Paleomagnetism of the Joban Seamount Chain, Northwestern Pacific

抄録

We conducted a detailed bathymetric and magnetic total force survey of five seamounts in the Joban seamount chain during cruise KH90-1 of the R/V HAKUHO MARU in 1990. The Joban seamount chain is situated to the east of the southern Japan Trench, trends along N53°E (oblique to magnetic anomaly lineations whose trend is N68°) and extends over a distance of about 394 km. We applied three-dimensional magnetic inversion to each seamount. The three northern seamounts show relatively complex magnetization structures, whereas the two southern seamounts show simple magnetization structures. The latter yielded reliable results with VGPs (Virtual geomagnetic pole) at 55.5°N/348.9°E and 52.1°N/352.4°E. We estimated the ages of the two southern seamounts to be ca. 80 to 90 Ma by comparing their VGPs with known Pacific plate apparent polar wander path. We also estimated the ages for two guyot seamounts in the northern group to be ca. 110 to 130 Ma by backtracking their crests along crustal age-depth curve to sea level. The Joban seamount chain apparently shows presence of at least two groups of inclinations. This suggests that the origin of this seamount chain is not the passage of the Pacific plate over a single stationary hotspot.