Seismic image constraints on the geodynamic evolution of the Hegenshan Suture (Eastern CAOB)

The Hegenshan Suture represents a critical paleotectonic and paleobiological boundary in the Central Asian Orogenic Belt (CAOB). Nevertheless, the absence of high-resolution, lithospheric-scale constraints on accretionary architectures has hindered a comprehensive understanding of tectonic evolution in the CAOB. Here, two high-resolution deep seismic reflection profiles crossing the Hegenshan Suture are presented and comparatively analyzed, revealing fine lithospheric accretionary structures for the first time. Multiple sets of prominent north-dipping reflectors can be traced in the crust‒mantle transition zone on both seismic profiles, which depict multistage northward oceanic subduction relics. More importantly, high-amplitude imbricate structures are accompanied by fossil subduction zones in the middle–lower crust, which represent accretionary complexes that developed during oceanic subduction. Furthermore, these geophysical features are superimposed by south-dipping thrust structures in the upper crust, forming tectonic crocodile structures that record later tectonic overprinting. Integrating geological, geochemical, and other geophysical evidence, we conclude that multistage northward oceanic subduction–accretion contributed to the formation of the Hegenshan Suture in the Paleozoic, which was superimposed by Mesozoic thrust–nappe structures. Our study provides a paradigm for using multiple methods to detect multistage accretion and superimposition regions.