Significance of systematic changes in crenulation asymmetries within metasediments across the Ogcheon Supergroup in the Goesan area, southern Korea

Abstract

Garnet bearing metasediments from the Ogcheon Supergroup in the Goesan area, southern Korea, preserve evidence of several earlier deformation and metamorphic events, previously unrecognized. This study, based on a 3-D thin section observation of the rock, has revealed six distinctive planar structures including five foliations and micro-fold acial planes inside the porphyroblasts (S₁ to S₃) and five foliations in the matrix (S₂ to S₆), besides weak structures locally overprinting some of these matrix foliations. The rocks studied experienced early formation of shallow foliation during D₁, succeeded by NE-SW shortening (D₂), vertical shortening towards the NE-SW (D₃), NW-SE shortening (D₄) that developed the regional NE strike, vertical shortening (D₅) causing the variable dips of early planar structures, E-W shortening (D₆) causing local northwards rotation of the NE structures and some younger weak deformation.