Vol 55, No 7 (2017)

We present the results of electrochemical measurements of the intrinsic oxygen fugacity of olivine separates representing seven rock types from the central part and southwestern termination of the Yoko–Dovyren mafic—ultramafic massif. The \({f_{{O_2}}}\) values were determined using a high-temperature solid-electrolyte double-cell assembly developed at the Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. A total of 59 experiments were performed (from 7 to 16 for each sample) at the atmospheric pressure and within the temperature range of 800–1050°C at the 30–50°C increment. The results were interpreted using the calculated log \({f_{{O_2}}}\) – 1/T(K) and log \({f_{{O_2}}}\) – T(°C) dependences. It was shown that the subsolidus temperature range of the rocks (below ~1050°C) is characterized by lowest intrinsic oxygen fugacity of olivine, which is 1–4 log units below the QFM buffer. For the solidus temperatures of ~1100°C, the more oxidized conditions ranging approximately from QFM to ~QFM-3 were measured. Extrapolating the log \({f_{{O_2}}}\) – T°C dependences to the temperatures of the original magmas (~1200–1300°C) produces the maximum scatter in oxygen fugacities from ~QFM+2.5 to QFM-1. The estimated range of redox conditions for the Dovyren magma crystallization lies between the QFM and ~QFM-2.5 buffer equilibria. This is consistent with the complete absence of primary magmatic titanomagnetite and the presence of ilmenite in the Dovyren rocks.

The study of coronitic textures in ferrogabbros and data on rhythmic layering of the Elet’ozero Massif supports the existence of a specific low-temperature Fe-rich liquid in nature. This liquid was formed during solidification of intrusion owing to the local multiple accumulation of Fe and Ti contents in a parental Fe-rich Fe–Ti basaltic melt. According to obtained data, this occurred on micro- and macroscale: 1) in the interglanular (intercumulus) space of the crystallization zone where intercumulus melt becomes rich in Fe and Ti owing to the crystallization of cumulus silicate minerals and is transformed into Fe-rich liquid, which concentrates residual components of an intergranular melt; 2) during formation of rhythmic layering when Fe-rich residual melt is accumulated before the upper part of the moving front of solidification; when Fe content reaches a certain limit, the melt is also transformed in a separate Fe-rich liquid, the interlayers of which form the upper (lowest temperature) members of rhythms. It was concluded that the emergence of a Fe-rich melt is related to its specific structure, which is formed when the Fe content reaches certain critical values in a liquid. Thus, this liquid is not a product of immiscible splitting of a melt, but represents a peculiar phenomenon. The preservation of primary textures and structures of the rocks is supposedly related to the lyophobic properties of surfaces, i.e., “repulsion” of nonwetting liquid by facets of cumulus crystals, especially plagioclase. Owing to this, the drops and even horizons of heavy Fe-rich liquid are retained in situ of their formation.

The paper presents results of radiocological monitoring at the site of the Kraton-3 accidental underground nuclear test in Yakutia. The distribution and migration of ¹³⁷Cs, ⁹⁰Sr, ²³⁷Np, and ^238–240Pu in the soil and its living cover of the northern taiga are analyzed, and it is demonstrated that the radioecological conditions at the territory are still adverse in spite of the rehabilitation measures.

The paper presents pioneering data on the composition of pyroxenes and the distribution of trace elements in this mineral in small geological bodies that were formed by single magma injections and their subsequent rapid crystallization: the Niva intrusion and an agpaitic syenite dyke. The pyroxene is highly alkaline and shows continuous compositional trends with an increase in the aegirine concentration. The Ti concentrations of the pyroxene are much higher than in pyroxenes in agpaitic syenites in other alkaline complexes. In spite of the fact that the pyroxene is hosted in small bodies, the evolution of these pyroxenes was similar to that of pyroxenes in the Lovozero and Khibina alkaline massifs.