共查询到20条相似文献，搜索用时 875 毫秒
1.
It is shown that, in accordance with the data used when determining velocity distribution in the Earth’s core [14], so called “precursor” earthquakes cannot be produced by wave scattering to lower mantle inhomogeneities, because seismic rays linking the earthquake sources and seismic stations are located in different inner zones of the Earth and travel at different azimuths, producing a stable wave pattern on aggregate. Thus, the present work considers the fundamental problem regarding what precursor earthquakes are. Solution of this problem will guide ideas about the structure of the Earth’s core. 相似文献
2.
Tectonomagmatic evolution of the Earth and Moon 总被引：1，自引：0，他引：1
The Earth and Moon evolved following a similar scenario. The formation of their protocrusts started with upward crystallization
of global magmatic oceans. As a result of this process, easily fusible components accumulated in the course of fractional
crystallization of melt migrating toward the surface. The protocrusts (granitic in the Earth and anorthositic in the Moon)
are retained in ancient continents. The tectonomagmatic activity at the early stage of planet evolution was related to the
ascent of mantle plume of the first generation composed of mantle material depleted due to the formation of protocrusts. The
regions of extension, rise, and denudation were formed in the Earth above the diffluent heads of such superplumes (Archean
granite-greenstone domains and Paleoproterozoic cratons), whereas granulite belts as regions of compression, subsidence, and
sedimentation arose above descending mantle flows. The situation may be described in terms of plume tectonics. Gentle uplifts
and basins (thalassoids) in lunar continents are probable analogues of these structural elements in the Moon. The period of 2.3–2.0 Ga ago was a turning point in the
tectonomagmatic evolution of the Earth, when geochemically enriched Fe-Ti picrites and basalts typical of Phanerozoic within-plate
magmatism became widespread. The environmental setting on the Earth’s surface changed at that time, as well. Plate tectonics,
currently operating on a global scale, started to develop about ∼2 Ga ago. This turn was related to the origination of thermochemical
mantle plumes of the second generation at the interface of the liquid Fe-Ni core and silicate mantle. A similar turning point
in the lunar evolution probably occurred 4.2–3.9 Ga ago and completed with the formation of large depressions (seas) with thinned crust and vigorous basaltic magmatism. Such a sequence of events suggests that qualitatively new material previously
retained in the planets’ cores was involved in tectonomagmatic processes at the middle stage of planetary evolution. This
implies that the considered bodies initially were heterogeneous and were then heated from above to the bottom by propagation
of a thermal wave accompanied by cooling of outer shells. Going through the depleted mantle, this wave generated thermal superplumes
of the first generation. Cores close to the Fe + FeS eutectics in composition were affected by this wave in the last turn.
The melting of the cores resulted in the appearance of thermochemical superplumes and corresponding irreversible rearrangement
of geotectonic processes. 相似文献
3.
New W-isotope evidence for rapid terrestrial accretion and very early core formation 总被引：1，自引：0，他引：1
Ronny SchoenbergBalz S. Kamber Kenneth D. CollersonOtto Eugster 《Geochimica et cosmochimica acta》2002,66(17):3151-3160
The short-lived 182Hf-182W-isotope system is an ideal clock to trace core formation and accretion processes of planets. Planetary accretion and metal/silicate fractionation chronologies are calculated relative to the chondritic 182Hf-182W-isotope evolution. Here, we report new high-precision W-isotope data for the carbonaceous chondrite Allende that are much less radiogenic than previously reported and are in good agreement with published internal Hf-W chronometry of enstatite chondrites. If the W-isotope composition of terrestrial rocks, representing the bulk silicate Earth, is homogeneous and 2.24 ε182W units more radiogenic than that of the bulk Earth, metal/silicate differentiation of the Earth occurred very early. The new W-isotope data constrain the mean time of terrestrial core formation to 34 million years after the start of solar system accretion. Early terrestrial core formation implies rapid terrestrial accretion, thus permitting formation of the Moon by giant impact while 182Hf was still alive. This could explain why lunar W-isotopes are more radiogenic than the terrestrial value. 相似文献
4.
