Revisiting the formation ages of Tangjiazhuang Group: Insights from new U-Pb zircon ages in TTG gneisses of the Jiaobei terrane, North China Craton

Abstract

The Jiaobei terrane is a typical and representative early Precambrian terrane of the North China Craton (NCC) characterized by extensively metamorphosed supracrustal rocks. These supracrustal units are of great importance for deciphering the NCC’s tectonic evolution, mineralization processes, and environmental responses during the early Earth. However, the distribution of Archean supracrustal rocks in the Jiaobei terrane is not as extensive as in other parts of the NCC. Despite the most commonly used classification of the Archean supracrustal rocks in the Jiaobei terrane into the Mesoarchean Tangjiazhuang Group and the Neoarchean Jiaodong Group, the precise formation age of the Tangjiazhuang Group has remained elusive. Addressing this gap, this study introduces new zircon U–Pb geochronological insights from TTG (Tonalite-Trondhjemite-Granodiorite) gneisses that intruded the Tangjiazhuang Group. The analyzed zircons predominantly exhibit magmatic cores with metamorphic overgrowth rims, indicative of complex geological processes. Our findings reveal two distinct age groups at 2794 ± 27 Ma and 1914 ± 36 Ma, corresponding to the intrusion of TTG gneisses during the late Mesoarchean and their subsequent metamorphism in the Paleoproterozoic, respectively. They were later intruded by the Paleoproterozoic granitic gneiss at 2194 ± 16 Ma. Combined with field observation and previous studies, the new age data definitively suggest that the Tangjiazhuang Group was formed by at least the late Mesoarchean, thereby offering crucial refinements to the temporal framework for the early crustal formation and evolution of the NCC. The lack of continent-derived components (pelitic rocks) in this lithological unit implies submerged environment for the Mesoarchean Jiaobei terrane of the eastern NCC.