Research activity information

• Intermittent non-axial dipolar-field dominance of twin Laschamp excursions

  Hyodo, Masayuki, Nakagawa, Takeshi, Matsushita, Hayato, Kitaba, Ikuko, Yamada, Keitaro, Tanabe, Shota, Bradak, Balazs, Miki, Masako, McLean, Danielle, Staff, Richard A., Smith, Victoria C., Albert, Paul G., Ramsey, Christopher Bronk, Yamasaki, Akiteru, Kitagawa, Junko

  Geomagnetic excursions represent the dynamic nature of the geodynamo. Accumulated palaeomagnetic records indicate that such excursions are dominated by dipolar-fields, but exhibit different structures. Here we report a palaeomagnetic record from the varved sediments of Lake Suigetsu, central Japan, which reveals fine structures in the Laschamp Excursion and a new post-Laschamp excursion that coincides with the Δ14C maxima. The record's high-resolution chronology provides IntCal20 mid-ages and varve-counted durations. Both excursions comprise multiple subcentennial directional-swings. Simulations of filtering effects on sediment-magnetisations demonstrate that this high-resolution record replicates most of the features in existing, lower-resolution Laschamp excursion records, including the apparent clockwise open-loop of the virtual geomagnetic pole pass. The virtual geomagnetic poles during the ‘swing’ phases make four clusters centred in hemispherically-symmetric regions, three of which encompass the virtual geomagnetic poles associated with the Laschamp Excursion recorded in lavas at various locations. The stationary dipolar-field sources under each cluster should have intermittently dominated one after another during the excursions.

  Apr. 2022, Communications Earth & Environment, 3(1) (1), 79, English

  [Refereed]

  Scientific journal


• Paleomagnetism, paleointensity and geochronology of a Proterozoic dolerite dyke from southern West Greenland

  Masako Miki, Hanae Seki, Yuhji Yamamoto, Chitaro Gouzu, Hironobu Hyodo, Koji Uno, Yo-ichiro Otofuji

  Elsevier BV, Sep. 2020, Journal of Geodynamics, 139, 101752 - 101752

  [Refereed]

  Scientific journal


• A centennial-resolution terrestrial climatostratigraphy and Matuyama–Brunhes transition record from a loess sequence in China

  Hyodo, Masayuki, Banjo, Kenta, Yang, Tianshui, Katoh, Shigehiro, Shi, Meinan, Yasuda, Yuki, Fukuda, Jun-ichi, Miki, Masako, Bradák, Balázs

  Terrestrial records of the last geomagnetic reversal often have few age constraints. Chronostratigraphy using suborbital-scale paleoceanic events during marine isotope stage 19 may contribute to solving this problem. We applied the method to an 8 m long, high-resolution paleomagnetic record from a loess sequence in China and revealed millennial-to-sub-centennial scale features of the Matuyama–Brunhes (MB) transition. All samples were subjected to progressive thermal demagnetization with 14–15 steps up to 650–680 °C. As a result, 96% of the samples yielded a high-quality remanent magnetization. The MB transition terminated with a 75 cm thick zone with nine polarity flips. The polarity flip zone, dated at about 779–777 ka, began between the warm events “I” and “J” and terminated at the end of the cooling event coincident with the lowest axial-dipole strength interval. Most polarity flips occurred within 70 years. The virtual geomagnetic poles (VGPs) in the upper polarity flip zone clustered in the SW Pacific region, where the MB transitional VGPs from lavas of the Hawaiian and Canary Islands and lacustrine deposits of Java also clustered. These sites were probably dominated by dipolar fields. The absence of transitional fields across polarity flips implies a short time span for averaging fields due to a thin loess-magnetization lock-in zone. The reverse-to-normal polarity reversal dated at about 778 ka in Lingtai occurred at the end of the SW Pacific VGP zone, an important key bed for MB transition stratigraphy. The reversal is a good candidate for the main MB boundary. We found an excursion at about 766 ka spanning about 1 ka.

  Jun. 2020, Progress in Earth and Planetary Science, 7, 26 - 26, English

  [Refereed]

  Scientific journal


• Tectonic evolution of the Malay Peninsula inferred from Jurassic to Cretaceous paleomagnetic results

  Yo-ichiro Otofuji, Yuji T. Moriyama, Maiko P. Arita, Masanari Miyazaki, Kosuke Tsumura, Yutaka Yoshimura, Mustaffa Kamal Shuib, Masatoshi Sone, Masako Miki, Koji Uno, Yutaka Wada, Haider Zaman

  Feb. 2017, Journal of Asian Earth Sciences, 134, 130 - 149, English

  [Refereed]

  Scientific journal


• Paleomagnetism of Late Jurassic to Early Cretaceous red beds from the Cardamom Mountains, southwestern Cambodia: Tectonic deformation of the Indochina Peninsula

  Yukiho Tsuchiyama, Haider Zaman, Sieng Sotham, Yos Samuth, Eiichi Sato, Hyeon-Seon Ahn, Koji Uno, Kosuke Tsumura, Masako Miki, Yo-ichiro Otofuji

  Elsevier BV, Jan. 2016, Earth and Planetary Science Letters, 434, 274 - 288

  [Refereed]


