共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
Parameterized thermal model of a mixed mantle convection 总被引：4，自引：0，他引：4
IntroductionTectonicevolutionisinfluencedbythermalhistoryoftheEarth.TheEarthhasabout4.6Gahistory.ThermalenergyfromtheinterioroftheEachprovidesthemainpowerfortectonicevolution.ItnotonlycontrolstheformationofthelayeredstructuresinsidetheEarth,butalsopromotesthetectonicmovementsofthesurfaceplatesduringthegeologicalera.ThestudyofthethermalhistoryoftheEarthhaspassedseveralstages.Inearlystudies,onlyconductivemechanism(Lubimova,1958)isdiscussedinthethermalevolution.However,theimpotalceofthermalco… 相似文献
3.
Estimates of the chemical composition of the Archaean mantle, derived from elemental abundance ratios in komatiites combined with ultramafic xenolith data, support a model of a multistage heterogeneous accretion history of the Earth and synchronous core formation, 4.6 Ga ago.Most refractory lithophile element abundance ratios in komatiites and xenoliths are close to chondritic except for V/Ti and Ca/Al. Depletion of vanadium is likely due to its partial incorporation into the iron core; whereas fractionation of Ca/Al observed in Archaean Al-undepleted komatiites (1.20 times chondrites) and in some modern fertile spinel lherzolite xenoliths (1.15 times chondrites) could be due to small amounts of garnet (rich in Al but poor in Ca) segregation into the lower mantle during partial or complete melting of the upper mantle in the very early history of the Earth. However, this process may have had only a small effect on the overall chemical composition of the upper mantle.Simultaneous occurrence of early Archaean Al-undepleted (Al/Ti chondrites) and Al-depleted (Al/Ti 0.5 chondrites, and depletion of Sc and heavy REE) peridotitic komatiites in the Barberton area, S. Africa, and late Archaean Newton Township, Canada, argue against derivation of peridotitic komatiites from a circum-global magma ocean. Garnet separation from a mantle diapir which intersects the solidus at great depth ( 200 km) in a hotter early Archaean mantle could explain the chemical characteristics of Al-depleted komatiites. Alternatively, these two types of komatiites could have been derived from different layers in a fractionated mantle. A limited amount of Hf isotope data for Archaean komatiites seems to suggest that both mechanisms are important. This chemically and minerallogically layered mantle, if it existed, was homogenized by mantle convection after early Archaean times.Constant P2O5/TiO2, Ni/Mg, Co/Mg, Fe/Mg ratios (siderophile/lithophile) and PGE abundances, estimated for the mantle sources of komatiites from Archaean to modern times, strongly argue against continuous growth of the Earth's core since the early Archaean.Extensive crustal contamination might have been involved in the generation of Archaean-early Proterozoic siliceous high magnesian basalts with “boninite affinity”. However, involvement of chemically modified ancient continental lithosphere may also be important in the generation of these basalts. 相似文献
4.
Siderophile and chalcophile element abundances in oceanic basalts, Pb isotope evolution and growth of the Earth''s core 总被引：1，自引：0，他引：1
H.E. Newsom W.M. White K.P. Jochum A.W. Hofmann 《Earth and Planetary Science Letters》1986,80(3-4):299-313
We have investigated the hypothesis that mantle Pb isotope ratios reflect continued extraction of Pb into the Earth's core over geologic time. The Pb, Sr and Nd isotopic compositions, and the abundance of siderophile and chalcophile elements (W, Mo and Pb) and incompatible lithophile elements have been determined for a suite of ocean island and mid-ocean ridge basalt samples. Over the observed range in Pb isotopic compositions for oceanic rocks, we found no systematic variation of siderophile or chalcophile element abundances relative to abundances of similarly incompatible, but lithophile, elements. The high sensitivity of theMo/Pr ratio to segregation of Fe-metal or S-rich metallic liquid (sulfide) and the observed constantMo/Pr ratio rules out the core formation model as an explanation for the Pb paradox. The mantle and crust have the sameMo/Pr and the sameW/Ba ratios, suggesting that these ratios reflect the ratio in the Earth's primitive mantle.
