The Huai'an Complex is situated in the northern segment of the Trans-North China Orogen (TNCO), a continent-continent collisional belt along which the discrete Archean Eastern and Western Blocks amalgamated to form the basement of the North China Craton. The complex consists of six distinct lithologic units: the Huai'an TTG gneisses, the Manjinggou high-pressure mafic granulites, the Khondalite Series, the Dongjiagou granitic gneiss, the Huai'an charnockite, and the Dapinggou K-feldspar granite. SHRIMP U–Pb geochronology, combined with Th and U data and cathodoluminescence (CL) imaging of zircons, enables resolution of magmatic and metamorphic events that can be directed towards understanding the late Archean to Paleoproterozoic history of the TNCO. CL images reveal the coexistence of magmatic and metamorphic zircons in most lithologies of the Huai'an Complex, of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating oscillatory-zoned magmatic zircon cores. SHRIMP U–Pb analyses on magmatic zircons reveal that the tonalitic, trondhjemitic and granodioritic protoliths of the Huai'an TTG gneisses were emplaced at 2515 ± 20 Ma, 2499 ± 19 Ma and 2440 ± 26 Ma, respectively, much earlier than the emplacement of the Dongjiagou granitic gneiss dated at 2036 ± 16 Ma. However, their metamorphic zircons yield similar concordant ²⁰⁷Pb/²⁰⁶Pb ages of 1847 ± 17 Ma, 1842 ± 10 Ma and 1847 ± 11 Ma for the tonalitic, trondhjemitic and granodioritic gneisses, respectively, and 1839 ± 46 Ma for the Dongjia granitic gneiss. These ages demonstrate that the Huai'an Complex underwent a regional metamorphic event at ∼1850 Ma, which is further supported by a mean ²⁰⁷Pb/²⁰⁶Pb age of 1848 ± 19 Ma for metamorphic zircons in the Manjinggou high-pressure mafic granulite and 1849 ± 10 Ma and 1850 ± 17 Ma for igneous zircons in the anatectic Huai'an charnockite and Dapinggou garnet-bearing S-type granite, respectively. The timing of late Archean to Paleoproterozoic magmatism and regional metamorphism in the Huai'an Complex is in general agreement with recent SHRIMP zircon data for other metamorphic complexes in the TNCO. These data prove that the high-grade gneiss complexes were not the basement to the low-grade granite-greenstone terranes in the TNCO. Furthermore, the lithologies of the orogen are considered to have developed as a long-lived magmatic arc that was subsequently tectonically disrupted and juxtaposed during the collision of the Eastern and Western Blocks at ∼1.85 Ga, leading to final assembly of the North China Craton.

The Hengshan–Wutai–Fuping belt is located in the middle segment of the Trans-North China Orogen, a Palaeoproterozoic continental collisional belt along which the Eastern and Western blocks amalgamated to form the North China Craton. The belt consists of the medium- to high-grade Hengshan and Fuping gneiss complexes and the intervening low- to medium-grade Wutai granite–greenstone terrane, and most igneous rocks in the belt are calc-alkaline and have affinities to magmatic arcs. Previous tectonic models assumed that the Hengshan and Fuping gneiss assemblages were an older basement to the Wutai supracrustal rocks, but recent studies indicate that the three complexes constitute a single, long-lived Neoarchaean to Palaeoproterozoic magmatic arc where the Wutai Complex represents an upper crustal domain, whereas the Hengshan and Fuping gneisses represent the lower crustal components forming the root of the arc. The earliest arc-related magmatism in the belt occurred at 2560–2520 Ma, marked by the emplacement of the Wutai granitoids, which was followed by arc volcanism at 2530–2515 Ma, forming the Wutai greenstones. Extension driven by widespread arc volcanism led to the development of a back-arc basin or a marginal sea, which divided the belt into the Hengshan–Wutai island arc (Japan-type) and the Fuping relict arc. At 2520–2480 Ma, subduction beneath the Hengshan–Wutai island arc caused partial melting of the lower crust to form the Hengshan tonalitic–trondhjemitic–granodioritic (TTG) suites, whereas eastward-directed subduction of the marginal sea led to the reactivation of the Fuping relict arc, where the Fuping tonalitic–trondhjemitic–granodioritic suite was emplaced. In the period 2360–2000 Ma, sporadic phases of isolated granitoid magmatism occurred in the Hengshan–Wutai–Fuping region, forming 2360 Ma, c. 2250 Ma and 2000–2100 Ma granitoids in the Hengshan Complex, the c. 2100 Ma Wangjiahui and Dawaliang granites in the Wutai Complex, and the 2100–2000 Ma Nanying granitoids in the Fuping Complex. At c. 1920 Ma, the Hengshan–Wutai island arc underwent an extensional event, possibly due to the subduction of an oceanic ridge, leading to the emplacement of pre-tectonic gabbroic dykes that were subsequently metamorphosed, together with their host rocks, to form medium- to high-pressure granulites. At 1880–1820 Ma, the Hengshan–Wutai–Fuping arc system was juxtaposed, intensely deformed and metamorphosed during a major and regionally extensive orogenic event, the Lüliang Orogeny, which generated the Trans-North China Orogen through collision of the Eastern and Western blocks. The Hengshan–Wutai–Fuping belt was finally stabilized after emplacement of a mafic dyke swarm at 1780–1750 Ma.