Vol 477, No 2 (2017)

Geological, geochemical, and geochronological studies of rocks have been performed at the Okunyovo rare-metal ore magmatic complex (Western Sayan Mountains) composed of alkali granites and related F–Be mineralization. The geological data obtained and the features of the geochemical similarity of granite and ore mineralization identified are indicative of their genetic relation. Riebeckite from two granite samples has been subjected to ⁴⁰Ar/³⁹Ar analyses. The estimated age values of 481.5 ± 2.7 Ma and 486.5 ± 5.8 Ma are consistent within the limits of error and determine the age of Okunyovo alkali granite within 481–486 Ma ago. These data have made it possible to relate the studied rock and ore formation to the development of the Early Paleozoic ASFR controlled by the mantle plume. Along with the Okunyovo rare-metal granite massif, within the Sayan Region of the magmatic province, there are a number of Early Paleozoic alkali massifs related to the Aryskan, Raduga, and Kazyr rare-metal deposits. They are located in the conjugation area of the Western and Eastern Sayan ridges, in the Early Paleozoic Eastern Sayan rare-metal magmatism zone specialized in Be, W, Mo, Zr, Nb, and REEs.

Complex study of the U–Pb and Lu–Hf systems of zircon from a lhertzolite lens of Archean gneiss enderbites of the Bug complex, Ukrainian Shield, showed that ultramafic magma was contaminated by the material of the country gneiss enderbites. The age of the zircons of 2.81 ± 0.05 Ga corresponds to the period of ultramafic magmatism within the Bug complex. Previously, this peak of endogenic activity was considered the stage of manifestation of metamorphism and magmatism of mafic composition.

In the late Neoproterozoic a prolonged active continental margin mode dominated the southwestern margin of the Siberian craton. Based on results of geological, petrological-geochemical, U–Th–Pb and Sm–Nd, Rb–Sr isotope investigations, for the first time we established that on the final evolution stage of this margin 576–546 Ma, intrusions of adakites and gabbro-anorthosites of the Zimoveyniy massif were emplaced in the South Yenisei Ridge. These new data indicate genetic relationships of the studied adakites and host NEB-metabasites. The formation of adakites could have been due to a crustal or a mantle-crustal source in a setting of transform sliding of lithospheric plates after the subduction stopped.

It is shown that the reaction ability of metal cations of ore minerals in Fe–Mn crusts of the Marcus Wake Rise increases in the following manner: (Co²⁺ < Cu²⁺ < Ni²⁺) < (Mg²⁺ < Mn²⁺ < K⁺ ≈ Ca²⁺ ≈ Na⁺). The composition of the exchange complex of the ore minerals is constant and includes these metal cations. Ca²⁺ and Na⁺ are major contributors to the exchange capacity of the ore minerals. The capacity of the ore minerals by cations of alkali and base metals is 0.43–0.60 and 2.08–2.70 mg-equiv/g, respectively. The exchange capacity of the ore minerals by cations of base metals increases linearly with the increase in the MnO₂ content of the crust and does not depend on the geographical locations of the Marcus Wake guyots.

The results of study of the chemical and phase compositions of three Ag-, Au-, platinum group element-, As-, Bi-, and Te-bearing samples, which are the product of directed crystallization of the Cu–Fe–Ni sulfide melt, are presented. One sample contained only metals, the second one was additionally doped with As, and the third one was enhanced in As, Bi, and Te. The mechanism of formation of the minerals of the platinum group metals during fractionation crystallization of multicomponent sulfide melts was proposed on the basis of interpretation of experimental data.

New data on the mineral composition of Kargapole meteorite, which was found in Kurgan oblast in 1961, are presented. It has been established that the meteoritic material is represented by olivine (chrysolite), orthopyroxene (bronzite), clinopyroxene (diopside), plagioclase (oligoclase), chromite, Fe and Ni metal particles (kamacite, taenite, tetrataenite), sulfides (troilite, pentlandite), chlorapatite, and merrillite. For the first time, diopside, tetrataenite, pentlandite, chlorapatite, and merrillite were identified in the Kargapole meteorite. The chemical compositions of all minerals studied are given in Table 1. In terms of petrology, the meteorite is classified a common H4 chondrite.

New data were obtained on δ¹³С_carb and δ¹⁸O variations in the sequence of deposits of the Dal’nyaya Taiga series at the western and eastern flanks of the Ura anticline. The summary δ¹³С curve was plotted in view of the correlation of sequence–stratigraphic data of the basin analysis. A series of positive anomalies was found within the succession. Alternatives for global chemostratigraphic correlation of the Dal’nyaya Taiga series of the Ura uplift were considered.

Study of the magmatics in the Nakyn kimberlite field, with consideration of the isotope dating results, allowed us to establish a sequence of their formation. First, 368.5–374.4 Ma ago intrusions of the Vilyui–Markha dike belt formed. Then (363–364 Ma) intrusion of kimberlites took place. In the Early Carboniferous (338.2–345.6 Ma), alkaline basaltic magma intruded through faults controlling the kimberlites. The magmatic activity finished 331–324.9 Ma ago with the formation of explosive breccias. It has been found that the Nyurba kimberlite pipe consists of two bodies: their kimberlite melts have successively intruded through independent channels.

