Imaging carbon-rich melts in the Earth's mantle

Carbon-rich melts are believed to play a key role in the long-term geodynamic carbon cycle. Their origin and how these melts reach the Earth's surface is still an area of debate Due to their lack of polymerization, carbon-rich melts present particular physical and chemical properties such as a low viscosity and fast diffusion, which make them potentially powerful metasomatic agents in mantle rocks. Although there is evidence for carbon-rich melt in the mantle, little is known about their properties at mantle conditions. Accurate knowledge of the density contrast between the melt and residual rocks at high-pressure and temperature is thus needed in order to understand the extraction and the transportation mechanisms of melts through the Earth's mantle. Here, we will discuss an x-ray imaging technique which has only recently been used for in-situ high pressure work, and its promise for deep carbon research: nanoscale X-ray computed tomography (nano-XCT). Nano-XCT represents a powerful tool to investigate in situ the evolution of density of silicate and carbon-rich melts at mantle pressures which cannot be measured by more conventional synchrotron techniques like X-ray diffraction. Nano-XCT can also be applied for imaging the connectivity changes of carbon-rich melts in contact with solid silicates with varying conditions covering the Earth mantle. The data set resulting from this technique would provide critical constraints for modelling how carbon-rich melts behave in the Earth's mantle and ultimately improving our understanding of the deep carbon cycle.