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1.
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
2.
当人们使用长波长的地震层析数据利用地震波速和密度的实验关系外推而直接计算地球大地水准面异常时惊奇地发现，计算大地水准面异常和观测大地水准面异常无论在异常型态或者异常幅度上均相差甚远。因而不能将地幔看做“刚性”地幔，而真实的地幔应当是一“动力”的地幔，它的内部，甚至被看做固体地幔内部也存在物质流动，否则无法解释上述两种水准面的差异。地幔，特别是下地幔远比人们设想的要活跃得多。地幔内部存在一个复杂的热动力系统。全球规模的大尺度对流、上地幔范围的二级对流、层状对流、核－幔边界上部Ｄ″层内很小尺度对流以及地幔热柱形式的对流可能同时存在于地幔之中，它们相互独立又相互影响，而形成多层次、多形态的运动格局。为了进一步完善、丰富人类对其赖以生存的地球的认识，除了需要建立更为合理的非线性的地幔热动力学模型之外，更加精细的、更加精确的大地测量、地球物理和地球动力学观测资料是必需的。 相似文献
3.
V. P. Trubitsyn 《Doklady Earth Sciences》2012,445(2):1025-1028
This paper presents the numerical models built for convection in a three-component mantle with heavy matter in the form of the D“ layer and a light highly viscous supercontinent. The models explain deformation of the heavy layer by mantle flows with hot provinces concentrating on the mantle bottom. The role played by supercontinents in plume generation is also explained, as well as the regularities of how plumes, which produce hot spots, traps, and basaltic plateaus on the Earth’s surface and ore diamond deposits in the lithosphere, are generated on the mantle bottom. 相似文献
4.
地幔柱构造理论研究若干问题及研究进展 总被引：3，自引：0，他引：3
介绍了目前地幔柱构造理论研究中若干重要问题和最新进展,许多证据显示,地幔柱是严自于核幔边界附近的Ｄ″层发生热扰动并产生地幔柱的热动力源于外地核的不均匀加热作用;一个新启动的地幔柱在穿过整个地幔的缓慢上升过程会形成巨大球状顶冠和狭窄尾柱;地幔柱巨大球状顶冠会导致地壳发生上隆、区域变质作用、地壳深熔作用、构造变形作用和大规模火山作用,形成大陆或大洋溢流玄武岩;地幔柱狭窄尾柱的长期活动会在上覆运动板块上 相似文献
5.
基于海洋地质地球物理观测建立的板块构造理论意味着板块和浅部地幔共同演化,然而地幔底部尤其是大型横波低速异常区(LLSVP)与板块(尤其微板块)运动和演化之间是否存在关联仍有争议。一些研究认为LLSVP长期保持稳定,而另一些模型则认为它与各级板块存在相互作用。为此,本文通过总结前人成果,并基于近期发表的板块重建和地幔对流模型进行进一步分析,探讨微板块运动和LLSVP的演化关系。模拟结果表明,微板块与大板块类似,俯冲后通常会下沉至核幔边界。微幔块会推动地幔底部热的物质聚集并形成大的热化学结构。该热化学结构与层析成像揭示的LLSVP基本吻合。下地幔径向流速场和温度场的二阶结构与地表速度场散度的二阶结构随时间的移动轨迹相似,表明深浅部圈层的耦合演化,但是下地幔结构演化一般会滞后于浅表。在微幔块推挤之下,地幔柱优先沿着地幔底部热化学结构的边缘形成,且有时会被推至热化学结构的内部。地幔柱上升至浅部后,能够导致岩石圈弱化甚至裂解或板块边界跃迁,形成微板块。因此,地幔底部LLSVP不是稳定或静止的,而是与微板块动态协同演化,并通过地幔柱与浅表板块边界发生遥相关,从而控制微板块生成场所。 相似文献
6.
地幔动力系统与演化最新进展评述 总被引：9，自引：1，他引：8
评述了９０年代以来地幔动力学研究的一些最新的观测和理论模拟的进展,探讨该领域的几个主要热点问题,包括地幔内部转换带和核幔边界的物理化学性质与演化,俯冲板片热结构及其与地幔的相互作用,热点物理化学性质与地幔柱动力学模拟,地幔对流系统及其对表层地质过程的影响等。这些结果是在多学科交叉研究的背景下取得的。地震层析的结果超越了８０年代取得的大尺度地幔结构,得到了越来越精细的结构,如俯冲板片的结构,６６０ｋｍ间断面的起伏,ＣＭＢ的超低速层和各向异性等。俯冲板片在某些区域平躺在上地幔底部,造成６６０ｋｍ间断面的凹陷。已有明显的迹象表明,俯冲板片至少在某些区域达到了地幔底部,说明下地幔是驱动地表板块运动的地幔对流不可分隔的一部分。全地幔对流模式对地幔中存在不同的地幔地球化学源区的看法提出重大挑战,计算机模拟三维球坐标地幔对流已经成为现实,新的研究正试图把地表板块加入到对流的模拟之中,并再造板块运动的动力学演化史。最后,对这些领域的最新进展提出自己的分析和看法,认为地球动力系统演化研究所面临的难题是地球内部动力状态演变的历史记录问题。而这样的记录,尤其是早期记录,只能从地球表面的造山带和盆地记录中去寻找。认为建立地质记录与? 相似文献
7.
