Geochemical Journal, Vol. 42, pp. 61 to 74, 2008
Relationship between geological structure and helium isotopes in deep groundwater from the Osaka Basin: Application to deep groundwater hydrology
NORITOSHI M ORIKAWA ,1* KOHEI KAZAHAYA ,1 HARUE MASUDA,2 M ICHIKO OHWADA,1 ATSUKO NAKAMA,1
KEISUKE NAGAO3 and H IROCHIKA S UMINO3
1
Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology,
AIST Tsukuba Central 7, Higashi 1-1-1, Tsukuba, 305-8567, Japan
2
Department of Geoscience, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
3
Laboratory for Earthquake Chemistry, Graduate School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
(Received April 7, 2007; Accepted October 12, 2007)
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 3He/ 4He 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 3He/ 4He ratio (0.27–8 × 10 –6), which seems to
reflect the geological structure. The moderately high 3He/ 4He ratios, not as high as those in the mantle value, are due to a
contribution of radiogenic 4He 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 4He flux is rather spatially constant throughout the lowermost part of the Osaka Basin.
Keywords: helium isotopes, noble gas, groundwater, hydrology, Osaka basin
1979). Many authors attributed these observations to external 4He flux from deep seated crust (e.g., Andrews,
1985; Torgersen and Clarke, 1985; Stute et al., 1992;
Marty et al., 1993; Castro, 2004; Zhou and Ballentine,
2006). The validity of estimated groundwater residence
time depends on the accurate estimation of 4He accumulation rates and some hydrological parameters such as
porosity and thickness of aquifers (Weise and Moser,
1987; Stute et al., 1992; Morikawa et al., 2005).
Ballentine et al. (2002) stated that the 4He accumulation
rates are thought to be highly variable, from virtually no
external 4He contribution required to 4He accumulation
rates apparently exceeding the 4He flux from the whole
continental crust. In contrast, Mazor and Nativ (1992)
suggested that hydraulic calculations often underestimated
groundwater ages due to the lack of hydraulic interconnection between wells from which data were applied. The
radiometric dating methods such as 14C, 36Cl and 129I
(Phillips and Castro, 2003 and references therein) have
their specific dating ranges according to their half lives
and usually require complex corrections for water-rock
interactions. Therefore, there is no ideal groundwater
dating method for both deep and old groundwater.
INTRODUCTION
Noble gases in groundwater can be used as potential
tracers in isotope hydrology. Among the noble gas isotopes, helium is most useful for investigating the groundwater flow regime, age of groundwater and its origin since
4
He is continuously produced in an aquifer and surrounding rocks by radioactive decay of uranium and thorium
and dissolves into groundwater over geologic time spans.
Helium-4 concentrations in many aquifers are observed
to increase with the groundwater residence time estimated
from other dating methods (e.g., Andrews and Lee, 1979;
Torgersen and Clarke, 1985; Castro et al., 2000). However, the residence time deduced from He concentration
assuming that 4He originated from an in situ produced
component in an aquifer often yields very old ages compared with hydrodynamic age (Torgersen and Clarke,
1985; Marty et al., 1993) and with those from radiometric dating methods such as 14C (e.g., Andrews and Lee,
*Corresponding author (e-mail: [email protected])
Copyright © 2008 by The Geochemical Society of Japan.
61
The reliability of He dating method depends on the
accurate estimates of the He accumulation rate, which is
affected by the contribution of various sources of He. A
number of 3He sources (atmosphere, 3H decay, in situ
production from 6Li neutron reaction, mantle He) in
groundwater show a wide variation in the 3He/4He ratio.
It is well documented that the He isotopic ratio (3He/4He)
in the Mid-Ocean Ridge basalt (MORB), which represents a mean upper mantle value, falls around a value of
1 × 10–5 (Ozima and Podosek, 2002). Typical crustal rock
3
He/4He production ratios have been estimated to be about
1 × 10–8 (Andrews, 1985), which is much lower than the
mantle and atmospheric value. Therefore, the He isotopic
ratio as well as its concentration reflects the nature of He
dissolved in groundwater.
In this study, we discuss the relationship between geological structure and He isotopes in deep groundwaters
from the Osaka sedimentary basin to understand dissolved
He in groundwater for hydrological use. The Osaka Basin is located on the northwest side of the Kii Peninsula,
southwest Japan. The north border of the basin has unique
characteristics of a high-temperature and -chlorine (up to
40,000 ppm) thermal water, so called Arima-type thermal brine (Matsubaya et al., 1973; Masuda et al., 1985,
1986). The 3He/4He ratios of hot spring gases in this region are exceptionally high, sometimes up to the MORB
value, in spite of a fore-arc region with no Quaternary
volcanism (e.g., Nagao et al., 1981; Sano and Wakita,
1985). Although many noble gas studies have been undertaken for hot spring gases in the vicinity of the Osaka
Basin, they are focused on discussing the mechanism of
mantle He release from fore-arc regions and their relation with the tectonics of the Kii Peninsula (Wakita et
al., 1987; Okada et al., 1994; Matsumoto et al., 2003;
Umeda et al., 2006). In this paper, we present the noble
gas data dissolved in deep groundwaters from the Osaka
Basin and discuss the distribution of the 3He/ 4He ratio in
the shallower region with emphasis on the hydrological
application of noble gases. Since geological and geophysical surveys were intensively carried out for constructing
the underground geological structure of this basin, the
Osaka Basin is suitable for studying the relationship between the geological structure and noble gases in groundwater.
S AMPLING SITES
The Osaka sedimentary basin is located on the northwest side of the Kii Peninsula, the fore-arc region of southwest Japan, where the Philippine Sea plate is subducting
to the northwest under the Eurasian plate (e.g., Seno et
al., 1993). This region has distinct structural and tectonic
features characterized by high seismicity in the crust and
subducting Philippine Sea slab (Ikeda et al., 2001). The
62
N. Morikawa et al.
tremor activity in the Kii Peninsula is related to the movement of aqueous fluid along the existing faults and/or
newly created hydraulic fractures induced by fluid addition (Obara, 2002).
The Osaka Basin is a tectonic subsidence basin, which
consists of 500–2,000 m thick Late Pliocene to Pleistocene
sediments, so called Osaka Group. This area is characterized by the alternative arrangement of basin and range,
which is the topographic expression of the differential
movements of the faulted blocks of granitic basement
(Huzita, 1990). Within the studied area, mountainous
ranges of the Cretaceous plutonic rocks and pre-Tertiary
sedimentary rocks surround Tertiary sedimentary basins.
The Plio–Pleistocene Osaka Group is found basically
under alluvial plains. Based on lithology, the Osaka Group
is divided into the Lower, Middle and Upper Subgroups
(Huzita and Kasama, 1982). The lower subgroup consists
of coarse sand and gravel of lacustrine facies, while the
Middle and Upper Subgroups alternate between marine
clays and non-marine sand/gravel beds. The granitic basement rocks of the Osaka Basin have been broken into two
major blocks called West and East Osaka blocks by the
Uemachi fault trending north to south. These two basement blocks have been tilting separately, but both have
continuously subsided with the rate of 0.7–0.2 m/ky since
ca. 1.2 Ma (Uchiyama et al., 2001). The northeastern
Osaka Basin (Kobe Basin) is bounded by the Awaji–
Rokko fault system to the northwest, and divided by the
northern branch of the Osaka-wan fault (Yokokura et al.,
1996). There are a large number of active fault systems
in the Cretaceous basement. The major tectonic divide in
the Kii Peninsula is the Median Tectonic Line (MTL)
which is a vertical right-lateral strike-slip fault with an
E-W strike.
