Geographic Patterns of Volcanism at Intraplate Hotspots

Abstract:

Geodynamic models of mantle plumes predict a relatively simple “bulls eye” pattern of melt generation, with maximum melt flux above the center of the conduit. However, in detail the spatial distribution of surface volcanism at hotspots is typically complex and rarely forms a simple linear array. This spatially variable geometry affords an important opportunity to probe the geochemical structure of the underlying plume, as it allows the plume conduit to be sampled at multiple locations (e.g., Loa and Kea chains at Hawaii). It also suggests that the relationship between patterns of surface volcanism at hotspots and melt generation within the underlying mantle plume is poorly understood.

Here we report on a systematic characterization of the spatial distribution of recent (3 Ma – present) magmatism, as reflected in topography, at ten prominent oceanic intraplate hotspots. At eight of these hotspots, we find that the average topographic profile across the hotspot track (i.e., perpendicular to plate motion) shows a distinct double peak. The spacing between these peaks ranges from 19 – 45 km. This pattern conflicts with the simple single-peak pattern predicted by existing geodynamic models of melting in mantle plumes. We suggest that this double-peak pattern of surface volcanism reflects a bifurcated distribution of melt generation caused by interaction between the conduit of the plume and the overriding oceanic lithosphere.