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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 98 (1988), S. 148-162 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The activity of Fe3O4 component in MgAl2O4-Fe3O4 spinels has been measured at 900° and 1000° C and 1 atm total pressure using a zirconia oxygen electrolyte. As previously reported for the dilute Fe3O4 concentration region (Mattioli and Wood 1986a), magnetite activity at 1000° C is greater than at 900° C at constant Fe3O4 mole fraction, for compositions across the MgAl2O4-Fe3O4 join between 20 and 80 mol% Fe3O4 component. The 1-atm solvus crest lies between 900° and 1000° C and, at 900° C the limbs are at Fe3O4 mole fractions of 0.2 and 0.6 approximately. Application of the O'Neill and Navrotsky (1983, 1984) cation distribution model indicates that the unusual activity — composition behavior of Fe3O4 is caused by changes in the equilibrium state of disorder of mixed MgAl2O4-Fe3O4 spinels relative to the disordered Fe3O4 standard state. In addition, both stoichiometric volumes (Mattioli et al. 1987) and activities across the MgAl2O4-Fe3O4 join suggest that short range order is significant for this binary. Excess free energy terms must be added to “ideal” Fe3O4 activities formulated from equilibrium cation distributions in complex MgAl2O4-Fe3O4 spinels in order to increase Fe3O4 activities to values consistent with observation and to generate the apparent region of immiscibility at 900° C. We have applied our activity data to the estimation of upper mantle spinel-lherzolite oxygen fugacities. We calculated that minimum $$f_{O_2 }$$ 's are about 2 log units below the synthetic QFM buffer at 15 kbar total pressure for Fe3O4 concentration of 2 mol%, in a Cr-free spinel phase. If a preliminary calibration of an additional 25 mol% Fe2+-substitution as FeCr2O4 or FeAl2O4 component is incorporated into Fe3O4 activity, then olivine-orthopyroxene-spinel assemblages of depleted-Type 1-spinel-lherzolite xenoliths indicate $$f_{O_2 }$$ 's close to QFM at 15 kbar. This is in good agreement with previous thermobarometric $$f_{O_2 }$$ estimates and in sharp contrast to 1 atm intrinsic $$f_{O_2 }$$ measurements near IW.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 322 (1986), S. 626-628 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The fo2 recorded by mantle spinel may be determined from either thermobarometric5'7 or intrinsic1'4 measurements. In the thermobarometric method, a heterogeneous equilibrium, such as 2 Fe3O4 (in spinel)+ 6 FeSiO3 (in orthopyroxene) = 6 Fe2SiO4 (in olivine) + O2 (D is used together with analysed ...
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0819
    Keywords: Key words Mt. Pelée ; Aerial photography ; Volcanic hazard ; Island arc ; Lesser Antilles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A desktop image processing and photogrammetric method was developed for digitizing black-and-white aerial photographs. The technique was applied to airborne optical images of Mt. Pelée, Martinique, a historically active volcano in the tropical Lesser Antilles island arc, to evaluate its utility for rapid geologic mapping and hazard assessment in vegetated areas. The digital approach provides several advantages over traditional air-photo interpretation by allowing for change detection in time-series images, morphologic characterization, development of digital elevation models from stereopairs, and geo-referencing with other digital data sets. A digital mosaic of Mt. Pelée was created from air photos acquired in 1951, which covered the region affected by the 1902 eruption. Severe mismatches occurred along edges of adjacent photographs prior to correction, which precluded quantitative morphologic analysis of the volcanic edifice. Geometric corrections and histogram equalization of digitized air photos allowed creation of a continuous mosaic. Comparison of the mosaic and a map based on differences in gray scale and texture to a volcanostratigraphic map revealed that not only the various deposits produced during the 1902 event were easily differentiated, but that older eruptive products were identified, suggesting that this approach may be used for rapid hazard evaluation of historically active tropical volcanoes.
    Type of Medium: Electronic Resource
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