1978 年 17 巻 2 号 p. 86-94
The results of both palaeomagnetic and magneto-chemical analyses on the Quaternary volcanic ash layers and also loam deposits around the eastern foot of the Yatsugatake volcanoes in Central Japan will be briefly presented in this note, namely:
1. The variations of N.R.M.s of these pyroclastic deposits probably suggest the excursion and secular variation of the geomagnetic field.
2. The greater part of ferromagnetic minerals in the present volcanic ash are titanomagnetites. A small amount of high-temperature oxidated titanomagnetites, ilmenites, hematites is recognized. Maghemites by low-temperature oxidation are rare.
3. The sequences of these volcanic ash layers and loam deposits may be subdivided into at least three parts, on the basis of the analysis of the Curie temperatures which gradually shift from lower to higher temperature. This may suggest the variation of Ti-content of titanomagnetites occurred during the volcanic activities.