共查询到20条相似文献，搜索用时 46 毫秒
1.
J.Peter Watt 《Physics of the Earth and Planetary Interiors》1981,25(1):57-63
Mean atomic weight profiles for the lunar mantle have been calculated from velocity-density systematic relations using lunar density and seismic velocity models. Despite large variability among the models, the calculation including Poisson's ratio yields a range of mean atomic weight values between 22 and 23 g mol?1 below 150 km. A similar calculation for the Earth's mantle produces a mean atomic weight of 21.1 ±0.4 g mol?1. This suggests that the Moon cannot be derived directly from the Earth's mantle, or that it has had a differentiation history different from the Earth's. The lunar require an Fe mole fraction between 0.25 and 0.33 for a pure olivine mantle, or between 0.33 and 0.45 for pure pyroxene.The present profiles are 0.5–3.0 g mol?1 higher than those calculated from lunar compositional models based on lunar rock compositions and petrology and assumed lunar histories, indicating inadequacies in either the seismic or compositional models, or in both. The mean atomic weight approach provides a method of comparing the consistency of seismic and compositional models of planetary interiors. 相似文献
2.
An expression for the inviscid horizontal velocity field at the surface of the Earth's core necessary to account for the poloidal main magnetic field and its secular variation seen at the Earth's surface is derived for an insulating mantle in the limit of infinite core conductivity. The starting point of derivation is Ohm's law rather than the magnetohydrodynamic induction equation. Maps of the resulting motion for epoch 1965.0 at different truncation levels are presented and discussed. 相似文献
3.
B.S. Volvovsky I.S. Volvovsky N.Sh. Kambarov 《Physics of the Earth and Planetary Interiors》1983,31(4):307-312
Deep seismic sounding studies carried out in 1974–79 allowed an important peculiarity of the deep structure of the Pamir-Himalayas region to be established: the thickness of the Earth's crust is almost twice as large here as on the stable plates (65–75 and 35–37 km, respectively). The absence of any evidence for doubling of crustal thickness provides grounds for rejecting the hypothesis of subduction of the rigid Hindustan plate under the geosynclinal folded constructions of the Punjab syntaxis of the Himalayas. The steep inclination of all major faults, dissecting the Earth's crust and often dislocating the M surface, is also counter to this hypothesis. Several faults reflect the dynamics and conditions of formation of deep layers of the lithosphere. For example, the structural seam of the Indus, which has an almost sheer tilt and which penetrates to subcrustal depths, is a channel along which ophiolite associations of crystalline rocks were squeezed from the mantle. The Fore Himalayan and Major Himalayan faults are the boundaries between different structural facial zones. The band of greatest thickness of crust extends within the zone of greatest thickness of the asthenospheric layer; a deep minimum in the Bouguer anomalies (?550 mGal) corresponds to this zone, as does also a depression on the surface of the geoid.Seismicity of the lithosphere of the Pamir-Himalayas region is caused by geodynamic processes manifested in the higher lithospheric layers by block displacements of the Earth's crust (mostly uplifts), and in the lower parts by shifts of the steeply inclined mantle blocks (the Pamir-Hindukush seismic focal zone). 相似文献
4.
《Physics of the Earth and Planetary Interiors》1981,24(4):325-332
Upwelling flows in the Earth's mantle are accompanied by mass, momentum and energy transports from deep to upper layers. Those flows beneath the mid-ocean ridges give rise to sea-floor spreading. Mantle plumes, on the other hand, cause hot spots to be formed on the Earth's surface. Using the basic equations of fluid dynamics, temperature and velocity distributions in two-dimensional upwelling and cylindrical plumes can be obtained by an integral-relation method. Then the mass, momentum and energy transported to the lithosphere by these upwelling flows can readily be calculated. Based on those results we can more thoroughly discuss problems of plate dynamics, such as the driving mechanism of plate motion, the causes of formation of rift valleys over mid-ocean ridges, and the effect of mantle plumes on sea-floor spreading. 相似文献
5.
6.
