Vol 482, No 2 (2018)

The results of U–Pb zircon age dating of ultramafic massifs occurring as a chain along the Main Ural Fault zone (MUF) are given. Three groups of ages were obtained (Ma): 2500−2800, 600−2100, and 430−440. The first age group represents the time of origin of the ultramafic rocks in the Earth’s mantle. The second age group records the time of metamorphism of these rocks prior to intrusion into the host rocks. The third age group determines the time of the intrusion of ultramafic magma into the host rocks. It was established that the intrusion of ultramafic magma along the entire length of the Ural ultramafic belt occurred in the age range of 430−440 Ma.

The first historical eruption of Kambalny volcano began on March 24, 2017 with the powerful ash emission from the summit crater reaching as high as 6 km above sea level. The explosive activity continued without interruption from March 24 to March 30. The most powerful ash emission was registered on March 25–26, when the ash plume drifted several thousand kilometers SW, S, and SE from the volcano. On April 2 and April 9, after several calm days, powerful ash explosions occurred generating ash plumes up to 7 km high. The area of the land and sea over which the ash plume drifted during the day of March 25, was 650000 km²; the area of the ash accumulation on the land that was formed from March 24 to April 9, exceeded 1500 km². These parameters were measured using the satellite-based data in the VolSatView information system. Domination of the silty fraction and the presence of secondary minerals (pyrite, gypsum, sulfur, and others) in the ash point to the phreatic character of the volcanic eruption.

New U–Pb zircon (TIMS) results allow dating of protoliths of tonalite–trondhjemite orthogneisses of the Olekma Complex in the central part of the Chara–Olekma Geoblock (Aldan Shield) to 2825 ± 3 Ma and 2994 ± 3 Ma. Together with the results of previous geochronological studies, this proves that the Olekma Complex comprises heterochronous igneous rocks intensively reworked under amphibolite facies conditions and formed during different stages of geological evolution of the Aldan Shield.

Detrital zircons (DZs) from arkose sandstones of the Upper Riphean Zilmerdak Formation (Southern Urals) yielded ages in the range of 3039–964 Ma. Grains with Late Karelian and Early and Middle Riphean ages compose 35, 34, and 26% of the total number of the analyzed zircons, respectively. This is similar to the age spectra of the Vendian sandstones (Asha Group), but it differs significantly from the age distribution typical of the Riphean stratotype sandstones.

This article discusses problems of global metallogenic zonality of the Pacific Ore Belt (POB), which is understood as the complex of volcanogenic–plutonogenic units related to the evolution of the lithosphere of marginal seas; this lithosphere combines both continental and oceanic metallogenic features and also possesses a characteristic specificity of ore accumulation. It is shown that the ideas by S.S. Smirnov about the POB zonality have not considerably changed with time and, moreover, have been supported by the new global tectonic concepts. Nevertheless, the nature of metallogenic homogeneity of the external (Ag–Cu) and internal (Sn–W) zones of the POB seems to be more complicated and ambiguous. The metallogenic role of the Ag/Au ratio in ores of POB deposits is shown.

The Dotulur alkalic granite and Usugli Depression volcanics (West Stanovoi Superterrane of the Central Asia Fold Belt) have been dated by the U–Pb method, and their geochemistry has been analyzed. The geochemistry of the rocks suggests their intraplate nature. The alkalic granite and volcanics have similar ages of 142 ± 1 Ma and 138 ± 3 Ma, respectively. Considering the Usugli Depression structural position as an upper fault slice of the Elikan metamorphic core, the obtained dates allow the formation of the mentioned core and, accordingly, the collapse of central part of the Mongol–Okhotsk orogeny to have occurred not prior to 140 Ma.

A new interpretation of the geological and seismic data demonstratd a correlation between the surface structures of endogenic ore regions of the Baltic Shield, the Moho surface relief, and local heterogeneities in the Earth’s crust. As a result, based on consistent analysis of the geological and seismic data, models of the deep structure of the Pechenga and Onega ore regions were constructed and compared.

New ⁸⁷Sr/⁸⁶Sr, δ¹³C, and δ¹⁸О chemostratigraphic data were obtained for carbonate rocks of the Lower Riphean Yusmastakh and the Vendian Starorechenskaya formations. The δ¹³С values in dolomites of the Yusmastakh Formation varies from–0.6 to–0.1‰ and in dolomites and dolomitic limestones of the Starorechenskaya Formation, from–1.2 to–0.4‰ PDB, and δ¹⁸О values, from 24.4 to 26.4‰ and from 25.3 to 27.6‰ SMOW, respectively. The Rb–Sr systematics of carbonate rocks was studied using the refined method of stepwise dissolution of samples in acetic acid, including chemical removal of up to one-third of the ground sample by preliminary acid leaching and subsequent partial dissolution of the rest of the sample. Owing to this procedure, secondary carbonate material is removed, which enables one to improve the quality of the Sr-chemostratigraphic data obtained. The initial ⁸⁷Sr/⁸⁶Sr ratios in carbonate rocks of the Yusmastakh (0.70468–0.70519) and Starorechenskaya (0.70832–0.70883) formations evidence the Riphean–Vendian boundary in the Precambrian sequence of the Anabar Uplift.

