Extensional tilt blocks on Miranda: Evidence for an upwelling origin of Arden Corona

Subparallel ridges and troughs in the outer belt of Arden Corona, on the Uranian satellite Miranda, are interpreted as tilt blocks formed by extension and normal faulting. Fault scarps generally face outward from the corona, exposing dark material in the subsurface. Reconstruction of faults along a deep rift zone bounding the corona suggests initial dips of ∼50°. Local extension reaches ∼70%, extremely high in comparison to previous estimates of strain on icy satellites. A rise adjacent to the rift zone is modeled as flexural and indicates an effective elastic lithospheric thickness of ∼2 km at the time of flexure. The assumption that faulting has significantly weakened the lithosphere suggests a mechanical lithosphere thickness of ∼5 to 10 km. Corresponding thermal gradients in a frictionally controlled ice lithosphere are ∼8 to 20 K km-1, and lithospheric tensional strength is ∼0.4 to 1.8 MPa. Normal faulting in Arden Corona indicates that internal upwelling likely formed the corona, and the outward facing direction of faults is consistent with such a model. An upwelling origin of Miranda's coronae eliminates the need to invoke catastrophic breakup and reaccretion of the satellite as an explanation for its surface geology.