Laboratory investigation of the interaction of off-axis mantle plumes and spreading centres

Abstract

MANTLE plumes and mid-ocean ridge spreading centres are the dominant phenomena through which mass and heat are transported from the mantle to the Earth's surface. It now seems that the dispersion of near-ridge plumes beneath the lithosphere is modulated strongly by mid-ocean ridges ; in particular, geochemical and geophysical observations have suggested that rising plumes are diverted towards and feed nearby ridges 1-7 . Here we confirm the feasibility of this model with laboratory experiments that incorporate the essential physical and fluid dynamic aspects of a plume-ridge upper mantle system. Our results indicate that an off-axis plume may communicate thermally and chemically with a spreading ridge through a narrow, sub-horizontal conduit instead of a broader, radially spreading plume head. A necessary condition for this communication is the presence of a lithospheric or rheological boundary layer that thickens away from the ridge axis owing to conductive cooling. Interestingly, we find that for high plume temperatures, increasing the plume thermal buoyancy may inhibit rather than enhance plume-ridge interaction, as a result of increased erosion of the overlying lithosphere.