Morphology of the Enterprise Rupes Lobate Scarp on Mercury: Implications for Structural Kinematics and Fault Scaling

Merten, Andreia Correia

Undergraduate Honors Thesis

Morphology of the Enterprise Rupes Lobate Scarp on Mercury: Implications for Structural Kinematics and Fault Scaling Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/gf06g4127

Abstract

This research addresses the development of a unique geologic structure on Mercury, Enterprise Rupes. Its purpose is to determine the change in the shape of the thrust fault that forms Enterprise and its implications for the strength of the crust on Mercury early in its history when it was formed ca 3.8 billion years ago. The large Rembrandt impact crater is offset by the forelimb of Enterprise Rupes, which is the largest lobate scarp identified on Mercury at close to 900 km in length with up to 6.7 kilometers of relief. Kinematic and Trishear models developed by Karl Mueller at the University of Colorado Boulder (CU) and Nestor Cardozo of Stavanger University of this structure, using a topographic profile across the scarp and a crater shortening analysis, have helped define the fault dip. Professor Cardozo’s model showed a best model with a dip of 16.17°, this is still an estimate. The fault geometry supports a detachment at ~ 40 km depth. My work encompassed creating slope and curvature maps of the area, building topographic profiles from North to South across the uplift in the simplest areas that avoided regions affected by higher surface roughness associated with impact craters, as well as heterogeneous shear apparent across the forelimb. The topographic profiles were then used to better determine the shape of the forelimb and variation in vertical relief along it, which led to the calculation of the Displacement/Length value. This value in comparison to Dr. Schultz’s work in “Displacement-length scaling relations for faults on the terrestrial planets”, was at the upper end of his results meaning we obtained a higher displacement in comparison with length. Measurements of the scarp width led to the interpretation that the crust of Mercury seems largely isotropic, with similar rock strength implying that the scarp most likely propagated at the same depth. Additional work may be able to better validate our thrust dip value using the relationship between the younger trace of the forelimb and relief across the ejecta blanket around the margin of a smaller crater. This smaller crater was identified through this research and its relief across the scarp should be smaller in comparison with the main scarp.

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