The Hf isotopic data show the 鈭?.5 Ga magmatic zircons have variable 蓻Hf(t) values, including both positive and negative values and with crustal model ages of 2.7-2.9 Ga, which can be interpreted to indicate mixed sources for their parental rocks, i.e., ancient crust (3.8 Ga or 3.3 Ga) and depleted mantle, implying significant continental crustal growth at 鈭?.5 Ga. However, Paleoproterozoic magmatic zircons all have negative 蓻Hf(t) and Archean Hf model ages, suggesting that their parental rocks were formed from recycled Archean materials.
The widespread 鈭?.5 Ga metamorphism in the Eastern Block, coupled with extensive 鈭?.5 Ga magmatism and crustal growth, are consistent with a mantle plume beneath the Eastern Block of the NCC during the Neoarchean. Whereas, a progressive increase in 鈭?.85 Ga metamorphic zircon westward across the Eastern Block toward the Trans-North China orogen is best explained by collision between the Eastern and Western blocks at this time.