Attribution and age of gneissose quartz diorite in Futagojima Island, Koshikijima Islands, Kagoshima, Japan

Abstract

We investigate zircon U-Pb age of the gneissose quartz diorite in Futagojima Island. There are two types of zircon; clear fine grains and dusty coarse grains. The former indicate weighted mean age of 103.7 ± 1.6 Ma which is interpreted as protolith age whereas the latter indicate scattered younger ages which is considered to be rejuvenation by a later thermal effect. The metamorphism which formed gneissose texture of the rock is considered not to be Higo but a younger one.