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New mineralogical and isotope–geochemical data for zircon megacrysts (n = 48) from alluvium of Kholomolokh Creek (a tributary of the Ebelakh River) are reported. Using the geochemical classification schemes, the presence of zircons of kimberlitic and carbonatitic genesis was shown. The U–Pb dating of zircons revealed two major age populations: the Triassic (258–221 Ma, n = 18) and Jurassic (192–154 Ma, n = 30). Weighted mean 206Pb/238U ages allowed us to distinguish the following age stages: 155 ± 3, 161 ± 2, 177 ± 1.5, 183 ± 1.5, 190 ± 2, 233 ± 2.5, and 252 ± 4 Ma. It is suggested that the Ebelyakh diamonds could have been transported from the mantle depths by kimberlite, as well as by other related rocks, such as carbonatite, lamprophyre, lamproite, olivine melilitite, etc. Diamonds from the Ebelyakh placers most likely have polygenic native sources and may be associated with polychronous and multistage Middle Paleozoic and Mesozoic kimberlite and alkaline–ultrabasic magmatism in the eastern slope of the Anabar Shield (the Ebelyakh, Mayat, and Billyakh river basins).

The data available indicate the complex evolution of deformed peridotites of mantle xenoliths, the P–T parameters of which indicate that they are fragments of the metasomatized lower part of the cratonic lithosphere. The zoning established in garnets from xenoliths in kimberlite pipes is interpreted as a result of metasomatism that occurred shortly before xenoliths reached the surface. Metasomatic alterations in xenoliths of deformed harzburgites were manifested not only in the development of zoning of minerals. The study results show that there is a discrepancy between the data calculated based on the contents of incompatible elements in minerals of xenoliths and those obtained due to direct measurements of the bulk composition of xenoliths. To determine the balance of incompatible elements, we have carried out experiments on leaching xenoliths of deformed lherzolites from the Udachnaya kimberlite pipe. It was established that a significant part of LREEs in the studied xenoliths occurs in the intergranular space. The distribution pattern of incompatible elements and, in particular, the presence of a positive Eu anomaly indicate that the appearance of the intergranular component is not associated with contamination of xenoliths by the kimberlite melt. Quite a few xenoliths demonstrate a positive Eu anomaly, which indicates the influence of the subducted crustal component at one of the modification stages of xenoliths.

In the present paper, the results of our isotope–geochemical studies on eclogites of the ultrahighpressure metamorphic complex of the Kokchetav massif are reported. The fact that the distribution of nonmobile elements in most of the samples was close to that of E-type MORB basalts is shown by using geochemical multielement diagrams normalized to N-MORB. Six samples were found to have a negative anomaly over niobium that may have resulted from contamination with crustal material. For eclogites of the Kokchetav massif, the 147Sm/144Nd ratio was found to range widely from 0.143 to 0.367. The eNd-values calculated for the age of the highly barometric stage of metamorphism (530 million years) varied from–10.3 to +8.1. Eclogites show a dispersion of model ages from 1.95 billion years to 670 million years. On the graphs in the eNd(T)–87Sr/86Sr and eNd(T)–T coordinates, eclogites were shown to form trends that can be interpreted as a result of contamination of the eclogite protolith by the host rocks. Based on the data obtained, it is proposed that the basalts of rift zones that may have geochemical characteristics of N-MORB basalts and at the same time may be contaminated by the continental crust may have served as proxies for eclogite protoliths of the Kokchetav massif.

Mineralogical, petrographic, and geochemical studies of mafic granulites of the South Muya Block (Central Asian Orogenic Belt) have been carried out. The granulite protoliths were olivine- and plagioclase- rich cumulates of ultramafic–mafic magmas with geochemical affinities of suprasubduction rocks. The isotope–geochemical characteristics of the granulites indicate the enriched nature of their source, associated with recycling into the mantle of either ancient crust or oceanic sediments, or intracrustal contamination of melts at the basement of the ensialic arc. Formation of garnet-bearing parageneses has occurred during high-pressure granulite metamorphism associated with accretion in the eastern part of the Baikal–Muya composite terrane.

