日本地球惑星科学連合2018年大会

講演情報

[JJ] Eveningポスター発表

セッション記号 S (固体地球科学) » S-CG 固体地球科学複合領域・一般

[S-CG61] 海洋底地球科学

2018年5月23日(水) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:沖野 郷子(東京大学大気海洋研究所)

[SCG61-P12] Magnetic anomaly lineations of the Jurassic Pacific Plate

*加倉井 玲子1中西 正男2石原 丈実3 (1.千葉大学理学部地球科学科、2.千葉大学大学院理学研究院 地球科学研究部門、3.国立研究開発法人産業技術総合研究所地質調査総合センター)

キーワード:ジュラ紀、太平洋プレート、磁気異常縞模様

We present the magnetic anomaly lineation map of the Jurassic Pacific plate. The study area is bounded to the west by the Izu-Ogasawara and Mariana trenches. The Marcus Island is located in the central portion of the study area. The Jurassic Pacific plate was formed at the plate boundaries between Pacific and Izanagi plates and Pacific and Farallon plates. Magnetic anomaly lineations younger than M29 (159 Ma) in the study area were identified by Nakanishi et al. (1989) and (1992), but those older than M29 have been not clearly identified. The ambiguity of the older magnetic anomaly lineations are mainly due to the small amplitude of magnetic anomalies and that the vagueness of the Jurassic geomagnetic polarity time scale. Several studies proposed the geomagnetic polarity time scales, but no conclusive timescale has been established (e.g., Sager et al. 1998; Tivey et al., 2006).

The geomagnetic data used for this study were acquired by the Hydrographic and Oceanographic Department of the Japan Coast Guard for the Extended Continental Shelf Survey (e.g., Fujisawa, 2009). Additional shipboard geomagnetic data were obtained from the databases of National Oceanic and Atmospheric Administration/National Centers for Environmental Information (NOAA/NCEI) and Japan Agency for Marine-Earth Science and Technology (JAMSTEC). We also used unpublished data obtained by Geological Survey of Japan (GSJ) and Ocean Research Institute, the University of Tokyo (ORI, UT). We used the leveling method proposed by Ishihara (2015) to reduce crossover differences of geomagnetic data.

Our magnetic anomaly map revealed the lineated magnetic anomalies in the areas where previous works did not identify any magnetic anomaly lineations. The strikes of the lineated magnetic anomalies are the same as that of the lineation younger than M29. Our temporary identification indicates the age of the lineated magnetic anomalies is older than Lineation M29. We found several magnetic bights in the study area, implying the configuration of the Pacific-Izanagi-Farallon triple junction was a ridge-ridge-ridge before M29.