Krasnoshchekov D. N. Ovtchinnikov V. M. Usoltseva O. A. 《Doklady Earth Sciences》2019,488(2):1186-1189
Doklady Earth Sciences - Analysis of PKIIKP waves reflected off the inner surface of the solid core boundary and recorded close to the antipode indicates that the shear wave velocity at its top can... 相似文献
5.
6.
Isotopic constraints on the age of the Earth’s core: Mutual consistency of the Hf-W and U-Pb systems
Yu. A. Kostitsyn 《Geochemistry International》2012,50(6):481-501
The estimation of the time of Earth??s core formation on the basis of isotopic systems with short-lived and long-lived parent nuclides gives significantly different results. Isotopic data for the 182Hf-182W system with a 182Hf half-life of approximately 9 Myr can be interpreted in such a way that the core was formed 34 Myr after the origin of the solar system assuming complete core-mantle equilibrium. Similar estimates on the basis of the U-Pb isotopic system suggest a significantly longer mean time of core formation of approximately 120 Myr. If the Earth??s core were formed instantaneously, both isotopic systems would have shown identical values corresponding to the true age. The discrepancy between the U-Pb and Hf-W systems can be resolved assuming prolonged differentiation of prototerrestrial material into silicate and metallic phases, which occurred not simultaneously and uniformly in different parts of the mantle. This resulted in the isotopic heterogeneity of the mantle, and its subsequent isotopic homogenization occurred slowly. Under such conditions, the mean isotopic compositions of W and Pb in the mantle do not correspond to the mean time of the separation of silicate and metallic phases. This is related to the fact that the exponential function of radioactive decay is strongly nonlinear at high values of the argument, and its mean value does not correspond to the mean value of the function. There are compelling reasons to believe that the early mantle was heterogeneous with respect to W isotopic composition and was subsequently homogenized by convective mixing. This follows from the fact that the lifetime of isotopic heterogeneities in the mantle is close to 1.8 Gyr for various long-lived isotopic systems. There is also no equilibrium between the mantle and the core with respect to the contents of siderophile elements. Because of this, the mean isotopic ratios of W and Pb cannot be used for the direct computation of the time of metal-silicate differentiation in the Earth. Such estimation requires more sophisticated models accounting for the duration of the differentiation process using several isotope pairs. Given the prolonged core formation, which has probably continued up to now, the question about its age becomes ambiguous, and only the most probable growth rate of the core can be estimated. The combined use of the U-Pb and Hf-W systems constrains the time of formation of 90% of the core mass between 0.12 and 2.7 billion years. These model estimates could have been realistic under the condition of complete disequilibrium between the silicate and metallic phases, which is as improbable as the suggestion of complete equilibrium between them on the whole Earth scale. 相似文献
7.
中国含油气盆地波状运动特征研究 总被引：11，自引：0，他引：11
以地壳波状运动理论为指导思想，综合分析岩芯、钻井、测井、录井等资料，应用沉积盆地波动过程分析方法，研究了塔里木盆地、渤海湾盆地、三水盆地演化过程中的主要周期。研究成果表明：２２０±Ｍａ周期是银河年周期对地球的影响，６５±Ｍａ周期反映了太阳系在银道面上、下的运动周期及地幔对流周期对地表作用结果；１０±Ｍａ周期是太阳能量的变化周期在地表沉积物中的反映。这些不同级别的周期波作用于地球表面，其叠加耦合的结果将造成不同时期地层的沉积或剥蚀速度的变化及其量级的差异，以及剥蚀事件的非等时性。地壳的波状运动说明，地壳的负向运动（沉降）与正向运动（抬升）是对立统一的，它们都应隶属构造运动的范畴，正向运动仅是构造运动的一个方面。 相似文献
8.
A numerical–analytical approach is used to investigate irregular effects in oscillations of the Earth’s pole related to variations in the Chandler and annual components. An approach to studying oscillations in the motion of the Earth’s pole based on a joint analysis of the Chandler and annual components of this motion is proposed. A transformation to a new coordinate system in which the motion of the pole is synchronous with the precession of the lunar orbit can be found in this approach. Estimates of the precision of predictions of the coordinates of the Earth’s pole taking into account additional terms due to lunar perturbations are presented.
