JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG63] [EE] Crust-Mantle Connections / Hard-Rock Drilling

Wed. May 24, 2017 10:45 AM - 12:15 PM 104 (International Conference Hall 1F)

convener:Yoshihiko Tamura(R & D Center for Ocean Drilling Science, Japan Agency for Maine-Earth Science and Technology), Katsuyoshi Michibayashi(Institute of Geosciences, Shizuoka University), Eiichi TAKAZAWA(Department of Geology, Faculty of Science, Niigata University), Katy Jane Chamberlain(Japan Agency for Marine-Earth Science and Technology), Tomoaki Morishita(School of Natural System, Colleage of Science and Technology, Kanazawa University), Henry JB Dick(Woods Hole Oceanographic Institution), Mark K Reagan(University of Iowa), Susanne M Straub(Lamont Doherty Earth Observatory of Columbia University), Chairperson:Yoshihiko Tamura(R & D Center for Ocean Drilling Science, Japan Agency for Maine-Earth Science and Technology), Chairperson:Katsuyoshi Michibayashi(Institute of Geosciences, Shizuoka University)

11:30 AM - 11:45 AM

[SCG63-04] Volcanic Ashes Recovered by IODP Expedition 350 Site U1436 in the Izu Arc: A Prologue of Submarine Caldera Formation?

*Yoshihiko Tamura1, Julie Christin Schindlbeck2, Martin Jutzeler3, Alexander Nichols4, Susan DeBari5, Graham D. M. Andrews6, James Gill7, Cathy Busby8, Peter Blum9, Yukari Kido10 (1.ODS, JAMSTEC, 2.GEOMAR Helmholtz Centre for Ocean Research, 3.School of Physical Sciences and Centre of Excellence in Ore Deposits (CODES), University of Tasmania, 4.Department of Geological Sciences, University of Canterbury, 5.Department of Geology, Western Washington University, 6.Department of Geology & Geography, West Virginia University, 7.University of California, Santa Cruz, 8.University of California, Davis, 9.IODP, Texas A & M University, 10.CDEX, JAMSTEC)

Keywords:Higashi Aogashima Caldera, Izu arc, rhyolite, submarine caldera, IODP

International Ocean Discovery Program (IODP) Site U1436 (32°23.88’N, 140°21.93’E) lies 1,776 m below sea level and about 60 km east of the arc front volcano Aogashima, and was drilled as a geotechnical survey for proposed D/V Chikyu drilling at Site IBM-4. Coring at Site U1436 recovered a 132 m record of Quaternary explosive volcanism in the Izu arc. Because the prevailing wind blows from west to east across the Izu arc, the forearc is a repository of medial and distal aerially dispersed ashes and tuffs from Izu and Japan, as well as eastward flowing density currents from the frontal arc. Effusive eruptive products (e.g., lavas) are better preserved on the frontal arc islands, while deep marine depocenters form a complement, by chiefly preserving products from explosive eruptions. However, which volcano or volcanoes did these ashes erupt from? Could the ash record at Site U1436 be nothing but a haphazard collection of Izu arc volcanoes?
There are several interesting features of Site U1436 cores.
1) The biostratigraphic datums indicate a possible hiatus between 66 mbsf and 74 mbsf. The 66 m of the cores above the hiatus provides a nearly complete record of the Late Pleistocene (< 0.91 Ma). They show higher linear sedimentation rates (LSRs) and mass accumulation rates (MARs) than the lower parts below the hiatus (> 1.5 Ma).
2) Ash fallout and volcaniclastic flow deposits (~150 intervals) are present at Site U1436. The majority of tephra fall layers at Site U1436 are from volcanoes of the Izu volcanic front as well as from mainland Japan (Schindlbeck et al., pers. comm.).
3) Site U1436 is bathymetrically isolated from all Quaternary volcanic front volcanoes through submarine troughs and edifices except for Higashi Aogashima caldera. Therefore, Higashi Aogashima caldera is the only likely source for eruption-fed density currents at Site U1436
4) One distinctive interval of black ash (~55 mbsf, 0.75 Ma) is comprised of glassy shards of basaltic andesite (~55 wt% SiO2) that comprise an extension of the dominantly basaltic compositional array of Aogashima volcano (major and trace elements). The evolution of magma chemistry of this black glassy ash and its possible Higashi Aogashima caldera origin are consistent with the hypothesis of submarine rhyolite caldera formation in the Izu arc by Tamura et al. (2009) as follows. Rhyolite calderas have no mantle roots beneath the crust. Instead, Tamura et al. (2009) proposed that dikes from the adjacent basalt volcanoes provide the heat source to partially melt the surrounding crust to produce rhyolite magmas. Thus, dikes from Aogashima volcano and their fractional crystallization may have resulted in andesitic magmas and transferred latent heat to the crust. They could be the heat source that produced the rhyolites and resulting Higashi Aogashima caldera.

Tamura, Gill, Tollstrup et al. (2009). Silicic Magmas in the Izu-Bonin Oceanic Arc and Implications for Crustal Evolution. Journal of Petrology 50, 685-723.