Variation in noble gas isotopic composition of gas samples from the Aegean arc, Greece

In contrast to most other arcs with oceanic plate subduction, the Aegean arc is characterized by continent–continent subduction. Noble gas abundances and isotopic compositions of 45 gas samples have been determined from 6 volcanoes along the arc, 2 islands in the back-arc region and 7 sites in the surrounding areas. The ³He/⁴He ratios of the samples ranged from 0.027R_A to 6.2R_A (R_A denotes the atmospheric ³He/⁴He ratio of 1.4×10⁻⁶), demonstrating that even the maximum ³He/⁴He ratio in the region is significantly lower than the maximum ratios of most oceanic subduction systems, which are equal to the MORB value of 8±1 R_A. Regional variations in the ³He/⁴He ratio were observed both along and across the arc. The maximum ³He/⁴He ratio was obtained from Nisyros volcano located in the eastern end of the arc, and the ratio decreased westward possibly reflecting the difference in potential degree of crustal assimilation or the present magmatic activity in each volcano. Across the volcanic arc, the ³He/⁴He ratio decreased with an increasing distance from the arc front, reaching a low ratio of 0.063R_A in Macedonia, which suggested a major contribution of radiogenic helium derived from the continental crust. At Nisyros, a temporal increase in ³He/⁴He ratio due to ascending subsurface magma was observed after the seismic crisis of 1995–1998 and mantle neon was possibly detected. The maximum ³He/⁴He ratio (6.2R_A) in the Aegean region, which is significantly lower than the MORB value, is not probably due to crustal assimilation at shallow depth or addition of slab-derived helium to MORB-like mantle wedge, but inherent characteristics of the subcontinental lithospheric mantle (SCLM) beneath the Aegean arc.     

Radiogenic, fissiogenic and nucleogenic noble gases in zircons

The concentrations and isotopic compositions of argon, krypton and xenon have been determined in a grain size suite of zircons separated from pyroxene syenite of the Botnavatn Igneous Complex, southwestern Norway. The UPb systematics of these zircons has been studied previously.Kr and Xe are mixtures of fissiogenic gas from the spontaneous fission of²³⁸U and a component with atmospheric isotopic composition. From correlation diagrams the fissiogenic component is determined to be:⁸³Kr :⁸⁴Kr :⁸⁶Kr = (4.6 ± 1.3) : (11.0 ± 2.0) : 100 and¹²⁹Xe :¹³¹Xe :¹³²Xe :¹³⁴Xe :¹³⁶Xe = (0.6 ± 0.3) : (8.8 ± 0.2) : (56.8 ± 0.3) : (82.8 ± 0.4) : 100. The fissiogenic¹³⁶Xe/⁸⁶Kr is 6.0 ± 0.4.The Ar isotopic composition shows radiogenic⁴⁰Ar and a small excess of³⁸Ar. The excess³⁸Ar of about 1 × 10⁻¹¹ cm³ STP/g can be explained by reactions of α-particles with chlorine. Asymmetric fission of²³⁸U which has been postulated to cause argon isotope anomalies in U-rich minerals is unnecessary to explain the observed³⁸Ar concentrations.UXe ages are (1.19 ± 0.07) Ga, in agreement with UPb ages. However, if the recoil loss of fissiogenic Xe is considered the UXe ages of these zircons are about 1.53 Ga, which is comparable with the KAr ages and some RbSr ages observed in basement rocks in this region. The uncertainty of the product of fission yield times spontaneous fission decay constant of²³⁸U prevents to decide which age is the true crystallization age.     

Primordial noble gases in separated meteoritic minerals,II

Eight silicate samples from the Orgueil carbonaceous chrondrite were analyzed for He, Ne, Ar, and Xe by a stepwise heating technique. Six of the samples, including two etched with NaOH, were density fractions covering the following ranges: < 2.35, 2.35–2.45, 2.45–2.48, and > 2.48 g/cm³. Two others were grain-size fractions, separated according to their ability to form a colloid at pH 11.5.All fractions are grossly deficient in cosmogenic neon, having retained only 8–33% of their normal complement. Retentivity increases with density.All fractions give low²⁰Ne/²²Ne ratios above 950°C, suggestive of D.C. Black's exotic “Neon-E” component of²⁰Ne/²²Ne ≤ 3.4. The lowest ratios were found in the low-density and especially the non-colloidal fractions. This suggests that the host phase of Ne-E is a clay mineral of lower iron content and coarser grain size than the main silicates of Orgueil.The main fraction,ρ = 2.35–2.45g/cm³, is inhospitable to Xe; it contains less Xe and releases it more readily at low temperatures (30–35% in 1 hour at 550°C) than do any of the other fractions.     

