Search Results - (Author, Cooperation:V. Melezhik)

2011-12-07

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

*Atmosphere ; Carbon Cycle ; Carbon Isotopes/*analysis ; Carbonates ; *Earth (Planet) ; Geologic Sediments/*chemistry ; Nitrogen Isotopes/analysis ; Organic Chemistry Processes ; Oxidation-Reduction ; *Oxygen ; Russia ; Time

1432-1866

Springer Online Journal Archives 1860-2000

Geosciences

Abstract Fourteen stratiform, stratabound and vein-type sulphide occurrences in the Upper Allochthon of the Central–North Norwegian Caledonides have been studied for their sulphur, oxygen and hydrogen isotope composition. Depositional ages of host rocks to the stratabound and stratiform sulphide occurrences range from 590 to 640 Ma. The sulphides and their host rocks have been affected by polyphase deformation and metamorphism with a peak temperature of 650 °C dated to 432 Ma. A total of 104 sulphide and 2 barite samples were analysed for δ34S, 16 whole-rock and quartz samples for δ18O and 12 samples of muscovite for δD. The overall δ34S values range from −14 to +31‰ with the majority of sampled sulphides lying within a range of +4 to +15‰. In most cases δ34S within each hand specimen behaves in accordance with the equilibrium fractionation sequence, δ34Sgn〈δ34Scp〈δ34Ssph〈δ34Spy. A systematic increase in δ34S from the vein sulphides (−8‰) through schist/amphibolite-hosted (+6‰) and schist-hosted (+7 to +12‰) to dolomite-hosted (+12 to +31‰) occurrences is documented. The δ34S averages of the stratiform schist-hosted sulphides are 17 to 22‰ lower than in the penecontemporaneous seawater sulphate. The Bjørkåsen (+4 to +6‰) occurrence is a volcanogenic massive sulphide (VMS) transitional to sedimentary massive sulphide (SMS), exhalative, massive, pyritic deposit of Cu–Zn–Pb sulphides formed by fluids which obtained H2S via high-temperature reduction of seawater sulphate by oxidation of Fe2+ during the convective circulation of seawater through underlying rock sequences. The Raudvatn, volcanic-hosted, disseminated Cu sulphides (+6 to +8‰) obtained sulphur via a similar process. The Balsnes, stratiform, ‘black schist’-hosted, pyrite–pyrrhotite occurrence (−6 to −14‰) is represented by typical diagenetic sulphides precipitated via bacteriogenic reduction of coeval (ca. 600 Ma) seawater sulphate (+25 to +35‰) in a system open to sulphate supply. The δ34S values of the Djupvik–Skårnesdalen (+7 to +12‰), Hammerfjell (+5 to 11‰), Kaldådalen (+10 to +12‰) and Njallavarre (+7 to +8‰) stratiform, schist-hosted, massive and disseminated Zn–Pb (±Cu) sulphide occurrences, as well as the stratabound, quartzite-hosted, Au-bearing arsenopyrite occurrence at Langvatnet (+7 to +11‰), suggest that thermochemically reduced connate seawater sulphate was a principal sulphur source. The Sinklien and Tårstad, stratabound, dolomite- and dolomite collapse breccia-hosted, Zn (±Cu–Pb) sulphides are marked by the highest enrichment in 34S (+20 to +31‰). The occurrences  are assigned to the Mississippi-Valley-type deposits. High δ34S values require reduction/replacement of contemporaneous (ca. 590 Ma) evaporitic sulphate (+23 to +34‰) with Corg-rich fluids in a closed system. The Melkedalen (+12 to +15‰), stratabound, fault-controlled, Cu–Zn sulphide deposit is hosted by the ca. 595 Ma dolomitised Melkedalen marble. The deposit is composed of several generations of ore minerals which formed by replacement of host dolomite. Polyphase hydrothermal fluids were introduced during several reactivation episodes of the fault zone. The positive δ34S values with a very limited fractionation (〈3‰) are indicative of the sulphide-sulphur generated through abiological, thermochemical reduction of seawater sulphate by organic material. The vein-type Cu (±Au–W) occurrences at Baugefjell, Bugtedalen and Baugevatn (−8 to −4‰) are of hydrothermal origin and obtained their sulphur from igneous sources with a possible incorporation of sedimentary/diagenetic sulphides. In a broad sense, all the stratiform/stratabound, sediment-hosted, sulphide occurrences studied formed by epigenetic fluids within two probable scenarios which may be applicable separately or interactively: (1) expulsion of hot metal-bearing connate waters from deeper parts of sedimentary basins prior to nappe translation (late diagenetic/catagenetic/epigenetic fluids) or (2) tectonically driven expulsion in the course of nappe translation (early metamorphic fluids). A combination of (1) and (2) is favoured for the stratabound, fault-controlled, Melkedalen and Langvatnet occurrences, whereas the rest are considered to have formed within option (1). The sulphides and their host rocks were transported from unknown distances and thrust on to the Fennoscandian Shield during the course of the Caledonian orogeny. The displaced/allochthonous nature of the Ofoten Cu–Pb–Zn ‘metallogenetic province’ would explain the enigmatically high concentration of small-scale Cu–Pb–Zn deposits that occur only in this particular area of the Norwegian Caledonides.

