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1.
Aleksandre Kandilarov Rolf Mjelde Rolf-Birger Pedersen Bjarte Hellevang Cord Papenberg Carl-Joerg Petersen Lars Planert Ernst Flueh 《Marine Geophysical Researches》2012,33(1):55-76
The Jan Mayen microcontinent was as a result of two major North Atlantic evolutionary cornerstones—the separation of Greenland
from Norway (~54 Ma), accompanied by voluminous volcanic activity, and the jump of spreading from the Aegir to the Kolbeinsey
ridge (~33 Ma), which resulted in the separation of the microcontinent itself from Eastern Greenland (~24 Ma). The resulting
eastern and western sides of the Jan Mayen microcontinent are respectively volcanic and non-volcanic rifted margins. Until
now the northern boundary of the microcontinent was not precisely known. In order to locate this boundary, two combined refraction
and reflection seismic profiles were acquired in 2006: one trending S–N and consisting of two separate segments south and
north of the island of Jan Mayen respectively, and the second one trending SW–NE east of the island. Crustal P-wave velocity
models were derived and constrained using gravity data collected during the same expedition. North of the West Jan Mayen Fracture
Zone (WJMFZ) the models show oceanic crust that thickens from west to east. This thickening is explained by an increase in
volcanic activity expressed as a bathymetric high and most likely related to the proximity of the Mohn ridge. East of the
island and south of the WJMFZ, oceanic Layers 2 and 3 have normal seismic velocities but above normal average crustal thickness
(~11 km). The similarity of the crustal thickness and seismic velocities to those observed on the conjugate M?re margin confirm
the volcanic origin of the eastern side of the microcontinent. Thick continental crust is observed in the southern parts of
both profiles. The northern boundary of the microcontinent is a continuation of the northern lineament of the East Jan Mayen
Fracture Zone. It is thus located farther north than previously assumed. The crust in the middle parts of both models, around
Jan Mayen island, is more enigmatic as the data suggest two possible interpretations—Icelandic type of oceanic crust or thinned
and heavily intruded continental crust. We prefer the first interpretation but the latter cannot be completely ruled out.
We infer that the volcanism on Jan Mayen is related to the Icelandic plume. 相似文献
2.
Magnetic fabric study of the SE Rhenohercynian Zone (Bohemian Massif): Implications for dynamics of the Paleozoic accretionary wedge 总被引:2,自引:0,他引:2
The progressive deformation recorded in the magnetic fabric of sedimentary rocks was studied in the SE Rhenohercynian Zone (RHZ), eastern margin of the Bohemian Massif, Czech Republic. Almost 800 oriented samples of the Lower Carboniferous mudstones and graywackes were collected from the SSE part of the Czech RHZ, so-called the Drahany Upland. The anisotropy of magnetic susceptibility (AMS) is predominantly controlled by the preferred orientation of paramagnetic phyllosilicates, mainly iron-bearing chlorites. A regional distribution of the magnetic fabric within the Drahany Upland revealed an increasing deformation from the SSE to the NNW. In the SE, the magnetic fabric is bedding-parallel with magnetic lineation scattered in the bedding plane or trending N–S to NNE–SSW. Further to the NW, the magnetic foliation rotates from the bedding-parallel orientation to the orientation parallel to the evolving cleavage. This rotation is accompanied by a decrease of the anisotropy degree and the prolate nature of the anisotropy ellipsoids. The magnetic lineation is parallel to the strike of the bedding, bedding/cleavage intersection, pencil structure or the fold axes on a regional scale. In the NW part of the Drahany Upland, the magnetic foliation becomes parallel to the cleavage accompanied by an increase of the anisotropy degree and the oblate nature of the anisotropy ellipsoids. The increasing trend of deformation corresponds to the SSE–NNW increase in the degree of anchimetamorphism; both trends being oblique to the main lithostratigraphic formations as typically observed in the sedimentary rocks of the accretionary wedges. The SSE–NNW increase in deformation and anchimetamorphism continues to the Nízký Jeseník Mts., representing the northern part of the same accretionary wedge. The kinematics of deformation could not be unambiguously assessed. The observed magnetic fabric may reflect either lateral shortening or horizontal simple shear or a combination of both mechanisms. Regarding the subduction process, it seems that the sedimentary sequences of the Drahany Upland were subducted, partly offscraped and accreted frontally or partly underplated as opposed to the Nízký Jeseník Mts. where some return flow must have occurred. 相似文献
3.
