Lateral variation of phenocryst assemblages in volcanic rocks of the Japanese islands

Abstract

To understand the origin of calc-alkaline rocks and island arc volcanism, knowledge of the lateral variation of the petrological characters of volcanic rocks is essential. The lateral variation of chemical compositions of volcanic rocks has been investigated by several authors^1–4 and correlated to the depth of the Benioff zone. The east volcanic zone of Japanese Islands, which contains about 140 discrete Quaternary volcanoes, is the most extensively studied volcanic zone in the world. I have examined the petrological data of these volcanoes, particularly with respect to the phenocryst assemblages in volcanic rocks and their changes during the history of respective volcanoes. The references have been mostly taken from 200 papers compiled by Isshiki et al.⁵.