The involvement of deep plume-related materials in the South Atlantic Ocean asthenosphere as indicated by isotopic independent component analysis of basalts

Mantle convection plays a key role in magmatism and volcanism on Earth. The final distribution of deep mantle material upwelled into the asthenosphere cannot be clearly tracked using seismic imaging techniques. Where mid-ocean ridges and plumes interact, the along-ridge variations in plume-affected basalts constrain the spatial extent of the plume-related flow in the asthenosphere. These variations are helpful for revealing convection throughout the mantle from the core-mantle boundary (CMB) to the bottom of the lithosphere. In this study, regional geophysical data, as well as the results of geochemical independent component analysis of radiogenic Sr–Nd-Pb isotopes of South Mid-Atlantic Ridge (SMAR) basalts, were used to analyze the distribution characteristics of the plume-affected asthenosphere beneath the South Atlantic Ocean. We determined that the ridge scope of the Ascension plume-influenced SMAR segments is bounded by the Ascension transform fracture (~ 7.5°S) to the north and the Bode Verde transform fracture (~ 11.1°S) to the south, while the Saint Helena plume-contaminated SMAR segments are bounded by the Cardno transform fracture (~ 14.2°S) to the north and the Trinidade transform fracture (~ 20.8°S) to the south. Furthermore, we determined that the melt extraction process taking place between the mantle plume and ridge system may weaken the plume-related geochemical signals of these plume-affected MORBs. Our results suggest that the distribution of plume-related asthenosphere under the South Atlantic is influenced by large transform faults that block the propagation of the plumes along the bottom of the lithosphere, as well as the propagation of plume-affected materials along the ridge system.