Here, we address the sediment dynamics in the Black Sea based on analysis of remote sensing data from the Medium Resolution
Imaging Spectrometer and numerical simulations with Nucleus for European Modelling of the Ocean model. Boundary conditions
consist of realistic meteorological forcing, including significant wave height generated by wave prediction model. A number
of sensitivity runs was analysed with the aim to find the most suitable parameters governing sediment fluxes. The comparison
between numerical simulations and remote sensing data gives credibility to the quality of simulations. The combined effect
of wind waves and currents in the bed layer controls the sediment resuspension that appears to be the major basin-wide source
of sediment. Sensitivity experiments included or excluded different forcing terms, e.g. sediment flux from rivers enable to
determine the spatial extensions of different point sources. It is concluded that wind-wave forcing is manifested in the sediment
dynamics through episodic high energy events contributing to the increase of horizontal sediment fluxes over the northwestern
shelf. Both satellite images and numerical model simulations demonstrated that the penetration of suspended sediment into
the basin interior was governed by the dynamics of coastal and open-ocean eddies. While fine sediment at sea surface could
cross the continental slope propagating into the open ocean, coarser fractions follow the bottom and their penetration into
the open ocean is limited. The conclusion is thus that the deposition patterns correlate with the specific shape of Black
Sea topography, and the largest depositions are observed in the area of continental slope. 相似文献
4.
Crustal structure of the ultra-slow spreading Knipovich Ridge,North Atlantic,along a presumed ridge segment center 总被引:1,自引:1,他引:0
Aleksandre Kandilarov Hildegunn Landa Rolf Mjelde Rolf B. Pedersen Kyoko Okino Yoshio Murai 《Marine Geophysical Researches》2010,31(3):173-195
A combined ocean bottom seismometer, multichannel seismic reflection and gravity study has been carried out along the spreading
direction of the Knipovich Ridge over a topographic high that defines a segment center. The youngest parts of the crust in
the immediate vicinity of the ridge reveal fractured Oceanic Layer 2 and thermally expanded and possibly serpentinized Oceanic
Layer 3. The mature part of the crust has normal thickness and seismic velocities with no significant crustal thickness and
seismic velocity variations. Mature Oceanic Layer 2 is in addition broken into several rotated fault blocks. Comparison with
a profile acquired ~40 km north of the segment center reveals significant differences. Along this profile, reported earlier,
periods of slower spreading led to generation of thin crust with a high P-wave velocity (Vp), composed of a mixture of gabbro and serpentinized mantle, while periods of faster spreading led to generation of more
normal gabbroic crust. For the profile across the segment center no clear relation exists between spreading rate and crustal
thickness and seismic velocity. In this study we have found that higher magmatism may lead to generation of oceanic crust
with normal thickness even at ultra-slow spreading rates. 相似文献
5.
Crustal structure of the ultra-slow spreading Knipovich Ridge,North Atlantic,along a presumed amagmatic portion of oceanic crustal formation 总被引:4,自引:4,他引:0
Aleksandre Kandilarov Rolf Mjelde Kyoko Okino Yoshio Murai 《Marine Geophysical Researches》2008,29(2):109-134
The ultra-slow, asymmetrically-spreading Knipovich Ridge is the northernmost part of the Mid Atlantic ridge system. In the
autumn of 2002 a combined ocean-bottom seismometer multichannel seismic (OBS/MCS) and gravity survey along the spreading direction
of the Knipovich Ridge was carried out. The main objective of the study was to gain an insight into the crustal structure
and composition of what is assumed to be an amagmatic segment of oceanic crust. P-wave velocity and Vp/Vs models were built
and complemented by a gravity model. The 190 km long transect reveals a much more complex crustal structure than anticipated.
