Magmatism of Shatsky Rise controlled by plume–ridge interaction

Shatsky Rise is a large oceanic plateau formed at a spreading ridge triple junction, but its origin mechanism is unclear. Voluminous magmatism at Shatsky Rise has been regarded either as the product of decompression melting of fertile recycled material in a divergent plate boundary setting (plate model) or a hot mantle plume head (plume model). Here we use thermodynamic models to simulate decompression melting of heterogeneous mantle sources. We provide constraints on both mantle potential temperature and fertile source abundance under seafloor spreading and plume–ridge interaction scenarios. As constrained by crustal thickness and lava chemical compositions, a seafloor spreading origin requires mantle potential temperatures of 1,490–1,585 °C, which are unreasonably high for mid-ocean ridge systems far from hotspots. In contrast, the plume–ridge interaction model can explain observations with mantle potential temperatures of 1,470–1,515 °C for the buoyant plume and upwelling rates up to six times the rate of plate separation during the formation of the main massifs. Fertile recycled material comprises less than 7% of the mantle source, and predicted melt fractions are consistent with independent estimates. We thus suggest that Shatsky Rise magmatism is best explained by plume–ridge interaction—a combination of the plume and plate models.