共查询到19条相似文献，搜索用时 171 毫秒
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假定地幔为一个均匀的、粘滞系数为常数、同时均匀分布放射性热源的流体球层,其内部存在的对流则由流体力学3个基本方程:运动方程、能量方程和连续性方程确定.如果假定地幔处于低瑞利数的状态（临界瑞利数1.5倍左右）,那么上述方程中的非线性项可以忽略不计.作为一类可能的模型,本文计算一组用6个边界条件确定6个未知数的线性方程组.这些条件包括板块绝对运动极型场、地球大地水准面异常和地震层析结果提供的地幔密度分布横向不均匀相应的“刚性地球”水准面异常等.模型计算表明:1.地幔中流体运动格局不仅受地幔热动力学参数（瑞利数）控制,而且强烈地受边界条件的影响.2.若不限定下边界为等温边界,则上、下地幔之间并不呈现出活动性明显差异;但是在模型瑞利数加大到一定值时,核-幔边界附近将出现一些局部的小尺度对流环.3.当模型瑞利数从很小增加时,对流格局将发生变化,这些格局可能反应由地幔热动力学参数决定的地幔固有特性.4.当瑞利数为50000和80000时,核-幔边界形变与PcP波得到的结果吻合较好. 相似文献
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本文分别基于数值结果和地质学模型,在假定地球的上地幔存在稳定Rayleigh-Bénard对流的基础上,模拟了直径为10 km（陨石坑直径约180 km,以Chicxulub为例）和直径为100 km（陨石坑直径约1000 km）的小行星撞击对地球的上地幔对流格局的影响.本文将直径10 km小行星的撞击效果等效为热异常,将直径100 km小行星的撞击效果等效为热异常和速度异常（主要指陨石坑底部的回弹）的叠加.计算结果表明,当小行星的直径在10 km左右时,撞击对上地幔对流的影响十分微弱,热扰动时间仅2—3 Ma;而当小行星的直径达到100 km时,撞击就会对上地幔对流产生强烈影响.这时,对流从扰动到新的稳态有一定模式可循（依次为：调整、多个对流环、调整、稳定）,扰动的持续时间受黏度和撞击点位置影响,同时稳定后地幔热柱会向着撞击点的方向产生一定的位移. 相似文献
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以岩石蠕变实验为基础, 利用同一地震的余震序列和震后形变的资料来估算震源附近的地壳黏度. 首先进行了3类岩石9块样品在恒定压力下的蠕变实验, 直接得到了岩石的蠕变曲线. 反演结果认为用标准线性体模型来表示地球介质的黏弹性较好, 它在短时间内, 表现出明显的弹性性质；而在较长时间内, 表现出明显的的流变特性. 然后计算和分析了标准线性体模型的元件模量μ2与整体模量以及μ2与真实地球介质模量μ的数值关系. 在得出μ2=25 μ的基础上, 处理了青海共和地震后的余震序列, 得到累计应变释放与时间的关系曲线, 结合实验结果来估算该区的地壳介质黏度. 对同一地震之后测量得到的垂直形变资料, 也结合实验结果分别用开尔文模型反演、形变差值和黏弹位错理论等三种方法进行了计算, 也得出了弛豫时间和地球介质的黏度, 不同的资料和计算方法一致得出青海共和地区在震源深度32 km附近的地壳介质黏度为1019 Pa∙s, 与国内外有关文献研究结果为同一量级. 相似文献
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地球深部地震学研究进展索恩莱（美）梁慧云译全球地震学研究正系统地揭示着地球深部的结构、成分及动力学特征。最新的重大进展包括有：全球地幔内部不连续面的层析成象图、第一代地震粘滞性非球状模型，高分辨度的消减板三维图像，及核－幔边界附近复杂结构的图像。我们... 相似文献
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对花岗岩样品进行逐次加载的蠕变实验,得到了加载过程中的蠕变曲线和蠕变破裂的全过程曲线.对加载过程中的杨氏模量、蠕变量、蠕变速率等参数用加卸载响应比方法进行了分析,认为有二种不同形态的响应曲线.在中低应力的弹性阶段其响应比都近似为1,而在高应力的膨胀阶段其响应比都随应力而增加.对应力不变时的蠕变破裂全过程曲线进行了分解,在蠕变破裂过程中,瞬态、稳态和加速3个阶段的持续时间分别为全部时间的18%,75%和7%;在加速蠕变阶段蠕变速率及其响应比明显增加.这一结果是预测蠕变破裂的明显指标. 相似文献
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Inferences on the rheology of the mantle based on theoretical and experimental rate equations for steady state creep are discussed and compared with results from geophysical models. The radial increase of viscosity by one to three orders of magnitude across the mantle, required by inversion of postglacial rebound and geodynamic data, is confirmed by microphysical models based on the estimation of continuous and discontinuous changes of creep parameters with depth. The upper mantle (viscosity 1020–1021 Pa s) is likely to show non-Newtonian rheology (power-law creep) for average grain sizes larger than 0.1 mm as an order of magnitude. Given the variability of both grain size and stress conditions, local regions of linear rheology can be present. The rheology of transition zone and lower mantle (viscosity 1022–1024 Pa s) cannot be definitely resolved at present. Estimation of creep parameters leads to possible nonlinear or mixed rheology, if grain sizes are not lower than 0.1 mm and flow conditions can be approximated by a constant strain rate of about 10−15 s−1. This conclusion can be modified by different flow conditions (e.g. a decrease in strain rate or constant viscous dissipation). Furthermore, experiments on fine-grained garnetites and perovskite analogues have shown that diffusion creep is predominant at laboratory conditions. However, the pressure dependence of creep in these phases is unknown, and therefore direct extrapolation to lower mantle conditions is necessarily speculative. Lateral variations of viscosity, largest in the upper and lowermost mantle (up to 2–4 orders of magnitude) are predicted by models based on lateral temperature anomalies derived from seismic tomographic models. 相似文献
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Siegfried Franck Christine Bounama 《Physics of the Earth and Planetary Interiors》1997,100(1-4):189-196
