Identification and characterization of the active hydrothermal deposits in Okinawa Trough, SW Japan; estimates from logging-while-drilling

Author(s): Saito, Saneatsu; Sanada, Yoshinori; Moe, Kyaw; Kido, Yukari Nakasa; Hamada, Yohei; Kumagai, Hidenori; Nozaki, Tatsuo; Takai, Ken; Suzuki, Katsuhiko
Author Affiliation(s): Primary:
Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan
Kochi Institute for Core Sample Research, Japan
Volume Title: AGU 2015 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2015; American Geophysical Union 2015 fall meeting, San Francisco, CA, Dec. 14-18, 2015. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: A scientific drilling expedition was conducted at an active hydrothermal field on the Iheya-North Knoll by D/V Chikyu in 2014 (Expedition 907) as a part of "Next-generation Technology for Ocean Resources Survey" of the Cross-ministerial Strategic Innovation Promotion Program. During the expedition logging while drilling (LWD) was deployed to constrain the area of the fluid reservoir beneath seafloor followed by three coring holes down to 150 meter below the seafloor (mbsf). The LWD system is composed of arcVISION for resistivity and natural gamma ray measurement and TeleScope for real-time transmission of drilling parameters and arcVISION data. Five sites (C9011-15) at the Iheya-North Original Site and one site (C9016) at Aki Site were drilled with LWD. At C9012 and C9016, the arcVISION detected temperature anomaly up to 84°C at 234 mbsf and up to 39°C at 80 mbsf, respectively. The temperature quickly increases at that depth and it would reflect the existence of high-temperature heat source along borehole. Due to the continuous fluid circulation during drilling, the measured temperature does not indicate in-situ temperature, but it reflects the heat disturbed by the cold circulated water instead. High quality resistivity and natural gamma ray data were acquired at six sites. The log curves at Site C9016 show characteristic response; the natural gamma ray log exhibits extremely high radiation (>500 gAPI) at 7-13 and 23-31 mbsf (Zone A). In the underlying interval of 31-40 mbsf, the resistivity log exhibits extremely low value (<0.2 ohm-m) (Zone B). Then the resistivity log exhibits higher value (∼10 ohm-m) and the natural gamma ray log shows very low radiation (<50 gAPI) at the interval of 41-48 mbsf (Zone C). The log characteristics in Zone A, B, and C can be interpreted as a series of K-rich alteration zone, sulfide zone, and low-K hard (silicified) sediments, respectively. The LWD-based lithological interpretation was confirmed by the following core description. Zones A and B can be correlated to altered clay zone and sulfide zone including sphalerite, galena, chalcopyrite, and pyrite. Our results show that LWD is a powerful tool for the identification and characterization of submarine hydrothermal deposits and LWD survey enhances the successful recovery of sulfide samples.
Year of Publication: 2015
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; Cores; Expedition 907; IODP Site C9012; IODP Site C9016; International Ocean Discovery Program; Marine sediments; North Pacific; Northwest Pacific; Okinawa Trough; Pacific Ocean; Sediments; West Pacific
Record ID: 2016096105
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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