Japan Geoscience Union Meeting 2016

Presentation information


Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS16] Drilling Earth Science

Thu. May 26, 2016 3:30 PM - 4:45 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Yasuhiro Yamada(Japan Agency for Marine-Earth Science and Technology (JAMSTEC), R&D Center for Ocean Drilling Science (ODS)), Minoru Ikehara(Center for Advanced Marine Core Research, Kochi University), Yusuke Suganuma(National institute of Polar Research), Kazuno Arai(Japan Agency for Marine-Earth Science and Technology), Keita Umetsu(Japan Agency for Marine Earth Science and Technology)

3:30 PM - 4:45 PM

[MIS16-P09] Physical properties of Fore-arc-basalt and Boninite inthe drilled cores during the IODP Expedition 352

*Mutsumi Honda1, Katsuyoshi Michibayashi2, Yuzuru Yamamoto3, Nana Kamiya4, Tohru Watanabe5, Tetsuya Sakuyama6 (1.Graduate School of Integrated Science and Technology, Shizuoka University, 2.Institute of Geosciences, Shizuoka University, 3.JAMSTEC, 4.Graduate School of Integrated Sciences, Nihon University, 5.Graduate School of Science and Engineering, Toyama University, 6.Faculty of Science, Osaka City University)

Keywords:IODP Exp.352, Izu-Bonin forearc, volcanic rocks, density, P-wave velocity, Magnetic Susceptibility

The Izu-Bonin-Mariana (IBM) arc, which is located to the southeast from Japan, is a typical intra-oceanic arc system and is the type locality for subduction initiation. IBM project, which is a part of International Ocean Discovery Program (IODP) expeditions, is aimed to understand subduction initiation, arc evolution, and continental crust formation. Expedition 352 is one of the IBM projects and that has drilled four sites at the IBM fore-arc in the period from 30th of July to 29th of September, 2014. Expedition 352 has successfully recovered fore-arc basalts and boninites related to seafloor spreading during the subduction initiation as well as the earliest arc development. The fore-arc basalts were recovered from two sites (U1440 and U1441) at the deeper trench slope to the east, whereas the boninites were recovered from two sites (U1439 and U1442) at the shallower slope to the west.
In this study, we studied textures and physical properties of both the fore-arc basalt and the boninite samples recovered by IODP Expedition 352. The fore-arc basalt samples showed aphyric texture, whereas the boninites showed hyaloclastic, aphyric and porphyritic textures. For the physical properties, we measured density, porosity, P-wave velocity and anisotropy of magnetic susceptibility. P-wave velocities were measured under ordinary and confining pressure.
As a result, the densities are in a range between 2 g/cm3 and 3 g/cm3. The porosities are in a range between 5 % and 40 %. The P-wave velocities are in a wide range from ~3 km/s to ~5.5 km/s and have a positive correlation to the densities. The magnetic susceptibilities showed bimodal distributions so that the physical properties were classified into two groups: a high magnetic susceptibility group (>5×10-3) and a low magnetic susceptibility group (<5×10-3). The high magnetic susceptibility group is almost identical with the fore-arc basalt and boninite samples with the higher correlation trend between the P-wave velocities and the densities, whereas the low magnetic susceptibility group is only the boninite samples with the lower correlation trend between the P-wave velocities and the densities. It suggests that the densities could be related to the occurrence of magnetite in the samples, since the magnetic susceptibilities were remarkably correlated with the relationships between P-wave velocities and densities. In addition, these trends have also been found in the physical properties measured on board during Expedition 352.