Modelling of thermochemical plumes and implications for the origin of the Siberian traps     

Nickolay L. Dobretsov  Alexey A. Kirdyashkin  Anatoliy G. Kirdyashkin  Valery A. Vernikovsky  Igor N. Gladkov 《Lithos》2008,100(1-4):66-92

Thermochemical plumes form at the base of the lower mantle as a consequence of heat flow from the outer core and the presence of local chemical doping that decreases the melting temperature. Theoretical and experimental modelling of thermochemical plumes show that the diameter of a plume conduit remains practically constant during plume ascent. However, when the top of a plume reaches a refractory layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped plume head develops. Main parameters (melt viscosity, ascent time, ascent velocity, temperature differences in the plume conduit, and thermal power) are presented for a thermochemical plume ascending from the core–mantle boundary. In addition, the following relationships are developed: the pressure distribution in the plume conduit during the ascent of a plume, conditions for eruption-conduit formation, the effect of the P–T conditions and controls on the shape and size of a plume top, heat transfer between a thermochemical plume and the lithosphere (when the plume reaches the bottom of a refractory layer in the lithosphere), and eruption volume versus the time interval t₁ between plume formation and eruption. These relationships are used to determine thermal power and time t₁ for the Tunguska syneclise and the Siberian traps as a whole.

The Siberian and other trap provinces are characterized by giant volumes of lavas and sills formed a very short time period. Data permit a model for superplumes with three stages of formation: early (variable picrites and alkali basalts), main (tholeiite plateau basalts), and final (ultrabasic and alkaline lavas and intrusions). These stages reflect the evolution of a superplume from the ascent of one or several independent plumes, through the formation of thick lenses of mantle melts underplating the lithosphere and, finally, intrusion and extrusion of differentiated mantle melts. Synchronous syenite–granite intrusions and bimodal volcanism abundant in the margins of the Siberian traps are the result of melting of the lower crust at depths of 65–70 km under the effect of plume melts.  相似文献   

Jusa and Barsuchi Log Volcanogenic Massive Sulfide Deposits from the Southern Urals of Russia: Devonian Analogs of the Kuroko Deposits of NE Honshu, Japan     

Geoffrey P. Glasby    Valery V. Maslennikov    Irina A. Prozherova  Sergey I. Petukhov 《Resource Geology》2008,58(3):313-324

Chemical analysis of 60 samples from the Jusa and Barsuchi Log volcanogenic massive sulfide (VMS) deposits by inductively coupled plasma–mass spectrometry shows that, on average, the Jusa deposit is more enriched in the chalcophilic elements than the Barsuchi Log deposit, whereas the Barsuchi Log deposit is more enriched in the lithogenous elements and Te. In addition, the yellow ores in these deposits are more enriched on average in Cu, As and Mo and the black ores more enriched in Zn, Ga, Cd, Sb, Ba , Hg and Pb relative to each other. Both these deposits are similar in composition to the Kuroko deposits of NE Honshu and may be considered to be analogs of these deposits. The Kuroko deposits, however, contain much higher concentrations of As, Ag, Sb, Ba, Hg and lower contents of Te on average than the Jusa and Barsuchi Log deposits. Based on the higher contents of Te in the Barsuchi Log deposit compared to the Jusa deposit, as well as on textural considerations, it is concluded that the Barsuchi Log deposit is intermediate between the Urals- and Kuroko-type deposits, whereas the Jusa deposit is more analogous to the Kuroko-type deposits. Based on the compositional data presented here, the Jusa and Barsuchi Log deposits may be described as Zn-Pb-Cu-Ba deposits rather than as Zn-Cu-Ba deposits, as the Baimak-type deposits of the west Magnitogrosk zone have previously been described.  相似文献   

The amphipod Orchomenella pinguis – A potential bioindicator for contamination in the Arctic     

Lis Bach  Valery E. Forbes  Ingela Dahllf 《Marine pollution bulletin》2009,58(11):1664-1670

