共查询到17条相似文献，搜索用时 430 毫秒
1.
下地幔及核幔边界结构及地球动力学 总被引：9，自引：2，他引：9
新一代高分辨率下地幔及核幔边界的地震层析成像,改变了我们对全球构造模式及地球动力过程的认识。古海洋岩石圈板片一直俯冲到下地幔底部,其残留体在核幔边界积累,并支持了地幔整体对流模式。位于核幔边界上的D″层有着十分复杂而精细的结构。紧靠核幔边界的地幔一侧发现了超低速层(ULVZ),它们可能是D″层内的局部熔融物,是引起地表热点的上升地幔柱的源头。 相似文献
2.
3.
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
4.
核幔边界层在地球演化过程中扮演着极为重要的作用,是人们认识地球的主要研究对象之一。文中综述了近十多年来对核幔边界D″区开展地震学研究的主要方法及成果,内容涵盖了核幔边界D″区上部间断面、不均匀性、各向异性和超低速层等4个主要研究对象。结合多个相关学科的研究进展,从对热-化学-动力学三方面的耦合作用的分析,来探讨形成D″区各种观测现象的原因和机制,以及在此基础上提出的动力学演化模型。最后简要叙述了有关核幔边界研究的地震学、矿物实验、理论分析及计算科学的发展方向和挑战。随着对D″区认识的不断更新,逐步揭示地表观测到的可能受核幔边界因素控制的多种地质及地球物理现象。 相似文献
5.
地球自转十年尺度波动与核幔耦合的可能机制 总被引：2，自引：1，他引：2
简要介绍了地球自转变化的一般规律可能的地球物理激发因素，十年尺度波动与核幔边界耦合之间的联系，以及几种可能的核幔耦合机制。强调了地震波探测手段对于获限地球内部信息的重要性，同时指出将空间大地测量，重力测量和地磁怀地球物理学方面的理论与模型研究相结合，对于最终分析和确认地球自转变化中的各种信息及其激当因素是十分重要的。 相似文献
6.
地球核幔边界即D"层的矿物成分一直以来都被认为是MgSiO3钙钛矿. 随着高温高压实验技术的不断提高,各国学者对该层物质成分的认识也在不断深化.近年,日本学者通过实验,率先合成了一种新的高温高压矿物,即MgSiO3后钙钛矿,并认为后钙钛矿物相是核幔边界的主要特征.这项重大成果解决了长期困扰学术界的D"层地震波各向异性成因问题,揭示了地震波不连贯性的本质原因.该项成果被誉为21世纪实验岩石学的重大突破,对人们深入探索地球深部的奥秘具有重大理论价值.随着对地球核幔边界认识的继续深入,有可能解决岩石圈板块运动的本质原因以及地磁场成因机制等重大问题. 相似文献
7.
20世纪90年代以来，人们正在探索建立一个统一的全球动力学体系及各圈层相互作用的热、物质运动机制。通过对地核、核幔边界、过渡带、岩石圈—软流圈地幔、地幔柱理论、壳幔边界和地壳内热、物质的交换和圈层流变运动方式等进行分析，讨论了地球各圈层之间存在的热与物质的交换机制以及底侵作用、拆沉作用和岩浆部分熔融作用等壳幔相互作用过程。认为壳幔作用过程表现为一种阶段式、递进式动力学和物理化学演化过程。壳幔相互作用不仅是大陆动力学演化的主要机制，而且与深部地幔的交代及上地壳变形、造山带、盆地形成和演化之间存在耦合过程。基于壳幔热和物质相互作用的研究可以对上地幔及更深层次的地质作用过程进行限定。 相似文献
8.
正三十年前地震学家们发现核幔边界之上存在分布不均的超低速区(ultralow velocity zones,简为ULVZs),通常和大低速省(large low shear velocity provinces,简为LLSVPs)紧密相连。虽然认识其成因对于理解核幔边界的热和化学状态乃至于深部地球的演化历史至关重要,但是目前尚未有定论。硅酸盐熔体常被用来解释ULVZs的成 相似文献
9.
