SMALL-SCALE WRINKLE RIDGES ON THE MARTIAN DICHOTOMY BOUNDARY: EVIDENCE FOR CHANGE IN PRINCIPAL STRESS DIRECTION

Wrinkle ridges (WRs), geological features found on terrestrial planetary bodies, are widely interpreted to have formed by tectonic compression and folding above blind thrust faults. Mapping and analysis of WRs can contribute to a better understanding of the tectonic and geologic history of a region. WRs on Mars have been observed at a wide range of spatial scales, from regional (100s of km along strike) to local (10s of km along strike). For this study, WRs have been identified and mapped in the Aeolis Dorsa (AD) region of Mars as part of an official USGS geologic map of the AD region. These ridges are much smaller in length (<20 km) and width (<1 km) than those previously studied on Mars and other planetary bodies, and so can provide insight into more localized tectonic deformation. Our null hypothesis is that WRs in AD formed under a regionally homogeneous stress regime. To test this hypothesis and to quantify the magnitude of deformation of the WRs, their orientation, amount of shortening, and strain were determined. During mapping, WRs were classified into certainty levels – certain, probable, and possible – based on several criteria from the literature. Preferred orientations were determined based on measured geographic orientation. Results from the 37 mapped ridges indicate two preferred orientations: one at N15W and one at N30E. The amount of shortening and strain from faulting and folding across each WR is being determined from multiple (~30) topographic profiles across each ridge. Folding associated with one ridge was found to have resulted in a maximum of 5 m of shortening, and approximately 0.19% strain. Faulting associated with this ridge has resulted in a maximum of 55 m of shortening and 2.3% strain. The difference in shortening from faulting vs folding is consistent with previous analyses of large WRs. In future work, we will correlate locations, certainty classifications, and orientations for all mapped ridges, as well as completing the calculations and analyses of shortening and strain for all WRs in AD. In addition, statistical analysis of shortening and strain measurements of all WRs will be used to determine whether they are statistically similar or different across the region. In the data collected to date, the two preferred orientations suggest that the principal stress directions changed during WR formation.