EXTENSIONAL TILT BLOCKS ON MIRANDA - EVIDENCE FOR AN UPWELLING ORIGINOF ARDEN CORONA

Subparallel ridges and troughs in the outer belt of Arden Corona, on t he Uranian satellite Miranda, are interpreted as tilt blocks formed by extension and normal faulting. Fault scarps generally face outward fr om the corona, exposing dark material in the subsurface. Reconstructio n of faults along a deep rift zone bounding the corona suggests initia l dips of similar to 50 degrees. Local extension reaches similar to 70 %, extremely high in comparison to previous estimates of strain on icy satellites. A rise adjacent to the rift zone is modeled as flexural a nd indicates an effective elastic lithospheric thickness of similar to 2 km at the time of flexure. The assumption that faulting has signifi cantly weakened the lithosphere suggests a mechanical lithosphere thic kness of similar to 5 to 10 km. Corresponding thermal gradients in a f rictionally controlled ice lithosphere are similar to 8 to 20 K km-1, and lithospheric tensional strength is similar to 0.4 to 1.8 MPa. Norm al faulting in Arden Corona indicates that internal upwelling likely f ormed the corona, and the outward facing direction of faults is consis tent with such a model. An upwelling origin of Miranda's coronae elimi nates the need to invoke catastrophic breakup and reaccretion of the s atellite as an explanation for its surface geology.