共查询到20条相似文献，搜索用时 31 毫秒
1.
Using energy and entropy constraints applicable to the Earth's core, the heat flow at the core–mantle boundary (CMB) needed to sustain a given total dissipation in the core can be computed. Reasonable estimates for the present Joule dissipation in the core gives a present heat flow of 6 to 10 TW at the CMB. Palaeointensity data acquired from rocks younger than 3.5 Ga provide support that the Joule dissipation in the core before inner core crystallization was between today's value and four times lower than today. Prior to inner core crystallization (around 1 Ga), the magnetic field was maintained by thermal convection driven by core cooling, and our calculations of the two extreme cases predict that the heat flow at the CMB at that time was either 14 to 24 TW in the case of constant dissipation, or essentially the same as today in the lower field intensity case. 相似文献
2.
This study investigates the mechanism of formation of convection plumes of mushroom shape in sub-solidus mantle and their prediction.The seismic-tomographic images of columnar structures of several hundreds kilometers in diameter have been reported by several researchers,while the much cherished mushroom-shaped plume heads could only be found in computational geodynamics(CGD) models and simple small-scale laboratory analogue simulations.Our theory of transient instability shows that the formation of conv... 相似文献
3.
在核幔界面之上的下地幔一侧,地震波速分布极不均匀,厚度在50~300 km范围内变化的一层物质称为地幔底层。地幔底层由具有高地震波速和高密度的D″区和超低速带(ULVZ)组成。地幔底层是地核热能向地幔传播的必经之路,也是地幔中温度和温度梯度最高的地区。地幔底层既是俯冲板块的最终归宿,又是热柱和超级热柱的源区。因此,地幔底层既是全地幔对流的起点,又是全地幔对流的终点。在地幔底层可能发生地幔物质(包括俯冲板块物质在内)的部分熔融作用,也可能存在外核液态铁与地幔硅酸盐的化学反应。所以地幔底层在全球物质演化中占有重要的地位。 相似文献
4.
《Comptes Rendus Geoscience》2014,346(5-6):101-109
Numerical calculations of thermochemical convection in a rotating, electrically conducting fluid sphere with heterogeneous boundary conditions are used to model effects of asymmetric inner core growth. With heterogeneous inner core growth but no melting, outer core flow consists of intense convection where inner core buoyancy release is high, weak convection where inner core buoyancy release is low, and large scale, mostly westward flow in the form of spiraling gyres. With localized inner core melting, outer core flow includes a gravity current of dense fluid that spreads over the inner core boundary, analogous to the seismic F-layer. An analytical model for gravity currents on a sphere connects the structure of the dense layer to the distribution of inner core melting and solidification. Predictions for F-layer formation by asymmetric inner core growth include large-scale asymmetric gyres below the core-mantle boundary and eccentricity of the geomagnetic field. 相似文献
5.
Compositional and thermal convection in magma chambers 总被引：7，自引：1，他引：7
Daniel Martin Ross W. Griffiths Ian H. Campbell 《Contributions to Mineralogy and Petrology》1987,96(4):465-475
Magma chambers cool and crystallize at a rate determined by the heat flux from the chamber. The heat is lost predominantly through the roof, whereas crystallization takes place mainly at the floor. Both processes provide destabilizing buoyancy fluxes which drive highly unsteady, chaotic convection in the magma. Even at the lowest cooling rates the thermal Rayleigh number Ra is found to be extremely large for both mafic and granitic magmas. Since the compositional and thermal buoyancy fluxes are directly related it can be shown that the compositional Rayleigh number Rs (and therefore a total Rayleigh number) is very much greater than Ra. In the case of basaltic melt crystallizing olivine Rs is up to 106 times greater than Ra. However compositional and thermal buoyancy fluxes are roughly equal. Therefore thermal and compositional density gradients contribute equally to convection velocities in the interior of the magma. Effects of thermal buoyancy generated by latent heat release at the floor are included.The latent heat boundary layer at the floor of a basaltic chamber is shown to be of the order of 1 m thick with very low thermal gradients whereas the compositional boundary layer is about 1 cm thick with large compositional gradients. As a consequence, the variation in the degree of supercooling in front of the crystal-liquid interface is dominated by compositional effects. The habit and composition of the growing crystals is also controlled by the nature of the compositional boundary layer. Elongate crystals are predicted to form when the thickness of the compositional boundary layer is small compared with the crystal size (as in laboratory experiments with aqueous solutions). In contrast, equant crystals form when the boundary layer is thicker than the crystals (as in most magma chambers). Instability of the boundary layer in the latter case gives rise to zoning within crystals. Diffusion of compatible trace elements through the boundary layer can also explain an inverse correlation, observed in layered intrusions, between Ni concentration in olivine and the proportion of Ni-bearing phases in the crystallizing assemblage. 相似文献
6.
