Direct observation and analysis of a trapped COH fluid growth medium in metamorphic diamond

The mechanism by which diamonds grow in Earth's mantle has been a subject of discussion for many years. Arguments have been advanced for growth from a melt, from a COH fluid, and in the solid state. The discovery of microdiamonds within ultra-high pressure terranes of continental collision settings re-energized this debate because of their very different but well-defined continental crust environment. We report here the discovery of filled nanometric fluid bubbles in diamonds from marble of the Kokchetav massif, Kazakhstan, and the serendipitous measurement of their contents due to bursting of a bubble very shortly after a measurement of chemical composition in the transmission electron microscope, thereby allowing immediate re-analysis with exactly the same settings of all parameters of the microscope. The chemical composition of the fluid is C, H, O, Cl, S, Ca, Fe and K. The direct observation and composition of a low-viscosity trapped fluid in microdiamond unambiguously establish their fluid growth medium.