Our data also indicate that thePb/Ce ratio of the mantle is essentially constant, but the presentPb/Ce ratio in the mantle ( 0.036) is too low to represent the primitive value ( 0.1) derived from Pb isotope systematics. HigherPb/Ce ratios in the crust balance the lowPb/Ce of the mantle, and crust and mantle appear to sum to a reasonable terrestrialPb/Ce ratio. The constancy of thePb/Ce ratio in a wide variety of oceanic magma types from diverse mantle reservoirs indicates this ratio is not fractionated by magmatic processes. This suggests crust formation must have involved non-magmatic as well as magmatic processes. Hydrothermal activity at mid-ocean ridges may result in significant non-magmatic transport of Pb from mantle to crust and of U from crust to mantle, producing a higherU/Pb ratio in the mantle than in the total crust. We suggest that the lower crust is highly depleted in U and has unradiogenic Pb isotope ratios which balance the radiogenic Pb of upper crust and upper mantle. The differences between thePb/Ce ratio in sediments, this ratio in primitive mantle, and the observed ratio in oceanic basalts preclude both sediment recycling and mixing of primitive and depleted reservoirs from being important sources of chemical heterogeneities in the mantle. 相似文献
5.
In this study, from the travel time data recorded in the Tianshan passive seismic array experiment, we present the P-wave velocity structure of the upper mantle down to 660 km along the Kuqa-Kuitun pro-file in terms of seismic tomography technique. Based on the P-wave velocity model, we derive the corresponding 2D upper mantle density model. The 2D small-scale convection of the upper mantle underneath the Tianshan Mountains in China driven by the density anomalies is simulated using the hybrid finite element method combining with the marker-in-cell technique. The main features of the upper mantle convection and the reciprocation between the convection and mountain building are in-vestigated. The results manifest that (1) in the upper mantle underneath the Junggar basin and North Tianshan exists a counterclockwise convection, which scale is ~ 500 km; (2) underneath the Tarim ba-sin and South Tianshan exists a clockwise northward convection, which is relatively weak; (3) the convective velocity at the top of the upper mantle underneath the Tianshan Mountains in China should not be less than 20 mm/a, while considering the dependent of convective velocity on the viscosity; (4) the northward extrusion of the Tarim block plays a key role in the Cenozoic Tianshan mountain building and the present-day tectonic deformation of the Tianshan range is related closely to the upper mantle convection; and (5) the northward subduction of the Tarim block does not influence obviously the up-per mantle convection. 相似文献
6.
K. Righter M. J. Drake G. Yaxley 《Physics of the Earth and Planetary Interiors》1997,100(1-4):115-134
We report new metal-silicate partition coefficients for Ni, Co and P at 7.0 GPa (1650–1750°C), and Ni, Co, Mo, W and P at 0.8, 1.0 and 1.5 GPa (1300–1400°C). Guided by thermodynamics, all available metal-silicate partition coefficients, D(i), where i is Ni, Co, P, Mo and W, are regressed against 1/T, P/T, lnf(O2), ln(1 − Xs) (XS is mole fraction of S in metallic liquid) and nbo/t (non-bridging oxygen/tetrahedral cation ratio, a silicate melt compositional-structural parameter) to derive equations of the following form: ln D(i) = aln f(O2) + (b/T) + (cP/T) + d(nbo/t) + eln(1 − XS) + f. Expressions for solid metal-liquid silicate and liquid metal-liquid silicate partition coefficients are derived for S-free and S-bearing systems.
We investigate whether Earth's upper-mantle siderophile element abundances can be reconciled with simple metal-silicate equilibrium. Sulfur-free metallic compositions do not allow a good fit. However, Ni, Co, Mo, W and P abundances in the upper mantle are consistent with simple metal-silicate equilibrium at mantle pressures and temperatures (27 GPa, 2200 K, ΔIW(iron-wüstite) = −0.15, nbo/t = 2.7; XS = 0.15). Although these conditions are near the anhydrous peridotite solidus, they are well above the hydrous solidus and probably closer to the liquidus. A hydrous magma ocean and early mantle are consistent with predicted planetary accretion models. These results suggest that siderophile element abundances in Earth's upper mantle were established by liquid metal-liquid silicate equilibrium near the upper-mantle-lower-mantle boundary. 相似文献
7.
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
8.