The origins and concentrations of water,carbon, nitrogen and noble gases on Earth

The isotopic compositions of terrestrial hydrogen and nitrogen are clearly different from those of the nebular gas from which the solar system formed, and also differ from most of cometary values. Terrestrial N and H isotopic compositions are in the range of values characterizing primitive meteorites, which suggests that water, nitrogen, and other volatile elements on Earth originated from a cosmochemical reservoir that also sourced the parent bodies of primitive meteorites. Remnants of the proto-solar nebula (PSN) are still present in the mantle, presumably signing the sequestration of PSN gas at an early stage of planetary growth. The contribution of cometary volatiles appears limited to a few percents at most of the total volatile inventory of the Earth. The isotope signatures of H, N, Ne and Ar can be explained by mixing between two end-members of solar and chondritic compositions, respectively, and do not require isotopic fractionation during hydrodynamic escape of an early atmosphere.The terrestrial inventory of ⁴⁰Ar (produced by the decay of ⁴⁰K throughout the Earth's history) suggests that a significant fraction of radiogenic argon may be still trapped in the silicate Earth. By normalizing other volatile element abundances to this isotope, it is proposed that the Earth is not as volatile-poor as previously thought. Our planet may indeed contain up to ~ 3000 ppm water (preferred range: 1000–3000 ppm), and up to ~ 500 ppm C, both largely sequestrated in the solid Earth. This volatile content is equivalent to an ~ 2 (± 1) % contribution of carbonaceous chondrite (CI-CM) material to a dry proto-Earth, which is higher than the contribution of chondritic material advocated to account for the platinum group element budget of the mantle. Such a (relatively) high contribution of volatile-rich matter is consistent with the accretion of a few wet planetesimals during Earth accretion, as proposed by recent dynamical models.The abundance pattern of major volatile elements and of noble gases is also chondritic, with two notable exceptions. Nitrogen is depleted by one order of magnitude relative to water, carbon and most noble gases, which is consistent with either N retention in a mantle phase during magma generation, or trapping of N in the core. Xenon is also depleted by one order of magnitude, and enriched in heavy isotopes relative to chondritic or solar Xe (the so-called “xenon paradox”). This depletion and isotope fractionation might have taken place due to preferential ionization of xenon by UV light from the early Sun, either before Earth's formation on parent material, or during irradiation of the ancient atmosphere. The second possibility is consistent with a recent report of chondritic-like Xe in Archean sedimentary rocks that suggests that this process was still ongoing during the Archean eon (Pujol et al., 2011). If the depletion of Xe in the atmosphere was a long-term process that took place after the Earth-building events, then the amounts of atmospheric ¹²⁹Xe and ^131–136Xe, produced by the short-lived radioactivities of ¹²⁹I (T_1/2 = 16 Ma) and ²⁴⁴Pu (T_1/2 = 82 Ma), respectively, need to be corrected for subsequent loss. Doing so, the I–Pu–Xe age of the Earth becomes ≤ 50 Ma after start of solar system formation, instead of ~ 120 Ma as computed with the present-day atmospheric Xe inventory.     

Anomalous noble gases in josephinite and associated rocks?

In this paper we report Ne, Ar, Kr and Xe analyses of josephinite, Josephine Peridotite, and serpentinized Josephine Peridotite. In all three samples the elemental abundance patterns resemble patterns associated with surface waters, the Ne data do not exhibit the large²¹Ne enrichments observed earlier, and the Kr and Xe compositions are indistinguishable from atmospheric composition at all isotopes, including¹²⁹Xe. Our data thus offer no significant evidence for isotopic anomalies in the noble gases. We also argue that the previous claims for primordial atmospheric-like Ar, anomalous Kr and Xe, excess¹²⁹Xe, and 4.6 × 10⁹-year age are all questionable interpretations which cannot be defended against more prosaic alternatives. This leaves excess²¹Ne as the only noble gas argument for exotic origin; we suggest that this might be an experimental artifact. Until the²¹Ne question can be settled by more definitive experimentation, we feel that noble gas data cannot be used to support arguments that the origin of josephinite is more exotic than crustal serpentinization.     