地球内核快速旋转的发现与全球变化的轨道效应 总被引：3，自引：0，他引：3
科里奥利效应是产生内核快速旋转的主要原因。科氏力使上升物质向西漂移，下降物质向东漂移；造成地球外层自转减速，地球内层自转加速。所以，自旋体中的垂直运动可以产生大规模的水平运动——圈层差异旋转。地震波测量结果表明，内核旋转速度每年比地壳地幔快１°。对于一个内核差异旋转的地球，太阳辐射不仅形成地磁场的内外磁尾和地壳与内核的反向振动，而且影响核幔角动量交换和电磁耦合，从而控制了地球内能的释放，形成天文周期与地质旋回的一一对应关系。地球轨道和太阳轨道的全球变化响应，为太阳辐射量变化控制地球内能释放提供了证据 相似文献
7.
地球内部物理和演化的几个核心论题：I.地球内部结构和物理性质 总被引：1，自引：0，他引：1
本文综述研究地球内部结构和物理特性的几种常见规方法和主要研究结果,并首重讨论地球物理状态方程,地震成象,综合反演,高温高压实验和有关对比研究方法,均匀各向同性球对球模型仍不失其参考意义,但最新研究结果表明,地球内部状态是非均匀和各向异性的,横向不均匀对称地球模型仍不其参考意义,但最新研究结果表明,地球内部状态是非均匀和各向异性的,横向不均匀性主要表现在上地幔部分,下地幔和液态外核似乎比较均匀,但核－幔边界过渡带(D″)可能代表一个内含非均匀化学边界的热边界层,其形态起伏和横向变化影响地球模壁的球对称性。3-D地震成象实质上反映地震波建与温度异常的关系．而温度变化又会引起密度异常,因而密度变化是控制地幔对流的关键参数之一。 相似文献
8.
地球内部物理和演化的几个核心论题：Ⅱ地球动力体系 总被引：1，自引：0，他引：1
生成于岩石圈底部的“大陆根”与地幔羽的形成过程有关,其主要证据来自3－D地震成象和实验、数值模拟结果。地幔上涌和地幔下涌分别代表高温、低速带和低温、高速带。长波长的地幔构造与表层构造特征相关,地球内部边界层－热边界层或化学边界层将对全球动力体系产生直接或间接的效应。因此,深入研究这些边界层的结构、形态、热力学和物理化学特性,对解决地幔整体对流与成层对流体系中某些相冲突的问题具有关键意义。全球地震成象和深源地震资料表明,某些破碎的早期俯冲板片可能连续或间断性地下沉到核－幔边界处,并返回到起源于该边界层的地幔羽中。今后的任务不是重提地幔整体对流或是成层对流的问题．而是如何建立两者的统一模式。整体地幔对流体系在时间和空间演化过程中与成层对流、局部小规模对流或次生对流相伴生的理论、实验和数值模拟将是地球动力学研究的主要趋势。 相似文献
9.
