EVALUATING FLAT-CRATER FLOOR FILL COMPOSITIONS AND MORPHOLOGIES: INSIGHT INTO FORMATION PROCESSES

The process responsible for the formation of high thermal inertia, flat-crater floor deposits has remained unclear since they were first observed. Several processes have been proposed, like impact melt ponding, aeolian sedimentation and lacustrine sedimentation may fill the craters. However, another process has been proposed as the processes of impact melt and sedimentation cannot account for all occurrences of infilled craters. In this study, we investigate the compositional, thermophysical, and morphological properties of a crater subset of high thermal inertia craters, and constrain the filling processes of the crater floor materials (such as volcanic, sedimentary, impact melt, etc.).

We first created a subset of 160 impact craters with high thermal inertia floor materials using the selection criteria from two previous studies. In order to examine the mineralogies of the crater floors, we used Thermal Emission Imaging System (THEMIS) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) images and to characterize the associated morphologies, we used High Resolution Imaging Science Experiment (HiRISE) and Context Imager (CTX) images.

As a part of this work, the aforementioned 160 craters have been classified to volcanic origin, sedimentary origin, and unknown based on a preliminary evaluation of the characteristics of the high thermal inertia materials within crater floor. Ninety-nine craters were classified as volcanic in origin based on the analysis of fill material morphologies, and compositions. The craters with volcanic filling processes are widely distributed within the southern highlands—they are not clustered to once geographic region. The results suggest that a significant portion of craters have volcanic fill materials, which is consistent with the hypothesis that the infilled arose through some yet-to-be constrained post-impact volcanic process. It may also indicate that volcanic resurfacing may be a widespread geologic process within martian impact craters. The remaining craters were classified as either sedimentary or unknown. Based on the results of this work, we find it is likely that multiple processes are operating to fill craters on Mars.