SAMPLE C OLLECTION AND A NALYTICAL PROCEDURE
Figure 1 shows the sampling points of deep
groundwaters. As noble gases are highly volatile, it is
important to avoid gas exchange between the water sample and the atmosphere during sampling. The samples for
noble gas analyses were collected in annealed copper
tubes (3/8 inch o.d., 30 cm length). The copper tubes were
connected to sampling wells and flushed sample water
thoroughly in order to remove air bubbles completely from
a water sample, and were then tightly closed at both ends
by customized steel clamps, which were equipped with
0.5 mm stainless steel spacers.
Noble gases dissolved in water samples were extracted
into glass bulbs following a procedure described in JeanBaptiste et al. (1992). The copper tubes were attached to
the extraction line equipped with the thick glass flask and
the glass bulb (Schott AR-Glas®) connected by a capillary tube (0.6 mm i.d., 40 mm length). The lines were
Fig. 1. Map of the studied area, showing the locations of sampling points and topographic contours at 100 m intervals. The
samples from the Kobe Basin and Rokko mountains (A-9, -10, -37, C-36, E-40, EK-1, -2, -6, -7) are previously reported in
Morikawa et al. (2005). The dashed line (A–A ′) is the cross section line of Fig. 6.
pumped down to 10–8 torr and isolated from the vacuum
unit. The clamp on the copper tube was removed, and the
tube was re-opened slightly to allow the water to flow
down into the glass flask. The glass flask was placed in
an ultra-sonic bath to facilitate the extraction of dissolved
gases. After an equilibration period of 15 min, the AR
glass bulb was immersed in liquid nitrogen. All gases are
transport into the bulb by the water vapor streaming from
the line to the glass bulb where it is frozen.
In the early stage of this work in 2002, some water
samples were collected into 150 ml Pyrex glass containers with vacuum cocks on both ends. Dissolved gases in
the water samples were extracted by a vacuum line and
were transferred into two breakable seals.
Gas samples were also collected by a displacement
method using Pyrex glass reservoirs with vacuum-tight
stopcocks at both ends. The gas samples were split into a
few fractions in about 8 cm3 glass ampoules attached to
an all-metal ultra-high vacuum line, and the pressure and
temperature were measured before flame sealing.
Noble gases in glass ampoules were attached to a noble gas purification line and purified by exposure to a
Ti–Zr getter at about 800°C and two SAES Getters (GP50). The sample gases were then split into two fractions
for He–Ne and Ar–Kr–Xe measurements. The He–Ne
fraction was further purified using two charcoal finger
held at liquid N2 temperature and a cryogenic sintered
stainless steel trap at 20 K. Helium isotopic ratio and noble
Relationship between geological structure and He isotopes in deep groundwater
63
64
N. Morikawa et al.
2005/9/14
2005/9/19
2005/10/13
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
27
28
OSK05003
OSK05004
OSK05005
OSK05006
OSK05007
OSK05008
OSK05009
OSK05010
OSK05011
OSK05012
OSK06001
OSK06002
OSK06003
OSK06004
OSK06005
OSK06006
OSK06007
OSK06008
OSK06009
OSK06010
OSK06011
OSK06012
OSK06015
OSK06016
2006/11/9
2006/11/8
2006/11/7
2006/11/7
2006/11/7
2006/11/7
2006/11/7
2006/11/6
2006/11/6
2006/11/6
2006/11/6
2006/11/6
2006/11/6
2005/10/19
2006/11/6
2005/8/5
2005/8/5
2005/8/5
2005/8/5
2005/8/4
2005/8/4
2005/8/4
2005/8/4
(y/m/d)
1
2
OSK05001
OSK05002
Sampling
date
Sample
No.
Sample name
34°37′29″
34°52′16″
34°25′22″
34°27′43″
34°28′08″
34°50′07″
34°50′06″
34°31′22″
34°27′47″
34°22′21″
34°22′22″
34°40′55″
34°47′53″
34°47′47″
34°39′10″
34°39′27″
34°42′37″
34°41′11″
34°32′50″
34°41′24″
34°40′00″
34°28′38″
34°34′51″
34°44′22″
34°50′26″
34°47′47″
Latitude
135°31′42″
135°35′31″
135°34′35″
135°35′52″
135°35′01″
135°28′20″
135°28′19″
135°34′15″
135°35′08″
135°27′08″
135°27′08″
135°37′10″
135°29′40″
135°26′43″
135°33′28″
135°30′55″
135°35′01″
135°27′40″
135°33′18″
135°33′04″
135°27′49″
135°23′37″
135°32′11″
135°35′32″
135°33′58″
135°35′08″
Longitude
48.1
18.9
17.6
9.5
7.0
6.3
6.1
21.1
24.3
8.6
8.2
8.5
8.3
6.2
7.0
6.9
8.0
7.1
7.0
6.9
7.0
7.1
6.9
8.1
8.2
8.0
6.9
6.8
7.5
7.4
6.0
pH
24.7
19.9
23.6
19.4
21.4
26.3
42.6
25.1
50.7
27.7
35.1
46.5
50.5
38.0
36.0
47.0
38.0
43.5
30.5
29.1
24.5
(°C)
Temp.
He
110
1.34 ± 0.01
0.83 ± 0.01
91.8
275
10.4
46.9
11.3
8.78
47.8
192
4.47
22.2
11.6
1.35 ± 0.02
1.92 ± 0.02
5.36 ± 0.10
1.20 ± 0.02
3.51 ± 0.05
6.21 ± 0.15
250−351
1097−1291
594−696
n.k.
297−402
706−857
706−857
488−603
1.16 ± 0.02
0.24 ± 0.02
4.81 ± 0.04
1.03 ± 0.02
3.61 ± 0.03
81.0
0.55 ± 0.01
n.k.(c)
1067−1187, 1358−1635
n.k.
