Home – Home – Jornals – Russian Geology and Geophysics 2018 number Неопубликованное

Experimental studies on modelling of diamond resorption processes during mantle oxidative metasomatosis in solid-phase matrix in the presence of intergranular fluid have been carried out. The reaction between diamond and periclase with formation of magnesite was realised, which can be considered as a model variant of such reactions as EMOD (enstatite-magnesite/olivine-diamond) or DCDD (dolomite-coesite/diopside-diamond). The studies were performed at a pressure of 6.3 GPa in the temperature range 1100-1400 °C under redox conditions corresponding to the WM (wustite/magnesite) buffer. It was found that the reaction between diamond and periclase to form magnesite occurs only in the presence of 0.5-0.8 wt.% water at temperatures above 1200 °C. The morphology of diamond crystals partially dissolved by intergranular H₂O-fluid at fO₂ at WM buffer level is typomorphic for diamond dissolution/resorption in water-containing carbonate and carbonate-silicate melts. The main microrelief elements of diamond dissolution shapes are inversely orientated triangular etch pits on relict octahedral faces, shield-shaped or ditrigonal dissolution layers, and drop-shaped hills. The obtained resorption rates at these P-T-fO₂ parameters indicate that the absence of diamond or poor diamondiferousness of potentially diamondiferous kimberlite pipes may be due to oxidative metasomatosis in the mantle regions of pipe formation.