Crustal growth and intracrustal recycling in the middle segment of the Trans-North China Orogen, North China Craton: a case study of the Fuping Complex

The most important crustal growth on Earth occurred at ∼ 2.7 Ga, but the North China Craton (NCC) is characterized by prevalent development of ∼ 2.5 Ga juvenile crust, with relatively rare records of ∼ 2.7 Ga crustal growth. The Fuping Complex in the middle segment of the Trans- North China Orogen (TNCO) between the Eastern andWestern blocks of the NCC is composed mainly of ∼ 2.5 Ga Fuping tonalitic-trondhjemitic-granodioritic (TTG) gneisses and Longquanguan augen gneisses, ∼ 2.1 Ga Nanying granitic gneisses and theWanzi supracrustal rocks. Previous studies have suggested one major phase of crustal growth at ∼ 2.5 Ga, possible intracrustal recycling at ∼ 2.1 Ga and the presence of older rocks in the Fuping Complex, but there has been no record of ∼ 2.7 Ga crustal growth. The Fuping TTG gneisses are dominated by stromatic migmatite, and new U-Pb dating of magmatic zircons from two stromatic migmatite samples yielded three different ages: (1) 2.75 Ga, which is the oldest age obtained from the Fuping TTG gneisses, (2) 2.54 Ga, which just falls in the published zircon U-Pb age range of 2.53 to 2.47 Ga for the Fuping TTG gneisses, and (3) 2.11 Ga, which is almost the same as the age of the Nanying granitic gneisses. Therefore, there are two generations of TTG gneisses in the Fuping Complex. Importantly, both of the 2.75 and 2.54 Ga zircons have the highest eHf(t) values, almost equal to the contemporaneous depleted mantle. This indicates high contributions of juvenile material to the two generations of TTG gneisses. In contrast, the 2.11 Ga zircons have apparently low eHf(t) values of -0.47 to +2.04, just falling in between 2.55 and 2.75 Ga continental crust values. This strongly suggests the reworking of the two generations of TTG gneisses at 2.1 Ga. Zircon U-Pb and Hf isotopes convincingly reveal two major phases of crustal growth in the Fuping Complex at ∼ 2.7 and ∼ 2.5 Ga, the same as in the northern and southern segments of the TNCO, and also confirm one major phase of intracrustal recycling at ∼ 2.1 Ga, which may be responsible for the Nanying granitic gneisses.