Shock origin of carbon phases in ureilites

One of the main problems in studying diamonds in ureilites (and in general in meteorites) is the conflicting hypotheses about diamond formation. In detail, such hypotheses were the following: i) formation by chemical vapour deposition, ii) formation within a deep interior of a differentiated planetary body and iii) formation by shock event on prior graphite in a parent body. This PhD thesis aims to shed light on the origin of carbon phases in ureilites meteorites using a multimethodological approach by Scanning Electron Microscopy (SEM), Micro-Raman Spectroscopy, Micro-X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). I investigated the carbon phases (graphite and diamond) of various ureilites focusing on their characterization, determination of their crystallite size and temperature recorded by graphite. One of the most crucial goals of this PhD project is to understand the diamond formation process in ureilites. I am confident that the results obtained during my PhD research will contribute to understand the best formation process candidate among the above hypotheses. In addition, I was able to investigate a) the role of Fe-Ni phases in diamond growth in ureilites and b) the temperature recorded by graphite on all studied meteorites (by Micro-Raman Spectroscopy) to understand if such temperature is related to the shock levels.One of the main problems in studying diamonds in ureilites (and in general in meteorites) is the conflicting hypotheses about diamond formation. In detail, such hypotheses were the following: i) formation by chemical vapour deposition, ii) formation within a deep interior of a differentiated planetary body and iii) formation by shock event on prior graphite in a parent body. This PhD thesis aims to shed light on the origin of carbon phases in ureilites meteorites using a multimethodological approach by Scanning Electron Microscopy (SEM), Micro-Raman Spectroscopy, Micro-X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). I investigated the carbon phases (graphite and diamond) of various ureilites focusing on their characterization, determination of their crystallite size and temperature recorded by graphite. One of the most crucial goals of this PhD project is to understand the diamond formation process in ureilites. I am confident that the results obtained during my PhD research will contribute to understand the best formation process candidate among the above hypotheses. In addition, I was able to investigate a) the role of Fe-Ni phases in diamond growth in ureilites and b) the temperature recorded by graphite on all studied meteorites (by Micro-Raman Spectroscopy) to understand if such temperature is related to the shock levels