Estimates of Martian crustal thickness from viscous relaxation of topography
F. Nimmo and D. Stevenson, J. Geophys. Res., 106, 5085-5098, 2001.
Isostatically compensated crustal thickness variations and associated
topographic contrasts at the surface of a planet result in lateral pressure
gradients, which may cause the lower crust to flow and reduce the relief.
Areas of thicker crust are generally associated with more rapid relaxation
of topography. On Mars, topographic features such as impact basins and the
hemispheric dichotomy have survived for 4 Gyr. We use a finite difference
representation of depth-dependent, non-Newtonian lower crustal flow to
investigate how topography decays with time. For a dry diabase rheology,
total radiogenic concentrations greater than or equal to 80% of terrestrial
values, and crustal radiogenic concentrations similar to terrestrial
basalts, we find that an upper bound on the mean planetary crustal thickness
is similar to 100 km. In the probably unrealistic case where all the
radiogenic elements are in the crust; this maximum crustal thickness can be
increased to similar to 115 km, The main uncertainty in these results is the
total radiogenic abundances on Mars. Comparing our results with the observed
shape of the crustal dichotomy provides no evidence that this slope is
primarily the result of lower crustal flow. Both Hellas and the dichotomy
are isostatically compensated; if the mechanism is Airy isostasy, then the
lower bound on mean crustal thickness is similar to 30 km. Crustal
thicknesses of 30-100 km on Mars can be produced by mid-ocean ridge
spreading at potential temperatures of 1350 degrees - 1600 degreesC.
However, for such crustal thicknesses the lithosphere is likely to be
positively buoyant, making subduction difficult.
Francis' Page
Department of Earth Sciences
home page
nimmo@esc.cam.ac.uk
This page was last modified on 11 April 2001.