Multi-proxy provenance of the Jurassic Bansong Group wedge-top deposits, Korean Peninsula: Structural inheritance controls orogenic unroofing during paleo-Pacific subduction

The Bansong Group in the northeastern Okcheon Belt (Taebaeksan Basin), Korean Peninsula, represents wedge-top deposits formed during Jurassic paleo-Pacific subduction. We present a multi-proxy provenance analysis combining paleocurrent patterns, conglomerate and sandstone petrography, detrital zircon U-Pb geochronology, and whole-rock geochemistry to constrain sediment sources. Paleocurrent data indicate overall southeastward dispersal consistent with the thrust vergence, identifying northwestern structural highs as primary sediment sources. Clast compositions dominated by siliciclastic (meta)sedimentary fragments and recycled orogenic sandstone compositions indicate that recycling of pre-existing sedimentary successions was the dominant supply process. Detrital zircon U-Pb age spectra closely matching the Pyeongan Supergroup specify the source formations within these structural highs. This selective exposure documents a thrust system configuration in which Pyeongan Supergroup-dominated hanging walls shielded underlying Joseon Supergroup carbonates from erosion. Syn-depositional zircon populations at ca. 186 Ma, consistent with dated basal pyroclastic rocks, constrain the onset of sedimentation to the Early Jurassic, implying that thrust reactivation had initiated by at least this time. Middle-Late Triassic zircons, combined with geochemical signatures suggesting relatively higher first-cycle felsic igneous contributions, suggest additional input from distant igneous terrains beyond the local thrust belt. The concentration of Early Jurassic shortening within the Okcheon Belt, coeval with extension in adjacent regions, indicates contractional deformation localization along the inherited Songrim-age fold-thrust architecture. The coincidence of ca. 186 Ma arc magmatism in and around the belt suggests that thermal weakening may have helped trigger this reactivation and modification. These results suggest that pre-existing orogenic framework and crustal thermal state are significant controls on tectonic responses to shifts in convergent margin regimes.