126−358
60.7
108
180
191
336
76.8
583
0.81 ± 0.01
2.83 ± 0.03
0.71 ± 0.01
3.02 ± 0.03
1.59 ± 0.02
0.59 ± 0.01
0.80 ± 0.01
46.8
1900
0.27 ± 0.01
3.44 ± 0.03
4.84 ± 0.04
(10 −14)
3
2490
41.8
189
7650
(10 −6)
He/ 4He
1.03 ± 0.01(b)
1.21 ± 0.01
3
508−646
813−951
577−648
1336−1492
851−1249
691−795
910−1063
908−930
730−957
885−1010
882−985
555−665
555−585
1015−1195
(m)
Depth of
the sampling point(a)
Table 1(a). Noble gas concentrations and 3He/ 4He ratios in groundwaters from the Osaka Basin
He
0.72
91.2
10.0
7.29
13.6
39.9
1.94
13.0
11.0
67.8
143
147
85.9
134
67.5
305
211
95.5
193
56.7
82.6
393
2400
34.6
697
2230
(10 −8)
4
Ne
Ar
(10 −6)
36
0.073
2.77
1.44
1.53
1.65
0.295
0.241
2.25
1.56
0.147
0.058
1.76
0.034
0.137
0.481
0.037
0.200
1.86
0.125
1.97
1.03
2.05
1.39
0.731
1.82
0.348
0.0412
1.39
0.501
0.887
0.901
0.165
0.0583
1.47
1.00
0.531
0.0754
0.0454
0.0835
0.0783
0.566
0.0465
0.357
1.38
0.165
1.40
0.956
1.45
1.56
0.801
1.09
0.441
(cm STP/gH2O)
3
(10 −7)
20
Kr
0.146
5.35
1.67
3.31
3.38
0.679
5.63
3.86
0.165
2.22
0.278
0.158
0.587
0.405
2.78
0.247
1.96
5.58
0.956
5.58
4.18
5.71
4.76
3.09
4.04
2.20
(10 −8)
84
Xe
0.142
3.70
1.03
2.23
2.23
0.545
3.92
2.69
0.122
1.79
0.204
0.0363
0.733
0.452
2.17
0.287
1.76
3.88
0.926
3.78
3.06
3.81
5.09
2.59
2.57
1.80
(10 −9)
132
He/ 20N e
0.987
3.29
0.694
0.477
0.827
13.5
0.577
0.705
0.806
8.35
46.1
246
62.7
390
63.4
181
105
5.12
154
2.88
4.03
38.2
160
329
1.90
200
4
Relationship between geological structure and He isotopes in deep groundwater
65
2001/12/12
2001/12/12
2002/8/27
2002/8/27
2002/8/29
2002/8/29
2002/2/9
2002/2/10
2002/10/7
K14
K20
K60
K68
K77
A-9(e)
A-10(e)
EK-1(e)
EK-2(e)
EK-6(e)
EK-7(e)
A-37(e)
C-36(e)
E-40(e)
KNK02021C
KNK02022C
KNK02042C
KNK02034C
KNK02035C
KOB01036
KOB01037
KOB02001
KOB02003
KOB02005
KOB02006
KNK02037A
KNK02036C
KNK02040E
2002/2/9
2002/2/11
2002/2/7
2002/2/7
2002/2/5
34°47′38″
34°48′03″
34°42′37″
34°41′46″
34°41′46″
34°40′24″
34°42′24″
34°42′39″
34°43′20″
34°50′37″
34°41′21″
34°23′43″
34°51′05″
34°22′01″
34°24′50″
34°20′15″
34°22′17″
Latitude
135°11′54″
135°11′55″
135°10′33″
135°13′24″
135°14′34″
135°18′50″
135°15′11″
135°13′02″
135°22′45″
135°21′43″
135°11′20″
135°18′18″
135°35′50″
135°36′06″
135°32′10″
135°22′39″
135°24′22″
Longitude
15
15
24.5
41.0
29.6
35.9
31.8
43.1
13.4
31.3
41.4
45.8
28.0
23.8
15.6
15.0
24.9
18.4
10.5
(°C)
Temp.
6.5
7.7
4.6
6.3
7.7
8.1
7.2
7.1
6.5
8.2
6.1
6.8
8.1
9.3
7.9
9.2
7.6
pH
0
300
1500
727
1006
602
700
600
1000
1008
7
1200
n.k.
532
350
n.k.
275
(m)
Depth of
the sampling point(a)
He
1.38
1.38
6.27
5.18
250
865
4210
4350
813
3070
6860
1370
1380
82.4
1.83 ± 0.04
3.60 ± 0.07
3.78 ± 0.10
5.30 ± 0.13
7.73 ± 0.12
7.43 ± 0.18
5.69 ± 0.15
10.74 ± 0.07
9.18 ± 0.05
4.29 ± 0.15
172
4.39 ± 0.04
6.17 ± 0.13
56.9
2690
4600
533
3.03 ± 0.05
6.96 ± 0.06
2.12 ± 0.05
6.70 ± 0.04
(10 −14)
3
62.7
117
(10 −6)
He/ 4He
0.63 ± 0.04
3
He
4.56
3.77
58.2
152
392
474
215
579
888
184
383
27.9
44.9
76.5
26.8
402
1050
99.5
38.8
(10 −8)
4
Ne
Ar
(10 −6)
36
1.74
1.42
0.762
0.639
1.49
0.041
0.597
0.998
1.44
0.466
0.623
0.852
1.70
2.82
1.55
1.77
1.81
2.05
1.83
18G
K19G
K228G
OSK06006(a)
KNK02024C(b)
1.16
0.912
n.a.
n.a.
n.a.
n.a.
2006/11/6
2002/2/7
2002/10/7
(y/m/d)
Sampling date
34°25′22″
34°25′22″
34°40′00″
Latitude
135°27′49″
135°34′35″
135°34′35″
Longitude
3
7.96 ± 0.07(c)
7.44 ± 0.09
7.77 ± 0.10
He/ 4He (10−6)
3
3.45
1.71
1.25
He (10−5)
He
4.34
2.30
1.61
4
Ne
36
Ar
0.0571
0.339
0.222
(ppm)
0.00758
0.174
0.0994
20
Kr
0.00271
0.00905
0.00630
84
Xe
0.000318
0.000240
0.000386
132
(b)
4
572
13.2
16.2
He/ 20N e
4.52
3.51
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
Same sample location as Sample No. 18.
Same sample location as Sample OSK06012 (No. 24) in Table 1(a).
(c)
Error are 1 σ and include a statistical error of an individual measurement of the samples and an error of correction factor determined by standard gases.
(a)
KNK02041E(b)
Sample No.
Sample name
Table 1(b). Noble gas concentrations and 3He/ 4He ratios in gas samples from the Osaka Basin
(b)
Kr
(10 −8)
84
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a. (d)
(cm STP/gH2O)
3
(10 −7)
20
The depth of the screen from the ground surface, i.e., the depth of the groundwater comes from. The depth of the borehole for KNK and KOB-series samples.
Error are 1σ and include a statistical error of an individual measurement of the samples and an error of correction factor determined by standard gases.
(c)
Not known.
(d)
Not analyzed.
(e)
Data are from Morikawa et al. (2005).
(f)
Air-saturated water (ASW) and sea water (SW) at 1 atm pressure and a temperature of 15° C (Benson and Krause, 1980; Smith and Kennedy, 1983).
(a)
ASW (f)
SW (f)
2002/2/10
K13
KNK02012C
2002/2/4
2002/2/4
(y/m/d)
K1
K2
KNK02006C
KNK02007C
Sampling
date
Sample
No.
Sample name
Xe
3.04
2.40
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
(10 −9)
132
61.5
39.6
36.1
58.0
61.4
3.27
2.65
4.32
1.48
14.2
67.8
4.84
2.12
He/ 20N e
0.261
0.265
20.1
61.4
31.8
143
4
RESULTS AND DISCUSSION
Abundances of 20Ne, 36Ar, 84Kr and 132Xe
Total amount of each noble gas in groundwater can be
expressed as follows;
NG = NGatm + NGea + NGmantle + NG cr
(1)
where NG atm and NGea are the amounts of each noble gas
resulted from equilibrium solubility with the atmosphere
and from air itself because of excess air during the recharge process (e.g., Heaton and Vogel, 1981), respectively. The NGmantle and NGcr are the amount of the components from the mantle and crust, respectively. Since a
large amount of heavy noble gases dissolved in groundwater generally originates from the atmosphere (NGatm
and NGea), both NGmantle and NGcr will be negligible when
we discuss the abundance of heavy noble gases for the
purpose of the following discussion. Air contamination
during the sampling procedure enhances the amount of
all noble gases. Depletion of noble gases in thermal water was also observed and considered to be a result of a
boiling process and associated phase separation between
66
N. Morikawa et al.
0.010
0.009
50
0.008
0.007
50
10
Xe /36Ar
0.006
132
gas abundances were measured with a noble gas mass
spectrometer, model MM-5400 (Micromass), which was
installed at the Geological Survey of Japan (GSJ) in 2003.
