Regional geological and tectonic structures of the North Sea area from potential field modelling   总被引：2，自引：1，他引：2  

S.B. Lyngsie  H. Thybo  T.M. Rasmussen   《Tectonophysics》2006,413(3-4):147-170

The spatial distribution of large-scale crustal domains and their boundaries are investigated in the North Sea area by combining gravity, magnetic and seismic data. The North Sea is situated on the plates of three continents, Avalonia, Laurentia and Baltica, which collided during the Caledonian orogeny in the middle Palaeozoic. The location and continuation of the collisional sutures are debated. We apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures. The transformations reveal intrinsic features of crustal transitions between the Caledonian plates and their relation to later extensional structures. The transformations include the Hough Transform applied to the gravity field, calculation of fractional derivatives and integrals of the gravity and magnetic fields, the pseudogravity field and the horizontal gradient field as well as upward continuation. The results indicate a fundamental difference between the lithosphere of Avalonia, Laurentia and Baltica. The location of the Mesozoic rift system (the Central Graben and Viking Graben), may have been partly determined by the presence of the sutures between these three plate, indicative of extensional reactivation of compressional structures. A significant lineament across the entire North Sea between Scotland and North Germany indicates that the lower crust of Baltica provenance may extend as far south-westward as to this lineament. Comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties. This lineament could represent the suture between lithosphere of Caledonian origin (Avalonia) versus lithosphere of Precambrian origin (Baltica) in the lower crust and upper mantle. If this is the case, the lineament is the missing link in the reconstruction of the triple plate collision.  相似文献   

The Greenland Ice Core Chronology 2005, 15–42 ka. Part 1: constructing the time scale     

Katrine K. Andersen  Anders Svensson  Sigfus J. Johnsen  Sune O. Rasmussen  Matthias Bigler  Regine Rthlisberger  Urs Ruth  Marie-Louise Siggaard-Andersen  Jrgen Peder Steffensen  Dorthe Dahl-Jensen  Bo M. Vinther  Henrik B. Clausen 《Quaternary Science Reviews》2006,25(23-24):3246

The Greenland Ice Core Chronology 2005, GICC05, is extended back to 42 ka b2k (before 2000 AD), i.e. to the end of Greenland Stadial 11. The chronology is based on independent multi-parameter counting of annual layers using comprehensive high-resolution measurements available from the North Greenland Ice Core Project, NGRIP. These are measurements of visual stratigraphy, conductivity of the solid ice, electrolytical melt water conductivity and the concentration of Na⁺, Ca²⁺, SO₄²⁻, NO₃⁻, NH₄⁺. An uncertainty estimate of the time scale is obtained from identification of ‘uncertain’ annual layers, which are counted as 0.5±0.5 years. The sum of the uncertain annual layers, the so-called maximum counting error of the presented chronology ranges from 4% in the warm interstadial periods to 7% in the cold stadials. The annual accumulation rates of the stadials and interstadials are on average one-third and half of the present day values, respectively, and the onset of the Greenland Interstadials 2, 3, and 8, based on 20 year averaged δ¹⁸O values, are determined as 23,340, 27,780, and 38,220 yr b2k in GICC05.  相似文献   

An overview of trace metals in the environment, from mobilization to remediation   总被引：10，自引：0，他引：10  

A. C. L. Larocque  Patricia E. Rasmussen 《Environmental Geology》1998,33(2-3):85-91

  相似文献   

CHARACTERISTICS OF MESOSCALE FLOOD-MAKING TORRENTIAL RAIN SYSTEM SIMULATED BY HIGH RESOLUTION LIMITED AREA MODEL—NUMERICAL SIMULATION OF A HEAVY RAIN PROCESS DURING MEIYU SEASON IN 1991   总被引：1，自引：0，他引：1  

朱禾  E.Rasmussen 《Acta Meteorologica Sinica》1996,(3)

An experimental work on the transplant of high resolution limited area model(HIRLAM) isfirstly introduced into China.For the implementation,first of all is to adjust a new geographicalcoordination and to remove the instability caused by the Tibetan Plateau,the roof of the world.Then,we have applied this model to simulate a flood-making torrential rain process which occurredin the Changjiang-Huaihe River Valley in July 1991.That revealed the formation,development andmovement of a mesoseale heavy rain system which had made a disastrous flood event in the middleand lower reaches of Changjiang River Valley.The result encourages us to use the HIRLAM for the researches on the Meiyu belt,the salientfeature of precipitation of East Asia,and the numerical prediction of heavy rains in China.  相似文献   

ON THE SENSITIVITY OF PRECIPITATION FORECASTS TO THE MOIST PHYSICS AND THE HORIZONTAL RESOLUTION OF NUMERICAL MODEL     

俞小鼎  Leif Laursen  Erik Rasmussen 《Acta Meteorologica Sinica》1997,(4)

The impacts of the enhanced model's moist physics and horizontal resolution upon the QPFs(quantitative precipitation forecasts)are investigated by applying the HIRLAM(high resolutionlimited area model)to the summer heavy-rain cases in China.The performance of the control run,for which a 0.5°×0.5°grid spacing and a traditional“grid-box supersaturation removal+Kuo typeconvective paramerization”are used as the moist physics,is compared with that of the sensitivityruns with an enhanced model's moist physics(Sundqvist scheme)and an increased horizontalresolution(0.25°×0.25°),respectively.The results show:(1)The enhanced moist physics scheme(Sundqvist scheme),by introducing the cloud watercontent as an additional prognostic variable and taking into account briefly of the microphysicsinvolved in the cloud-rain conversion,does bring improvements in the model's QPFs.Althoughthe deteriorated QPFs also occur occasionally,the improvements are found in the majority of thecases,indicating the great potential for the improvement of QPFs by enhancing the model's moistphysics.(2)By increasing the model's horizontal resolution from 0.5°×0.5°,which is already quitehigh compared with that of the conventional atmospheric soundings,to 0.25°×0.25°without thesimultaneous enhancement in model physics and objective analysis,the improvements in QPFs arevery limited.With higher resolution,although slight amelioration in locating the rainfall centersand in resolving some finer structures of precipitation pattern are made,the number of the mis-predicted fine structures in rainfall field increases with the enhanced model resolution as well.  相似文献   

