MADAM · Discovering Mineral nAnoinclusions in DiAaMonds

Diamonds are the only geological materials able to travel hundreds of kilometres vertically, horizontally and through time for billions of years, being un-modified since the day of their formation. Not just a time capsule, when diamonds incorporate mineral inclusions captured from the deep mantle, they represent an open window into otherwise inaccessible regions of Earth. Based on their formation depths, diamonds are classified as lithospheric (formed between about 120 and 200 km depth) and sublithospheric (formed much deeper, between 300 up to 1000 km depth). However, a third class of diamonds - “fibrous diamonds” - is much less studied and the origin of such enigmatic diamonds is still contentious. While lithospheric and sublithospheric diamonds can capture mineral inclusions providing crucial information about the deep Earth, fibrous diamonds are typically characterized by the presence of billions of submicrometric fluid inclusions. Such inclusions provide information about the composition of the diamond-forming fluid, but the scarcity of mineral inclusions means that their formation depths and rock substrates are poorly constrained.Based on the PI’s recent pilot study, the MADAM project will, for the first time, investigate the structure and nature of nanometric mineral inclusions in fibrous diamonds, providing unprecedented information about these enigmatic diamonds. If funded, the MADAM project will enable the PI to acquire the first electron diffractometer applied to geoscience worldwide. This quantum leap in technology now allows the determination of the structure of any crystalline material at nanometric scale in less than 2 minutes. Application to fibrous diamonds this technique will allow the study of a large number of samples (> 100 diamonds per year) from a global distribution of sources, providing a definitive resolution of their depth of formation and geological significance.