How contact metamorphism can trigger global climate changes: Modeling gas generation around igneous sills in sedimentary basins   总被引：2，自引：0，他引：2  

Ingrid Aarnes  Henrik Svensen  Yuri Y. Podladchikov 《Geochimica et cosmochimica acta》2010,74(24):7179-7195

Large volumes of greenhouse gases such as CH₄ and CO₂ form by contact metamorphism of organic-rich sediments in aureoles around sill intrusions in sedimentary basins. Thermogenic gas generation and dehydration reactions in shale are treated numerically in order to quantify basin-scale devolatilization. We show that aureole thicknesses, defined as the zone of elevated metamorphism relative to the background level, vary within 30-250% of the sill thickness, depending on the temperature of the host-rock and intrusion, besides the sill thickness. In shales with total organic carbon content of >5 wt.%, CH₄ is the dominant volatile (85-135 kg/m³) generated through organic cracking, relative to H₂O-generation from dehydration reactions (30-110 kg/m³). Even using conservative estimates of melt volumes, extrapolation of our results to the scale of sill complexes in a sedimentary basin indicates that devolatilization can have generated ∼2700-16200 Gt CH₄ in the Karoo Basin (South Africa), and ∼600-3500 Gt CH₄ in the Vøring and Møre basins (offshore Norway). The generation of volatiles is occurring on a time-scale of 10-1000 years within an aureole of a single sill, which makes the rate of sill emplacement the time-constraining factor on a basin-scale. This study demonstrates that thousands of gigatons of potent greenhouse gases like methane can be generated during emplacement of Large Igneous Provinces in sedimentary basins.  相似文献   

Density variations in the thickened crust as a function of pressure, temperature, and composition     

Julia Semprich  Nina S. C. Simon  Yuri Yu. Podladchikov 《International Journal of Earth Sciences》2010,99(7):1487-1510

Constraints on density as a function of pressure, temperature, and composition are crucial to understand isostatic movements during geodynamic processes. Here, we provide a systematic series of density diagrams extracted from thermodynamic calculations for a variety of crustal compositions within a wide P–T range. We quantify systematic density changes in collisional settings for relevant compositional variations and attempt to simplify the density–composition relationships. Rock densities depend strongly on pressure, temperature, and composition. Densities at some selected pressure–temperature conditions increase linearly with increasing Al₂O₃ as well as MgO/FeO contents in pelitic rocks. Al- and Fe-rich pelites yield the highest densities, which is mostly due to the formation of garnet but also depends on other minerals and changes of reactions. The effect of loading on densities is investigated, and we show that for deep burial, a meta-pelite rich in Fe and Mg yields much larger density changes than a dry basalt and that the burial of such a rock with a composition close to typical lower crust may result in significant negative buoyancy. Metamorphism of hydrous lower crust due to pressurization and heating thus leads to densification of thickened lower crust, while heating of dry crust leads to a decrease in density. Hence, water-loaded isostatic subsidence due to metamorphism of water-saturated lower crust is substantial and increases with the thickness and depth of the reacting layer, while dry compositions show much less or only transient densification and subsidence. The density change due to thermal expansion, an extensively used concept in geodynamic models, predicts uplift under the same P–T conditions and is an order of magnitude smaller than the density variation calculated from petrologically consistent diagrams.  相似文献   

Mollisols properties and changes in Ukraine and China   总被引：4，自引：2，他引：2  

Yuri S KRAVCHENKO  Richard M CRUSE 《中国地理科学(英文版)》2011,21(3):257-266

Soils are the foundation of civilizations and the basis for human food production.Mollisols in Ukraine and Northeast China are two out of the four major Mollisol regions in the world.The natural areas from which Mollisols developed are the prairies and steppes that experience temperate and freezing conditions.This review paper introduces the general climate,vegetation,and topography of Mollisols regions in Ukraine and Northeast China,analyzes their properties,including soil texture,soil organic matter content,soil bulk density,pH,cation exchange capacity and other chemical properties,and compares the property changes and management practices of Mollisols in relation to sustainable grain production.  相似文献   

Starbursts near supermassive black holes: young stars in the Galactic Centre, and gravitational waves in LISA band     

Yuri Levin 《Monthly notices of the Royal Astronomical Society》2007,374(2):515-524

