Attempted Ultradeep Drilling to the Nankai Trough Subduction Zone Plate Boundary: The Saga of IODP NanTroSEIZE Expedition 358
Abstract
IODP Expedition 358 was carried out for 167 days (October 2018 - March 2019) on D/V Chikyu, in an attempt to reach a plate boundary fault zone at seismogenic depths for the first time in scientific ocean drilling. This was the intended culmination of the NanTroSEIZE project. The goal was to extend IODP Hole C0002P from 3058 meters below sea floor (mbsf) to ~5200 mbsf, crossing the seismically-interpreted main décollement fault zone with logging while drilling tools (LWD), cuttings and mud gas sampling, and coring, employing a drilling sidetrack to create a new hole designated C0002Q. Although drilling reached 3262.5 mbsf, the deepest to date in all of scientific ocean drilling, the effort to drill to and sample the target - the megathrust fault zone - was not successful. Multiple operational challenges in drilling and borehole engineering stymied the effort to deepen the hole, leading to its termination after 130 days on site. With the remaining time, drilling of contingency Sites C0024 and C0025 was performed.
Site C0024 targeted the frontal thrust region to sample and log hanging wall rocks and the shallow décollement zone, while Site C0025 accessed sediments of the Kumano forearc basin. Site C0002 samples and logs provided new insight into the tectonic history of the inner accretionary wedge. Site C0024 logs were used to characterize the frontal plate boundary fault zone at >800 mbsf, finding a ~40 m wide zone of fracture and deformation with several localized apparent fault zones. Borehole breakouts indicate a stress orientation consistent with other forearc sites in the NanTroSEIZE transect. Site C0025 provided a sedimentary record of the development of the Kumano forearc basin and the gas hydrate system contained within it. Initial results from the expedition will be reviewed, and a preliminary assessment of the challenges for deep riser drilling will be made.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T41I0233T
- Keywords:
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- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8158 Plate motions: present and recent;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS;
- 8488 Volcanic hazards and risks;
- VOLCANOLOGY