Chemical stratigraphy of the Paraná lavas (South America): classification of magma types and their spatial distribution

A new classification scheme has been developed to assign the lava flows of the Paraná continental flood basalt province (South America) into geochemically distinct magma types, with six basaltic major and trace element abundances and/or ratios. By mapping out the spatial distribution of these magma types within the lava sequences, it has been possible to determine the internal stratigraphy of the lava pile on a regional scale. Previous studies on road profiles traversing the well-exposed coastal Serra Geral escarpment of southern Brazil are summarised together with results from some new sampled sections. More widespread stratigraphical investigations of the Paraná lavas have been hampered by the lack of sufficient topographic relief and the cover of sedimentary rocks. However, access to drill-core chippings from nine boreholes in the central Paraná region has provided a unique opportunity to investigate the stratigraphy of the otherwise inaccessible deeper levels of the lava pile and to map out stratigraphic variations in three dimensions. The borehole samples have indicated cated a stacking of units of different magma types all overlapping towards the north, which suggests that the main locus of magmatism moved northwards with time within the Paraná basin. This migration could be related to the northward propagation of rifting during the initiation of the South Atlantic Ocean. Maps of the surface distribution of samples of each magma type show a pattern consistent with the stratigraphy inferred from the boreholes, although suggesting that the shift in magmatism may have been towards the northwest. On the basis of geochemical similarities between magma types and their inferred stratigraphical relationships, it is proposed that the Paraná can be divided into two principal magmatic centres: (1) an older one in the south, comprising the Gramado, Esmeralda and Urubici magma types; and (2) a younger one, developed about 750 km to the north, formed by the Pitanga, Paranapanema and Ribeira magma types.