Mantle convection modeling of the supercontinent cycle： Introversion,extroversion, or a combination？
The periodic assembly and dispersal of continental fragments,referred to as the supercontinent cycle,bear close relation to the evolution of mantle convection and plate tectonics.Supercontinent formation involves complex processes of"introversion"(closure of interior oceans),"extroversion"(closure of exterior oceans),or a combination of these processes in uniting dispersed continental fragments.Recent developments in numerical modeling and advancements in computation techniques enable us to simulate Earth’s mantle convection with drifting continents under realistic convection vigor and rheology in Earth-like geometry(i.e.,3D spherical-shell).We report a numerical simulation of 3D mantle convection,incorporating drifting deformable continents,to evaluate supercontinent processes in a realistic mantle convection regime.Our results show that supercontinents are assembled by a combination of introversion and extroversion processes.Small-scale thermal heterogeneity dominates deep mantle convection during the supercontinent cycle,although large-scale upwelling plumes intermittently originate under the drifting continents and/or the supercontinent. 相似文献
8.
We present a thermophysical model for interaction between the conduit of a thermochemical plume and horizontal free convection flows in the mantle: The mantle flow incident on the plume conduit melts at the conduit boundary (front part) and crystallizes at its back. Geological data on the intensity of plume magmatism over the last 150 Myr are used to estimate the total thermal power of mantle plumes. A possible scenario for plume-related mantle recrystallization is proposed. Over the lifespan of a thermochemical plume, mantle melts and recrystallizes owing to the motion of the plume source and interaction between the plume conduit and horizontal free convection flows. The plume conduits can melt and recrystallize the entire mantle over a certain period of time. The model for the interaction of drifting plume conduits with mantle flows and the estimated total thermal power of mantle plumes are used to estimate the duration of plume-related melting and recrystallization of the entire mantle. The influence of mantle plumes on the convective structure of the mantle through melting is judged from the model for plume interaction with horizontal mantle flows. 相似文献
9.
Venus is similar to the Earth in size， mass， composition and distance to the sun. However， Venus has neither plate tectonics nor dynamo that exists on the Earth. The lithosphere of Venus is very thick based on its topography and gravity. The admittance and correlation between Venusian geoid and topography are very high， suggesting that they are strongly influenced by the internal dynamical process of Venus. Analyses show that there may be 10 Hawaii-like mantle plumes in Venusian mantle. Data from Venus Express has shown evidence for recent active volcanism among several of these plumes. The distribution of impact craters on Venus shows that Venusian surface has a young age and the age is averaged about 500 Ma， suggesting that Venus may have experienced a global resurfacing event. However， whether this resurfacing is catastrophic or equilibrium is still under debate. It is also unclear whether Venus had plate tectonics in the past， is it always in stagnant lid regime， or might it have an entirely different mode？In general， the style of mantle convection on Venus is quite different from that of the Earth which is manifested by the plate tectonics. Here we reviewed the main observations including gravity， topography and surface tectonics which provide constrains on the interior structure and dynamics of Venus， and recent advance in the interior structure and dynamics of Venus. This review aims to provide new insights into the interior dynamics of Venus. 相似文献
10.
Both seismology and geochemistry show that the Earth's mantle is chemically heterogeneous on a wide range of scales. Moreover, its rheology depends strongly on temperature, pressure and chemistry. To interpret the geological data, we need a physical understanding of the forms that convection might take in such a mantle. We have therefore carried out laboratory experiments to characterize the interaction of thermal convection with stratification in viscosity and in density. Depending on the buoyancy ratio B (ratio of the stabilizing chemical density anomaly to the destabilizing thermal density anomaly), two regimes were found: at high B, convection remains stratified and fixed, long-lived thermochemical plumes are generated at the interface, while at low B, hot domes oscillate vertically through the whole tank, while thin tubular plumes can rise from their upper surfaces. Convection acts to destroy the stratification through mechanical entrainment and instabilities. Therefore, both regimes are transient and a given experiment can start in the stratified regime, evolve towards the doming regime, and end in well-mixed classical one-layer convection. Applied to mantle convection, thermochemical convection can therefore explain a number of observations on Earth, such as hot spots, superswells or the survival of several geochemical reservoirs in the mantle. Scaling laws derived from laboratory experiments allow predictions of a number of characteristics of those features, such as their geometry, size, thermal structure, and temporal and chemical evolution. In particular, it is shown that (1) density heterogeneities are an efficient way to anchor plumes, and therefore to create relatively fixed hot spots, (2) pulses of activity with characteristic time-scale of 50–500 Myr can be produced by thermochemical convection in the mantle, (3) because of mixing, no ‘primitive’ reservoir can have survived untouched up to now, and (4) the mantle is evolving through time and its regime has probably changed through geological times. This evolution may reconcile the survival of geochemically distinct reservoirs with the small amplitude of present-day density heterogeneities inferred from seismology and mineral physics. 相似文献
11.
