EXPERIMENTAL MODELING OF DIAMOND RESORPTION DURING THE IMPLEMENTATION OF EMOD AND DCDD REACTIONS
A.F. Khokhryakov1,2, I.D. Novoselov1, D.V. Nechaev1, Yu.N. Palyanov1,2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences,
Novosibirsk, Russia
2Novosibirsk State University, Russia
Keywords: Diamond resorption, mantle metasomatism, oxygen fugacity, HP-HT experiment
Abstract
Experimental studies were conducted to model diamond resorption during oxidative mantle metasomatism at a pressure of 6.3 GPa, a temperature of 1000-1300 °C, and fO2
corresponding to WM (wustite-magnetite) and HM (hematite-magnetite) buffers. Diamond crystals were placed in forsterite and diopside aggregates with the addition of water in amounts ranging from 1 wt.% to 4 wt.%. As a result, diamond oxidation reactions were realized in the forsterite-diamond-H2O and diopside-diamond-H2O systems in a solid-phase matrix, in accordance with the EMOD (enstatite-magnesite/olivine-diamond) and DCDD (dolomite-coesite/diopside-diamond) equilibria. Changes in the morphology of resorbed diamonds and the composition of newly formed phases depending on the water content in the systems were studied. It has been established that at relatively low water contents (up to 2 wt.%) in the system, diamond dissolution/resorption occurs predominantly through negative trigons and trigonal layers. As a result, the diamond forms obtained during resorption are similar to so-called laminar dodecahedrons or octahedral habit crystals with a polycentric face structure, which are traditionally considered typical diamond growth forms. At higher water concentrations (4 wt.%), diamond resorption occurs with the formation of ditrigonal and shield-shaped layers on the {111} faces, which are typomorphic for diamond dissolution processes in hydrous melts and fluids. Typical rounded diamond crystals have not been observed in the forsterite-diamond-H2O system due to uneven surface resorption.
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