Age and evolution of a late Archean to Paleoproterozoic upper to lower crustal section in the Wutaishan/Hengshan/Fuping terrain of northern China

The Taihangshan-Wutaishan area forms part of the central North China Craton and consists of three main components: the Hengshan and Fuping complexes, containing predominantly ductilely deformed late Archean to Paleoproterozoic high-grade granitoid orthogneisses, intruded by mafic dykes of gabbroic composition, and the low-grade late Archean Wutai greenstone belt, developed between the high-grade terrains and consisting of bimodal volcanic rocks and metasediments, associated with coeval granitoids. Zircon dating shows that both the Hengshan and Fuping complexes were intruded by major granitoid bodies between 2.52 and 2.48 Ga, with rare occurrences of 2.7 Ga gneisses. Wutai granitoids adjacent to the Fuping complex also contain 2.7 Ga xenocrysts, all possibly reflecting the same older basement. Rare granitic gneisses in the Hengshan have emplacement ages of ∼2.35 Ga and show the same structural features as the older rocks, indicating that the main deformation occurred after ∼2.3 Ga. Deposition of supracrustal rocks and emplacement of mafic dykes occurred in the Paleoproterozoic, together with intrusion of granitic bodies at ∼2.1-2.0 Ga, and all underwent regional metamorphism at 1.88-1.85 Ga. We interpret the Hengshan and Fuping granitoid gneisses as the lower, plutonic, part of a late Archean to early Paleoproterozoic Japan-type magmatic arc, with the upper, volcanic part represented by the Wutai complex. Components of this arc may have evolved at a continental margin as indicated by the 2.7 Ga zircons. Virtually all magmatic events are recorded in all three complexes. However, the 1.85 Ga metamorphic event is only recorded in the higher-grade portions of the Wutai, since low-grade and presumably high crustal level precluded metamorphic zircon growth. Shear zones in the Hengshan are interpreted as major lower crustal discontinuities post-dating the peak of high-pressure granulite metamorphism. We suggest that they formed during orogenic collapse and uplift of the Hengshan complex in the late Paleoproterozoic (>1800 Ma).