  相似文献   

Thermophysical Modelling of Comet P/Borrelly Effects of Volume Energy Absorption and Volume Sublimation     

Skorov  Yuri V.  Keller  Horst U.  Jorda  Laurent  Davidsson  Bjørn J. R. 《Earth, Moon, and Planets》2002,90(1-4):293-303

In this work, we continue revising the theoretical basis ofnumerical models describing the transport of matter andenergy inside a porous dust-ice mixture at low temperature. Amodel of a light-absorbing near-surface layer of a comet nucleus isinvestigated. Gas transport is considered simultaneously with thesolution of the general heat transfer equation. Thequasi-stationary temperature distribution and the H₂O massflux and sublimation rate are computed for a nucleus model ofcomet 19P/Borrelly at the Deep Space 1 (DS1) encounter. Theenergy is deposited in a layer of about 20 particle radii: Thiscorresponds to a solid-state greenhouse effect. The surfacetemperature of the layer-absorbing model as well as the gasproduction rate are significantly smaller than the ones in thesurface-absorbing model. An active fraction of 40–50% would berequired to explain the observed water production rate ofP/Borrelly with our layer-absorption model at the time of the DS1encounter.  相似文献   

The influence of gravitational acceleration on the supernova-driven Parker instability     

Adriane Steinacker †  Yuri A. Shchekinov 《Monthly notices of the Royal Astronomical Society》2001,325(1):208-220

Within a framework of 2D magnetohydrodynamic (MHD) simulations, we explore the dynamical regimes initiated by a supernova explosion in a magnetized stratified interstellar medium (ISM). We concentrate on the formation of large-scale magnetic structures and outflows connected with the Parker instability. For the sake of simplicity we only show models with a fixed explosion energy corresponding to a single supernova (SN) occurring in host galaxies with different fixed values of the gravitational acceleration g and different ratios of specific heats. We show that in general, depending on these two parameters, three different regimes are possible: a slowly growing Parker instability on time-scales much longer than the galactic rotation period for small g; the Parker instability growing at roughly the rotation period, which for ratios of specific heats larger than one is accompanied by an outflow resulting from the explosion for intermediate g; and a rapidly growing instability and a strong blow-out flow for large g . By means of numerical simulations and analytical estimates we show that the explosion energy and gravitational acceleration which separate the three regimes scale as Eg ²∼constant in the 2D case. We expect that in the 3D case this scaling law is Eg ³∼constant . Our simulations demonstrate furthermore that a single SN explosion can lead to the growth of multiple Parker loops in the disc and large-scale magnetic field loops in the halo, extending over 2–3 kpc horizontally and up to 3 kpc vertically above the mid-plane of the disc.  相似文献   

Current climate change effects on the ground thermal regime in Central Yakutia     

Stepan Varlamov  Yuri Skachkov  Pavel Skryabin 《寒旱区科学》2014,6(4):0282-0292

The evolution of ground thermal state has been studied to assess impacts of current climatic warming on permafrost in Central Yakutia. The analysis of long-term data of regional weather stations has revealed one of the highest increasing trends in mean annual air temperature in northern Russia. A forecast of surface air temperature fluctuations has been made by applying a frequency analysis method. Monitoring of ground thermal conditions allows us to identify inter-annual and long-term variability among a wide range of natural conditions. Experimental research has indicated a long-term dynamics of ground thermal state evolution： ground temperatures at the depth of zero annual amplitude and seasonally thawed layer depth. Long-term variability of thaw depth shows near-zero to weak positive trends in small valleys in contrast to weak negative trends on slopes. With significant climatic warming, the thermal state of near-surface layers of permafrost demonstrates steadiness. Anthropogenic impacts on ground thermal regime in various terrain types have been qualitatively evaluated. Clear-cutting, ground cover stripping, and post-fire deforestation in inter-alas type terrains result in a significant increase of temperature and seasonal ground thaw depth, as well as adverse cryogenic processes. The dynamics of mean annual ground temperature in slash and burn sites have been evaluated in reference to stages of successive vegetation recovery.  相似文献   

Geochemistry of volcanic and hydrothermal gases of Mutnovsky volcano,Kamchatka: evidence for mantle,slab and atmosphere contributions to fluids of a typical arc volcano     

