Modeling the thermal evolution of the Martian lithosphere

Abstract

The purpose of this research is to demonstrate that the thickness of, and temperatures within, the Martian lithosphere from 4.5 Ga to the present can be modeled using published methods. Several variables are used to calculate this, such as: surface temperature, mantle heat flux, radiogenic heat production, crustal thickness, and coefficients of thermal conductivity. The sensitivity of each of these variables was tested in order to ascertain the robustness of the model. Under conditions of increased temperature and pressure, unconsolidated material, or sediment, undergoes diagenesis, becoming a sedimentary rock. Under still higher pressures and temperatures, metamorphic rocks are formed. In this work, lithification is considered to occur at temperatures between 50 and 150 °C, and metamorphism to start at temperatures greater than 150 °C. On Earth, tectonic processes, such as orogenies, coupled with erosion, can exhume sedimentary and metamorphic rocks formed at depth. On Mars, although plate tectonics may have been active in its early history, it appears that such processes have not been in place for at least 4 Ga years. Therefore, the principle means by which sedimentary and metamorphic rocks can be exhumed in more recent geological times is by impact. Using the above-mentioned model, the thickness of the lithosphere and the depths at which sedimentary and metamorphic rocks are expected to be found can be estimated. The sensitivity of the model to changes in the input variables was tested. The model was insensitive to variations in the following variables: radiogenic heat productivity of the crust, coefficient of thermal conductivity of the mantle, and surface temperature. The model was sensitive to variations in the following variables: mantle heat flux, coefficient of thermal conductivity of the crust, and thickness of the crust. Therefore, in order to decrease the range of possible answers, better estimates of the mantle heat flux, coefficient of thermal conductivity of the crust, and thickness of the crust are needed. By comparing these to the depths of impact exhumation, the likelihood of sedimentary and metamorphic rocks being lofted from the surface of Mars to potentially yield Earth-crossing meteors can be resolved.