Basal Mantle Flow Over LLSVPs Explains Differences in Pacific and
Indo-Atlantic Hotspot Motions
Abstract
Surface hotspot motions are approximately a factor of two faster in the
Pacific than the Indo-Atlantic, and the Pacific large low shear velocity
province (LLSVP) appears to be significantly shorter than the
Indo-Atlantic LLSVP. Hypothesizing that surface hotspot motions are
correlated with the motion of plume sources on the upper surface of
chemically distinct, intrinsically dense LLSVPs, we use 3D spherical
mantle convection models to compute the velocity of plume sources and
compare with observed surface hotspot motions. No contrast in the mean
speed of Pacific and Indo-Atlantic hotspots is predicted if the LLSVPs
are treated as purely thermal anomalies and plume sources move laterally
across the core-mantle boundary. However, when LLSVP topography is
included in the model, the predicted hotspot speeds are, on average,
faster in the Pacific than the Indo-Atlantic, even when modest
topography is assigned to both LLSVPs (e.g., 100-300 km). The difference
in mean hotspot speed increases to a factor of two for larger and
laterally variable LLSVP topography estimated from seismic tomographic
model S40RTS (up to 1100-1500 km for the Indo-Atlantic region versus
700-1400 km for the Pacific region) and our results also broadly
reproduce the convergence of Pacific hotspots toward the center of the
Pacific LLSVP. These largescale features of global hotspot motions are
only reproduced when ambient mantle material flows over large,
relatively stable topographical features, suggesting that LLSVPs are
chemically distinct and intrinsically dense relative to ambient mantle
material.