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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L22201, doi:10.1029/2005GL024260, 2005

Buried mass anomalies along the hemispheric dichotomy in eastern Mars: Implications for the origin and evolution of the dichotomy

Walter S. Kiefer

Lunar and Planetary Institute, Houston, Texas, USA


Abstract

Gravity observations indicate the presence of buried, high-density material along the hemispheric dichotomy in eastern Mars. This material is unrelated to present-day topography and is probably the result of localized thinning of the crust. This thinning may be the result of an epoch of edge-driven convection that occurred shortly after the dichotomy formed. Initiation of edge-driven convection requires that lateral variations in lithospheric structure be created on a timescale that is shorter than the conductive cooling time for the lithosphere, a few tens of million years at most. This timescale cannot be achieved if the dichotomy boundary is created solely by large-scale convective flow. Formation or modification of the boundary by large impact basins such as Utopia can create the required lithospheric structure in a geologic instant. This suggests that large impacts were important in shaping the dichotomy, at least on a regional scale.

Received 29 July 2005; accepted 12 October 2005; published 17 November 2005.

Index Terms: 5417 Planetary Sciences: Solid Surface Planets: Gravitational fields (1221); 5475 Planetary Sciences: Solid Surface Planets: Tectonics (8149); 6225 Planetary Sciences: Solar System Objects: Mars; 8120 Tectonophysics: Dynamics of lithosphere and mantle: general (1213); 8121 Tectonophysics: Dynamics: convection currents, and mantle plumes.

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Citation: Kiefer, W. S. (2005), Buried mass anomalies along the hemispheric dichotomy in eastern Mars: Implications for the origin and evolution of the dichotomy, Geophys. Res. Lett., 32, L22201, doi:10.1029/2005GL024260.