In the available numerical models, mantle plumes are represented by homogeneous ascending streams of thermal convection. Pulses are considered to be possible only in thermochemical plumes within the compositionally inhomogeneous mantle. We show that pulses can also occur under regular thermal convection in the homogeneous mantle. As the intensity grows, the flow in the tail of a thermal plume first begins pulsing and then the plume breaks up into a set of sequentially emerging thermals. For the present-day mantle, the pulsation periods for plumes in the lower mantle can range up to 10 Ma and about 1 Ma in the upper mantle. 相似文献
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13.
N.L. Dobretsov 《Russian Geology and Geophysics》2010,51(6):592-610
The paper is a synthesis of models for basic geodynamic processes (spreading, subduction transient into collision, mantle plumes) in relation with the Earth's evolution and regularly changing geodynamic parameters. The main trends and milestones of this evolution record irreversible cooling of the Earth's interior, oxidation of the surface, and periodic changes in geodynamic processes. The periodicity consists of cycles of three characteristic sizes, namely 700–800 Myr global cycles, 120, 90, and 30 Myr smaller cycles, and short-period millennial to decadal oscillations controlled by changing Earth's orbital parameters and, possibly, also by other extraterrestrial factors. Major events and estimates of mantle and surface temperatures, heat flow, viscosity, and the respective regimes of convection and plume magmatism have been reported for the largest periods of the Earth's history: Hadean (4.6–3.9 Ga), Early Archean (3.9–3.3 Ga), Late Archean (3.3–2.6 Ga), Early Proterozoic (2.6–1.9 Ga), Middle Proterozoic (1.9–1.1 Ga), Neoproterozoic (1.1–0.6 Ga), and Phanerozoic with two substages of 0.6–0.3 and 0.3–0 Ga.Current geodynamics is discussed with reference to models of spreading, subduction, and plume activity. Spreading is considered in terms of double-layered mantle convection, with focus on processes in the vicinity of mid-ocean ridges. The problem of mafic melt migration through the upper mantle beneath spreading ridges is treated qualitatively. Main emphasis is placed on models of melting, comparison of experimental and observed melt compositions, and their variations in periods of magmatic activity (about 100 kyr long) and quiescence. The extent and ways of interaction of fluids and melts rising from subduction zones with the ambient mantle remain the most controversial. Plume magmatism is described with a “gas torch” model of thermochemical plumes generated at the core-mantle boundary due to local chemical doping with volatiles (H2, CH2, KH, etc.) which are released from the metallic outer core, become oxidized in the lower mantle, and decrease the melting point of the latter. The concluding section concerns periodicities in endogenous processes and their surface consequences, including the related biospheric evolution. 相似文献
14.
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
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16.
Recent advances in three-dimensional numerical simulations of mantle convection have aided in approximately reproducing continental movement since the Pangea breakup at 200 Ma. These have also led to a better understanding of the thermal and mechanical coupling between mantle convection and surface plate motion and predictions of the configuration of the next supercontinent. The simulations of mantle convection from 200 Ma to the present reveals that the development of large-scale cold mantle downwellings in the North Tethys Ocean at the earlier stage of the Pangea breakup triggered the northward movement of the Indian subcontinent. The model of high temperature anomaly region beneath Pangea resulting from the thermal insulation effect support the breakup of Pangea in the real Earth time scale, as also suggested in previous geological and geodynamic models. However, considering the low radioactive heat generation rate of the depleted upper mantle, the high temperature anomaly region might have been generated by upwelling plumes with contribution of deep subducted TTG(tonalite-trondhjemite-granite) materials enriched in radiogenic elements. Integrating the numerical results of mantle convection from 200 Ma to the present, and from the present to the future, it is considered that the mantle drag force acting on the base of continents may be comparable to the slab pull force, which implies that convection in the shallower part of the mantle is strongly coupled with surface plate motion. 相似文献
17.
