Some Developments in Computer Applications in Petrology
During the last decade most of the computer applications in petrology have been concerned with data bases, petrological mixing models, the use of multivariate statistical techniques and, more recently, the modeling of igneous differentiation trends.
The characteristics of three of the major data bases, that is RKNFSYS (approximately 16,000 analyses), CLAIR (approximately 26,000 analyses), and PETROS (approximately 35,000 analyses) are compared. As a result of the experience gained in building these bases, a new international igneous data base (IGBA) is being organized, which will supercede eventually the others due to the inclusion of mineralogical and more textural information.
Recent developments in petrological mixing models include a better understanding of the principles behind the various models, in particular the fact that for constant sum major element data, a constrained model should be used. A completely generalized model capable of dealing with metamorphic reactions of the type A + B + C +.. =D+E+F+G.. also has been developed.
The use of principal-components analysis, factor analysis, and discriminant analysis in the interpretation of the chemistry of igneous rocks and mineral groups has become increasingly popular, but unfortunately, either through ignorance or the use of statistical packages, some of the interpretations have been incorrect. In particular, principal-component analysis based on the correlation matrix seems difficult to justify for major element geochemical data.
The modeling of igneous differentiation trends has been approached in two different ways. One mainly empirical method predicts the path of crystallization of any given anhydrous liquid composition at 1 atmosphere pressure. The inclusion of H2Oand pressure into the method is only a question of time. The other method is based on Rayleigh’s Law of fractional crystallization.
KeywordsDiscriminant Analysis Igneous Rock Fractional Crystallization Carnegie Inst Metamorphic Reaction
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