CHEMICAL VARIATION WITHIN AND BETWEEN VOLCANIC ROCK SERIES - A STATISTICAL APPROACH

Using the statistical method of principal component analysis a new type of variation diagram is developed which combines simplicity with a large amount of available information. With the aid of this principal latent vector variation diagram the differentiation processes within the alkali and sub-alkali volcanic rock series and the origin of basic magma types are discussed. A study of the frequency distribution of the oxides within the alkali and sub-alkali volcanic rock series leads to the unexpected conclusion that the differentiation processes within the two series must be fundamentally different. By means of simple discriminant functions rock analyses of the alkali series can be distinguished from those of the sub-alkali series with a high degree of certainty. The mean of the discriminant values of a province can be used as an indication of the 'degree of alkalinity' of that province. Techniques such as these are ideally suited to the interpretation and comparison of the vast numbers of computerised chemical analyses that will invitably be obtained from X-ray fluorescence analysis and allied methods. © 1968 Oxford University Press.