Keywords:
The earliest stage of Izu rear-arc volcanism revealed by drilling at Site
U1437, IODP Expedition 350
Tomoki Sato1, Takashi Miyazaki1, *Yoshihiko Tamura1, James B Gill2, Martin Jutzeler3, Ryoko
Senda4, Jun-Ichi Kimura1
1. Research Institute for Marine Geodynamics, Japan Agency for Maine-Earth Science and Technology, 2. Department
of Earth and Planetary Science, University of California Santa Cruz, Santa Cruz, California, USA, 3. School of Natural
Sciences and Centre for Ore Deposit and Earth Sciences, University of Tasmania, Tasmania, Australia, 4. Faculty of
Social and Cultural Studies, Kyushu University, Fukuoka, Japan 
International Ocean Discovery Program Expedition 350 drilled between two Izu rear-arc seamount chains
at Site U1437 and recovered the first complete succession of rear-arc rocks. The drilling reached 1,806.5
m below seafloor. In-situ hyaloclastites, which had erupted before the rear-arc seamounts came into
existence at this site, were recovered in the deepest part of the hole (~15-16 Ma). Here we show that the
composition of the oldest rocks recovered do not have rear-arc seamount chain geochemical signatures,
but instead show affinities with volcanic front or some of the extensional zone basalts between the
present volcanic front and the rear-arc seamount chains. We infer that following the opening of the
Shikoku back-arc basin, Site U1437 was a volcanic front or a rifting zone just behind the volcanic front,
and was followed at ~9 Ma by the start of rear-arc seamount chains volcanism. This geochemical change
records variations in the subduction components with time, which might have followed eastward moving
of hot fingers in the mantle wedge and deepening of the subducting slab below Site U1437after the
cessation of Shikoku back-arc basin opening. 
Izu-Ogasawara arc, subduction zone, slab 
SCG64-P03JpGU-AGU Joint Meeting 2020
©2020. Japan Geoscience Union. All Right Reserved.- SCG64-P03 -
SCG64-P03JpGU-AGU Joint Meeting 2020
©2020. Japan Geoscience Union. All Right Reserved.- SCG64-P03 -