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1.
《Comptes Rendus Geoscience》2014,346(5-6):119-129
The improvements of the knowledge of the seismic structure of the inner core and the complexities thereby revealed ask for a dynamical origin. Sub-solidus convection was one of the early suggestions to explain the seismic anisotropy, but it requires an unstable density gradient either from thermal or compositional origin, or from both. Temperature and composition profiles in the inner core are computed using a unidimensional model of core evolution including diffusion in the inner core and fractional crystallisation at the inner core boundary (ICB). The thermal conductivity of the core has been recently revised upwardly and, moreover, found to increase with depth. Values of the heat flow across the core mantle boundary (CMB) sufficient to maintain convection in the whole outer core are not sufficient to make the temperature in the inner core super-isentropic and therefore prone to thermal instability. An unreasonably high CMB heat flow is necessary to this end. The compositional stratification results from a competition of the increase of the concentration of light elements in the outer core with inner core growth, which makes the inner core concentration also increase, and of the decrease of the liquidus, which makes the partition coefficient decrease as well as the concentration of light elements in the solid. While the latter (destabilizing) effect dominates at small inner core sizes, the former takes over for a large inner core. The turnover point is encountered for an inner core about half its current size in the case of S, but much larger for the case of O. The combined thermal and compositional buoyancy is stabilizing and solid-state convection in the inner core appears unlikely, unless an early double-diffusive instability can set in. 相似文献
2.
《Comptes Rendus Geoscience》2014,346(5-6):148-157
We present a framework for simulating the measurement of seismic anisotropy in a model inner core by computing travel time residuals of synthetic seismic rays propagated through the model. The method is first tested on simple inner core structural models consisting of layers with distinct anisotropy, as often proposed in the literature. Those models are not consistent with geodynamics. Hence, we extend the method to a numerically grown inner core composed of ɛ-Fe with flow generated from an excess of crystallization in the equatorial belt, inducing polycrystalline textures. The global inner core anisotropy is seven times smaller than that of the single-crystal. Compositional stratification amplifies the global anisotropy by 15% while the addition of solidification textures reduces it by a factor of two. As such, and within the tested geodynamical models, no published elastic model of ɛ-Fe at inner core conditions allows one to reproduce the 3% cylindrical anisotropy reported in seismology publications. In addition, our models demonstrate that additional information, such as the depth dependence and the spread of the observed anisotropy is a key for revealing the dynamics and history of the inner core. 相似文献
3.
Stability and dynamics of the continental tectosphere 总被引：1，自引：0，他引：1
Continental cratons overlie thick, high-viscosity, thermal and chemical boundary layers, where the chemical boundary layers are less dense than they would be due to thermal effects alone, perhaps because they are depleted in basaltic constituents. If the continental tectosphere is the same age as the overlying Archaean crust, then the continental tectosphere must be able to survive for several billion years without undergoing a convective instability, despite being both cold and thick. Since platforms and shields correlate only weakly with Earth's gravity and geoid anomalies, acceptable models of the continental tectosphere must also satisfy this gravity constraint. We investigate the long-term stability of the continental tectosphere by carrying out a number of numerical convection experiments within a two-dimensional Cartesian domain. We initiate our experiments with a tectosphere (thermal and chemical boundary layers) immersed in a region of uniform composition, temperature, and viscosity, and consider the effects on the stability of the tectosphere of (1) activation energy (used to define the temperature dependence of viscosity), (2) compositional buoyancy, and (3) linear or non-linear rheology. The large lateral thermal gradients required to match oceanic and tectosphere structures initiate the dominant instability, a “drip” which develops at the side of the tectosphere and moves to beneath its center. High activation energies and high background viscosities restrict the amount and rate of entrainment. Compositional buoyancy does not significantly change the flow pattern. Rather, compositional buoyancy slows the destruction process somewhat and reduces the stress within the tectosphere. With a non-Newtonian rheology, this reduction in stress helps to stiffen the tectosphere. In these experiments, dynamical systems that adequately model the present ocean-continent structures have activation energy E*≥180 kJ mole−1 — a value about one third the estimate of activation energy for olivine, E*≈520 kJ mole−1. Although for E*≈520 kJ mole−1, compositional buoyancy is not required for the tectosphere to survive, the joint application of longevity and gravity constraints allows us to reject all models not containing compositional buoyancy, and to predict that the ratio of compositional to thermal buoyancy within the continental tectosphere is approximately unity. 相似文献
4.
