Doctor of Philosophy
Planetary Science and Exploration
Osinski, Gordon R.
Banerjee, Neil R.
This thesis seeks to understand the mechanism of hypervelocity impacts, lunar origin and geology, and stable isotope techniques and its application to lunar material. Three lunar regolith breccias, Dhofar 1673, Dhofar 1983, and Dhofar 1984, were examined. The petrography, mineralogy, isotope chemistry, and bulk chemistry of these meteorites were quantified to investigate their origin. The chemistry of the impact melt rock and bulk chemical analysis suggests sourcing from either the Feldspathic or Outer Feldspathic Highland Terranes. Given the similarities in the meteorites, and the proximal location of each find (within 500 m), this thesis proposes strong evidence for their pairing.
Impact glass from the Mistastin Lake impact structure was used to investigate the evolution of impact melt produced during the impact event. Impact glass clasts were found in a range of lithologies across five outcrops. The clasts were subdivided into three petrographic subgroup based on clast content, prevalence of schlieren, colour, texture, and habit. Though the various groups of glasses show significant overlap in their major oxide composition, subtle variations were observed in the least-squares mixing model. This modelling approximated the proportions of each target lithology required to make each glass group. To determine if the compositional variations follow textural difference in the glass, quantitative image analysis was used to examine the geometry of the glass clasts.
A novel technique for determining the isotope ratios of silicon and oxygen from the same aliquot of anhydrous silicate material was developed. This technique was applied to lunar samples and found lunar rocks to be significantly (>2σ) lower in the heavier silicon isotope (30Si) compared to the Earth (by around 0.3 parts per thousand). No resolvable offset was observed within the oxygen isotope composition of the Moon and Earth. From this offset, the Si isotope composition of the impactor, Theia, was modelled; however, given that several isotope systems do not reveal the presence of Theia, alternative models were also explored. Si partitioning into the Earth’s core, concurrent with the impact event, would explain this offset and would be consistent with models that show the Moon and the Earth to be isotopically identical.
Hill, Patrick, "Impact Cratering Processes on the Earth and Moon: Meteorites, Complex Craters, and the Origin of the Moon" (2019). Electronic Thesis and Dissertation Repository. 6212.
Available for download on Sunday, May 31, 2020