2013

Estimation of rare elements concentration in chambers of diamond-forming carbonate-silicate melts formed in the mantle peridotite based on experimental К_D^RE mineral-melt at 7.0 – 8.5 GPa

Kuzyura A.V., Litvin Yu.A.

Institute of Experimental Mineralogy RAS, Chernogolovka, Russia; shushkanova@iem.ac.ru

A formation of growth media for the bulk of natural diamonds and minerals included in them syngenetically is a part of a common process of magmatic evolution of the mantle substance and integrated to it by physico-chemical way and spatially. It can be assumed that a chamber of diamond-forming melts was formed within the host garnet lherzolite mantle when it was affected by a reactive "metasomatic agent» (Litvin, 2011, 2012). It is of interest to identify those rare elements (RE) that came to diamond-forming melts with the mantle components, as well as those RE that were infused by the "agent".

Based on the experimental data at 7.0-8.5 GPa (Kuzyura et al, 2011, 2012) RE in the diamond-forming mantle peridotite-carbonatite and eclogite-carbonatite systems are characterized by similar partitioning coefficients (K_D^RE) mineral-melt. These values are also closely comparable with those for the silicate and carbonatite melts in equilibrium with mantle silicate minerals (Litvin, 2011).

The contents of RE in diamond-forming carbonatite melt chambers were calculated based on the real content of RE in minerals of peridotite and eclogite parageneses in diamonds and diamond xenoliths of several kimberlite pipes (Harte & Kirkley, 1997; Ionov, 2004; Stachel & Harris, 1997) and experimental K_D^RE (fig.1).

Fig. 1. Model concentrations of RE in melts of parental media of xhenoliths from kimberlite pipes, inclusions in diamonds for comparison to the primitive mantle (Lyubetskaya & Korenaga, 2007).

 The main contribution of RE in them is made by the mantle component. Parental melt of diamonds and inclusions in them are depleted by medium (Sm, Eu, Gd) and heavy RE (Tb, Dy, Ho, Er, Yb, Lu, Hf), in contrast to primitive peridotite. They are enriched in light (Sc, Rb, Sr, Ba, La, Ce, Pr, Nd) RE and Nb, but their content by 1-2 orders of magnitude lower than in the primitive mantle peridotite. High Sr can be concerned with "the metasomatic agent".

 Support: Grants of the President # МК-1386.2013.5, the Ministry of education and science of RF (agreements 8317, 8378) и RFBR 11-05-00401, 12-05-33044, 13-05-00835