Asthenosphere flow model of hotspot–ridge interactions: a comparison of Iceland and Kerguelen

We develop a numerical model to test the asthenosphere flow paradigm in which hotspots feed the low viscosity asthenosphere, and lithosphere growth consumes the asthenosphere. The dynamics of this flow model are controlled by the relative position of the hotspot to the ridge, absolute plate velocities, lithosphere and asthenosphere rheologies, and tectonic boundary conditions. The model is applied to two distinct regions — the Iceland hotspot centered on the Mid-Atlantic Ridge, and the Kerguelen hotspot located near the Southeast Indian Ridge. The Iceland model generates along-ridge flow rates as high as 30 cm/y for an asthenosphere viscosity of 5×1018 Pa s. These flow rates are consistent with previous interpretations of the origin of southward pointing Vʹs south of Iceland. The preferred Kerguelen model produces significant hotspot-to-ridge flow followed by along-ridge flow; velocities from the off-axis hotspot to the ridge are 66 cm/y for a model within which asthenosphere viscosity varies from 5×1018 to 5×1019 Pa s. The asthenosphere flow paradigm can explain major features of hotspot-ridge interactions for both on-axis and off-axis hotspots.