Martin Vaz island geochronology: Constraint on the Trindade Mantle Plume track from the youngest and easternmost volcanic episodes

Abstract

The oceanic basins are dotted by seamounts, guyots and islands formed by the mantle plumes and oceanic lithosphere interaction. These plumes are responsible for several intraplate volcanisms such as the Emperor-Hawaii Chain in the Pacific Ocean with a remarkable bend at ca. 47 Ma. Comparatively, the Vitória-Trindade Ridge (VTR) in the South Atlantic Ocean was also generated by a mantle plume and in response to the lithosphere interaction and tectonic settings it shows three remarkable bends through time. One occurred after 85 Ma associated with the Trindade plume tail movement under the Archean São Francisco Craton, and another one ca. 52 Ma after the formation of the Abrolhos Bank in the Brazilian platform (Mohriak, 1989; Thompson et al., 1998) when the Trindade Plume encountered a thinner lithosphere in the Brazilian coast and formed a chain of seamounts and islands of W-E direction. The last bend marked in the Trindade plume trajectory is ca. 20°00′lat, around Davis Bank, marking a Miocene (21.07 Ma - 40Ar/39Ar whole-rock method) subtle clockwise rotation in the South American Plate. The easternmost part of this ridge is composed of Trindade-Martin Vaz Archipelago subject of this study. Located ca. 1200 km away from the Brazilian coastline at the Vitória (ES) parallel, its geology is an important preserved record of an alkaline Pliocene-Pleistocene volcanism, the youngest one recorded in the Brazilian territory. Martin Vaz and the nearby islets are located on the easternmost part of the VTR. Its geological features include phono-tephritic to tephri-phonolitic domes; nosean-phonolitic dykes and sub-horizontal layers formed by pyroclastic rocks and subordinate lava flows (melanephelinites) of Volcanian-style magmatism (mostly). 40Ar/39Ar ages yielded values ranging from 336 to 721 ka representing a young and short period of intraplate magmatic activity in the South American Plate offshore. These new ages associated with compiled radioisotopic ages from onshore and offshore volcanic rocks represent a strong decreasing age correlation related to Trindade Mantle Plume. Moreover, Trindade-Martin Vaz Archipelago is a contemporaneous product of a terminal plume expression in the offshore portion of a long-lived track (ca. 90 Ma) with a slow shear velocity (VS) placing its origin at the Upper Mantle suggesting a shallow mantle plume rising from the asthenosphere.