Crustal History Indicators on Mercury

Fegan, Emma Rosalind (2018). Crustal History Indicators on Mercury. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000d342

Abstract

In this thesis, I investigated curvilinear features on the surface of Mercury and the impact of illumination bias upon observations of those features. I also demonstrated their utility with regard to photostratigraphy and suggest areas where BepiColombo will provide beneficial additional data.

Basin-edge scarps occur within volcanically-filled impact basins in all areas of the surface of Mercury. Many large impact basins are filled with Smooth Plains (volcanic) units. I hypothesise that fault nucleation occurs on the mechanically weak interface between the base of the volcanic fill units and the original floor of the impact basin. Using crater size-frequency distribution analysis I have established that resolvable deformation of basin-edge scarps ceased between 1.1 and 0.6 Ga.

Based upon location and morphology, I concluded that catenae are likely to be formed by secondary impact ejecta. They are of use when establishing stratigraphic relationships between impact basins, since they extend further away from the primary basin than the ejecta blanket, and tend to remain observable for longer. The stratigraphic map of impact basins Aneirin, Sanai and the immediately surrounding areas demonstrated this, as – despite the basins being the same morphological class (C2) – catenae related to Aneirin were formed after the formation of Sanai. Aneirin is therefore the younger basin.

Mercury’s near-zero obliquity means that curvilinear features aligned parallel with the illumination azimuth (east-west at low-mid latitudes) would be likely to be underrepresented in the global population. Using shaded-relief models with alternative artificial illumination to complete resurveys, I found that my global survey of basinedge scarps has been affected. Consequently, I advise the use of shaded-relief models in addition to imagery when mapping curvilinear features.

I anticipate that the improved instrumentation of BepiColombo MPO will be invaluable when carrying out stratigraphic mapping and global surveys of specific features such as basin-edge scarps and catenae.

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