Abstract
Abstract. Much effort is being made to extract the dynamic components of the Earth's
topography driven by density heterogeneities in the mantle. Seismically
mapped density anomalies have been used as an input into mantle convection
models to predict the present-day mantle flow and stresses applied on the
Earth's surface, resulting in dynamic topography. However, mantle convection
models give dynamic topography amplitudes generally larger by a factor of
∼2, depending on the flow wavelength, compared to dynamic
topography amplitudes obtained by removing the isostatically compensated
topography from the Earth's topography. In this paper, we use 3-D numerical
experiments to evaluate the extent to which the dynamic topography depends
on mantle rheology. We calculate the amplitude of instantaneous dynamic
topography induced by the motion of a small spherical density anomaly
(∼100 km radius) embedded into the mantle. Our experiments
show that, at relatively short wavelengths (<1000 km), the
amplitude of dynamic topography, in the case of non-Newtonian mantle
rheology, is reduced by a factor of ∼2 compared to isoviscous
rheology. This is explained by the formation of a low-viscosity channel
beneath the lithosphere and a decrease in thickness of the mechanical
lithosphere due to induced local reduction in viscosity. The latter is often
neglected in global mantle convection models. Although our results are
strictly valid for flow wavelengths less than 1000 km, we note that in
non-Newtonian rheology all wavelengths are coupled, and the dynamic
topography at long wavelengths will be influenced.
Funder
Australian Research Council
Subject
Paleontology,Stratigraphy,Earth-Surface Processes,Geochemistry and Petrology,Geology,Geophysics,Soil Science
Cited by
7 articles.
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