Collapsed orogens controlled Mesozoic structural evolution along the East Asian continental margin: Evidence from the central-western Korean Peninsula

Orogenic collapse creates fundamental structural architectures that profoundly influence later tectonic evolution. We document how Late Triassic post-collisional collapse structures governed Jurassic–Cretaceous contractional deformation in the Hongseong-Imjingang Belt (HIB), central-western Korean Peninsula. Integrated structural, microstructural, and geochronological data from Deokjeok, Soya, and Ijak islands reveal NW-striking extensional shear zones (Deokjeok and Ijak) that accommodated top-to-the-northeast displacement during Late Triassic gravitational collapse (∼231–217 Ma). These detachment systems exhumed mid- to lower-crustal rocks while syn-extensional basins formed in their hanging walls, accompanied by prolonged magmatism and thermal overprinting. Quantitative grain-shape fabric analysis of K-feldspar porphyroclasts reveals contrasting fabric geometries: preserved extensional fabrics record constrictional geometry while overprinted domains display flattening geometry. During Late Jurassic–Early Cretaceous contraction (∼150–130 Ma), these extensional structures underwent positive inversion. This created basement-involved thrust systems that emplaced crystalline slivers within Mesozoic basin fill and reversed the kinematics of inherited shear zones. The Soya Shear Zone exemplifies this structural inheritance, preserving domains with original extensional kinematics adjacent to strongly inverted zones. Our findings highlight that collapse-derived extensional structures act as persistent mechanical weaknesses, critically influencing how continental margins respond to changing tectonic regimes.