Experimental evidence for lava-like mud flows under Martian surface conditions

Abstract

Large outflow channels on ancient terrains of Mars have been interpreted as the products of catastrophic flood events. The rapid burial of water-rich sediments following such flooding could have led to sedimentary volcanism, in which mixtures of sediment and water (mud) erupt to the surface. Tens of thousands of volcano-like landforms populate the northern lowlands and other local sedimentary depocenters on Mars. However, it is difficult to determine whether the edifices are related to igneous or mud extrusions, partly because the behaviour of extruded mud under martian surface conditions is poorly constrained. Here, we investigate the mechanisms of mud propagation on Mars using experiments performed inside a low-pressure chamber at cold temperatures. We find that low viscosity mud under martian conditions propagates differently from on Earth, because of rapid freezing and the formation of an icy crust. Instead, the experimental mud flows propagate like terrestrial pahoehoe lava flows, with liquid mud spilling from ruptures in the frozen crust, then refreezing to form a new flow lobe. We suggest that mud volcanism can explain the formation of some lava-like flow morphologies on Mars, and that similar processes may apply to cryovolcanic extrusions on icy bodies in the Solar System. The physics behind igneous volcanism on Mars is better understood [e.g., 1-4] than that of sedimentary volcanism in which mixtures of water and sediment, subsequently referred to as mud, are extruded onto the surface. On Earth, sedimentary volcanism manifests at the surface as eruptions of fluids (water, gas, occasionally oil), fine grained sediments (e.g. clays) and clasts from the country-rock. These geological phenomena are the result of fluid (on Earth typically associated with methane) overpressure [5], generated at several hundred to several thousand metres depth, combined with gravitational instability of buoyant sedimentary units buried at deeper stratigraphic levels [6]. The viscosity of ascending mud varies, and affects the shapes, sizes and thicknesses of resulting flows. The higher the water

Dwarf planet (1) Ceres surface bluing due to high porosity resulting from sublimation

“…Flow features associated with craters like Occator and Haulani have been interpreted as impact melt involving liquid water 29 , 30 . In a recent experiment under low-pressure conditions, a frozen crust quickly formed on the surface of a flowing, low viscosity mud by evaporative cooling, akin to basaltic lavas flows on Earth 31 . Vigorous boiling was observed, which did not impede formation of the crust.…”

Impact heat driven volatile redistribution at Occator crater on Ceres as a comparative planetary process

“…Thus, impact melts on Ceres are likely much wetter than on terrestrial planets. These muddy impact brine-melt slurries on Ceres will be mobile while molten and behave much like (instantly emplaced) volcanic deposits, as recently demonstrated experimentally in a Mars context 34 .…”

“…1, 2b, and 3) similar to those seen in the mantling units on terraces, suggesting rapid cooling and solidification of the outer layer of mobile impact deposits that were stranded on high terrains during or after emplacement. This mud-like, brine-melt impact slurry coated large areas, ponded in closed depressions and flowed downslope to form lobate lava-like flows 34 ( Supplementary Figs. 7 and 8) but also quickly formed a flashfrozen upper carapace and the resistant cliffs ( Figs.…”

“…2 and 3, Supplementary Figs. 6 and 13) are likely related to fracturing owing to gravitational adjustment of the crater floor, but others are associated with small pits and thin secondary lava-like 34 muddy flow units (Fig. 3b, Supplementary Fig.…”

“…The differences in surface morphology of impact deposits on Ceres compared with the Moon and Mars shown here must be related to the higher fraction of salts and water ice in Ceres' outer layers [19][20][21] and to different impact conditions on Ceres (including 40°K cooler near-surface temperatures 10 , 5-to-15 times lower surface gravity, and factor~2 lower mean impact velocities 10 ), which result in lower heating rates for a given size projectile on Ceres 10 relative to Mars or Earth. These lower impact heating levels preclude melting of silicates on Ceres, resulting in muddy deposits that behave as volcanic flows 9,34 , and may result in a more centrally concentrated distribution of hydrothermal fluids and salt/carbonate surface precipitation compared with those observed on impact-derived materials and structures on the Moon, Earth, and Mars 1,29 . The irregular pits and pit clusters, thin lava-like mud flows, and sinuous troughs observed within the thick LFDs and other floor materials at Occator are both less common and are different in expression to those within lunar and Mars craters (e.g., Figs.…”