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381.
The expert system approach enables geochemical evidence to be integrated with geological, petrological and mineralogical evidence in identifying the eruptive setting of ancient volcanic rocks. This paper explains the development of ESCORT, an Expert System for Characterization of Rock Types. ESCORT uses as its knowledge base a set of dispersion matrices derived from a geochemical data bank of some 8000 immobile element analyses, together with tables of magma-type membership probabilities based on a-priori knowledge, the dominant flow type, the facies of intercalated sediment, the basement to the volcanic sequence, the presence or absence of an iron-enrichment trend and the phenocryst phase assemblage. Inferencing is based on the Bayes Decision Rule, adapted to take into account possible uncertainties in the geological evidence. Upper and lower probability thresholds are used to decide whether an interpretation is likely or unlikely. Evaluation of the system shows that it is able to overcome many of the well-publicized ambiquities attached to geochemical discrimination diagrams, as well as providing a unified method of decision making and a measure of the correctness of the interpretation. 相似文献
382.
Alan Matthews Julian R. Goldsmith Robert N. Clayton 《Geochimica et cosmochimica acta》1983,47(3):645-654
Oxygen isotope fractionations between zoisite and water have been studied at 400–700°C, PH2O = 13.4 kbar, using the three-isotope method described by Matsuhisaet al. (1978) and Matthewset al. (1983a). The zoisite-waier exchange reaction takes place extremely slowly and consequently direct-exchange calibration of equilibrium fractionation factors was possible only at 600 and 700°C. Fractionation factors at 400–600°C were determined from samples hydrothermally crystallized from a glass of the anhydrous zoisite composition. At 600°C, both exchange procedures gave identical fractionations within experimental error. Scanning electron microscope studies showed that the zoisite-water exchange reaction occurs largely by solution-precipitation mass-transfer mechanisms. The slow kinetics of zoisite-water exchange may be typical of hydrous silicates, since additional experiments on tremolite-water and chlorite-water exchange also showed very low rates. When the zoisite-water fractionation factors determined in this study are combined with the quartz and albite-water data of Matsuhisaet al. (1979) and the calcite-water data of O'Nellet al. (1969), mineral-pair fractionations are obtained for which the coefficients “A” in the equation 1000 In α = A × 106T?2 are:
Ab | Cc | Zo | |
Q | 0.50 | 0.50 | 1.56 |
Ab | 0.00 | 1.06 | |
Cc | 1.06 |