Statistic behavior of major and minor elements in basic, intermediate and acidic rocks of the Serra Geral Formation and Arapey Group, Paraná Large Igneous Province, South America

Abstract

The evolutionary processes of the South American portion of the Paraná-Etendeka Province, composed of the Serra Geral Formation (Brazil, Argentina and Paraguay) and Arapey Group (Uruguay) had been developed in 1.2 Ma with a climax located of 134.7 Ma, giving rise to extrusive rocks (flows) and intrusive rocks (dykes and sills) of composition ranging from basalts to rhyolites. In the last four decades, many authors have produced geochemical data sets on these rocks, which were published or remain unpublished. The compilation of these data sets and its standardization from the geochemical and geographic viewpoints, gave rise to a database containing analysis of SiO , TiO , Al O , FeO , MnO, 2 2 2 3 total CaO, Na O, K O, P O , Ba, Ce, Cr, La, Ni, Rb, Sr, Zr, and Y from 4,257 outcrop and subsurface (core) samples. 2 2 2 5 In this article we present the techniques used for the construction and standardization of the database and the statistical analysis of the geochemical data. The application of statistical techniques, especially the modeling of probability plots, showed that most variables are polymodal, which, from the statistical point of view, means the existence of different populations and, from the geological and geochemical points of view, suggest a complex combination of processes of generation, mixing, contamination and differentiation. These data gave rise to statistical reference levels for the set of basic , intermediate and acid rocks of Paraná LIP. The results indicate thus the need for geochemical studies considering a prior stratification of data by referencing the thresholds of populations for each variable. The authors also suggested some simple rules for publishing geochemical data in order to facilitate its aggregation to the database.