Serra Geral Group plumbing system and 3D geological framework in Morungava region, southern Paraná-Etendeka LIP (Brazil): Evidence from borehole, geochemical, and petrophysical data

Abstract

The Morungava region (east of Porto Alegre-Rio Grande do Sul, Brazil), in the southern half of the Paraná-Etendeka Large Igneous Province (LIP), hosts Serra Geral Group subvolcanic intrusions (sill complex). These intrusions comprise various chemical compositions, including high-Mg rocks. So far, only a few examples of high-Mg rocks have been discovered in the Paraná-Etendeka LIP. Many investigations have been conducted in the Morungava region, yet several questions regarding the distribution, geometry, composition, and structural framework of the subvolcanic bodies in the subsurface remain unanswered. Therefore, we built a three-dimensional geological model of the Serra Geral Group sills and their associated stratigraphic framework in the Morungava region. This was achieved through the combined analysis of geological data (boreholes and geological maps), as well as petrophysical and chemical data, to improve the understanding of these subvolcanic bodies underground. The stratigraphic framework depicts the Precambrian basement topography, the distribution of the Paraná Basin units, and the Rio Grande do Sul Coastal Plain strata, which span the majority of the examined area. To categorize the Serra Geral Group rocks intersected by the boreholes, we established a validation and correlation technique using three separate data sources: laboratory geochemical data, portable X-ray fluorescence measurements, and gamma-ray logs. Using this technique, we classified the Serra Geral Group rocks in the Morungava region into three types (1, 2, 3), which share compositional similarities with Palmas, Vale do Sol, and Torres formations, respectively. Additionally, we identified a fourth type that could be compared to the Lomba Grande Complex, Silica Saturated Olivine Tholeiite-type dikes, and some high-Mg rocks from Namibia.