Abstract
AbstractNew viscosity experiments at superliquidus temperatures and during cooling at a rate of 10 K/hr have been performed at different shear rates on a synthetic pyroxenite melt. Results revealed that this melt is extremely fluid at temperature between 1646 and 1530 K and measured viscosities are between 2.2 and 7.8 Pa·s. Such very low viscosities allow the lava to flow in turbulent regime as confirmed by the high Reynolds numbers, which are always >2,000. As a consequence, very long distance could be covered by the lava flow. If we consider this studied composition as proxy for Mars lava flows coupled with very high effusion rates, our results might explain the presence of extraordinary large volcanic channels, as recently hypothesized for the Kasei Valles on Mars, even considering that the gravity is approximately one third that of Earth. Few literature data tracking viscosity during cooling are available, and they reported shear thinning effect on different compositions. Our experiments performed at 0.1 and 1 s−1 have shown complex variation in the apparent viscosity, confirming that nonequilibrium rheology represents a still unexplored field of investigation useful to better understand the real geological scenarios occurring in magmatic and volcanic systems.
Highlights
Experiments under constant temperature were performed in order to study the behavior of lavas in different geological settings on both Earth and other Earth‐like planets (; Chevrel et al, 2013; Rossi et al, 2017; Sehlke & Whittington, 2015; Vona et al, 2011, and references therein)
If we consider this studied composition as proxy for Mars lava flows coupled with very high effusion rates, our results might explain the presence of extraordinary large volcanic channels, as recently hypothesized for the Kasei Valles on Mars, even considering that the gravity is approximately one third that of Earth
Experimental data are in good agreement with this estimate since the experiment performed at T = 1530 K did not show the presence of crystals, whereas experiments performed at 1516 K showed an increase in viscosity, confirming a possible rearrangement of the melt structure and/or nucleation and growth processes
Summary
Experiments under constant temperature were performed in order to study the behavior of lavas in different geological settings on both Earth and other Earth‐like planets (; Chevrel et al, 2013; Rossi et al, 2017; Sehlke & Whittington, 2015; Vona et al, 2011, and references therein). Experimental study on crystallization induced by variable decompression rates allowed scientists to shed new light on processes governing magma ascent dynamics (Fiege et al, 2015, and references therein). Following the pioneering work of Carmichael (1974), reporting the rheological importance of the coexistence of crystals and liquid material, melt solidification processes have been investigated via experiments under different applied cooling rates (see Hammer, 2008, for a general summary). Diverse studies at crystal‐melt disequilibrium conditions have been performed (e.g., Lofgren, 1980; Cashman, 1993; Lange et al, 1994; Arzilli & Carroll, 2013; Vetere et al, 2015, and reference therein), but only recently has even the deformation acting on lavas been taken into account with both laboratory
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