Axial Surface Mapping of Wrinkle Ridges on Solis Planum, Mars from Mola Topography: Constraints on Subsurface Blind Thrust

Introduction: We undertook axial surface mapping of selected wrinkle ridges on Solis Planum, Mars in order to assess the subsurface geometry of blind thrusts proposed to exist beneath them. This work builds on previous work [1] that defined structural families of wrinkle ridges based on their surface morphology in this region. Although a growing consensus exists for models of wrinkle ridge kinematics and mechanics, a number of current problems remain. These include the origin of topographic offset across the edges of wrinkle ridges, the relationship between broad arches and superposed ridges, the origin of smaller wrinkles, and perhaps most importantly, the trajectory of blind thrusts that underlie wrinkle ridges and accommodate shortening at deeper crustal levels. We are particularly interested in defining the depths at which blind thrusts flatten under wrinkle ridges in order to provide constraints on the brittle-ductile transition during Early Hesperian time. We also seek to test whether wrinkle ridges on Solis Planum develop above reactivated faults or newly formed ones. Stategy and Methods: Previous work [1] that measured ridge morphology from over 4000 topographic profiles on Lunae and Solis Plana suggests that a variety of wrinkle ridge types exist in these regions. These include four end-member ridge types, including: 1) arch with high-relief superposed hill; 2) simple asymmetric ridges without a broad arch; 3) blocky ridges that have no clear asymmetry; and 4) monoclinal ridges [1]. We limited our analysis to simple asymmetric ridges in order to avoid structural complexities associated with other ridge types, in particular the development of backthrusts [2].