K-Ar ages for the Setouchi volcanic rocks in Shitara district central Japan

Abstract

K-Ar ages were determined for the Shitara volcanic rocks, which belong to the middle Miocene Setollchi volcanic rocks in southwestern Japan are. The Shitara volcanic rocks are mainly composed of alkaline volcanic rocks, whereas high-Mg andeites (HMAs), which are the main constituents of the Setollchi volcanic rocks of other districts were not observed. The samples for K-Ar age determination were selected from intrusive rocks that bdong to the latest magmatic activity in this district. The obtained ages range from 134|04 Ma to 126 |04 Ma and thee ages are similar to those of the other districts These indicate that the magma activity in the Shitara district ceased at about 13 Ma, and the origin of the Shitara volcanic rocks is closely related to that of the HMAs, althollgh the prtrological characteristics of the Shitara volcanic rocks are diffrent from those of the HMAs. © 2002, Japan Association of Mineralogical Sciences. All rights reserved.