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
5.
地球液核的动力学效应研究进展 总被引：2，自引：1，他引：1
简要介绍了液核动力学研究的方法及液核动力学效应检测的进展和研究结果,着重介绍了超导重力仪在液核动力学研究中的作用。基于初始参考地球模型（PREM）,采用球对称、非自转、完全弹性和各向同性地球的弹性引力形变理论研究了液核动力学扰动导致的地球固体部分的形变和重力位扰动。根据重力潮汐观测中的近周日共振特征,利用国际超导重力仪观测资料研究了地球的自由核章动（FCN）,精密确定了有关的共振参数,其中FCN的本征周期为429.0（424.3,4 433.7）恒星日,品质因子为 9543（6405,18714）,复共振强度为（－6.10±0.20,－0.01±0.20）×10－4°/h。最近,我们还估计了全球地球动力学观测网中全球分布的14台超导重力仪21个长期、连续重力观测序列的"积谱密度"以检测固体内核的平动振荡运动。 相似文献
6.
笔者对地球内部压力分析提出了楔状体压力模式,即地球内部某深度单位面积(水平)上的压力(垂向)等于由该截面和所有经由该截面边缘的重力线所围限的楔状岩体的重量。据此模式,理论上地球内部压力随深度呈抛物线状急增,在地心处无穷大。但由于地球固液(塑)圈层交替存在及冷收缩,导致楔状岩体重力引起的作用力可分解成水平的侧向压力和垂向静岩压力,并随深度呈锯齿状升降变化。当岩石圈侧向压力增加导致岩石圈破裂(构成板块),在重力的向心力作用下,板块间相互错动形成俯冲带和拉张带,继而牵引软流圈构成远程对流运动,进而引发一系列地质构造作用。因此认为,地球的构造动力源于地球重力本身,其中侧向压力是地质构造的初始起动力和驱动力,引起的对流运动既是地质构造运动学表征又是动力学作用,重力势能及其转变的热能构成对流运动的最主要动力能源。 相似文献
7.
《Comptes Rendus Geoscience》2014,346(5-6):130-139
The Earth's core is constituted of iron and nickel alloyed with lighter elements. In view of their affinity with the metallic phase, their relative high abundance in the solar system and their moderate volatility, a list of potential light elements have been established, including sulfur, silicon and oxygen. We will review the effects of these elements on different aspects of Fe–X high pressure phase diagrams under Earth's core conditions, such as melting temperature depression, solid–liquid partitioning during crystallization, and crystalline structure of the solid phases. Once extrapolated to the inner–outer core boundary, these petrological properties can be used to constrain the Earth's core properties. 相似文献
8.
Ductilely deformed veins consisting of quartz+andalusite, in which the andalusite is partially replaced by fibrous sillimanite, locally occur in garnet–sillimanite schist near a margin of the Niğde metamorphic core complex in south-central Turkey. Mineral assemblages, reaction textures and structural features of the veins record low-pressure–high-temperature deformation during exhumation of mid-crustal rocks. The partial replacement of andalusite by sillimanite may indicate a late-stage increase in temperature and/or fluid pressure, possibly related to Miocene magmatism, during extensional unroofing of the core complex. Aluminosilicate-bearing veins are observed at the eastern margin of the massif where metapelitic rocks were deformed during unroofing of the core complex. Veins formed in aluminous rocks where deformation-enhanced permeability allowed fluid flow during extensional shear. The cm-scale veins are typically boudinaged and form asymmetric lenses concordant with the host rock foliation and are parallel to the down-dip lineation defined by sillimanite and stretched biotite. Aluminosilicate-bearing boudins record top-to-the-east shear sense, which is compatible with the extensional shear sense displayed by structures in the host rock. 相似文献
9.
深部盐岩层绳索取心钻井液技术研究与应用 总被引：1，自引：0，他引：1
由于次生应力场的作用以及盐岩易溶于水的特性,深部盐岩层钻进存在岩层蠕动、钻井液易遭受盐钙侵等问题;钻进参数选择不合理易导致盐岩层取心效率低、岩心冲蚀严重。本文以河南省叶舞凹陷ZK3井为例,采用石油钻井与绳索取心相结合的措施,解决了普通固体矿产钻探设备在深部地层取心中效力不足的问题;通过阳离子交换容量测定、矿物组分鉴定、钻井液体系优选及性能测试等试验,确定了针对上部泥岩地层的聚合物钻井液体系,中部含膏泥岩的欠饱和盐水钻井液体系,下部盐岩层取心段的饱和盐水钻井液体系。通过确定合适的钻井液密度与临界环空返速,可以有效控制深部盐岩层蠕变与井壁冲蚀,适度提高排量以成倍提高钻进速度。钻进过程中钻井液性能稳定,体系转换顺利且性能易于调整,为取心任务的顺利完成提供了有力保证。 相似文献
10.