The probability of obtaining of ash-free coal extracts, so-called “hyper-coals,” has been shown for coals of the Pechora basin for the first time. The ash content in them does not exceed a few percent, whereas initial coals contain up to 20% ash. High-resolution ¹³C NMR shows the similarity in the structure of the initial coal and the extract. It is demonstrated that the solvent selected for hyper-coal extraction is not chemically inert, and the products of interaction of N-metylpyrrolidone and organic matter of coal are present in the composition of the extracts obtained.

Synthesis of hydrocarbons by the interaction of a CO₂ fluid with hydrogen mantle domains has been simulated in an experiment at 7.8 GPa and 1350°C. The synthesized fluid contains mainly aldehydes; lower amounts of ketones, alcohols, esters, and ethers; as well as noticeable amounts of isobutane and butane, alkenes, arenes, and polycyclic aromatic and heterocyclic hydrocarbons. The fluid is compositionally close to volatiles found in inclusions from mantle olivines and picroilmenites.

New results of experimental studies into ice deformation and structural changes are presented. A sequence of structural mechanisms of deformation from polygonization to formation of cracks, cavities and shattering of crystals that replace each other primarily relatively to the load value and the deformation rate is developed. The principal mechanism of creep deformation is crack formation and crystal shattering. A brittleness index for ice deformation is proposed. It is shown that the vesicular texture of ice can be the result of the regeneration of open cracks during deformation.

Various human footprints on the flux of biogenic greenhouse gases from permafrost-affected soils in Arctic and boreal domains in Russia are considered. Tendencies of significant growth or suppression of soil CO₂ fluxes change across types of human impact. Overall, the human impacts increase the mean value and variance of local soil CO₂ flux. Human footprint on methane exchange between soil and atmosphere is mediated by drainage. However, all the types of human impact suppress the sources and increase sinks of methane to the land ecosystems. N₂O flux grew under the considered types of human impact. Based on the results, we suggest that human footprint on soil greenhouse gases fluxes is comparable to the effect of climate change at an annual to decadal timescales.

A theoretical model explaining the effect of anomalous suppression of the energy (up to 70%) of tsunami-type waves by thin (compared to the wavelength) underwater obstacles is developed based on the integral laws of conservation of mass and energy fluxes. It is shown that the analytical dependences for the coefficients of reflection and transmission of waves across an underwater obstacle that have been obtained using the theoretical model proposed by the author agree with the results of the experiments and numerical simulation based on the complete Navier–Stokes equations.

On the basis of the negative binomial distribution of the duration of wet periods calculated per day, an asymptotic model is proposed for distributing the maximum daily rainfall volume during the wet period, having the form of a mixture of Frechet distributions and coinciding with the distribution of the positive degree of a random variable having the Fisher–Snedecor distribution. The method of proving the corresponding result is based on limit theorems for extreme order statistics in samples of a random volume with a mixed Poisson distribution. The adequacy of the models proposed and methods of their statistical analysis is demonstrated by the example of estimating the extreme distribution parameters based on real data.

The results of study of the Hovsgol earthquake with M_w = 4.9, which occurred on December 5, 2014, in the northern part of Hovsgol Lake in Mongolia, are presented. An infrasonic signal of ~140 s long was recorded by the Tory infrasonic station for the first time for the Baikal Rift System. On the basis of the source parameters and focal mechanism of this earthquake determined, displacements in the epicentral zone of the Hovsgol earthquake are modeled. It is shown that they could not have produced an infrasonic sound. The use of acceptable values of group velocities of infrasonic waves (0.28–0.35 km/s) demonstrates that the signal source was located approximately midway between the Tory station and the epicenter of the Hovsgol earthquake, indicating it was a secondary source. Based on the data on the azimuth and arrival time of the acoustic wave at the Tory station, the location of this secondary source is determined to have been on the northern slopes of the Khamar Daban Range. The infrasonic signal formed most likely by interaction between seismic waves from the earthquake and the mountain relief.

A simple index of convective instability (3D-index) is used for analysis of weather and climate processes that favor to the occurrence of severe convective events including tornadoes. The index is based on information on the surface air temperature and humidity. The prognostic ability of the index to reproduce severe convective events (thunderstorms, showers, tornadoes) is analyzed. It is shown that most tornadoes in North Eurasia are characterized by high values of the 3D-index; furthermore, the 3D-index is significantly correlated with the available convective potential energy. Reanalysis data (for recent decades) and global climate model simulations (for the 21st century) show an increase in the frequency of occurrence of favorable for tornado formation meteorological conditions in the regions of Northern Eurasia. The most significant increase is found on the Black Sea coast and in the south of the Far East.