VOLCANISM AT OLYMPUS MONS, MARS: RESULTS FROM GEOLOGIC MAPPING

We have completed a NASA-funded project to map the morphology and structure of the Olympus Mons (OM) shield volcano on Mars, using ArcGIS™ software by ESRI. This geologic map, to be published at a scale of 1:1,000,000, was made using Mars Reconnaissance Orbiter Context Camera (CTX) and Mars Express High Resolution Stereo Camera (HRSC) image mosaics as the mapping base. To address our science questions we also conducted mapping at the ~1:300,000 scale, which enables a distinction between sinuous rilles and leveed channels, which is fundamental for interpreting abundances among, and changes between, tube- and channel-forming eruptions. The scientific questions upon which this mapping project is based include understanding the volcanic development, including identification of volcanic unit source areas, and subsequent modification by structural, aeolian, and possibly glacial processes. We have combined our map with a map of the Olympus Mons Caldera that was produced at 1:200,000 scale, which provides additional detail on the summit region. We identified 27 units that are divided among Flank Units, Scarp and Apron Units, Plains Units, and Crater Materials. The Flank Units include 13 units, plus 7 caldera units. The basic morphological difference across the flank involves mottled and channeled units. The channel unit is typified by sub-parallel linear flows with levee structures. The mottled unit is hilly at the horizontal scale of 10s to 100s of meters. Because a motivating question involves the identification of flank unit sources we subdivided channels and mottled units according to their apparent origin. These include Fan-sourced, Ridge-sourced, and Flank units (which can be traced to the caldera or have a source that is unclear). Fans and ridges are up to 100 m in height. Fans are delta-shaped whereas ridges are elongate, generally radial to the caldera. The geologic contacts between morphologic units are now completely mapped. Small vent structures in the plains to the SE and lava fans on the volcano’s flank have been cross referenced with the Catalog of Small Volcanic Vents in the Tharsis Province. The final map draft will be submitted to the USGS shortly for review upon completion of the Correlation of Map Units and Description of Map Units.