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.