R.G. Roberts 《Physics of the Earth and Planetary Interiors》1983,33(3):198-212
The composition of the upper mantle is of great significance to our understanding of plate tectonics and global evolution. Information about the physical properties of the Earth at upper mantle depths, including lateral variations in electrical conductivity, can be deduced from measurements of the electric and magnetic fields at the Earth's surface. Electromagnetic methods appear to give poorer resolution than do some other methods, for example seismics, but as they are sensitive to quite different properties of a medium they provide a different and complementary class of information.The basic theory of electromagnetic sounding methods is briefly reviewed below, and evidence regarding lateral conductivity inhomogeneities in the Earth's upper mantle is examined. While lateral electrical conductivity inhomogeneities appear to be the rule rather than the exception, the interpretation of electromagnetic data still presents difficulties and the results from many regions are not as yet unambiguous. Where the data are of sufficient resolution, a rapid increase in electrical conductivity can usually be identified within the upper mantle. The depth to this highly conductive zone is different in different tectonic environments, but is broadly consistent between analogous but widely separated tectonic environments. A comparatively shallow conducting region is found beneath the ocean lithosphere. The depth of this region is dependent on lithospheric age. Many of the more shallow conducting regions in both continental and oceanic environments are associated with high heat flow values and seismic low velocity zones. These highly conducting regions may be zones of partial melt. 相似文献
7.
Edward Stolper 《Earth and Planetary Science Letters》1979,42(2):239-242
The average concentrations of 19 siderophile and volatile elements in shergottite meteorites differ from those in terrestrial basalts by less than a factor of ten. This observation undermines claims that the abundances of siderophile and volatile elements in the Earth's upper mantle are uniquely terrestrial. Claims that similarities in the Moon's siderophile element pattern imply a terrestrial origin for the Moon are also weakened. The implication that basalt source regions on the asteroidal parent body of the shergottites resembled the terrestrial upper mantle constrains models of planetary formation and evolution. Heterogeneous accretion models may explain many of the similarities between these planets. Alternatively, separation of sulfide from basaltic magmas or their source regions on the Earth and the shergottite parent body may explain some of these similarities. 相似文献
8.
D.P. Zidarov 《Physics of the Earth and Planetary Interiors》1985,37(1):74-86
The advantages of the approximation of the Earth's magnetic field by means of the field of the so-called natural magnetic sources are discussed. The shifting of these natural magnetic sources, determined for different epochs, is used to forecast the Earth's magnetic field and to draw conclusions about the motion of the corresponding part of the Earth. On the basis of the representation of the Earth's magnetic field from several past geological epochs as a field of one optimum dipole a new theory about the Earth's evolution is proposed. 相似文献
9.
S.I. Braginsky 《Physics of the Earth and Planetary Interiors》1976,11(3):191-199
A short review of the present state of the nearly axially-symmetrical dynamo model is given. A simplified theory for hydromagnetic dynamos taking into account the forces acting in the Earth's core is considered. The role of weak core-mantle friction is discussed and a form of solution is suggested which is characterized by a large geostrophic velocity in the core and by a boundary layer of a new type. The consequences of such a model (called model Z) for the Earth's dynamo are discussed. 相似文献
10.
The study of Poisson's ratio (σ) behaviour in various crystalline rocks under different temperatures and pressures shows this parameter to depend upon the rock composition rather than upon P-T conditions. The results of this study are presented in the form of a comparison of σ(z) distributions within the consolidated crust and continental upper mantle and the specific variations of σ in crust and mantle rocks underlying the Voronezh crystalline massif (VCM). These investigations, which are based upon seismic and seismological data as well as high pressure experiments, should clarify in particular the composition and petrology of the Earth's interior. 相似文献
11.
The studies on the structure and physical properties of the Earth‘s interior done by Chinese geophysicists from 1999 to 2002 were reviewed in this paper. It includes several research areas: the structure of the Earth‘s interiors using seismic tomography, anisotropy of the upper mantle in China and its adjacent areas, quality factor Qβ for S waves, subduction zone, mantle discontinuities, physical properties of Earth‘s materials and others. The review concerns mainly the contents, the methods and the results of the studies. It can be seen that new progress in the study on the structure and physical properties of the Earth‘s interior has been made in the last 4 years in China. It is shown on three aspects: advancement made on some preexistent areas; pioneering on some new fields and new methods adopted. 相似文献
12.
