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M. Sato

Publications and source records attributed to M. Sato.

12 recordsLinked to original sources
USGS2002

Helium and carbon gas geochemistry of pore fluids from the sediment-rich hydrothermal system in Escanaba Trough

Ocean Drilling Program (ODP) Leg 169, which was conducted in 1996 provided an opportunity to study the gas geochemistry in the deeper part of the sediment-rich hydrothermal system in Escanaba Trough. Gas void samples obtained from the core liner were analyzed and their results were compared with analytical data of vent fluid samples collected by a submersible dive program in 1988. The gas geochemistry of the pore fluids consisted mostly of a hydrothermal component and was basically the same as that of the vent fluids. The He isotope ratios (R/RA = 5.6-6.6) indicated a significant mantle He contribution and the C isotopic compositions of the hydrocarbons [??13C(CH4) = -43???, ??13C(C2H6) = -20???] were characterized as a thermogenic origin caused by hydrothermal activity. On the other hand, the pore fluids in sedimentary layers away from the hydrothermal fields showed profiles which reflected lateral migration of the hydrothermal hydrocarbons and abundant biogenic CH4. Helium and C isotope systematics were shown to represent a hydrothermal component and useful as indicators for their distribution beneath the seafloor. Similarities in He and hydrocarbon signatures to that of the Escanaba Trough hydrothermal system were found in some terrestrial natural gases, which suggested that seafloor hydrothermal activity in sediment-rich environments would be one of the possible petroleum hydrocarbon generation scenarios in unconventional geological settings. ?? 2002 Elsevier Science Ltd. All rights reserved.

Applied Geochemistry↗
USGS1992

Persistency-field Eh-pH diagrams for sulfides and their application to supergene oxidation and enrichment of sulfide ore bodies

At temperatures prevailing near the Earth's surface, metastable co-existence of chemical substances is common because chemical reactions that would directly lead to the attainment of thermody-namically most stable equilibria are often blocked by high activation energy barriers. The persistency of a metastable assemblage is then governed by alternative reaction paths that provide lower activation energy barriers. Comparison of observed mineral assemblages in the supergene oxidized and enriched sulfide ores with corresponding stability Eh-pH diagrams reveals that the supergene assemblages are mostly metastable due primarily to the persistency of sulfide minerals beyond stability boundaries. A new set of diagrams called persistency-field Eh-pH diagrams has been constructed for binary metal sulfides on the basis of electrochemical and other experimental data. Each diagram delineates the persistency field, which is a combined field of thermodynamic stability and reaction path-controlled metastability, for a specific sulfide mineral. When applied to the supergene assemblages, these new diagrams show much better correspondence to the field observations. Although there may still be room for further refinement, the new diagrams appear to provide a strong visual aid to the understanding of the behavior of sulfide minerals in the supergene conditions.

Geochimica et Cosmochimica Acta↗
USGS1985

Anomalous hydrogen emissions from the San Andreas fault observed at the Cienega Winery, central California

We began continuous monitoring of H2 concentration in soil along the San Andreas and Calaveras faults in central California in December 1980, using small H2/O2 fuel-cell sensors. Ten monitoring stations deployed to date have shown that anomalous H2 emissions take place occasionally in addition to diurnal changes. Among the ten sites, the Cienega Winery site has produced data that are characterized by very small diurnal changes, a stable baseline, and remarkably distinct spike-like H2 anomalies since its installation in July 1982. A major peak appeared on 1-10 November 1982, and another on 3 April 1983, and a medium peak on 1 November 1983. The occurrences of these peaks coincided with periods of very low seismicity within a radius of 50 km from the site. In order to methodically assess how these peaks are related to earthquakes, three H2 degassing models were examined. A plausible correlational pattern was obtained by using a model that (1) adopts a hemicircular spreading pattern of H2 along an incipient fracture plane from the hypocenter of an earthquake, (2) relies on the FeO-H2O reaction for H2 generation, and (3) relates the accumulated amount of H2 to the mass of serpentinization of underlying ophiolitic rocks; the mass was tentatively assumed to be proportional to the seismic energy of the earthquake. ?? 1985 Birkha??user Verlag.

Pure and Applied Geophysics PAGEOPH↗
USGS1984

Intrinsic oxygen fugacity measurements on seven chondrites, a pallasite, and a tektite and the redox state of meteorite parent bodies

