Geochronological aspects of polar wandering derived from Czechoslovak hydrothermal deposits     

Miroslav Krs 《Pure and Applied Geophysics》1964,57(1):96-102

Summary The present contribution contains a brief review of palaeomagnetic investigation carried out in Czechoslovak hydrothermal deposits. So far polar wandering has been considered on the basis of palaeomagnetism of lavas and red sediments; to first approximation it agrees with palaeoclimatic data. Since the products of hydrothermal mineralizations have displayed a high stability of the magnetic parameters used in palaeomagnetism, the treatment of a greater amount of statistical material yielded data for deriving the polar wandering path during geological history. By analyzing the curve obtained it is possible to derive some geochronological conclusions concerning the age of the ore-yielding processes in the principal Czechoslovak metallogenic areas. In this way a new dating technique for products of hydrothermal mineralizations is presented based on the study of palaeomagnetic properties. At the same time, these new results are consistent with the geophysical interpretation of the polar wandering curve for Europe.  相似文献   

Textural evidence of magma decompression, devolatilization and disequilibrium quenching: an example from the Western Krušné hory/Erzgebirge granite pluton     

Miroslav Štemprok  David Dolejš  Axel Müller  Reimar Seltmann 《Contributions to Mineralogy and Petrology》2008,155(1):93-109

We report new occurrences of “two-phase” granitic textures from the Western Krušné hory/Erzgebirge pluton (central Europe) and use crystal-size distribution data and thermodynamic modeling to interpret their crystallization conditions. The two-phase texture consists of (1) early phenocrysts of quartz, plagioclase, K-feldspar and biotite, (2) medium-grained matrix of the same phases and (3) interstitial channels and patches of a late-stage, very fine-grained matrix. The porphyritic two-mica microgranites, which host two-phase textures, occur as minor intrusions in early low-F biotite granites or as marginal parts of evolved high-F Li-mica granites. Measurements of the crystal-size distribution of quartz revealed three grain populations: (1) early phenocrysts (0.5–3.0 mm) showing partial resorption by residual melt, (2) a medium-grained population of the equigranular rock matrix (0.05–0.50 mm) that experienced minor coarsening by subsolidus annealing and (3) a fine-grained population (<0.03 mm) in the interstitial channels and patches formed during rapid devolatilization; this quartz group shows no or poor grain coarsening. All samples exhibit similar fraction of the fine-grained population (44–52%) but proportions of phenocrysts to medium-grained matrix vary significantly. Thermodynamic modeling of liquidus equilibria and experimental data in the hydrous haplogranite system require: (1) ascent of a granitic suspension (15–25% phenocrysts) under H₂O-undersaturated conditions at 25–45 bar/°C and a cooling rate of 40 J/(g kbar) in order to produce partial resorption of quartz phenocrysts and continued growth of feldspar phenocrysts, followed by (2) emplacement as discrete intrusions or bodies along pluton roof accompanied by sudden devolatilization. At the onset of matrix nucleation, disequilibrium undercooling of 70–85°C was inferred from the presence of micrographic intergrowths of quartz and K-feldspar. The two-phase granites in the Western Krušné hory/Erzgebirge pluton and in the Southeast Asian batholith form compositionally narrow groups with high-silica and moderate volatile enrichments but they differ in peraluminosity and phosphorus concentrations. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Gravity in the expansive nondecelerative universe     

Vladimír Skalský  Miroslav Súkeník 《Astrophysics and Space Science》1992,193(2):329-331

The gravity in the expansive nondecelerative universe originates in the process of permanent constant maximum possible creation of matter .  相似文献   

P-wave dispersion and attenuation in fractured and porous reservoirs – poroelasticity approach     

Boris Gurevich  Miroslav Brajanovski  Robert J. Galvin  Tobias M. Müller  Julianna Toms-Stewart 《Geophysical Prospecting》2009,57(2):225-237