It is known that the Р–Т parameters of diamond-bearing kimberlite xenoliths correspond to subductive paleogeotherms lying between the 36 and 41 mW/m² conductive models. There are some studies showing the correlation of diamond ability with oxygen fugacity and the fluid composition of mantle xenoliths. The most diamondiferous samples correspond to the water compositions of the calculated O–H–C fluid with a minimum atomic carbon content in it. From the calculations it follows that the fluid carbon atomic content increases with a temperature increase and with the pressure decreasing. The most minor C contents have the 35 mW/m² conductive model in comparison with the 40 and 45 mW/m² models. As a result, it is possible to conclude that the low temperature fields (less than 1100°C) of the “cold” geotherms have the highest diamondiferous ability.

The petrological model of type IIa diamond formation is proposed. By the model these diamonds were formed from fluids on the last stages of kimberlite magma formation at 600–700°C and in the range of 20–30 kbar. The model explains the main specific of the type IIa diamonds. They are the enrichment of light carbon, low nitrogen content, the absence of silicate inclusions, the large size and cleanliness, a high degree of desorption.

The isotope fractionation β-factors have been determined for hydroxyapatite, fluorapatite, and carbon–apatite upon ¹⁸O/¹⁶O, ¹³C/¹²C, and ⁴⁴Ca/⁴⁰Ca substitutions depending on the temperature. Calculations were performed based on density functional theory (DFT). The results are expressed in terms of cubic polynomials against x = 10⁶/T(K)² and can be utilized as geothermometers if combined with β-factors of the coexisting phases. The new values of β-factors completely supersede the conventional semi-empirical (estimated by the method of increments) calibrations of isotopic equilibria involving apatite.

High-carbon rocks at the northern margin of the Khanka terrane (Primorskii krai) have been found to host new occurrences of noble and rare-earth metals: the largest of them is the Filinskoye deposit. The graphite ores, hosting copper-bearing high-grade gold, silver, monazite, xenotime, sulfides, rutile, barite, and uraninite, demonstrate high ties of carbon with gold and rare earths. The graphite demonstrates δ¹³C from–2.1 to–5.5‰, corresponding to the mantle isotope composition. This suggests that the primary sources of the ore-forming system were deep carbon-bearing fluids.

The archeological site of Machpelah Temple (Cave of the Patriarchs), Israel, was studied. At the moment, the first stage of investigations is finished: it included the study of a certain part inside the temple proper. New high-frequency impulse sounding hardware was applied, and its depth and spatial resolution of physical inhomogeneities exceeded the capabilities of existing electromagnetic prospecting methods by an order of magnitude.

Statistically significant asymmetry of geothermal data was established by statistical analysis of the heat flow density along the geotraverses intersecting the West Indian Ridge in the southwestern part of the ocean. To compare the samples of the heat flow density, the Cramer–Welch criterion was applied. It was found that the heat flow on the western slope of the ridge and in the adjacent abyssal basins is higher than in the same structural elements located east of the ridge axis. Asymmetry in the crust structure and in the magnetic field is also noted. To explain this phenomenon, a model that takes the Coriolis force into consideration was proposed. The Coriolis force affects the ascending magma flux in the divergent zone of the ridge.

The methods and results of magnetotelluric sounding in the range of 0.0001–1000 s and more with the use small portable magnetotelluric stations are considered. Data on the distribution of electrical conductivity at depths beneath the Avacha–Koryak zone of contemporary volcanism are obtained. The obtained data are interpreted using the modern techniques and methods.

The REE distribution was studied in the bottom sediments of the East Arctic shelf of Russia. It is established that sediments of the Laptev and western East Siberian seas are significantly enriched in REEs, the contents of which are much higher than those of other near-continental basins. The main REE sources are runoff of the Lena River, the basin of which comprises ancient crystalline shields and magmatic rocks enriched in LREEs with significant contribution from the coastal erosion of the ice complex from the Laptev Sea and western East Siberian Sea. The terrigenous flux with a specific REE composition is supplied to the Chukchi Sea through the Bering Strait.