K-Ar Ages of Andesites from Two Volcanic Arrays in Western Chugoku, Southwest Japan

Abstract

The volcanic front in the Southwest Japan Arc formed relative to the subducting Philippine Sea Plate. In the west Chugoku district, the volcanic front changes direction from E-W to NNE-SSW. Twenty-two Quaternary lava domes in this area can be topographically classified into two arrays (East and West arrays) based on the degree of dissection. K-Ar age results show that domes of the East array formed earlier (0.6-0.3 Ma) than those of the West array (0.2 Ma-recent). The two arrays in different ages may result from the migration of volcanic front caused by westward migration of the PSP slab.