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
11.
变质核杂岩与岩浆作用成因关系综述 总被引：12，自引：0，他引：12
对岩浆与伸展作用的关系、伸展作用中岩浆的成因和需加强的工作进行了讨论,并重点论述了变质核杂岩形成机制与侵入作用的关系。在造山带重力势能差和深部作用等各种因素导致的拉伸应力场作用下,岩石圈地幔和地壳通过减压或深部热活动发生部分熔融而形成岩浆,岩浆的上涌强化了地壳伸展,对地壳的弱化作用触发伸展构造的发生。岩浆作用是变质核杂岩形成的主导因素之一,其主要包括对地壳的加热、弱化导致拆离断层的形成及由其浮力和密度产生不均一隆升而形成穹隆。 相似文献
12.
Although there has been significant progress in the seismic imaging of mantle heterogeneity,the outstanding issue that remains to be resolved is the unknown distribution of mantle temperature anomalies in the distant geological past that give rise to the present-day anomalies inferred by global tomography models.To address this question,we present 3-D convection models in compressible and self-gravitating mantle initialised by different hypothetical temperature patterns.A notable feature of our forward convection modelling is the use of self-consistent coupling of the motion of surface tectonic plates to the underlying mantle flow,without imposing prescribed surface velocities(i.e.,plate-like boundary condition).As an approximation for the surface mechanical conditions before plate tectonics began to operate we employ the no-slip(rigid) boundary condition.A rigid boundary condition demonstrates that the initial thermally-dominated structure is preserved,and its geographical location is fixed during the evolution of mantle flow.Considering the impact of different assumed surface boundary conditions(rigid and plate-like) on the evolution of thermal heterogeneity in the mantle we suggest that the intrinsic buoyancy of seven superplumes is most-likely resolved in the tomographic images of present-day mantle thermal structure.Our convection simulations with a plate-like boundary condition reveal that the evolution of an initial cold anomaly beneath the Java-Indonesian trench system yields a long-term,stable pattern of thermal heterogeneity in the lowermost mantle that resembles the presentday Large Low Shear Velocity Provinces(LLSVPs),especially below the Pacific.The evolution of subduction zones may be,however,influenced by the mantle-wide flow driven by deeply-rooted and longlived superplumes since Archean times.These convection models also detect the intrinsic buoyancy of the Perm Anomaly that has been identified as a unique slow feature distinct from the two principal LLSVPs.We find there is no need for dense chemical ’piles’ in the lower mantle to generate a stable distribution of temperature anomalies that are correlated to the LLSVPs and the Perm Anomaly.Our tomography-based convection simulations also demonstrate that intraplate volcanism in the south-east Pacific may be interpreted in terms of shallow small-scale convection triggered by a superplume beneath the East Pacific Rise. 相似文献
13.
This paper presents the first hydrogeological model that fully couples transient fluid flow, heat and solute transport associated with the formation of the HYC SEDEX deposit in the McArthur Basin, northern Australia. Numerical results reveal that salinity plays an important role in controlling hydrothermal fluid migration. In particular, it appears that it is the distribution of evaporitic units within a given basin, rather than their absolute abundance, that controls the development of free convection. Relatively saline conditions at the seafloor strengthen the thermally-induced buoyancy force and hence promote free convection of basinal solutions; whereas high salinities at the bottom counteract the thermal function of natural geothermal gradient and suppress the development of convective hydrothermal fluid circulation. In the latter case, higher thermal gradients are required to initiate substantial free convective fluid flow.Numerical experiments also suggest the position of an ore body with respect to its vent system may be controlled by the spatial and temporal salinity distributions in the basin. Vent-distal ore formation, a result of exhalation of brines that are denser than seawater and hence can flow away from the vent region, is promoted by moderate salinity at the seafloor and higher salinity in the aquifer. Vent-proximal ore accumulation, a result of pluming upon exhalation of brines less dense than seawater, is favored by the highest salinity conditions occurring near the level of the seafloor.Editorial Handling: G. Beaudoin 相似文献
14.