Cosmogenic and radiogenic noble gases in the Dhajala chondrite

Whole rock and chondrules of the Dhajala chondrite were analyzed for Ne, Ar, Kr and Xe by total melting as well as by stepwise heating techniques. The cosmic ray exposure ages for the whole rock and the chondrules are6.2 ± 0.8 and6.3 ± 1.0m.y. as determined by the²¹Ne method and4.8 ± 1.5 and4.2 ± 2.0m.y. by the³⁸Ar method, respectively. The K-Ar age of the whole rock is4.2 ± 0.4b.y. The elemental composition of the trapped gas in this chondrite is of “planetary” type. The radiogenic¹²⁹Xe contents in the whole rock and chondrules are similar and this component is very retentively sited in the chondrules.     

Variations in the chemical and isotopic composition of fluids discharged from the Taupo Volcanic Zone, New Zealand

Contents of H₂O, CO₂ and Cl in well discharges from six explored geothermal systems of the Taupo Volcanic Zone, New Zealand, point to the existence of two distinct source fluids. The fluid present in discharges from systems along the eastern boundary is characterised by high CO₂ contents, 1.6 ± 0.5 , at mole ratios of 3.9 ± 1.5. High (0.06) and (12) weight ratios in these waters suggest that all four constituents are derived from associated andesitic rock. Geothermal discharges in the western parts of the TVZ, dominated by rhyolitic magmatism, are characterised by low CO₂ contents, 0.12 ± 0.05 , and low (0.14 ± 0.1) ratios. Again, relative Cl, B, Li and Cs contents agree with those of this potential source rock. High and ratios in the east are typical of fluids affected by the addition of volatiles released from subducted marine sediments. For the western systems, these ratios resemble more closely those expected for mantle-derived volatiles. The isotopic compositions of all deep waters point to the presence of variable amounts of a magmatic component, some 14 ± 5% in the eastern and 6 ± 2% in the western systems. The observed variations are explained in terms of interaction of volatiles released from the subducted sediments with material of the mantle wedge to form a volatile-charged, high-alumina basalt. Its convective rise, in a direction opposite to that of the down-going slab, leads to high enrichment in volatiles of the magmas generated beneath the eastern parts of the TVZ and increases their ability to intrude the continental crust. Further fractional crystallisation and assimilation leads to the formation of volatile-rich andesitic melts, partly extruded to form the volcanoes of the andesitic arc, partly intruded to act as source rocks for the high-gas geothermal systems. Batches of high-alumina basalt, depleted in subducted volatiles, travel farther west to pond beneath a zone of crustal extension. Following extensive fractionation, highly siliceous melts, carrying predominantly mantle-type volatiles, rise beneath the western part of the TVZ to supply both heat and volatiles to the geothermal systems there.     

Diffusive fractionation of noble gases and helium isotopes during mantle melting

The large differences in He and Ar diffusivities in silicate minerals could result in fractionation of the He/Ar ratio during melting of the mantle, producing He/Ar ratios in the primary mantle melts that are higher than those of the bulk mantle. Modeling noble gas diffusion out of the bulk mantle into fast diffusion pathways (such as fractures or melt channels) suggests that significant (order of magnitude) He/Ar fractionation will occur if the fast diffusion channels are spaced several meters apart and the noble gas residence in these diffusion channels is of the order days to weeks. In addition, the 15% difference in ³He and ⁴He diffusivities could also produce isotopic fractionation between the melt and its solid source. Modeling the behavior of He and Ar during melting shows that small increases (few %) in ³He/⁴He should be correlated with larger variations (factor of 5) in ⁴He/⁴⁰Ar. However, in order to test this hypothesis the effects of subsequent He–Ar fractionation that occur during degassing have to be corrected. I describe a scheme that can separate He/Ar variations in the primary melt from overprinted fractionation during magmatic degassing. Using the degassing-corrected data, there is a correlation between the primary melt’s ⁴He/⁴⁰Ar and ³He/⁴He in mid-ocean ridge basalts (MORBs). The slope of the correlation is consistent with the models of preferential diffusion of ³He relative to ⁴He and of ⁴He relative to ⁴⁰Ar from the solid mantle into the melt. Diffusive fractionation of noble gases during melting of the mantle can also account for low ⁴He/⁴⁰Ar ratios commonly found in residual mantle xenoliths: preferential diffusion of He relative to Ar will produce some regions of the mantle with low ⁴He/⁴⁰Ar, the complement of the high ⁴He/⁴⁰Ar ratios in basalts. Diffusive fractionation cannot, however, account for differences between the He and Ne isotopic compositions of MORBs compared with ocean island basalts (OIBs); not only are the extremely high ³He/⁴He ratios of OIBs (up to 50 Ra) difficult to produce at reasonable mantle time and lengthscales, but also the Ne isotopic compositions of MORBs and OIBs do not lie on a single mass fractionation line, therefore cannot result from diffusive fractionation of a single mantle Ne source. If preferential diffusion of He from the solid mantle into primary melts is a significant process during generation of MORBs, then it is difficult to constrain the He concentration of the mantle: He concentrations in basalts and the He flux to the ocean essentially result from extraction of He from a larger (and unknown) volume of mantle than that that produced the basalts themselves. The He concentration of the mantle cannot be constrained until more accurate estimates of the diffusion contribution are available.     

