Vol 469, No 2 (2016)

The Sr and C isotopic compositions of Precambrian carbonate rocks are determined for Amderma Rise, in the northeastern margin of Pai-Khoi Ridge. Based on the Sr isotopic chemostratigraphy, it is established for the first time that the Amderma Formation is referred to the Early Vendian, while the Morozovsk Formation is Late Riphean in age. This conclusion along with detailed mapping proves that the Precambrian “section” of the Amderma Rise is a series of tectonic plates combined in a nonchronostratigraphic order. Volcanic and sedimentary rocks of the Morozovsk and Sokolninsk formations make up the allochthon proper, while carbonate rocks of the Amderma Formation make up the para-autochthon. The high values of δ¹³С (up to +9.5‰) identified in limestones of both formations suggest a considerable distance of the Pai-Khoi paleobasin from the passive margin of the Baltic Region upon facies similarity to the Laurentia active margins.

Large Au-sulfide deposits (GSDs) of disseminated ores occur worldwide in metallogenic provinces of various ages (from Precambrian to Pliocene). The studies performed showed that the great genetic diversity of GSD is determined by the similar oregenesis conditions that appear in different tectono-metallogenic settings (TMSs). A GSD is included in a certain TMS by the respective changes in the mineral and geochemical assemblages of ores. However, in the majority of cases, the GSDs of different TMSs are convergent (quasi-identical) in the texture, structure, and mineral composition of ores. All types of the above TMSs are found in Russia, which allows forecasting the discovery of new GSDs in each setting.

The distribution of large and superlarge mineral deposits (LSMD) of the most important raw materials is correlated with supercontinent cycles in the geological history of the Earth. The latter displays the distinct correlation between metallogenic activity and cyclic global endogenous processes reflected in quasi-regular cycles, which result eventually in the assembly and breakup of supercontinents. In the framework of these cycles, the maximums in the LSMD assembly coincide with periods of intense growth of the subcontinent crust owing to growth of the matter originated from juvenile sources (Kenoran, Columbian cycles) or with epochs of intense recycling of the mature crust (Pangean, Amasian cycles). The Rodinian cycle with minimum activity of these both endogenous processes demonstrates simultaneously minimum metallogenic activity. The distribution of most LSMD types generally follows these main tendencies.

Basaltoids of the Vendian–Cambrian Kulbyurstyug volcanic complex in the eastern part of Kuznetsk Alatau have a high content of titanium (TiO₂ 3–4 wt %). They are relatively enriched with LILE and HFSE (Ba 360–900, Zr 160–726, Nb 66–101, ΣREE up to 225–329 ppm), and demonstrate a fractionated spectrum of REEs (La/Yb ∼ 13–17), high Nb/U (44–66), and low Th/Ta and Th/Nb. These features are comparable with derivatives of OIB (Ocean Island Basalts) magmatism. The rock geochemistry suggests the possible formation of an initial mafic melt in the garnet-bearing peridotite mantle with 2–4% degree of melting and the presence of a small amount of spinel. By the age and composition, the studied volcanics are correlated with the OIB magmatism products, occurring in the adjacent Gorny Altai and also considered to be derivatives of intraplate magmatism of Riphean–Early Cambrian age. This magmatism was caused by plume activity during formation of the Paleo-Asian Ocean.

According to the materials of geochemical study in the core of the ultradeep hole SV-27 of aromatic fractions of bitumoids of the Vilyui syneclise (East Siberia) by the method of chromatography–mass spectrometry, starting from the depth of >5000 m, four diastereomers of previously unknown hydrocarbons, which become predominant in the fraction at a depth of ∼6500 m, were distinguished. Similar hydrocarbons were found in organic matter of Upper Paleozoic rocks of the Kharaulakh anticlinorium in the Verkhoyansk folded area. According to the intense molecular ion m/z 366 and the character of the basic fragmental ions (m/z 238, 309, and 323), the major structure of the compounds studied was determined as 17-desmethyl-23-methylmonoaromatic steroid C₂₇. The absence of such steroids in oil of the Vilyui syneclise shows that deep micro-oils did not participate in the formation of oil fringes of gas condensate deposits of the region.

The results of study of phase equilibria in the MgO–SiO₂–ZrO₂ system at 1450–1550°C are reported. The studied system contains two eutectic points and six fields: (I) MgSiO₃ + SiO₂; (II) MgSiO₃ + ZrO₂; (III) ZrSiO₄ + SiO₂; (IV) MgSiO₃ + Mg₂SiO₄; (V) ZrO₂ + MgO; (VI) ZrSiO₄ + ZrO₂. The presence of fields (II) and (III) on the diagram shows that zircon in equilibrium with olivine and pyroxene crystallizes at very low concentrations of ZrO₂ in the system. This provides a solution for one of the most important problems in zirconology of dunites: the probability of the formation and preservation of zircon in the course of the formation and evolution of dunite.

