Skip to main content

Advertisement

Paleomagnetism of Unzen volcano: A volcanic record (Senbongi excursion) of the Iceland Basin event and the Brunhes VGP distribution for Japan

Abstract

A paleomagnetic study was carried out on volcanic rocks from Unzen volcano: samples were collected from a total of 69 sites with 19 sites in pyroclastic flows and 50 sites in lava flows. Ages for the flows were determined either by K-Ar methods or detailed field surveys, and indicate that all of the flows were deposited during the Brunhes chron. After demagnetization 10 pyroclastic and 48 lava flows had stable site-mean directions. One lava flow in the Senbongi area with a K-Ar age of 197±17 ka had an intermediate virtual geomagnetic pole (VGP) at 8.3°N, 21.6°E. The age and VGP position apparently correlate with the Iceland Basin event, suggesting that it is a record of the event on volcanic rocks. Our study added 53 Brunhes-aged VGPs to the overall collection for Japan, increasing it by 40% to a total of 175 VGPs. After excluding all site-mean directions having α95 > 10° and VGP latitude < 50°, the remaining 148 VGPs have a mean pole at 89.7°N, 40.9°E (A95 = 2.2°) showing no significant deviation from the geographic pole. The angular standard deviation (ASD) was calculated as 15.2° ± 1.2° (N = 148), which is compatible with paleosecular variation models from the literature. However, the data set was found to deviate from a Fisher distribution. The actual meaning of the ASD value after removing the intermediate VGPs needs to be reconsidered.

References

  1. Champion, D. E., M. A. Lanphere, and M. A. Kuntz, Evidence for a new geomagnetic reversals in the Brunhes and Late Matuyama polarity chrons, J. Geophys. Res., 93, 11667–11680, 1988.

  2. Channell, J. E. T., Geomagnetic paleointensity and directional secular variation at Ocean Drilling Program (ODP) Site 984 (Bjorn Drift) since 500 ka: Comparisons with ODP Site 983 (Gardar Drift), J. Geophys. Res., 104, 22937–11951, 1999.

  3. Channell, J. E. T., D. A. Hodell, and B. Lehman, Relative geomagnetic paleointensity and δ18O at ODP Site 983 (Gardar Drift, North Atlantic) since 350 ka, Earth Planet. Sci. Lett., 153, 103–118, 1997.

  4. Cox, A., A paleomagnetic study of secular variation in New Zealand, Earth Planet. Sci. Lett., 6, 257–267, 1969a.

  5. Cox, A., Confidence limits for the precision parameter κ, Geophys. J. R. astr. Soc., 18, 545–549, 1969b.

  6. Danhara, T., H. Iwano, H. Hoshizumi, and K. Watanabe, Fission track dating of very young zircon from the Unzen volcano, Prog. Abstr., Volcanol. Soc. Jpn., 2, 51, 1993 (in Japanese).

  7. Heki, K., Paleomagnetic study of the Higashi-Izu monogenetic volcano group and pyroclastic flow deposits in Kagoshima Prefecture: Paleosecular variation during the last 40,000 years in Japan, J. Geomag. Geoelectr., 35, 383–390, 1983.

  8. Herrero-Bervera, E., C. E. Helsley, A. M. Sarna-Wojcicki, K. R. Lajoie, C. E. Meyer, M. O. McWilliams, R. M. Negrini, B. D. Turrin, J. M. Donnelly-Nolan, and J. C. Liddicoat, Age and correlation of a paleo-magnetic episode in the western United States by 40Ar/39Ar dating and tephrochronology: The Jamaica, Blake, or a new polarity episode?, J. Geophys. Res., 10, 24091–24103, 1994.

  9. Hoshizumi, H., K. Uto, and K. Watanabe, Geology and eruptive history of Unzen volcano, Shimabara Peninsula, Kyushu, SW Japan, J. Volcanol. Geotherm. Res., 89, 81–94, 1999.

  10. Hoshizumi, H., K. Uto, and A. Matsumoto, Geology and petrology of Unzen volcano, Field Guidebook, A3: Unzen and Aso Volcanoes, XXIII General Assembly of the International Union of Geodesy and Geophysics, p. 11–19, 2003.

  11. Ishikawa, N. and T. Tagami, Paleomagnetism and fission-track geochronology on the Goto and Tsushima Islands in the Tsushima strait area: Implications for the opening mode of the Japan Sea, J. Geomag. Geoelectr., 43, 229–253, 1991.

  12. Kawai, N., K. Yaskawa, T. Nakajima, M. Torii, and S. Horie, Oscillating geomagnetic field with a recurring reversal discovered from Lake Biwa, Proc. Jpn. Acad., 48, 186–190, 1972.

  13. Laj, C., C. Kissel, and A. P. Roberts, Geomagnetic field behavior during the Iceland Basin and Laschamp geomagnetic excursions: A simple transitional field geometry?, Geochem. Geophys. Geosyst., 7, Q03004, doi:10.1029/2005GC001122, 2006.

  14. McElhinny, M. W. and P. L. McFadden, Palaeosecular variation over the past 5 Myr based on a new generalized database, Geophys. J. Int., 131, 240–252, 1997.