Natural fractures in hydrocarbon reservoirs can cause significant seismic attenuation and dispersion due to wave induced fluid flow between pores and fractures. We present two theoretical models explicitly based on the solution of Biot's equations of poroelasticity. The first model considers fractures as planes of weakness (or highly compliant and very thin layers) of infinite extent. In the second model fractures are modelled as thin penny-shaped voids of finite radius. In both models attenuation is a result of conversion of the incident compressional wave energy into the diffusive Biot slow wave at the fracture surface and exhibits a typical relaxation peak around a normalized frequency of about 1. This corresponds to a frequency where the fluid diffusion length is of the order of crack spacing for the first model and the crack diameter for the second. This is consistent with an intuitive understanding of the nature of attenuation: when fractures are closely and regularly spaced, the Biot's slow waves produced by cracks interfere with each other, with the interference pattern controlled by the fracture spacing. Conversely, if fractures are of finite length, which is smaller than spacing, then fractures act as independent scatterers and the attenuation resembles the pattern of scattering by isolated cracks. An approximate mathematical approach based on the use of a branching function gives a unified analytical framework for both models.  相似文献   

Geoelectrical and geological structure of the crust in Western Slovakia     

Vladimír Bezák  Josef Pek  Ján Vozár  Miroslav Bielik  Jozef Vozár 《Studia Geophysica et Geodaetica》2014,58(3):473-488

Electrical resistivity of the Earth’s crust is sensitive to a wide range of petrological and physical parameters, and it particularly clearly indicates crustal zones that have been tectonically or thermodynamically disturbed. A complex geological structure of the Alpine nappe system, remnants of older Hercynian units and Neogene block tectonics in Western Slovakia has been a target of recent magnetotelluric investigations which made a new and more precise identification of the crustal structural elements of the Western Carpathians possible. A NW-SE magnetotelluric profile, 150 km long, with 30 broad-band and 3 long-period magnetotelluric sites, was deployed, crossing the major regional tectonic elements listed from the north: Brunia (as a part of the European platform), Outer Carpathian Flysch, Klippen Belt, blocks of Penninic or Oravicum crust, Tatricum and Veporicum. Magnetotelluric models were combined with previous seismic and gravimetric results and jointly interpreted in the final integrated geological model. The magnetotelluric models of geoelectrical structures exhibit strong correlation with the geological structures of the crust in this part of the Western Carpathians. The significant resemblance in geoelectrical and crustal geological structures are highlighted in shallow resistive structures of the covering formations represented by mainly Tertiary sediments and volcanics. Also in the deeper parts of the crust highly resistive and conductive structures are shown, which reflect the original building Hercynian crust, with superposition of granitoids or granitised complexes and lower metamorphosed complexes. Another important typical feature in the construction of the Western Carpathians is the existence of young Neogene steep fault zones exhibited by conductive zones within the whole crust. The most significant fault zones separate individual blocks of the Western Carpathians and the Western Carpathians itself from the European Platform.  相似文献   

Oscillations and Waves in Radio Source of Drifting Pulsation Structures     

Marian Karlický  Ján Rybák  Miroslav Bárta 《Solar physics》2018,293(4):62

Drifting pulsation structures (DPSs) are considered to be radio signatures of the plasmoids formed during magnetic reconnection in the impulsive phase of solar flares. In the present paper we analyze oscillations and waves in seven examples of drifting pulsation structures, observed by the 800?–?2000 MHz Ond?ejov Radiospectrograph. For their analysis we use a new type of oscillation maps, which give us much more information as regards processes in DPSs than that in previous analyses. Based on these oscillation maps, made from radio spectra by the wavelet technique, we recognized quasi-periodic oscillations with periods ranging from about 1 to 108 s in all studied DPSs. This strongly supports the idea that DPSs are generated during a fragmented magnetic reconnection. Phases of most the oscillations in DPSs, especially for the period around 1 s, are synchronized (“infinite” frequency drift) in the whole frequency range of DPSs. For longer periods in some DPSs we found that the phases of the oscillations drift with the frequency drift in the interval from ?17 to \(+287~\mbox{MHz}\,\mbox{s}^{-1}\). We propose that these drifting phases can be caused (a) by the fast or slow magnetosonic waves generated during the magnetic reconnection and propagating through the plasmoid, (b) by a quasi-periodic structure in the plasma inflowing to the reconnection forming a plasmoid, and (c) by a quasi-periodically varying reconnection rate in the X-point of the reconnection close to the plasmoid.  相似文献   

Temporal trends of bulk precipitation and stream water chemistry (1977–1997) in a small forested area,Krusné hory,northern Bohemia,Czech Republic     