The melting curves of CaCO3 and MgCO3 have been extended to pressures of 36 kb by experiments in piston-cylinder apparatus. At 30 kb, the melting temperatures of calcite and magnesite are 1610°C and 1585°C, respectively. New data for the magnesite dissociation reaction permit the location of an invariant point for the assemblage magnesite + periclase + liquid + vapor near 26 kb-1550°C. New data are also presented for the calcite-aragonite transition at 800°C, 950°C and 1100°C. At pressures above 36–50 kb, calcite and magnesite melt at temperatures lower than the solidus of dry mantle peridotite. Natural and experimental evidence suggests that carbon dioxide in the Earth's mantle could be present in a variety of forms: (a) a free vapor phase, (b) vapor dissolved in silicate magma, (c) crystalline carbonate, (d) carbonatite liquid, (e) carbon-bearing silicate analogs, or (f) carbonato-silicates (such as scapolite, spurrite, tilleyite, and related compounds). 相似文献
13.
U.R. Christensen 《Physics of the Earth and Planetary Interiors》1984,35(4):264-282
The case is presented that the efficiency of variable viscosity convection in the Earth's mantle to remove heat may depend only very weakly on the internal viscosity or temperature. An extensive numerical study of the heat transport by 2-D steady state convection with free boundaries and temperature dependent viscosity was carried out. The range of Rayleigh numbers (Ra) is 104?107 and the viscosity contrast goes up to 250000. Although an absolute or relative maximum of the Nusselt number (Nu) is obtained at long wavelength in a certain parameter range, at sufficiently high Rayleigh number optimal heat transport is achieved by an aspect ratio close to or below one. The results for convection in a square box are presented in several ways. With the viscosity ratio fixed and the Rayleigh number defined with the viscosity at the mean of top and bottom temperature the increase of Nu with Ra is characterized by a logarithmic gradient β = ?ln(Nu)/? ln(Ra) in the range of 0.23–0.36, similar to constant viscosity convection. More appropriate for a cooling planetary body is a parameterization where the Rayleigh number is defined with the viscosity at the actual average temperature and the surface viscosity is fixed rather than the viscosity ratio. Now the logarithmic gradient β falls below 0.10 when the viscosity ratio exceeds 250, and the velocity of the surface layer becomes almost independent of Ra. In an end-member model for the Earth's thermal evolution it is assumed that the Nusselt number becomes virtually constant at high Rayleigh number. In the context of whole mantle convection this would imply that the present thermal state is still affected by the initial temperature, that only 25–50% of the present-day heat loss is balanced by radiogenic heat production, and the plate velocities were about the same during most of the Earth's history. 相似文献
14.
Toshihiro Suzuki Syun-iti Akimoto Yuh Fukai 《Physics of the Earth and Planetary Interiors》1984,36(2):135-144
The system iron-enstatite-water was investigated at pressures around 5 GPa and at temperatures ranging from 1000 to 1200°C, using several different kinds of starting materials. Quenched samples showed the coexistence of iron, olivine and pyroxene. Synthesis of the Fe-containing olivine in the run products proves that a series of reactions, Fe + H2O → FeHx + FeO and FeO + MgSiO3 → (Mg, Fe)2SiO4, have taken place. Spherical “balls of iron” were observed in the 1200°C run. This strongly indicates that the melting temperature of iron decreased by ～ 500 K by the possible dissolution of hydrogen. Following geophysical implications are derived from these experimental results. If water was retained in the hydrous minerals in the primordial material, the iron-water reaction is expected to occur throughout the core-formation process. The reaction product FeHx will melt and then sink to form a proto-core and iron oxide will be dissolved in the Earth's mantle. The dissolution of hydrogen in the Earth's core is a natural consequence of the core-formation process. 相似文献
15.
Hiroshi Mizuno Kiyoshi Nakazawa Chushiro Hayashi 《Earth and Planetary Science Letters》1980,50(1):202-210
We have shown in a previous paper that, if the primordial solar nebula existed when the Earth was formed, the Earth was once surrounded by a dense and massive primordial atmosphere, whose temperature and pressure were about 4000 K and 900 atm, respectively, at the bottom. We suppose that this hydrogen-rich atmosphere escaped from the Earth after the solar nebula itself disappeared, both phenomena probably being due to the effect of strong solar wind and radiation.Using the results of our previous and new calculations on the structure of the primordial atmosphere, we have investigated the amount of dissolution of the rare gases, which were contained in the primordial atmosphere, into the molten Earth's material.The amount of the dissolved rare gases is found to be strongly dependent on the grain opacity of the atmosphere, i.e., on the amount of fine grains. However, their isotopic ratios and relative abundance are independent of the opacity and approximately equal to those in the primordial solar nebula, that is, to the present solar values. Especially, the dissolved neon is expected to have remained in the present mantle. Therefore, if a considerable amount of neon with nearly the solar isotopic ratio is discovered in present mantle material, this offers direct evidence for the proposition that the proto-Earth was once surrounded by the primordial atmosphere. 相似文献
16.
