Viscosity and Density of Fe-Rich Silicate Melts Relevant to Mars

Observations from Mars missions have revealed that Mars has had a very active igneous history. While volcanism on Mars is thought to have occurred in the first half of the planet's history, recent evidences suggest that Mars may, in fact, still be volcanically active. An improved understanding of the unique geological history and evolution of Mars relies on the development of models for the planet's interior and hypotheses regarding the planet's formation and evolution. This, in turn, requires a knowledge of the physico-chemical properties of Martian magmas. Of all the properties of interest, viscosity and molar volume are those that most tightly control the dynamics of magmas.\The composition of Martian magma has been derived from the composition of the SNC Martian meteorites and it is generally accepted that Martian magma may contain up to 18 wt% of iron. Unfortunately existing models to calculate the physico-chemical properties of Martian magmas are insufficient in at least one important aspect: they are not calibrated for the high iron contents inferred in Martian magmas. In order to rectify this we are developing an experimental program to determine the physico-chemical properties of iron-rich silicate melts relevant to Mars, from which the partial molar properties of both iron components (FeO and Fe₂O₃) will be derived.\In a first step, compositions in simple iron-bearing systems have been studied. Variable amounts of iron (up to 30 wt%) have been added to the anorthite-diopside eutectic composition, a basalt analogue. The high-temperature viscosities and densities of these melts have been measured in air by concentric cylinder method and using the Pt-based double-bob Archimedean method, respectively. These measurements suggest a decrease of the viscosity with increasing Fe-content and an increase of the density with increasing Fe-content. In addition, the oxidation state of iron in these samples as a function of temperature was investigated by wet chemistry methods. Preliminary results show that Fe₂O₃-content decreases with increasing temperature (i.e., about 10% within the temperature range investigated, namely between 1300 and 1600°C).