Implications of Large Elastic Thicknesses for the Composition and Current Thermal State of Mars
Grott, M. and Breuer, D. (2008) Implications of Large Elastic Thicknesses for the Composition and Current Thermal State of Mars. In: Eos Trans. AGU, Fall Meet. Suppl., 89 (53), . AGU Fall meeting, 2008-12-14 - 2008-12-19, San Francisco, California (USA).
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The elastic lithosphere thickness at the Martian north polar cap has recently been constrained using radar sounding data obtained by SHARAD, the shallow radar onboard the Mars Reconnaissance Orbiter. Analysis of the SHARAD radargrams showed that the amount of deflection caused by ice loading at the polar caps is negligible - less than 100 m. Quantitative analysis yielded a lower bound on the elastic lithosphere thickness T<sub>e</sub> of 300 km, a value twice as large as previous estimates from theoretical considerations and flexure studies. Such large elastic thicknesses are only compatible with the planet's thermal evolution if the planetary interior is relatively cold and this could have direct bearing on the admissible amount of radioactive elements in the Martian interior. On the other hand, if the concentration of heat producing elements in the Martian interior is indeed reduced, the resulting low interior temperatures could possibly inhibit partial mantle melting and magmatism. However, geological evidence suggests that Mars has been volcanically active in the recent past. We have investigated the Martian thermal evolution and identified models which are consistent with a present day elastic thickness in excess of 300 km. We find that a wet mantle rheology is best compatible with the observed elastic thicknesses, but in this case the bulk concentration of heat producing elements in the silicate fraction cannot exceed 50 % of the chondritic concentration if 50 % of the radioacitve elements are concentrated in the crust. Furthermore, due to the efficient cooling of the planet for a wet mantle rheology, recent volcanism can only be explained by hydrous mantle melting. This requires the mantle water content to exceed 1500 ppm and although this is within the range reported for the shergottite parent magmas, it is certainly on the boundary of the plausible parameter range. If a dry mantle rheology is assumed, bulk Mars does not need to be sub-chondritic, but at least 70 % of the radiogenic elements need to be concentrated in the crust to be consistent with the large elastic thicknesses. For a dry mantle, recent volcanism could be driven by decompression melting in the heads of strong mantle plumes which are present in numerical simulations of mantle convection if the viscosity is strongly pressure dependent or endothermic phase transitions are present near the core-mantle boundary.
|Document Type:||Conference or Workshop Item (Poster)|
|Title:||Implications of Large Elastic Thicknesses for the Composition and Current Thermal State of Mars|
|Journal or Publication Title:||Eos Trans. AGU, Fall Meet. Suppl.|
|In ISI Web of Science:||No|
|Keywords:||Interiors, Volcanism, Mars, Planetary Sciences, SHARAD, Mars Reconnaissance Orbiter, MRO|
|Event Title:||AGU Fall meeting|
|Event Location:||San Francisco, California (USA)|
|Event Type:||international Conference|
|Event Dates:||2008-12-14 - 2008-12-19|
|HGF - Research field:||Aeronautics, Space and Transport|
|HGF - Program:||Space|
|HGF - Program Themes:||W EW - Erforschung des Weltraums|
|DLR - Research area:||Space|
|DLR - Program:||W EW - Erforschung des Weltraums|
|DLR - Research theme (Project):||W - Vorhaben Vergleichende Planetologie (old)|
|Institutes and Institutions:||Institute of Planetary Research > Planetary Physics|
|Deposited By:||Stefanie Hempel|
|Deposited On:||05 Jan 2009|
|Last Modified:||27 Apr 2009 15:39|
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