Intrinsic oxygen-fugacity ( f O 2 ) measurements were made on five ordinary chondrites, a carbonaceous chondrite, an enstatite chondrite, a pallasite, and a tektite. Results are of the form of linear log f O 2 − 1 T "> fO 2 −1T plots. Except for the enstatite chondrite, measured results agree well with calculated estimates by others. The tektite produced f O 2 values well below the range measured for terrestrial and lunar rocks. The lowpressure atmospheric regime that is reported to follow large terrestrial explosions, coupled with a very high temperature, could produce glass with f O 2 in the range measured. The meteorite Salta (pallasite) has low f O 2 and lies close to Hvittis (E6). Unlike the other samples, results for Salta do not parallel the iron-wüstite buffer, but are close to the fayalite-quartz-iron buffer in slope. Minor reduction by graphite appears to have taken place during metamorphism of ordinary chondrites. f O 2 values of unequilibrated chondrites show large scatter during early heating suggesting that the constituent phases were exposed to a range of f O 2 conditions. The samples equilibrated with respect to f O 2 in relatively short time on heating. Equilibration with respect to f O 2 in ordinary chondrites takes place between grades 3 and 4 of metamorphism. Application of P − T − f O 2 relations in the system C-CO-CO 2 indicates that the ordinary chondrites were metamorphosed at pressures of 3–20 bars, as it appears that they lay on the graphite surface. A steep positive thermal gradient in a meteorite parent body lying at the graphite surface will produce thin reduced exterior, an oxidized near-surface layer, and an interior that is increasingly reduced with depth; a shallow thermal gradient will produce the reverse. A body heated by accretion on the outside will have a reduced exterior and oxidized interior. Meteorites from the same parent body clearly are not required to have similar redox states.

Geochimica et Cosmochimica Acta↗
USGS1977

Measured oxygen fugacities of the Angra dos Reis achondrite as a function of temperature

Measurements of the oxygen fugacity (ƒO 2 ) as a function of temperature ( T ) were made on an interior bulk sample of the cumulate achondrite, Angra dos Reis. Data clustered between the ƒO 2 -T relationship of the iron-wüstite assemblage and 1.2 log atm units above iron-wüstite. Interpretation of the data indicates that, throughout most of the cooling history of the meteorite, ƒO 2 values were defined by equilibria involving iron-bearing species at values close to the ƒO 2 of the assemblage iron-wüstite. Measured ƒO 2 data are compatible with crystallization and cooling at pressures greater than 50 bars.

Earth and Planetary Science Letters↗
USGS1970

Phase relations of a simulated lunar basalt as a function of oxygen fugacity, and their bearing on the petrogenesis of the Apollo 11 basalts

A glass of Apollo 11 basalt composition crystallizing at 1 atm at low ƒ 0 2 ">ƒ ƒ02 showed the following crystallization sequence; ferropseudobrookite at 1210°C, olivine at 1200°C, ilmenite and plagioclase at 1140°C, clinopyroxene at 1113°C. Ferropseudobrookite and olivine have a reaction relation to the melt. This sequence agrees with that assumed on textural grounds for some Apollo 11 basalts. It also indicates that the Apollo 11 basalts cannot have been modified by low-pressure fractionation.

Geochimica et Cosmochimica Acta↗
USGS1966

Half-cell potentials of semiconductive simple binary sulphides in aqueous solution

Theoretical consideration of the charge-transfer mechanism operative in cells with an electrode of a semiconductive binary compound leads to the conclusion that the half-cell potential of such a compound is not only a function of ionic activities in the electrolytic solution, but also a function of the activities of the component elements in the compound phase. The most general form of the electrode equation derived for such a compound with a formula M i X j which dissociates into M j+ and X i− ions in aqueous solution is E Mi Xj = E MiXj 0 + R T "> RT 2 ij "> 2 ij ln [ ( sua M j+ ) aq i · ( sua X) j M i X j "> (suaM j+ ) aq i · (suaX) j M i X j / ( sua X i− ) aq j · ( sua M) i M i X j "> (suaXi−)aq j · (suaM) i M i X j ], where E Mi Xj 0 = 1 2 "> 12 ( E M,M j+ 0 + E X i− , X ). The equation can be modified to other forms. When applied to semiconductive simple binary sulphides, these equations appear to give better descriptions of the observed electrode potentials of such sulphides than any other proposed equations.

Electrochimica Acta↗
USGS1966

Oxygen fugacities directly measured in magmatic gases

An electrochemical device was used to measure the fugacity of oxygen ( f O2 ) in holes drilled through the crust of Makaopuhi lava lake, Kilauea Volcano, Hawaii. Results obtained within 6 months of the lake formation show that log f O2 normally varies linearly with the reciprocal of the absolute temperature, and that chemical changes occurring in the cooling tholeiitic basalt are reflected in the f O2 values measured in the holes.

Hawaii↗
USGS1965

Electrochemical geothermometer: A possible new method of geothermometry with electro-conductive minerals

It was demonstrated with artificially processed sulfides that the minimum temperature of equilibration of a pair of electro - conductive minerals can be determined electrochemically. The procedure consists of setting up an electrochemical cell with the mineral electrodes and a suitable electrolyte, changing the temperature of the cell slowly in a furnace, and finding the temperature at which the emf of the cell becomes zero. The experimental results strongly suggest that this electrochemical method could be used as a new method of geothermometry .

Economic Geology↗
USGS1962

Glass electrodes sensitive to divalent cations

Glass electrodes suitable for measurement of divalent cations have been made and tested. Empirical and theoretical electrode equations have been presented to describe electrode behavior in a variety of aqueous solutions. Most electrodes show response interpretable as showing nearly ideal solid-solution behavior of the cations in the glass surface. The electrodes should be useful in the measurement of divalent-cation activities in natural waters and biological fluids, and useful in general analytical chemistry.

Science↗