Volatiles around two dimensional defect structures as indicated by micro diamonds in decompression cracks

Abstract

New evidence exist that micro diamonds do not only form at high pressure and under high temperature conditions in the diamond window, but can also be synthesized by polycondensation of light carbon-bearing molecules at medium to low pressure conditions under favourable thermodynamic, stoichiometric and kinetic circumstances. This process may even occur close to the Earth´s surface. The studied eclogites contain OH, CO2, CO, CH4, CH2O and CH3OH. These C:O:H-bearing volatiles can be found around totally embedded micro cracks in nominally anhydrous minerals (NAMS). Micro cracks act like monomineralic and interphase grain boundaries, and can also be interpreted as two dimensional defect structures. High-resolution synchrotron based FT-IR was used in the study to detect C:O:H-bearing volatiles around two-dimensional defect structures in NAMS; for example garnet. A correlation between the different C:O:H-bearing volatiles is visible in the micro diamond bearing defect structures, whereas in inclusion free defect structures, no correlation of the different C:O:H containing volatiles can be recognized. The findings from the study shows that the C:O:H-bearing volatiles, and their distribution pattern around the studied micro cracks, are indicators for the formation of micro diamonds in natural eclogites. The outcomes confirm the results from experimental studies on the growth and synthesis of diamond crystals as a consequence of polycondensation of light carbon molecules.