K-Ar ages of volcanic rocks from the Himeshima volcanic group, northern Kyushu, Japan

Abstract

Quaternary adakitic volcanism along the volcanic front of Western Honshu and northern Kyushu has been attributed to slab melting of the young, hot Shikoku Basin oceanic crust. However, the timing and magnitude of magma production at the northernmost end of the Kyushu volcanic front, represented by the Himeshima volcanic group, remain insufficiently constrained. In this study, we present new K-Ar ages obtained using the unspiked sensitivity method combined with petrographic and whole-rock geochemical data to refine the volcanic history of the Himeshima volcanic group.

The new K-Ar dating results indicate that volcanic activity in Himeshima was short-lived and concentrated between 89 and 59 ka. By integrating these age constraints with previously reported erupted volumes (0.05 km³), we estimate an average eruption rate of 1.7 × 10⁻³ km³/kyr. This rate is the lowest among the volcanoes of the Kyushu volcanic front and is one to two orders of magnitude lower than those of the adakitic volcanoes in Western Honshu, Japan, such as Daisen, Sanbe, and Aonoyama. We infer that the notably low eruption rate at Himeshima reflects the combined influence of shallow slab dehydration processes of the Shikoku Basin crust, a relatively cool mantle wedge beneath Himeshima, and a prevailing compressional stress regime.