Petrological and Geochemical study of Late Cenozoic volcanic rocks in Shimokita Peninsula, Aomori, NE Japan

Abstract

The volcanic front temporally moved to eastward ca. 20 km in the middle Miocene during the syn-opening stage of Japan Sea back-arc basin. Tomari Formation (M. Mio.) in the east Shimokita Peninsula, Aomori, NE Japan, was formed the volcanic front at middle Miocene. This volcanic formation demonstrates enriched geochemical characteristics at the rifting progressing stage. On the other hand, volcanic rocks after 20 Ma distributed in the west Shimokita Peninsula, where is the volcanic front in the Quaternary, show more depleted isotopic compositions in the mafic-intermediate rocks than Tomari volcanic rocks, whereas felsic rocks correspond to isotopic composition of lower crustal materials from Ichino-megata maar. In the western area, isotopic composition of volcanic rocks have not changed at least last 20 Myr. In the eastern area, it is implied that Tomari volcanic rocks were affected by lower crustal materials.※This study was supported by Shimokita Geopark research grant in 2020.