Timing and Origin of Two Regional Unconformities on the Northern Margin of the North China Block: Insights into Arc Accretion-to-Subduction in the Central Asian Orogenic Belt

Abstract

The northern margin of the North China Block preserves multiple regional unconformities that archive accretion-subduction processes within the Central Asian Orogenic Belt. To constrain their timing and origin, we conducted integrated petrographic and geochronologic analyses on two newly identified unconformity sections in the Chifeng area. Our findings reveal two distinct tectonic episodes: (1) At the Shidafen section, the Xibiehe gravelly sandstone (432 ± 2 Ma, tuff) unconformably overlies granitic gneiss basement (2556 ± 5 Ma) of the North China Craton. Paleogeographic evidence excludes Paleoproterozoic–Ordovician hiatuses, instead linking this unconformity to the Silurian collision between the Bainaimiao arc and North China Craton. (2) Yangshuwan section records a Carboniferous unconformity where the Qingfengshan gravelly sandstone (≤327 Ma, detrital zircon) disconformably overlies the Chaotugou tuff (355 ± 2 Ma). This unconformity (355–327 Ma) correlates with Carboniferous unconformities on the eastern segment of the northern North China Block, representing a regional response to the transition from retreating to advancing subduction of the Paleo-Asian Ocean slab. These two regional unconformities document Silurian arc–continent collision and Carboniferous subduction-mode switch in the Central Asian Orogenic Belt, providing critical insights into accretion-to-subduction processes in accretionary orogens.

Keywords

Bainaimiao arc / Central Asian orogenic belt / North China Craton / stratigraphic framework / unconformity / zircon U-Pb ages

RIGHTS & PERMISSIONS

2026 Geological Society of China.