[SIT26-P01] Noble gas and major element composition of deep groundwater in the fore-arc region of southwest Japan; widespread distribution of fluids dehydrated from the Philippine Sea Plate
Keywords:noble gas, groundwater, Philippine Sea Plate, helium, Kii Peninsula
As already reported by Dogan et al. (2006) and Umeda et al (2006), moderately high-3He/4He groundwater has been observed on Shikoku Island, west of the Kii Peninsula, although no sampling point exceeded 4 Ra. By analogy with the Kii Peninsula, incorporation of the ascending fluids along faults accounts for the groundwater of this area, but this moderately high 3He/4He ratio (< 4 Ra) is possible to relate the slab configuration. The depth of the slab surface is relatively shallow, and therefore the thickness of the mantle wedge beneath Shikoku Island is less than that below the Kii Peninsula, resulting in a low mantle-He budget around the pathway of the fluids.
References: Dogan et al. (2006) Chem. Geol., 233, 235-248, Morikawa et al. (2016) Geochim. Cosmochim. Acta, 182, 173-196, Umeda et al. (2006) Geochem. Geophys. Geosyst. 7, Q04009, doi:10.1029/2005GC001210