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31.
Jaroslava Hajná Ji?í ?ák Václav Kachlík Martin Chadima 《International Journal of Earth Sciences》2012,101(7):1855-1873
The Teplá–Barrandian unit (TBU) has long been considered as a simply bivergent supracrustal ‘median massif’ above the Saxothuringian subduction zone in the Variscan orogenic belt. This contribution reveals a much more complex style of the Variscan tectonometamorphic overprint and resulting architecture of the Neoproterozoic basement of the TBU. For the first time, we describe the crustal-scale NE–SW-trending dextral transpressional Krakovec shear zone (KSZ) that intersects the TBU and thrusts its higher grade northwestern portion severely reworked by Variscan deformation over a southeastern very low grade portion with well-preserved Cadomian structures and only brittle Variscan deformation. The age of movements along the KSZ is inferred as Late Devonian (~380–370?Ma). On the basis of structural, microstructural, and anisotropy of magnetic susceptibility data from the KSZ, we propose a new synthetic model for the deformation partitioning in the Teplá–Barrandian upper crust in response to the Late Devonian to early Carboniferous subduction and underthrusting of the Saxothuringan lithosphere. We conclude that the Saxothuringian/Teplá–Barrandian convergence was nearly frontal during ~380–346?Ma and was partitioned into pure shear dominated domains that accommodated orogen-perpendicular shortening alternating with orogen-parallel high-strain domains that accommodated dextral transpression or bilateral extrusion. The synconvergent shortening of the TBU was terminated by a rapid gravity-driven collapse of the thickened lithosphere at ~346–337?Ma followed by, or partly simultaneous with, dextral strike-slip along the Baltica margin-parallel zones, driven by the westward movement of Gondwana from approximately 345?Ma onwards. 相似文献
32.
Franti?ek?Pato?ka Petr??torchEmail author 《International Journal of Earth Sciences》2004,93(5):728-741
Cambrian and Ordovician-Middle Devonian sequences of two successive Early Palaeozoic basins of the Barrandian unconformably overlie Cadomian basement in the Bohemian Massif NW interior (Teplá-Barrandian unit) which is the easternmost peri-Gondwanan remnant within the Variscides. Correlation of stratigraphy and geochemistry of the Early Palaeozoic siliciclastic rocks elucidated sediment provenances. Sandstones of the Middle Cambrian Píbram-Jince Basin were derived from a Cadomian Neoproterozoic island arc. The source area of the Ordovician shallow-marine siliciclastics of the successor Prague Basin is a dissected Cadomian orogen. Late Cambrian acid volcanics of the Barrandian and Cambrian (meta)granitoids emplaced in the W part of the Teplá-Barrandian Cadomian basement are also discernible in these sediments. Old sedimentary component increased during the Ordovician. Early Llandovery siliciclastic rocks show characteristics of an abruptly weakened supply of terrigenous material and an elevated proportion of synsedimentary basic volcanics as a result of Silurian transgression. Emsian siliciclastics (intercalated in the Late Silurian to Early Devonian limestone suite) presumably comprise an addition of coeval basic/ultrabasic volcaniclastics. Middle Devonian flysch-like siliciclastics indicate reappearance of Cadomian source near the Barrandian during early Variscan convergences of Armorican microplates that preceeded accretion of the Teplá-Barrandian unit within the Bohemian Massif terrane mosaic.Dr. Patoka deceased in July 2004. 相似文献
33.
Michael E.?PasyanosEmail author William R.?Walter Megan P.?Flanagan Peter?Goldstein Joydeep?Bhattacharyya 《Pure and Applied Geophysics》2004,161(2):235-281
We construct and evaluate a new three-dimensional model of crust and upper mantle structure in Western Eurasia and North Africa (WENA) extending to 700 km depth and having 1° parameterization. The model is compiled in an a priori fashion entirely from existing geophysical literature, specifically, combining two regionalized crustal models with a high-resolution global sediment model and a global upper mantle model. The resulting WENA1.0 model consists of 24 layers: water, three sediment layers, upper, middle, and lower crust, uppermost mantle, and 16 additional upper mantle layers. Each of the layers is specified by its depth, compressional and shear velocity, density, and attenuation (quality factors, Q
P
and Q
S
). The model is tested by comparing the model predictions with geophysical observations including: crustal thickness, surface wave group and phase velocities, upper mantle
n
velocities, receiver functions, P-wave travel times, waveform characteristics, regional 1-D velocities, and Bouguer gravity. We find generally good agreement between WENA1.0 model predictions and empirical observations for a wide variety of independent data sets. We believe this model is representative of our current knowledge of crust and upper mantle structure in the WENA region and can successfully be used to model the propagation characteristics of regional seismic waveform data. The WENA1.0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified. Eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the Eurasian continent. 相似文献
34.
