Rare gas isotopic compositions in natural gases of Japan

Nagao, Keisuke; Takaoka, N.; Matsubayashi, Osamu

doi:10.1016/0012-821x(81)90152-7

Cited by 125 publications

(77 citation statements)

References 15 publications

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“…Ne and Ar concentrations are high in N2-rich samples. 20Ne/22Ne and 40Ar/36Ar ratios in natural gases in Japan are generally similar to the atmospheric values (Nagao et al, 1981;Sano and Wakita, 1985). First, if Ne, Ar and N2 originate from the atmosphere, the most probable step is the dissolution of air into surface water.…”

Section: General Trends In Chemical Compositionsmentioning

confidence: 52%

“…Thus, if atmospheric Ne and Ar are adsorbed preferentially by the sedi ments, the heavier Ar could be enriched in gas phase by degassing. According to Nagao et al (1981), the relative enrichment in heavy rare gases of C02-rich gases is attributed to a selective adsorption of heavy rare gases in sedimentary materials. Another interpretation for low Ne/Ar ratios is the possible contribution of radiogenic 40Ar in thee sediment .…”

Section: General Trends In Chemical Compositionsmentioning

confidence: 99%

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Chemical compositions of natural gases in Japan.

et al. 1985

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Chemical compositions of 96 natural gas samples from various locations and gas sources at 67 sampling sites in Japan were analyzed. A gas chromatograph system was developed for precise analyses of concentra tions of N2, CH4, C02, 02, Ar, He, Ne, H2, C2H6 and H2S. Overall analytical errors were estimated to be less than 5% for most samples. A sampling reservoir was newly designed in this work. Main components of natural gas samples were C02, N2 and CH4. Whereas N2 showed positive correlations with 4He and 3He concentrations, CO2 and CH4 showed negative correlations with them. Either a mechanism of dilution of the N2 gas enriched in magmatic He by CO2 and/or CH4, or of dissipation of CO2 from magmatic fluid was suggested. Concentrations of Ar and Ne were high in N,2-rich gas samples. Ratios Ne/N2 and Ar/N2 imply the presence of N2 of non-atmospheric origin. The close relationship between CO2 discharge and volcanic activities was pointed out. A possible source of CO2 is carbonates of sedimentary rocks from which CO2 may be released either by pyrolysis or by decomposition due to magmatic activity. Nitrogen and CO2 derived from oceanic sediments may be included in Japanese natural gases associated with subduction of a down-going slab. INTRODUCTIONThe JapaneseIslands are located in the subduction zone of the circum-Pacific orogenic belt. Geophysical features of NE Japan represent a typical island arc system. More than 2,000 hot springs and mineral springs are distributed in the islands and from some of them bubble gases are released.Gases are released also from gas and oil fields.Natural gases studied in this work include various types of occurrence, such as gases emerged from above sources. Chemical composition data on natural gases provide useful information regarding their origin, primordial volatiles of the Earth, and the evolution of the atmosphere.Chemical studies of natural gases started in 1900's (Moureu, 1904(Moureu, , 1923Yamada, 1922;Pencheff, 1929). Since 1960's, a number of data have been reported with the progress in gas chromatography (Gunter and Musgrave, 1966; Maki et al., 1966;Inai et al., 1967) It is difficult to determine Ne with ordinary gas chromatographic technique owing to its retention time close to that of He and low sen sitivity. Kawabe et al. (1981) reported Ne values in terms of Ne/Ar or Ne/N2 ratio using a 11 12 A. Urabe et al.TCD (thermal conductivity detector) gas chromatograph with He carrier gas. Sensitivity of Ne on the TCD, however, is not high enough to analyze samples with low Ne concentrations. Sugisaki et al. (1982) separated He from Ne in atmospheric samples using an 8-m MS 5A column.The method, however, is not ap propriate for natural gas analyses, because He/ Ne ratios in natural gases are generally 2 to 3 orders of magnitude higher than those of the atmosphere, which would result in insufficient separation of Ne from He.In this study a USD (ultrasonic detector)gas chromatograph with He carrier gas was used for the Ne determination.The USD is particu larly effective to det...