《Russian Geology and Geophysics》2016,57(8):1135-1142
A fluid model for the formation of mantle plumes is proposed. During the emission of gas from the Earth’s core, it accumulates as lenses at the core-mantle boundary. Reaching a critical size, the lenses burst out into the mantle and migrate to the surface. A relatively stationary transmantle fluid flow from the core-mantle boundary arises, which heats the mantle and the layer interacting with it. The flow stops in the base of the hard lithosphere and spreads laterally, causing its melting accompanied by the formation of magma chambers, which, reaching critical sizes, massively intrude and flow out. 相似文献
15.
地球内核与地球深部动力学 总被引：11，自引：2，他引：9
地球内核由外核富含铁元素的液态物质结晶而成。经证实,内核正以约１（°）／ａ的速率相对于地幔向东转动。内核的旋转是通过穿过内核的地震波的走时随时间变化推测得到的。这种变化是最近十多年来揭示出的内核各向异性在空间方位的改变所造成。内核的各向异性被认为起因于各向异性的铁晶体的有序排列,但这种有序排列的机制还不清楚。内核在地球发电机中起着重要的作用。利用大型的并行计算机,人们已得到能产生像地磁场一样的三维发电机数值模拟。地震学观测到的内核差速旋转为最近的发电机数值模拟提供了支持。这种数值模拟曾预测：导体内核与外核产生的磁场的电磁耦合驱动了内核每年几度向东旋转。地核通过核幔边界的接触及内核与地幔的引力耦合与地幔存在强烈的相互作用。多学科领域的突破为认识地球的深部动力过程提供了极好的机会和手段。 相似文献
16.
Development of a discontinuous approach for modeling fluid flow in heterogeneous media using the numerical manifold method 
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下载免费PDF全文 In the numerical modeling of fluid flow in heterogeneous geological media, large material contrasts associated with complexly intersected material interfaces are challenging, not only related to mesh discretization but also for the accurate realization of the corresponding boundary constraints. To address these challenges, we developed a discontinuous approach for modeling fluid flow in heterogeneous media using the numerical manifold method (NMM) and the Lagrange multiplier method (LMM) for modeling boundary constraints. The advantages of NMM include meshing efficiency with fixed mathematical grids (covers), the convenience of increasing the approximation precision, and the high integration precision provided by simplex integration. In this discontinuous approach, the elements intersected by material interfaces are divided into different elements and linked together using the LMM. We derive and compare different forms of LMMs and arrive at a new LMM that is efficient in terms of not requiring additional Lagrange multiplier topology, yet stringently derived by physical principles, and accurate in numerical performance. To demonstrate the accuracy and efficiency of the NMM with the developed LMM for boundary constraints, we simulate a number of verification and demonstration examples, involving a Dirichlet boundary condition and dense and intersected material interfaces. Last, we applied the developed model for modeling fluid flow in heterogeneous media with several material zones containing a fault and an opening. We show that the developed discontinuous approach is very suitable for modeling fluid flow in strongly heterogeneous media with good accuracy for large material contrasts, complex Dirichlet boundary conditions, or complexly intersected material interfaces. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
17.
