U-Pb zircon ages and Hf isotopes of ∼2.5 Ga granitoids from the Yinshan Block, North China Craton: Implications for crustal growth

The North China Craton (NCC) is the oldest continental fragment in China. It contains magmatic rocks as old as 3.8 Ga, but is dominated by crustal components that formed in the Neoarchean, and also includes Paleoproterozoic rocks. The Neoarchean is an important time of crustal growth of the NCC, although many investigations of zircon U-Pb and Hf isotope between different domains have been made, its crustal formation ages and evolution history are still matters of debate. In order to constrain the crustal growth record of the NCC, we undertook a geochemical and geochronological study of granitoids in the Siziwangqi area of central Inner Mongolia, which lies in the craton's Yinshan Block, along its northern margin. The granitoids comprise a tonalite-trondhjemite-granodiorite (TTG) association and alkali feldspar granite. U-Pb zircon dating of the TTG association yielded crystallization ages of 2.52–2.49 Ga, whereas the alkali feldspar granites gave ages of 2.47–2.44 Ga. Hf isotope data, coupled with zircon ages for Siziwangqi granitoids indicate that the main phase of crustal growth in the studied area occurred in the late Neoarchean and involved ∼2.5 Ga crustal accretion and minor ∼3.0 Ga crustal components, and it probably occurred in arc setting. Integration of our U-Pb and Hf isotope data with regional data, indicate that the crustal growth of the NCC involved both 2.8–2.7 Ga and 2.6–2.5 Ga events.