K-Ar dating of quaternary volcanics: Methodology and interpretation of results     

I. V. Chernyshev  V. A. Lebedev  M. M. Arakelyants 《Petrology》2006,14(1):62-80

The K-Ar method and its modifications play a unique role in the geochronology of young volcanic rocks, which has important fundamental and economic aspects. This method provides an opportunity for dating Quaternary rocks, from the oldest (1–2 Ma) to the most recent ones (<30 ka). This paper discusses physical and geochemical prerequisites for the use of the K-Ar method in the solution of this problem. The key factor providing favorable proportions of radiogenic and nonradiogenic ⁴⁰Ar for the K-Ar system in volcanic rocks is the low solubility of argon (0.n–0.0n ppb) in silicate melts and crystallizing rocks and minerals. The sources and controlling factors of errors in the K-Ar dating of young rocks were evaluated in detail. The main analytical problem in the K-Ar dating of young rocks is concerned with the conditions and methods of measurements of very low (0.0n–0.00n ppb) contents of radiogenic ⁴⁰Ar accompanied by much higher (by a factor of 3–10 or even more) contents of nonradiogenic ⁴⁰Ar. The main stages in the development of the K-Ar method in Russia and other countries that provided a solution to this problem are described. We describe the analytical mass spectrometer system and method designed in the Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, which allowed us to carry out for the first time in Russia systematic studies on the geochronology of Quaternary volcanics up to late Pleistocene-Holocene age. The main characteristics of the method are the absolute sensitivity of measurements (5 × 10^?3 A/Torr) and background signal levels for argon isotopes (3 × 10^?3 ng ⁴⁰Ar and 1 × 10^?5 ng ³⁶Ar). The problems of excess radiogenic argon and variations in the initial ⁴⁰Ar/³⁶Ar ratio in young volcanics are discussed. The results of an investigation of the distribution of K-Ar isotopes among various constituents of young volcanics and the corresponding approach to the choice of material (geochronometer) for analysis are presented. This approach is illustrated by the example of geochronological results for three volcanic centers of the Caucasus differing in the time of occurrence and duration of the active phase: Elbrus, Samsari, and Aragats. A tentative regional time scale was proposed for Neogene-Quaternary magmatic events. This scale generalized the available data for the Greater and Lesser Caucasus and embraces the period from the late Miocene (8.5 Ma) to the late Neopleistocene-Holocene (<35 ka). An interesting feature of the young magmatism of the Caucasus is the synchronous occurrence of distinctive types of volcanic activity in particular volcanic areas. An important prognostic aspect related to the proposed time scale of the young magmatism of the Caucasus is the evidence that the most recent stage of volcanic activity, the youngest occurrences of which were dated at a few thousands to tens of thousands of years, is not yet finished.  相似文献   

Chronicle of the Sixth Conference “Physicochemical and Petrophysical Studies in Earth Sciences” (Moscow,October 3–5, 2005)     

E. B. Lebedev  Yu. S. Genshaft  A. V. Zharikov 《Geochemistry International》2006,44(12):1250-1256

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K-Ar age and Sr-Nd characteristics of subalkali basalts in the Central Georgian Neovolcanic region (Greater Caucasus)     

V. A. Lebedev  I. V. Chernyshev  A. V. Chugaev  O. Z. Dudauri  G. T. Vashakidze 《Doklady Earth Sciences》2006,408(4):657-661

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Modeling Magnetic Tower Jets in the Laboratory     

A. Ciardi  S. V. Lebedev  J. P. Chittenden  D. J. Ampleford  S. N. Bland  B. S. Bott  J. Rapley 《Astrophysics and Space Science》2005,298(1-2):277-286

The twisting of magnetic fields threading an accretion system can lead to the generation on axis of toroidal field loops. As the magnetic pressure increases, the toroidal field inflates, producing a flow. Collimation is due to a background corona, which radially confines this axially growing “magnetic tower”. We investigate the possibility of studying in the laboratory the dynamics, confinement and stability of magnetic tower jets. We present two-dimensional resistive magnetohydrodynamic simulations of radial arrays, which consist of two concentric electrodes connected radially by thin metallic wires. In the laboratory, a radial wire array is driven by a 1 MA current which produces a hot, low density background plasma. During the current discharge a low plasma beta (β < 1), magnetic cavity develops in the background plasma (β is the ratio of thermal to magnetic pressure). This laboratory magnetic tower is driven by the magnetic pressure of the toroidal field and it is surrounded by a shock envelope. On axis, a high density column is produced by the pinch effect. The background plasma has >rsim1, and in the radial direction the magnetic tower is confined mostly by the thermal pressure. In contrast, in the axial direction the pressure rapidly decays and an elongated, well collimated magnetic-jet develops. This is later disrupted by the development of m = 0 instabilities arising in the axial column.  相似文献   

Magnetic tower outflows from a radial wire array Z-pinch     

S. V. Lebedev  A. Ciardi  D. J. Ampleford  S. N. Bland  S. C. Bott  J. P. Chittenden  G. N. Hall  J. Rapley  C. A. Jennings  A. Frank  E. G. Blackman  T. Lery 《Monthly notices of the Royal Astronomical Society》2005,361(1):97-108

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Procedures Used for Airborne Measurements of Upwelling Infrared Radiation     

Lebedev  N. E.  Stanichnyi  S. V. 《Physical Oceanography》2002,12(3):163-172

We analyze the errors of airborne radiometric measurements of the infrared upwelling radiation I _x of the surface performed using conventional and modified procedures (with calibrators in the form of flat reflecting mirror-like surfaces oriented to reflect the measured radiation I _x to the radiometer in the process of calibration) for the modes of operation of a radiometer with and without thermostatic control. We propose relations for finding I _x as well as for the instrumental and procedural errors and give recommendations for their reduction. It is shown that the modified procedure leads to smaller errors than the conventional procedure.  相似文献   

The Paleozoic age of high-pressure metamorphic rocks in the Dakhov Salient, northwestern Caucasus: Results of U-Pb geochronological investigations     

M. L. Somin  O. A. Levchenkov  A. B. Kotov  A. F. Makeev  A. N. Komarov  N. I. Ro  V. A. Lavrishchev  V. A. Lebedev 《Doklady Earth Sciences》2007,416(7):1018-1021

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In memory of Aleksandr Aleksandrovich Mossakovsky (1929–2006)     

K. M. Rychkova  A. D. Duchkov  V. I. Lebedev  I. L. Kamenskii 《Geotectonics》2007,41(2):167-169

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Seasonal variations of the Arabian Sea level anomaly fields and circulation     

V. N. Eremeev  A. N. Zhukov  A. S. Zapevalov  N. E. Lebedev  A. A. Sizov 《Oceanology》2014,54(3):289-297

The changes in the field of the Arabian Sea level anomaly and the geostrophic currents are analyzed based on the data of satellite altimetry measurements in 1993–2008 within the framework of the AVISO project. On the intra-annual scale, the current field generally agrees with the circulation schemes published in a number earlier works. Their differences are due to the occurrence of the mesoscale eddies and jet currents revealed by the authors.  相似文献   

Tenth international conference on physicochemical and petrophysical studies in earth sciences (in Tribute to the Memory of Prof. Yu.S. Genshaft)     

E. V. Lebedev  A. Ya. Saltykovskii  A. V. Zharikov 《Geochemistry International》2011,49(2):207-211

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