HOTSPOT EPEIROGENY

Hotspot locations are plotted on a global map of oceanic residual depth anomalies. There is a strong correlation between hotspots and unusually shallow seafloor, indicating that the broad crustal swells surrounding hotspots are the major form of epeirogeny on the ocean floor, besides the normal increase of ocean depth with increasing crustal age. The existing gravity and subsidence data are consistent with the hypothesis that most hotspot swells are caused by lithospheric thinning over a mantle heat source. Several continental swells are associated with intraplate volcanism, and the available data suggest that these are also formed by lithospheric thinning. Approximately 10% of the earth's surface is presently part of a hotspot swell, which implies that hotspot epeirogeny is a process of major tectonic importance. A stochastic model of continental hotspot epeirogeny shows that, for any particular continental area, the mean time between episodes of hotspot uplift is only 600 m.y. The amount of heat delivered to the upper mantle by the lithospheric thinning process is sufficient to explain the background heat flux of about 25 mW m-2 which is observed on the continents. © 1979.