Trace Elements in Chromian Spinels from Four Siberian Kimberlites

We analysed the major, minor and trace elements chemistry of forty-two Cr-spinels from four Siberian kimberlites. They showed a wide range in Mg# (Mg/(Mg + Fe2+); 0.42–0.78) and Cr# (Cr/(Cr + Al); 0.32–0.92) and a common trend of increasing Cr# with decreasing Mg#. The major element classification schemes suggested that there were spinels deriving from a peridotitic source (Xen) and spinels crystallised from kimberlitic melts (Chr). Laser-Ablation Inductively Coupled Plasma Mass Spectrometry on both groups showed that the trace elements with the highest abundance were Mn (985–3390 ppm), Ni (531–3162 ppm), V (694–2510 ppm) and Zn (475–2230 ppm). Testing the effectiveness of trace elements in determining the source for Cr-spinels, we found out that Cr-spinels crystallised directly from a kimberlitic melt usually showed higher Mn, Ni, Sc and V concentrations with respect to those of peridotitic origin. In addition, using the available partitioning models, we found that the correlations between major elements and Ni, Co, Sc and Ga in the Xen group could be explained by subsolidus equilibration between spinel, olivine and clinopyroxene at 800–1000 °C, thus supporting a peridotitic source for this group. Finally, we calculated the composition of the possible melts in equilibrium with the Cr-spinels of the Chr group, using a selected set of partition coefficients. Calculated abundances of Cu, Ga and Zr were comparable to those of the kimberlite, while V was never close to the kimberlite composition. This simulation highlighted the need for new data on the trace elements partition coefficients between kimberlitic melts and Cr-spinel

Diamond-inclusion system recording old deep lithosphere conditions at Udachnaya (Siberia)

Diamonds and their inclusions are unique fragments of deep Earth, which provide rare samples from inaccessible portions of our planet. Inclusion-free diamonds cannot provide information on depth of formation, which could be crucial to understand how the carbon cycle operated in the past. Inclusions in diamonds, which remain uncorrupted over geological times, may instead provide direct records of deep Earth’s evolution. Here, we applied elastic geothermobarometry to a diamond-magnesiochromite (mchr) host-inclusion pair from the Udachnaya kimberlite (Siberia, Russia), one of the most important sources of natural diamonds. By combining X-ray diffraction and Fourier-transform infrared spectroscopy data with a new elastic model, we obtained entrapment conditions, Ptrap = 6.5(2) GPa and Ttrap = 1125(32)–1140(33) °C, for the mchr inclusion. These conditions fall on a ca. 35 mW/m2 geotherm and are colder than the great majority of mantle xenoliths from similar depth in the same kimberlite. Our results indicate that cold cratonic conditions persisted for billions of years to at least 200 km in the local lithosphere. The composition of the mchr also indicates that at this depth the lithosphere was, at least locally, ultra-depleted at the time of diamond formation, as opposed to the melt-metasomatized, enriched composition of most xenoliths

Study of semi-polar gallium nitride grown on m-sapphire by chloride vapor-phase epitaxy

In this study, we analyzed the result of the influence of the non-polar plane of a sapphire substrate on the structural, morphological, and optical properties and Raman scattering of the grown epitaxial GaN film. It was found that selected technological conditions for the performed chloride-hydride epitaxy let us obtain the samples of structurally qualitative semi-polar wurtzite gallium nitride with (11¯22) orientation on m-sapphire. Using a set of structural and spectral methods of analysis the structural, morphological, and optical properties of the films were studied and the value of residual bi-axial stresses was determined. A complex of the obtained results means a high structural and optical quality of the epitaxial gallium nitride film. Optimization of the applied technological technique in the future can be a promising approach for the growth of the qualitative GaN structures on m-sapphire substrates

PLAYS BY BORIS ZAYTSEV IN RUSSIAN DRAMA OF THE EARLY TWENTIETH CENTURY

Th e beginning of the 20th century is the heyday of Russian dramatic art. Moscow and St.  Petersburg became a  meeting place for a  considerable amount of  artistic talent that allowed, based on  the preceding theatrical tradition,creating outstanding works of theatrical art. Th e distinguishing feature of the poetics of the new Russian drama was plot collision, that does not derive from external events but from intentionally occasional, impulsive emotional movements of  the characters. Th e article reviews dramas of Boris Zaytsev, written in the fi rst half of the 20th century. For the plays of that period is typical impressionism, associative composition, weakness of  the plot. Th eir content is characterized by tense psychologism, the dynamics of emotional experience and philosophizing. Key themes developed in dramas become the theme of redemption by love, search for spiritual wholeness and overcoming of existential confl ict the heroes are faced wit

Types of Xenogenic Olivine from Siberian Kimberlites

This work is devoted to the systematization of the composition of xenogenic olivine from kimberlites as the main mineral composing the lithospheric mantle. Based on data on the composition of olivines from xenoliths and megacrysts from kimberlites, a general division into four types is proposed: olivines of ultrahigh-temperature (HTP-1), high-temperature (HTP-2) and low-temperature (LTP) peridotites, as well as olivines of low-chromium megacryst association (MCA). The separation scheme uses the CaO content as an indicator of the formation temperature and the Mg/(Mg + Fe) ratio as an indicator of the degree of enrichment in olivines. In contrast to Al, the Ca content in olivines from cratonic peridotites is high enough to use only EPMA when applying the proposed scheme. According to this scheme the study of more than 1500 individual olivine xenocrysts from a number of kimberlite bodies of the Siberian platform was made. It revealed three characteristic distributions of olivine types: without high-temperature differences (Obnazhennaya pipe), with significant development of HTP-2 (Olivinovaya and Vtorogodnitsa pipes), and with a significant development of HTP-1 (Dianga pipe). Only the latter type of distribution is characterized by the presence of a noticeable amount of megacryst association olivines. The study of other minor elements (TiO2 and NiO) in olivines allowed us to propose a model for the formation of high-temperature olivines of two different types due to the interaction of megacryst melt of various fractionation stages on depleted rocks of the lithospheric mantle. HTP-2 olivines arose upon exposure to a fractionated melt of the late stages of crystallization, and HTP-1 olivines appeared upon exposure to unfractionated (less enriched with incompatible components) megacryst melt at higher temperatures of the initial stage of crystallization