ABSTRACT

In this study, we performed U-Pb dating on 1295 zircon grains from 24 samples originating from the North China Craton (NCC); an additional 440 Lu-Hf isotopic analyses were conducted on select zircon grains. The U-Pb ages revealed that the strongest magmatic event in the NCC occurred ca. 2.5 Ga, and a subordinate magmatic event occurred ca. 1.8 Ga. The crustal model ages from Hf isotopic analyses showed that the best estimate for the age of the NCC mantle extraction is ca. 2.8-2.7 Ga, which is consistent with the age of global continental crusts. In recent years, numerous 2.7 Ga rocks have been identified within the NCC. A strong and widespread superimposed tectono-thermal event at ca. 2.5 Ga differentiates the NCC from many other worldwide cratons. However, the timing of the majority of NCC continental crust growth remains highly controversial. In this paper, a quantitative method was used to calculate a continental crust reworking rate. The results revealed that the lowest reworking rate in the NCC occurred at ca. 2.7 Ga and was below 13%. At 2.9 Ga, the reworking rate was 73%, suggesting that a strong intra-crustal magmatic event took place at that time. Combining the reworking rates and Hf isotopic model ages for each period, we concluded that approximately 25% and 23% of the continental crust volume in the NCC was formed at ca. 2.8 Ga and 2.7 Ga, respectively. Approximately 12% of the continental crust volume formed at 2.6 Ga, and only 6% of the continental crust formed at ca. 2.5 Ga. Even with a high reworking rate, 6% of the continental crust formed at 2.9 Ga. Therefore, the main continental crustal growth in the North China Craton occurred at ca. 2.8-2.7 Ga (48% continental crust).