Unusual microdiamonds discovered in metamorphic rocks of continental affinities during the 1990^th in Kazakhstan, China, Norway and Germany provided new geochemical data that led to revisions in the understanding of the plate tectonic subduction and exhumation processes [1,2,3,4].

Diamond, due to its chemical inertness, is considered the perfect “geological container” where gas, fluid, and solid inclusions can be preserved. High-resolution Scanning and Transmission Electron Microscopy, Focused Ion Beam technology, Synchrotron X-ray diffraction, Fourier Transformed Infra-Red, and Raman spectroscopic studies exemplify the remarkable interaction between 21st-century science and technology. These advancements have led to a paradigm shift regarding microdiamonds formation in geological environments of metamorphic belts previously believed to be “forbidden” for their crystallization.

Our studies revealed that nanoscale gas and fluid inclusions in microdiamonds consist of light and heavy elements such as  Cl, S, H, K, Cr, Ba, Ti, Pb, Mo, Co, Al [5,6]. The presence of the negative crystals of diamonds filled with a C-O-H fluid provided evidence that such a fluid was in equilibrium with the diamond at T= 800-1200^oC and P=7-9 GPa and it can be considered as the diamond-forming media [5,6]. Studies of microdiamond carbon isotopes characteristics suggest that the diamond was formed from “organic” carbon (average δ13C = -10 to – 33 ^o%) [6]. The measurements of noble gases in microdiamonds from the Kokchetav terrane of Kazakhstan indicate that the ³He/⁴He ratio is consistent with values associated with geochemical interactions between a continental crust slab and a mantle plume [6].

We have conducted a series of successful experimental reproductions of diamonds crystallization from C-O-H-rich fluids at geological conditions close to those of their host rocks [6]. Studies of microdiamonds from recently discovered UHPM terranes continue to release new geochemical observations on organic carbon cycling into deep mantle, geochemical crust-mantle interaction and rejuvenation of the mantle which are critical components for understanding of mantle dynamics.