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Noncondensible gases from hot springs, fumaroles, and deep wells within the Valles caldera geothermal system (210–300°C) consist of roughly 98.5 mol% CO2, 0.5 mol% H2S, and 1 mol% other components. 3He/4He ratios indicate a deep magmatic source (R/Ra up to 6) whereas δ13C–CO2 values (−3 to −5‰) do not discriminate between a mantle/magmatic source and a source from subjacent, hydrothermally altered Paleozoic carbonate rocks. Regional gases from sites within a 50-km radius beyond Valles caldera are relatively enriched in CO2 and He, but depleted in H2S compared to Valles gases. Regional gases have R/Ra values ≤1.2 due to more interaction with the crust and/or less contribution from the mantle. Carbon sources for regional CO2 are varied. During 1982–1998, repeat analyses of gases from intracaldera sites at Sulphur Springs showed relatively constant CH4, H2, and H2S contents. The only exception was gas from Footbath Spring (1987–1993), which experienced increases in these three components during drilling and testing of scientific wells VC-2a and VC-2b. Present-day Valles gases contain substantially less N2 than fluid inclusion gases trapped in deep, early-stage, post-caldera vein minerals. This suggests that the long-lived Valles hydrothermal system (ca. 1 Myr) has depleted subsurface Paleozoic sedimentary rocks of nitrogen. When compared with gases from many other geothermal systems, Valles caldera gases are relatively enriched in He but depleted in CH4, N2 and Ar. In this respect, Valles gases resemble end-member hydrothermal and magmatic gases discharged at hot spots (Galapagos, Kilauea, and Yellowstone). 相似文献
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We report the use of new apparatus for the direct determination of the activities of components in minerals and melts by the measurement of their intrinsic vapour pressures at high temperatures using a Knudsen-cell mass spectrometer combination. The activity coefficients of Fe, Ni and Co have been determined using this technique in binary and ternary Fe-Co-Ni alloys over the temperature range 1200–1650°C. The results show negative deviations from ideality in the Fe-Ni system and both positive and negative deviations in Fe-Co. Activity coefficients determined in the ternary system were used to calculate the compositions of Fe-Ni-Co alloys in equilibrium with a gas of chondritic composition and the results are consistent with the compositions of metallic particles in Ca, Al rich inclusions in chondritic meteorites. 相似文献
106.
A latite dome in northwest Arizona contains a rare occurrence of primary SO4-rich scapolite phenocrysts. The total phenocryst assemblage consists of plagioclase (An20?An33), hornblende, biotite, and scapolite (Me68). Microphenocrysts include allanite and oxidized low-Ti magnetite. Electron microprobe analyses show that the scapolite contains about 1.74 wt.% S, which indicates an atomic S/(S + C) of 0.58. Although scapolite occurs in xenoliths in volcanic rocks and diatremes, as well as a metamorphic mineral in granulites, its occurrence as a primary igneous mineral is extremely rare.Ca-rich scapolite has been crystallized experimentally by others from melts with a wide range of SiO2, CaO, and Na2O contents, at temperatures above 825°C and pressures ranging from 3 to 15 kbar. Comparison of scapolite from this latite with synthetic scapolite crystallized from nepheline syenite melt suggests that the Arizona phenocrysts crystallized under conditions of 850 to 900°C, 3–6 kbar total pressure, and unusually high ?CO2 and ?SO2. The rarity of scapolite as a phenocryst mineral suggests that high partial pressures of CO2 and SO2 are rare in the magmatic environment. 相似文献
107.
Gerald K. Czamanske Glen R. Himmelberg Fraser E. Goff 《Earth and Planetary Science Letters》1976,33(1):111-118
Zoned spinel of unusual composition and morphology has been found in massive pyrrhotite-chalcopyrite-pent-landite ore from the La Perouse layered gabbro intrusion in the Fairweather Range, southeastern Alaska. The spinel grains show continuous zoning from cores with up to 53 wt.% Cr2O3 to rims with less than 11 wt.% Cr2O3. Their composition is exceptional because they contain less than 0.32 wt.% MgO and less than 0.10 wt.% Al2O3 and TiO2. Also notable are the concentrations of MnO and V2O3, which reach 4.73 and 4.50 wt.%, respectively, in the cores. The spinel is thought to have crystallized at low oxygen fugacity and at temperatures above 900°C, directly from a sulfide melt that separated by immiscibility from the gabbroic parental magma. 相似文献
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109.
An Operational Application of Automatic Feature Extraction: The Measurement of Cracks in Concrete Structures 总被引:1,自引:1,他引:1
Paul Dare Harry Hanley Clive Fraser Björn Riedel & Wolfgang Niemeier 《The Photogrammetric Record》2002,17(99):453-464
An understanding of the evolution of cracks in concrete structures due to long term natural deformation is important to civil engineers, but quantitative measurements can be difficult to make. However, digital imaging offers a potential solution. This short paper illustrates the operational application of automated image processing techniques for accurate, multi-temporal crack measurements. The first part of this paper provides an overview of automatic feature extraction, essential for automatic crack detection. The latter part describes the methods developed for detecting and measuring cracks. Due to the long term nature of the application, operational results have yet to be finalised, although sample results are presented 相似文献
110.
P. G. Simmonds R. G. Derwent A. J. Manning P. J. Fraser P. B. Krummel S. O'Doherty R. G. Prinn D. M. Cunnold B. R. Miller H. J. Wang D. B. Ryall L. W. Porter R. F. Weiss P. K. Salameh 《Journal of Atmospheric Chemistry》2004,47(3):243-269
In situ AGAGE GC-MS measurements of methyl bromide (CH3Br) and methyl chloride (CH3Cl) at Mace Head, Ireland and Cape Grim, Tasmania (1998–2001) reveal a complex pattern of sources. At Mace Head both gases
have well-defined seasonal cycles with similar average annual decreases of 3.0% yr−1 (CH3Br) and 2.6% yr−1 (CH3Cl), and mean northern hemisphere baseline mole fractions of 10.37 ± 0.05 ppt and 535.7 ± 2.2 ppt, respectively. We have used
a Lagrangian dispersion model and local meteorological data to segregate the Mace Head observations into different source
regions, and interpret the results in terms of the known sources and sinks of these two key halocarbons. At Cape Grim CH3Br and CH3Cl also show annual decreases in their baseline mixing ratios of 2.5% yr−1 and 1.5% yr−1, respectively. Mean baseline mole fractions were 7.94 ± 0.03 ppt (CH3Br) and 541.3 ± 1.1 ppt (CH3Cl). Although CH3Cl has astrong seasonal cycle there is no well-defined seasonal cycle in the Cape Grim CH3Br record. The fact that both gases are steadily decreasing in the atmosphere at both locations implies that a change has
occurred which is affecting a common, major source of both gases (possibly biomass burning) and/or their major sink process
(destruction by hydroxyl radical). 相似文献