Arcanite from Fumarole Exhalations of the Tolbachik Volcano (Kamchatka,Russia) and Its Crystal Structure

The crystal structure (R = 0.0194) of arcanite β-K₂SO₄ was studied on a single crystal from exhalations of the Arsenatnaya fumarole, Tolbachik Volcano (Kamchatka, Russia). The mineral crystallizes at a temperature of ≥350–430°C and associates with langbeinite, aphthitalite, hematite, tenorite, johillerite, and others. Arcanite is orthorhombic, Pnma, a = 7.4763(2) Å, b = 5.77262(16) Å, c = 10.0630(3) Å, V = 434.30(2) ų, Z = 4. Its structure contains isolated SO₄ tetrahedra, whereas K cations center ten- and nine-fold polyhedra.     

First Results of U–Pb LA–ICP–MS Isotope Dating of Detrital Zircons from Arkose Sandstone of the Biryan Subformation of Zilmerdak Formation (Upper Riphean,South Urals)

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.     

Cambrian Magmatism in the Northern Urals: New Data on the Age and Formation Conditions

Cambrian igneous formations in the Northern Urals were identified and described for the first time. It was established that the Timanide orogeny terminated in the Early Cambrian and was followed by continental rifting above a mantle plume in the Late Cambrian.     

Formation of Water-Bearing Defects in Olivine in the Presence of Water–Hydrocarbon Fluid at 6.3 GPa and 1200°C

The main trends of water dissolution in Fe-bearing olivine have been investigated in the olivine–H₂O–hydrocarbon fluid system in experiments at a pressure of 6.3 GPa, a temperature of 1200°C, and hydrogen fugacity ( fH₂) buffered by the Mo–MoO₂ equilibrium. The content and contribution of ОH defects of different types in Fe-bearing olivines depend on the composition of reduced fluids in the system. As the fraction of hydrocarbons in the fluid increases, the H₂O content in olivine crystals decreases from 900 to 160–180 ppm, while the ОН absorption peaks become lower at high frequencies and occupy a larger part of the infrared spectrum in the low-frequency region. According to the experimental results, even the deepest seated mantle olivines with OH defects were not equilibrated with a fluid rich in light alkanes or oxygenated hydrocarbons.     

Foidite and Meimechite Lavas of Polar Siberia (Some Questions of Petrogenesis)

Doklady Earth Sciences - For the Permian–Triassic foidite and meimechite lavas of Polar Siberia, both the whole-rock petrochemistry and geochemistry and that of melt inclusions in olivine...     

The Deep Geoelectrical Section of the Avacha–Koryak Zone of Contemporary Volcanism,Kamchatka

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.

     

Geochemical Features of Cupriferous Sandstones in the Orenburg Area of the Ural Region

The new geochemical data obtained of cupriferous sandstones of the Orenburg area of the Ural region show that the Permian host stratum could have served as the source of rare-earth elements and other microelements for the ore-forming fluids. They confirm the possibility of using a convection model to explain the genesis of the copper ores studied. This model indicates the likely multistage development of mineralization to significant depths, like in the Manto deposits in Chili. Consequently, the Permian cupriferous sandstones of the southwestern area of the Ural region can be considered a very promising source of raw material for the development of copper industry in the area.

     

Electroconducting Elements of the Ultradeep Fluid–Fault Systems as Indicators of Seismically Active Zones of the Eastern Margin of the Eurasian Continent: Evidence from Magnetotelluric Data

Doklady Earth Sciences - A fundamentally new conclusion that zones of high seismic activity are controlled by electroconducting (fluid-saturated) fragments rather than by the entire deep fault is...