核—幔相互作用及其地球动力学意义 总被引：1，自引：0，他引：1
核－幔边界是地球内部反差最大的一个边界,也是最重要的边界,界区的核－幔相互作用过程在整个地球动力学系统中起着重要的作用。本文在概述了该－边界基本特征的基础上,系统地总结了有关核幔物质的化学反应和Ｄ”层的形成,核－幔间的质量传递及其对地幔对流之贡献,核－幔耦合与动量传递等的研究成果及有关问题。 相似文献
10.
11.
关于地核和核慢边界区物质的成分及运动特征的研究进展 总被引：1，自引：1，他引：1
近年来关于地核和核幔边界区的研究有了较大进展，特别是高压矿物物理学和高压岩石学提供了大量有关的实验依据。本文对核幔边界区Ｄ＂层物质的运动状态、外核中轻元素成分的实验研究结果、内核地震波各向异性的物质解释及有关地磁场成因的新认识等方面的研究成果进行简要介绍和评述。 相似文献
12.
地球节律的成因 总被引：1，自引：0，他引：1
地球节律主要受地球内部能量间歇性的释放所控制。旋转系统有不同于非旋转系统的位能、热能和旋转能的相互转换方式。在重力分异和热对流过程中，地核不仅有巨量热能，而且有巨量的旋转能和放射性蜕变能。这是地球能量释放的内因。天文因素使地球内核周期性地南北振动，使地球轨道、体积，形状、自转速度、公转速度和差异旋转状态周期性地变化。这是地球能量间歇性释放的外因。对作差异旋转的内核而言，万有引力常数Ｇ的变化可以改变太阳辐射量和太阳系体积，影响核幔的角动量交换和地壳地幔容积，造成热幔柱的形成与喷发，控制了核幔边界的能量交换过程。这是天文周期与地质旋回一一对应的原因，也是地球节律产生的根本原因。这使人们可以从天文周期预测地质变动。 相似文献
13.
S.A. Morse 《Geochimica et cosmochimica acta》2002,66(12):2155-2165
Mushy zones, assemblages of crystals and their pore-space liquids, have been invoked for both the upper and lower boundaries of the liquid outer core. The timescale of very slow accumulation compared with solidification at either of these interfaces militates against such zones, where instead hard ground should be expected to form by solidification at the interface. Such adcumulus growth involves isothermal, isocompositional solidification by successful exchange of evolving solute with fresh melt from an infinite reservoir. At both boundaries of the outer core, the removal of rejected material is significantly aided by compositional convection. The accumulation rates at the outer core boundaries are orders of magnitude slower than required for adcumulus growth, as calibrated both by field and experimental evidence in silicate melts. A conceptual phase diagram for the core-mantle boundary helps to visualize the relevant equilibria. Capture of core metal into the mantle has been suggested to occur via a mushy zone, to explain a high electrical conductivity there, as plausibly required by the secular behavior of the Earth’s nutation. One conjecture is that the rejected light elements from the freezing of the inner core might be able to congregate as a porous flotation sediment at the top of the core. The idea of porosity in such a mushy zone must be rejected from experience with solidification of cumulates from magmas.A high electrical conductivity might instead be caused by solution of core metal by mantle, followed by exsolution. The hottest part of the mantle lies in contact with the molten outer core, where the maximum solubility of Fe must occur in the major mantle phases. On leaving the core-mantle boundary, the mantle must cool and may exsolve metal on the metal-silicate solvus. If the iron-rich metal resides chiefly in the rheologically weaker metal oxide phase, which coats the deforming perovskite grains, it may furnish a short circuit for mantle conductivity in the basal mantle. At still cooler and higher levels, the mantle encounters more normal mantle redox conditions, and any exsolved Fe metal should oxidize to FeO in the metal oxide and perovskite phases, ceasing to be a conductor. 相似文献
14.
