| Heat flow and hot spots: How hot are the spots? University of Illinois at Chicago Summary The small size or absence of a heat flow anomaly (measured heat flow less that expected for unperturbed oceanic lithosphere) at midplate hotspots such as Hawaii has been crucial for assessing possible mechanisms causing the volcanism and uplifted topography. The uplift was originally thought to reflect a hot mantle plume, rising from deep in the mantle, penetrating the approximately 100-km-thick oceanic lithosphere and causing heating to about 50-75 km of the surface. Although anomalously high heat flow was initially reported, as expected from this mechanism, subsequent analysis showed that most if not all of the apparent anomalies resulted from comparing the heat flow data to reference thermal models that underestimated heat flow elsewhere. Hence subsequent models generally assume that the uplift results from the dynamic effects of rising plumes and the associated compositional buoyancy, whose thermal effects are concentrated at the base of the lithosphere and hence would raise surface heat flow at most slightly, given that tens of millions of years are required for heat conduction to the surface. |