Olivine in the Udachnaya-East kimberlite (Yakutia, Russia): types, compositions and origins

Olivine is the principal mineral of kimberlite magmas, and is the main contributor to the ultramafic composition of kimberlite rocks. Olivine is partly or completely altered in common kimberlites, and thus unavailable for studies of origin and evolution of kimberlite magmas. The masking effects of alteration, common in kimberlites worldwide, are overcome in this study of exceptionally fresh diamondiferous kimberlites of the Udachnaya-East pipe from the Daldyn-Alakit province, Yakutia, northern Siberia. The serpentine-free kimberlites contain large amount of olivine (~ 50 vol%) in a chloride-carbonate groundmass. Olivine is represented by two populations (olivine-I and groundmass olivine-II) differing in morphology, colour and grain size, and trapped mineral and melt inclusions. The large fragmental olivine-I is compositionally variable in terms of major (Fo85-94) and trace element concentrations, including H2O content (10-136 ppm). Multiple sources of olivine-I, such as convecting and lithospheric mantle, are suggested. The groundmass olivine-II is recognised by smaller grain sizes and perfect crystallographic shapes that indicate crystallisation during magma ascent and emplacement. However, a simple crystallisation history for olivine-II is complicated by complex zoning in terms of Fo values and trace element contents. The cores of olivine-II are compositionally similar to olivine-I, which suggests a genetic link between these two types of olivine. Olivine-I and olivine–II have oxygen isotope values (+5.6 ± 0.1 ‰ VSMOW, 1 std. dev.) that are indistinguishable from one another, but higher than values (+5.18 ± 0.28 ‰) in “typical” mantle olivine. These elevated values most likely reflect equilibrium with the Udachnaya carbonate melt at low temperatures and 18O - enriched mantle source. The volumetrically significant rims of olivine-II have constant Fo values (89.0 ± 0.2 mol%), but variable trace element compositions. Uniform Fo compositions of the rims imply absence of fractionation of the melt’s Fe2+/Mg, which can be possible in the carbonatite melt – olivine system. The kimberlite melt is argued to have originated in the mantle as a chloride-carbonate liquid, devoid of “ultramafic” or “basaltic” aluminosilicate components, but became olivine-laden and olivine-saturated by scavenging olivine crystals from the pathway rocks and dissolving them en route to the surface. During emplacement the kimberlite magma changed progressively towards an original alkali-rich chloride-carbonate melt by extensively crystallising groundmass olivine and gravitational separation of solids in the pipe

Spectra of supernovae in the nebular phase

When supernovae enter the nebular phase after a few months, they reveal spectral fingerprints of their deep interiors, glowing by radioactivity produced in the explosion. We are given a unique opportunity to see what an exploded star looks like inside. The line profiles and luminosities encode information about physical conditions, explosive and hydrostatic nucleosynthesis, and ejecta morphology, which link to the progenitor properties and the explosion mechanism. Here, the fundamental properties of spectral formation of supernovae in the nebular phase are reviewed. The formalism between ejecta morphology and line profile shapes is derived, including effects of scattering and absorption. Line luminosity expressions are derived in various physical limits, with examples of applications from the literature. The physical processes at work in the supernova ejecta, including gamma-ray deposition, non-thermal electron degradation, ionization and excitation, and radiative transfer are described and linked to the computation and application of advanced spectral models. Some of the results derived so far from nebular-phase supernova analysis are discussed.Comment: Book chapter for 'Handbook of Supernovae,' edited by Alsabti and Murdin, Springer. 51 pages, 14 figure

Functional classification of proteins based on projection of amino acid sequences: application for prediction of protein kinase substrates

<p>Abstract</p> <p>Background</p> <p>The knowledge about proteins with specific interaction capacity to the protein partners is very important for the modeling of cell signaling networks. However, the experimentally-derived data are sufficiently not complete for the reconstruction of signaling pathways. This problem can be solved by the network enrichment with predicted protein interactions. The previously published <it>in silico </it>method PAAS was applied for prediction of interactions between protein kinases and their substrates.</p> <p>Results</p> <p>We used the method for recognition of the protein classes defined by the interaction with the same protein partners. 1021 protein kinase substrates classified by 45 kinases were extracted from the Phospho.ELM database and used as a training set. The reasonable accuracy of prediction calculated by leave-one-out cross validation procedure was observed in the majority of kinase-specificity classes. The random multiple splitting of the studied set onto the test and training set had also led to satisfactory results. The kinase substrate specificity for 186 proteins extracted from TRANSPATH^®database was predicted by PAAS method. Several kinase-substrate interactions described in this database were correctly predicted. Using the previously developed ExPlain™ system for the reconstruction of signal transduction pathways, we showed that addition of the newly predicted interactions enabled us to find the possible path between signal trigger, TNF-alpha, and its target genes in the cell.</p> <p>Conclusions</p> <p>It was shown that the predictions of protein kinase substrates by PAAS were suitable for the enrichment of signaling pathway networks and identification of the novel signaling pathways. The on-line version of PAAS for prediction of protein kinase substrates is freely available at <url>http://www.ibmc.msk.ru/PAAS/</url>.</p