• Palaeomagnetism and geochronology of the Proterozoic dolerite dyke from southwest Greenland: indication of low palaeointensity

  Masako Miki, Aya Taniguchi, Masahiko Yokoyama, Chitaro Gouzu, Hironobu Hyodo, Koji Uno, Haider Zaman, Yo-ichiro Otofuji

  Lead, Oxford University Press (OUP), Oct. 2009, Geophysical Journal International, 179(1) (1), 18 - 34

  [Refereed]

  Scientific journal


• Geomagnetic paleosecular variation in Easter Island, the southeast Pacific

  Masako Miki, Hiroo Inokuchi, Satoru Yamaguchi, Jun-ichi Matsuda, Keisuke Nagao, Nobuhiro Isezaki, Katsumi Yaskawa

  Lead, Elsevier BV, Mar. 1998, Physics of the Earth and Planetary Interiors, 106(1-2) (1-2), 93 - 101

  [Refereed]

  Scientific journal


• Preliminary palaeomagnetic results of an Archaean dolerite dyke of west Greenland: geomagnetic field intensity at 2.8 Ga

  Chiyo Morimoto, Yo-ichiro Otofuji, Masako Miki, Hidefumi Tanaka, Tetsumaru Itaya

  Oxford University Press (OUP), Mar. 1997, Geophysical Journal International, 128(3) (3), 585 - 593

  [Refereed]

  Scientific journal


• Two‐phase opening model for the Okinawa Trough inferred from paleomagnetic study of the Ryukyu arc

  Masako Miki

  Tertiary volcanic and sedimentary rocks were collected at 50 sites of both the central Ryukyu arc and the southern Ryukyu arc for a paleomagnetic and geochronological study, in an attempt to understand the opening of the Okinawa Trough back arc basin. Stable primary components of remanent magnetization were isolated through both thermal and alternating field demagnetization experiments from 12 sites of three geological units of the central Ryukyu arc and from 12 sites of two geological units of the southern Ryukyu arc. The paleomagnetic results were compared with the Tertiary apparent pole wander path of Eurasia in order to investigate the tectonic movement of the Ryukyu arc with respect to the Asian continent. The comparison and the radiometric ages indicate that the southern Ryukyu arc rotated clockwise through 25° between 10 Ma and 6 Ma. In contrast, the central Ryukyu arc experienced little rotational motion since 17 Ma. We propose the following two‐phase opening model for the Okinawa Trough opening. The first stage took place between 10 Ma and 6 Ma. The southern part of the trough opened by means of a “wedge” mode to cause the clockwise rotation of the southern Ryukyu arc. In the central part the “parallel” opening occurred, and the Ryukyu arc drifted without any rotation. The second phase started recently in the whole Okinawa Trough. It is observed as the present activities in the trough.

  Lead, American Geophysical Union (AGU), May 1995, Journal of Geophysical Research: Solid Earth, 100(B5) (B5), 8169 - 8184

  [Refereed]


• Palaeomagnetism and K-Ar Ages of Neogene Rocks of Northern Taiwan: Tectonics of the Arc Junction of Ryukyu and Luzon Arcs

  Masako Miki, Masahide Furukawa, Yo-Ichiro Otofuji, Shuhjong Tsao, Tunyow Huang

  Lead, Oxford University Press (OUP), Aug. 1993, Geophysical Journal International, 114(2) (2), 225 - 235

  [Refereed]


• Reply to comment by L. Ratschbacher and E. Appel on “Paleomagnetic study of the Eocene Quxu pluton of the Gangdese Belt: Crustal deformation along the Indus-Zangbo suture zone in Southern Tibet”

  Yo-ichiro Otofuji, Masako Miki, Fumiyuki Murata

  Elsevier BV, Mar. 1993, Earth and Planetary Science Letters, 115(1-4) (1-4), 292 - 294

  [Refereed]

  Scientific journal


• Paleomagnetic study of Cretaceous rocks from the Yangtze block, central Yunnan, China: implications for the India-Asia collision

  Shoubu Funahara, Nobukazu Nishiwaki, Masako Miki, Fumiyuki Murata, Yo-ichiro Otofuji, Yi Zhao Wang

  Elsevier BV, Sep. 1992, Earth and Planetary Science Letters, 113(1-2) (1-2), 77 - 91

  [Refereed]


• Report on DELP 1988 Cruises in the Okinawa Trough : Part 5. Measurement of the Three Components and Total Intensity of the Geomagnetic Field in the Okinawa Trough

  Furukawa Masahide, Kondo Shinya, Miki Masako, Isezaki Nobuhiro

  application/pdf

  東京大学地震研究所, Jun. 1991, Bulletin of the Earthquake Research Institute, University of Tokyo, 66(1) (1), 91 - 150, English


• Opening mode of the Okinawa Trough: paleomagnetic evidence from the South Ryukyu Arc

  M. Miki, T. Matsuda, Y. Otofuji

  Lead, Elsevier BV, Apr. 1990, Tectonophysics, 175(4) (4), 335 - 347

  [Refereed]

  Scientific journal

• American Geophysical Union

  - Present


• Society of Geomagnetism and Earth, Planetary and Space Sciences