Tectonic Implication of A-type Granites across the Yangsan Fault, Gigye and Gyeongju Areas, Southeast Korean Peninsula

Abstract

Based on field relations and petrographic characteristics, alkali-feldspar granite in the Gigye area on the western side of the Yangsan fault is classified as an A-type granite. It is mainly composed of quartz, perthitic K-feldspar, and interstitial ferri-annite plus sodic amphiboles such as riebeckite and arfvedsonite, indicating crystallization under hypersolvus, anhydrous conditions. These petrographic features are the same as those of the A-type granite in the Gyeongju area on the east side of the Yangsan fault. These distinctive, pre-Eocene granites are separated by about 21.3 km, indicating Cenozoic dextral strike-slip of this amount along the Yangsan fault.