T. A. Velivetskaya

Geochemistry of stable oxygen and hydrogen isotopes in minerals and corundum-bearing rocks in northern Karelia as an indicator of their unusual genesis

The paper presents newly obtained data on the oxygen and hydrogen isotopic composition of minerals in corundum occurrences and their host rocks in northern Karelia. Minerals in the Khitoostrov and Varaka corundum-bearing zones have extremely low δ18O (lower than −26‰) and δ D (lower than −215‰), which suggest that the mineral-forming process involved glacial waters and that the minerals preserve the isotopic ratios of their protolith. Aluminous corundum plagioclasites were produced by high-pressure Svecofennian (1.9-1.8 Ga) metamorphism of Paleoproterozoic rocks that had been metasomatized with the involvement of meteoric waters during the Guronian glaciation epoch.

Ag-Sb Mineralization of the Yana-Kolyma Belt, Northeast Russia

The mineral assemblages of the Ag-Sb deposits from the Yana-Kolyma Foldbelt were studied. The compositions of ore minerals, the isotopic compositions of sulfur in ore minerals, and the carbon and oxygen in carbonates are given. Arsenopyrite of the deposits is significantly enriched in Sb (1–16 wt %), which is related to the primary enrichment of the ore-hosting sequences in Sb and the ore formation at shallow depths. Based on the fluid inclusions study, the deposits were formed at T = 329–149°C and P = 0.30–1.04 kb from low-salinity chloride-sulfate-bicarbonate solutions enriched in Sb and Ag. The sequence of precipitation of Ag-Sb minerals was mainly controlled by the Sb concentration and the sulfur fugacity and potential in the fluid.

New data on stable isotopes in minerals from corundum-bearing formations of Northern Karelia (Russia)

Corundum occurrences in Northern Karelia at a small number of minerals are characterized by a wide diversity of textural and structural peculiarities. Varia� tions of quantitative relationships, abundance of gen� erations of mineral phases (garnet, amphibole, and plagioclase), and the presence of early corroded min� eral relics in late newly formed assemblages are con� trolled by the zoned structure of the bodies and evolu� tion of parageneses formed in a wide range of temper� atures and pressures [6]. This paper contains the

A Method for Determining Argon Isotopes in a Continuous Helium Flow for K/Ar Geochronology

A new method for the measurement of the argon isotope composition in a continuous helium flow using isotope mass spectrometers is described for potassium-argon geochronology. Argon was extracted from the samples in a chamber with a multiple-sample holder by successively heating the samples with a continuous infrared laser. Argon extracted in the chamber was preconcentrated in a capillary, separated on a chromatographic capillary column in a helium flow, and then injected into the ion source of a mass spectrometer through an open splitter. Measurements of the 36Ar, 38Ar, and 40Ar isotopes were carried out on isotope mass spectrometers in a dynamic mode using a triple-collector ion detector and three electrometric amplifiers. Preliminary experiments on the developed device for measuring argon isotopes in a continuous helium flow have shown that the proposed method can be used for the determination of radiogenic argon in an amount of n × 10−12 g with the accuracy satisfying the solution of many geochronological problems. In sensitivity and reproducibility, the proposed method is highly competitive to the isotope dilution method for measuring argon and simpler than the conventional methods for measuring radiogenic argon.

Stable Carbon Isotope Ratio in Xylotrophic Fungi and Their Substrates

Data on the ratio of stable carbon isotopes in xylotrophic fungi and their xylic substrates are presented for the first time. It is shown that coniferous substrates are more enriched in the heavy carbon isotope, compared to deciduous substrates. In both cases, however, their carbon isotope composition is characterized by low variability and does not correlate with the species or physiological type of decomposer fungus but shows a statistically significant correlation with the degree of wood mineralization. The ratio of stable carbon isotopes in the fungi depends on that in their substrates but is shifted in favor of the heavier isotope. This trophic shift lacks species specificity, is equally manifested in decomposers of deciduous and coniferous substrates, remains unchanged along the latitudinal climatic gradient, and is positively correlated with the carbon isotope composition of substrates, in the absence of correlation with the degree of their mineralization.

Sources of mesozoic polyformation magmatism in the Ketkap-Yuna Igneous Province, Aldan Upland: Isotopic data

The KetkapYuna Igneous Province (KKYuIP) can be considered as a tectonotype of tectonomag� matic activation (TMA) zones within the Aldan Shield. The KKYuIP is represented by a series of mul� tiphase volcanicplutonic edifices of the central type stretching more than 300 km, from Kondyor Ridge (AyanMaya district of Khabarovsk Krai) to South Yakutia, as an arcshaped structure of igneous origin (Fig. 1). Rocks that are coeval and cogenetic to the KKYuIP rocks have been found in 12 areas within the Aldan Shield (2). Their origin corresponds in time to the intensive intraplate magmatism episode in the Late Mesozoic. The foundation age, degree and pattern of deformations, petrogenesis of igneous products, and duration of magmatism in the KKYuIP are the key points required for assessment of the validity of the existing geodynamical models describing evolution of the Siberian continent (5, 14, 15, etc.) and for reveal� ing the fundamental causes of origination and fading of magmatism in TMA zones.

