ASTHENOSPHERE FLOW MODEL OF HOTSPOT-RIDGE INTERACTIONS - A COMPARISONOF ICELAND AND KERGUELEN

We develop a numerical model to test the asthenosphere flow paradigm i n which hotspots feed the low viscosity asthenosphere, and lithosphere growth consumes the asthenosphere. The dynamics of this flow model ar e controlled by the relative position of the hotspot to the ridge, abs olute plate velocities, lithosphere and asthenosphere rheologies, and tectonic boundary conditions. The model is applied to two distinct reg ions - the Iceland hotspot centered on the Mid-Atlantic Ridge, and the Kerguelen hotspot located near the Southeast Indian Ridge. The Icelan d model generates along-ridge how rates as high as 30 cm/y for an asth enosphere viscosity of 5 x 10(18) Pa s. These flow rates are consisten t with previous interpretations of the origin of southward pointing V' s south of Iceland. The preferred Kerguelen model produces significant hotspot-to-ridge flow followed by along-ridge flow; velocities from t he off-axis hotspot to the ridge are 66 cm/y for a model within which asthenosphere viscosity varies from 5 x 10(18) to 5 x 10(19) Pa a. The asthenosphere flow paradigm can explain major features of hotspot-rid ge interactions for both on-axis and off-axis hotspots. (C) 1998 Elsev ier Science B.V. All rights reserved.