The magmatic crust is thinner than the global average of 7.1 ± 1.0 km. The young fractured portion of Oceanic Layer 2 has
low seismic velocities while the older part has normal seismic velocities and is broken into several rotated fault blocks
seen as thickness variations of Layer 2. The youngest part of Oceanic Layer 3 is also dominated by low velocities, indicative
of fracturing, seawater circulation and thermal expansion. The remaining portion of Layer 3 exhibits inverse variations in
thickness and seismic velocity. This is explained by a sequence of periods of faster spreading (estimated to be up to 8 mm/year
from interpretation of magnetic anomalies) when more normal gabbroic crust was being generated and periods of slower spreading
(5.5 mm/year) when amagmatic stretching and serpentinization of the upper mantle occurred, and crust composed of mixed gabbro
and serpentinized mantle was generated. The volumetric changes and upward fluid migration, associated with the process of
serpentinization in this part of the crust, caused disruption to the overlying sedimentary layers. 相似文献
6.
Pavel Koten Pavel Spurný Jií Borovi
ka Stephen Evans Andrew Elliott Hans Betlem Rostislav tork Klaas Jobse 《Meteoritics & planetary science》2006,41(9):1305-1320
Abstract— In this paper, we provide an overview of meteors with high beginning height. During the recent Leonid meteor storms, as well as within the regular double station video observations of other meteor showers, we recorded 164 meteors with a beginning height above 130 km. We found that beginning heights between 130 and 150 km are quite usual, especially for the Leonid meteor shower. Conversely, meteors with beginning heights above 160 km are very rare even among Leonids. From the meteor light curves, we are able to distinguish two different processes that govern radiation of the meteors at different altitudes. Light curves vary greatly above 130 km and exhibit sudden changes in meteor brightness. Sputtering from the meteoroid surface is the dominating process during this phase of the meteor luminous trajectory. Around 130 km, the process switches to ablation and the light curves become similar to the light curves of standard meteors. The sputtering model was successfully applied to explain the difference in the beginning heights of high‐altitude Leonid and Perseid meteors. We show also that this process in connection with high altitude fragmentation could explain the anomalously high beginning heights of several relatively faint meteors. 相似文献
7.
Jiří Borovička Pavel Koten Pavel Spurný Rostislav Štork 《Earth, Moon, and Planets》2008,102(1-4):485-493
We present an analysis of sporadic meteor number 07406018, observed by image intensified video cameras at two stations, which
showed a pronounced deceleration along its trajectory. We have applied the erosion model to analyze simultaneously the deceleration
and light curve. We have found that the meteoroid had a low density of about 500 kg m−3, consistent with its cometary orbit. The meteoroid structure was, nevertheless, markedly different from the Draconid meteoroids,
studied recently with the same model. The size of the constituent grains was larger and the erosion energy was higher than
in Draconids. The meteor spectrum was also different from Draconid spectra and showed very bright Na lines. The meteoroid
composition was probably different from normal cometary composition. 相似文献
8.
Environmental risks associated with aeration of a freshwater sediment exposed to mine drainage water 总被引:1,自引:0,他引:1
The study examined freshwater sediments from a pond receiving waters from an open-pit lignite quarry located in Europe's Black Triangle in the northern part of the Czech Republic. Sediments were studied with respect to chemical changes upon aeration to assess the risks associated with their acidification and release of toxic metals. Three types of sediments were sampled: orange precipitates of ferric oxides, underlying black anoxic material and brown clayey material from the original bottom of the pond. The experiment revealed that only black anoxic sediment presents environmental concerns upon aeration. Its redox potential rose steeply from -124 up to +412 mV within the first 50 h of aeration, afterwards, it increased only slowly and reached a finale value of +663 mV after 362 h of aeration. The redox changes were accompanied by sulphate production. Up to 97,037.8 mg of sulphate was released into the solution from 1 kg of the sediment. Consequently, the pH values dropped from 6.7 down to 3.3 within the first 50 h of aeration and reached a value of 2.7 at the end of the experiment. The decrease of pH values was followed by increased zinc and manganese mobility. Iron solubilisation was not continuous. An initial drop in iron mobility was followed by an increase, after which the mobility decreased again. This fluctuation reflected the changes in iron solubility depending on the oxidation state and pH changes in the sediment suspension. 相似文献
9.
