Southern Hemisphere Hotspots Traced Back to Distinct Paleo-Subduction Zones

Mantle plumes beneath the South-Atlantic and Southwest-Indian Ocean hotspots are widely assumed to rise from the margins of the African large low–shear-velocity province (LLSVP). Here we integrate plate reconstructions, joint seismic–geodynamic tomography, and time-reversed particle tracking in a back-and-forth nudged (BFN) mantle convection model to test that premise. Our mantle flow reconstructions trace Tristan–Gough–Discovery and Kerguelen plume particles to paleo-subduction zones along the southern Panthalassa margin of Pangea, whereas trajectories feeding Réunion, Grande Comore and Mayotte converge on slabs that foundered beneath the Paleo-Tethys suture. In both cases the mantle parcels skirt -- rather than penetrate -- the high-density core of the present-day African LLSVP. Pb–Sr–Nd isotope arrays mirror this bifurcation, with DUPAL-rich signatures confined to the Panthalassan lineage and more depleted compositions characterising the Paleo-Tethyan lineage. The results suggest that Indo-Atlantic plume heterogeneity is inherited from Mesozoic subduction zones remote from the African superplume and retained during whole-mantle transport. Our findings call into question a dominant plume–LLSVP origin for isotopic heterogeneity and highlight the need to follow material pathways in time-dependent convective flows to decipher mantle geochemistry.