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1.
在小尺度地幔对流模型的基础上,建立了顾及岩石层与地幔耦合的地幔对流模型,考虑到岩石层对上地幔小尺度对流的弹性响应,将上地幔视为一均匀的等粘滞系数的牛顿粘滞流体,其对注能量来源于下地幔,用热流体动力学基本方程得到地上地幔对流在壳幔边界处的垂向应力作为弹性板弯曲方程的垂直加载,来耦合弹性岩石层和可流动地幔,推导了两者耦合下区域重力异常和上地幔小尺度对流的相关方程,用以反演上地幔小尺度对流场模式和岩石层底部拖力场格局,对比了有,无弹性岩石层影响的模型之间的差异,并对模型应用范围,特别要板块边界水平均造力可能产生的影响,作了进一步探讨。 相似文献
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用数值模拟方法模拟了增厚大陆岩石层热边界层被对流地幔剥离并为软流层物质替代的动力学过程．结果表明,在初始温度分层分布、侧向均匀但存在微小热扰动的流场中,80km厚的增厚岩石层热边界层约需60Ma才能被完全剥离,剥离的速率微弱地依赖扰动的强度;在已建立好的流场中,同样厚度的增厚热边界层只需约10Ma就可被剥离．模拟结果暗示青藏高原地壳及岩石层在岩石层增厚和剥离以前就很热,其下伏地馒中可能已存在建立好的上地幔小尺度对流系统,而该尺度的对流系统很可能是由特提斯海洋岩石圈俯冲和消减诱发的 相似文献
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地幔热动力学模型 总被引：5，自引：5，他引：5
地幔,特别是下地幔,远比人们先前的设想活跃.地球物理学、地质学和地球动力学的观测和地球热动力学模拟表明:(1)地幔底部与地核交界处有一厚度为200km 左右的D″层,这是一个非常活跃的区域,它的运动和变化直接与地核的行为有关,仅仅将其看成全地幔对流的以热传导为主体的热边界层是不够的,小尺度的热对流或许主导这一层内部的物质运动,它加热地幔同时又通过热柱将其部分热量输运到地球外层;(2)地幔热柱有可能源于地球初期不均匀的残存堆积,其存储的热量不断地或穿透整个地幔形成热点或消失在软流层中与该层中的次一级对流相耦合;(3)上地幔在670km 深度范围内广泛存在次一级对流体系。其尺度为500—700km 这一对流体系决定了岩石层板块内部的构造和动力活动,其活动周期远比全球规模的板块运动活动周期小得多;(4)全球规模的大尺度全地幔对流与板块构造动力学密切相关。它以不到10亿年左右的时间完成一个周期,它不断地更新地球表层,也搅拌着地幔,同时还输运地球内部的热能向外层空间散发;(5)地幔局部地区层状相互耦合的对流结构在地震层析剖面上有明显的显示,它表明了地幔对流结构的复杂性,仅管我们对此相知甚少,但它或许是无法避免的;(6)岩石层是人类熟知的赖以生存的方舟,它的运动和构造反映了上述所有运动信息,仅仅将其视为一对流体系的热边界层是不够的,它自身作为一个独立的力学单元影响了整个地幔的热动力学过程.因此,面对如此活跃的、复杂的地幔,用一个单一的模型去描述它是不合适的.上述各种热动力学单元及其运动均有自身的力学特征及运行机制和规律,但它们又是相互作用和影响而构成地幔整体,这就是一个真实的但又模糊不清的地幔热动力学模型.为了完善这一模型,需要更多的、细致的地球物理和地球动力学的观测资料以及需要我们更深刻地理解和更认真地解释这些资料的地幔热动力学背景. 相似文献
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上地幔小尺度对流是控制区域地球动力学过程的主要机制之一,蒙古-贝加尔地区的一些区域动力学过程被认为与上地幔小尺度对流相关.本文目的在于利用重力资料研究蒙古-贝加尔地区的上地幔小尺度对流,并探讨其与构造动力学的关系.基于区域均衡重力异常与上地幔小尺度对流的相关方程,本文利用区域均衡重力异常资料反演了蒙古-贝加尔地区上地幔小尺度对流流场及作用于岩石层底部的应力场.结果显示,蒙古-贝加尔地区地幔流场及对流应力场呈现非常复杂的图像,流场及应力场分布与地表构造具有很好的相关性.西伯利亚地台和蒙古褶皱带下地幔流场和对流应力场均较弱,这与这些地区现今较弱的构造活动性是一致的.贝加尔裂谷区下存在地幔上升流,对流应力场呈拉张状态,但应力场的幅值较小(约8 MPa),表明地幔对流不是贝加尔裂谷开裂的主要控制因素.Hangay高原、阿尔泰和戈壁-阿尔泰下存在地幔上升流,对流应力场为拉张状态,这一方面可能构成Hangay高原隆升的深部动力机制,另一方面,也为Amurian板块西边界划分提供了动力背景. 相似文献
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《地球物理学进展》1986,(2)
本文给出地球的地幔热状态和热系统的简化形式,假定地幔内的大规模对流是双层的,在上地幔内的对流是由来自下面的热流量来测定,而在下地幔内的对流是用内部加热来测定。估算上地幔的热弛豫时间是～10~8年,下地幔的热弛豫时间τ_(1m)是～1.5×10~9年,地球的热弛豫是由τ_(1m)来测定。在对流的地幔内的超绝热的温度降是在热的边界层内形成的:在上地幔内,△T_1≤600K;在下地幔顶部,△T_2≤650K;在下地幔底部,△T_3≤650K。核-幔边界上的绝热温度是～2900K,真实温度一定是～3500—4500K。地幔中的热边界层都是过热区,必须跟低Qμ区(Qμ是对S波的力学品质因数)一致。低Qμ的第一层的深度是～100—250公里,第二层的深度是670—850公里,第三层是2700—2900公里。热点的热源区可能在第二个热边界层内,有意义的是,该层的水平速度(～1公分/年)可以确定在“板块构造”中绝对速度的精确度范围。因为上地幔是地壳之源,所以上地幔和下地幔之间的边界一定是弱的化学边界。第三个热边界层(深度在2600—2900公里)的热系统及其不稳定性在地核的磁流体动力学方面尤其是对于地磁偶极子的极性改变以及对地磁场时间尺度的了解有非常重要的作用。 相似文献
