A Global Map of Renormalised Mantle Dynamic Topography

Comparison of predicted mantle dynamic topography with observed residual topography shows that the amplitude of predicted dynamic topography is too great (Cowie & Kusznir, EPSL, 2018). This over prediction of dynamic topography amplitude most probably arises from uncertainties in the conversion of seismic velocity anomalies from mantle tomography into density anomalies and uncertainties in upper and lower mantle viscosity structure, both of which are required to compute predicted dynamic topography.

Dynamic topography renormalisation, consisting of its rescaling and shifting, is determined by comparing predicted dynamic topography with observed residual topography for “normal” oceanic crust where observations are less prone to errors than for continents, margins and oceanic plateaus. Renormalisation is then applied globally to generate an improved map of dynamic topography for the continents, other remaining oceanic areas, and the Antarctic and Arctic polar regions. An important caveat is that the renormalisation can only be calibrated for oceanic regions, and we assume that the same rescaling of predicted mantle dynamic topography can be applied to the continents.

We present and examine a new global map of mantle dynamic topography produced by renormalising the predicted dynamic topography of Steinberger et al. (2017) which includes seismic tomography above 220 km depth to determine shallow upper mantle densities.

Renormalised maximum amplitudes of mantle dynamic topography uplift for East Africa, the S.W. Pacific and Iceland are 1000, 750 and 750 m respectively. For mantle dynamic subsidence in the Argentine Basin of the S. Atlantic, the maximum amplitude is -750 m. Elongated regions of mantle dynamic uplift are predicted for the Western Cordillera of North America and West Antarctica with maximum values of 500 and 750 m respectively.