ICE-SHEET ENHANCEMENT OF VOLCANISM AND GEOTHERMAL HEAT FLUX: A STRESS MODELING APPROACH

Abstract:

Bore-hole and geophysically inferred geothermal heat fluxes beneath the Greenland Ice Sheet, particularly at the head of the Northeast Greenland Ice Stream, are in some places higher than suggested by the underlying geology. Geologically rapid changes in lithospheric loading during ice-sheet growth and decay produce large changes in the effective stress state beneath and nearby. Oscillating loads will cause oscillating melt volume in deep rocks, and the nonlinear increase of melt migration velocity with melt fraction means that extended ice-age cycling will enhance upward melt migration. Our numerically efficient simulations of ice-sheet/lithosphere interactions produce crustal stresses similar to values estimated to allow dike emplacement and vug-wave migration. Maximum tensile and shear stresses shift both horizontally and vertically during ice sheet growth and decay, suggesting multi-step transport of melt upwards to or near the base of the ice sheet. We thus suggest that regions of high geothermal heat flux arose from cyclic ice-sheet loading, which enhanced melt extraction from a deep source (possibly linked to passage of the Iceland hot spot). We further suggest that similar processes may have been important elsewhere beneath or near present or former ice sheets, potentially enhancing volcanism as well as geothermal flux.