Laszlo P. Keszthelyi
Paul M. Schenk
Moses P. Milazzo
Rosaly Lopes
Julie A. Rathbun
Ronald Greeley
David A. Williams
2005
<p><span>We have studied data from the </span><i>Galileo</i><span> spacecraft's three remote sensing instruments (Solid-State Imager (SSI), Near-Infrared Mapping Spectrometer (NIMS), and Photopolarimeter-Radiometer (PPR)) covering the Zamama–Thor region of Io's antijovian hemisphere, and produced a geomorphological map of this region. This is the third of three regional maps we are producing from the </span><i>Galileo</i><span> spacecraft data. Our goal is to assess the variety of volcanic and tectonic materials and their interrelationships on Io using planetary mapping techniques, supplemented with all available </span><i>Galileo</i><span> remote sensing data. Based on the </span><i>Galileo</i><span> data analysis and our mapping, we have determined that the most recent geologic activity in the Zamama–Thor region has been dominated by two sites of large-scale volcanic surface changes. The Zamama Eruptive Center is a site of both explosive and effusive eruptions, which emanate from two relatively steep edifices (Zamama Tholi A and B) that appear to be built by both silicate and sulfur volcanism. A ∼100-km long flow field formed sometime after the 1979 </span><i>Voyager</i><span> flybys, which appears to be a site of promethean-style compound flows, flow-front SO</span><sub>2</sub><span> plumes, and adjacent sulfur flows. Larger, possibly stealthy, plumes have on at least one occasion during the </span><i>Galileo</i><span> mission tapped a source that probably includes S and/or Cl to produce a red pyroclastic deposit from the same vent from which silicate lavas were erupted. The Thor Eruptive Center, which may have been active prior to </span><i>Voyager</i><span>, became active again during the </span><i>Galileo</i><span> mission between May and August 2001. A pillanian-style eruption at Thor included the tallest plume observed to date on Io (at least 500 km high) and new dark lava flows. The plume produced a central dark pyroclastic deposit (probably silicate-rich) and an outlying white diffuse ring that is SO</span><sub>2</sub><span>-rich. Mapping shows that several of the new dark lava flows around the plume vent have reoccupied sites of earlier flows. Unlike most of the other pillanian eruptions observed during the </span><i>Galileo</i><span>mission, the 2001 Thor eruption did not produce a large red ring deposit, indicating a relative lack of S and/or Cl gases interacting with the magma during that eruption. Between these two eruptive centers are two paterae, Thomagata and Reshef. Thomagata Patera is located on a large shield-like mesa and shows no signs of activity. In contrast, Reshef Patera is located on a large, irregular mesa that is apparently undergoing degradation through erosion (perhaps from SO</span><sub>2</sub><span>-sapping or chemical decomposition of sulfur-rich material) from multiple secondary volcanic centers.</span></p>
application/pdf
10.1016/j.icarus.2005.03.005
en
Elsevier
The Zamama-Thor region of Io: Insights from a synthesis of mapping, topography, and Galileo spacecraft data
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