Avaliação petrológica e geoquímica do basanito subaflorante no Município de Fortaleza (CE) e sua correlação com o vulcanismo de Fernando de Noronha, Brasil

Abstract

The Cenozoic volcanism in Ceará State, in the metropolitan region of Fortaleza is alkaline, represented by necks, plugs and domes of phonolites and trachytes, with rare described dikes of tephrites and phonotephrites. The new subsurface volcanic rock in Fortaleza is classified as a basanite, which is almost 400 by 320 meters in area and at least 20 meters of thickness. Geochemistry data suggests this occurrence would be the mafic member of the Messejana Volcanism (VMess), which is in the continental prolongation of the Fernando Noronha Fracture Zone, suggesting a bimodal character to this event. A comparison of Fernando de Noronha Volcanism samples, which had originated the namesake archipelago with ages between 12.5±0.1 e 1.3±0.1 My, with the study area data shows both strong petrographic and geochemical resemblance among in both localities. The magma which originated this basanite shows a strong fractionation of REEL and a soft fractionation ofREEH, absent Eu anomaly. It also presents a depletion of Sm, Eu, TI, Tb, Y, and Yb, while shows enrichment of Cs and Rb, which could be related to the OIB pattem. However, Ba, Th and U enrichment and Sr and P depletion reveal crustal influence.