WRINKLE RIDGES, REVERSE FAULTING, AND THE DEPTH PENETRATION OF LITHOSPHERIC STRAIN IN LUNAE-PLANUM, MARS

Wrinkle ridges in the Lunae Planum region of Mars formed in response t o compressional stresses associated with the development of the Tharsi s rise. In this study, we investigate the accomodation of lithospheric strain associated with wrinkle ridge development in order to constrai n the depth penetration of deformation associated with the formation o f Tharsis. Using observations that indicate that the shallow martian l ithosphere in Lunae Planum consists of a surface plains unit underlain successively by an unconsolidated megaregolith and competent basement , we construct models of an elastic lithosphere in which a ridge nucle ates along a single fault in either the surface plains unit or basemen t. We then calculate strain and displacement fields for a range of pla usible lithosphere structures assuming uniform horizontal shortening o f the lithosphere. Transmission of strain between the surface layer an d basement is most effective for a thin megaregolith and small Young's modulus contrast between the surface layer, megaregolith, and basemen t. However, results under a broad range of conditions for both models show straining of both the surface layer and basement. If lithosphere structure information and strains estimated by kinematic studies of th e wrinkle ridges are applicable, then Tharsis-related compressional de formation must have involved the lithosphere, rather than being restri cted to the near-surface. (C) 1995 Academic Press, Inc.