Other
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....8497b&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #8497
Other
Scientific paper
On Mars volcanism, tectonic activity and anomalies in the gravity field are concentrated in only one region, the Tharsis region. These observations suggest that thermal convection in the martian mantle is different from that in the Earth's mantle. It is possible that convection in the martian mantle is dominated by only a single plume under the Tharsis region. A possible reason for this strong reduction to only one plume can be the endothermic phase boundary from γ-spinel to perovskite and magnesiowüstite, which may appear in Mars close to the core-mantle boundary. In three-dimensional models the evolution of the martian mantle and its convection pattern is simulated including secular cooling and the endothermic phase boundary from γ-spinel to perovskite. In our models the viscosity is depth-dependent and varies with the radial averaged temperature following an Arrhenius term. According to changes in the temperature the viscosity varies with time and allows to simulate the thickening of the lithosphere. In addition to models with a fixed temperature contrast between the core-mantle boundary and the surface models which include the cooling of the core are calculated. In these models the temperature at the core-mantle boundary is determined by the heat given to the mantle. The results show that the presence of the endothermic phase boundary near to the core-mantle boundary causes a strong reduction of the number of upwellings. In the models which include the cooling core a reduction to two plumes after 4.5 billion years is observed. Variations of the thickness of the perovskite-layer and the phase parameter show that the effect of the phase boundary depends on its position in the thermal boundary layer. If big parts of the thermal boundary layer are above the phase boundary the influence is smaller. In addition the phase boundary has an effect on heat-release from the core. Without the phase boundary the core cools down by 500 K in 4.5 billion years. In the same time with a phase boundary the cooling is between 400 K and 450 K. In the models with the cooling core the phase boundary has only a small influence on the thickness of the lithosphere at the end of the evolution, which is about 150 km.
Buske Monika
Christensen Ulrich
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