Measurements of temperature and velocity microstructure near and downstream of a shallow seamount are used to compare fossil turbulence versus non-fossil turbulence models for the evolution of turbulence microstructure patches in the stratified ocean. According to non-fossil oceanic turbulence models, all overturn length scales LT of the microstructure grow and collapse in constant proportion to each other and to the turbulence energy (Oboukov) scale LO and the inertial buoyancy (Ozmidov) scale
of the patches; that is, with LTrms ≈1.2LR and viscous dissipation rate ≈ 0*. According to the Gibson fossil turbulence model, all microstructure originates from completely active turbulence with 0 ≈ 3LT2N3(≈ 280*) and LT/√6 ≈ LTrms, but this rapidly decays into a more persistent active-fossil state with 0F ≈ 30vN2, where N is the buoyancy frequency and v is the kinematic viscosity and, without further energy supply, finally reaches a completely fossil turbulence hydrodynamic state of internal wave motions, with F. The last turbulence eddies, with ≈ F, vanish at a buoyant-inertial-viscous (fossil Kolmogorov) scale LKF that is much smaller than the remnant overturn scales LT for large 0/F ratios. These density, temperature, and salinity overturns with LT ≈ 0.6 LR0 0.6 LR persist as turbulence fossils (by retaining the memory of o) and collapse very slowly. In the near wake below the summit depth of Ampere seamount, a much larger proportion of completely active turbulence patches was found than is usually found in the ocean interior away from sources. Dissipation rates and turbulence activity coefficients
of microstructure patches were found to decrease downstream, suggesting that the active turbulence indicated by the patches with AT 1 was caused by the presence of the seamount as a turbulence source. Therefore, the turbulence and mixing processes of ocean layers far away from turbulence sources probably have been undersampled by microstructure data sets lacking any AT 1 patches. This is because large fractions of the mixing and viscous dissipation of the patches occur in short-lived active turbulence regimes that are too brief to be detected. Consequently, large underestimates of the true space-time average turbulence fluxes and turbulence and scalar dissipation rates may result if non-fossil turbulence models are assumed in ocean microstructure data interpretation. 相似文献
10.
Aleksandre Kandilarov Kuvvet Atakan Jens Havskov Dragomir Gospodinov 《Bulletin of Earthquake Engineering》2009,7(1):181-198
Plovdiv is the second largest city in the Republic of Bulgaria. A large part of the city is located on Holocene alluvial sediments
and the oldest neighborhoods are situated on syenitic rock outcrops. We believe that local site effects may be an important
contributor to the destruction caused by earthquakes. The primary objective of this study was to estimate quantitatively the
local site effects in the central area of Plovdiv in terms of fundamental site frequency and amplification factor. Another
important objective was to see how these correlate with the geological structures underlying the city. Measurements of the
seismic noise at more than two hundred regularly placed points were made in the central area of the city. The H/V spectra
were then calculated and analyzed to determine the spatial distribution of the fundamental site frequency and the amplification
factor. The results exhibit very good correlation with the local geology. They were also compared with an intensity map from
the strong 1928 Plovdiv earthquake. The comparison clearly demonstrates that the local site effects were the main factor in
the destruction of buildings—the zones where the most damage was observed are also the zones where we have low fundamental
site frequencies and high amplifications. Similarly the areas with high fundamental site frequencies and low amplification
factors cover the neighborhoods where less damage has been observed. This study may form a basis for a more comprehensive
and systematic microzonation study in Plovdiv. 相似文献