of the felsic gneisses are characterized by tonalitic to trondhjemitic magmas that are usually considered to be generated by partial melting of hydrated, thickened metamorphosed mafic crust with garnet as residues, suggesting that the rock associations are not of true migmatites but migmatite-like rocks. Our study reveal that protoliths of the migmatite-like rocks from the Guandi complex, were likely formed via magmatism in a continental arc setting, followed by accretion and collision of the continental arc as well as the intro-oceanic arc terranes to the Eastern Block of the North China Craton in the transition from the Late Neoarchean to Early Paleoprnterozuic.