Petrogenetic relationship between the Abrolhos Volcanic Complex (AVC) and the Vitória-Trindade Ridge (VTR) magmatism, Southeast Brazilian Margin, South Atlantic Ocean

Abstract

The Abrolhos Volcanic Complex (AVC) is an igneous province (63,000 km2), located at the Southeast Brazilian Margin. The AVC emerges as five islands called Santa Bárbara, Redonda, Siriba, Sueste, and Guarita, which compose the Abrolhos Archipelago, located ca. 55 km southeast of Caravelas city (BA). The Vitória-Trindade Ridge (VTR), ca. 110 km south, corresponds to a ca. 1200 km long west-east direction ridge composed of volcanic edifices that extend from the Brazilian eastern bank to the deep-water portion of the Atlantic, latitude ca. 20ºS, in the city of Vitória (ES). The AVC and the VTR show slight age-progressive volcanism from the older ca. 60 Ma Abrolhos Complex to the younger Martin Vaz and Trindade Islands, consistent with the motion of the South American plate toward the west and thus supporting a Trindade hotspot origin for these magmatism. After almost thirty years without any detailed published article for the petrology of the Abrolhos magmatism, this work presents new field work mapping, petrographic, lithogeochemical, and Sr-Nd isotopic data for the Abrolhos Islands. We also present a possible petrogenetic link between the AVC and VTR magmatism, and some new modeling data for some VTR seamounts. Abrolhos Archipelago rocks comprise a Paleocene-Eocene transitional basalt series of alkaline affinity with relatively evolved rocks with high TiO2 contents, while VTR volcanic edifices rocks comprise a Miocene-Pleistocene strongly undersaturated alkaline affinity series with the less evolved samples. Mapped magmatic rocks in the Abrolhos Islands are shallow intrusions, mostly sills, and should be grouped into diabase units. Major and trace element diagrams of the Abrolhos Islands show a large data dispersion when plotted as a function of fractionation index (e.g., MgO and Zr) thus suggesting a complex evolution. Differentiation by magma replenishment, tapping, and fractionation (RTF) seems to have been the predominant process, potentially linked to the subvolcanic plumbing system evolution. Trace element compositions of VTR Seamounts (Vitória, Montague, Jaseur, Dogaressa, Davis, and Colúmbia) are consistent with ≤ 4% partial melting of the mantle source in the garnet stability field. New and compiled isotope AVC data suggest a peridotitic mantle source (represented by depleted MORB mantle – DMM) metasomatized by an enriched mantle I (EMI) component and a HIMU-type constituent. Our model mixing calculations suggest a mixture with 75% of DMM, <15% of EMI, and possibly up to 10% of HIMU in the AVC source. For VTR seamounts and islands the mixture would be 90% of DMM with <10% of EMI, and for Vitória Seamount and Davis Bank the EMI contributions vary from 20% to 25% in the DMM. The volcanic alignment between the VTR and AVC, along with the overlap of geochemical and isotopic data of their different igneous rocks, cannot be a random feature but instead represent the sampling of similar shallow mantle reservoirs, thus suggesting a cogenetic relationship. Finally, a possible petrogenetic link between the AVC and VTR magmatism is discussed.