Neon was released from the cryogenic trap at 50 K. Before introducing the Ne sample, 40Ar peaks were checked
by a quadrupole mass spectrometer. Since there were no
significant peaks at mass 40, the contribution of Ar++ peak
on 20Ne + mass was negligible for calculated Ne abundances. After He and Ne measurements and evacuation
of the sample, the Ar–Kr–Xe fraction was expanded to
the purification line and introduced into the mass
spectrometer. For the isotope discrimination correction,
HESJ (Helium Standard of Japan) with R/Ra of 20.63 ±
0.10 (Matsuda et al., 2002) was used as standard. The
3
He/4He ratio of the HESJ at GSJ, which was determined
by using atmospheric helium as a primary standard, is
20.75 ± 0.21 R/Ra. This value is within a recommended
value. From the repeated analyses of air saturated water
(ASW) at GSJ, the reproducibility of 3He/ 4He and noble
gas abundances are about 3% except 132Xe for 6% (n =
10, 1σ ). Total blanks which includes extraction procedure and hot blanks in purification line were 2, 0.8, 0.6,
<0.01 and <0.01 for 4He, 20Ne, 36Ar, 84Kr and 132Xe, respectively (in unit of 10 –9 cm3STP). For the eight water
and two gas samples collected in 2002, 3He/4He and 4He
and 20Ne concentrations of the samples were determined
with a modified VG-5400 (MS-III), at the Laboratory for
Earthquake Chemistry, the University of Tokyo. Details
of the purification and measurement procedures were
described by Aka et al. (2001).
50
5
10
0.005
10
0.004
0.003
Water-Gas
fractionation
5
1
5
Addition
of Air
0.5
ASW (0°C)
1 0.5
1
0.5
0.002
Addition of Air
ASW (50°C)
0.001
0.000
10–9
10–8
20
10–7
10–6
10–5
Ne(cm3STP/gH2O)
Fig. 2. Plot of 132Xe/36Ar ratio versus 20Ne concentrations. Bold
gray solid line indicates the air saturated water (ASW) value
at 0–50°C (Smith and Kennedy, 1983). The dashed lines represent addition of air to ASW at 0, 20 and 50 °C. Fractionation of
the 132 Xe/ 36Ar ratio versus 20Ne concentrations in residual
groundwater after water-gas separation is shown by solid gray
lines using Henry’s constant of Crovetto et al. (1982) at 30°C
assuming batch equilibration as well as Gas/Water volume ratio (expressed in %).
the gas and liquid phases (e.g., Winckler et al., 2000).
Therefore, the concentrations of heavy noble gases reflect the recharge condition and phase separation of the
groundwater. These factors also affect the He concentration and thus should be considered before discussing the
He isotopes and concentrations.
The measured noble gas concentrations are given in
Table 1 together with the data previously published by
Morikawa et al. (2005). The solubility data of noble gases
into pure water and sea water are also listed for comparison because groundwater of meteoric origin initially dissolves atmospheric noble gases during the recharge process. The 20Ne concentration of deep groundwater presented in this paper ranges from 0.034 to 2.82 × 10 –7
cm3STP/gH2O. About half of the samples contain less than
1 × 10–7 cm3STP/gH2O of 20Ne, which is significantly
lower than the value of air saturated water (ASW). With
0.010
10–5
MORB
50
0.008
ASW
He/4He
10–6
3
50
10
132
Xe /36Ar
0.006
10–7
50
10
5
10 5
0.004
5
1
0.5
10–8
0.1
Water-Gas
fractionation
ASW(0°C)
0.5
ASW(50°C)
Addition of Air
Air
0.03
0.04
0.05
84
1
Crust
10
4
1
0.002
0.000
0.02
This Work
Literature Data
0.06
0.07
0.08
100
He/ Ne
1,000
10,000
20
Fig. 4. Correlation diagram between 3He/4He and 4He/ 20Ne
ratios of the groundwater samples in the vicinity of the Osaka
Basin. Solid lines show the mixing lines between He in air saturated water (ASW) and MORB He and between those in ASW
and radiogenic He. The value of ASW at 15°C is calculated
from the solubility data of Benson and Krause (1980) and Smith
and Kennedy (1983). Open circles are data from Nagao et al.
(1981), Sano and Wakita (1985), Okada et al. (1994) and
Matsumoto et al. (2003).
36
Kr/ Ar
Fig. 3. Plot of 132Xe/ 36Ar ratio versus 84Kr/ 36Ar ratio. The
fractionation lines are calculated by those in the same manner
in Fig. 2.
the formation of a vapor phase, preferential transfer into
a gas phase leads to depletion of noble gases in the residual phase and an elemental fractionation among noble
gases. Figure 2 plots the 132Xe/36Ar ratio versus 20Ne concentration in water with the predicted fractionation lines
by batch water—gas separation in the manner of
Ballentine et al. (2002). Rayleigh fractionation of the
water phase show a similar trend, although the extent of
vapor separation will be different between the two modes.
Many of the samples with low 20Ne concentrations show
high 132Xe/36Ar ratios relative to the values of ASW. These
trends are consistent with fractionation between the water and gas phase. The plot of 132Xe/36Ar versus 84Kr/36Ar
ratios also supports this fractionation (Fig. 3). The 132Xe/
36
Ar ratios of four samples shift from the fractionation
pattern of water-gas separation (Fig. 2). However, a small
amount of air addition to the residual water phase could
explain the data of these four samples.
Helium isotopes and concentration
Total amount of He in groundwater can be expressed
in the same manner as other noble gases:
He = He atm + Heea + Hetr (for 3He) + Hemantle + Hecr (2)
where Hetr is the amount of tritiogenic 3He, decay products of 3H. The amount of tritiogenic 3He (3Hetr) is negligible for the samples in this study because tritiogenic 3He
concentration in groundwater would be about 1.3 × 10–14
cm3STP/gH2O even if all tritium in groundwater with 5.5
T.U. (natural production level; Kauffman and Libby, 1954)
would decay to 3He. Air-saturated water contains up to 5
× 10 –8 cm3STP/gH 2O of 4He. The He concentrations in
the deep groundwaters collected in this study are, however, considerably high (7–2,400 × 10–8 cm3STP/gH2O)
with the exception of the sample Nos. 18 and 24 (Table
1). Since the contribution of both excess air component
and/or air contamination will be negligible inferred from
heavy noble gas abundances, a significant amount of nonatmospheric He must be accumulated. Accumulation of
non-atmospheric He would increased the 4He/20Ne ratio
because of the scarcity of the mantle and crustal Ne. The
only two samples, Nos. 18 and 24, contain less 4He than
ASW. Helium accumulation is, however, proceeding even
for these samples because their 4He/20Ne ratios are higher
than that of ASW. We could collect free gas samples for
these site and obtained high 3He/ 4He ratios (Table 1(b)).
Significant water-gas separation and following separation
of gas phases, observed for this sample as described
above, will diminish the original He concentration.
The 3He/4He ratio shows a wide variation, ranging
from 2.4 × 10–7 to 1.1 × 10–5 (Table 1). Some samples
have relatively low 4He/20Ne ratios indicating a large con-
Relationship between geological structure and He isotopes in deep groundwater
67
Table 2. Relative Contribution of 4He derived from air, mantle and crust, and corrected mantle 3He and crustal 4He concentration in each sample
Sample name
Sample No.