We investigate the thermal and degassing history of the Earth with the help of a parameterized mantle convection model including the volatile exchange between mantle and surface reservoirs. The weakening of mantle silicates by dissolved volatiles is described by a functional relationship between creep rate and water fugacity. We use flow law parameters of diffusion creep in olivine under dry and wet conditions. The mantle degassing rate is considered as directly proportional to the seafloor spreading rate, which is also dependent on the mantle heat flow and the continental area. To calculate the spreading rate, we assume three different continental growth models: constant growth, delayed growth, and the one proposed by Reymer and Schubert (1984, Tectonics, 3: 63–77). The rate of regassing also depends on the seafloor spreading rate, as well as on other factors. Both mechanisms (degassing and regassing) are coupled self-consistently with the help of a parameterized convection model under implementation of a temperature and volatile-content dependent mantle viscosity. We calculate time series for the Earth's evolution over 4.6 Gyr for the average mantle temperature, the mantle heat flow, the mantle viscosity, the Rayleigh number, the Urey ratio, the volatile loss, and the seafloor spreading rate. In those numerical simulations with continental growth from the beginning and a high initial average mantle temperature water is outgassed rapidly. In the delayed continental growth model there is a very early outgassing event and the delayed continental growth has no remarkable influence on the thermal and outgassing history. A similar situation is found for the linear continental growth model but not for the Reymer and Schubert (1984) model. 相似文献
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Grain growth experiments in dunite, clinopyroxenite, and wehrlites with various forsterite/diopside ratios were performed to investigate the effect of modal composition on grain growth kinetics in the Earth's uppermost mantle. The experiments were conducted using a piston-cylinder apparatus at 1200 °C and 1.2 GPa for 2-763 h under dry conditions. Normal grain growth (NGG) occurred in dunite, clinopyroxenite, and relatively forsterite-poor wehrlites (≤70 vol.% of forsterite). Grain growth rates of forsterite and diopside in relatively forsterite-poor wehrlites were much slower than those in dunite and clinopyroxenite. In the forsterite-rich wehrlites (≥80 vol.% of forsterite), NGG of diopside and abnormal grain growth (AGG) of forsterite occurred. The growth rate of diopside was significantly slower than that in clinopyroxenite, while the growth rate of forsterite by AGG was found to be similar to that by NGG in dunite. The presence of ≤20 vol.% diopside had the effect of inhibiting the forsterite grain growth during the initial stage, resulting in AGG of forsterite, thus overtaking the growth rate in dunite. Our experimental results suggest that there would be a significant difference in grain growth rate and consequently in effective viscosity between olivine-rich peridotites (depleted mantle) and relatively olivine-poor peridotites (fertile mantle) in the case of grain size-sensitive creep. Variation of mean grain sizes in the upper mantle would result not only from differences in temperature and phase assemblage, but also from the variation of modal compositions. 相似文献
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Hans-Peter Plag Bjrn Engen Thomas A. Clark John J. Degnan Bernd Richter 《Journal of Geodynamics》1998,25(3-4)
