Ureilite meteorites and the unknown proto-planet: using EBSD to construct a geological history

Lowe, Hayley (2023) Ureilite meteorites and the unknown proto-planet: using EBSD to construct a geological history. MSc(R) thesis, University of Glasgow.

Abstract

The ureilites are a group of ultramafic achondrite meteorites composed primarily of olivine and pigeonite, with accessory minerals and a high abundance of carbon in the form of graphite and diamond. There are many hypotheses as to how the ureilite group formed, but the majority of authors are now in agreement that they represent a mantle restite of a now destroyed planetesimal that may have been as large as Mercury (Nabiei et al., 2018). This planetesimal was large enough for the ureilites to form through igneous processing, but not large enough to become a full planet. At some point, possibly within the first 10 million years (Rai et al., 2020) of its life the ureilite parent body (UPB) was subjected to a catastrophic impact which destroyed the planetesimal and created daughter asteroids which are the current parent bodies of the ureilites (Goodrich et al., 2015). This study aims to construct a comprehensive geological history of the samples using Electron Backscatter Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS), Raman spectroscopy and geochemical data. Here we show using Raman peak Full Width Half Maximum (FWHM) data that the majority of diamonds present in the ureilite suite are formed through shock related processes. This is combined with the EBSD data and optical microscopy data to discuss a range of shock features present within the ureilites such as mosaicism. Various slip systems are shown to be activated across the samples indicating deformation occurred during a variety of temperature and pressure conditions throughout ureilite formation. Evidence of shear processes affecting the majority of the samples studied is also presented using the EBSD datasets. A proposed geological history is presented to tie shock and shear features together. Our results agree with recent studies about diamond formation (Nestola et al., 2020) on the UPB which goes some way to negating the need for a large planetesimal to be required in order to explain ureilite formation.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Subjects: Q Science > QE Geology
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
• Supervisor's Name: Daly, Dr. Luke and Lee, Prof. Martin
• Date of Award: 2023
• Depositing User: Theses Team
• Unique ID: glathesis:2023-83722
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 06 Jul 2023 14:18
• Last Modified: 06 Jul 2023 14:18
• Thesis DOI: 10.5525/gla.thesis.83722
• URI: https://theses.gla.ac.uk/id/eprint/83722