套管式地埋管换热器是深层地源热泵系统常用的换热装置。基于流体流动换热方程，建立套管式地埋管换热器与周围岩体之间的传热模型。以第一个供暖季为例，分析内管导热系数和循环水流量对换热性能的影响，并引入换热器效能对热短路现象进行评估，研究结果显示:内管导热系数越大，热短路现象越显著；热短路使内外管中循环水温差降低，管内出现热堆积，导致换热器换热功率降低；套管式地埋管换热器的换热功率随循环水流量的增大逐渐增大；内外管之间存在热短路时，出口水温随循环水流量的增大先升高后降低，随着流量增大，换热器效能增大。研究成果可为深层地源热泵系统中地埋管换热器的设计提供借鉴。 相似文献
15.
The mean depth of the mantle transition zone depends on the global mantle temperature through the Clapeyron slope. Numerical models of mantle convection with endothermic phase change at 670 km are characterized by quiet periods of partial layering alternating with catastrophic events. During an avalanche, global thermal anomalies, reaching several tens of degrees, and lasting several tens of million years occur that induce a global deepening of the mantle transition zone. The resulting inertia tensor perturbations lead to acceleration of the Earth’s rotation. The bottom heat fluxes remains strong as a consequence of the steep thermal gradient at the CMB level; whereas it decreases to a low level during quiet periods. The upper surface heat flux displays a more complex behavior due to the re-heating of upper mantle by plumes generated at the transition zone and at the CMB. Following these numerical results, two significantly different regimes of mantle convection may have alternated several times during the Earth’s history. The avalanche periods are also associated with a global increase of plate tectonic activity (ridge accretion and continental break-up) due to an increase of the surface velocity during the avalanche process. This work shows the richness of the behavior in surfaces and bottom heat fluxes that arises from the alternation of quiet periods of partial layering with catastrophic avalanche events. Complexities in the real Earth displays are surprisingly simular to those caused by the consequences of mantle avalanches. 相似文献
16.
Accompanied with rifting and detaching of the north continental margin of the South China Sea,the ernst and the lithosphere become thinner away from the continental margin resulting from the tectonic activities,such as tensile deformation,thermal uplift,and cooling subsidence,etc..Integrated with thermal,gravimetric,and isostatic analysis techniques,based on the seismic interpretation of the deep penetration seismic soundings across the northern margin of the South China Sea,we reconstructed the lithospheric thermal structure and derived the variation of the crust boundary in the east and west parts of the seismic profde by using gravity anomaly data.We mainly studied the thermal isostasy problems using the bathymetry of the profiles and calculated the crust thinning effect due to the thermal variety in the rifting process.The results Indicate that the thermal isostasy may reach 2.5 kin,and the compositional variations in the ilthospheric density and thickness may produce a variation of 4.0 kin.Therefore,the compositional isostatic correction is very important to recover the relationship between surface heat flow and topography.Moreover,because of the high heat flow characteristic of the continental margin,building the model of lithospheric geotherm in this region is of great importan for studying the Cenozoic tectonic thermal evolution of the north passive continental margin of the South China Sea. 相似文献
17.
Philippe Machetel 《Comptes Rendus Geoscience》2003,335(1):91-97
The numerical models of mantle convection agree to depict avalanches behaviour according to the level of endothermicity of the spinel → perovskite phase change. Their potential effects on the global thermal and dynamical states of the mantle have been computed thanks to a numerical code, which takes into account both the 400-km exothermic and the 660-km endothermic phase changes. The cycle followed by the avalanches is: local layering, destabilization of the 660-km thermal layer, travelling and spreading on the core, and reappearing of the local layering. Therefore, mantle convection is characterized by quiet periods of partial layering embedded in catastrophic events. During the avalanche, the amplitude of the surface velocity is multiplied by two, which would imply an enhanced plate tectonic and ridge activities. The global thermal effects of the avalanche are compatible with a high mantle temperature and an acceleration of Earth's rotation during the Cretaceous. They also offer a coherent explanation to locate the origin of mantle plumes both within the CMB and just below the transition zone. 相似文献
18.
