TERRESTRIAL ANALOGS TO PLANETARY VOLCANISM: IMPLICATIONS FOR THE ORIGINS OF FLOOD BASALT LAVA FLOWS ON MARS

Volcanic activity provides a record of the compositional and thermophysical history of planetary interiors and can have profound effects on the evolution of surfaces and atmospheres. This presentation draws on examples from Hawai‘i, New Mexico, and Iceland to document a range of lava flow types that can help to inform the origin of lava flow units on Mars in terms of magmatic source depths, eruption durations, and emplacement styles. Basaltic flow types are traditionally viewed along a spectrum from pāhoehoe to ‘a‘ā, with lobate pāhoehoe flows being indicative of low viscosity lavas emplaced at low shear strain rates, whereas channelized ‘a‘ā flows imply higher viscosity lavas emplaced at higher strain rates. However, “transitional” flow types (e.g., platy, slabby, and rubbly lavas) do not fit well within this classification structure. Here, an alternative classification framework is proposed, which considers the stability/instability of the lava flow surface. This ternary system includes three types of lava crust: (1) stable; (2) continuously disrupted; and (3) episodically disrupted. Pāhoehoe exemplifies lava with a stable crust, whereas ‘a‘ā surfaces are continuously disrupted. However, transitional lavas can only be formed through the episodic disruption of initially stable surfaces and do not lie along the pāhoehoe to ‘a‘ā continuum. On, Mars high effusion rate eruptions sourced from the deep martian mantle will tend to favor the formation of transitional lavas because they are more likely to inundate basins and drain rapidly when they overtop their confinement, thereby disrupting the surface into platy, slabby, and rubbly lavas. In contrast, more shallowly sourced magmas will tend to be erupted at lower effusion rates leading to the emplacement of pāhoehoe-like flow units. Examination of lava flows in the Elysium Volcanic Province reveals that both of these two distinct eruptions styles have occurred on Mars during the Late Amazonian Epoch.