The WEGENER† activities related to the study of post-glacial rebound are presented together with a review of the present state-of-the-art in this study field. Post-glacial rebound research is an unique tool for studying the viscoelastic behaviour of the Earth's mantle on time scales of thousands of years. The viscosity structure of the Earth's mantle determined from an inversion of observations of glacially induced deformations is a basic requirement for modelling long-term phenomena such as the convection in the Earth's mantle, and for better understanding unsolved questions such as the nature of the mantle discontinuities or the vertical scale of convection.First, an introduction to the scientific background is given, and the three principal ingredients for post-glacial rebound studies, namely the ice model, the Earth model, and the observations are briefly considered. For the ice model, the uncertainties due to a trade-off between ice model and Earth rheology are outlined. The different approaches used to model the Earth and its deformations in post-glacial rebound studies are discussed emphasising the preliminary nature of the derived rheologies and depth dependencies. The observations, in particular the relative sea-level changes and three-dimensional surface deformations, are described with special emphasis on observational gaps. Based on the discussion of the ingredients, an outline of the future developments in post-glacial rebound research is attempted with particular emphasis on the Earth model and the theory of deformations.For several decades extreme efforts have been made to precisely monitor the land uplift in Scandinavia. However, for the height component the existing data still are associated with large uncertainties while reliable data on the horizontal component are practically nil. The ongoing long-term (longer than ten years) spacegeodetic measurements are likely to provide the three-dimensional deformations with the spatial resolution and accuracy required in order to substantially contribute to post-glacial rebound studies. Thus, present-day three-dimensional deformations of the Earth's surface beneath and around the former ice sheets as a constraint for the mantle rheology and viscosity structure will increasingly become important as they become known from space-geodetic measurements with high spatial resolution and an accuracy approaching the mm/a-level. 相似文献
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B. I. Birger 《Izvestiya Physics of the Solid Earth》2007,43(8):635-641
Analysis of results of laboratory studies on creep of mantle rocks, data on seismic wave attenuation in the mantle, and rheological micromechanisms shows that the universal, i.e., relevant to all time scales, rheological model of the mantle can be represented as four rheological elements connected in series. These elements account for elasticity, diffusion rheology, high temperature dislocation rheology, and low temperature dislocation rheology. The diffusion rheology element is described in terms of a Newtonian viscous fluid. The high temperature dislocation rheology element is described by the rheological model previously proposed by the author. This model is a combination of a power-law non-Newtonian fluid model for stationary flows and the linear hereditary Andrade model for flows associated with small strains. The low temperature dislocation rheology element is described by the linear hereditary Lomnitz model. 相似文献
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通过研究地球对表面载荷的响应来反演确定地球深部的物理参数.采用分为4层的地球模型,各层的介质被看作Maxwell粘弹性体.将柴达木盆地沉降发育过程中积累的沉积物作为随时间变化的载荷加于地表,通过拟合柴达木盆地沉降中心附近地区的沉降过程来研究该地区地壳的厚度及剪切模量、岩石层地幔的粘性及软流层的粘性等物理参数.计算结果表明,该地区地壳的剪切模量不会超过全球平均值的60％,岩石层地幔的粘性系数不大于1.5×1023Pa·s.通过研究对该地区的深部物理参数得出了新的认识. 相似文献
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Parameterized thermal model of a mixed mantle convection 总被引：4，自引：0，他引：4
IntroductionTectonicevolutionisinfluencedbythermalhistoryoftheEarth.TheEarthhasabout4.6Gahistory.ThermalenergyfromtheinterioroftheEachprovidesthemainpowerfortectonicevolution.ItnotonlycontrolstheformationofthelayeredstructuresinsidetheEarth,butalsopromotesthetectonicmovementsofthesurfaceplatesduringthegeologicalera.ThestudyofthethermalhistoryoftheEarthhaspassedseveralstages.Inearlystudies,onlyconductivemechanism(Lubimova,1958)isdiscussedinthethermalevolution.However,theimpotalceofthermalco… 相似文献