Experimental simulation of silica melting and amorphization under extreme shock conditions

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The proposed research project focuses on the characterization of the structures of silica glasses formed under extreme high-pressure conditions recorded during hypervelocity impacts of planetary bodies. Temperature, pressure, and shock duration can affect the mechanisms of formation of silica glasses – rapid quenching of a silica melt or solid-state transformation of quartz – and their short- and intermediate-range order, namely, the coordination number of silicon and the size of the polyhedral rings, respectively. Thus, constraining both the mechanisms of formation and the structures of silica glasses will be possible to shed light on the impact cratering process. In order to reach this goal, three types of high-pressure experiments, which differ mainly in terms of shock duration, will be performed on quartz: laser irradiation (a few nanoseconds), high explosive (around one microsecond), and diamond anvil cell (up to a few minutes). The characterization of the short- and intermediate-range order of the newly formed glasses will be pursued by the combined use of several analytical methods: Raman, electron energy loss spectroscopy, X-ray absorption spectroscopy, electron diffraction, and X-ray diffraction. For the interpretation of the diffraction data, pair distribution functions will be calculated and compared with theoretical models of silica glasses. After the first experiments and the acquisition of the first structural data, selected natural silica impact glasses from craters of different sizes (i.e., different shock duration) will be investigated through the same analytical methods and procedures. The comparison with natural samples will be the key to relate the experimental approaches to nature, and then, to gain a better understanding of the melting and amorphization processes under extreme high-pressure conditions induced by extraterrestrial impacts. Thanks to the combination of different experimental and analytical techniques and the parallel study of natural samples, this project will be the first comprehensive work entirely devoted to understanding the mechanisms of formation and the structures of silica impact glasses.