Petrogenetic insights on tephritic magmatism from Davis Bank (South Atlantic Ocean - Vitória-Trindade Ridge (VTR), Brazil): The role of a CO2-enriched mantle source

Abstract

Davis Bank is one of the largest physiographic features in the Vitória-Trindade Ridge (VTR), which is located offshore of the Eastern Brazilian margin, midway between the coastline and the South Atlantic mid-ocean ridge. The VTR is related to a linear volcanic track of ca. 1200 km in length, composed of several volcanic seamounts that are lithologically characterized by nephelinitic/tephritic alkaline rocks. The Davis Bank lies between the parallels 20°29′ and 20°32′ S and the meridians 29°17′ and 29°21′ W, and is located southeast of the Abrolhos Volcanic Complex (AVC), at the middle of the volcanic ridge, far from the Brazilian coast. This work focuses on the 40Ar/39Ar age determination of the rocks recovered from the seamount and characterization of Sr–Nd isotopes, mineral chemistry and whole-rock composition, aiming to access information about physical properties of magmas, source composition, magmatic evolution of the volcanic ridge, and the regional tectonic interpretation in the context of other seamounts along the Vitória-Trindade Ridge (VTR). Davis Bank presents 40Ar/39Ar age of ca. 21 Ma and is in an oceanic lithosphere of ca. 100 km thickness, which represents a recharging area in the oceanic lithospheric mantle for CO2-metasomatism enrichment. It is associated with mantle anomalies caused by a hotspot or mantle plume that was influenced by the E-W direction of leaking transform fracture zones in the South Atlantic Ocean. Age constraints indicate decreasing ages eastward of the AVC, favoring the hotspot hypothesis for the generation of magmatic rocks in the Vitória-Trindade Ridge.