Relationship between 3He/4He ratios and subduction of the Philippine Sea plate beneath southwest Japan

摘要: [1] Regional and local variations in mantle helium provide insight into the coupling of mantle-crust tectonics, heat and/or mass transfer from Earth's interior. In order to further elucidate geographic distribution of3He/4He ratios southwest Japan, data a total 924 sites were compiled synthesized. These include 48 additional hot spring drinking water well on northern Kyushu Island Chugoku region. There appears be good correlation between isotope geophysical evidence used determine configuration subducting Philippine Sea plate (PHS). Seismological studies reveal that leading edge aseismic slab does not extend region nor Osaka Bay area, where gas samples with significantly elevated 3He/4He occur. This is consistent mantle-derived these areas, melts fluids ascribed upwelling asthenosphere without being hindered by descending PHS slab. contrast, regions overriding crust comes direct contact are dominated radiogenic derived because absence wedge, most plausible source helium. Owing abrupt changes seismicity focal mechanisms intraplate earthquakes, considered have tears beneath Kii Channel eastern Peninsula oriented NW-SE direction. However, lenear alignment anomalously high3He/4He appear trending along assumed but rather forms an broad, ENE-WSW zone low-frequency events The emanation elevated3He/4He central peninsula can explained upward mobilization volatiles wedge above transferred hydrated through N-S fractured medium within PHS. Accordingly, isotopes observed surface may efficient geochemical indicators relatively younger, warm slab, especially useful seismically inactive areas.