Current Results From High-Resolution Structural Mapping in Southwest Candor Chasma

High-resolution topography generated from stereo HiRISE imagery reveals the 10- to 100-meter-scale structure of Light-Toned Layered Deposits (LTLD) in southwest Candor Chasma. The study area is located near the contact of the LTLD and the wall rock and is in an area where chasma-forming normal faults have been previously proposed. Structural mapping is conducted using digital terrain models (DTMs) and orthorectified imagery constructed from two adjacent HiRISE stereo pairs (PSP_001918_1735 / PSP_001984_1735 and PSP_003474_1735 / PSP_003540_1735). These two DTMs are offset in longitude by roughly 3 km. CTX imagery is used to correlate interpretations between DTMs and to place these structural observations in the regional geologic context established by previous studies. Stratigraphic members, consisting of massive to weakly bedded, ~100m thick, layers within the LTLD, are used to draw these correlations between datasets. Populations of crosscutting thrust faults, normal faults and folds are observed in the mapped area. These folds are generally the oldest deformational structures in the study area, followed in age by the normal faults and then the thrust faults. The normal faults measure less than a few km in map length and thus are not sufficiently large, and are also not appropriately located nor oriented, to accommodate the roughly northeast-southwest extension that is required for normal faults that can be attributed to chasma formation. Further, bedding exposed in the local LTLD generally dips toward the center of Candor Chasma, consistent with sediment deposition in a preexisting basin. Independent lines of evidence such as these support a post-chasma age for these LTLD exposed at the surface. Approximately 2 km of conformable stratigraphy is exposed in the study area, and therefore at least several kilometers of the local LTLD were deposited subsequent to any chasma-related normal faulting that may have occurred in this part of Candor Chasma. Rather than being attributed to regional tectonism, the observed deformation appears to be endogenic in nature and may reflect local slumping prior to pervasive erosion and exposure of these LTLD.