Neoarchean (2.5–2.8 Ga) crustal growth of the North China Craton revealed by zircon Hf isotope: A synthesis

The crustal growth of the North China Craton (NCC) during the Neoarchean time (2.5–2.8 Ga) is a hotly controversial topic, with some proposing that the main crustal growth occurred in the late Neoarchean (2.5–2.6 Ga), in agreement with the time of the magmatism, whereas others suggest that the main crustal accretion took place during early Neoarchean time (2.7–2.8 Ga), consistent with the time of crustal-formation of other cratons in the world. Zircon U-Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC. In this contribution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U-Pb geochronology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC. The results suggest that both 2.7–2.8 Ga and 2.5–2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested. The Eastern block is characterized by the main 2.7–2.8 Ga crustal growth with local new crustal-formation at 2.5–2.6 Ga, and the Yinshan block is characterized by ∼2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group. Detrital zircon data of the Khondalite Belt indicate that the main crustal growth period of the Western block is Paleoproterozoic involving some ∼2.6 Ga and minor Early- to Middle-Archean crustal components, and the crustal accretion in the Trans-North China Orogen (TNCO) has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy. Zircon Hf isotope compositions, coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO, and the evolution and tectonic division of the NCC is more complex than previously proposed, probably involving multi-stage crustal growth and subduction processes. However, there is no doubt that 2.7–2.8 Ga magmatism and crustal-formation are more widely distributed than previously considered, which is further supported by the data of zircons from Precambrian lower crustal rocks, overlying sedimentary cover, modern river sediments and Late Neoarchean syenogranites.