Litoestratigrafia dos derrames de basalto da Província Magmática do Paraná na região de Joaçaba-Caçador (SC)

Abstract

The Paraná Magmatic Province (PMP) is in Brazil and represents the south american portion of the Paraná-Etendeka Magmatic Province. The study area comprises the basalts of the central portion of the PMP, in the state of Santa Catarina, around the cities of Joaçaba, Videira, and Caçador. The aim of this work is to discriminate the emplacement conditions of the lava flows. Lithofacies discrimination and lithofacies association analysis are fundamental techniques for understanding the evolutionary history and the reconstruction of volcano- sedimentary environments in the PMP. This work presents the complex volcanic framework of the central portion of the PMP through detailed fieldwork, petrographic, and lithogeochemical data. Eleven lithofacies were recognized in the study area and grouped into three lithofacies associations: pahoehoe, rubbly pahoehoe, and peperite. The pahoehoe and rubbly pahoehoe flows were geochemically classified into low-TiO2 (Gramado and Esmeralda) and high-TiO2 (Urubici) magma types. The volcanic succession is characterized by the low-Ti Gramado magma type at the base, followed by an unusual intercalation of the Urubici and Esmeralda magma types, a relationship that diverges from the typical stratigraphy previously recognized within the PMP. The peperite thin layers, characterized by a matrix derived from fine-grained lacustrine sediments, are interbedded with the upper flows (Urubici and Esmeralda magma types), providing evidence for a climatic shift from arid to humid conditions of the PMP volcanism. The interpretation of geochemical data is consistent with fissural volcanic episodes involving both distinct and similar batches of lavas, sourced from magma chambers connected by kilometer-long subvolcanic fissures. These results demonstrate the significant lateral heterogeneity of the PMP and challenge the direct extrapolation of stratigraphic models from other regions. Therefore, a revision of the current framework that defines the stratigraphic position of the Urubici magma type in the central PMP seems necessary for a comprehensive understanding of the PMP volcanism.