Corrected 3He/4He (×10−6)
4
He contribution (%)(a)
Mantle 3He (b) (×10 −14)
Crustal 4He(b) (×10−8)
3
ASW
Mantle
Crustal
7.99
3.26
7.33
6.80
4.40
10.8
9.25
26.4
12.3
6.0
1.8
0.4
0.4
0.8
52.1
25.4
61.4
59.5
39.0
95.8
81.8
21.4
62.3
32.6
38.7
60.6
3.7
17.3
101
106
520
1660
5180
11500
5100
3.61
3.80
5.32
7.76
7.47
5.75
4.34
1.88
0.4
0.7
0.4
0.4
0.7
1.3
1.8
9.9
32.0
33.6
47.2
68.9
66.2
50.6
38.0
15.0
67.6
65.7
52.4
30.7
33.1
48.1
60.2
75.1
3850
2370
5370
8330
5120
1980
10800
77.8
727
414
532
331
229
168
1550
34.7
Osaka Basin (West block)
OSK05005
5
OSK05006
6
OSK05009
9
OSK05012
12
4.86
1.33
3.02
2.83
0.7
6.5
0.2
0.1
43.0
11.0
26.8
25.1
56.3
82.5
73.0
74.7
3220
86.9
8100
8930
376
58.2
1970
2370
Osaka Basin (North side of east block)
OSK05001
1
OSK05002
2
OSK05003
3
OSK05007
7
OSK05008
8
OSK05010
10
OSK05011
11
OSK06001
13
OSK06003
15
OSK06016
28
1.03
1.18
0.269
0.767
0.772
1.59
0.589
0.704
0.524
1.01
0.1
13.7
0.1
9.1
5.1
0.2
0.4
0.4
3.1
37.6
9.1
9.0
2.2
6.1
6.4
14.0
5.1
6.1
4.4
5.6
90.8
77.3
97.6
84.8
88.5
85.7
94.5
93.5
92.5
56.8
5850
33.3
882
34.5
64.4
2900
632
751
72.0
7.61
5220
25.7
3420
42.7
79.4
1580
1050
1030
135
6.90
Osaka Basin (South side of east block)
OSK05004
4
OSK06006
18
OSK06007
19
OSK06010
22
OSK06011
23
3.44
7.31
5.51
4.51
4.88
0.2
32.3
45.2
31.5
1.9
30.6
43.8
26.6
27.3
42.6
69.3
23.9
28.2
41.1
55.4
9590
69.2
30.1
44.3
1130
1940
3.37
2.84
5.95
131
Izumi Group
OSK06004
OSK06005
KNK02006C
KNK02021C
16
17
K1
K14
1.35
1.92
0.586
2.28
0.6
0.1
5.4
17.6
11.9
17.0
4.8
16.7
87.6
82.9
89.8
65.7
1070
8220
45.8
48.3
706
3570
76.3
17.0
Others
OSK06002
OSK06008
OSK06009
OSK06015
KNK02034C
14
20
21
27
K68
0.810
0.801
0.955
0.141
6.59
0.1
37.0
54.7
7.9
8.0
7.1
4.5
3.9
1.0
54.0
92.9
58.5
41.4
91.0
38.0
5410
6.21
3.64
6.71
347
6340
7.21
3.45
52.4
21.8
Montainous range (Crystalline rock)
OSK06012
24
KNK02007C
K2
KNK02012C
K13
KNK02022C
K20
KNK02042C
K60
KNK02037A
A-37
KNK02036C
C-36
Kobe Basin
KOB01036
KOB01037
KOB02001
KOB02003
KOB02005
KOB02006
KNK02040E
KNK02035C
A-9
A-10
EK-1
EK-2
EK-6
EK-7
E-40
K77
(a)
(cm STP/gH2O)
3.70
23.1
24.7
96.5
718
40.2
96.6
Air corrected 3He/4He ratio and relative contributions of air, mantle and crustal components are estimated by assuming the endmember 3He/
He and 4He/ 20Ne ratio as follows: Air (ASW at 15° C): 3He/ 4He = 1.38 × 10–6, 4He/20Ne = 0.261; Mantle: 3He/4He = 1.1 × 10 –5, 4He/ 20Ne =
10,000; Crust: 3He/4He = 2 × 10 –8, 4He/20Ne = 10,000.
(b)
Corrected mantle 3He and crustal 4He concentrations are calculated from corrected He concentrations by multiplying relative concentrations
of mantle and crustal components, respectively. Corrected He concentrations before degassing were estimated from their measured 4He and 20Ne
concentrations. The depletion factor of 4He are assumed to be the same as those for 20Ne, which is estimated from measured 20Ne concentration
and ASW value at 15° C (Table 1).
4
68
N. Morikawa et al.
Fig. 5. Map of corrected 3He/ 4He ratio (× 10–6) of deep groundwater in the vicinity of the Osaka Basin with surface geology (after
Geological Survey of Japan/AIST, 2005). The values with asterisks (*) are data from Nagao et al. (1981), Sano and Wakita
(1985), Okada et al. (1994) and Matsumoto et al. (2003).
tribution of the atmospheric component (Fig. 4). One of
the procedures for eliminating atmospheric He component is to subtracting the amount of Heatm and Heea from
the total amount of He (Fourrè et al., 2002; Morikawa et
al., 2007). The Heatm can be estimate from solubility data.
An excess air component (Heea) can be determined using
Ne concentration (Morikawa et al., 2007);
4
He ea = ( 20Netot –
20
Neatm)•R(4He/20Ne)
(3)
where R(4He/20Ne) is the 4He/20Ne ratio in the atmosphere
(0.318; Ozima and Podosek, 2002). However, water-gas
separation altered the original amount of both atmospheric
and non-atmospheric He. We employ the procedure of
Craig et al. (1978). Table 2 lists 3He/4He ratios corrected
for the dissolved atmospheric component. Nagao et al.
(1981) first observed an unusual high 3He/4He ratio of
hot spring gases in the middle to south part of the Kinki
district. Sano and Wakita (1985) called this region the
“Kinki Spot”. Although the samples in this study are all
from this “Kinki Spot”, the 3He/4He ratios of many samples from the Osaka Basin are far lower than those from
previously reported data from the Kii Peninsula and adjacent region. Sixteen out of 43 samples show even lower
values than the atmospheric value (1.4 × 10–6), which indicates crustal 4He accumulation is dominant. The data
of Okada et al. (1994), which is also from the Osaka Basin, are similar to our data. In the following section, we
Relationship between geological structure and He isotopes in deep groundwater
69
Fig. 6. Geological cross section along A–A′ illustrated in Fig. 1 (after Uchiyama et al., 2001). Solid bar and number are the
position of screen (sampling depth) and 3He/ 4He ratio (×10 –6) of each sample, respectively.
will discuss the modification of the 3He/4He ratio in the
near surface of the shallow crust and its implication to
deep groundwater hydrology.
Relationship between geological structure and He isotopes
In this section, we discuss the relationship between
observed 3He/4He ratio, geology of the aquifer, and subsurface geological structure. Helium in the deep groundwater evolves its concentration and isotopic ratio during
groundwater flow by means of dissolving crustal helium
produced in an aquifer and crustal (and mantle) He migrated from deeper region.
Figure 5 shows the geographical distribution of aircorrected 3He/ 4He ratios of deep groundwater samples.
Helium isotopes in this region are distinctly different over
the region. The highest 3He/4He ratio was observed in
the northwest and southeast region of the studied area.
Both regions are in a mountainous range where the basement granites (or rhyolite) are outcropped with a dense
distribution of active faults. Highest ratio of over 10 –5
was observed in the Arima area, northern slope of Rokko
Mountains. This value is overlapping with the highest
value of mantle wedge beneath Japan (Nagao and
Takahashi, 1993) and is identical to the MORB value
(Graham, 2002). The samples of the Arima area have been
collected from artesian wells, located along the large tectonic line (Arima–Takatsuki Tectonic Line). A dense distribution of active faults is also shown in the southeastern part of studied area, located near the Median Tectonic
Line. Release of mantle He from the Median Tectonic Line
is also suggested by Doğan et al. (2006) for Shikoku Island, west of the Kii Peninsula.
