Hargraves Crater Ejecta and Implications for Impact Processes
Abstract
Impact craters and their ejecta deposits offer insights into the structure and composition of planet crusts. Hargraves Crater, Mars, demonstrates an unusual balance of exposure and preservation in its ejecta. Analysing its morphologic, morphometric, thermophysical, and stratigraphic characteristics, we interpret two predominant units: an underlying ballistic lithic breccia and an overlying impact melt-bearing deposit. The lower unit is a lithic breccia composed of sub-angular, unsorted clasts (~10-12 m mean diameter), while the overlying unit is a smooth, dark toned, smaller clast-bearing (~1 m diameter at image resolution) impact melt-bearing unit with polygonal fracturing. There appears to be a sharp contact between these units visible through “windows” in the overlying unit that reveal the underlying breccia. These orbital observations link well with terrestrial field observations. Future study of this “Hargraves-type” ejecta, which reveals the stratigraphy and structure of ejecta deposits, will improve our understanding of ejecta and ejecta emplacement processes.