Mikhail Zelenski  Yuri Taran 《Bulletin of Volcanology》2011,73(4):373-394

We report chemical compositions (major and trace components including light hydrocarbons), hydrogen, oxygen, helium and nitrogen isotope ratios of volcanic and geothermal fluids of Mutnovsky volcano, Kamchatka. Several aspects of the geochemistry of fluids are discussed: chemical equilibria, mixing of fluids from different sources, evaluation of the parent magmatic gas composition and contributions to magmatic vapors of fluids from different reservoirs of the Kamchatkan subduction zone. Among reactive species, hydrogen and carbon monoxide in volcanic vapors are chemically equilibrated at temperatures >300°C with the SO₂-H₂S redox-pair. A metastable equilibrium between saturated and unsaturated light hydrocarbons is attained at close to discharge temperatures. Methane is disequilibrated. Three different sources of fluids from three fumarolic fields in the Mutnovsky craters can be distinguished: (1) magmatic gas from a large convecting magma body discharging through Active Funnel, a young crater with the hottest fumaroles (up to 620°C) contributing ~80% to the total volcanic gas output; (2) volcanic fluid from a separate shallow magma body beneath the Bottom Field of the main crater (96–280°C fumaroles); and (3) hydrothermal fluid with a high relative and absolute concentrations of CH₄ from the Upper Field in the main crater (96–285°C fumaroles). The composition of the parent magmatic gas is estimated using water isotopes and correlations between He and other components in the Active Funnel gases. The He-Ar-N₂ systematics of volcanic and hydrothermal fluids of Mutnovsky are consistent with a large slab-derived sedimentary nitrogen input for the nitrogen inventory, and we calculate that only ~1% of the magmatic N₂ has a mantle origin and <<1% is derived from the arc crust.  相似文献   

Chloride and Boron behavior in fluids of Los Humeros geothermal field (Mexico): A model based on the existence of deep acid brine     

Ruben Bernard  Yuri Taran  Maddalena Pennisi  Enrique Tello  Alejandro Ramirez 《Applied Geochemistry》2011,26(12):2064-2073

Geothermal field Los Humeros, Mexico, is characterized by a high steam fraction in the well fluids, by extremely high B concentrations in separated water (grams per liter, with a magmatic B signature, δ¹¹B ± 2σ = −0.8 ± 1.6‰), by the absence of correlation between B and Cl concentrations and by positive correlation between B content in separated water and fluid enthalpy. Such behavior is consistent with the existence of moderately acid brine (pH 3–5) at depth with a high B concentration (500–600 mg/kg). In this case a 3-level model can be suggested for Los Humeros: (1) immature, moderately acid brine at depth which is boiling at a temperature ∼350 °C producing the HCl-bearing vapor with a high B content; (2) partial condensation of this vapor at the upper level accompanying water–rock interaction and neutralization; (3) formation of a shallow water-dominated aquifer above a lithologic low-permeability boundary as has been proposed by other authors. A thermochemical computer code has been used to model boiling of an aqueous fluid at 350 °C with 0.1 M of NaCl, 0.05 M of H₃BO₃ and variable amount of HCl (0.001–0.1 M), then a partial condensation of the produced vapor at 250 °C and then separation of the steam–water mixture at 150 °C. Results of simulation are in a qualitative agreement with the observed data.  相似文献   

Circumzenithal sky region survey at the frequency of 30 GHz with 32-element radiometer matrix of the RATAN-600     

Yu. N. Parijskij  N. N. Bursov  A. B. Berlin  M. G. Mingaliev  N. A. Nizhelskij  V. A. Stolyarov  P. G. Tsybulev  T. A. Semenova  V. B. Khaikin  A. A. Grechkin 《Astrophysical Bulletin》2013,68(2):236-242

We report the preliminary results of a deep sky survey in the field of 00^h < RA < 24^h, 40 _. ^° 5 < 42 _. ^° 5 with the RATAN-600 and its new focal 32-feed receiver matrix at the limiting radio frequency of 30 GHz, with the resolution up to 5″ in right ascension and 30″ in declination. The first results, including new estimates of the anisotropy of background radiation at the scales of (l > 3000) and noise from discrete radio sources in the wavelength range between the NVSS and IRAS catalogs are listed.  相似文献