Vol 55, No 8 (2017)

Over 60 zircon grains from apoharzburgite serpentinite were dated using SHRIMP–IIe/mc at the Laboratory IBERSIMS of the Granada University (Spain). The apoharzburgite serpentinite represents an oceanic mantle of the Uralian paleoocean, which was exhumed in the crustal structures of the Paleozoic Ural Mobile Belt during obduction. Individual grains span a huge ²⁰⁶Pb/²³⁸U age range from 2740 to 250 Ma and are clustered into six discrete age groups (in Ma): (I) > 2500, (II) 2500–1950, (III) 1260–1210, (IV) 480–400, (V) 370–330, and (VI) < 280. Two last groups were formed under the effect of granitoids on serpentinites. The traces of this effect were studied in outcrops and confirmed by age of zircon from contact talc–carbonate rock. The morphologies of zircon crystals from serpentinite bear signs typical of both magmatic and metamorphic varieties, which indicate their polygenetic–polychronous nature. No striking morphological features and peculiar U and Th contents were found in the studied zircons to discriminate unambiguously between different age groups. Pre-Paleozoic events with ages of groups I–III were found in zircons from many oceanic mantle rocks. The similarity of age groups of zircons from Paleozoic and modern oceanic lithosphere is caused by global mantle reworkings, which provoke magma generation and metasomatism probably accompanied by zircon crystallization.

Physicochemical parameters of the origin of Cu and Mo deposits are reviewed based on an original database that currently includes information from more than 21000 publications on fluid and melt inclusions hosted in various minerals. The deposits are classified into three types: (i) Cu–Mo (usually porphyry), (ii) Cu (usually without Mo but often with base metals), and (iii) Mo (without Cu but often with Be and W). For these deposits, the temperature and pressure of their origin and the density, salinity, and gas composition of the fluids are discussed. The average composition of the dominant volatile components of natural fluids is reported for Cu and Mo deposits and is compared with the composition of volatiles in fluids at Au, Sn, W, Pb, and Zn deposits. Data on individual inclusions are used to evaluate the Cu and Mo concentrations in the magmatic silicate melts and mineral-forming fluids.

The quantitative and qualitative compositions of polycyclic aromatic hydrocarbons (PAHs) were determined, and the vertical stratification of PAHs was characterized along profiles in hummocky tundra peatlands. In perennially frozen peat layers, PAHs occur in a conserved state and do not undergo transformation in contrast to seasonally thawed layers. Statistically significant correlations were detected between the mass fraction of 5–6-ring structures (especially, benzo[ghi]perylene), individual PAHs, and botanical composition of the peat at the thawing–freezing boundary; and profile relations for various combinations of PAHs were calculated. The radiocarbon and paleobotanical analysis of peatlands in combination with the obtained results can be used for assignment of initial vegetation to periods of peat formation in the Holocene and as markers of the response of the peatland permafrost to climate changes at high latitudes.