N. E. Peters  Jiri Cerny  Miroslav Havel  Radovan Krejci 《水文研究》1999,13(17):2721-2741

The Krusné hory (Erzgebirge or Ore Mountains) has been heavily affected by high atmospheric pollutant deposition caused by fossil fuel combustion in an adjacent Tertiary coal basin. Long‐term routine sampling of bulk precipitation (1977–1996) and stream water (1977–1998) in a forested area on the south‐eastern slope of the mountains were used to evaluate trends and patterns in solute concentration and flux with respect to controlling processes. From 1977 to 1996, the annual volume‐weighted Ca²⁺ and SOconcentrations decreased in bulk precipitation. However, after 1989, when a pronounced and continuous decrease occurred in coal production, annual volume‐weighted concentrations decreased for most solutes, except H⁺. The concentration decreases were marked, with 1996 levels at or below 50% of those in 1989. The lack of a trend in H⁺ is attributed to similar decreases in both acid anions and neutralizing base cations. Stream water concentrations of most solutes, i.e. H⁺, Ca²⁺, Mg²⁺, SONOwere highest at the onset of sampling in 1977, decreased markedly from 1977 to 1983 and decreased more gradually from 1983 to 1998. The spruce forest die‐back and removal reduced dry deposition of these solutes by reducing the filtering action, which was provided by the forest canopy. A notable decrease in stream water Ca²⁺ concentrations occurred after 1995 and may be due to the depletion of Ca²⁺, which was provided by catchment liming in 1986, 1988 and 1989. Solute flux trends in bulk atmospheric deposition and stream water generally were not significant and the lack of trend is attributed to the large interannual variability in precipitation quantity and runoff, respectively. All solutes except Na⁺ varied seasonally. The average seasonal concentrations varied between the solutes, but for most solutes were highest in winter and spring and lowest in summer, correlating with the seasonal trend in runoff. For Ca²⁺, Mg²⁺ and SOthe concentration minimum occurs in September and the maximum occurs in February or March, correlating with the seasonal baseflow. These solutes are primarily controlled by the contribution of soil water and groundwater to stream flow. During snowmelt, the meltwater generally causes concentrations to decrease as soil water and groundwater are diluted. For NO₃ , average minimum concentrations occur in August at the end of the growing season concurrent with the lowest stream flow, and the maximum occurs in February and March with high stream flow during snowmelt. Seasonal stream water NOconcentration variations are large compared with the long‐term decrease. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Landslide-dammed lake sediment volume calculation using waterborne ERT and SONAR profiling     

Filip Hartvich  Petr Tábořík  Miroslav Šobr  Bohumír Janský  Zdeněk Kliment  Jakub Langhammer 《地球表面变化过程与地形》2020,45(14):3463-3474

Lake sediment volume calculation is a challenging task, namely in cases when detailed drilling is complicated, expensive, or impossible, information on the pre-sedimentation surface unavailable, and record of siltation rate non-existent or too short. This study shows how waterborne, non-invasive geophysical survey, such as electrical resistivity tomography (ERT) can be very effective in acquiring the missing data, namely when combined with sound navigation ranging (SONAR) water depth measurements and supported by information from auxiliary sources. However, ERT surveying in water environment requires specific approaches, as we illustrate on the case of the Mladotice lake study. The lake was created after a landslide in May 1872, and since its formation, the depth has gradually decreased due to sedimentation. We have reconstructed the original surface, calculated the sediment volume, and compiled information on sedimentation to estimate its remaining life span. To achieve this, we measured nine waterborne ERT profiles across the lake. To reach the necessary depth, all ERT profiles were extended on land and crossed the lake using custom-built flotation pads. ERT profiling was combined with SONAR depth measurements, historical bathymetric surveys, borehole core analysis, sediment flux measurements, volumetric calculations, and water conductivity probing. The study has achieved three main results. First, practical applicability and advantages of stationary waterborne ERT profiling in combination with bathymetric sounding were demonstrated. Second, the original lake volume and accumulated sediment was calculated. We estimate that the volume of lake sediment is 187 000 m³, two-thirds of the original lake volume (over 275 000 m³). Finally, based on three volumetric data sets from 1972, 2003, and 2017, and recent monitoring of the sediment inflow, we propose scenarios of lake filling and its future development. Most interestingly, the sedimentation rate has decreased significantly in the last 20 years, suggesting that the lake may survive much longer than hitherto expected. © 2020 John Wiley & Sons, Ltd.  相似文献   