A new ¹⁹⁰Pt–⁴He method for dating isoferroplatinum has been developed at the Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences. Here we publish the first results of dating of isoferroplatinum from the main mineralogical and geochemical types of PGE mineralization in dunite. The obtained ¹⁹⁰Pt–⁴He age of isoferroplatinum is 129 ± 6 Ma. The gained ¹⁹⁰Pt–⁴He age of isoferroplatinum specimens of different genesis (magmatic, fluid–metamorphogenic, and metasomatic) from the Kondyor Massif indicates that the PGM mineralization took place synchronously and successively with evolution of primarily picrite, followed by subalkaline and alkaline melts of the Mesozoic tectonic–magmatic activation of the Aldan Shield.

Thermodynamic calculations using the HCh software were made for mineral equilibriums including REEs in the fluoride–sulfide–chloride–carbonate–sulfate–system in the presence of Na, Ca, and P with fluids of various acidities–alkalinities [11]. The obtained thermodynamic characteristics of thenardite allowed us to carry out the calculations for this phase under complicated hydrothermal conditions simulating the presence of oxidized fluids at 500–100°C and 2000–125 bar. Among other solid phases, REEs–fluorite, monazite, and REE–F–apatite were formed as CaF₂–(Ln,Y)F₃, LnPO₄, and Ca₅(PO₄)₃F–(Ln,Y)₃(PO₄)₃ ideal solid solutions, respectively, where Ln is La, Ce, Pr, Nd, Sm, Eu, and Gd. Xenotime, anhydrite, elemental sulfur, and calcite were found as well.

The first data on the multi-isotope composition of sulfur (³²S, ³³S, ³⁴S) in samples from the Fennoscandian Shield were obtained by the laser local method. An anomalous concentration of the stable isotope ³³S was registered in some samples. Δ³³S ranges from–0.45 to +0.24‰, which indicates the mass-independent fractionation of S isotopes and provides evidence for the processes of primarily sedimentary accumulation of sulfides in the Archean oxygen-free atmosphere.

A new mineral phase was discovered in the course of studies at the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM) of fine-grained fractions of the lunar regolith delivered to the Earth by the Luna 16, Luna 20, and Luna 24 automatic stations. The grain of native niobium was identified in the regolith sample from the Mare Crisium. Presumably, this phase was formed during the fractioning process in a gas–plasma cloud under an impact event on the Moon.

The Mikhnevo Seismic Group of the Institute of Geosphere Dynamics, Russian Academy of Sciences (IGD RAS), and the Malin mini-group in the region of the Dnieper–Donets aulacogen, within which prospecting and mountain-explosion works were carried out from 2007 to 2015 on industrial scales, recorded a series of seismic events. Special attention has been focused on analysis of the nature of three earthquakes in 2015. Application of the spectral discrimination method log(Pg/Lg) and cross-correlation tools allowed us to identify the seismic events in 2015 as a special technogenic-tectonic type.

The inconsistency between the position of the submarine permafrost table in the East Arctic seas revealed by simulation and anomalies in the distribution of dissolved methane associated with ascending torchlike ejections of bubbling methane made it necessary to develop a representative geophysical express method, which allows the position of the submarine permafrost table to be determined. The method is based on sounding of the generated primary electromagnetic field in the near zone of the medium and measurement of the induced secondary EM field. The reliability of the method is confirmed by core drilling in the Laptev Sea.

This paper considers the results of development of the bilayer hydrosphere concept of the Earth offered by the author in 2000. The bilayering concept is logically based on the classical works in the field of geochemistry and is in the context of mid-twentieth century studies on the structure of the biosphere. The research methods based on this concept are interdisciplinary in nature and make it possible to unify and thereby to facilitate the solution of many problems in the field of oceanology, hydrology and other geographic sciences related to geochemistry.

The interlayers of the cryptotephra of different episodes of the catastrophic eruption of the Baitoushan volcano (Paektu-san, Changbaishan-Tianchi) in the 10th century were discovered in the sedimentary cover of Amur Bay in the Sea of Japan by the geochemical and paleomagnetic characteristics. The petrochemistry of the volcanic glass indicates the possible occurrence of pyroclastic material in the B–Tm layer and more recent episodes that have not been identified before in the sediments of the Sea of Japan. The impact of the eruption on the bay environment is noted. It is shown that the medieval state of Balhae occupying vast areas and adjacent to the volcano no longer existed after the more earlier episodes of eruption.