On the distribution of noble gases in Allende: a differential oxidation study

We have developed a closed-system combustion technique and utilized it to progressively oxidize a gas-rich, highly carbonaceous acid residue and a fine-grained (<4 μm) matrix sample from the Allende C3V meteorite and analyze the released gases mass spectrometrically. For the residue complete gas mobilization occurs at temperatures below 600°C. The temperature interval over which most of the gases are released coincides with that for combustion of most of the carbon. Release is primarily due to chemical attack rather than thermal activation of the gases. There are somewhat different oxidation thresholds for the heavy gases (Ar, Kr, and Xe) and the light gases (He, Ne), indicating chemically different sites for the two groups. Relative enhancement of isotopically anomalous components near 600°C is as large as in any open-system oxidation method. Differential combustion of the matrix sample reveals three distinct outgassing peaks, the first matching the release from the carbonaceous residue (“combustibles”), the second attributed to sulfides, and the third tentatively assigned to silicates. They comprise about 53%, 7% and 40% of the total heavy gases respectively. While the “sulfides” exhibit a small fission-like component, the Xe in the “silicates” appears isotopically uniform with roughly AVCC composition. The “combustibles” of the matrix contain relatively less excess¹²⁹Xe than the residue, perhaps indicating that ～10% of the total¹²⁹Xe in the residue was acquired from “silicates” by redistribution during acid treatment. We cannot rule out the possibility that planetary gases assigned to “sulfides” or “silicates” actually reside in carbonaceous phases somehow sheltered within soluble mineral assemblages, or in acid-soluble carbonaceous phases resistant to oxidation. Integrated releases below and above 600°C during the matrix combustion exhibit virtually identical heavy gas elemental composition, implying similar fractionation during planetary gas entrapment in various materials or in the same material in various environments.     

Chemical and stable isotopic models for boundary creek warm springs, southwestern Yellowstone National Park, Wyoming

Thermal springs of the Boundary Creek hydrothermal system in the southwestern part of Yellowstone Park outside the caldera boundary vary in chemical and isotopic composition, and temperature. The diversity may be accounted for by a combination of processes including boiling of a deep thermal water, mixing of the deep thermal water with cool meteoric water and/or with condensed steam or steam-heated meteoric water, and chemical reactions with surrounding rocks. Dissolved-silica, Na⁺, K⁺ and Ca²⁺ contents of the thermal springs could result from a thermal fluid with a temperature of 200 ± 20°C. Chloride-enthalpy and silica-enthalpy mixing models suggest mixing of 230°C, 220 mg/l Cl⁻ thermal water with cool, low-Cl⁻ components. A 350 to 390°C component with Cl⁻ ≥ 300 mg/l is possibly present in thermal springs inside the caldera but is not required to fit observed spring chemical and isotopic compositions. Irreversible mass transfer models in which a low-temperature water reacts with volcanic glass as it percolates downward and warms, can account for observed pH and dissolved-silica, K⁺, Na⁺, Ca²⁺ and Mg²⁺ concentrations, but produces insufficient Cl⁻ or F⁻ for measured concentrations in the warm springs. The ratio of a_Na/a_H, and Cl⁻ are best accounted for in mixing models. The water-rock interaction model fits compositions of acid-sulfate waters observed at Summit Lake and of low-Cl⁻ waters involved in mixing.The cold waters collected from southwestern Yellowstone Park have δD values ranging from −118 to −145 per mil and δ¹⁸O values of −15.9 to −19.4 per mil. Two samples from nearby Island Park have δD values of −112 and −114 per mil and δ¹⁸O values of −15.1 and −15.3 per mil. All samples of thermal water plot significantly to the right of the meteoric water line. The low Cl⁻ and variable δD values of the thermal waters indicate isotopic compositions are derived by extensive dilution with cold meteoric water and by steam separation on ascent to the surface. Many of the hot springs with higher δD values may contain in addition a significant amount of high-D, low-Cl⁻, acid-sulfate or steam-heated meteoric water. Mixing models, Cl⁻ content and isotopic compositions of thermal springs suggest that 30% or less of a deep thermal component is present. For example, the highest-temperature springs from Three Rivers, Silver Scarf and Upper Boundary Creek thermal areas contain up to 70% cool meteoric water and 30% hot water components, springs at Summit Lake and Middle Boundary Creek spring 57 are acid-sulfate or steam-heated meteoric water; springs 27 and 48 from Middle Boundary Creek and 49 from Mountain Ash contain in excess of 50% acid-sulfate water; and Three Rivers spring 46 and Phillips could result from mixing hot water with 55% cool meteoric water followed by mixing of acid-sulfate water. Extensive dilution by cool meteoric water increases the uncertainties in quantity and nature of the deep meteoric, thermal component.     

