An Observational Test of a Moving Hotspot Reference Frame

Hotspots are the surface expression of deep mantle plumes, which are a manifestation of thermal convection in the mantle. In a convecting mantle, hotspots and plumes cannot be stationary, and many published models predict that hotspots move relative to a mean mantle reference frame (e.g. Steinberger & O'Connell, 1998). The speeds of hotspots predicted by some models vary from millimeters per year to tens of millimeters per year (e.g., Hassan et al. 2016).

Here we examine the velocities of hotspots predicted by the Global Moving Hotspot Reference Frame (GMHRF) of Doubrovine et al. (2012). In the GMHRF the median predicted hotspot speed is 11 mm/yr. Doubrovine et al. (2012) assert that the GMHRF fits hotspot tracks better than the fixed hotspot approximation. We test this claim by comparing the fit of the GMHRF and of fixed hotspots with the observed trends of young portions of globally distributed hotspot tracks. Surprisingly we find that the GMHRF fits the data significantly worse (p = 0.005) than the fixed hotspot approximation. If we assume that the GMHRF correctly predicts the direction and relative speeds of the hotspots, but is incorrect in magnitude by a uniform scale factor, γ, we find that γ=0.03 gives the best fit. This corresponds to a median speed of hotspots of merely 0.3 mm/yr. We conclude that either plume conduits are not passively advected with the mantle flow calculated for the GMHRF or Earth's actual mantle velocity field differs substantially from that calculated for the GMHRF.