Rim formation in complex impact craters: field survey, remote sensing, and analogue modeling
Final Report Abstract
The elevated rim in simple craters results from the structural uplift of pre-impact 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 and the question arose in this project. 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 uplift at the final crater rim of complex craters makes 81% of the total rim elevation, while the mean ejecta thickness contributes 19%. A similar study on the Moon using craters with diameters ranging between 16 km and 45 km reveal a similar result: The mean structural rim uplift amounted to 71% and the ejecta thickness to 29%. 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 that could be restored to the pre-modification stage, to estimate the transient cavity of nine complex Martian impact craters and several lunar craters. The final crater radii are ~1.38–1.87 times the transient cavity radii for Martian craters and 1.08-1.37 times for the investigated lunar craters. We propose that target uplift at the position of the final crater rim was established during the excavation stage. The analysis of the final crater rims at the 26 km diameter Ries crater and the 6 km diameter Jebel Waqf as Suwwan crater revealed that reverse faulting exist at or close to the crater rim and hence substantiate the finding that crater rim faults of complex craters are pre-formed during the excavation stage of crater formation. Analogue modelling also shows that upward and outward directed movements occur during the excavation stage outside the transient cavity.
Publications
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(2015). Jebel Waqf as Suwwan, Jordan: Results of a Field Campaign 2015. Bridging the Gap III: Impact cratering in nature experiment and modeling, Freiburg, Sept. 20-26, 2015, #1074
Kenkmann, T., Sturm, S., Krüger T., Salameh, E., and Konsul, K.
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(2015). Structural rim uplift and ejecta thickness measurements of martian complex impact craters: Rim formation of complex impact craters. Geo-Berlin conference, Berlin, Oct. 4-7, 2015
Sturm, S., Krüger, T., and Kenkmann, T.
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(2016). Ejecta thickness and structural rim uplift measurements of Martian impact craters: Implications for the rim formation of complex impact craters. Journal of Geophysical Research Planets 121
Sturm, S., Kenkmann, T., and Hergarten, S.
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(2016). New insights into the formation of complex crater rims: Structural uplift, ejecta thickness and transient crater measurements of complex lunar mare craters. 47th Lunar and Planetary Science Conference, #2079
Krüger, T., and Kenkmann, T.
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(2016). The tectonic inventory of small complex impact structures: A case study at the Jebel Waqf as Suwwan, Jordan. 47th Lunar and Planetary Science Conference, #1299
Kenkmann, T., Sturm, S., Krüger, T., Salameh, E., Al-Raggad, M., and Konsul, K.
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(2017). The structural inventory of a small complex impact crater: Jebel Waqf as Suwwan, Jordan. Meteoritics and Planetary Science
Kenkmann, T., Sturm, S., Krüger, T., Salameh, E., Al-Raggad, M., and Konsul, K.
