Provenance analysis of the Cretaceous Gyeongsang Basin, SE Korea: A synthesis and tectonic implications for active continental margin in East Asia

Abstract

In the middle to late Mesozoic period, the Korean Peninsula was in an active continental margin with an accretionary complex developed in the direction of trench to the southeast. The Cretaceous Gyeongsang Basin is the largest nonmarine basin distributed in the southeastern part of the Korean Peninsula and is generally considered to be a transtensional or an extensional basin formed by the oblique subduction of the Paleo-Pacific (Izanagi) Plate or Izanagi slab rollback. The pre-volcanic sedimentary succession of the Gyeongsang Basin is subdivided into the Sindong and Hayang groups as the age decreases and this sedimentary succession is un-conformably overlain by the Yucheon Group, which consists of intermediate to felsic volcanic rocks with minor volcaniclastic sediments and forms a volcanic arc (the Gyeongsang Arc). Because the Gyeongsang Basin was geographically developed behind the Japanese Arc during the Cretaceous period, and the Gyeongsang Arc was considered an extension of the Japanese Arc, the Gyeongsang Basin was considered a backarc basin, although sedimentation in the basin occurred before the development of the Japanese Arc and Gyeongsang Arc. Here, we reinterpret the tectonic setting and basin formation mechanism in the pre-volcanic stage of the Gyeongsang Basin by synthesizing the results of provenance studies on the Sindong and Hayang groups. The sediments were derived from western and northwestern sources (the Yeongnam Massif), which currently do not contain records of Early Cretaceous arc magmatism. The modal and geochemical compositions of these sediments and detrital zircon U-Pb ages suggest that the sediments were derived from arc-related crystalline basement rocks of the Yeongnam Massif with a record of Early Cretaceous (143-100 Ma) arc magmatism. We propose that the pre-volcanic stage of the Gyeongsang Basin was a forearc basin formed between the Yeongnam Massif (then arc) and the Jurassic accretionary complex on the seaside and that the basin may have been formed by extensional stresses related to the subduction of an oceanic plateau during the Early Cretaceous.