The Regional Geology of Conamara Chaos: Stratigraphic Relations and Implications for Future Exploration. D. A. Senske, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109.

Abstract:

Much of the previous geologic analysis of the Conamara Chaos region has focused on the history and reconstruction of the crustal blocks within the chaos itself. To better understand the geologic context of this relatively young outcrop of disrupted crust, its relation to regional geologic events, and the evolution of the entire area over time, we have performed comprehensive geologic mapping. Using image data centered at 10°N, 271°W with a resolution of 180 m/pixel and covering an area of approximately 90,000 km², the interrelation between tectonic structures (arrays of bands, ridges, and fractures) and cryovolcanic units is established. Our analysis shows that in addition to the major outcrop of chaos (~75x100 km), there are approximately 80 additional smaller (10’s of km across) areas of chaos or lenticulae. By identifying key cross cutting and superposition relations, it is possible to identify a set of distinct trends in the formation of tectonic features. The tectonic stratigraphy shows an alternating and cyclical pattern with one set of ~N20°W tectonic features subsequently superposed by ~N30°E bands and ridges. This sequence appears to repeat three times over the history of the region. The identification of a fracture that cross cuts older regional units but is preserved in some of the larger crustal blocks within Conamara indicates that the chaos postdates both the adjacent Astenus and Agave Lineae. The mapping shows little or no emplacement of cryovolcanic deposits in the earliest history of this region. Instead, volcanic processes appear to be a part of later geologic activity.

Regional geologic mapping reveals tectonic patterns that are consistent with those mapped over a more limited area [Spaun et al., 2003]. The restriction of cryovolcanism to the latter part of the history, suggests a change in geologic setting and possibly crustal structure with time. Data to be collected by the Europa mission now in formulation will allow: (1) the mapped contact relations to be examined in greater detail, providing higher clarity of geologic relations; (2) the extension of regional-scale mapping to adjacent unimaged parts of Europa, through a global map at regional scale and; (3) insight into the structure of the crust (through radar sounding) to aid in better understanding cryovolcanic processes.