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在地震层析成像计算的地幔密度异常直接驱动地幔对流的新方法的基础上,发展了在上、下地幔不同黏性结构框架下,密度异常驱动地幔对流的物理模型.利用 Grands和S12 WM13等地震层析成像模型推得的地幔密度异常分布,设置板块绝对运动极型场为运动上边界,考虑深度660km地震波不连续面为界的上、下地幔之间存在黏滞性的差异,直接反演了不同黏滞系数的双层地幔结构下地幔对流的模式.研究中选取地幔平均密度为ρ=5500kg/m3, 上层地幔平均黏滞系数为μ=1021Pa·s,计算了上、下地幔黏滞系数之比为1∶1, 1∶10, 1∶100和1∶1000时地幔大圆剖面、以及区域剖面上的流场.结果表明,两种模型在球谐展开1～13阶的范围内其对流的基本格局相似.当下地幔黏滞性超过上地幔的100倍时,下地幔流场速度与上地幔的流场速度相比显著减小,但是对流仍然表现出单层对流环的基本格局.论文还用 240km深度球面上的对流格局讨论了对流和全球构造之间的关系. 相似文献
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5 外围层很明显,岩石层和软流层已经失去了它在现代地质学和地球化学文献中最初确切的地球物理含义。很难讨论OLB,CFB和MORB储层可能位置,因为现在预想它们与岩石层、软流层、上地幔和下地幔有联系。富集的、亏损的和较少亏损的岩浆很可能都起源于上地幔。甚至亏损上地幔的主张也需要热柱头或分层的CL在需要热点岩浆时局部补充软流层,或者用各种构造环境中的岩浆解释CL,热柱或下地幔。有一个时期曾经把大陆玄武岩的全部富集归因于地壳污染。那么在通过地壳之前,浅部地幔需要有一些玄武岩和富集方 相似文献
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首先计算了欧亚地区均衡残差大地水准面．基于地幔热对流的内负荷理论和最新全球层析成像结果，探讨了欧亚地区中波长均衡残差大地水准面的地球动力学意义．研究结果表明，中波长均衡残差大地水准面主要受上地幔粘滞度和岩石层强度的影响，进而得出欧亚地区一些古老地盾和构造稳定地区的上地幔与年轻山脉及构造活动地区的上地幔结构存在着差异．这个差异主要是占老地盾和构造稳定地区，如波罗的海地盾、中西伯利亚地台、东欧等区域，冷却的上地幔已穿透地幔较深，上地幔与岩石层之间耦合较好;而年轻山脉和构造活动区，如帕米尔、天山、贝加尔活动带、青藏高原、日本海周围地区，在上地幔可能存在着热物质即粘滞度很低的软流层，上地幔与岩石层耦合程度较差，甚至有可能解耦．从欧亚地区上地幔属性的差异，可以解释该地区的一些地球动力学问题． 相似文献
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The theory of three-dimensional and finite-amplitude convection in a viscous spherical shell with temperature and pressure dependent physical parameters is developed on the basis of a modified Boussinesq fluid assumption. The lateral dependences of the variables are resolved through their spherical harmonic representations, whereas their radial and time dependences are determined by numerical procedures. The theory is then applied to produce thermal evolution models for Venus. The emphasis is on illustrating the effects of certain physical parameters on the thermal evolution rather than proposing a specific thermal history for the planet. The main conclusions achieved in this paper are (1) a significant portion of the present temperature in the mantle and heat flux at the surface of Venus is probably owing to the decay of a high temperature established in the planet at the completion of its core formation, (2) the effective Rayleigh number of the mantle is so high that even the lower order modes of convection cool the planet sufficiently and maintain an almost adiabatic temperature gradient in the convecting region and high temperature gradients in the thermal boundary layers, (3) the convection is oscillatory with avalanche type properties which induces oscillatory features to the surface heat flux and the thickness of the crustal layer, and (4) a planetary model with a recycling crust cools much faster than those with a permanently buoyant crust.The models presented in this paper suggest that Venus has been highly convective during its history until ～ 0.5 Ga ago. The vigorous convection was bringing hot and fresh material from the deep interior to the surface and dragging down the crustal slags, floating on the surface, in to the mantle. The rate of cooling of the planet was so high that its core has solidified. In the last 0.5 Ga the vigour of convection diminished considerably and the crustal slags developed into a global and permanently buoyant crustal layer. The tectonic style on Venus has, consequently, changed from the recycling of crustal plates to hot spot volcanics. At the present time the planet is completely solid, except in the upper part of its mantle where partial melting may occur. 相似文献
