Fachbereich 14 - Geowissenschaften
Institut für Planetologie
Planetenphysik

Thermal evolution, crustal growth, and magnetic field history of Mars

The thermal evolution, the crustal growth, and the magnetic field history of Mars have been examined with parameterized models for mantle convection. Comparing the results of these models with observations of recent missions to Mars, several important aspects of its evolution can be constrained including the evolution of the tectonic style, the temperature distribution immediately after formation of the core, and the mantle viscosity. In order to model the thermo-chemical evolution, the effects of crust differentiation, the associated redistribution of radioactive elements, and the latent heat of melting are included in the parameterization.The results of the thermo-chemical evolution models fit the observations if Mars cools by stagnant lid convection throughout its evolution from a comparatively hot initial state after core formation with potential mantle temperatures of about 2000 ± 100 K and if the Martian mantle has a stiff rheology (viscosity of about 10²¹ Pas at a reference temperature of 1600 K) consistent with that of a dry mantle. The post-accretional temperature distribution, which suggests a 700 to 1100 km deep magma ocean, is estimated from an energy balance for the core formation process and the initial temperature distribution determined with the thermo-chemical evolution models. Furthermore, a superheating of the core by 100 K or more due to the release of gravitational energy during core formation is required to generate an early, thermally driven dynamo. The evolution of the core temperature and of the core heat flow suggest that the dynamo switched off a few hundred million years later and did not rejuvenate until today. An alternative evolution scenario suggesting an early phase of plate tectonics cannot reconcile the observed crustal evolution. Crust formation is inefficient during the early phase of plate tectonics and is also frustrated later in the subsequent stagnant lid regime after plate tectonics cooled the interior efficiently.

Beteiligte Wissenschaftler:

Dr. Doris Breuer, Dr. Tilman Spohn, Sandra Schuhmacher

Veröffentlichungen:

Breuer D. and T. Spohn, 2001:Crustal evolution on Mars: Is an early plate tectonic regime likely? 26th General Assembly of the EGS, Nice, Geophysical Reasearch Abstratcs, (on CD-ROM).

Breuer D. and T. Spohn, 2001: Is the Tharsis bulge caused by plume volcanism? 26th General Assembly of the EGS, Nice, Geophysical Reasearch Abstracts, (on CD-ROM).

Breuer D. and T. Spohn, 2003: Early plate tectonics versus single-plate tectonics on Mars: Evidence from magnetic field history and the crust evolution, J. Geophys. Res.-Planets, in press.