Chemical and isotopic investigation of warm springs associated with normal faults in Utah

Thermal springs associated with normal faults in Utah have been analyzed for major cations and anions, and oxygen and hydrogen isotopes. Springs with measured temperatures averaging greater than 40°C are characterized by Na + K- and SO₄ + Cl-rich waters containing 10³ to 10⁴ mg/l of dissolved solids. Lower temperature springs, averaging less than 40°C, are more enriched in Ca + Mg relative to Na + K. Chemical variations monitored through time in selected thermal springs are probably produced by mixing with non-thermal waters. During the summer months at times of maximum flow, selected hot springs exhibit their highest temperatures and maximum enrichments in most chemical constituents.Cation ratios and silica concentrations remain relatively constant through time for selected Utah thermal springs assuring the applicability of the geothermometer calculations regardless of the time of year. Geothermometer calculations utilizing either the quartz (no steam loss), chalcedony or Mg-corrected Na/K/Ca methods indicate that most thermal springs in Utah associated with normal faults have subsurface temperatures in the range of 25 to less than 120°C. This temperature range suggests fluid circulation is restricted to depths less than about three kilometers assuming an average thermal gradient of about 40°C/km.Thermodynamic calculations suggest that most thermal springs are oversaturated with respect to calcite, quartz, pyrophyllite, (Fe, Mg)-montmorillonite, microcline and hematite, and undersaturated with respect to anhydrite, gypsum, fluorite and anorthite. Chalcedony and cristobalite appear to be the only phases consistently at or near saturation in most waters. Theoretical evaluation of mixing on mineral saturation trends indicates that anhydrite and calcite become increasingly more undersaturated as cold, dilute groundwater mixes with a hot (150°C), NaCl-rich fluid. The evolution of these thermal waters issuing from faults appears to be one involving the dissolution of silicates such as feldspars and micas by CO₂-enriched groundwaters that become more reactive with increasing temperature and/or time. Solution compositions plotted on mineral equilibrium diagrams trend from product phases such as kaolinite or montmorillonite toward reactant phases dominated by alkali feldspars.Isotopic compositions indicate that these springs are of local surface origin, either meteoric (low TDS, < 5000 mg/l) or connate ground water (high TDS, > 5000 mg/l). Deviations from the meteoric water line are the result of rock-water isotopic exchange, mixing or evaporation. Fluid source regions and residence times of selected thermal spring systems (Red Hill, Thermo) have been evaluated through the use of a σ D-contour map of central and western Utah. Ages for waters in these areas range from about 13 years to over 500 years. These estimates are comparable to those made for low-temperature hydrothermal systems in Iceland.     

