Palaeoproterozoic episodic magmatism and high-grade metamorphism in the North China Craton: Evidence from SHRIMP zircon dating of magmatic suites in the Daqingshan area

摘要

The Daqingshan area in the North China Craton (NCC) incorporates several suites of magmatic intrusives including gabbros, granodiorites, charnockites and syenogranites, which were overprinted by subsequent metamorphic events. In this study, we report detailed morphological and textural characteristics as well as sensitive high resolution ion microprobe (SHRIMP) U-Pb ages of zircons from ten representative samples of the magmatic suites including syenogranites, charnockites and granodiorites. The zircons in these rocks are characterized by typical magmatic crystallization features including elongate prismatic grains with angular to sub-angular faces which are overprinted by a variety of reworked textures indicating strong recrystallization. These structures are terminated by thin and variable metamorphic overgrowths. U-Pb analyses of the zircons reveal multiple tectono-thermal events including magmatic crystallization at 2.30-2.00, 1.96-1.94 and 1.85-1.82Ga and metamorphic overprint at 1.97-1.94 and 1.87-1.82Ga. The episodic magmatism and regional metamorphism recorded in our study show a complex sequence of tectonic processes during the early to late Palaeoproterozoic associated with the amalgamation of crustal blocks within the NCC, with the youngest episode of the syenogranites representing regional extension at the end of the final cratonization of the NCC.