Helium isotopes as geochemical indicators of a serpentinized fore-arc mantle wedge
| Autor: | Atusi Ninomiya, Glen F. McCrank, Koji Umeda |
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| Rok vydání: | 2007 |
| Předmět: |
Atmospheric Science
Mantle wedge Geochemistry Soil Science chemistry.chemical_element Aquatic Science Oceanography Mantle (geology) Geochemistry and Petrology Earth and Planetary Sciences (miscellaneous) Isotopes of helium Helium Earth-Surface Processes Water Science and Technology Ecology Isotope Paleontology Forestry Geophysics Geographic distribution chemistry Space and Planetary Science Slab Far East Geology |
| Zdroj: | Journal of Geophysical Research. 112 |
| ISSN: | 0148-0227 |
| DOI: | 10.1029/2007jb005031 |
| Popis: | New helium isotope data from hot springs on eastern Kyushu Island were obtained in order to elucidate the geographic distribution of 3 He/ 4 He ratios in the fore-arc regions of southwest Japan. Systematic, regional variations in 3 He/ 4 He ratios are clearly distinguished across the fore arc from Kyushu Island (0.093-0.79 R A , where R A denotes the atmospheric 3 He/ 4 He ratio of 1.4 x 10 -6 ), to Shikoku Island (0.17-3.6 R A ) and to the Kii Peninsula (0.24-7.4 R A ). The distribution of mantle helium relative to total helium reveals a close association with the geophysical evidence of a serpentinized fore-arc mantle wedge including the occurrence of deep, nonvolcanic, low-frequency tremors (LFTs), believed to be caused by upwardly mobile aqueous fluids derived from slab dehydration. Flux of mantle helium carried by aqueous fluids via a non serpentinized fore-arc mantle wedge is very low on Kyushu Island where LFTs have not been detected and 3 He/ 4 He ratios are lower than the atmospheric ratio. On the other hand, hot springs above the regions where LFTs occur in the Kii Peninsula and northern Shikoku Island have high 3 He/ 4 He ratios, indicating a significant contribution of mantle helium carried by aqueous fluids via a serpentinized fore-arc mantle wedge. The helium isotopes in hot and natural spring gases may be a useful geochemical indicator of a serpentinized fore-arc mantle wedge, especially in areas with sparse seismic station coverage. |
| Databáze: | OpenAIRE |
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