The evolution of the Earth is characterized by irreversible processes: radioactive decay of the major heat-producing elements, thermal convection and chemical segregation. The prevailing heating from within and the temperature dependence of the viscosity are essential for thermal convection. In the present paper, the chemical and thermal evolution of the mantle and the generation of the continent material are represented by a two-dimensional and finite-difference Boussinesq convection model. We have incorporated the above-mentioned principal features in this model, a geochemical paper by Hofmann (1988, Earth Planet. Sci. Lett., 90: 297–314) constituting our starting point for the distribution of the radionuclides. The concentration of the radionuclides and the viscosity are functions of the location and time developing according to our system of differential equations. Although the real Earth is a much more complex system, we have dared to make a comparison with observed geophysical and geological data; we obtain a depleted upper mantle and acceptable values for the heat flow on the surface of the Earth as well as for the distribution of temperature, viscosity and of the velocity of creep in the mantle. The ups and downs of the convective vigour of the model roughly resemble the supercontinental cycles, the world-wide distribution of mineral dates in time, the sea-level variations and the variations of a number of geochemical parameters. 相似文献
9.
《Physics of the Earth and Planetary Interiors》2004,141(4):269-279
We investigate the stability of hypothetical layered convection in the mantle and the mechanisms how the downwelling structures originating in the lower layer are generated. The stability is studied by means of numerical simulations of the double-diffusive convection in a 2D spherical model with radially dependent viscosity. We demonstrate that the stability of the layering strongly depends not only on the density contrast between the layers but also on the heating mode and the viscosity profile. In the case of the classical Boussinesq model with an internally heated lower layer, the density contrast of about 4% between the compositionally different materials is needed for the layered flow to be maintained. The inclusion of the adiabatic heating/cooling in the model reduces the temperature contrast between the two layers and, thus, enhances the stability of the layering. In this case, a density contrast of 2-3% is sufficient to preserve the layered convection on a time scale of billions of years. The generation of the downwelling structures in the lower layer occurs via mechanical or thermal coupling scenarios. If the viscosity dependent on depth and average temperature at each depth is considered, the low viscosity zone develops at a boundary between the two convecting layers which suppresses mechanical coupling. Then the downwelling structures originating in the lower layer develop beneath upper layer subductions, thus resembling continuous slab-like structures observed by seismic tomography. 相似文献
10.
11.
假定地幔为一个均匀的、粘滞系数为常数、同时均匀分布放射性热源的流体球层,其内部存在的对流则由流体力学3个基本方程:运动方程、能量方程和连续性方程确定.如果假定地幔处于低瑞利数的状态（临界瑞利数1.5倍左右）,那么上述方程中的非线性项可以忽略不计.作为一类可能的模型,本文计算一组用6个边界条件确定6个未知数的线性方程组.这些条件包括板块绝对运动极型场、地球大地水准面异常和地震层析结果提供的地幔密度分布横向不均匀相应的“刚性地球”水准面异常等.模型计算表明:1.地幔中流体运动格局不仅受地幔热动力学参数（瑞利数）控制,而且强烈地受边界条件的影响.2.若不限定下边界为等温边界,则上、下地幔之间并不呈现出活动性明显差异;但是在模型瑞利数加大到一定值时,核-幔边界附近将出现一些局部的小尺度对流环.3.当模型瑞利数从很小增加时,对流格局将发生变化,这些格局可能反应由地幔热动力学参数决定的地幔固有特性.4.当瑞利数为50000和80000时,核-幔边界形变与PcP波得到的结果吻合较好. 相似文献
12.
We present here a new model of core formation which is based on the current understanding of planetary accretion and discuss its implications for the chemistry of the Earth's mantle and core. Formation of the Earth by hierarchical accretion of progressively larger bodies on a time scale much longer than that of solid body differentiation in the nebula indicates that a significant fraction of metal in the core could be inherited from preterrestrially differentiated planetesimals. An analysis of the segregation of this iron to form the core suggests that most of the metal settles to the core without interaction with silicates; only a small fraction of the metal chemically equilibrates at high temperatures and pressures with the silicates. The siderophile element abundances in the mantle are considered to be a consequence of a two-step equilibration with iron, once preterrestrially in the planetesimals at low temperatures and pressures, and later in the Earth at high temperatures and pressures. The highly siderophile elements such as Re, Au and the platinum group elements in the mantle are essentially excluded from silicates from the preterrestrial equilibration. We attribute the abundances of these elements in the mantle to the later equilibration in the Earth at substantially reduced metal-silicate partition coefficients (Dmet/sil), for which there is a considerable experimental evidence now. Mass balance considerations constrain the fraction of core metal involved in such an equilibration at approximately 0.3 – 0.5%. The model accounts for the levels and the near-chondritic ratios of the highly siderophile elements in the mantle. The mantle abundances of the less siderophile elements are largely determined by preterrestrial metal-silicate equilibrium and are not significantly affected by the second equilibration. The extreme depletion of sulfur and the lack of silicate melt-sulfide signature in the noble metal abundances in the mantle are natural consequences of this mode of core formation. Sulfur was added to the magma ocean during the high-T, high-P equilibration in the Earth, not extracted from it by sulfide segregation to the core. Except for Ni and Co, the overall siderophile abundances of the mantle can be well matched in this two-step equilibration model.