Xiong Xiong Institute of Geodesy Geophysics Chinese Academy of Sciences Wuhan Institute of Geology Geophysics Chinese Academy of Sciences Beijing Hsu Houtze Institute of Geodesy Geophysics Chinese Academy of Sciences 《中国地质大学学报(英文版)》2001,12(2)
ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｔｅｍｐｅｒａｔｕｒｅｓｔｒｕｃｔｕｒｅｏｆｔｈｅｅａｒｔｈｉｎｔｅｒｉｏｒｈａｓａｐｒｏ ｆｏｕｎｄｓｃｉｅｎｔｉｆｉｃｓｉｇｎｉｆｉｃａｎｃｅｆｏｒｔｈｅｓｔｕｄｙｏｎｔｈｅｄｙｎａｍｉｃｅｖｏｌｕｔｉｏｎｐｒｏｃｅｓｓｏｆｔｈｅｅａｒｔｈ .Ｉｎｇｅｎｅｒａｌ,ｔｈｅｃｒｕｓｔａｌａｎｄｌｉｔｈｏｓｐｈｅｒｉｃｔｅｍ ｐｅｒａｔｕｒｅｆｉｅｌｄｉｓｄｅｔｅｒｍｉｎｅｄｂｙｔｈｅｅｑｕａｔｉｏｎｏｆｔｈｅｒｍａｌｃｏｎｄｕｃｔｉｏｎｗｉｔｈｔｈｅｓｕｒｆａｃｅｈｅａ… 相似文献
19.
A speculation on the structure of the D″ layer: The growth of anti-crust at the core–mantle boundary through the subduction history of the Earth 总被引：1，自引：1，他引：0
The growth curve of the continental crust shows that large amounts of continental crust formed in the early part of the Earth history are missing. In order to test a hypothesis that the former crust was subducted to the deep mantle, we performed phase assemblage analysis in the systems of mid-oceanic ridge basalt (MORB), anorthosite, and tonalite–trondhjemite–granite (TTG) down to the core–mantle boundary (CMB) conditions. Results show that all these materials can be subducted to the CMB leading to the development of a compositional layering in the D″ layer. We speculate that there could be five layers of FeO-enriched melt from partial melting of MORB, MORB crust, anorthosite, TTG, and slab or mantle peridotite in ascending order. Although the polymorphic transformation of perovskite to post-perovskite in (Mg,Fe)SiO3 may explain the seismic discontinuity at the top of the D″ layer (D″ discontinuity), the effects of solid solution on the sharpness of the transformation suggest that the compositional layering is more plausible for the origin of the D″ discontinuity. The D″ layer can be an “anti-crust” made up mostly of TTG + anorthosite derived from the former continental crust. Tectonic style of the anti-crust at the CMB is similar to that at the surface. At both places, chemically distinct layers are density stratified and are also characterized by the processes of accretion, magmatism, and metasomatism. 相似文献
20.
L. Bodri 《Tectonophysics》1981,72(1-2)
A geothermal model of the hyperthermal zone of the Pannonian basin is constructed. On the basis of results of seismic measurements along five deep seismic sounding profiles on the territory of the basin and the surrounding areas and also of measurements of heat flow, heat production by radioactive elements and thermal conductivity of rocks, the variation of temperature with depth and maps of Mono-temperatures and heat flux through this surface are calculated and constructed, respectively. It is shown by numerical-model calculations that the heat anomaly of the Pannonian basin indicated by a number of surface measurements is mainly of mantle origin. Inhomogeneities of the heat-flow increase with depth down to the upper mantle and the temperature on the Moho-surface below the hyperthermal zone has values on average 400–500°C more than those in the surrounding areas. Heat flux through the Moho under the Pannonian basin is also higher by about 40–50 mW m−2. On the basis of the present calculations, it can be suggested that the upper mantle is probably partially molten beneath the annonian basin. As a most reasonable source mechanism of formation of this heat anomaly, the frictional heating arising in areas of induced secondary convection that probably has proceeded also beneath the basin from the Triassic to the Miocene is suggested here. 相似文献