Indigenous organisms can be used as bioindicators for effects of contaminants, but no such bioindicator has been established for Arctic areas. Orchomenella pinguis is a benthic amphipod, ubiquitous in the Arctic and can be found in high numbers. We collected O. pinguis at sites with different contamination levels. Population characteristics (body length distribution, average dry weight and amphipod organic content) were related to sediment contaminant concentrations, in order to identify suitable endpoints for using this species as a bioindicator. We show that O. pinguis was prevalent in both clean and contaminated areas, easy to sample and that its population characteristics could be linked to both contamination and sediment organic content. We suggest that O. pinguis is a suitable bioindicator for the Arctic, but that endpoints such as reproductive effects and phenotypic and genotypic responses are needed together with population characteristics to assess impacts of contamination.  相似文献   

A possible mechanism of stimulation of seismic activity by ionizing radiation of solar flares     

Valery M. Sorokin  Alexey K. Yashchenko  Victor A. Novikov 《地震科学（英文版）》2019,32(1):26-34

A possible mechanism of earthquake triggering by ionizing radiation of solar flares is considered. A theoretical model and results of numerical calculations of disturbance of electric field, electric current, and heat release in lithosphere associated with variation of ionosphere conductivity caused by absorption of ionizing radiation of solar flares are presented. A generation of geomagnetic field disturbances in a range of seconds/tens of seconds is possible as a result of large-scale perturbation of a conductivity of the bottom part of ionosphere in horizontal direction in the presence of external electric field. Amplitude-time characteristics of the geomagnetic disturbance depend upon a perturbation of integral conductivity of ionosphere. Depending on relation between integral Hall and Pedersen conductivities of disturbed ionosphere the oscillating and aperiodic modes of magnetic disturbances may be observed. For strong perturbations of the ionosphere conductivities amplitude of pulsations may obtain ~10² nT. In this case the amplitude of horizontal component of electric field on the Earth surface obtains 0.01 mV/m, electric current density in lithosphere –10^–6 A/m², and the power density of heat release produced by the generated current is 10^–7 W/m³. It is shown that the absorption of ionizing radiation of solar flares can result in variations of a density of telluric currents in seismogenic faults comparable with a current density generated in the Earth crust by artificial pulsed power systems (geophysical MHD generator " Pamir-2” and electric pulsed facility " ERGU-600”), which provide regional earthquake triggering and spatiotemporal variation of seismic activity. Therefore, triggering of seismic events is possible not only by man-made pulsed power sources but also by the solar flares. The obtained results may be a physical basis for a novel approach to solve the problem of short-term earthquake prediction based on electromagnetic triggering phenomena.  相似文献   

Grid computing for atmospheric composition studies in Bulgaria     

Angelina Todorova  Dimiter Syrakov  Georgi Gadjhev  Georgi Georgiev  Kostadin G. Ganev  Maria Prodanova  Nikolai Miloshev  Valery Spiridonov  Andrej Bogatchev  Kiril Slavov 《Earth Science Informatics》2010,3(4):259-282

Three Grid applications from the SEE-GRID-SCI Environmental VO are developed by the Bulgarian project team: Climate Change Impact on Air Quality (CCIAQ); Multi-scale atmospheric composition modeling (MSACM); Modeling System for Emergency Response to the Release of Harmful Substances in the Atmosphere (MSERRHSA). The three applications concern problems of significant socio-economic significance. They are all dedicated to air pollution studies, but address different goals and so face different problems and requirements. The applications are briefly presented in the paper. Examples of the different applications validations are given. Some application results are shown and commented.  相似文献   

On the covering of a Hill’s region by solutions in the restricted three-body problem     

Valery Kozlov  Ivan Polekhin 《Celestial Mechanics and Dynamical Astronomy》2017,127(3):331-341

We consider two classical celestial-mechanical systems: the planar restricted circular three-body problem and its simplification, the Hill’s problem. Numerical and analytical analyses of the covering of a Hill’s region by solutions starting with zero velocity at its boundary are presented. We show that, in all considered cases, there always exists an area inside a Hill’s region that is uncovered by the solutions.  相似文献   

Huge Ice‐age lakes in Russia     

Jan Mangerud  Valery Astakhov  Martin Jakobsson  John Inge Svendsen 《第四纪科学杂志》2001,16(8):773-777

