TESTING FOR A LISTRIC FAULT SYSTEM OUTSIDE THE ARDEN CORONA BOUNDARY ON URANUS' MOON MIRANDA

Miranda, a ~470 km mean diameter icy satellite of Uranus, has complex surface structures that form at least three coronae. We hypothesize that the normal faults bounding Arden Corona are listric, which would indicate the presence of a brittle-ductile transition zone at depth.

We test our hypothesis by investigating the corona boundary geometry. If the boundary is a listric fault system, blocks would be tilted and scarp dips would decrease toward the coronae boundary, while each back-tilted face would increase in slope in that direction. The heave along each fault would decrease toward the boundary. A rollover structure would likely be present and slope in the opposite direction of the fault dip direction.

To investigate these four characteristics, Voyager 2 images near Arden Corona were analyzed using the USGS Integrated Software for Imagers and Spectrometers (ISIS). In previous work on faults within the Arden Corona boundary, measurements of scarp dips, slopes of back-tilted faces, and heave were taken, and a feature on the outer boundary of the corona was interpreted to be a rollover structure. Those results support our hypothesis.

Here we used the Ames Stereo Pipeline to derive digital elevation models (DEMs) for an area that includes two large scarps near Inverness Corona and took measurements of their dips and back-tilted slopes. Like the faults within the boundary, these two fault blocks are tilted, and the angle of dip decreases in the down dip direction with distance from Arden. However, the back-tilted faces in this area do not consistently increase in slope in the down dip direction across strike. This observation may be due to either hanging wall deformation, or sediment deposition along the hanging wall.

This evidence supports the interpretation of a listric extensional fault system both within and outside the Arden Corona boundary. Continued work involves collecting additional dip and displacement measurements outside Arden and analyzing a potential rollover structure. If additional data continue to support a listric geometry, then the depth to the detachment layer and then the thermal gradient at the time of faulting can be estimated.