SHRIMP U-Pb zircon dating and geochemistry of the 3.8–3.1 Ga Hujiamiao Complex in Anshan (North China Craton) and the significance of the trondhjemites for early crustal genesis.

[Display omitted] • A new complex, named as the Hujiamiao Complex, was discovered in the Anshan area, NCC. • Trondhjemitic rocks of different ages from 3.79 to 3.11 Ga have been identified. • It is the first time in Anshan to identify trondhjemitic rocks with relatively high (La/Yb) n ratios. • Magmatic zircons have ε Hf (t) of −12.3 to 1.6, t DM (Hf) and t CC (Hf) ages of 4.1 to 3.6 Ga and 4.3 to 3.7 Ga. • All the Anshan 3.8–3.3 Ga complexes are the relics of the same larger complex in the area. Anshan is located in the northeastern North China Craton and has a long-term geological history back to 3.8 Ga. Four complexes with ages of 3.8–3.1 Ga have been identified previously, namely the Baijiafen, Dongshan, Shengousi and Guodishan complexes. Being similar to the neighbouring Beijiafen Complex, the newly-discovered Hujiamiao Complex extends in a northwest-southeast direction and shows tectonic contacts on one side with the Chengtaigou granite and on the other with the Chengtaigou supracrustal rocks. In the Hujiamiao Complex, trondhjemitic rocks of 3789 Ma, 3786 Ma, 3698 Ma, 3617 Ma, 3566 Ma, 3504 Ma and 3106 Ma have been identified. More work is required to establish if a gabbro also has a formation age of 3.8 Ga. The trondhjemitic rocks show similar compositional features in being high in SiO 2 (72.37–76.71 %) and Na 2 O (5.00–6.47 %) and low in K 2 O (0.60–1.95 %), ∑REE contents (32.83–91.83 ppm) and (La/Yb) n ratios (11.09–48.64). They have whole-rock ε Nd (t) values of 0.35–4.43, t DM (Nd) of 3.74–3.46 Ga and t CC (Nd) ages of 3.74–3.43 Ga, and in situ magmatic zircon ε Hf (t) values of −12.3 to 1.56, t DM (Hf) ages of 4.2 to 3.5 Ga and t CC (Hf) ages of 4.6 to 3.7 Ga. Combined with previous work, it is concluded that all the Anshan area 3.8–3.3 Ga complexes are the relics of a larger complex which was once more widely distributed in the Anshan area. The trondhjemitic rather than tonalitic character of the Anshan Eoarchean rocks shows diversity in the formation and evolution of the earliest continental crust with a range of T/P for crustal anatexis. [ABSTRACT FROM AUTHOR]