Relationship between geological structure and helium isotopes in deep ground-water from the Osaka Basin: Application to deep groundwater hydrology

Abstract

The relationship between geological structure and helium isotopes is discussed for deep groundwaters from the Osaka sedimentary basin, southwest Japan, to understand dissolved He in groundwater for hydrological application. Although this area shows no Quaternary volcanic activity, nearly upper mantle-like 3 He/ 4 He ratio (1.1 × 10 -5 ) has been observed in the area along the fault system where the basement rocks are outcropped. In contrast, deep groundwaters from the lowest part of the aquifers beneath the Osaka Basin showed a wide variation in 3 He/ 4 He ratio (0.27-8 × 10 -6 ), which seems to reflect the geological structure. The moderately high 3 He/ 4 He ratios, not as high as those in the mantle value, are due to a contribution of radiogenic 4 He within the aquifer. The flux of mantle He through the Uemachi thrust fault into the aquifers in the east block (hanging wall of the fault) of the Osaka Basin will be smaller than those in the west block (foot wall), because mantle He through this fault encountered the aquifers in the west block and dissolved in this aquifer. The model for the Osaka Basin presented in this study implies that there are at least two different sources of He flux into an aquifer; mantle He flux through the fault system and crustal He from the underlying formation. The former should be spatially heterogeneous, while crustal 4 He flux is rather spatially constant throughout the lowermost part of the Osaka Basin.

Arima hot spring waters as a deep-seated brine from subducting slab

“…(6) Helium and neon concentrations and the helium isotope ratios were measured with a noble gas mass spectrometer, model MM5400 (Micromass UK Ltd., Manchester, UK). Technical details of the extraction of dissolved noble gases and the mass spectrometry, including the purification procedures, have been described by Morikawa et al (2008). (7) Sr concentrations were measured with an inductively coupled plasma mass spectrometer (ICPMS; ELAN DRC II, Perkin Elmer, Waltham, MA, USA) after dilution of the sample with HNO 3 containing the indium internal standard.…”

“…Despite its presence in non-volcanic regions in the forearc domain, in which Quaternary volcanoes do not appear (Figure 1), the oxygen and hydrogen isotope compositions have affinities to magmatic/metamorphic fluids; thus, the presence of a deep brine distinct from near-surface water, including meteoric water and seawater, has been long argued for the origin of Arima hot springs (e.g., Matsubaya et al 1973;Tanaka et al 1984;Masuda et al 1985 and the references therein; overview presented in Sakai and Matsuhisa 1996). Although a precise definition of Arima-type brine has not been presented, nonvolcanic hot springs with high chlorine (approximately 40,000 ppm) and other solute contents, as well as the distinct oxygen and hydrogen isotopic ratios, occur in the Osaka to Kii areas, southwestern Japan, along large fault zones (Matsubaya 1981;Nishimura 2000), where high He of gases occur associated with spring waters (Nagao et al 1981;Sano and Wakita 1985;Okada et al 1994;Matsumoto et al 2003;Umeda et al 2006;Morikawa et al 2008).…”

Passive degassing of magmatic volatiles from Iwate volcano, NE Japan, based on three‐dimensional measurement of helium isotopes in groundwater

“…Helium and neon concentrations and the helium isotope ratios were measured with a static noble gas mass spectrometer, model MM5400 (Micromass), which was installed at the Geological Survey of Japan, AIST. Technical details of the extraction of dissolved noble gases and the mass spectrometry, including the purification procedures, are described by Morikawa et al [2008b]. The reproducibility of the 3 He/ 4 He ratio and the helium and neon concentrations obtained from the replicated measurement of air saturated water (ASW) were about 2%, 3% and 3%, respectively.…”

Groundwater studies using isotopes and noble gases as a tracer: Review and prospect

“…15,000 Hendry and Wassenaar, 1999;Gimmi et al, 2007 DIC DIC DOC Kortelainen andKarhu, 2006 1 Drimmie et al, 1991 DOC DIC CO2 Rueedi et al, 2007Atekwana et al, 2005Desmarais and Rojstaczer, 2002Gramling et al, 2003 Rose and Davisson 1996 CO2 He/ 4 He=1.4 10 -6 (Air) 1.1 10 -5 (MORB*) 10 -7 -10 -8 (Crust) Morikawa et al, 2007Mahara, 1995Ohwada et al, 2007;Morikawa et al, 2008) Mahara (1995 Excess Air Kipfer et al, 2002 Wilson andMcNeill (1997) Excess et al, 1986b;Torgersen et al, 1991Milk River Phillips et al, 1986Nolte et al, 1990Bentley et al (1986b Mahara et al, 2006). Hainsworth et al, 1994;Knies et al, 1994Davis et al, 1998 36 Cl Plummer et al, 1997;Baumgartner et al, 1998 36 Cl/Cl U Th Andrews et al, 1986;Loosli, 1991 2006 36 Cl/Cl Cl Stute et al, 1993;Andrews et al, 1994;Purdy et al, 199636 Cl Bentley et al, 1982Phillips et al, 1988Scanlon, 1992;Cook et al, 1994Cook and Robinson, 2002Balderer et al, 2004Corcho Alvarado et al, 2005Tosaki et al, 2007 3 …”