Insights into the petrogenesis of an intraplate volcanic province: Sr-Nd-Pb-Hf isotope geochemistry of the Bathymetrists Seamount Province, eastern equatorial Atlantic

Abstract

Unlike the well-studied narrow hotspot tracks, the origin of broadly distributed seamount provinces remains a topic of conjecture. Here we present major and trace element and Sr-Nd-Hf-Pb double spike isotope data of a comprehensive sample suite from the Bathymetrists Seamount Province, a broad belt of submarine volcanoes in the eastern equatorial Atlantic, and from the neighboring Cape Verde Ridge, a topographic high on the shoulder of a local fracture zone. The major and trace element results are consistent with the Bathymetrists Seamount Province having formed in an intraplate setting. The isotopic composition of the seamount lavas resemble a HIMU-like signature (206Pb/204Pbin = 19.23–20.35) similar to the nearby St. Helena hotspot composition. Based on plate tectonic reconstructions, a formation of the Bathymetrists Seamount Province by the postulated Sierra Leone plume, believed to be responsible for the geochemical anomaly at the mid ocean ridge at 1.7°N and the nearby St. Peter and Pauls rocks, is not supported. An alternative model that the Bathymetrists Seamount Province was created by edge driven convection in the upper mantle along the boundary of the neighboring Sierra Leone Rise plateau is also not supported by the available data. Plate tectonic reconstructions, however, are consistent with a hotspot origin for the Bathymetrists Seamount Province, as is the presence of a seismic tomographic anomaly at the southwest end of the seamount belt.