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

摘要

We report SHRIMP U-Pb, rare earth element, Hf isotope, and laser Raman spectroscopic data on zircons fromultrahightemperature(UHT) granulites from the Jining Complex of the Khondalite Belt in the Western Block of the NorthChina Craton (NCC). These UHT rocks form part of an ultrahot orogen that formed along the collisional margin ofthe NCC associated with the tectonics of assembly of the Paleoproterozoic supercontinent Columbia. Despite thecore-rim textures displayed by some of the UHT zircons, their age values sharply converge within error, yieldingweighted mean 207Pb/206Pb 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 Euanomalies. The Hf isotope data from the UHT zircons also display a fairly uniform character, with the majority ofthem characterized by positive Hf values, without any indication of mixing between reworked crust and juvenilematerial. The majority of mineral inclusions in the UHT zircons, as revealed by laser Raman study, also support amagmatic source. Our results confirm extreme crustal metamorphism in the NCC and suggest asthenospheric upwelling,magmatic underplating, and plume activity in response to the collision-extension events during the finalassembly of the Paleoproterozoic supercontinent Columbia.