During an early phase of the Last Ice Age (Weichselian, Valdaian), about 90 000 yr ago, an ice sheet formed over the shallow Barents and Kara seas. The ice front advanced on to mainland Russia and blocked the north‐flowing rivers (Yenissei, Ob, Pechora, Dvina and others) that supply most of the freshwater to the Arctic Ocean. The result was that large ice‐dammed lakes were formed between the ice sheet in the north and the continental water divides to the south. Here we present reconstructions and calculations of the areas and volumes of these lakes. The lake on the West Siberian Plain was nearly twice as large as the largest lake on Earth today. The well‐mapped Lake Komi in northeast Europe and a postulated lake in the White Sea Basin would also rank before the present‐day third largest lake. The lakes overflowed towards the south and thus the drainage of much of the Eurasian continent was reversed. The result was a major change in the water balance on the continent, decreased freshwater supply to the Arctic Ocean, and increased freshwater flow to the Aral, Caspian, Black and Baltic seas. A sudden outburst of the lakes' water to the Arctic Ocean when the ice sheet thinned is postulated. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Pleistocene glaciations of northern Russia – a modern view     

Valery I. Astakhov 《Boreas: An International Journal of Quaternary Research》2013,42(1):1-24

The size, age and dynamics of Pleistocene glaciers, especially ice sheets that periodically covered the northern seaboard of Eurasia, are crucial for understanding the evolution of arctic climates, sea‐level changes, the biota and tectonism. General ideas on the glacial history of the vast areas of northern Russia between 48° and 148°E, beyond the limits of the Fennoscandian glaciation, have considerably changed during the last two decades. The change towards modern views may even be considered as a paradigm shift from the conventional wisdom of the previous half‐century. The transformation of the main landmarks of late Quaternary glacial history started in the 1970s and accelerated after 1993 as a result of international collaboration in the Russian Arctic. A wealth of new sedimentological, geomorphic and stratigraphic data has recently accumulated for the sedimentary record of the last 200 ka. This information, together with data collected from native geological surveys, has been synthesized in the form of digital maps of ice limits based on key stratigraphic sites. The results have been published as contributions to the international programs QUEEN and APEX and also as parts of global compilations. These publications give general overviews of the Eurasian glacial history, but some important modern data are reported only in the Russian literature and therefore are hardly known to the international community. In this paper I will first consider the background material on the non‐Scandinavian glaciations and then follow this with a review of the modern results obtained in the course of international cooperation. The outcome is inevitably influenced (or biased) by my long‐term experience in studying the Pleistocene of northern Russia. I will not discuss here the extreme northeast of Siberia (western Beringia), as this is a distinct topic partly overviewed in recent publications.  相似文献   

Holocene Treeline History and Climate Change Across Northern Eurasia   总被引：1，自引：0，他引：1  

Glen M. MacDonald  Andrei A. Velichko  Constantine V. Kremenetski  Olga K. Borisova  Aleksandra A. Goleva  Andrei A. Andreev  Les C. Cwynar  Richard T. Riding  Steven L. Forman  Tom W. D. Edwards  Ramon Aravena  Dan Hammarlund  Julian M. Szeicz  Valery N. Gattaulin 《Quaternary Research》2000,53(3):302

Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P. Forest establishment and retreat was roughly synchronous across most of northern Russia. Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5° to 7.0°C warmer than modern. The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level, and extreme Arctic penetration of warm North Atlantic waters. The late Holocene retreat of Eurasian treeline coincides with declining summer insolation, cooling arctic waters, and neoglaciation.  相似文献   

Ejecta deposition after oblique impacts: An influence of impact scale     

Valery SHUVALOV 《Meteoritics & planetary science》2011,46(11):1713-1718

Abstract– Simple estimates suggest that ejecta blankets around larger craters should be more asymmetric than around smaller craters for the same oblique impact angle. Numerical simulations presented in the paper confirm that an increase in the scale of gravity‐dominated craters (and in the size of the corresponding projectiles) increases the asymmetry of both impact craters and ejecta blankets around them.  相似文献