地球是重力分异和热力对流的对立统一体。重力分异使地内重物质下沉、轻物质上浮，并分划成壳－幔－核结构圈层。核幔间巨大的温度差、压力差、粘度差和速度差的存在，导致源于“超临界层”的热物质流呈柱状上涌形成地幔热柱及其多级演化。由于地球圈层结构及其间的差异，分别在670km、100km深处，即核－幔界面上和岩石圈底部形成地幔亚热柱和幔枝构造。地幔热柱、地幔冷柱共同驱动幔壳运动，并控制着板块运动，形成复杂的大陆（大洋）动力学系统。这种动力学模式越来越得到地球物理学的证实。 相似文献
10.
地幔柱构造——一种新的大地构造理论 总被引：1，自引：0，他引：1
俞 《四川地质科技情报》1994,(2):45-46
近年来，在大量实际观察、地球深部物理性质研究和各种模拟实验基础上，提出一个新的大地构造理论——地幔柱构造(mantle plume tectonics)。按照这一构造理论，地球深部核幔边界附近的高温低粘度屡(D^11层)可以产生呈柱状上升的热物质体。 相似文献
11.
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
12.
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
13.
Naira S.Martirosyan Konstantin D.Litasov Sergey S.Lobanov Alexander F.Goncharov Anton Shatskiy Hiroaki Ohfuji Vitali Prakapenka 《地学前缘(英文版)》2019,10(4):1449-1458
The fate of subducted carbonates in the lower mantle and at the core-mantle boundary was modelled via experiments in the MgCO3-Fe^0 system at 70-150 GPa and 800-2600 Kin a laser-heated diamond anvil cell.Using in situ synchrotro n X-ray diffraction and ex situ transmission electron microscopy we show that the reduction of Mg-carbonate can be exemplified by:6 MgCO3+19 Fe=8 FeO+10(Mg0.6Fe^0.4)O+Fe7 C3+3 C.The presented results suggest that the interaction of carbonates with Fe^0 or Fe^0-bearing rocks can produce Fe-carbide and diamond,which can accumulate in the D"region,depending on its carbon to Fe ratio.Due to the sluggish kinetics of the transformation,diamond can remain metastable at the core-mantle boundary(CMB)unless it is in a direct contact with Fe-metal.In addition,it can be remobilized by redox melting accompanying the generation of mantle plumes. 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.
N. L. Dobretsov A. A. Kirdyashkin A. G. Kirdyashkin I. N. Gladkov N. V. Surkov 《Petrology》2006,14(5):477-491
Thermochemical plumes develop at the core-mantle boundary in the presence of a heat flow from the outer core and at local chemical doping that decreases the melting temperature near the bottom of the lower mantle (this dope triggers the melting of the mantle material and the ascent of the plume). The paper presents evaluations for the heat power of the Hawaiian and Iceland plumes and the results of the experimental modeling of a thermochemical plume. The diameter of a plume conduit was determined to remain virtually unchanging in the course of plume ascent. When the top of a plume reaches a “refractory” layer, whose melting temperature is higher than the melt temperature in the plume conduit, a mushroom-shaped head of the plume develops beneath the bottom of this layer. The analysis of geological and geophysical data and the results of experimental modeling are used to develop a thermal physical model for a thermochemical plume. The balance relations for the mass and thermal energy and systematic tendencies in the heat and mass transfer during free convection were utilized to derive a system of equations for the heat and mass transfer of a thermochemical plume. Parameters were determined for a thermochemical plume ascending from the core-mantle boundary. Geodynamic processes are considered that occur during the ascent of a plume before it reaches the surface. The effect of the P-T conditions on the shape and size of a plume roof is analyzed, and a model is proposed for mass transfer between a thermochemical plume and the lithosphere, when the plume reaches the bottom of a “refractory” layer in the lithosphere. 相似文献
16.
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
17.
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