Corpos hipabissais correlacionados à Formação Serra Geral na região do Cerro do Coronel, RS: geologia e petrologia

Abstract

The Serra Geral Formation is characterized by an expressive volume of tholeiitic basic lava flows and a subordinate presence of acid volcanites. Intrusive bodies (dikes and sills) are correlated to this unit, and, along with volcanic deposits, constitute the Parana Magmatic Province. This research is about the geological and petrological investigation of basic-intermediate intrusions of the Cerro Coronel region, southeast of the city of Pantano Grande, RS. These hypabyssal bodies are stratigraphically linked to the Serra Geral Formation and form an alignment with NW-SE orientation. They are intrusive in sedimentary rocks of Irati and Rio Bonito Formations. All intrusives present columnar disjunctions and are affected by strong NE and NW fracturing. The small facies variation is predominantly constituted by fine equigranular rocks and, rarely, porphyritic terms. Intergranular texture is a very common feature, but subophitic texture is present too. Primary mineralogy is characterized by plagioclase, augite, opaque minerals and, scarcely, olivine. Apatite and quartz occur as accessory minerals. Mesostasis of felsic composition occurs as the final stage of crystallization. Geochemical data of major and trace elements allow the classification of the rocks as basaltic andesite with tholeiitic affinity, whose evolution occurred probably by fractioned crystallization mechanisms, involving mainly plagioclase and augite. The characteristics of the major, trace, and rare earth elements are compatible with those presented for magmatism related to large continental tholeiitic provinces such as Deccan Traps, Paraná-Etendeka, Columbia River, Siberian Traps and Karoo. These rocks have concentrations below 2% of TiO2, showing a tendency to Esmeralda magma-type of the Paraná Magmatic Province.