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Section: General Trends In Chemical Compositionsmentioning

confidence: 52%

Section: General Trends In Chemical Compositionsmentioning

confidence: 99%

Chemical compositions of natural gases in Japan.

et al. 1985

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“…Arima brines are highly saline (Cl = 1,000 ^• 36,000mg/1) and are considered to be mixtures of a unique deep brine of 6D = -32%o, 5180 = +10%o and Cl = 54g/1 and bicarbonate-rich dilute waters of meteoric origin. From the chemical and isotopic data presented in this paper and in the light of the high 3He/4He ratios observed in gases of Arima brines (Sano and Wakita, 1985;Nagao et al, 1981), it is likely that the deep brine originates from deep-lying magma underneath the Arima Spa or from sedimentary rocks during metamorphism induced by the magma.…”

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confidence: 75%

“…Recently, Nagao et al (1981) and Sano and Wakita (1985) reported much higher 3He/ 4He ratios in gases from the high and low -tem perature waters of Arima-Takarazuka Spas. Because 3He is definitely a mantle-derived com ponent, the high 3He/4He ratios imply the presence of a magmatic body underneath the Arima Spa, which could also be the heat source of this area.…”

Section: Chemical Characteristics Of Arima Brinesmentioning

confidence: 99%

“…3) Combined with the high 'He/'He ratios in gases carried by Arima brines (Nagao et al, 1981;Sano and Wakita, 1985), it was suggested that Arima brines and carbon dioxide respon sible for the other two types of water originated from a common magmatic fluid or formed simultaneously by metamorphic reactions caused by diapiric intrusion of andesitic magma into the crust underneath this area. The model sug gests that the deep brine and the carbon dioxide represent, respectively, the liquid and vapor phases evolved from the ascending deep fluid.…”

Section: Chemical Characteristics Of Arima Brinesmentioning

confidence: 99%

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Geochemical characteristics of Na-Ca-Cl-HCO3 type waters in Arima and its vicinity in the western Kinki district, Japan.

et al. 1985

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Triggering of earthquake swarms following the 2011 Tohoku megathrust earthquake

et al. 2015

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Earthquake swarms, often interpreted to result from fluids invading the brittle seismogenic zone, have seismicity patterns that are significantly different from an aftershock sequence. Following the M w 9.0 Tohoku-Oki earthquake, an unusual, shallow normal-faulting swarm sequence occurred near the Pacific coast in the southeast Tohoku district. An integrated approach combining geophysical and geochemical methods was utilized to establish the presence of aqueous fluids around the seismic source region and their derivation. Magnetotelluric inversion defined an anomalous conductor with a width of 20 km and clearly visible to depths of more than 20 km, extending to the base of the crust. Independent geophysical observations, including seismic, strongly support the suggestion that fluid-filled porous materials and fluids associated with slab dehydration are present in the convergent plate boundary. In order to provide geochemical constraints on the source of the fluids triggering the swarm activity, new helium isotope data were acquired from gas and water samples around the seismic source region. The observed 3 He/ 4 He ratios in these samples are significantly lower than the atmospheric value of 1.4 × 10 À6 , indicating that the mantle helium contribution is less than 10% of the total helium. Assuming the fluid-triggered swarm activity, the plausible explanations for the generation of fluids are limited to the following: (1) sediment porosity reduction and from smectite-illite and opal-quartz reactions in the subducting deep sea sediments, (2) metamorphism of fore-arc basin sediments, sedimentary, and/or volcanic rocks detached from the plate, or (3) dehydration reactions in the subducted oceanic crust and/or hydrated mantle below the fore-arc mantle wedge. Geophysical and geochemical findings suggest metamorphic fluids produced by isothermal decompression of altered sediments accompanying uplift and exhumation. Owing to continued fluid production at depths of~20 km, the fluids migrate into the seismic source region. The swarm sequence would have been triggered by stress changes associated with the Tohoku-Oki earthquake, enhanced by vertical metamorphic fluid expulsion from the reaction zone.

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Rare gas isotopic compositions in natural gases of Japan

Cited by 125 publications

References 15 publications

Chemical compositions of natural gases in Japan.

Chemical compositions of natural gases in Japan.

Geochemical characteristics of Na-Ca-Cl-HCO3 type waters in Arima and its vicinity in the western Kinki district, Japan.

Triggering of earthquake swarms following the 2011 Tohoku megathrust earthquake

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