Ejecta thickness and structural rim uplift measurements of Martian impact craters: Implications for the rim formation of complex impact craters

Abstract

The elevated rim in simple craters results from the structural uplift of preimpact target rocks and the deposition of a coherent proximal ejecta blanket at the outer edge of the transient cavity. Given the considerable, widening of the transient cavity during crater modification and ejecta thickness distributions, the cause of elevated crater rims in complex craters is less obvious. The thick, proximal ejecta in complex impact craters is deposited well inside the final crater rim and target thickening should rapidly diminish with increasing distance from the transient cavity rim. Our study of 10 complex Martian impact craters ranging from 8.2 to 53.0 km in diameter demonstrates that the mean structural rim uplift at the final crater rim makes 81% of the total rim elevation, while the mean ejecta thickness contributes 19%. Thus, the structural rim uplift seems to be the dominant factor to build up the total amount of the raised crater rim of complex craters. To measure the widening of the transient cavity during modification and the distance between the rim of the final crater and that of the transient cavity, we constructed balanced cross section restorations to estimate the transient cavity of nine complex Martian impact craters. The final crater radii are~1.38-1.87 times the transient cavity radii. We propose that target uplift at the position of the final crater rim was established during the excavation stage.

Determination of Mars crater geometric data: Insights from high‐resolution digital elevation models

“…Figure 7 illustrates that rim height may vary by several hundred meters for craters in the diameter rangẽ 9-17 km diameter. In addition to providing a more accurate measure of d t , we envision that this detailed analysis of the azimuthal variation in rim height might be of particular value, for instance, in assessing the rim topography in relation to the observed structural uplift of the rim (Sturm et al 2016); the same stratigraphic unit might have different elevations relative to the surrounding terrain (i.e., the preimpact surface). Each crater can be seen to have a unique pattern of rim height variations, but the smallest crater (D = 4.0 km) in our CTX sample of five craters in Fig.…”

Is the Linné impact crater morphology influenced by the rheological layering on the Moon's surface? Insights from numerical modeling

“…D) (Sharpton ; Sturm et al. ). The ring at depth −200 m occurred at the albedo transition and it can mark the extent of the breccia lens (cf.…”

Geologic Investigation of Deep Simple Craters in the Lunar Simple‐to‐Complex Transition

“…Wall slope is directly proportional to crater d/D as also indicated by the scatter plot in Figure . For similar‐sized craters formed by excavation (and no compaction), the rim height should increase with crater depth because an increased amount of ejecta results in larger depths and also larger rim heights (Sharpton, ; Sturm et al, ). However, the overlap in rim heights of our deep and normal‐depth craters can be explained by a modification in the cratering mechanics due to impact into a high porosity target.…”

“…Field studies and nuclear explosion experiments have revealed that the raised rim is a consequence of the structural uplift of the target rocks and the thickness of the ejecta blanket formed by the excavated material during the excavation stage (Roddy et al, ; Shoemaker, ; Shoemaker & Chao, ). Recent observational studies on lunar (Sharpton, ) and Martian craters (Sturm et al, ) have inferred structural uplift to be the primary contributor (>80%) of the elevated rim. The third stage, the modification stage, differentiates a simple crater from a complex crater.…”