Application of correspondence factor analysis to the study of major and trace elements in the Erta Ale Chain (Afar, Ethiopia)

Abstract

The lavas in the active volcanic chain of the Erta Ale were emplaced 1 million years ago on the new crust of oceanic character created by the separation of the Arabic plate and the African plate. This differentiated series ranges from the basalts to the hyperalkaline rhyolites, passing through all the intermediate members. It is characterized by an iron enrichment in the intermediate series, and the role of silica is secondary in the differentiation which is controlled by the fractionation of olivine, pyroxene, and calcic plagioclases. By applying correspondence factor analysis to the rock samples analyzed for major and trace elements, factors were found expressing the importance of certain associations between the samples and their elements. The variables were projected onto factorial axes and graphs were plotted automatically showing their positions. Ellipses corresponding to the groups based on the rock types, volcanoes, and the indices of Kuno were drawn so that their situation in relation to the oxides and trace elements could be seen. From the plan of the axes, the degree of differentiation of the samples in the considered series is indicated, and the petrological terminology of the rocks may be verified. Two graphs, representing the series, are proposed using indices for the oxides and traces obtained from the results of correspondence analysis.