Pierre?MasselotEmail author Fateh?Chebana Taha?B.M.J.?Ouarda 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(2):509-522
Regional frequency analysis is an important tool to properly estimate hydrological characteristics at ungauged or partially gauged sites in order to prevent hydrological disasters. The delineation of homogeneous groups of sites is an important first step in order to transfer information and obtain accurate quantile estimates at the target site. The Hosking–Wallis homogeneity test is usually used to test the homogeneity of the selected sites. Despite its usefulness and good power, it presents some drawbacks including the subjective choice of a parametric distribution for the data and a poorly justified rejection threshold. The present paper addresses these drawbacks by integrating nonparametric procedures in the L-moment homogeneity test. To assess the rejection threshold, three resampling methods (permutation, bootstrap and Pólya resampling) are considered. Results indicate that permutation and bootstrap methods perform better than the parametric Hosking–Wallis test in terms of power as well as in time and procedure simplicity. A real-world case study shows that the nonparametric tests agree with the HW test concerning the homogeneity of the volume and the bivariate case while they disagree for the peak case, but that the assumptions of the HW test are not well respected. 相似文献
35.
Ken?M.?FritzEmail author Jack?W.?Feminella 《Aquatic Sciences - Research Across Boundaries》2011,73(4):459-469
Ecological flows between habitats are vital for predicting and understanding structure and function of recipient systems.
Ecological flows across riparian areas and headwater intermittent streams are likely to be especially important in many river
networks because of the shear extent of these interfaces, their high edge-to-width ratio, and the alternation of wet and dry
conditions in intermittent channels. While there has been substantial research supporting the importance of riparian-stream
linkages above-ground, comparatively less research has investigated below-ground linkages. We tested the hypothesis that riparian
roots are colonized by invertebrates as a food source within stream beds of intermittent headwater streams. We compared benthic
invertebrate assemblages colonizing three types of buried substrates (leaves, roots, and plastic roots) among three intermittent
Coastal Plain streams, each with a different riparian management treatment (clearcut, thinned, and reference), over a 1-year
period. Invertebrate density was significantly lower in root litterbags than in plastic roots litterbags, but neither differed
from densities in leaf litterbags. Total invertebrate abundances, however, were significantly higher in leaf and root litterbags
compared to abundances in plastic root litterbags. Invertebrate biomass and richness did not vary among substrates, but invertebrate
density, abundance, and richness all declined from the wet phase (September–December) through the dry phase (June–August).
Meiofauna and aquatic dipterans were the primary colonizing invertebrates during the wet phase. Relative abundance of terrestrial
taxa increased during the dry phase, but their absolute abundance remained lower than aquatic taxa during the wet phase. Invertebrate
composition did not differ among substrate types, but was significantly different among streams and time periods. Cumulative
number of dry days, degree days, and redox depth all strongly correlated with assemblage structure as indicated by ordination
scores. Our results suggest that subsurface invertebrates respond to leaves and roots as food sources, but assemblage composition
is not substrate specific. Colonization of leaves and roots within stream beds by aquatic and terrestrial taxa supports the
idea that headwater intermittent streams are important interfaces for the reciprocal exchange of energy and materials between
terrestrial and aquatic ecosystems. 相似文献
36.
Junyu?He Alexander?KolovosEmail author 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(4):859-877
The present paper reviews the conceptual framework and development of the Bayesian Maximum Entropy (BME) approach. BME has been considered as a significant breakthrough and contribution to applied stochastics by introducing an improved, knowledge-based modeling framework for spatial and spatiotemporal information. In this work, one objective is the overview of distinct BME features. By offering a foundation free of restrictive assumptions that limit comparable techniques, an ability to integrate a variety of prior knowledge bases, and rigorous accounting for both exact and uncertain data, the BME approach was coined as introducing modern spatiotemporal geostatistics. A second objective is to illustrate BME applications and adoption within numerous different scientific disciplines. We summarize examples and real-world studies that encompass the perspective of science of the total environment, including atmosphere, lithosphere, hydrosphere, and ecosphere, while also noting applications that extend beyond these fields. The broad-ranging application track suggests BME as an established, valuable tool for predictive spatial and space–time analysis and mapping. This review concludes with the present status of BME, and tentative paths for future methodological research, enhancements, and extensions. 相似文献
37.
Hill Bohlender Landstreet Wade Manset & Bastien 《Monthly notices of the Royal Astronomical Society》1998,297(1):236-238
The magnetic Ap star 53 Cam has been described as the best object for testing theories of elemental diffusion in the presence of a stellar magnetic field. It is thus vital to determine the rotational period of this very important star as accurately as possible. An improved period (8.026 81±0.000 04 d) is derived here by combining new measurements of the effective magnetic field with previously published values. 相似文献
38.
39.
We present an atlas of the Zeeman spectral line polarisation throughout the visible spectrum of the cool F0p star β CrB based on MuSiCoS spectropolarimetry. Stokes I, V, Q and U spectra covering the full 4500–6600 Å MuSiCoS intermediate bandpass are shown at sufficient display resolution so as to be suitable for the identification of individual spectral features. This is foreseen as being useful, for example, in the planning of very high resolution spectropolarimetric studies of Ap star Zeeman signatures using high-dispersion instruments likely to have significantly smaller spectral bandwidth. 相似文献
40.
In understanding the nucleosynthesis of the elements in stars, one of the most important quantities is the reaction rate and
it must be evaluated in terms of the stellar temperature T, and its determination involves the knowledge of the excitation function σ(E) of the specific nuclear reaction leading to the final nucleus. In this paper, the effect of thermonuclear reaction rates
to the pre-main sequence evolution of low mass stars having masses 0.7, 0.8, 0.9 and 1M⊙ are studied by using our modified Stellar Evolutionary Program. 相似文献