Fig. 2: Dynamics of ridge capture and ridge de-anchoring.

Idealised 3D illustrations of plume–ridge interactions extracted from 3D numerical model of whole-mantle convection depict three stages of ridge capture (a–c) and de-anchoring (d–f) for two separate plume–ridge interactions. a The closeness of the ridge–plume system is accommodated by transform boundaries progressively stepping ridge segments towards the plume and a 10° lean by the mantle plume towards the spreading ridge. b As the plume buoyancy flux increases (>6000 kg/s) it thermally weakens the overriding plate and develops a proto-ridge extending from the original spreading ridge; c spreading establishes along the proto-ridge which forms a triple junction on top of the mantle plume. d A triple junction is centred on a waning mantle plume (<2000 kg/s buoyancy flux) with the 1350 °C plume isotherm elongated towards the direction of relatively faster plate motion; e seafloor spreading is abandoned on one arm of the triple junction establishing a single plate boundary with asymmetrical spreading rates. f The plume wanes below 1000 kg/s buoyancy flux and decouples from the spreading ridge, which subsequently migrates away from the plume by up to 12 cm/yr. The waning mantle plume tilts 15° in the upper mantle towards the migrating ridge. CMB core-mantle boundary, MOR mid-ocean ridge. Arrows indicate the direction of plate motion.