Davis Bank geodynamic context, South Atlantic Ocean: Insights into the Vitória-Trindade Ridge evolution

Abstract

Davis Bank is one of the biggest cone-like seamounts in the Vitória-Trindade Ridge (VTR) offshore Eastern Brazil. This volcanic structure is mostly constituted by peralkaline Eocene basanitic lavas (MgO ca. 4.0 wt%). The lithology comprises an inequigranular aphanitic rock composed of lath-like minerals scattered all over the matrix, containing microphenocrysts of plagioclase, clinopyroxene, and opaque minerals, immersed in a matrix displaying pseudo-trachytic and micro glomeroporphyritic textures. Regarding mineral chemistry, the plagioclase (labradorite to bytownite) and clinopyroxene (diopside to diopside salite) crystals were analyzed to obtain their chemical composition and retrieve the P-T crystallization conditions. The determination of these thermodynamic conditions was based on plagioclase-liquid and clinopyroxene-liquid thermobarometers. This analysis yielded crystallization conditions ranging from 4 to 9.9 kbar and from 1050 to 1173 °C, indicating crystallization in a magma chamber located at 12–30 km depth. Although the VTR seamounts have a common origin related to the Trindade plume, the integration of the petrological data with the geophysical and tectonic interpretations allowed the distinction between the Davis Bank from the other seamounts in the ridge. The radiometric age determinations suggest the voluminous tephritic (basanitic) magmatism in Davis Bank was synchronous with important tectono-magmatic events in the South American plate.