Investigating shock metamorphism features in feldspar

Riches, Liza (2023) Investigating shock metamorphism features in feldspar. MSc(R) thesis, University of Glasgow.

Abstract

Hypervelocity impact cratering processes are of key importance for the understanding of planetary formation and evolution in our Solar System. The investigation of shock deformation features within impact craters is therefore an invaluable practice that should help in the future identification of impact sites, as well as the general field of planetary materials. Due to the high abundance of feldspar group minerals on planetary surfaces, the study of shock metamorphism in feldspars is crucial. Shock barometry is the process by which certain diagnostic features can be used to determine the level of shock experienced within a mineral and therefore determine the shock conditions experienced by those minerals. The identification of diagnostic shock microstructure features has often focused on studying quartz using a polarising microscope. However, this thesis has instead investigated the use of feldspar, searching for shock features using a range of microanalytical techniques. This thesis has studied samples from the Chicxulub Impact Structure in the Yucatan Peninsula, Mexico using an optical microscope, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), backscatter electron images (BSE), electron backscatter diffraction (EBSD), cathodoluminescence (CL) and electron probe micro-analysis (EPMA) to identify shock deformation features in feldspar and investigate any connection between deformation features and chemical content. This thesis has several key findings.

1. No shock attenuation was observed over the depth interval that these samples covered (55.8m).
2. Typically, more deformation was observed in Na-rich feldspar than K-rich feldspar.
3. The Ca content within Na-rich feldspar was found to have been influenced by deformation within twins. EBSD maps identified deformation features within feldspar twins, specifically, partial amorphisation in alternating twins. These partially amorphised twins contained ~1-2 at. % less Ca than crystalline twins.

Previous research has not always recorded chemical content of feldspars in enough detail to determine if these observations are present in other locations. With further and closer examination of feldspar minerals of various chemical compositions and different impact sites, it is possible that a more exact and detailed shock barometer for feldspar could be made in the future. Finally, it has proven useful in this thesis to use multiple methods of analysis to provide more successful identification of shock deformation features, which is recommended in future when developing shock barometry in feldspars.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Subjects: G Geography. Anthropology. Recreation > GB Physical geography
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
• Supervisor's Name: Pickersgill, Dr. Annemarie and Daly, Dr. Luke
• Date of Award: 2023
• Depositing User: Theses Team
• Unique ID: glathesis:2023-83651
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2023 14:57
• Last Modified: 14 Jun 2023 14:58
• Thesis DOI: 10.5525/gla.thesis.83651
• URI: https://theses.gla.ac.uk/id/eprint/83651