Physical properties of fore-arc basalt and boninite in Izu-Bonin-Mariana Forearc recovered by IODP Expedition 352

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Author(s): Honda, M.; Michibayashi, K.; Almeev, R. R.; Christeson, G. L.; Sakuyama, T.; Yamamoto, Y.; Watanabe, T.
Author Affiliation(s): Primary:
Shizuoka University, Shizuoka, Japan
Leibniz University of Hannover, Institute of Mineralogy, Hanover, Germany
UTIG, United States
Osaka University, Japan
Japan Agency for Marine-Earth Science and Technology, Japan
University of Toyama, Japan
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Izu-Bonin-Mariana (IBM) arc is a typical intraoceanic arc system and is the type locality for subduction initiation. IODP-IBM project 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. 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 351.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Andesites; Basalts; Boninite; Expedition 352; IODP Site U1440; IODP Site U1441; Igneous rocks; International Ocean Discovery Program; Mineral composition; North Pacific; Northwest Pacific; Pacific Ocean; Volcanic rocks; West Pacific
Coordinates: N282659 N282700 E1424513 E1424513
N282538 N282538 E1424332 E1423332
Record ID: 2017062829
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