The Lateglacial and Holocene in Central Europe: a multi‐proxy environmental record from the Bohemian Forest,Czech Republic          下载免费PDF全文

Klára Vočadlová  Libor Petr  Pavla Žáčková  Marek Křížek  Lenka Křížová  Simon M. Hutchinson  Miroslav Šobr 《Boreas: An International Journal of Quaternary Research》2015,44(4):769-784

The Hercynian mountain ranges were islands of mountain glaciation and alpine tundra in a Central European ice‐free corridor during the Late Pleistocene. Today they are notable areas of glacial landforms, alpine‐forest free areas, peatlands and woodlands. However, our knowledge of the Lateglacial and early Holocene environmental changes in this region is limited. We present a new multi‐proxy reconstruction of a mid‐altitude environment in the Bohemian Forest spanning this period. A core (5.2 m length) in the ?erné Lake cirque (1028 m a.s.l.) was subjected to lithological, geochemical, pollen and macrofossil analysis supplemented by two optically stimulated luminescence (OSL) and 10 AMS radiocarbon dates. We determined the impact of regional and supraregional climate changes on the environment. The two most significant changes in sedimentation during the Lateglacial (17.6 and 15.8–15.5 cal. ka BP) were synchronous with regional glacial chronostratigraphy. Unlike Central European mountain ranges, in the Bohemian Forest the Younger Dryas was not coincident with glacier re‐advance, but was a dry, cold episode with low lake levels, which prevailed until the early Preboreal. Plant macrofossils indicate local establishment of Betula nana and Betula pendula/pubescens at 15.4–13.4 cal. ka BP. Comparison with Holocene records from Central Europe shows a similar immigration history of vegetation at mid and higher altitudes. The tree line exceeded an altitude of ~1000 m a.s.l. around 10.5 cal. ka BP and coincided with rapid geochemical changes in the sediment. The 8.2 ka BP event did not have any response in the sedimentary record, but corresponded to stabilization of the Picea abies population and expansion of Fagus. Fagus colonized the Bohemian Forest earlier than other Hercynian mid‐mountains, but never predominated in the composition of the forest at higher elevations. Abies alba was the last tree species that immigrated to the study area.  相似文献   

Expected changes in agroclimatic conditions in Central Europe     

Miroslav Trnka  Josef Eitzinger  Daniela Semer��dov��  Petr Hlavinka  Jan Balek  Martin Dubrovsky  Gerhard Kubu  Petr ?t��p��nek  Sabina Thaler  Martin Mo?ny  Zden��k ?alud 《Climatic change》2011,108(1-2):261-289

During the past few decades, the basic assumption of agroclimatic zoning, i.e., that agroclimatic conditions remain relatively stable, has been shattered by ongoing climate change. The first aim of this study was to develop a tool that would allow for effective analysis of various agroclimatic indicators and their dynamics under climate change conditions for a particular region. The results of this effort were summarized in the AgriClim software package, which provides users with a wide range of parameters essential for the evaluation of climate-related stress factors in agricultural crop production. The software was then tested over an area of 114,000 km² in Central Europe. We have found that by 2020, the combination of increased air temperature and changes in the amount and distribution of precipitation will lead to a prolonged growing season and significant shifts in the agroclimatic zones in Central Europe; in particular, the areas that are currently most productive will be reduced and replaced by warmer but drier conditions in the same time the higher elevations will most likely experience improvement in their agroclimatic conditions. This positive effect might be short-lived, as by 2050, even these areas might experience much drier conditions than observed currently. Both the rate and the scale of the shift are amazing as by 2020 (assuming upper range of the climate change projections) only 20?C38% of agriculture land in the evaluated region will remain in the same agroclimatic and by 2050 it might be less than 2%. On the other hand farmers will be able to take advantage of an earlier start to the growing season, at least in the lowland areas, as the proportion of days suitable for sowing increases. As all of these changes might occur within less than four decades, these issues could pose serious adaptation challenges for farmers and governmental policies. The presented results also suggest that the rate of change might be so rapid that the concept of static agroclimatic zoning itself might lose relevance due to perpetual change.  相似文献