Many of the samples from the basin also contain helium with a high 3He/ 4He ratio, but the ratio is distinctly
70
N. Morikawa et al.
lower than those from the mountainous range, suggesting a relatively minor contribution of radiogenic component in the basin (Table 2). Morikawa et al. (2005) suggested that these high 3He/ 4He ratios observed in deep
groundwaters from the Kobe Basin were due to the contribution of upwelling Arima-like fluid ( 3He/4He = 10–5)
through the faults. During the subsurface residence, the
dissolution of radiogenic component would caused a dilution of mantle He component resulting in lowering the
3
He/4He ratio. The high 3He/4He ratios were also observed
in the middle to south part of the basin along the Osaka
Bay (Sample Nos. 5, 9, 12). All these samples are near
and west of the Uemachi thrust fault (Fig. 5).
Exceptionally low 3He/4He ratios were observed from
the north to middle-east part of the Osaka Basin. The 3He/
4
He ratios less than atmospheric value are only found east
of the Uemachi fault of the north of the Yamato River.
Wakita et al. (1987) defined the region where hot spring
gases with a 3He/4He ratio over two times the atmospheric
ratio as the Kinki Spot. Our samples from the north to
middle-east part of the Osaka Basin show the ratios far
less than the atmospheric ratio, although these samples
are also from the Kinki Spot.
The subsurface geological structure of the Osaka Basin is well investigated by borehole data, seismic reflection survey and gravity data (e.g., Yoshikawa et al., 1987;
Inoue et al., 1998; Yokokura et al., 1998; Itoh et al., 2000;
Uchiyama et al., 2001). Figure 6 shows the geological
cross section along A–A′ of Fig. 1 which plotted with
sampling depth and corrected 3He/4He ratio. Most of the
samples are from the lowermost part of the Osaka Group
which is unconformably overlying the Cretaceous Ryoke
granitic rock. As described previously, the Osaka Basin
is a tectonic subsidence basin. The granitic basement rocks
of the basin have been broken into west and east blocks
The lowest 3He/ 4He ratios of groundwaters are distributed near the hollow granite basement.
0.14
1.3*
0.96
0.80
4.4
1.0
0.68
1.2
8.3*
0.81
0.27
5.7
4.5*
0.59 0.56*
0.56* 0.52
1.3 1.4*
0.77 0.77
1.6
2.8
1.0
4.2
1.9
3.4
Osaka Bay
3.0
5.5
4.6*
4.9
4.9
2.1*
8.0
10.4* 8.0
1.4
3.3
1.9
7.3
2.7*
4.5
8.3*
6.8
2.3
Depth of
the basement
Fig. 7. Plot of corrected 3He/ 4He ratio (×10–6) with a map
showing the depth to the top of the basement (after Horikawa
et al., 2002). The data sources of the values with asterisks (*)
are the same as those in Fig. 5.
by the Uemachi fault (Uchiyama et al., 2001). The plot
of the 3He/ 4He ratio in Fig. 6 indicates that higher 3He/
4
He ratios were observed from footwall blocks (west
block), while lower ratios are mainly from the hanging
wall one (east block). The existence of the Uemachi fault
obviously affects the aquifer in the lowermost part of the
Osaka Group and dissolved gases in this aquifer. The lowest 3He/4He ratio is observed in a region far from the thrust
fault on the hanging wall. Figure 7 shows the contour of
the depth of basement rocks. In the east block, the greatest degree of subsidence is observed in the middle part of
the block, and the depth of the basement rocks’ top gradually becomes shallower to the northern and southern side.
Spatial variation of mantle and crustal helium migration
controlled by geological structure
Deep groundwaters collected from the Osaka Basin
dissolved both mantle and crustal He. The difference in
the air corrected 3He/4He ratio for each sample indicates
different contribution of mantle and crustal He. Efficient
transportation of mantle He through the faults are proposed by Matsumoto et al. (2003) for the Kii Peninsula,
Doğan et al. (2006) for the Shikoku Island, Kennedy et
al. (1997) for the San Andreas fault and Kulongoski et
al. (2005) for the eastern Morongo Basin, California. The
groundwaters in the region where basement rocks are
outcropped retain the upper mantle 3He/4He value. It implies that mantle He comes up directly to the surface without being diluted with radiogenic 4He. Since moderately
high 3He/4He ratios were observed in the Kobe and Osaka
Basins, upwelling of mantle He through the faults could
have also occurred for these basins. As the basement granite beneath the Kobe and Osaka Basins are overlaid with
thick (500–2000 m) Plio–Pleistocene sedimentary rocks
(Osaka Group), mantle He would be prevented from
upwelling directly to the ground surface, but would be
trapped in the aquifer in the lowermost part of the Osaka
Group. Groundwaters in this aquifer accumulate 4He produced in an aquifer and surrounding rocks (crustal He).
The flux of mantle He through the Uemachi fault into the
aquifers in the east block will be smaller than those in the
west block because mantle He through this fault first encountered the aquifers in the west block and dissolved in
this aquifer (Fig. 6). The low 3He/4He ratio of the groundwater in the east block reflects this low flux of mantle
He. Characteristics of the He flux from the Ikoma fault,
east end of the east block, are not known because there
were no sampling points in the area. In the study area,
the tectonic movement started in Middle Pleistocene and
the aquifer was cuts off by the Uemachi fault. This resulted in a discontinuity of the aquifer and a distinctive
difference in the mantle He flux into the aquifer in the
lowermost part of the Osaka Basin. The data of shallow
groundwater in Okada et al. (1994) show low He concentration with a similar corrected 3He/4He ratio to those in
the deep groundwater from the same site. We suggest that
these observations indicate the limited flux of deep fluids into shallow aquifers due to the existence of deeper
aquifers.
Table 2 shows the relative contribution of air, mantle
and crustal helium. We have also listed the 3He concentration from the mantle component and 4He concentration from crustal component based on the calculated relative contribution of these components and 3He, 4He and
20
Ne concentrations. As described previously, many deep
Relationship between geological structure and He isotopes in deep groundwater
71
groundwaters have lost their original amount of noble
gases by water-gas separation. Helium concentrations
before degassing were estimated from their measured 4He
and 20Ne concentrations. The depletion factor of 4He are
assumed to be the same as those for 20Ne, which is estimated from the measured 20Ne concentration and ASW
value at 15°C (Table 1). The mantle 3He and crustal 4He
concentrations are calculated from corrected 4He concentrations by multiplying relative contributions of mantle
and crustal components, respectively. Both the concentrations of 3He originated from mantle and 4He from
crustal component are highly variable among the samples (Table 2). High crustal 4He concentrations (over
10 –5 cm 3STP/gH 2O) frequently appear in the samples
north of the east block (north of the Yamato River). Arithmetic mean values of crustal 4He concentrations are coincidentally the same value with the west block (1.3 ×
10 –5), despite the low contribution of mantle 3He in the
east block. If crustal 4He flux is also dominant through
the fault, crustal 4He is also selectively trapped in the
aquifer of the west block and will be limited for the east
block. The estimated crustal 4He concentration cannot
account for the flux through the faults but implies a relatively constant flux within the aquifer and/or from the
basement rock beneath the aquifer for the lowermost part
of the Osaka Basin.
