Geochemistry of basaltic flows from a basalt ring structure of the Serra Geral formation at Água Vermelha dam, Triângulo Mineiro, Brazil : implications for the magmatic evolution of the Paraná‑Etendeka Province.

Abstract

The Serra Geral Formation belongs to the Paraná-Etendeka Magmatic Province (PEMP) and its geochemical and petrographic characteristics are not homogeneous. Many studies segment this group into six basaltic and two rhyolitic magma-types. It is believed that its extrusion occurred through crustal fissures in the Cretaceous, but some authors described the presence of conduits in the shape of basaltic ring structures (BRS) in the Água Vermelha region in the North of the province. The BRS rocks, based on textures and structures, were divided into four groups—central flow, basal flow, main ring dyke and lava flow—with a very similar petrography, composed of plagioclase (labradorite-bytownite), clinopyroxene (augite) and oxide (titanomagnetite) with intergranular texture. The whole-rock analyses of the basal and lava flows allow classifying them as tholeiitic basalts of the Paranapanema magma-type. Geochemical data interpretation suggests an enriched magma source, with low degree of partial melting, high depth of melt generation and without significant crustal contamination. The BRS experienced fractional crystallization on shallow magma chamber, influenced by successive new injections from different parental magmas which would be responsible for the pulses of effusion and explosion. Thus, the singularities of the BRS of Água Vermelha are important to comprehend the evolution of the PEMP.