The strontium isotopic composition of seawater,and seawater-oceanic crust interaction

The⁸⁷Sr/⁸⁶Sr ratio of seawater strontium (0.7091) is less than the⁸⁷Sr/⁸⁶Sr ratio of dissolved strontium delivered to the oceans by continental run-off (～0.716). Isotope exchange with strontium isotopically lighter oceanic crust during hydrothermal convection within spreading oceanic ridges can explain this observation. In quantitative terms, the current⁸⁷Sr/⁸⁶Sr ratio of seawater (0.7091) may be maintained by balancing the continental run-off flux of strontium (0.59 × 10¹² g/yr) against a hydrothermal recirculation flux of 3.6 × 10¹² g/yr, during which the⁸⁷Sr/⁸⁶Sr ratio of seawater drops by 0.0011. A concomitant mean increase in the⁸⁷Sr/⁸⁶Sr ratio of the upper 4.5 km of oceanic crust of 0.0010 (0.7029–0.7039) should be produced. This required⁸⁷Sr enrichment has been observed in hydrothermally metamorphosed ophiolitic rocks from the Troodos Massif, Cyprus.The post-Upper Cretaceous increase in the strontium isotopic composition of seawater(～0.7075–0.7091) covaries smoothly with inferred increase in land area. This suggests that during this period the main factor which has caused variability in the⁸⁷Sr/⁸⁶Sr ratio of seawater strontium could have been variation in the magnitude of the continental run-off flux caused by variation in land area. Variations in land area may themselves have been partly a consequence of variations in global mean sea-floor spreading rate.     

Chemical composition of thermal springs, cold springs, streams, and gas vents in the Mt. Amiata geothermal region (Tuscany, Italy)

A geochemical study of thermal and cold springs, stream waters and gas emissions has been carried out in the Mt. Amiata geothermal region.The cold springs and stream waters do not seem to have received significant contribution from hot deep fluids. On the contrary, the thermal springs present complex and not clearly quantifiable interactions with the hot fluids of the main geothermal reservoir.The liquid-dominated systems in the Mt. Amiata area, like most of the high-enthalpy geothermal fields in the world, are characterized by saline, NaCl fluids. The nature of the reservoir rock (carbonatic and anhydritic), and its widespread occurrence in central Italy, favor a regional circulation of “Ca-sulfate” thermal waters, which discharge from its outcrop areas. Waters of this kind, which have been considered recharge waters of the known geothermal fields, dilute, disperse and react with the deep geothermal fluids in the Mt. Amiata area, preventing the use of the main chemical geothermometers for prospecting purposes. The temperatures obtained from the chemical geothermometers vary widely and are generally cooler than temperatures measured in producing wells.Other thermal anomalies in central Italy, apart from those already known, might be masked by the above-mentioned circulation. A better knowledge of deep-fluid chemistry could contribute to the calibration of specific geothermometers for waters from reservoirs in carbonatic rocks.     

Coseismic changes in the chemical composition of volcanic gases from the Owakudani geothermal area on Hakone volcano,Japan

The chemical and isotopic compositions of volcanic gases at a borehole and a natural fumarole in the Owakudani geothermal area, Hakone volcano, Japan, have been repeatedly measured since 2001, when a seismic swarm occurred in the area. The CO₂/H₂O and CO₂/H₂S ratios were high in 2001. It increased in 2006 and again in 2008 when seismic swarms occurred beneath the geothermal area. The observed increases suggest the injection of CO₂- and SO₂-rich magmatic gas into the underlying hydrothermal reservoir, implying that the magmatic gas was episodically supplied to the hydrothermal system in 2006 and 2008. The earthquake swarms probably resulted from the injection of gas through the shallow crust accompanying the break of the sealing zone.     

Rare gas isotopic compositions in natural gases of Japan

Isotopic and elemental compositions of rare gases in various types of gas samples collected in the Japanese Islands were investigated. Excess³He was found in most samples. Many samples showed a regionally uniform high³He/⁴He ratio of about 7 times the atmospheric ratio. The He concentrations varied from 0.6 to 1800 ppm, and they were low in CO₂-rich gases and high in N₂-rich gases. Ne isotopic deviations from the atmospheric Ne were detected in most volcanic gases. The deviations and the elemental abundance patterns in volcanic gases can be explained by a mixing between two components, one is mass fractionated rare gases and the other is isotopically atmospheric and is enriched in heavy rare gas elements. Ar was a mixture of mass fractionated Ar, atmospheric Ar and radiogenic Ar, and the contribution of radiogenic⁴⁰Ar was small in all samples. Except for He, elemental abundance patterns were progressively enriched in the heavier rare gases relative to the atmosphere. Several samples were highly enriched in Kr and Xe relative to the abundance pattern of dissolution equilibrium of atmospheric rare gases in water. The component which is highly enriched in heavy rare gases may be released from sedimentary materials in the crust.