Using the Oligocene to the Recent Izu-Bonin arc tephrostratigraphy from IODP expeditions 350 and 352 to unravel the arc history

Provenance studies of widely distributed tephras, integrated within a well-defined temporal framework, are important to deduce systematic changes in the source, scale, distribution and changes in regional explosive volcanism. Here, we established a robust tephro-chronostratigraphy of the last ~32 Myr from IODP (International Ocean Discovery Program) expeditions 352 and 350 in the Izu-Bonin fore- and reararc in order to assess provenance and eruptive volumes, as well as variations with time, respectively.

In total, we identified ~400 primary tephra layers. Tephra provenance was determined by means of major and trace element compositions of glass shards and distinguished between Japan and Izu-Bonin arc origin of the tephra layers. We infer at least three major phases of highly explosive volcanism during Oligocene to Pleistocene time. Four source regions along the Izu-Bonin arc are assigned. One, of exclusively Oligocene age, is proximal to the Bonin Ridge islands; two reflect eruptions within the volcanic front and back-arc of the central Izu-Bonin arc, and a fourth region corresponds to the Northern Izu-Bonin arc source.

First-order volume estimates imply eruptive magnitudes ranging from 6.3 to 7.6 for Japan-related eruptions and between 5.5 and 6.5 for IBM eruptions. Our results suggest tephras between 30 and 22 Ma that show a subtly different Izu-Bonin chemical signature compared to the recent arc. After a ~11 m.y. gap in eruption, tephra supply from the Izu-Bonin arc predominates from 15 to 5 Ma, and finally a subequal mixture of tephra sources from the (palaeo)Honshu and Izu-Bonin arcs occurs within the last ~5 Ma.

These results are used, together with new biostratigraphical, geochemical and magnetic evidence from IODP Expedition 352 to understand the sedimentary and tectono-magmatic development of the Izu-Bonin outer forearc region.