Seismic and magnetotelluric imaging of a crustal-scale fault beneath the eastern Central Orogenic Belt, North China Craton

The Central Orogenic Belt (COB) of the North China Craton (NCC) preserves a polyphase tectonic record involving Neoarchean crustal growth, Paleoproterozoic collision and Phanerozoic lithospheric reworking. Here we integrate deep seismic reflection (DSR) and magnetotelluric (MT) data acquired along a coincident 110-km-long transect across its eastern margin. The joint geophysical images reveal an east-dipping crustal-scale fault that can be traced from approximately 8–10 km depth to the Moho at approximately 30–36 km depth, and laterally for nearly 100 km. The structure juxtaposes crustal domains with contrasting seismic reflectivity and electrical resistivity, is followed at depth by an elongate low-resistivity band, and is merged into by younger basin-bounding normal faults, consistent with an earlier phase of contractional deformation followed by extensional reactivation. We evaluate four end-member interpretations: Neoarchean initiation during terrane accretion, Paleoproterozoic formation during continent–continent collision, Mesozoic-Cenozoic formation during lithospheric extension, and polyphase Precambrian inheritance followed by substantial younger reworking. Available regional constraints permit more than one interpretation, although an inherited Precambrian contractional structure subsequently reactivated during Phanerozoic extension provides a plausible explanation for the observed geometry. The east-dipping structure constitutes an independent deep constraint on models of crustal assembly, but its present orientation does not uniquely determine the original subduction polarity. If its initiation was Neoarchean, the structure would be consistent with large-scale horizontal convergence in the NCC by ca. 2.5 Ga; this remains a testable working hypothesis rather than a uniquely demonstrated conclusion.