CONCLUDING REMARKS AND HYDROLOGICAL
IMPLICATIONS FOR APPLYING HELIUM ISOTOPES
Based on these He results and relationship with geological and subsurface structure described above, we propose the following model to account for the distribution
of the 3He/4He ratio of groundwater in the vicinity of the
Osaka Basin. Mantle He is upwelling through the fault
system. Groundwaters in the region where basement rocks
are outcropped retain the upper mantle 3He/ 4He value
because mantle He comes up directly to the surface without being diluted with radiogenic 4He. Upwelling of mantle He through the faults should have also occurred for
the Osaka Basin. A deeply seated sedimentary layer in
the basin prevents the upwelling of mantle He to the surface because mantle He will be trapped in the aquifer in
the lowermost part of the Osaka Group. Groundwater in
this aquifer accumulates 4He produced in an aquifer and
surrounding rocks (crustal He). Since mantle He will be
dissolved in the aquifers in the west block, the flux to the
east block will be limited. The low 3He/ 4He ratios in deep
groundwater in the east block reflect this low flux of
mantle He.
Helium-4 concentration has the potential to be applied
to dating groundwater for a wide range of ages. However, there are many uncertain parameters; e.g., many
sources of He, magnitude of flux into an aquifer from an
72
N. Morikawa et al.
individual source, structure of the aquifer, and mixing of
groundwater. In order to improve the groundwater dating
method from 4He, it is essential to estimate the 4He flux
into the aquifer. One of the conventional ways to estimate the 4He flux is to divide the He concentration by the
age estimated from another dating method. Unfortunately,
there are no age data for these groundwaters. The model
for the Osaka Basin presented here implies that there are
at least two different sources of helium flux into an aquifer, mantle helium flux through a fault system and crustal
helium from underlying formation. The former should be
spatially heterogeneous, while crustal 4He flux is rather
spatially constant throughout the lowermost part of the
Osaka Basin.
Acknowledgments—We thank Mr. T. Kuramochi of Osaka
Prefecture for organizing the sampling in 2005 and 2006. Mr.
K. Nishikawa and K. Takashima of Oku Boring Co. Ltd. kindly
gave us assistance in the field. We also thank the well owners
for allowing us to take the groundwater samples. We are indebted to Drs. Y. Yechieli (Geological Survey of Israel), Li
Xiaodong (Osaka City Univ.), and Mr. M. Owa (Osaka City
Univ.) for their help in the field. We appreciate Drs. J. Matsuda
and D. R. Hilton for their careful reviews of the manuscript.
REFERENCES
Aka, F. T., Kusakabe, M., Nagao, K. and Tanyileke, G. (2001)
Noble gas isotopic compositions and water chemistry of
soda springs from the islands of Bioko, Sao Tome and
Annobon, along with Cameroon Volcanic Line, West Africa. Appl. Geochem. 16, 323–338.
Andrews, J. N. (1985) The isotopic composition of radiogenic
helium and its use to study groundwater movement in confined aquifers. Chem. Geol. 49, 339–351.
Andrews, J. N. and Lee, D. J. (1979) Inert gases in groundwater from the Bunter Sandstone of England as indicators
of age and paleoclimatic trends. J. Hydrol. 41, 233–252.
Ballentine, C. J., Burgess, R. and Marty, B. (2002) Tracing fluid
origin, transport and interaction in the crust. Rev. Mineral.
Geochem. 47, 539–614.
Benson, B. B. and Krause, D., Jr. (1980) Isotopic fractionation
of helium during solution: A probe for the liquid state. J.
Sol. Chem. 9, 895–909.
Castro, M. C. (2004) Helium sources in passive margin aquifers—new evidence for a significant mantle 3He source in
aquifers with unexpectedly low in situ 3He/4He production.
Earth Planet. Sci. Lett. 222, 897–913.
Castro, M. C., Stute, M. and Schlosser, P. (2000) Comparison
of 4He ages and 14C ages in simple aquifer systems: implications for groundwater flow and chronologies. Appl.
Geochem. 15, 1137–1167.
Craig, H., Lupton, J. E. and Horibe, Y. (1978) A mantle helium
component in Circum-Pacific volcanic gases: Hakone, the
Marianas and Mt. Lassen. Terrestrial Rare Gases (Alexander, E. C. and Ozima, M., eds.), 3–16, Center for Academic
Publishing Japan, Tokyo.
Crovetto, R., Fernandez-Prini, R. and Japas, M. L. (1982)
Solubilities of inert gases and methane in H2O and in D2O
in the temperature range of 300 to 600 K. J. Chem. Phys.
76, 1077–1086.
Doğan, T., Sumino, H., Nagao, K. and Notsu, K. (2006) Release of mantle helium from forearc region of the Southwest Japan arc. Chem. Geol. 233, 235–248.
Fourrè, E., LeGuern, F. and Jean-Baptiste, P. (2002) Helium
isotopes at Satsuma-Iwojima volcano, Japan. Geochem. J.
36, 493–502.
Geological Survey of Japan/AIST (ed.) (2005) 1:200000 seamless geological map of Japan (Dec. 8, 2005 version). RIODB 084, Geological Survey of Japan, AIST.
Graham, D. W. (2002) Noble gas isotope geochemistry of midocean ridge and ocean island basalts: characterization of
mantle source reservoirs. Rev. Mineral. Geochem. 47, 247–
318.
Heaton, T. H. E. and Vogel, J. C. (1981) “Excess air” in groundwater. J. Hydrol. 50, 201–216.
Horikawa, H., Mizuno, K., Satake, K., Sekiguchi, H., Kase, Y.,
Sugiyama, Y., Yokoto, H., Suehiro, M. and Pitarka, A. (2002)
Three-dimensional subsurface structure model beneath the
Osaka Plain. Annual Repor t on Active Fault and
Paleoearthquake Researches, No. 2, 291–324, Geological
Survey of Japan/AIST.
Huzita, K. (1990) Manchidani Unconformity and Rokko Movements—Middle Pleistocene fault-block movement and sealevel rise in Kinki, Japan. The Quaternary Research 29,
337–349 (in Japanese with English abstract).
Huzita, K. and Kasama, T. (1982) Geology of the OsakaSeihokubu District, Quadrangle Series, Scale 1:50,000.
Geological Survey of Japan, 112 pp.
Ikeda, R., Omura, K., Iio, Y., Ishii, H., Kabayashi, Y., Nishigami,
K. and Yamauchi, T. (2001) Crustal stress and strain measurements on land for studying the Nankai trough earthquake.
J. Geogr. 110, 554–556 (in Japanese with English abstract).
Inoue, N., Nakagawa, K. and Ryoki, K. (1998) Gravity anomalies and basement structure in Osaka Plain. Geophys. Expl.
(Butsuri-Tansa) 51, 1–16 (in Japanese with English abstract).
Itoh, Y., Takemura, K., Ishiyama, T., Tanaka, Y. and Iwaki, H.
(2000) Basin formation at a contractional bend of a large
transcurrent fault: Plio–Pleistocene subsidence of the Kobe
and northern Osaka Basins, Japan. Tectonophysics 321, 324–
341.
Jean-Baptiste, P., Mantisi, F., Dapoigny, A. and Stievenard, M.
(1992) Design and performance of a mass spectrometric
facility for measuring helium isotopes in natural waters and
for low-level tritium determination by the 3He ingrowth
method. Appl. Radiat. Isot. 43, 881–892.
Kauffman, S. and Libby, W. F. (1954) The natural distribution
of tritium. Phys. Rev. 93, 1337–1344.
Kennedy, B. M., Kharaka, Y. K., Evans, W. C., Ellwood, A.,
DePaolo, D. J., Thordsen, J., Ambats, G. and Mariner, R.
H. (1997) Mantle fluids in the San Andreas Fault system,
California. Science 278, 1278–1281.
