Steep Sided Domes on Venus: A Re-evaluation of Morphologies and Emplacement Mechanisms Abigail L. Gleason 1* , Robert R. Herrick 1 , Jeffrey M. Byrnes 2 , 1 Geophysical Institute, University of Alaska, Fairbanks *(903 Koyukuk Drive, P.O. Box 757320 Fairbanks, Ak 99775-7320, agleason@gi.alaska.edu), 2 School of Geology, Oklahoma State University Introduction: Venusian steep sided domes are a class of volcanic features noted for their circularity, steep sides, large volumes and relatively flat tops. Sev- eral researchers have assessed their composition, geo- logic association to the surrounding terrain and origins (i.e. [1], [2], [3] and [4]). Building upon previous works, we focus on three objectives: the first is to gen- erate high resolution Digital Elevation Models (DEMs) from stereo derived topography in order to evaluate differences in morphology within the dome population. We then combine the topography with detailed surface lineament mapping to evaluate em- placement mechanisms. Finally, treating the domes individually, we analyze possible causes for variations among the dome population, including magma viscos- ity, episodicity and effusion rate. Methods: This study utilizes SAR imagery col- lected by the Magellan mission from 1990 to 1993 at a resolution of ~100 m/pixel (resampled to 75m/pixel). The planet was mapped in three cycles with one right looking and two left looking geometries, resulting in ~45% of the planet covered by stereo imagery [5]. DEMs produced in this study are at a horizontal reso- lution of 225 – 1000 m/pixel. Both left-left and left- right stereo pairs are used for this study. For the lineament analysis part of this study, the ArcGIS soft- ware suite is utilized. Case Examples: In Figure 1, the stereo derived topography is shown overlaying the left looking image of the dome at 42˚N, 79˚E. This example shows the high resolution detail of our stereo derived DEMs. The central pit/depression is clearly resolved, as well as elevation differences between the west and east parts of the dome. The dome located at 3˚S, 151˚E has good exam- ples of surface lineaments and has not undergone any post-emplacement deformation (Figure 2). Two sets of lineamens are visible: one that is principly radial out from the center of the dome, and the other which is principly orthogonal to the first set, or circular around the center. These two sets of fractures could represent two different stages of cooling, or even growth and cooling. For example, the radial lineaments resemble fracturing related to growth of a dome in a study by [6]. In either case, these lineaments preserve some of the eruption histories of the domes and can give in- sight into the rheology of each dome’s crust. Three domes, located at 12˚N, 8˚E, are shown in Figure 3a. Despite their close proximity, cross-sections through the domes shown in Figures 3b and 3c demon- strate the range of morphologies found in the dome population. Dome B is depressed in the center with a deep central pit clearly resolved in cross section, that is believed to extend below the preexisting planetary surface. Dome C is relatively flat topped, has steeper sides, and has a much shallower central pit. Figure 1: dome located at 42˚N, 79˚E. The orthorecti- fied image is overlaid by the DEM derived from stereo tech- niques. The dome is 36.5 km in diameter. Figure 2: dome located at 3˚S, 151˚E. Radial and per- pendicular (orthogonal to radial direction) lineaments are outlined , as well as lineaments in the surrounding terrain, showing that this done has not undergone local tectonic de- formation after its emplacement. The diameter of this dome is 34.6 km. Elevation 42N 79E DEM High : 1945 Low : 394 10 Kilometers ´ Surface Lineaments orthogonal local terrain radial 10 Kilometers ´ Lunar and Planetary Science XXXIX (2008) 1863.pdf