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The thermochemical model of the authors is shown to be naturally related to the general theory of V.P. Myasnikov. A heterogeneous modification of this homogeneous theory is described in light of the present ideas on the differentiation of the mantle substance at the boundary with the core and its eclogitization during submersion from the outer boundary and at the endothermic phase transition at a depth of 670 km. The Earth’ls evolution from an initial hot state is numerically modeled. The evolution is shown to start with an abrupt mantle overturn followed by a long period of steady evolution. Global mantle overturns recur a few times, gradually weaken, and are transformed into regional avalanches. The spatial configuration of overturns is represented by a predominant funnel-shaped sink and a few (three to five) ascending superplumes, which convincingly explains the causes of the formation of supercontinents, the opening of oceans, and the observed asymmetry of the planet. The times of overturns remarkably correlate with geological data on the existence of supercontinents. The processes of core growth, mantle cooling, and crust formation exhibit a clearly expressed stepwise behavior. The supplementation of the endothermic phase transition by chemical transformations favors the overcoming of the phase barrier between the upper and lower mantle, enhances the nonlinearity of mantle convection, and imparts a heterocyclic pattern to the process of evolution. It is shown that the lower mantle plume of chemical origin is fragmented by the phase transition into parts that, interacting with the thermal convection, generate a system of upper mantle plumes. This modeling provides an explanation of the coeval systems of oceanic plateaus and continental traps observed on the surface. 相似文献
13.
热传导系数和热膨胀系数是影响板块俯冲动力学过程的两个重要参数. 由于地球介质的不均匀性,热系数也会随深度发生变化.然而,这种变化在地球动力学模拟研究中往往被忽略.本文针对随温度变化的热传导系数和热膨胀系数, 模拟板块俯冲的动力学过程,分析热系数、黏度对板块俯冲形态的影响及其对应的地幔对流特征.结果表明,依温度变化的热传导系数和热膨胀系数会影响地幔温度及黏度分布,进而改变板块的俯冲角度;黏度是控制板块俯冲动力学演化过程的重要因素;地幔对流受黏度结构的影响,呈现分层对流及局部多个对流环等多种不同形态的对流场特征. 相似文献
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V. P. Trubitsyn A. N. Evseev M. N. Evseev E. V. Kharybin 《Izvestiya Physics of the Solid Earth》2011,47(12):1027-1033
The process of multiple self-nucleation and ascent of mantle plumes is studied in the numerical models of thermal convection.
