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Near-Equilibrium Rheology Experiments on Martian Analog Lava

Presentation #212.10 in the session Martian Geomorphology, Ice Layers, Crust, and Habitability (Poster + Lightning Talk)

Published onOct 23, 2023
Near-Equilibrium Rheology Experiments on Martian Analog Lava

Modeling magma ascent and lava emplacement on Mars is challenging due to rheological changes during cooling and crystallization. High-resolution images from Mars orbiters have been used to derive lava properties such as effusion rates, yield strength, and viscosity [e.g.,1-2]. However, without understanding the rheological evolution of crystallizing lavas, the models likely underestimate lava viscosity at final emplacement, consequently impacting calculated dynamics, magma ascent time scales, and volcanic eruption styles [3].

In order to quantify rheological and thermal properties, experiments were conducted with liquids of picritic composition based on rock analyses performed by the MER Spirit mission at Gusev Crater [4-6]. Measurements are made with the High Temperature Rheometer in the PLANETAS (Planetary Exploration Through Analog Science) laboratory at NASA Ames Research Center. The rheometer head measures torque required to rotate a cylindrical spindle immersed in a cylindrical crucible containing the sample [7]. The initial sample is a crystalline material that was melted at 1500°C to ensure complete melting of all crystalline phases. The sample then cooled at a rate of 10 °C/min to a target temperature between 1180°C and 1225°C, maintaining a constant angular velocity of the spindle. Once the liquidus was crossed and crystals appeared (approximately 1250°C), the two-phase suspension exhibited non-Newtonian behavior. The sample temperature and spindle speed were held constant for 16 h to reach equilibriumconditions [8]. Torque measurements at varying spindle speeds provided data for calculating the flow index and viscosities at each temperature.

The quenched post-experiment samples revealed the coexistence of liquids, crystals, and gases. The calculated flow index n<1 indicate non-Newtonian behavior. The viscosity was over 103 Pa·s at ~1210°C, compared to 102 Pa·s at 1250°C. The high viscosity can be attributed to suspended crystals in the molten liquid. Moreover, experiments conducted at 1180 and 1190°C resulted in near-complete crystallization of the sample, suggesting a narrow temperature interval for Martian lava flow emplacement.

References: [1] Hulme, G. Geophys. J. Roy. Astr. Soc. 39, 361-383 (1974) [2] Wilson, L. et al. J. Volc. Geotherm. Res., 185, 28-46 (2009) [3] Sehlke, A. et al. Planet. Space Sci. 187 (2020) [4] Herzberg, C. et al. Earth Sci. Rev. 44, 39–79 (1998) [5] Hughes, S. S. et al. Astrobiology, 19, 260–283 (2019) [6] McSween, H.Y. et al. Science, 305, 842–845 (2004) [7] Sehlke, A. 53rd LPSC Conf. p.1171 (2022). [8] Sehlke A. et al. Bull Volc. 76, 876 (2014).

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