At the transition from the Permian to the Triassic, Eurasia was the site of voluminous flood-basalt extrusion and rifting. Major flood-basalt provinces occur in the Tunguska, Taymyr, Kuznetsk, Verkhoyansk–Vilyuy and Pechora areas, as well as in the South Chinese Emeishen area. Contemporaneous rift systems developed in the West Siberian, South Kara Sea and Pyasina–Khatanga areas, on the Scythian platform and in the West European and Arctic–North Atlantic domain. At the Permo–Triassic transition, major extensional stresses affected apparently Eurasia, and possibly also Pangea, as evidenced by the development of new rift systems. Contemporaneous flood-basalt activity, inducing a global environmental crisis, is interpreted as related to the impingement of major mantle plumes on the base of the Eurasian lithosphere. Moreover, the Permo–Triassic transition coincided with a period of regional uplift and erosion and a low-stand in sea level. Permo–Triassic rifting and mantle plume activity occurred together with a major reorganization of plate boundaries and plate kinematics that marked the transition from the assembly of Pangea to its break-up. This plate reorganization was possibly associated with a reorganization of the global mantle convection system. On the base of the geological record, we recognize short-lived and long-lived plumes with a duration of magmatic activity of some 10–20 million years and 100–150 million years, respectively. The Permo–Triassic Siberian and Emeishan flood-basalt provinces are good examples of “short-lived” plumes, which contrast with such “long lived” plumes as those of Iceland and Hawaii. The global record indicates that mantle plume activity occurred episodically. Purely empirical considerations indicate that times of major mantle plume activity are associated with periods of global mantle convection reorganization during which thermally driven mantle convection is not fully able to facilitate the necessary heat transfer from the core of the Earth to its surface. In this respect, we distinguish between two geodynamically different scenarios for major plume activity. The major Permo–Triassic plume event followed the assembly Pangea and the detachment of deep-seated subduction slabs from the lithosphere. The Early–Middle Cretaceous major plume event, as well as the terminal–Cretaceous–Paleocene plume event, followed a sharp acceleration of global sea-floor spreading rates and the insertion of new subduction zone slabs deep into the mantle. We conclude that global plate kinematics, driven by mantle convection, have a bearing on the development of major mantle plumes and, to a degree, also on the pattern of related flood-basalt magmatism. 相似文献
18.
The evolution of the mantle''s chemical structure 总被引：10，自引：0，他引：10
The geochemistry of flood basalts and their associated picrites, and of komatiites and their associated basalts, combined with a theoretical model for the structure of mantle starting plumes, can be used to decipher key elements of the geochemical structure of the deep mantle and show how it has varied through time. We argue that the thermal boundary layer above the core consisted mainly of depleted mantle similar to the present MORB source during the Archaean and this was largely replaced between 2.7 and 2.0 billion years ago by enriched mantle to form the OIB source. We suggest that this change in the nature of the hotspot source reflects a fundamental change in the dominant component of downward convection: from cold plumes breaking away from beneath a stable lithosphere during the pre-Archaean to subduction of lithosphere in the Archaean and post-Archaean mantles. 相似文献
19.
六十年代以来,由于卫星重力测量和计算技术的迅速发展,有些研究者,如Runcorn(1967)和Liu(1976-1980),根据卫星重力数据计算获得地幔对流及其应力场图象来研究全球板块构造和区域构造。愈来愈多的事实表明,构造运动不仅是地壳和岩石圈层物质运动的表现,而更重要的是地幔物质运动的反映。因此,本文应用作者计算获得的岩石圈层下面地幔流运动图象与大地构造及近代构造运动的资料相对比,探索我国岩石圈层下的地幔对流格局形成及其对构造运动的影响。 相似文献
20.
Nicolas Coltice Hervé Bertrand Patrice Rey Fred Jourdan Benjamin R. Phillips Yanick Ricard 《Gondwana Research》2009,15(3-4):254-266
Throughout its history, the Earth has experienced global magmatic events that correlate with the formation of supercontinents. This suggests that the distribution of continents at the Earth's surface is fundamental in regulating mantle temperature. Nevertheless, most large igneous provinces (LIPs) are explained in terms of the interaction of a hot plume with the lithosphere, even though some do not show evidence for such a mechanism. The aggregation of continents impacts on the temperature and flow of the underlying mantle through thermal insulation and enlargement of the convection wavelength. Both processes tend to increase the temperature below the continental lithosphere, eventually triggering melting events without the involvement of hot plumes. This model, called mantle global warming, has been tested using 3D numerical simulations of mantle convection [Coltice, N., Phillips, B.R., Bertrand, H., Ricard, Y., Rey, P. (2007) Global warming of the mantle at the origin of flood basalts over supercontinents. Geology 35, 391–394.]. Here, we apply this model to several continental flood basalts (CFBs) ranging in age from the Mesozoic to the Archaean. Our numerical simulations show that the mantle global warming model could account for the peculiarities of magmatic provinces that developed during the formation of Pangea and Rodinia, as well as putative Archaean supercontinents such as Kenorland and Zimvaalbara. 相似文献