Geographical distribution of 3He/4He ratios in the Chugoku District, Southwestern Japan

被引:49
作者
Sano, Y [1 ]
Takahata, N
Seno, T
机构
[1] Univ Tokyo, Ocean Res Inst, Ctr Adv Marine Res, Tokyo 1648639, Japan
[2] Univ Tokyo, Earthquake Res Inst, Div Geodynam, Tokyo 1130032, Japan
关键词
helium isotopes; magma source; subduction; Philippine Sea plate;
D O I
10.1007/s00024-006-0035-0
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
We have collected 34 hot spring and mineral spring gases and waters in the Chugoku and Kansai districts, Southwestern Japan and measured the He-3/He-4 and He-4/Ne-20 ratios by using a noble gas mass spectrometer. Observed He-3/He-4 and He-4/Ne-20 ratios range from 0.054 R-atm to 5.04 R-atm ( where Ratm is the atmospheric He-3/He-4 ratio of 1.39 x 10(-6)) and from 0.25 to 36.8, respectively. They are well explained by a mixing of three components, mantle-derived, radiogenic, and atmospheric helium dissolved in water. The He-3/He-4 ratios corrected for air contamination are low in the frontal arc and high in the volcanic arc regions, which are consistent with data of subduction zones in the literature. The geographical contrast may provide a constraint on the position of the volcanic front in the Chugoku district where it was not well defined by previous works. Taking into account the magma aging effect, we cannot explain the high He-3/He-4 ratios of the volcanic arc region by the slab melting of the subducting Philippine Sea plate. The other source with pristine mantle material may be required. More precisely, the highest and average He-3/He-4 ratios of 5.88 R-atm and 3.8 +/- 1.6 R-atm, respectively, in the narrow regions near the volcanic front of the Chugoku district are lower than those in Kyushu and Kinki Spot in Southwestern Japan, but close to those in NE Japan. This suggests that the magma source of the former may be related to the subduction of the Pacific plate, in addition to a slight component of melting of the Philippine Sea slab.
引用
收藏
页码:745 / 757
页数:13
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