Timing and Origin of Two Regional Unconformities in the Southeast North China Craton: Insight from Detrital Zircon and Monazite Geochronology

The Neoproterozoic–Early Palaeozoic strata in the southeastern North China Craton (NCC) contain two regional unconformities, namely the lower unconformity between the Suxian Group and Langan Group, and the upper unconformity between the Langan Group and Houjiashan Formation, which preserve crucial records of supercontinent assembly and breakup. This study presents a direct comparative investigation of laser ablation inductively coupled plasma mass spectrometry (LA‑ICP‑MS) U–Pb geochronology of detrital zircons and monazites from the Xuhuai Basin in the southeastern NCC. The primary objective is to better constrain the Mesoproterozoic to Early Palaeozoic provenance and stratigraphic framework of the region, as well as to refine its paleogeographic reconstruction. Detrital monazite ages cluster in three distinct intervals: ca. 2.0–1.8 Ga, 1.3–1.0 Ga, and 1.0–0.9 Ga. The older age groups (ca. 2.0–1.8 Ga and 1.3–1.0 Ga) are predominantly distributed in the Huaihe and Suxian Groups, whereas the 1.0–0.9 Ga age population dominates the Langan Group. The weighted mean age of the three youngest zircons from the Cambrian Houjiashan Formation constrains its maximum depositional age (MDA) to ~501 Ma. Combined with the weighted mean age of the youngest detrital zircons from the Jinshanzhai Formation (742 ± 13 Ma, after Yin et al., 2022), the time spans of the lower and upper unconformities between the Neoproterozoic and Cambrian strata in the Xuhuai area are approximately 150 Ma and 230 Ma, respectively. We propose that the 2.0–1.8 Ga zircons and monazites were likely derived from the underlying Jiao–Liao–Ji orogenic belt, whereas the younger age components (1.3–0.9 Ga) exhibit affinities with non-NCC provenances. By the time of the ca. 0.9 Ga Xuhuai large igneous province, the region had not become fully separated from surrounding cratonic blocks. The southeastern NCC was probably tectonically connected to the cratonic blocks within the East Gondwana landmass assemblage (then part of the Rodinia supercontinent) and received substantial detrital input from multiple episodes of orogenesis. The two stratigraphic successions, i.e., the Huaihe–Suxian Groups and the Langan Group, developed in an intraplate basin setting, represent two distinct sub-basins formed under different geodynamic mechanisms. The depositional hiatus between these two successions may be associated with mantle plume–lithosphere interactions linked to prolonged mantle plume activity (0.92–0.75 Ga) in the southeastern NCC. In contrast, the upper unconformity is inferred to be related to the tectonic quiescence of the NCC during the Ediacaran–Early Cambrian.