VOLCANISM ON IO: RESULTS FROM GLOBAL GEOLOGIC MAPPING

We have completed a new 1:15,000,000 global geologic map of Jupiter’s volcanic moon, Io, based on a set of 1 km/pixel global mosaics derived from NASA Galileo & Voyager spacecraft images. The map was produced using ArcGIS™ software, which enables accurate determination of the dimensions of linear features & structures and the areas of process-related material units. Io’s surface consists of plains mantled by volcanic deposits (~67%), lava flow fields (~28%), tectonic mountains (~3%), and paterae (caldera-like depressions, ~2%). Plains are geographically distributed on Io, with red-brown plains dominantly occurring >±30˚ latitude and thought to result from radiation-induced alteration of other plains units. White plains (typically enriched in SO₂) occur mostly in the equatorial antijovian region (±30˚, 90˚-230˚W), possibly indicative of a colder part of the satellite to preserve the SO₂. Why this one region is colder is a mystery, but the answer may be related to variations in crustal distribution of magma sources, or perhaps crustal thickness, relative to other parts of Io. 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 (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. We mapped a total of 425 paterae on Io, an increase from the 417 previously identified. Although paterae cover only 2% of Io’s surface, Io’s hot spots dominantly occur within paterae (63.9% of all hot spots). The fact that 93.5% of Ionian hot spots correlate with either dark (younger) or undivided (older) patera floors or lava flows suggests that silicate materials are the dominant component of Io’s recent volcanism. Diffuse deposits (DD) mantling other units cover ~18.2% of Io’s surface. The relative lack of pyroclast-bearing, dark and yellow DD compared to gas-derived, White and Red DD (14.8% vs. 85.1%) may suggest that sulfur and SO₂ do not have a major role as volatiles that disrupt or interact with sulfur or silicate magmas.