The role of partial melting and extensional strain rates in the development of metamorphic core complexes 总被引：1，自引：0，他引：1
Orogenic collapse involves extension and thinning of thick and hot (partially molten) crust, leading to the formation of metamorphic core complexes (MCC) that are commonly cored by migmatite domes. Two-dimensional thermo-mechanical Ellipsis models evaluate the parameters that likely control the formation and evolution of MCC: the nature and geometry of the heterogeneity that localizes MCC, the presence/absence of a partially molten layer in the lower crust, and the rate of extension. When the localizing heterogeneity is a normal fault in the upper crust, the migmatite core remains in the footwall of the fault, resulting in an asymmetric MCC; if the localizing heterogeneity is point like region within the upper crust, the MCC remains symmetric throughout its development. Therefore, asymmetrically located migmatite domes likely reflect the dip of the original normal fault system that generated the MCC. Modeling of a severe viscosity drop owing to the presence of a partially molten layer, compared to a crust with no melt, demonstrates that the presence of melt slightly enhances upward advection of material and heat. Our experiments show that, when associated with boundary-driven extension, far-field horizontal extension provides space for the domes. Therefore, the buoyancy of migmatite cores contributes little to the outer envelope of metamorphic core complexes, although it may play a significant role in the internal dynamics of the partially molten layer. The presence of melt also favors heterogeneous bulk pure shear of the dome as opposed to the bulk simple shear, which dominates in melt-absent experiments. Melt presence affects the shape of P-T-t paths only slightly for material located near the top of the low-viscosity layer but leads to more complex flow paths for material inside the layer. The effect of extension rate is significant: at high extension rate (cm yr− 1 in the core complex region), partially molten crust crystallizes and cools along a high geothermal gradient (35 to 65 °C km− 1); material remains partially molten in the dome during ascent. At low strain rate (mm yr− 1 in the core complex region), the partially molten crust crystallizes at high pressure; this material is subsequently deformed in the solid-state along a cooler geothermal gradient (20 to 35 °C km− 1) during ascent. Therefore, the models predict distinct crystallization versus exhumation histories of migmatite cores as a function of extensional strain rates. The Shuswap metamorphic core complex (British Columbia, Canada) exemplifies a metamorphic core complex in which an asymmetric, detachment-controlled migmatite dome records rapid exhumation and cooling likely related to faster rates of extension. In contrast the Ruby Mountain-East Humboldt Ranges (Nevada, U.S.A.) exhibits characteristics associated with slower metamorphic core complexes. 相似文献
18.
We present a network flow model to compute transport, through a pore network, of a compositional fluid consisting of water with a dissolved hydrocarbon gas. The model captures single-phase flow (below local bubble point conditions) as well as the genesis and migration of the gas phase when bubble point conditions are achieved locally. Constant temperature computational tests were run on simulated 2D and 3D micro-networks near bubble point pressure conditions. In the 2D simulations which employed a homogeneous network, negligible capillary pressure, and linear relative permeability relations, the observed concentration of CO2 dissolved in the liquid phase throughout the medium was linearly related to the liquid pressure. In the case of no gravity, the saturation of the gas phase throughout the medium was also linearly related to the liquid pressure; under gravity, the relationship became nonlinear in regions where buoyancy forces were significant. The 3D heterogeneous network model had nonnegligible capillary pressure and nonlinear relative permeability functions. While 100 % of the CO2 entered the 3D network dissolved in the liquid phase, 25 % of the void space was occupied by gas phase and 47 % of the CO2 exiting the outlet face did so via the gaseous phase after 500 s of simulation time. 相似文献
19.
This paper presents a review of recent results concerning the structure and the rotation of the inner core, as inferred from seismological observations. We first focus on the apparent hemispherical pattern of the inner core structure, observed in both the anisotropy and the heterogeneity of the uppermost layers, whereas isotropic velocities seem to be homogeneous in a broad wavelength domain. Then we present results on the radial variations of the attenuation and its possible anisotropy, for which viscoelasticity and wave scattering provide complementary explanations. Linked to these results is a discussion about the detection of the PKJKP phase, which propagates as S-wave inside the inner core. Finally, the seismological observations of a possible inner core rotation are discussed; recent results seem to favour rotation rates below 0.2° yr?1. 相似文献
20.
Three porous media flow problems, in which the fluid mechanical interactions are critical, are studied in a mesoscopic–microscopic coupling system. In this system, fluid flow in the pore space is explicitly modeled at mesoscopic level by the lattice Boltzmann method, the geometrical representation and the mechanical behavior of the solid skeleton are modeled at microscopic level by the particulate distinct element method (DEM), and the interfacial interaction between the fluid and the solids is resolved by an immersed boundary scheme. In the first benchmark problem, the well‐known and frequently utilized Ergun equation is validated in periodic particle and periodic pore models. In the second problem, the upward seepage problem is simulated over three stages: The settlement of the column of sphere under gravity loading is measured to illustrate the accuracy of the DEM scheme; the system is solved to hydrostatic state with pore space filled with fluid, showing that the buoyancy effect is captured correctly in the mesoscopic–microscopic coupling system; then, the flow with constant rate is supplied at the bottom of the column; the swelling of the ground surface and pore pressure development from the numerical simulation are compared with the predictions of the macroscopic consolidation theory. In the third problem, the fluid‐flow‐induced collapse of a sand arch inside a perforation cavity is tested to illustrate a more practical application of the developed system. Through comparing simulation results with analytical solutions, empirical law and physical laboratory observations, it is demonstrated that the developed lattice Boltzmann–distinct element coupling system is a powerful fundamental research tool for investigating hydromechanical physics in porous media flow. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献