Based on a considerable number of chemical analyses of the Paraná Basin basaltic province in Southern Brazil, the regional variations of eight major elements are studied. The technique involved the definition of isochemical surfaces on maps by means of trend surface analyses, finding whatever anomalies may exist with respect to previously calculated regional averages for each of the eight major elements. The results indicate a well-defined regional pattern of geochemical variations. Four geochemical anomalies were found - with anomalies II and III very similar to each other, and therefore grouped thogether - located in at least three different geographical regions. The geographical boundaries of these regions, although ill - defined, are as follows: region one, covering the central-eastern State of Rio Grande do Sul (Anomaly I); region two, including both the central-western State of Paraná and the central-eastern State of Sao Paulo (Anomalies H and III); and the third region, restricted to the northern coastline of the State of São Paulo (Anomaly IV). Anomalies I and IV, in contrast to anomalies II and III, are characterized by high SiO2 and Na2O + K2O contents; they differ from each other in Fe (total) and TiCb figures and also in their relative alkali contents; anomaly I has a potassic tendency, while the other shows a sodic one. These geochemical trends suggest that the whole province should be subdivided into at least three different subprovinces, each probably having a somewhat different igneous-tec tonic regime. The nature and characteristics of these regimes still have to be defined by future work.
