WRINKLE RIDGES OF ARCADIA-PLANITIA, MARS

Wrinkle ridges of Arcadia Planitia were examined to determine their morphology, spatial distribution, and the amount of crustal shortening and strain they accommodate. Ridges trend generally northward, but their orientation and distribution are strongly controlled by the relief of the underlying knobby material. Ridges begin or end at inselbergs of older terrain and are associated with buried craters. Arcadia Planitia ridges have an average width of 3425 m and accommodate an average folding shortening of 3 in and a faulting shortening of 55 m; mean total shortening is 57 m. Three east-west transects were constructed at 20-degrees 25-degrees, and 28-degrees-N to estimate regional shortening and strain. Average total shortening across the transects is about 900 m, corresponding to a regional compressive strain of 0.06%. The total shortening and compression across Arcadia Planitia are less than in Lunae Planum. Faults associated with the Arcadia ridges are inferred to have a westward dip compared with an eastward dip for Lunae Planum ridges. The generally levels of compression and symmetric orientation of the ridges suggest a regionally organized stress system. Differences in the shortening and strain between Lunae Planum and Arcadia Planitia may reflect the effects of local lithology or azimuthal variations in the stress field.