Temporal variations of geochemical characteristics of volcanic rocks from north of Kofu Basin, central Japan, and the role of Philippine Sea plate

Abstract

We analyzed the major and trace element and isotopic compositions of the volcanic rocks from the Kofu Basin, and investigated the temporal geochemical variations. As a result, these volcanics show the typical island arc magma. From the Sr/Y ratios, the magma genesis of this area is caused by slab dehydration of Pacific plate at Tertiary, and by slab melting of Philippine Sea plate at Quaternary. The isotopic compositions of Sr, Nd and Pb suggest that the materials derived from Philippine Sea plate contributed former magma genesis. From these observations, it can be concluded that the Philippine Sea plate was reached near below the studied area at Tertiary, and reached just below this area at Quaternary.