相似文献9.
同步辐射激光加温DAC技术及在地球深部物质研究中的应用 总被引：1，自引：1，他引：0
实验室模拟地球深部的温度和压力环境,研究地球相关材料的物理和化学性质,是解释地震波数据、进一步了解地球内部结构和动力学过程的重要途径。用高功率的红外激光光束,加温金刚石对顶砧压腔(DAC)中的样品,可以获得深部地幔乃至地核的极端温度和压力条件,已广泛地用于地球深部矿物的相变、熔融和状态方程研究。同步辐射微束技术的发展,为激光加温DAC技术的应用开辟了新的领域,也使地幔及地核条件下的矿物研究有了重要的突破。文章介绍激光加温DAC技术的发展;阐述高温高压原位的同步辐射X射线衍射方法;例举激光加温DAC技术在地球深部物质研究中的一些应用;并对一些关键的技术问题加以分析和讨论。 相似文献
10.
Chepurov A. I. Zhimulev E. I. Sonin V. M. Tomilenko A. A. Pokhilenko N. P. 《Doklady Earth Sciences》2018,480(2):823-825
The first results are presented for the synthesis of diamond at 6.5 GPa and 1600°C during migration of molten iron through a silicate matrix, which is composed of olivine crystals with interstitial graphite. The experiment shows that diamonds in the Earth’s mantle and the terrestrial planets could have formed during differentiation. Diamond crystals, which were formed during iron segregation of the Earth’s differentiation, could be centers for further crystallization of mantle diamonds.
相似文献11.
Dolgikh G. I. Budrin S. S. Dolgikh S. G. Ovcharenko V. V. Pivovarov A. A. Samchenko A. N. Shvyrev A. N. Chupin V. A. Yaroshchuk I. O. 《Doklady Earth Sciences》2017,475(1):811-815
On the basis of experimental data obtained during a comprehensive experiment in Vityaz Bay of the Sea of Japan using onshore laser strainmeters and a low-frequency hydroacoustic emitter generating complex phase-manipulated signals with a central frequency of 33 Hz, we developed the basic principles of contactless tomography of the Earth’s crust in the shelf regions of various seas, including those covered by ice, making it possible to determine efficiently the structure and composition of the upper Earth’s crust under seas.
相似文献12.
The results of instrumental observations have shown that the spectra of geomagnetic variations exhibit a quasi-harmonic component, the frequency of which is close to the basic spheroidal mode of the Earth 0S2. In periods 15 days long after three large earthquakes and in the absence of strong magnetic disturbances, the fine structure of this mode in geomagnetic variations is identified in the form of singlets. The frequencies of these singlets are similar to the theoretical values calculated using an ideal elastic isotropic model of the Earth of spherical symmetric form without its rotation.
相似文献13.
This paper reports on the geoecological state of landscapes of oil and gas fields in the Ural–Volga steppe zone. Large-scale direct disturbances and impacts with dramatic aftereffects have been revealed on the basis of field research using the geographic information system (GIS) and data from remote sensing of the Earth. It has been shown that the current land-use pattern in oil and gas production areas is in need of professional control to protect and recover the landscapes in the steppe zone.
相似文献14.
Summary ?We describe here a model of formation of the core and the early history of Earth based on recent experimental mineralogical
data. In a nebular setting, where differentiated planetesimals with their iron cores were plentiful, hot condensing solids
mixed with the planetesimal irons and formed the solid proto-core (Fe-Ni-S-C). FeO from unmixing in magnesiowustite and from
a dissociation of perovskite in the newly accreted mantle concentrated at the core-mantle interface and reacted with the nascent
core. The interface grew to form the liquid core (Fe-Ni-O-S-C) at the expense of the solid proto-core and the formation of
much of the outer core was complete within the first 500 million years. The model is consistent with geochemical data and
has important implications for the dynamics of the inner core.
