Spatial distribution and morphostructural control of Ediacaran Rodeio Velho volcanism, Camaquã Basin, southern Brazil

Abstract

The Ediacaran Rodeio Velho volcanism represents the last magmatic event within the Dom Feliciano Belt in southern Brazil. Located at the base of the Guaritas Group (Camaquã Basin), this volcanism outcrops along NE-SW elongated trends parallel to major regional shear and fault zones of the Dom Feliciano Belt. For a long time, this volcanism has been described as a unique feature within the Guaritas Group. Here, we investigate the morpho-structural control of this basic volcanism distribution based on airborne magnetic and gamma-ray data, supported by terrestrial profiles. Our results indicate the presence of three Guaritas Magnetic Domains (GMD) individualized according to the Guaritas rift system: GMD-West, GMD-Central, and GMD-East. The Rodeio Velho volcanism is restricted to two of these domains (West and East), each located on distinct tectonic blocks, the São Gabriel and Tijucas Block, respectively. We identify that mapped volcanics are closely associated with magnetic anomalies represented by deep NW-SE faults, generally perpendicular to the major shear zones in the Dom Feliciano Belt. This indicates the significance of basement fracturing during the collisional to post-collisional period of the Dom Feliciano Belt (∼660–550 Ma). Based on geophysical data, our results indicate that magma emplacement occurred during the post-collisional transtensive phase, filling the rift compartments. This highlights the importance of tectonic stress reversal in the regions's geological history.