The staged high-pressure annealing of natural cubic diamonds with numerous melt microinclusions from the Internatsional’naya kimberlite pipe was studied experimentally. The results mainly show that the carbonate phases, the daughter phases in partially crystallized microinclusions in diamonds, may undergo phase transformations under the mantle P–T conditions. Most likely, partial melting and further dissolution of dolomite in the carbonate–silicate melt (homogenization of inclusions) occur in inclusions. The experimental data on the staged high-pressure annealing of diamonds with melt microinclusions allow us to estimate the temperature of their homogenization as 1400–1500°C. Thus, cubic diamonds from the Internatsional’naya pipe could have been formed under quite high temperatures corresponding to the lithosphere/asthenosphere boundary. However, it should be noted that the effect of selective capture of inclusions with partial loss of volatiles in relation to the composition of the crystallization medium is not excluded during the growth. This may increase the temperature of their homogenization significantly between 1400 and 1500°C.

The results of the investigations of the transformation of impurity defects in natural diamonds of various habits at the stage of high-temperature annealing at P = 6 GPa and T = 2200°C are presented. The studies conducted allowed us to ascertain that the transformations of Aand B-defects in diamonds of octahedral and cubic habits follow general regularities. This fact shows that most of the diamonds of cubic habit with low degree of aggregation of nitrogen centers were not really annealed over a long-term interval. Unlike octahedral diamonds, those of cubic habit are characterized by a pronounced increase in the peak of H-containing defects (3107 cm–1) after annealing.

The first studies of diamond-hosted inclusions in xenoliths have demonstrated that the compositions of inclusions and minerals in xenoliths may differ substantially [1]. It was noted that a higher K content in clinopyroxene as compared with that in the matrix is among the most important differences [2]. The Mir Pipe yielded diamonds with numerous garnet and pyroxene inclusions with highly variable compositions [3, 4]. Some authors explain these compositional variations in inclusions by fractionation from the silicate melt [3].

The recently obtained data on the superimposed character of diamonds in eclogite xenoliths have compelled us to consider the problem of diamond formation in the upper mantle from a new standpoint [1]. In [2], we reported the first results of the study of a unique diamond-bearing xenolith (length18 cm, weight 6900 g) from the Udachnaya kimberlite pipe (Yakutia). The results testify to the superimposed character of diamonds (particularly, the chemistry of minerals) and suggest that diamond crystallized as a product of interaction between the high-K and C-bearing fluid with the ultramafic substrate [2]. The study of diamond-hosted inclusions from xenoliths and the comparison of their chemical composition with minerals of the xenolith groundmass would be of special interest for reconstructing conditions of formation, composition, and evolution of diamond. In this communication, we present results of the study of inclusions along with defects, impurities, and the internal structure of diamond from this xenolith. We selected from the xenolith 44 diamond crystals 1‐5 mm in size. The crystals with crystalline inclusions were polished along axes (110) and (100) until the exposure of inclusions. These inclusions were examined with a Camebax-micro electron microprobe. The internal structure of diamond crystals was investigated with cathode luminescence on a LEO 1430VP scanning electron microscope. The IR absorption spectra were recorded with a Bruker VERTEX 70 IR Fourier spectrometer to study the impurities and to estimate concentration of structural defects in diamonds from this xenolith. The diamonds in xenoliths occur largely in the intergranular space and as inclusions in pyroxene and mica. They have the shape of differently distorted octahedra. Cathode luminescent images distinctly show two zones (core and shell). As a rule, the core is characterized by a weak luminescence, while the shell reveals a more intense luminescence (Fig. 1). The nonuniform zoning and distorted growth layers confirm the previous conclusion on the growth of the xenolith-hosted diamonds in a confined space. According to the results of IR Fourier spectroscopy, diamonds from this xenoliths pertain to the IaA/B type, widespread among natural diamonds; i.e., they contain impurity centers A (a pair of nitrogen atoms that isomorphically replace carbon), B1 (four nitrogen atoms around a vacancy), and in some cases B2 (sheetlike defects oriented parallel to (001)) with linear dimensions varying from a few nanometers to a few micrometers [3]. The total content of nitrogen admixture in the crystals ranges from 40 to 800 ppm. Besides the absorption bands related to the main nitrogen impurity centers, additional lines 3310, 3237, 3150, 3107, 1405