LAVA FLOW EMPLACEMENT ON MARS AND IO: INSIGHTS FROM GEOLOGIC MAPPING

We are using geologic mapping from NASA and ESA spacecraft images to investigate the emplacement styles and types of lava flows that formed on Olympus, Arsia and Pavonis Montes in the Tharsis region of Mars, and on Jupiter’s volcanic moon Io. On Olympus Mons we find the main flank to be dominated by channel- and tube-fed flows, as well as lava fans (>80% of which are associated with tubes). Our original assessment that older tube-fed flows are buried by younger channel-fed flows is not consistent with more recent shield-wide mapping. Higher resolution, predominantly CTX, images provide new insight into the details of these fine scale contacts. For Io, global geologic mapping at the 1:15,000,000 scale shows that Io’s surface is ~28% lava flow fields, with another ~2% composed of paterae (caldera-like depressions containing lava flows or lava lakes). Bright (sulfur) lava flow fields outnumber dark (silicate) flow fields by a ratio of ~1.5:1. This suggests that secondary sulfur volcanism may only have a minor role in Io’s current volcanic activity relative to primary sulfur volcanism (although there may be a scale-dependence that requires further investigation). There is an unusual concentration of bright flows at ~45˚-75˚N, ~60-120˚W, perhaps indicative of past, extensive primary sulfur volcanism in this region. Higher-resolution Galileo observations show dark lava flow fields with morphologies similar to Hawaiian compound flow fields (Promethean style), whereas others are associated with larger eruptions and have morphologies similar to platy/ridged flows like Laki in Iceland or in the Cerberus region on Mars (Pillanian style). The fact that 93.5% of Ionian hot spots correlate with either dark (younger) or undivided (older) lava flows or patera floors (only <2% are low-temperature hot spots that correlate with bright, possibly sulfur flows) suggests that silicate materials are the dominant component of Io’s active volcanism.