Anatomy of Zircons from an Ultrahot Orogen: The Amalgamation of the North China Craton within the Supercontinent Columbia

We report SHRIMP U-Pb, rare earth element, Hf isotope, and laser Raman spectroscopic data on zircons from ultrahigh-temperature (UHT) granulites from the Jining Complex of the Khondalite Belt in the Western Block of the North China Craton (NCC). These UHT rocks form part of an ultrahot orogen that formed along the collisional margin of the NCC associated with the tectonics of assembly of the Paleoproterozoic supercontinent Columbia. Despite the core-rim textures displayed by some of the UHT zircons, their age values sharply converge within error, yielding weighted mean Pb-207/Pb-206 ages of ca. 1.92 Ga, indicating growth by recrystallization under extreme thermal conditions. In general, the zircons show moderate heavy rare earth element enrichment with sharp positive Ce and negative Eu anomalies. The Hf isotope data from the UHT zircons also display a fairly uniform character, with the majority of them characterized by positive epsilon(Hf) values, without any indication of mixing between reworked crust and juvenile material. The majority of mineral inclusions in the UHT zircons, as revealed by laser Raman study, also support a magmatic source. Our results confirm extreme crustal metamorphism in the NCC and suggest asthenospheric up-welling, magmatic underplating, and plume activity in response to the collision-extension events during the final assembly of the Paleoproterozoic supercontinent Columbia.