Paleomagnetism and rock-magnetism of basaltic basement rocks from IODP Site C0012, Shikoku Basin

Author(s): Oda, Hirokuni; Yamamoto, Y.; Yamamoto, Yuzuru; Lin, W.; Ishizuka, O.; Zhao, X.; Wu, H.; Torii, M.; Kitamura, Y.; Kanamatsu, Toshiyaki
Author Affiliation(s): Primary:
Advanced Industrial Science and Technology (AIST), Geological Survey of Japan, Tsukuba, Japan
Other:
Kochi University, Japan
Japan Agency for Marine-Earth Science and Technology, Japan
University of California, Santa Cruz, United States
China University of Geosciences, China
Okayama University of Science, Japan
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: The IODP Expeditions (Exps.) 322 & 333 penetrated sediments-basement boundary and recovered successive cores at Site C0012 situated on a topographic high named Kashinosaki Knoll, Shikoku Basin. The collected basement samples are composed of alternating beds of pillow basalts and hyaroclastite and were retrieved by rotary core barrel drilling system. Paleomagnetic measurements on basaltic basement rocks from Site C0012 show that the stable magnetization has reversed polarity. Rock magnetic experiments were conducted to understand the magnetic minerals contributing to the primary magnetization. Thermomagnetic curves during heating in air shows a hump around 500°C which cannot be seen for the curve in vacuum, Ar or He atmosphere. This can be interpreted as a result of oxidation of the magnetic mineral. The results in air, vacuum, Ar and He show maximum curvatures at 326°C, 332°C, 328°C and 303°C, which might show a Curie temperature of the natural magnetic mineral (titanomaghemite). The peaks at around 402°C, 392°C and 424°C in vacuum, Ar and He might correspond to break down (decomposition) of magnetic minerals (titanomaghemite) by heating. A hump at 493°C for the heating curve in He could not be resolved enough in the heating curve up to 527°C. This might be a result of the multiple heatings and heating rates, which suggest the progressive production of titanomagnetite (from titanomaghemite) and subsequent hematite production (reduction in magnetization intensity). Low-temperature magnetic measurements were also conducted and will be interpreted together with Curie temperatures. Paleomagnetic measurements were conducted on samples from Exps. 322&333 to understand the polarity of magnetization, paleolatitude and tectonic rotation. Paleomagnetic samples suffer from drilling induced remanent magnetization (DIRM), however, alternating field demagnetization at 10 mT was enough to remove DIRM to extract characteristic remanent magnetization (ChRM). Paleomagnetic measurements show that the ChRM has reversed polarity. Preliminary results on Exp.322 for 21 samples show that average inclination and paleolatitude was calculated as 26.5±5.5°N suggesting the northward latitudinal translation of 688±611 km since the formation of the seafloor, which is consistent with the northward latitudinal shift of Philippine Sea Plate (Yamazaki et al., 2010). Reconstruction of tectonic rotation was also attempted by using viscous remanent magnetization (VRM) acquired during Brunhes Chron. VRM components were extracted as intersections of great circles from overlapping DIRM and ChRM. The detailed results including those on Exp.333 will be discussed in the presentation.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Basaltic composition; Expedition 322; Expedition 333; IODP Site C0012; Integrated Ocean Drilling Program; Magnetic properties; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Pacific Ocean; Paleomagnetism; Shikoku Basin; West Pacific
Coordinates: N324453 N324453 E1365501 E1365501
Record ID: 2015046388
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