Localized gravity/topography admittance and correlation spectra on Mars: Implications for regional and global evolution
From gravity and topography data collected by the Mars Global Surveyor spacecraft we calculate gravity/topography admittances and correlations in the spectral domain and compare them to those predicted from models of lithospheric flexure. On the basis of these comparisons we estimate the thickness of the Martian elastic lithosphere (T_e) required to support the observed topographic load since the time of loading. We convert T_e to estimates of heat flux and thermal gradient in the lithosphere through a consideration of the response of an elastic/plastic shell. In regions of high topography on Mars (e.g., the Tharsis rise and associated shield volcanoes), the mass-sheet (small-amplitude) approximation for the calculation of gravity from topography is inadequate. A correction that accounts for finite-amplitude topography tends to increase the amplitude of the predicted gravity signal at spacecraft altitudes. Proper implementation of this correction requires the use of radii from the center of mass (collectively known as the planetary "shape") in lieu of "topography" referenced to a gravitational equipotential. Anomalously dense surface layers or buried excess masses are not required to explain the observed admittances for the Tharsis Montes or Olympus Mons volcanoes when this correction is applied. Derived T_e values generally decrease with increasing age of the lithospheric load, in a manner consistent with a rapid decline of mantle heat flux during the Noachian and more modest rates of decline during subsequent epochs.
Additional Information© 2002 by the American Geophysical Union. Received 30 January 2002; revised 26 July 2002; accepted 6 September 2002; published 31 December 2002. We thank Francis Nimmo and Norman Sleep for constructive reviews, and Mary Chapman, Walter Kiefer, Richard Schultz, and Kenneth Tanaka for helpful discussions. This research was supported by the National Aeronautics and Space Administration under grants NAG 5-4436, NAG 5-4077, and NAG 5-10165 (to the Carnegie Institution of Washington), and NASW-4574 (to the Lunar and Planetary Institute, operated by the Universities Space Research Association). This paper is Lunar and Planetary Institute Contribution 1121.
Published - MCGjgre02.pdf
Erratum - MCGjgre02corr.pdf