Geochemical stratigraphy of the Paraná Continental Flood Basalts: borehole evidence

Abstract

Stratigraphic studies can provide ao insight into the poorly understood geodynamic processes for the generation and emplacement of large continental f100d basalt provinces by revealing the structure and sequential evolution of the lava field. Such studies are still in their infancy in the Paraná, where lack of sufficient topographic reliefhas confined work mainly to the welI-exposed eoastal escarprnent in southeast Brazil. ln this paper, a newapproach is taken by analysing drillcore chippings from fOUI oil-company boreholes in the central Paraná basin. Major and trace elernent analyses distinguish three geochemical units by their low, intermediate, and high Ti02 contents.respectively, and demonstrate the validity of geochernical data from such material. Each borehole retains a coherent stratigraphy with the transition from low-Ti to high-Ti then intermediate-Ti lavas with time, and together they show an overlapping sequence of geochemical units dipping northwards, which could suggest a northwnrd migrating source for the Paraná magmatism in this central-north region. The available data on geochemical stratigraphy of the Paraná, is summarised in a north-south cross-section lhrough lhe lava field that shows the salient features of the Paraná stratigraphy; the stacking of units in the northem boreholes; the complex transition between low-Ti and higlr-Ti magma typesin the coastal pro files of Santa Catarina state; and the: concentration of acidic volcanics along the present day continental margino RESUMO