Variations in the He/He ratios of hot springs on Shikoku Island, Southwest Japan

Umeda, Koji; Kanazawa, Sunao; Kakuta, Chifumi*; Asamori, Koichi; Oikawa, Teruki

Geochemistry, Geophysics, Geosystems (Internet), 7(4), p.Q04009_1 - Q04009_11, 2006/04

New helium isotopic data from hot springs on Shikoku Island with much denser sampling than previous studies were obtained, in order to elucidate the geographical distribution of He/He ratios in the fore-arc regions of Southwest Japan. Systematic, regional variations in He/He ratios were observed on both Sikoku Island and the Kii Peninsula. Most of the hot springs having He/He ratios in the range 1.0 RA to 2.0 RA were determined throughout Shikoku Island. On the other hand, the majority of hot springs in the Kii Peninsula have He/He ratios higher than 2.0 RA. It has been suggested by some authors that the anomalously high He/He ratios in the fore-arc region of Southwest Japan are related to the migration of mantle-derived helium with aqueous fluids generated by dehydration of the subducting PHS and mixing with terrestrial waters [e.g., Matsumoto et al., 2003]. According to recent seismological observations of crustal microearthquakes and their focal mechanisms, the geotectonic environment beneath Shikoku Island is subject to a stress field without normal faulting and the extremely low crustal seismicity, which does not favor migration of aqueous fluids from the subcrustal lithosphere, resulting in a relatively small influence of MORB-type helium at surface. As a consequence, the regional variation in He/He ratios of hot springs on Shikoku Island are interpreted as a three-component mixture of mantle-derived helium associated with magmatism of Middle Miocene of age ( 3.4 RA), crustal, radiogenic helium and atmospheric helium.

Evaluation of Thermal Effect of a Large-Scale Pyroclastic Flow Deposits on Basement Rocks by Fission-Track Method

Kakuta, Chifumi; Kakuta, Chifumi; Matsuzaki, Tatsuji*; Ishimaru, Tsuneari; Kamata, Hiroki*; Danhara, Toru*; Iwano, Hideki*

Oyo Chishitsu, 45(4), p.238 - 248, 2004/00

https://doi.org/10.5110/jjseg.45.238

None

Literature survey of monogenetic volcanoes; Data collection

Ishimaru, Tsunenori; Kakuta, Chifumi; Tanase, Atsushi*

JNC TN7420 2002-001, 43 Pages, 2002/07

JNC-TN7420-2002-001.pdf:0.37MB

A literature survey was carried out in order to understand the spatial and temporal distribution of the igneous activity of monogenetic volcanoes. The contents of the survey are as follows: (1)A review of the distribution, age and volcanic history of monogenetic volcanoes in Japan since 15Ma. (2)A review of the origin, lower crustal-upper mantle models and magma processes of monogenetic volcanoes in island arcs(Japan and overseas).