Childhood exposure due to the Chernobyl accident and thyroid cancer risk in contaminated areas of Belarus and Russia

The thyroid dose due to 131I releases during the Chernobyl accident was reconstructed for children and adolescents in two cities and 2122 settlements in Belarus, and in one city and 607 settlements in the Bryansk district of the Russian Federation. In this area, which covers the two high contamination spots in the two countries following the accident, data on thyroid cancer incidence during the period 1991-1995 were analysed in the light of possible increased thyroid surveillance. Two methods of risk analysis were applied: Poisson regression with results for the single settlements and Monte Carlo (MC) calculations for results in larger areas or sub-populations. Best estimates of both methods agreed well. Poisson regression estimates of 95% confidence intervals (CIs) were considerably smaller than the MC results, which allow for extra-Poisson uncertainties due to reconstructed doses and the background thyroid cancer incidence. The excess absolute risk per unit thyroid dose (EARPD) for the birth cohort 1971-1985 by the MC analysis was 2.1 (95% CI 1.0-4.5) cases per 10(4) person-year Gy. The point estimate is lower by a factor of two than that observed in a pooled study of thyroid cancer risk after external exposures. The excess relative risk per unit thyroid dose was 23 (95% CI 8.6-82) Gy(-1). No significant differences between countries or cities and rural areas were found. In the lowest dose group of the settlements with an average thyroid dose of 0.05 Gy the risk was statistically significantly elevated. Dependencies of risks on age-at-exposure and on gender are consistent with findings after external exposures

The First Stars

The first stars to form in the Universe -- the so-called Population III stars -- bring an end to the cosmological Dark Ages, and exert an important influence on the formation of subsequent generations of stars and on the assembly of the first galaxies. Developing an understanding of how and when the first Population III stars formed and what their properties were is an important goal of modern astrophysical research. In this review, I discuss our current understanding of the physical processes involved in the formation of Population III stars. I show how we can identify the mass scale of the first dark matter halos to host Population III star formation, and discuss how gas undergoes gravitational collapse within these halos, eventually reaching protostellar densities. I highlight some of the most important physical processes occurring during this collapse, and indicate the areas where our current understanding remains incomplete. Finally, I discuss in some detail the behaviour of the gas after the formation of the first Population III protostar. I discuss both the conventional picture, where the gas does not undergo further fragmentation and the final stellar mass is set by the interplay between protostellar accretion and protostellar feedback, and also the recently advanced picture in which the gas does fragment and where dynamical interactions between fragments have an important influence on the final distribution of stellar masses.Comment: 72 pages, 4 figures. Book chapter to appear in "The First Galaxies - Theoretical Predictions and Observational Clues", 2012 by Springer, eds. V. Bromm, B. Mobasher, T. Wiklin

Can pyroxenes be liquidus minerals in the kimberlite magma?

Clinopyroxene and orthopyroxene are generally rare in kimberlites, and believed to originate from disintegrated mantle and crustal xenoliths. We report occurrence of inclusions of low-Ca and high-Ca pyroxenes in the olivine phenocrysts in the Udachnaya-East hypabyssal kimberlite (Yakutia, Russia), and make inferences on their relationships to the kimberlite magma. Pyroxenes are only found as either resorbed macrocrysts or small inclusions in olivine; both types are being very rare and volumetrically insignificant. All clinopyroxene and majority of orthopyroxene inclusions are hosted in the olivine cores (Fo86-92) that are compositionally similar to olivine macrocrysts. Major and trace element compositions of clinopyroxene inclusions in olivine phenocrysts and macrocrysts are similar, and resemble compositions of clinopyroxene from lherzolite xenoliths hosted in the Udachnaya-East kimberlite. Their high Na2O and Cr2O3 abundances (0.65-2.55 and 0.6-2.8 wt%, respectively) suggest deep mantle origin (>4.5 GPa). The majority of clinopyroxene inclusions have convex-upward trace element patterns that imply kimberlite-like compositions for the hypothetical equilibrium melts. Re-equilibration of clinopyroxene inclusions with the host kimberlite liquid through micro-cracks in olivine is our preferred explanation in this case, however, we cannot exclude their high-pressure crystallisation from the protokimberlite melt. Orthopyroxene inclusions show significant compositional overlap with the low-Al orthopyroxene from the Udachnaya peridotite nodules. Where such inclusions occur in olivine fragments and contact with the kimberlite groundmass, they are strongly resorbed and partially replaced by monticellite. The mantle origin of orthopyroxene and its host olivine and disequilibrium relationships with the kimberlite melt is most likely. Both clinopyroxene and orthopyroxene are completely absent in the kimberlite groundmass. We conclude that the parental melt of the Udachnaya-East kimberlite was not saturated in either clinopyroxene or orthopyroxene at low pressure. This argues against a perceived mafic-ultramafic lineage of the kimberlite primary melt, and provides further support for its essentially carbonate-chloride composition