Wrinkle Ridges, Reverse Faulting, and the Depth Penetration of Lithospheric Strain in Lunae Planum, Mars

Abstract

Wrinkle ridges in the Lunae Planum region of Mars formed in response to compressional stresses associated with the development of the Tharsis rise. In this study, we investigate the accomodation of lithospheric strain associated with wrinkle ridge development in order to constrain the depth penetration of deformation associated with the formation of Tharsis. Using observations that indicate that the shallow martian lithosphere 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 nucleates along a single fault in either the surface plains unit or basement. We then calculate strain and displacement fields for a range of plausible lithosphere structures assuming uniform horizontal shortening of the lithosphere. Transmission of strain between the surface layer and basement is most effective for a thin megaregolith and small Young's modulus contrast between the surface layer, megaregolith, and basement. 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 the wrinkle ridges are applicable, then Thatsis-related compressional deformation must have involved the lithosphere, rather than being restricted to the near-surface.