Jun-Ichi Kimura

Near-synchroneity and periodicity of back-Arc propagation of Quaternary explosive volcanism in the southern segment of Northeastern Honshu Arc, Japan: A study facilitated by tephrochronology

Abstract Six aligned, across-arc volcanoes in the southern segment of Northeastern Honshu Arc, Japan, have erupted repeatedly through the Quaternary. Tephras derived from these volcanoes represent the products of explosive volcanism, and can be seen in distal areas overlapping one another. The widespread nature of tephra makes it possible to compile and integrate the eruption sequences of the six volcanoes. A marked feature is that the explosive volcanism occurred periodically and essentially simultaneously. The simultaneous activities appeared at intervals of 50 to 100 thousand years. Within each episode of simultaneous eruptions, the volcanic front volcano erupted initially and then back-arc volcanoes erupted one after another. Tephrochronology, combined with a chronology derived from accumulation rates of tephric loess deposits, provided ages (resolution ± 5 ka) for the eruptions and their periodic short-term back-arc propagation. The Quaternary volcanism commenced at ca. 1.5 Ma (from published KAr ages). Long-term back arc spreading of volcanic activity is documented. The volcanic activity was restricted initially to the volcanic front, and sequentially spread to the back-arc at a nearly constant spreading rate.