The first data on the oxygen, carbon, and sulfur isotope composition of the Chelyabinsk meteorite

Meteorites are the main source of extraterrestrial material for investigation of regularities of the forma� tion and evolution of solar system matter. The genetic connection of a concrete meteorite to an assumed parental body is based on meteorite classification, which is mostly supported by study of their mineralog� ical and petrographic characteristics, as well as inves� tigation of the bulk chemical composition [1]. In 1973 R. Clayton et al. [2] discovered an anomalous concen� tration of the 17 O isotope in meteorites in comparison with terrestrial rocks. The main differences between terrestrial and extraterrestrial material are controlled by primary isotope heterogeneities in the early solar system. Further investigations of the relative concen� tration of stable isotopes 16 О, 17 О, and 18 O provided the oxygen isotope classification of meteorites and planets and allowed characterization of two important processes of the evolution of the solar system: chemi� cal fractionation and mixing of the components of protoplanetary materials with various isotope compo� sitions [3]. In recent years special attention has been paid to investigation of variations in the stable isotopes in meteorites during genetic identification of meteor� ites and study of the evolution of the matter of the solar system. For this purpose we investigated the oxygen, sulfur, and carbon isotope compositions of a fragment of Chelyabinsk meteorite. Chelyabinsk meteorite rain was registered on Feb� ruary 15, 2013, in Chelyabinsk oblast (Russia). The meteorite was related to the LL group of ordinary chondrites, petrological type 5, shock fraction S4, and weathering degree W0 [4]. An individual fragment of the Chelyabinsk meteorite with a weight of 7 g was used for preparation of bulk samples for the oxygen and carbon isotope analysis. The bulk sample with a total weight of 800 mg was collected from the light part of the meteorite and ground in an agate mortar. None of the chemical methods of treating was applied, since the weathering degree of the Chelyabinsk meteorite was zero (W0). A section with a thickness of 3 mm was cut from the meteorite fragment and polished for local analysis of the sulfur isotope composition.

Fractionation of stable nitrogen and carbon isotopes during oxidative conversion of organic matter of the woody pool forest ecosystems

369 Reductive conversion of atmospheric CO 2 in the woody pool of forest ecosystems results in accumulaa tion of large masses of carbon (for example, 240 Mt of CO 2 –C are deposited annually in the forests of Russia [1, p. 24]) and in a change in the isotopic composition of carbon towards enrichment in light isotopes relative to the composition of atmospheric CO 2 [2]. The subb sequent stage of the biogeochemical cycle, occurring on a scale similar to that of photosynthesis and deterr mining the isotope composition of the organic matter of the woody pool, is organic matter destruction by xylotrophic fungi [3, 4]. However, fractionation of staa ble isotopes of biogenic elements during the degradaa tion of woody debris by xylotrophic fungi was not investigated previously. The present paper is the first to describe the fracc tionation of stable carbon and nitrogen isotopes durr ing the oxidative conversion of organic matter of the woody pool by fungi in forest ecosystems of northern Eurasia and to elucidate the significance of this phee nomenon for the biosphere. The objects of research included polypores fungi most commonly occurring in the boreal region of northern Eurasia. Samples of wood infected by fungi (below, referred to as wood substrates) and fruit bodies of fungi collected in all major forest zones of Western Siberia (the northern, middle, and southern taiga, subtaiga, and forest–steppe zones) were used for the isotope analysis. A total of 124 samples of substrates and fruit bodies were analyzed; the set of fungi included Bjerkandera adusta (Fr. East Branch of the Russian Academy of Sciences using a Flash EA 1112 elemental analyzer (ThermoFinnii gan, Germany) coupled to a MAT 253 isotopic mass spectrometer (ThermoFinnigan, Germany). The results of the analysis are represented in the convenn tional form:

Chemical composition and geochemical characteristics of the Koksharovka alkaline ultrabasic massif with carbonatites, primorye

New geochemical data are discussed on the magmatic complexes of the Koksharovka alkaline ultrabasic massif of Late Jurassic age obtained by the ICP-MS method. Based on the first results on rare earth geochemistry of carbonatites and associating pyroxenites and geological observations, the magmatic origin of the Koksharovka carbonatites was substantiated, and the problems of formation of accompanying igneous rocks were considered.

The first data on mass-independent fractionation of sulfur isotopes in sulfides from rocks of the eastern part of the Fennoscandian Shield

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.