The plumes are observed even in the simplest isoviscous models of thermal convection that leave aside the more complex rheology
of the material, thermochemical effects, phase transformations, etc., which, although controlling the features of plumes,
are not necessary for their formation. The origin of plumes is mainly due to the instability of the mantle flows at highly
intense (low-viscous) thermal convection. At high viscosity, convective flows form regular cells. As viscosity decreases,
the ascending and descending flows become narrower and unsteady. At a further decrease in viscosity, the ascending plumes
assume a mushroom-like shape and occasionally change their position in the mantle. The lifetime of each flow can attain 100
Ma. Using markers allows visualizing the evolution of the shape of the mantle plumes. 相似文献
15.
《中国科学:地球科学(英文版)》2015,(10)
This paper presents a study on the effects of phase transitions on the mantle convection of Venus in a three-dimensional(3D)spherical shell domain.Our model includes strong depth-and temperature-dependent viscosity and exothermic phase change from olivine to spinel as well as endothermic phase change from spinel to perovskite.From extensive numerical simulations of the effects of Rayleigh number(Ra),and the Clapeyron slopes and depths of phase changes,we found the following:(1)The endothermic phase change prevents mass flow through the interface.Increasing the absolute value of the Clapeyron slopes decreases radial mass flux and normalized radial mass flux at the endothermic phase boundary,and decreases the number of mantle plumes.In other words,mass flow through the phase boundary decreases.The inhibition influence of phase changes increases,as do convective wavelengths.(2)Increasing Ra also increases the convective wavelength and decreases the number of mantle plumes,but it has less influence on the mass exchange.As Ra increases,the convective vigor increases along with the radial mass flux and the mass flow through the phase boundary;however,the normalized mass flux through the phase boundary varies little with Ra,which is different from the conclusion that increasing Ra will greatly increase the inhibition of mass flow through the phase boundary based on two-dimensional(2D)modeling.(3)Increasing the depth of endothermic phase change will slightly decrease the number of mantle plumes,but has little effect on the mass flow through the phase boundary.Consistent with previous studies,our results show that the phase change from spinel to perovskite could inhibit the mass flow through the phase boundary,but they also show that the buildup of hot materials under the endothermic phase boundary in the 3D model could not be so large as to cause strong episodic overturns of mantle materials,which is quite different from previous 2D studies.Our results suggest that it is difficult for phase changes to cause significant magmatism on Venus;in other words,phase changes may not be the primary cause of catastrophic resurfacing on Venus. 相似文献
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The gravity field and crustal thickness of Venus 总被引：1，自引：0，他引：1
The gravity and topography of Venus obtained from observations of the Magellan mission, as well as the gravity and topography from our numerical mantle convection model, are discussed in this paper. We used the hypothesis that the geoid of degrees 2–40 is produced by sublithospheric mantle density anomalies that are associated with dynamical process within the mantle. We obtained the model dynamical admittance(the geoid topography ratio based on a convection model) by a numerical simulation of the Venusian mantle convection, and used it to correct the dynamical effect in the calculation of crustal thickness. After deducting the dynamical effect, the thickness of the Venusian crust is presented. The results show that the gravity and topography are strongly correlated with the Venusian mantle convection and the Venusian crust has a significant influence on the topography. The Venusian crustal thickness varies from 28 to 70 km. Ishtar Terra, and Ovda Regio and Thetis Regio in western Aphrodite Terra have the highest crustal thickness(larger than 50 km). The high topography of these areas is thought to be supported by crustal compensation and our results are consistent with the hypothesis that these areas are remnants of ancient continents. The crustal thickness in the Beta, Themis, Dione, Eistla, Bell, and Lada regiones is thin and shows less correlation with the topography, especially in the Atla and Imdr regiones in the eastern part of Aphrodite Terra. This is consistent with the hypothesis that these highlands are mainly supported by mantle plumes. Compared with the crustal thickness calculated with the dynamical effect, our results are more consistent with the crust evolution and internal dynamical process of Venus. 相似文献
17.
