Viscosity of Synthetic Martian Basaltic Melts

Differences in the chemical composition of planetary mantles produce a large diversity of volcanic melts. In particular, differences in accretion history and oxidation state result in large variations of iron oxide concentration in the mantle, the most oxidized bodies having the most iron-rich mantles (e.g., Mars, Vesta). Viscosity, strongly dependent on magma composition and temperature, is the most important physical parameter controlling magma migration up to and beyond eruption as expressed in the flow characteristics of lava. To date, empirical models allowing prediction of the viscous behaviour of silicate melts from their chemistry are based on experiments using predominantly terrestrial composition and their analogs (GRD, 2008; Hue and Zhang, 2006). This study extends the capability of such models to predict the viscosity of non-terrestrial melts by providing data on extra-terrestrial compositions. First, a compilation of viscosity measurements on lunar compositions from the literature is provided. Second, viscosity of synthetic martian compositions have been experimentally determined over a wide range of temperature from superliquidus to supercooled conditions. The viscosity at high temperature was determined via the concentric cylinder method and the low temperature viscosities were calculated from the glass transition temperature obtained by differential scanning calorimetry. The iron-rich character of these composition yields low viscosities similar to lunar basalt and to some terrestrial basanites. The very fluid behaviour of these melts fits well with the observation of lava flow morphology at the surface of Mars and with the possibility of magma ascent through a thick lithosphere (recent volcanism on Mars).