Rim uplift and crater shape in Meteor Crater: Effects of target heterogeneities and trajectory obliquity

摘要

We have analyzed the rim structure of Meteor Crater, Arizona, in order to understand the mechanism of rim uplift in simple craters and the causes of the shape of polygonal impact craters. For this purpose, we systematically determined bedding orientation of the autochthonous crater wall and overturned flap and analyzed the kinematics of major radial faults. We found that rim uplift correlates with the crater shape and increases in the corners of the crater. The two main mechanisms of differential uplift are the formation of horizontal interthrust wedges, leading to the doubling of strata in the rim, and radial corner faults, or tear faults, that vertically displace bedrock. The development of Meteor Crater's quadrangular shape is caused by more effective crater excavation flow parallel to major joint sets. Additionally, we infer the impact direction with a newly developed technique, the two corners model, and review the arguments in favor of an oblique trajectory. While the data set is ambiguous, several indicators suggest an impact direction from the NNW. We conclude that oblique impacts should have an effect on early cratering and excavation flow, whereas target heterogeneities like joints start to play a prominent role in later stages when the stresses induced by the excavation flow are in the same order of strength as the material involved.