Open AccessPalaeomagnetism of the Older Ontake Volcano, Japan: contributions to the palaeosecular variation for 750–400 Ka, the lower half of the Brunhes Chron
Author(s) -
Tanaka Hidefumi,
Kamizaki Rieko,
Yamamoto Yuhji
Publication year - 2007
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2006.03306.x
Subject(s) - geology , volcano , paleomagnetism , seismology , variation (astronomy) , magnetic declination , geodesy , geophysics , earth's magnetic field , astronomy , magnetic field , physics , quantum mechanics
SUMMARY Studies of palaeodirections and palaeointensities were carried out on andesite lavas from the older part of the late Quaternary Ontake Volcano, Japan. Recently published K‐Ar ages of the Older Ontake lavas range from 740 to 393 Ka. Palaeomagnetic samples were collected at 24 sites which are either of the same locality or nearby the dating site. Determination of palaeodirections was straightforward at most of the sites. Exceptions are a few sites in which the site mean palaeodirections were obtained only by the great circle method due to large secondary components, possibly lightning strikes in origin. The obtained VGP angular dispersion of 14.3° ( N = 23) around the mean is smaller than the representative value for the site latitude of 36°N, which could be attributed to an insufficient number of sampling sites. Thellier's experiments were successful in 25 specimens from three lavas out of 54 specimens from nine lavas, giving a moderate success rate of 46 per cent. The obtained flow mean palaeointensities of 21, 40 and 53 μT conform well with the worldwide trend of the global palaeointensity during the Brunhes Chron, which indicates possible maxima of the global palaeointensity around 0.7 and 0.35 Ma with following gradual decrease.