Neoarchean-Paleoproterozoic magmatic arc evolution in the Wutai-Hengshan-Fuping area, North China Craton: New perspectives from zircon U-Pb ages and Hf isotopic data

The Wutai granite-greenstone belt, which formed in the Neoarchean-Paleoproterozoic, with the adjoining high-grade metamorphic Hengshan-Fuping region, record important transitions in crustal and tectonic evolution, although these evolutionary processes have still been in dispute. In this study, new U-Pb and Lu-Hf LA-ICP-MS zircon analyses were obtained from eight metamorphosed magmatic rocks in the Wutai-Hengshan-Fuping area in North China Craton (NCC). The results reveal that most of Wutai granitoids yield emplacement ages of 2.56-2.52 Ga, with corresponding epsilon(Hf(t2)) of + 4.7 to + 8.3. The tonalitic gneiss from Dongshandi intrusion, however, gives a new age of 2482 Ma and epsilon(Hf)((t2)) of + 2.5 to + 4.6, which are similar with Yixingzhai Pluton marked by ages of 2501-2499 Ma and epsilon(Hf)((t2) )of +3.2 to +4.4. Also, similar to 2.7 Ga and similar to 2.5 Ga continental crust generation are further revealed. But similar to 2.5 Ga crustal growth is more complicated due to the involvement of old crustal components, which can be identified by variable epsilon(Hf)((t2)) values ranging from - 1.8 to + 7.5. Thus, based on the distinctions of Hf isotopes, compositional and spatial features, two consecutive groups of 2.56-2.52 Ga and 2.52-2.48 Ga are recognized and a two-step tectonic evolution model for the Wutai-Hengshan-Fuping area is proposed. During 2.56-2.52 Ga, intra-oceanic subduction led to the formation of Wutai oceanic island arc, accompanied mainly by the development of Wutai granitoids (epsilon(Hf)((t2)) of + 4.7 to + 8.3) and coeval volcanics (predominant arc-tholeiitic chemical affinity), corresponding to the juvenile crustal growth. Between 2.52 Ga and 2.48 Ga, with intervening oceanic crust between intra-oceanic arc and continent consumed, the Wutai intraoceanic arc then collided and was obducted onto the western edge of the Hengshan-Fuping continental block. Large amounts of TTG gneisses produced in both the Wutai and Hengshan-Fuping epsilon(Hf)((t)) of - 1.8 to + 7.5), along with calc-alkaline volcanism in Wutai, possibly in response to the thickening through arc accretion and commencing the continental arc. This proposed two-step tectonic evolution model, combined with a late Neoarchean (2.6-2.5 Ga) intra-oceanic arc system along the northwestern of the Eastern Block (EB), probably provides a better explanation for the fundamental geodynamic mechanism for continental arc development at the Proterozoic dawn.