Received February 9, 1999;/revised version accepted April 9, 1999 相似文献
Zusammenfassung ?Das Innere der Erde: Ein Modell basierend auf mineralogischen Daten Wir pr?sentieren ein Modell zur Bildung des Erdkerns und der frühen Geschichte der Erde, das auf neuen experimentellen mineralogischen Daten basiert. In einem nebularen System, in dem differenzierte Planetesimals mit Eisenkernen sehr h?ufig waren, mischten sich kondensierte Festk?rper mit dem Eisen der Planetesimals, um einen festen Protokern (Fe-Ni-S-C) zu formen. FeO, das aus Magnesiowüstit entmischte und durch Dissoziation aus Perovskit im Mantel entstand, konzentrierte sich in der Kern – Mantel – Grenzzone und reagierte mit dem neugebildeten Kern. Diese Grenzzone wuchs und es entstand ein flüssiger (Fe-Mi-O-S-C) Kern auf Kosten des festen Protokerns. Die Bildung des ?u?eren Kerns war innerhalb der ersten 500 Millionen Jahre abgeschlossen. Dieses Modell ist mit geochemischen Daten konsistent und hat wichtige Auswirkungen auf die Dynamik des inneren Kerns.
Received February 9, 1999;/revised version accepted April 9, 1999 相似文献
15.
地球系统演化原因研究的回顾与展望 总被引：4，自引：1，他引：3
简略回顾了地球系统的研究历史,指出人类数千年来关于地球系统的研究可分为古代、大分化和大融合 3个阶段,提出"地球系统学"在今后相当一段时间内将是地学研究的主流。第二部分探索地球系统演化的原因,指出："热"是影响地球系统的途径,但地表面受热的准周期性变化不应是整个地球系统演化的主要原因;对于各种引力的准周期性变化对气候变化的影响,归纳出这样一条可能的途径：天体引力→地核环流变化→通过地幔热柱影响软流圈波动变化→通过地热影响气候变化;宇宙磁场通过"变压器效应"调制地核中的Lorenz力,使地核环流变化,进而影响地球系统演化。第三部分提出"外核环流是主导地表系统演化的总枢纽"假说。最后指出：一定要从宇地相互作用中寻求地球系统演化的原因;宇地之间相互联系的热、力和电磁三种物理过程中,"磁"是最值得予以关注的;核幔边界层很可能是推动地核环流和地幔对流的能源区。 相似文献
16.
The extreme depletion of the Earth’s mantle in sulfur is commonly seen as a signature of metal segregation from Earth’s mantle to Earth’s core. However, in addition to S, the mantle contains other elements as volatile as S that are hardly depleted relative to the lithophile volatility trend although they are potentially as siderophile as sulfur. We report experiments in metal-sulfide–silicate systems to show that the CI normalized abundances of S, Pb, and Sn in Earth’s mantle cannot be reproduced by element partitioning in Fe ± S–silicate systems, neither at low nor at high pressure. Much of the volatile inventory of the Earth’s mantle must have been added late in the accretion history, when metal melt segregation to the core had become largely inactive. The great depletion in S is attributed to the selective segregation of a late sulfide matte from an oxidized and largely crystalline mantle. Apparently, the volatile abundances of Earth’s mantle are not in redox equilibrium with Earth’s core. 相似文献
17.
18.
核幔成矿物质(流体)的反重力迁移——地幔热柱多级演化成矿作用 总被引：25，自引：0，他引：25
地壳中矿床分布极不均匀 ,这与地球的形成与演化密切相关。在地球演化的早期 ,由于在引力收缩和热力膨胀的统一作用支配下 ,放射性、卤族、稀有、稀土元素及碱金属向上迁移 ,而贵金属、有色、铁族、铂族等密度较大的元素则有逐渐向地核聚集的趋势 ,以至于铁、镍、金等元素主要聚集在地核之中。但是 ,在地球形成圈层结构的同时 ,由于地球内外温度差、压力差、粘度差等的存在 ,导致地球发生以地幔热柱多级演化为主要形式的垂向物质运动 ,两者互为依存 ,并构成幔壳运动的原动力。地幔热柱多级演化沟通了深部矿质的迁移通道 ,聚集在地核及核幔界面上的气态金等重元素得以作为地幔热柱的热物质流 ,呈反重力迁移至岩石圈 ,并进而以气 液态向近地表迁移 ,在有利的构造扩容带中聚集成矿。这可能是金银铜铅锌等多种元素的重要成矿作用方式。 相似文献
19.
