On the Spatial Variability of the Martian Elastic Lithosphere Thickness: Evidence for Mantle Plumes?

Details On the Spatial Variability of the Martian Elastic Lithosphere Thickness: Evidence for Mantle Plumes? On the Spatial Variability of the Martian Elastic Lithosphere Thickness: Evidence for Mantle Plumes?

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p22a..06g&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P22A-06

Other

[5400] Planetary Sciences: Solid Surface Planets, [5418] Planetary Sciences: Solid Surface Planets / Heat Flow, [5430] Planetary Sciences: Solid Surface Planets / Interiors, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

The elastic lithosphere thickness at the Martian North Pole has recently been constrained by estimating the flexural response of the lithosphere to loading at the polar caps and a minimum elastic thickness of 300 km has been determined. This is a factor of three to four larger than elastic thickness estimates for other Amazonian surface units like the Tharsis volcanoes, which exhibit elastic thicknesses around 75 to 90 km. Here we investigate the spatial heterogeneity of the Martian elastic lithosphere thickness and present a model which takes the locally varying crustal thickness, the local concentration of heat producing elements as well as variations of strain rate into account. The model predicts D = 225 km at the North Pole today, whereas D = 75-90 km is obtained at the Tharsis volcanoes if a mid Amazonian loading age is assumed. Therefore, although a large degree of spatial heterogeneity can be explained by the presented model, large elastic thicknesses in excess of 300 km cannot be reproduced. In order to fit all elastic thickness values derived from observations the mantle heat flow at the North Pole needs to be smaller than the global average. A local reduction of heat flow by 25% with respect to the chondritic value would be sufficient to explain the large elastic thicknesses observed there. However, a local reduction of heat flow can only be reconciled with a bulk chondritic concentration of heat producing elements in the Martian interior if the excess heat is deposited elsewhere. This could be achieved by mantle plumes, possibly active underneath Tharsis. The size and strength of such a plume is constrained by the elastic thickness at the Tharsis Montes and maximum average heat flows between 8 and 20 mW/m2, corresponding to central peak heat flows of 40 to 100 mW/m2, are consistent with the observations. Such a plume would leave a clear signature in the surface heat flow and should be readily detectable by in-situ heat flow measurements. Gray-scale Hammer projection map of the surface heat flow (in mW/m2) overlaid over a shaded relief map of MOLA topography assuming a mantle plume underneath Tharsis. The background heat flow provided to the base of the stagnant lid is assumed to be consistent with D > 300 km at the North Pole. The plume strength has been calculated assuming a plume footprint radius of 3000 km and a plume energy compatible with the elastic thicknesses observed at the Tharsis Montes

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