Correspondence Analysis in lithogeochemical relationships of Cenozoic volcanism in Borborema Province – NE Brazil

Abstract

The lithogeochemical correlation among samples generally uses pre-defined graphs in the literature or bivariate analysis for each of the elements analyzed. Applying a multivariate analysis to the geochemical data of a set of samples, which are naturally multivariate, allows to deal with these data in a reduced dimensional space, thus understanding the behavioral processes of individuals. Correspondence Analysis (CA) also permits comparing individuals (rows) and quantitative or qualitative variables (columns) of a set of data in the same workspace and in a symmetrical way. In this paper, the CA of a set of geochemical analyzes of Cenozoic volcanic rocks of the Borborema Province’s Northern portion correlated a newly discovered volcanic occurrence at Fortaleza to Fernando de Noronha’s alkaline volcanism, distinguishing itself from the volcanism of Macau, mainly due to its relative depletion in Rare Earth Elements. The method also allowed to distinguish some geochemical similarities between rocks from Fortaleza and Fernando de Noronha, such as higher values of Na₂O, K₂O, Al₂O₃, TiO₂, P₂O₅ and CaO₂, and smaller of SiO₂ e MgO relatively to those of Macau Volcanism. Trace elements like Rb, Nb, Th and Ga are correlated, and their values increase or decline together on each volcanism, while Sr and Ba have an inverse behavior of Cr and Ni.