无论在行星大小、质量还是轨道速度等方面,金星都是太阳系中与地球最相似的行星.自1960年代初期开始,金星一直是人类深空探测的重要目标.本文简要地回顾了人类探索金星的历史,总结了对金星已有的认识,梳理了金星的主要科学问题,最后介绍了未来的国际探测计划,并建议了我国的金星探测目标.早期对金星的探测以苏联的金星计划(Венера)和美国的水手系列(Mariner)为代表,后期的探测器以欧盟、日本等国家的“金星快车(Venus Express)”、“拂晓号(Akatsuki)”为代表.这些探测结果为我们认识金星大气成分、地表地形和内部结构提供了重要的数据.金星的大气组成以CO2为主,含少量N2,与现在地球的大气组成显著不同,类似早期地球的大气组成.虽然金星地表目前没有液态水,但部分理论模拟工作表明金星地表可能曾经有液态水.一系列探测器对金星地表成分的分析表明,金星地表主要由玄武岩组成.在地形地貌方面,由于金星特殊的地表环境,金星表面风化作用对地表地貌影响很小.金星的地表主要受控于比较年轻的火山作用,发育了许多不同于地球的地貌特征,主要包括区域平原、盾状火山平原、冕状地形以及瓦片状地形等,其动力学机制可能是地幔柱—岩石圈相互作用或地幔对流,至今未发现与板块构造相关的地貌.现阶段金星没有太多大型的、活跃的火山热点,虽然无法估测准确的火山活动速率,但相比地球来说火山活动速率小很多.在内部结构方面,金星具有与地球类似的核幔壳结构.金星的内部组成也与地球类似,例如金星地幔很可能是与地球相似的橄榄岩成分.不存在内部磁场和缺乏板块构造是金星区别于地球的两个重要特征.关于金星为什么没有自身磁场,主流观点是金星地核缺乏对流,无法演化出磁场.而针对金星为什么没有演化出板块构造,目前认为主要有三个可能的原因:地表温度过高,没有软流圈,金星缺乏液态水,其中液态水的缺乏接受度最广.从大气组成、地表岩石组合、构造作用等角度来看,金星都与早期地球非常相似,是我们理解类地行星演化的天然实验室.研究金星和地球为什么会朝不同方向演化,是深入理解包括系外行星在内的行星的宜居性形成与演变的重要途径。因此,金星一直是优先级别最高的深空探测目标之一.近几年,美国、俄罗斯以及欧洲等国家和地区分别针对金星目前主要的科学问题,例如金星是否存在早期海洋、金星的宜居性以及结构和重力场等,先后提出各自的金星探测计划.我国在新的国际竞争中应该、也必然有所作为. 相似文献
18.
In the kinematic theory of lithospheric plate tectonics, the position and parameters of the plates are predetermined in the initial and boundary conditions. However, in the self-consistent dynamical theory, the properties of the oceanic plates (just as the structure of the mantle convection) should automatically result from the solution of differential equations for energy, mass, and momentum transfer in viscous fluid. Here, the viscosity of the mantle material as a function of temperature, pressure, shear stress, and chemical composition should be taken from the data of laboratory experiments. The aim of this study is to reproduce the generation of the ensemble of the lithospheric plates and to trace their behavior inside the mantle by numerically solving the convection equations with minimum a priori data. The models demonstrate how the rigid lithosphere can break up into the separate plates that dive into the mantle, how the sizes and the number of the plates change during the evolution of the convection, and how the ridges and subduction zones may migrate in this case. The models also demonstrate how the plates may bend and break up when passing the depth boundary of 660 km and how the plates and plumes may affect the structure of the convection. In contrast to the models of convection without lithospheric plates or regional models, the structure of the mantle flows is for the first time calculated in the entire mantle with quite a few plates. This model shows that the mantle material is transported to the mid-oceanic ridges by asthenospheric flows induced by the subducting plates rather than by the main vertical ascending flows rising from the lower mantle. 相似文献
19.
