| Budget Amount *help |
¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 1988: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1987: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
By means of tephrochronology, especially by widespread tephra layers from distant sources as Aira tn Ash layer(Abbr.:AT), Daisen Krayoshi Pumice layer(DKP), Volcanic ash layer of Aso 4, Kikai-Tozurahara Ash(K-Tz) and so on, the isolated volcanic products belonging to Norikura volcanic zone are correlated each other for the purpose of investigating volcanic evolution of the zone. The volcanic history of the zone is supposed to relate to quaternary tectonic movement, because the volcanoes of the zone align well on the N-S trend overllapping to one of the most active uplift-axis of central japan in quaternary time and paralleling to the northern part of the Itoigawa-Shizuoka tectonic zone.
The tephrochronological research is effective in correlating the younger halves of Ontake and Tateyama volcanoes with their own numerous tephra layers, and tephra stratigraphy is not effective for Norikura, Yakedake and Washiba-Kumonotaira volcanoes and the older halves of the former two volcanoes.
Norikura volcanic zone started about 0.7-0.6 Ma ago and the volcanism contnued for perhaps 0.3 ma based on radiometric age. After the long inactive period, the younger activity simultaneously took place about 0.1 Ma ago and the earlier stage of the activity erupted the most acidic products on each volcano. Magmatic activity lasted about 30,000 years ago on Ontake and Tateyama volcano. And continued more later on Norikura and Yakedake volcanoes. Recently the phreatic activities repeated the volcanic zone.
To complete the study, we need the radiometric age data for the products on Norikura, Yakedake and Washiba-Kumonotaira volcanoes because they do not seem to have the extensive tephra layers.
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