5:15 PM - 6:30 PM
[SVC48-P05] Stratigraphy and radiometric ages of borehole core from the Matsukawa observation well, Sengan volcanic region, Northeast Japan.
Keywords:Sengan geothermal area, volcanic history, borehole core, landslide
The most characteristics of the lower part of Matsukawa core are unknown as strong alteration,but might be correlated to member of the Tamagawa Welded Tuffs. Volcanic rocks contained in the upper and middle part are likely derived from Matsukawa andesite and / or Nakakura (Marumori) volcano since K-Ar dating results of andesite blocks exhibited around about 1Ma. On the other hand 14C age of soil block and woods included are indicate depositional age of the upper part likely to be Holocene. The drilling site is located in ”Marumori landslide”. 14C age of 2390 ± 90yrBP have been reported from the soil that covers the surface structure of Marumori landslide body(Sumi, et.al.,1988). Since shear structure was developed in the middle part, the upper and middle part of Matsukawa core are considered that belong to the landslide body of Marumori landslide. And presumably the topsoil and vegetation were engulfed at the time of the occurrence of landslides at a few thousand years ago. However, the steep shear zone of the lower part is also likely to relate to reverse faults that were developed along eastern margin of the backbone range of NE Japan. There are required further research.