  15. McFadden, P. L., Rejection of palaeomagnetic observations, Earth Planet. Sci. Lett., 6, 392–395, 1982.

  16. McWilliams, M., Global correlation of the 223 ka Pringle Falls Event, Int. Geol. Rev., 43, 191–195, 2001.

  17. Morinaga, H., T. Matsumoto, Y. Okimura, and T. Matsuda, Paleomag-netism of Pliocene to Pleistocene lava flows in the northern part of Hyogo prefecture, Southwest Japan and Brunhes Chron paleosecular variation in Japan, Earth Planets Space, 52, 437–443, 2000.

  18. Nakada, S. and H. Kamata, Petrogenetical relationship of basalts and andesites in southern part of the Shimabara Peninsula, Kyushu, Japan, J. Volcanol. Soc. Jpn., 33, 273–289, 1988 (in Japanese with English abstract).

  19. Nakada, S., H. Shimizu, and K. Ohta, Overview of the 1990-1995 eruption at Unzen Volcano, J. Volcanol. Geotherm. Res., 89, 1–22, 1999.

  20. National Astronomical Observatory Japan, Rika Nenpyo (Chronological Scientific Tables) 2005, Maruzen, Tokyo, 2004.

  21. Oda, H., K. Nakamura, T. Ikehara, M. Nishimura, and O. Khlystov, Paleomagnetic record from Academician Ridge, Lake Baikal: A reversal excursion at the base of marine oxygen isotope stage 6, Earth Planet. Sci. Lett., 202, 117–132, 2002.

  22. Otake, H., H. Tanaka, M. Kono, and K. Saito, Paleomagnetic study of Pleistocene lavas and dikes of the Zao Volcano Group, J. Geomag. Geoelectr., 45, 595–612, 1993.

  23. Roberts, N. and J. D. A. Piper, A description of the behaviour of the Earth’s magnetic field, in Geomagnetism, Vol. 3, edited by J. A. Jacobs, pp. 163–260, Academic Press, London, 1989.

  24. Ryan, W. B. F. and J. D. Flood, Preliminary paleomagnetic measurements on sediments from the Ionian (Site 125) and Tyrrhenian (Site 132) basins of the Mediterranean Sea, Initial Rep. Deep Sea Drill. Proj., 13, 599–603, 1972.

  25. Shane, P., T. Black, and J. Westgate, Isothermal plateau fission-track age for a paleomagnetic excursion in the Mamaku Ignimbrite, New Zealand, and implication for late Quaternary stratigraphy, Geophys. Res. Lett., 21, 1695–1698, 1994.

  26. Shibuya, H., J. Cassidy, I. E. M. Smith, and T. Itaya, A geomagnetic excursion in Brunhes epoch recoreded in New Zealand basalts, Earth Planet. Sci. Lett., 111, 41–48, 1992.

  27. Shibuya, H., J. Cassidy, I. E. M. Smith, and T. Itaya, Paleomagnetism of young New Zealand basalts and longitudinal distribution of paleosecular variation, J. Geomag. Geoelectr., 47, 1011–1022, 1995.

  28. Tanaka, H. and T. Kobayashi, Paleomagnetism of the late Quaternary Ontake Volcano, Japan: directions, intensities, and excursions, Earth Planets Space, 55, 189–202, 2003.

  29. Tanaka, H., G. M. Turner, B. F. Houghton, T. Tachibana, M. Kono, and M. O. McWilliams, Palaeomegnetism and chronology of the central Taupo Volcanic Zone, New Zealand, Geophys. J. Int., 124, 919–934, 1996.

  30. Tanaka, H., H. Hoshizumi, Y. Iwasaki, and H. Shibuya, Applications of pa-leomagnetism in the volcanic field: A case study of the Unzen Volcano, Japan, Earth Planets Space, 56, 635–647, 2004.

  31. Tsunakawa, H. and Y. Hamano, Paleomagnetic study of the Ashitaka dike swarm in Central Japan, J. Geomag. Geoelectr., 40, 221–226, 1988.

  32. Tsunakawa, H., K. Heki, and K. Amano, Paleomagnetism of the Shimokura dike swarm in Northeast Japan, J. Geomag. Geoelectr., 37, 979–985, 1985.

  33. Vandamme, D., A new method to determine paleosecular variation, Phys. Earth Planet. Inter., 85, 131–142, 1994.

  34. Watanabe, K., H. Hoshizumi, and T. Itaya, K-Ar ages of Unzen volcano in Kyushu, Japan-with some aspects of geology of Mayu-yama, Mem. Fac. Educ. Kumamoto Univ., 42, 35–41, 1993.

  35. Wollin, G., D. B. Ericson, W. B. F. Ryan, and J. H. Foster, Magnetism of the Earth and climate changes, Earth Planet. Sci. Lett., 12, 175–183, 1971.

Download references

Author information

Correspondence to Hidetoshi Shibuya.

Rights and permissions

Reprints and Permissions

About this article

Key words

  • Geomagnetic excursion
  • Iceland basin event
  • PSVL
  • Unzen volcano