Methane,carbon monoxide and methylchloroform in the southern hemisphere   总被引：1，自引：0，他引：1  

P. J. Fraser  P. Hyson  R. A. Rasmussen  A. J. Crawford  M. A. K. Khalil 《Journal of Atmospheric Chemistry》1986,4(1):3-42

New observational data on CH₄, CO and CH₃CCl₃ in the southern hemisphere are reported. The data are analysed for long term trends and seasonal cycles. CH₃CCl₃ data are used to scale the OH fields incorporated in a two dimensional model, which in turn, is used to constrain the magnitude of a global CH₄ source function. The possible causes of observed seasonality of CH₃CCl₃, CH₄ and CO are identified, and several other aspects of observed CH₄ variability are discussed.Possible future research directions are also given.  相似文献   

Inclusion of ice cover in a storm surge model for the Beaufort Sea     

M. B. Danard  M. C. Rasmussen  T. S. Murty  R. F. Henry  Z. Kowalik  S. Venkatesh 《Natural Hazards》1989,2(2):153-171

Storm surges in the Beaufort Sea present a severe problem for navigation as well as for offshore oil drilling activities. Influence of ice cover on storm surges in the Beaufort Sea is examined making use of a numerical model as well as a set of observations. The automated shallow-water model of Henry has been modified to incorporate ice cover and is adapted to the Beaufort Sea. The leading edge of the permanent ice is calculated from the loci of identifiable points. Generalized similarity theory is employed to compute wind stresses. Simulations are made using model-predicted ice concentrations and observed ice concentrations. Ice motion is relatively small in units of model grid distance (approximately 18 km) during surges. Spherical effects are important and should be included in future adaptations of the model. Comparison of the computed surges with observed surges for eight different events showed reasonable agreement.  相似文献   

Compositional trends and cooling rates of group IVB iron meteorites     

Kaare L. Rasmussen  Daniel J. Malvin  Vagn F. Buchwald  John T. Wasson 《Geochimica et cosmochimica acta》1984,48(4):805-813

Based on new neutron activation data for group IVB we find that log-element — log-Ni trends are best understood in terms of core formation and fractional crystallization. The limited compositional range found in group IVB seems to reflect the fact that, because of the low concentrations of S, P and C and the high concentration of Ni, $\text{k}{}_{\mathrm{\chi }}$ values are nearer unity than are those in other magmatic groups. Mean volatile abundances in group IVB are much lower than those found in any group of chondritic meteorites, suggesting that these low abundances were not entirely the result of nebular processes, but that planetary outgassing was also involved.We calculated cooling rates on the basis of a computer simulation of the growth of kamacite crystals; these calculations are particularly straightforward for the high-Ni irons since no local bulk Ni enrichment is involved. We estimate a mean IVB cooling rate of 170–230 K/Ma, the lower values based on 20 K undercooling, the higher on no undercooling. There is no dependence of cooling rate on chemical composition. The mean cooling rate of the low-volatile groups IVB and IVA are both much higher than those typical of iron-meteorite groups. This indicates small parent bodies, and reinforces the above suggestion that the low volatile contents resulted from planetary outgassing.There is a small compositional hiatus in group IVB, but since the sets on both sides of the hiatus form continuous trends on log-element — log-Ni diagrams and have the same cooling rates, it appears that both sets originated in a single oxidized, refractory-rich parent body. This sampling hiatus corresponds to 26% of the original core, a value shown to be typical for a random sequence sampled 11 times.  相似文献   

Stress-induced variations of remanent magnetism in Late Quaternary varved clay     

Birger Schmitz 《Earth and Planetary Science Letters》1984,69(2):422-426

A study of the remanent magnetism in Swedish varved clay shows that, even in varves that macroscopically appear to be undeformed, the paleomagnetic record may be seriously altered due to stress-induced deformation of the micro-fabric in the sediment.In the studied area disturbed clays were rather the rule than the exception, but undisturbed sediments were found at two sites, Järna II and III. This clay formed 10,200 years B.P. and shows a declination of about 30° east, a value that could be obtained thanks to excellent lateral control of the magnetism.  相似文献   

Determination of the cooling rates and nucleation histories of eight group IVA iron meteorites using local bulk Ni and P variation     

K.L. Rasmussen 《Icarus》1982,52(3):444-453

Cooling rates and nucleation histories of six low-Ni and two high-Ni members of group IVA iron meteorites were calculated by a mid-taenite concentration-taenite lamella width method that included the effects of local bulk Ni and P variation. The local bulk Ni is determined experimentally as described in K. L. Rasmussen [Icarus45, 564–576 (1981)]. The local bulk P parameter, included for the first time in the present work, is estimated from the phase diagram during the simulation. Two parent bodies are suggested for group IVA. The body containing the high-Ni members had a cooling rate (～2°K/My) lower than earlier cooling rate determinations on IVA members. The variable (by a factor of 4) cooling rates found for the low-Ni members imply a raisin origin. The nucleation histories of the meteorites are interpreted as reflecting the very early shock histories of the meteorite parent bodies.  相似文献