INSIGHTS INTO AIRLESS BODY PROCESSES FROM IRON-NICKEL METAL: PHYSICAL PROPERTIES OF METEORITES, AND THE BEHAVIOUR OF METAL DURING IMPACT MELTING

Abstract

In this thesis, the main research goal was to explore how insights from Fe,Ni metal can be used to build our understanding of the airless bodies, such as asteroids and the Moon, from which extra-terrestrial samples are derived. This thesis has three key research aims, focussed on investigating the occurrence and modification of metal in impact melt settings, as well as physical properties of meteorite samples, which are closely linked to metal abundance and distribution. CBa chondrite Gujba preserves metal particles formed in an impact melt-vapour plume that have been modified by secondary impact melt veins. Electron backscatter diffraction studies show that Fe,Ni particles are re-crystallised, but less deformed particles preserve a pre-existing crystal structure. Particle compositions vary within the sample and are not significantly modified by proximity to impact melt. Melted metal shows some evidence of compositional modification, perhaps due to element partitioning during melting in the impact melt vein. In Gujba, impact melt seems not to have had a great effect. More extensive metal-impact melt interaction was studied in samples of lunar impact melt rocks returned from the Apollo 14 and 16 landing sites. Particles in impact melt exhibit diverse textures relate to differing processes of formation or modification. Compositions of metal particles from a given sample typically cluster, but there is no clear link with particle morphology, accessory minerals, or occurrence of metal alteration. Trace element compositions show most particles contain an exogenous component, but the extent of metal modification in impact melt is challenging to constrain. A workflow for the measurement of the bulk density of meteorite samples using photogrammetry to build three-dimensional models of samples was developed. Magnetic susceptibility and electrical conductivity were also measured. These three properties are strongly linked to the presence and distribution of metal in samples, and can be used to interpret sample composition, especially when combined. There are limitations on the method, which could be developed further, but they permit accessible, minimally invasive determination of properties which were demonstrated to be valuable in interpreting possible sample parent bodies. This thesis highlights the information about Solar System bodies and processes that we can glean from studying Fe,Ni metal in extra-terrestrial samples. The extent that impact melt could modify metal compositions in the general case is still not fully understood, and suggestions are made for avenues of further work. Our method for measuring meteorite physical properties could be refined, which would help contribute to our understanding of sample parent bodies.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Katherine Joy (Supervisor) & Rhian Jones (Supervisor)