Results of physical property measurements obtained during the CHIKYU cruise CK16-01 to hydrothermal fields of the middle Okinawa Trough

Author(s): Tanikawa, W.; Masaki, Y.; Komori, S.; Torimoto, Junji; Makio, M.; Ohta, Y.; Nozaki, T.; Ishibashi, J. I.; Kumagai, H.; Maeda, L.; Hamada, Y.
Author Affiliation(s): Primary:
Kochi Institute for Core Sample Research, Kochi, Japan
Other:
Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
Kyushu University, Fukuoka, Japan
Kyoto University, Kyoto, 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 middle Okinawa trough, along the Ryukyu-arc on the margin of the western Pacific, fosters several hydrothermal fields. The cruise CK16-01 of D/V CHIKYU targeted the Iheya-North Field and Noho hydrothermal site. More than ten-days extensive coring was carried out with Logging While Drilling (LWD) and deployment of Kuroko cultivation apparatus between February 29th to March 17th 2016. Here we present the results of the physical property measurements obtained using Chikyu's on-board laboratory. Cores were sampled among three sites where the seafloor environments were quite different: the Noho site (C9017), a site between the Natsu and Aki sites of the Iheya-North field (C9021), and the Iheya-North Aki site (C9023). Site C9017 was near the center of the hydrothermal activity, and the obtained core was limited 36 m in length and 30% in the recovery rate. At 70 mbsf (meters below seafloor), the grain density and bulk density of the sediment reached their maxim (3.7 g/m3 and 2.7 g/cm3, respectively), while thermal conductivity reached its lowest value (0.6 W/m·K). Site C9021 yielded a 54 m core, with a core recovery rate of 50%. Coarse pumiceous layers were found at 68 mbsf, with a hydrothermally altered layer appearing below 68 mbsf. The mean grain density value was 2.4 g/cm3 and was uniform throughout the core. The mean bulk density value of the pumiceous layers was 1.3 g/cm3, and of the hydrothermally altered layer was 2.1 g/cm3. Site C9023 was close to the active hydrothermal chimneys of the Iheya-North Aki site, and yielded 33 m of core with a core recovery rate of 16%. Massive sulfide layers were found below 48 mbsf with grain density and bulk density values varying between 2.8-4.7 g/cm3 and 1.5-3.9 g/cm3, respectively. Magnetic susceptibility exhibited a high anomaly in a sedimented anhydrite layer found between 95 and 135 mbsf, and a high porosity and low resistivity zone was found below 150 mbsf. Together, these data from drilling cores and onboard analysis provide the first insights into the physical properties of hydrothermal fields in the Okinawa trough. This work was supported by the Council for Science, Technology and Innovation (CSTI) Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation technology for ocean resources exploration" (Lead agency: JAMSTEC)
Year of Publication: 2016
Research Program: IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Geothermal energy; Geothermal fields; Hydrothermal vents; North Pacific; Northwest Pacific; Okinawa Trough; Pacific Ocean; West Pacific
Record ID: 2018001659
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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