Southern Mariana Trough back-arc spreading system with three different hydrothermal activities

Nobukazu Seama^1,4, Toshinori Sato², Takehi Isse³, Mariko Mizuno², Maho Kimura⁴, Yuki Shibata⁴ (Onboard Scientists)
Kyoko Okino⁵, Masanao Shinohara³, Yoshifumi Nogi⁶, Takeshi Tsuji⁷, Kimihiro Mochizuki³, Tomoaki Yamada³ (Scientists on land)
Satoshi Okada⁸ (Marine Technician)

¹ Research Center for Inland Seas, Kobe University, ² Graduate School of Science, Chiba University, ³ Earthquake Research Institute, University of Tokyo, ⁴ Graduate School of Science, Kobe University, ⁵ Atmosphere and Ocean Research Institute, University of Tokyo, ⁶ National Institute of Polar Research,⁷ Engineering Geology, Kyoto University, ⁸ Nippon Marine Enterprises, Ltd.

Summary

We successfully deployed 11 OBEMs and 15 OBS across the Southern Mariana Trough back-arc spreading system (Figure1 and Table 1). We started our observation; the measurement of magnetic and electric field variations by OBEMs and seismic observation by OBSs at the ocean bottom. The observation continues up to the recovery of OBEM and OBS during another Yokosuka cruise in this November. Further, we conducted surface geophysical survey to collect multi-narrow beam bathymetry, magnetic field, and gravity field data mainly during night time, which cover total 1040 miles in the survey area (Figure 2). These observed data will be used to provide geophysical constraint on geodynamics of the Southern Mariana Trough back-arc spreading system with three different hydrothermal activities. The observed data will be analyzed to derive upper mantle structure, crustal structure, hypocenter distribution, and tectonic history, which will provide important constraint on geodynamics of the Southern Mariana Trough back-arc spreading system with three different hydrothermal activities.

Figure 1a.
Location map of OBEM (crosses) and OBS (circles). Colors of circles show different types of OBSs (white, black, and red correspond to LTOBS_ERI, STOBS_ERI, and STOBS_Chiba types of OBSs, respectively). Location of Figure 1b is shown by square.

Figure 1b.
Location map of OBEM and OBS near the spreading center. Symbols are the same as Figure 1a. Three hydrothermal fields that extrude different water contents are also shown by yellow stars.

Table 1. Location and Time of OBEM and OBS deployment.

Figure 2.
Ship tracks (red and black lines) of the cruise in the survey area and black lines shows ship tracks for the surface geophysical survey

Acknowledgement
We gratefully recognize the efforts of the officers and crew (Satoshi Susami, captain) of the R/V Yokosuka during the cruise. We thank all the support staffs in JAMSTEC. This research was supported by the scientific program “TAIGA (Trans-crustal Advection and In-situ reaction of Global sub-seafloor Aquifer)” sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.