Electronic Resource

1572-9540

Springer Online Journal Archives 1860-2000

Physics

Abstract The cross-sections for low-energy scattering of muonic hydrogen on hydrogen molecules are calculated in a semi-classical approach. The molecular binding is described with the “mass-tensor approach” and the electronic screening corrections are calculated in the Glauber approximation. This rather simple computational scheme is applied to the scattering dµ + H2 and pµ + D2. The results obtained are in good agreement with the values reported by Adamczak et al.

Electronic Resource

1572-9540

Springer Online Journal Archives 1860-2000

Physics

Abstract The results of calculations of the total cross sections of spin-flip processes in low energy muonic hydrogen scattering on hydrogen molecules are presented. These calculations are based on the respective set of cross sections for muonic hydrogen scattering on hydrogen nuclei, obtained within the framework of the multichannel adiabatic method. All combinations of the three hydrogen isotopes are considered. Molecular binding effects are described in terms of the Fermi pseudopotential method. Electron screening effects are calculated in the distorted wave Born approximation. Rotational and vibrational transitions of the molecules, due to collisions with muonic hydrogen atoms, are taken into account. The molecular and electron screening corrections do not exceed a few tens per cent for lowest collision energies.

Electronic Resource

1573-9333

Springer Online Journal Archives 1860-2000

Mathematics

Physics

Abstract A system of three quantum particles with internal structure in which the two-body interactions are point interactions and are described in terms of two-channel Hamiltonians is considered. It is established that in the cases when the parameters of the model are such that the total Hamiltonian of the three-particle system is semibounded the Faddeev equations are Fredholm equations. Boundary conditions are formulated for the differential Faddeev equations whose solutions are the scattering wave functions.

Electronic Resource

1573-9333

Springer Online Journal Archives 1860-2000

Mathematics

Physics

Abstract Three-body systems with point-like interactions and internal structures are considered. A complete classification of these systems is carried out and the conditions for the corresponding energy operators to be semi-bounded from below are studied.

Electronic Resource

1434-6079

34.50.-s ; 36.10.Dr

Springer Online Journal Archives 1860-2000

Physics

Abstract Electron screening corrections to the cross sections for low energy scattering of muonic hydrogen on hydrogen atoms are calculated. It is shown that the presence of the electron influences considerably the elastic cross sections at collision energies below 1 eV. This influence is relatively small for the spin-flip and isotopic exchange processes.

Electronic Resource

1572-9540

muon-catalyzed fusion ; muonic hydrogen ; muonic atoms ; muonic molecules

Springer Online Journal Archives 1860-2000

Physics

Abstract Preliminary results are reported for an experiment at TRIUMF where a time-of-flight technique was tested for measuring the energy dependence of the rate for muon-catalyzed dt fusion. Muonic tritium atoms were created following transfer of negative muons from muonic protium in a layer of solid hydrogen (protium) containing a small fraction of tritium. The atoms escaped from the solid layer via the Ramsauer-Townsend mechanism, traversed a drift region of 18 mm, and then struck an adjacent layer of deuterium, where the muonic atom could form a molecular system. The time of detection of a fusion product (neutron or alpha) following muon arrival is dependent upon the energy of the muonic tritium atom as it traverses the drift region. By comparison of the time distribution of fusion events with a prediction based on the theoretical energy dependence of the rate, the strength of resonant formation can in principle be determined. The results extracted so far are discussed and the limitations of the method are examined.

Electronic Resource

1572-9540

Springer Online Journal Archives 1860-2000

Physics

Abstract A numerical scheme for solving the problem of slow collisions in the three-body adiabatic approach is applied for calculation of muon transfer rates in collisions of hydrogen isotope atoms on bare nuclei. It is demonstrated that the multichannel adiabatic approach allows to reach high accuracy results (∼3%) estimating the cross sections of charge transfer processes which are the best ones up to the present time. The method is applicable in a wide range of energies (0.001–50 eV) which is of interest for analysis of muon catalysed fusion experiments.

Electronic Resource