The composition of the Earth 总被引：317，自引：0，他引：317
Compositional models of the Earth are critically dependent on three main sources of information: the seismic profile of the Earth and its interpretation, comparisons between primitive meteorites and the solar nebula composition, and chemical and petrological models of peridotite-basalt melting relationships. Whereas a family of compositional models for the Earth are permissible based on these methods, the model that is most consistent with the seismological and geodynamic structure of the Earth comprises an upper and lower mantle of similar composition, an Fe---Ni core having between 5% and 15% of a low-atomic-weight element, and a mantle which, when compared to CI carbonaceous chondrites, is depleted in Mg and Si relative to the refractory lithophile elements.The absolute and relative abundances of the refractory elements in carbonaceous, ordinary, and enstatite chondritic meteorites are compared. The bulk composition of an average CI carbonaceous chondrite is defined from previous compilations and from the refractory element compositions of different groups of chondrites. The absolute uncertainties in their refractory element compositions are evaluated by comparing ratios of these elements. These data are then used to evaluate existing models of the composition of the Silicate Earth.The systematic behavior of major and trace elements during differentiation of the mantle is used to constrain the Silicate Earth composition. Seemingly fertile peridotites have experienced a previous melting event that must be accounted for when developing these models. The approach taken here avoids unnecessary assumptions inherent in several existing models, and results in an internally consistent Silicate Earth composition having chondritic proportions of the refractory lithophile elements at 2.75 times that in CI carbonaceous chondrites. Element ratios in peridotites, komatiites, basalts and various crustal rocks are used to assess the abundances of both non-lithophile and non-refractory elements in the Silicate Earth. These data provide insights into the accretion processes of the Earth, the chemical evolution of the Earth's mantle, the effect of core formation, and indicate negligible exchange between the core and mantle throughout the geologic record (the last 3.5 Ga).The composition of the Earth's core is poorly constrained beyond its major constituents (i.e. an Fe---Ni alloy). Density contrasts between the inner and outer core boundary are used to suggest the presence ( 10 ± 5%) of a light element or a combination of elements (e.g., O, S, Si) in the outer core. The core is the dominant repository of siderophile elements in the Earth. The limits of our understanding of the core's composition (including the light-element component) depend on models of core formation and the class of chondritic meteorites we have chosen when constructing models of the bulk Earth's composition.The Earth has a bulk Fe/Al of 20 ± 2, established by assuming that the Earth's budget of Al is stored entirely within the Silicate Earth and Fe is partitioned between the Silicate Earth ( 14%) and the core ( 86%). Chondritic meteorites display a range of Fe/Al ratios, with many having a value close to 20. A comparison of the bulk composition of the Earth and chondritic meteorites reveals both similarities and differences, with the Earth being more strongly depleted in the more volatile elements. There is no group of meteorites that has a bulk composition matching that of the Earth's. 相似文献
20.
A simple mechanical model explaining the long-period (about 100-year) variations in the Earth’s rotational velocity is proposed. This model takes into account the gravitational interaction of the mantle with the solid core of the Earth and the fact that the core rotation leads that of the mantle. Well-known Earth parameters provide estimates of the gravitational torque that support the proposed model. The mathematical problem involved reduces to the classical problem of a nonlinear oscillator exposed to a constant torque. The well-known parameters of the core-mantle system result in a stable equilibrium and a stable limiting cycle on the phase cylinder of this oscillator. This equilibrium corresponds to a single angular velocity for the mantle and solid core, with no long-period oscillations in the length of the day. The limiting cycle corresponds to the core rotation leading the mantle rotation. In this case, the ellipsoidality of the gravitationally interacting bodies provides a periodic interchange of kinetic angular momentum between the mantle and solid core that results in long-period variations in the length of the day. The proposed model does not support the formerly widespread opinion that the core rotates more slowly than the mantle. 相似文献