Paleomagnetic records of core samples of the plate-boundary thrust drilled during the IODP Japan Trench Fast Drilling Project (JFAST)

Author(s): Mishima, T.; Yang, Tao; Ujiie, K.; Kirkpatrick, James D.; Chester, F. M.; Moore, J. Casey; Rowe, Christie D.; Regalla, Christine; Remitti, Francesca; Kameda, J.; Wolfson-Schwehr, Monica; Bose, Santanu; Ishikawa, T.; Toy, Virginia G.
Author Affiliation(s): Primary:
Osaka City University, Graduate School of Science, Osaka, Japan
Other:
China Earthquake Administration, China
University of Tsukuba, Japan
Colorado State University, United States
Texas A&M University, United States
University of California, Santa Cruz, United States
McGill University, Canada
Pennsylvania State University, United States
Universita di Modena e Reggio Emilia Largo, Italy
University of Tokyo, Japan
University of New Hampshire, United States
University of Calcutta, India
Japan Agency for Marine-Earth Science and Technology, Japan
University of Otago, New Zealand
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: IODP Expedition 343, Japan Trench Fast Drilling Project (JFAST), drilled across the plate-boundary decollement zone near the Japan Trench where large slip occurred during the March 2011 Tohoku-oki earthquake. We conducted paleomagnetic measurements of the core sample retrieved from the highly-deformed sediments comprising the plate-boundary decollement zone. Whole-round samples for structural analyses from five depth intervals of the core (0-12 cm, 12-30 cm, 43-48 cm, 48-58 cm, and 87.5-105 cm), were trimmed into oriented slabs with typical dimensions of 3×3×5 cm that are now being used to make petrographic sections for microstructural and chemical study. The remainder of the core sample was split into working and archive halves. We measured remanent magnetization of 16 trimmed slabs and the archive half of the core sample. The slabs were subjected to natural remanent magnetization (NRM) measurements in 0.5-1 cm intervals and progressive alternating field demagnetization (AFD) up to 80 mT with a 2G755 pass-through superconducting rock magnetometer at Kochi University. The archive half of the core sample was subjected to NRM measurement and AFD up to 20 mT with a 2G760 superconducting rock magnetometer installed on R/V Chikyu. Typically, two or three paleomagnetic components were isolated during the AFD of slab samples up to 80 mT. One 'soft' component was demagnetized below 20-30 mT, and another 'hard' component was not demagnetized even with AFD in 80 mT. A third component may be separated during AFD at the intermediate demagnetizing field, and may overlap the soft and hard components. The multiple slab samples cut from an identical whole-round sample have generally consistent paleomagnetic direction of the hard component. Contrastingly, the direction of the soft component is less consistent between adjacent slabs, and even varies within a single slab. The direction variation of the soft component possibly reflects the cm-scale strain and rotation of the highly-deformed sediments within the plate-boundary decollement zone. Studies of the relationship of the direction variation to the microstructure are ongoing, and will be reported at the meeting. The consistency of the hard component direction within highly deformed sediment implies it was recently acquired. Further studies of the acquisition mechanism of the hard component are also intended.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Expedition 343; Expeditions 343/343T; Integrated Ocean Drilling Program; Japan Trench; Japan Trench Fast Drilling Project; North Pacific; Northwest Pacific; Pacific Ocean; Paleomagnetism; Plate boundaries; Plate tectonics; West Pacific
Coordinates: N375619 N375620 E1435449 E1435447
Record ID: 2015031182
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