Kulongoski, J. T., Hilton, D. R. and Izbicki, J. A. (2005) Source
and movement of helium in the eastern Morongo groundwater Basin: The influence of regional tectonics on crustal
and mantle helium fluxes. Geochim. Cosmochim. Acta 69,
3857–3872.
Marty, B., Torgersen, T., Meynier, V., O’Nion, K. and de
Marsily, G. (1993) Helium isotopic fluxes and groundwater
ages in the Dogger Aquifer, Paris Basin. Water Resour. Res.
29, 1025–1035.
Masuda, H., Sakai, H., Chiba, H. and Tsurumaki, M. (1985)
Geochemical characteristics of Na–Ca–Cl–HCO 3 type waters in Arima and its vicinity in the western Kinki district,
Japan. Geochem. J. 19, 149–162.
Masuda, H., Sakai, H., Chiba, H., Matsuhisa, Y. and Nakamura,
T. (1986) Stable isotopic and mineralogical studies of hydrothermal alteration at Arima Spa, southwest Japan.
Geochim. Cosmochim. Acta 50, 19–28.
Matsubaya, O., Sakai, H., Kusachi, I. and Satake, H. (1973)
Hydrogen and oxygen isotopic ratios and major element
chemistry of Japanese thermal water systems. Geochem. J.
7, 123–151.
Matsuda, J., Matsumoto, T., Sumino, H., Nagao, K., Yamamoto,
J., Miura, Y., Kaneoka, I., Takahata, N. and Sano, Y. (2002)
The 3He/4He ratio of the new internal He standard of Japan
(HESJ). Geochem. J. 36, 191–195.
Matsumoto, T., Kawabata, T., Matsuda, J., Yamamoto, K. and
Mimura, K. (2003) 3He/4He ratios in well gases in the Kinki
district, SW Japan: surface appearance of slab-derived fluids in a non-volcanic area in Kii Peninsula. Earth Planet.
Sci. Lett. 216, 221–230.
Mazor, E. and Nativ, R. (1992) Hydraulic calculation of groundwater flow velocity and age: examination of the basic
premises. J. Hydrol. 138, 211–222.
Morikawa, N., Kazahaya, K., Yasuhara, M., Inamura, A., Nagao,
K., Sumino, H. and Ohwada, M. (2005) Estimation of
groundwater residence time in a geologically active region,
by coupling 4He-concentration with helium isotopic ratios.
Geophys. Res. Lett., 32, L02406, doi:10.1029/
2004GL021501.
Morikawa, N., Kazahaya, K., Fourrè, E., Takahashi, H. A., JeanBaptiste, P., Ohwada, M., LeGuern, F. and Nakama, A.
(2007) Magmatic He distribution around Unzen volcano
inferred from intensive investigation of helium isotopes in
groundwater. J. Volcan. Geotherm. Res. (submitted).
Nagao, K. and Takahashi, E. (1993) Noble gases in the mantle
wedge and lower crust: an inference from the isotopic analyses of xenoliths from Oki-Dogo and Ichinomegata, Japan.
Geochem. J. 27, 229–240.
Nagao, K., Takaoka, N. and Matsubayashi, O. (1981) Rare gas
isotopic compositions in the natural gases from Japan. Earth
Planet. Sci. Lett. 53, 175–188.
Obara, K. (2002) Nonvolcanic deep tremor associate with subduction in southwest Japan. Science 296, 1969–1981.
Okada, T., Itaya, T., Sato, M. and Nagao, K. (1994) Noble gas
isotopic composition of deep underground water in Osaka
plain, central Japan: Evidence for mantle He and model for
new volcanism. The Island Arc 3, 221–231.
Ozima, M. and Podosek, F. A. (2002) Noble Gas Geochemistry.
Cambridge University Press, 286 pp.
Phillips, F. M. and Castro, M. C. (2003) Groundwater dating
and residence-time measurements. Surface and Groundwater, Weathering, and Soils, Treatise on Geochemistry Vol.
Relationship between geological structure and He isotopes in deep groundwater
73
5 (Holland, H. D. and Turekian, K. K., eds.), 451–497,
Elsevier, Oxford.
Sano, Y. and Wakita, H. (1985) Geophysical distribution of 3He/
4
He ratios in Japan: implications for arc tectonics and incipient magmatism. J. Geophys. Res. 90, 8729–8741.
Seno, T., Stein, S. and Gripp, A. E. (1993) A model for the
motion of the Philippine Sea plate consistent with NUVEL1 and geological data. J. Geophys. Res. 98, 17941–17948.
Smith, S. P. and Kennedy, B. M. (1983) The solubility of noble
gases in water and in NaCl brine. Geochim. Cosmochim.
Acta 47, 503–515.
Stute, M., Sonntag, C., Deak, J. and Schlosser, P. (1992) Helium in deep circulating groundwater in the Great Hungarian Plain—Flow dynamics and crustal and mantle helium
fluxes. Geochim. Cosmochim. Acta 56, 2051–2067.
Torgersen, T. and Clarke, W. (1985) Helium accumulation in
groundwater: I. An evaluation of sources and continental
flux of crustal 4He in the Great Artesian Basin. Geochim.
Cosmochim. Acta 49, 1211–1218.
Uchiyama, M., Mitamura, M. and Yoshikawa, S. (2001) Displacement rate of the Uemachi Fault and basement block
movements of the Osaka Plain, Southwest Japan. J. Geol.
Soc. Jpn. 107, 228–236 (in Japanese with English abstract).
Umeda, K., Ogawa, Y., Asamori, K. and Oikawa, T. (2006)
Aqueous fluids derived from a subducting slab: Observed
high 3 He emanation and conductive anomaly in a nonvolcanic region, Kii Peninsula southwest Japan. J. Volcanol.
Geotherm. Res. 149, 47–61.
74
N. Morikawa et al.
Wakita, H., Sano, Y. and Mizoue, M. (1987) High 3He emanation and seismic swarmsobserved in a nonvolcanic, forearc
region. J. Geophys. Res. 92, 12539–12546.
Weise, S. and Moser, H. (1987) Groundwater dating with helium isotopes. Techniques in Water Resource Development,
105–126, International Atomic Energy Agency.
Winckler, G., Kipfer, R., Aeschbach-Hertig, W., Botz, R.,
Schmidt, M., Schuler, S. and Bayer, R. (2000) Sub sea floor
boiling of Red Sea Brines: New indication from noble gas
data. Geochim. Cosmochim. Acta 64, 1567–1575.
Yokokura, T., Kano, N., Yamaguchi, K., Miyazaki, T., Ikawa,
T., Ohta, Y. and Kawanaka, T. (1996) On fault system and
basement structures in and around the epicentral region of
the 1995 Hyogo-ken Nanbu Earthquake: a brief report.
Geophys. Expl. (Butsuri-Tansa) 49, 435–451 (in Japanese
with English abstract).
Yokokura, T., Kano, N., Yamaguchi, K., Miyazaki, T., Ikawa,
T., Ohta, Y., Kawanaka, T. and Abe, S. (1998) Seismic profiling of deep geological structure in the Osaka Bay area.
Bull. Geol. Surv. Jpn. 49, 571–590 (in Japanese with English abstract).
Yoshikawa, S., Nakagawa, K., Kawabe, T., Furutani, M. and
Daishi, M. (1987) Reconsideration of the OD-2 and OD-1
core samples in Osaka City, central Japan. J. Geol. Soc. Jpn.
9, 653–665 (in Japanese with English abstract).
Zhou, Z. and Ballentine, C. J. (2006) 4He dating of groundwater associated with hydrocarbon reservoirs. Chem. Geol.
226, 309–327.