We present a broad-based review of the observational evidence that pertains to or otherwise implies solid-state convection to be occurring (or have occurred) in the interiors of the terrestrial planets.For the Earth, the motion of the plates is prima facie evidence of large-scale mantle convection. Provided we understand upper-mantle thermal conductivity correctly, heat flow beneath the old ocean basins may be too high to be transported conductively from the upper mantle through the base of the lithosphere and therefore convection on a second smaller scale might be operative. The horizontal scale of plate dimensions implies, due to typical cell aspect ratios observed in convection, that the motion extends to the core-mantle boundary. Improved global data coverage and viscoelastic modeling of isostatic rebound due to Pleistocene deglaciation imply a uniform mantle viscosity, and thus indicate that whole-mantle convection could exist. Additionally, there is some seismic evidence of lithospheric penetration to depths deeper than 700 km. We discuss some salient features and assumption boundedness of arguments for convection confined to the upper mantle and for convection which acts throughout the mantle since the vertical length scale has a profound effect upon the relevance of geophysical observations. The horizontal form of mantle convection may be fully three-dimensional with complex planform and, therefore, searching for correlative gravity patterns in the ocean basins may not be useful without additional geophysical constraints. Many long-wavelength gravity anomalies may arise from beneath the lithosphere and must be supported dynamically, although thermal convection is not a unique explanation. Topography is an additional geophysical constraint, but for wavelengths greater than a few hundred kilometers, a general lack of correlation exists between oceanic residual gravity and topography, except at specific locations such as Hawaii. Theoretical calculations predict a complex relationship between these two observational types. Oceanic gravity data alone shows no regular planform and there is no correlation with any small-scale convective pattern predicted by laboratory experiments.All of the observational evidence argues against Martian plate tectonics occurring now or over much of the history of this planet, but lack of plate tectonics is not an argument against interior convection. The Tharsis uplift on Mars may have resulted from convective processes in the mantle, and the present-day gravity anomaly associated with Tharsis must be supported by the finite strength of the lithosphere or by mantle convection. Stresses imparted by the present topographic load would be greater than a kilobar, in excess of long-term finite strength. Observed fracture patterns are probably a direct result of this load, and the key question concerns the level of resultant strain relief. The global topographic and geomorphic dichotomy between the northern and southern hemisphere required a solid-state flow process to create the accompanying center-of-figure to center-of-mass offset.Lunar heat flow values, in analogy with oceanic heat flow on the Earth, strongly imply a convective mechanism of heat transport in the interior which, based on seismic Q values, is limited to the lower mantle. The presence of moonquakes in this region does not preclude solid-state convective processes. Lunar conductivity profiles provide no information on convection because of the difficulty in conductivity modeling, uniqueness of models, and the uncertainty in the conductivity-temperature relationship. The excess oblateness of the lunar figure over the hydrostatic value does not require convective support; in fact, such a mechanism is unlikely.The presence of a dipole magnetic field on Mercury does not provide a constraint on mantle convection unless its existence can be inextricably linked to a molten core. The non-hydrostatic shape of the equatorial figure, required for the observed resonance between Mercury's rotational and orbital periods, is most likely related to surface processes, as opposed to convection. The resonance implies escape from a 2n resonance and, therefore, is related to the question of a molten core. Further dynamical data is needed to constrain interior models.Interpretation of limited radar imagery for the surface of Venus is enigmatic in terms of plate tectonics and therefore interior convection. Linear tensional and possibly compressional features are observed, but there are also crustal regions which appear to show large impact structures and are thus geologically old and may not have been recycled. 相似文献
20.
Important though indirect information about the internal structure of Venus is provided by its topography and geoid. In the last decades this information has been used to constrain the Venus mantle viscosity structure and its dynamic regime. Recently, the geodynamic inversion of the Venus?? geoid and topography resulted in a group of best fitting viscosity profiles. We use these viscosity models here as an input to our mantle convection code. We carry out simulations of the Venus?? mantle evolution in a 3D spherical shell with depth dependent viscosity and check whether the character of the dynamic topography and the geoid represented by their power spectra fits the observed quantities. We compare the results with several other models obtained for different viscosity stratifications (constant, constant with highly viscous lithosphere, linear increase of viscosity). Further, we estimate the effect of other factors such as internal heating and varying Rayleigh number. We use a 2D spherical axisymmetric convection code to study the effect of lateral viscosity variations. In these 2D models we monitor the topography and the geoid developing above the axisymmetric plume and compare them with the observed elevations of Venus?? geoid and topography in several Regia. Though none of the models fits observed data perfectly, we can generally conclude, that the best fit between the observed and predicted quantities is reached for viscosity profiles with 200 km thick lithosphere followed by a gradual increase of viscosity with depth and with the upper mantle viscosity of 2 × 10 21 Pa s. For all viscosity profiles the predicted geoid and topography spectra match the observed ones only up to the degree 40, thus indicating other than dynamic origin of these quantities for higher degrees. 相似文献