Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmdi43a1952m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #DI43A-1952
Physics
[5400] Planetary Sciences: Solid Surface Planets, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5480] Planetary Sciences: Solid Surface Planets / Volcanism, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
We have reinvestigated the coupled thermal and crustal evolution of Mars using 1D parametrized thermal evolution models [1] and taking new data concerning the content and distribution of heat producing elements [2] as well as new laboratory data concerning the flow behavior of iron-rich olivine [3] into account. The high enrichment of radioactive elements in the crust leads to a less efficient heat transport from the lithospheric base, resulting in a thinning of the stagnant lid. If the stagnant lid becomes thinner than the crust, crustal material can be recycled back into the mantle by the vigourous convective motion. However, crustal recycling appears to be incompatible with an early separation of geochemical reservoirs [4] and valid models are required to show no episodes of crustal recycling. Furthermore, admissible models have to reproduce the Martian crust formation history and to allow the formation of partial melt under present-day mantle conditions. Taking dehydration stiffening of the mantle into account, we find that admissible models have low initial upper mantle temperatures between 1600 and 1700 K, a primordial crustal thickness of 30 km, and an initially wet mantle rheology. The crust formation process on Mars would then have been driven by the extraction of a primordial crust after core formation which was cooling the mantle to temperatures close to the peridotite solidus. The second stage of global crust formation took place over a more extended period of time, waning at around 1300-1700 Myr, and was driven by heat produced by the decay of radioactive elements. Finally, present-day volcanism is explained by convective mantle plumes and thermal insulation under regions of locally thickened crust. Water extraction from the mantle was found to be relatively efficient and close to 50 percent of the total inventory is lost from the mantle in most models. Assuming an initial mantle water content of 100 ppm and that 10% of the extracted water is supplied to the surface by extrusive volcanism, this amount is equivalent to a 20 m thick global surface layer, suggesting that volcanic outgassing of H2O could have significantly influenced the early Martian climate and increased the planet's habitability. To further investigate the potential for an early wet and warm Mars, we self-consistently calculate the amount of volcanically outgassed CO2. This is done by directly coupling thermodynamic models of CO2 solubility in basaltic melt [5] to the thermal evolution models. Using the range of admissible models, we find that an equivalent of 1 bar of CO2 can be outgassed if the redox state of the mantle is assumed to be at the upper limit of the plausible range (IW+1). This is probably sufficient to raise the mean global surface temperature above the triple point of water [6]. However, erosive processes could have been very strong under an active young sun, thus leading to considerable atmospheric loss within the Noachian period [7]. [1] Breuer, D and Spohn, T, PSS, 54, 153, 2006. [2] Taylor, GJ et al., JGR, 111, E03S10, 2006. [3] Zhao, YH et. al., EPSL, 287, 229, 2009. [4] Jagoutz, E, SSR, 56, 13, 1991. [5] Hirschmann, MM and Withers, AC, EPSL, 270, 147, 2008. [6] Forget, F and Pierrehumbert, RT, Sci., 278, 1273-1276, 1997. [7] Tian, F et. al., GRL, 36, L02205, 2009.
Breuer Doris
Grott Matthias
Morschhauser A.
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