Japan Geoscience Union Meeting 2016

Presentation information


Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG59] Ocean Floor Geoscience

Wed. May 25, 2016 3:30 PM - 5:00 PM 301B (3F)

Convener:*Kyoko Okino(Ocean Research Institute, University of Tokyo), Keiichi Tadokoro(Research Center for Seismology, Volcanology and Earthquake and Volcano Research Center, Nagoya University), Osamu Ishizuka(Geological Survey of Japan, AIST), Tomohiro Toki(Faculty of Science, University of the Ryukyus), Narumi Takahashi(Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology), Chair:Yojiro Yamamoto(Japan Agency for Marine-Earth Science and Technology), Mikiya Yamashita(Japan Agency for Marine-Earth Science and Technology)

4:15 PM - 4:30 PM

[SCG59-10] The crustal structure of the Ojin-Rise Seamounts, North Pacific.

*Shoka Shimizu1, Masao Nakanishi1, Takashi Sano2 (1.Chiba University, 2.National Museum of Nature and Science)

Keywords:Ojin-Rise Seamounts, Shatsky Rise, admittance analysis, gravity, bathymetry feature

Ojin-Rise Seamounts is located between Shatsky Rise and Emperor Seamount Chain. The main portion of Shatsky Rise was formed by impact of the mantle plume head after 148 Ma (Nakanishi et al., 1999). Shatsky Rise consists of three plateau, TAMU, ORI, and Shirshov massifs. The radiometric ages of drilling samples of the three massifs are about 144 Ma for TAMU, 134 Ma for ORI, and about 128 Ma for Shirshov, respectively (Geldmacher et al., 2014; Heaton and Koppers, 2014). The seafloor age around Orin Rise Seamounts is estimated to be 134-125 Ma (Nakanishi et al., 1999). The geophysical measurements (bathymetry, gravity and geomagnetism) and rock sample sampling were conducted in 2014 summer (R/V KAIREI cruise, KR14-07). We therefore present the crustal structure of the Ojin-Rise Seamounts based on the analysis of bathymetric and gravity data.
We use multibeam bathymetric data obtained in KR14-07 and bathymetric grid data reported by Sager et al. (1999) and free-air gravity anomaly data by Sandwell and Smith (2009). We have estimated the oceanic crustal thickness using the method by Kuo and Forsyth (1988) and the state of isostasy and effective elastic thickness using the admittance analysis by McKenzie and Bowin (1976).
Our result shows that the crustal thickness beneath the Ojin-Rise Seamounts is about 12 km, which is two-times thicker than the normal oceanic crustal (e.g., 6 km). The effective elastic thickness is calculated to be about 2.6 km. The state of isostasy is Airy type. We conclude that the Ojin-Rise Seamounts was formed near the spreading ridige about 134-125 Ma. The timing of the formation is close to that of Shirshov Massif, impling that the same volcanic activity might form both Shirshov Massif and Ojin-Rise Seamounts.