INVERSION OF TRIASSIC TO JURASSIC TWO-PHASE EXTENSIONAL BASIN SYSTEMS IN THE SW KOREAN PENINSULA: IMPLICATION FOR MESOZOIC LARAMIDE-STYLE OROGENY ALONG THE EAST ASIAN CONTINENTAL MARGIN

During subduction of oceanic plate, continental margins may experience contraction along with the structural inversion of extensional basins. Here we present a new structural and tectonic scenario for inversion of the Chungnam Basin, southwestern Korean Peninsula, where the Early to Middle Jurassic intra-arc basin was imprinted on the Late Triassic to Early Jurassic post-collisional basin in the East Asian continental margin. The two-stage sedimentary sequences are detached from the underlying basement by means of low-angle thrust faults ad related folds. Meanwhile, the basement shortening is accommodated mostly by high-angle reverse faults as well as low-angle thrust faults, compatible with those preserved in the sedimentary sequences in aspects of geometry and kinematics. Propagation of high-angle basement reverse fault enhanced the shortening of the overlying sedimentary cover sequences. The basement-involved contractional deformation of the former two-stage extensional basin systems might be strongly controlled by initial basin geometry and inherited extensional structures, as manifested by basement sliver carried by shortcut fault as well as switching of transport direction due to buttressing effect, during basin inversion. New altered K-feldspar ⁴⁰Ar-³⁹Ar ages from stacked thrust sheets and illite-polytype (2M₁ and 1M/1M_d) K-Ar ages of fault gouges, along with previously reported geochronological data, constrain the timing of the Late Jurassic to Early Cretaceous (ca. 158 - 110 Ma) basin inversion, contemporaneous with the timing of magmatic quiescence across the southern Korean Peninsula. The temporal and spatial relationships between the contractional tectonic phase and arc magmatism make it possible to interpret the role of flat subduction of the Late Jurassic to Early Cretaceous Paleo-Pacific Plate on the development of “Laramide-style” basement-involved orogenic event along the East Asian continental margin.