Martian surface features such as quasi-circular structures in polar regions have been previously cited as evidence of polar wander (i.e., large-scale relative motion between a body-fixed axis and the rotation pole). Another feature, the Coprates (Valles Marineris) trough assemblage, is proposed as further, plausible evidence of such wander. This trough assemblage is explained as a failure due to curvature changes in Mars' lithosphere, in the manner of certain hypotheses explaining terrestrial features (e.g. East African Rift System). In the Earth's case plate tectonics cause lithospheric curvature changes, whereas, in Mars' case polar wander is most probable. Membrane stresses which can reach 10 kbars are shown to most likely over-shadow bending stresses. Flattening changes are judged to be inappropriate. Simple wander scenarios are constructed to illustrate the hypothesis. 相似文献
17.
D. Crossley 《Physics of the Earth and Planetary Interiors》1984,36(1):1-16
There has been renewed interest lately in the possibility that at least a part of the Earth's liquid core may be stably stratified. A gravitationally stable region would permit the existence of inertia-gravity or gravity-inertia waves in addition to the Rossby and Kelvin waves which exist due to rotational effects and which are well known in oceanography and atmospheric dynamics. These wave motions are of interest because their periods are dependent on the density stratification as specified by the buoyancy frequency N which in turn determines the amplitude of large-scale radial motions in the core.The waves have too high a frequency to be connected dynamically to the magnetic field in the core, but if they do exist they may be detectable by sensitive long-period gravimeters at the Earth's surface. This paper examines the available evidence for the frequency regimes, excitation and damping mechanisms of the core waves. It is concluded that although the waves may exist theoretically, their detection and interpretation as a method for determining N is a difficult proposition. 相似文献
18.
K. Ramaswamy M. Dheenathayalu S. Bharathan 《Physics of the Earth and Planetary Interiors》1985,40(1):61-64
A detailed study of the ancient intensity of the Earth's magnetic field in Tamilnadu, India is presented using pottery, bricks, tiles etc., obtained from the excavations that have been carried out at some of the important places of historical and archaeological interest. An attempt is made to reconstruct the secular variation of the geomagnetic field intensity. The results reported here reveal considerable changes in the Earth's magnetic field in this region during the past 2400 y. It is observed that the intensity of the geomagnetic field has been previously 57% greater than at present. 相似文献
19.
From the partial differential equations of hydrodynamics governing the movements in the Earth's mantle of a Newtonian fluid with a pressure- and temperature-dependent viscosity, considering the bilateral symmetry of velocity and temperature distributions at the mid-plane of the plume, an analytical solution of the governing equations near the mid-plane of the plume was found by the method of asymptotic analysis. The vertical distribution of the upward velocity, viscosity and temperature at the mid-plane, and the temperature excess at the centre of the plume above the ambient mantle temperature were then calculated for two sets of Newtonian rheological parameters. The results obtained show that the temperature at the mid-plane and the temperature excess are nearly independent of the rheological parameters. The upward velocity at the mid-plane, however, is strongly dependent on the rheological parameters. 相似文献
20.
With the compelling evidence for orthorhombic perovskite ABO3 structures in a major part of the earth's mantle, the question of whether any of these are ferroelectric (FE) or antiferroelectric should be of supreme importance. To answer this question the authors have conducted dielectric property studies at pressures up to 5.5 GPa on single crystals and polycrystalline aggregates of BaTiO3 as well as other FE materials representing FE polarization mechanisms. The results indicate that: (1) h.p.-induced FE phases are indeed likely to play an important part in the earth's mantle; and (2) existing FE state, occuring as elastic and dielectric inhomogeneities, can persist to much higher pressures than expected on the basis of the pressure dependence of isolated and unclamped FE crystals. It is suggested that the presence of FE states in the earth's mantle may be responsible for some of its anomalous elastic and dielectric features, especially its attenuating properties. It is conjectured that effects of FE states on properties of the Jovian planets might even be more prominant, especially those involving dielectric constant and polarization. 相似文献