Zircon U–Pb geochronology and Hf isotopic composition of the Hongqiyingzi Complex, northern Hebei Province: New evidence for Paleoproterozoic and late Paleozoic evolution of the northern margin of the North China Craton

The Hongqiyingzi Complex, located at the northern margin of the North China Craton, was previously defined as a Paleoproterozoic unit. It consists of volcanic and sedimentary rocks, which underwent greenschist- to amphibolite-facies metamorphism. This study presents zircon U–Pb ages and Hf isotopic composition and whole-rock Nd isotopic composition of metamorphosed igneous and sedimentary rocks from the Hongqiyingzi Complex. The age dating results show that different gneisses of this complex contain mainly late Paleoproterozoic (~ 1800 Ma) and late Paleozoic (~ 275 to ~ 300 Ma) zircons and minor late Archean zircons. Late Paleozoic zircons either occur as magmatic grains or as metamorphic overgrowth and both types of zircon can be distinguished by their Th/U ratios and internal structures. Most zircon grains of a Paleozoic magmatic rock (sample Hq14) have high εHf(t) values of 1.5 to 10.8, suggesting significant contribution of mantle or juvenile crustal material to the magma source(s). The results imply that the Hongqiyingzi Complex contains Precambrian supracrustal sequences and Paleozoic rocks of magmatic origin that underwent strong metamorphism and deformation during the late Paleozoic related to the closure of the Paleo-Asian Ocean between Siberia and the North China Craton.