HIGH-GRADE METAMORPHIC INCLUSIONS IN CENOZOIC VOLCANIC ROCKS FROM WEST SANIN, SOUTHWEST JAPAN

Abstract

Several types of granulitic inclusions were found in the Cenozoic volcanic rocks from West Sanin, Southwest Japan. They are composed essentially of anhydrous minerals such as olivine, clinopyroxene, orthopyroxene, garnet, plagioclase and quartz, accompanied by small quantities of hornblende and biotite, and lack potash feldspar. Judging from their chemical compositions, physical properties and chemistry of the constituent minerals, these inclusions are possibly derivatives of the lower crust under the granulite facies metamorphic condition. The stratified crustal structure consisting of upper (granitic), intermediate (amphibolite facies) and lower (granulite facies) layers, is presumed beneath the inner side of Southwest Japan.