A second track of the Réunion hotspot in the Mascarene Basin

Hotspots are generally interpreted as the surface expression of lithospheric plates moving over mantle plumes, progressively forming volcanic chains aligned with plate motion. However, it is increasingly recognized that hotspots—such as Hawaii, Samoa, and Tristan–Gough— can exhibit two volcanic lineaments that are not necessarily parallel and display distinct geochemical characteristics.

Here we report the discovery of a previously unrecognized volcanic chain related to the Réunion hotspot in the Mascarene Basin (western Indian Ocean), which we term the Mascarene Chain (MASC). This chain extends from the Seychelles across the seafloor through a series of seamounts and records a southward progression of volcanism from ca. 67 to 6 Ma. This age progression is constrained by multi-technique geochronology (⁴⁰Ar/³⁹Ar on biotite; U–Pb on zircon; (U–Th)/He on zircon and apatite) performed on dredged volcanic samples. Petrology, whole-rock major and trace elements and Sr–Nd–Pb isotopes, as well as zircon trace elements and δ¹⁸O–Hf isotopes, indicate that these volcanoes formed from extremely low (<1%) degrees of partial melting of a fertile, metasomatized mantle source with a clear enriched-mantle affinity, distinct from the Réunion plume signature.

The MASC is synchronous with the main Réunion hotspot track, from the Deccan Traps (67–65 Ma) to Réunion Island (5–0 Ma), and converges toward the current apex of the Réunion plume. The chain also lies along the boundary of an uplifted region in the Mascarene Basin, interpreted as resulting from plume-related buoyancy forces. We therefore propose that the MASC represents a secondary track of the Réunion hotspot, generated by the indirect action of the plume uplifting the Mascarene lithosphere. The progressive convergence of volcanism is consistent with a decreasing radius of influence as the plume waned. Our results further suggest that secondary hotspot tracks are generated by plume-induced upper-mantle melting, rather than by compositional heterogeneities within the plume source.