DIAMOND RESORPTION BY OXIDIZED INTERGRANULAR C-O-H FLUID
A.F. Khokhryakov1, Yu.M. Borzdov1, D.V. Nechaev1, Yu.N. Palyanov1,2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: Diamond resorption, mantle metasomatism, oxygen fugacity, HP-HT experiment
Abstract
Experimental studies on modeling the diamond resorption processes during mantle metasomatism accompanied by oxidation process in solid-phase matrix in the presence of intergranular fluid have been carried out. The reaction conducted between diamond and periclase to form magnesite can be considered as prototype EMOD (enstatite-magnesite/olivine-diamond) or DCDD (dolomite-coesite/diopside-diamond) reactions. The experimental studies were conducted at a pressure of 6.3 GPa in the 1100-1400 °C temperature range under redox conditions corresponding to the WM (wüstite/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 f O2 at the WM buffer level represents a typomorphic feature of diamond dissolution/resorption in water-containing carbonate and carbonate-silicate melts. The main microrelief elements of diamond dissolution forms are negatively orientated triangular etch pits on relict octahedral faces, shield-shaped or ditrigonal dissolution layers, and drop-shape hillocks. The obtained resorption rates at these P-T- f O2 parameters indicate that the absence of diamond in kimberlites or low-grade potentially diamondiferous kimberlite pipes might be caused by oxidizing metasomatic events in the lithospheric mantle in the regions of kimberlite emplacement.
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