ISSN 1028-334X, Doklady Earth Sciences, 2011, Vol. 439, Part 2, pp. 1175–1178. © Pleiades Publishing, Ltd., 2011. Original Russian Text © N.S. Tychkov, A.M. Agashev, N.P. Pokhilenko, I.S. Bazhan, 2011, published in Doklady Akademii Nauk, 2011, Vol. 439, No. 6, pp. 807–810. 1175 Udachnaya pipe is a unique geological object pre- senting quite a continuous section of the continental lithosphere from its roots to the upper crust level. Xenoliths and xenocrysts of deep-seated rocks, trans- ferred by kimberlites of this pipe, are fragments of ancient depleted rocks of the lithosphere mantle and testify to the superposed processes that occurred at the time of the kimberlite body formation. All these facts allow one to consider Udachnaya pipe as a model for studies of mantle sections in the regions of less infor- mative kimberlites. It is known that a general inverse relationship takes place for a volume fraction of garnet in mantle rocks and its chromousity (Cr/(Cr + Al)). This trend was first shown by the example of garnet lherzolites from the Bohemian massif [8]. However, this relationship is by no means pronounced and depends on several fac- tors [2]. For Udachnaya pipe, this relationship was found for high-temperature deformed lherzolites (DL) [4]. The authors performed an integrated study of the xenoliths in the lherzolites of Udachnaya pipe [1, 6]. A sufficient set of suitable data combined with those from other authors [10] allows one not only to confirm the presence of the mentioned relationship in the DL of Udachnaya pipe, but also to calculate first the curve describing this dependence. The use of various mineral thermobarometers shows that the DL are the deepest lithosphere mantle rocks transferred to the surface. It is thought that they are products of secondary enrichment of depleted rocks of the lower lithosphere mantle (dunites and harzburgites for Udachnaya pipe). The enrichment occurs resulting from the influence of melts of astheno- sphere origin (containing no Cr and enriched in Fe and Ti) against the background of tectonic processes reflected in the distinctive texture of the rocks [7]. In peridotite minerals, chromium is contained in garnet, chromite, and, to a lesser degree, in pyroxenes. Practically no chromite is found in DL [2] because, resulting from the secondary enrichment process, it transforms into garnet with the decrease of system chr- omousity (Cr/(Cr + Al)) [15]. Respectively, this garnet then contains the bulk of chromium in the DL. The described dependence of the amount of garnet in the rock on the garnet chromousity is an inverse relationship. The presence of the inverse relationship shows that the chromium content in a given rock does not increase proportionally to the increase in the amount of garnet. In the case of formation of new gar- net owing to secondary enrichment with no introduc- tion of Cr, the enrichment mechanism should be described by an equiangular hyperbola (y = a/x), because the product of the variables in this case is always constant and equal to а. Thus, the amount of chromium in the rock is not varied and is always equal to the chromium content in garnet multiplied by its volume fraction in the rock. It is seen in Fig. 1 that the mentioned relationship is described well by the curve y = a/x with а = 0.39, where x is a garnet chromuosity (Cr 2 O 3 , wt %), y is the volume fraction of garnet in the rock, and а is the total amount of chromium. This model conforms to the above common mechanism of the formation of high-temperature DL. According to published data, garnets from the DL of other regions show a similar character of the rela- tionship at different chromium contents in rocks: а = 0.36 for Jericho pipe [11], 0.23 for Bluefontain pipe [9], and 0.17 for peridotites of the Bohemian massif [8] (Fig. 1). At the same time, if the rocks were initially characterized by a wide range of chromuosity, the rela- tionship might be fuzzy. Xenoliths of mantle rocks give insight into the lithosphere composition and structure as well as into the processes of their changing. The data as such may be obtained by means of studies of mantle rock xenoc- Estimation of the Refertilization Grade of Lithosphere Roots by the Chemical Composition of Garnets from Siberian Kimberlites N. S. Tychkov, A. M. Agashev, Corresponding Member of the RAS N. P. Pokhilenko, and I. S. Bazhan Received April 22, 2011 DOI: 10.1134/S1028334X11080320 Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia e-mail: tychkovne@gmail.com GEOCHEMISTRY