The mantle characteristics of Ni and Co are unique to the Earth and hence suggest a terrestrial process as the likely cause. One such process is the flotation and addition of olivine to the primitive upper mantle. In our model of core formation, neither the elemental and isotopic data of Re---Os, nor the low sulfur content of the mantle remains as an objection to the existence of a magma ocean and olivine flotation.
The small fraction of core metal that equilibrates with silicates at high T and P suggests that the light elements O, Si or H are unimportant in the core, leaving S (and possibly C) as prime candidates. Sulfur, as FeS associated with incoming iron metal, is directly sequestered to the core along with the bulk of the iron metal. It appears unlikely that other light elements can be added to the core after its formation. U and Th are excluded from the core but the model allows for entry of some K; however, the extent to which K serves as a heat source in the core remains uncertain.
The model is testable in two ways. One is by investigation of the metal-silicate partitioning at high temperatures and pressures under magma ocean conditions to determine if the (Dmet/sil) values are lowered to the levels required in the model. The other is by experiments to determine if a solvus closure between metal and silicate liquids occurs at high temperatures relevant to a magma ocean. 相似文献
13.
Rare earth element abundances have been measured in pyroxenitic (19.6% MgO) to gabbroic (7.7% MgO) rocks from the upper part of a thick, layered komatiite lava flow (Fred's Flow) in Munro Township, Ontario. This flow apparently erupted as a highly basic liquid which subsequently differentiated into layers of ultramafic cumulate rocks and a basaltic residual liquid. The analyzed rocks have compositions and spinifex or equigranular textures interpreted to indicate that they represent the complete range of liquids that were present during the differentiation of the lava.All the analyzed rocks are depleted in light REE, and also exhibit a slight depletion of Yb and Er relative to Gd and Dy. Chondrite-normalized Ce and Yb abundances range from 3.2 to 7.8 and 5.1 to 9.7 respectively. Proportions of fractionating minerals were estimated using a major element petrological mixing program and petrographic data. REE modeling based on these results indicates that the dominant process relating the samples is low-pressure fractional crystallization of olivine, followed at lower temperatures by clinopyroxene and plagioclase. Except for Eu, correspondence between observed and calculated REE abundances obviates any need to appeal to processes of major REE redistribution during diagenesis and low-grade metamorphism. Major differences in REE patterns of other ultramafic and mafic komatiitic lava flows [6,11], therefore, probably reflect different episodes of partial melting and/or differences in mantle source composition. The consistency of the REE in the layered flow, however, supports the concept that mafic komatiites can also be derived from ultrabasic parental magmas by low-pressure fractional crystallization. The light-REE-depleted patterns of these komatiites resemble those of modern MORB, suggesting that the mantle source of the komatiites had undergone a previous melting episode. 相似文献
14.
本文利用数值法求解瞬时地幔对流问题以模拟大地水准面异常.利用两个较新的S波速度异常层析模型SEMUCB_WM1和TX2019slab,将其转换为密度异常作为控制方程的浮力驱动项;采取的黏度结构模型中,上下地幔的黏度比为1∶50.为了研究地幔不同结构对罗斯海海域大地水准面异常的影响,分别提取上、下地幔的密度异常正/负值,作为对流控制方程的输入项,计算相应的模拟大地水准面异常.将模拟大地水准面异常与观测值进行对比,发现罗斯海海域的大地水准面异常主要来自下地幔及上地幔的负密度(波速)异常,下地幔正密度异常对该区域大地水准面负异常也有一定的贡献.本文认为,地幔密度负异常在罗斯海海域大地水准面异常的形成中占据主导作用,地幔对流的动力学效应对该区域大地水准面异常的形成影响较弱. 相似文献
15.
Oxygen isotope evidence for the origin of enriched mantle beneath the mid-Atlantic ridge 总被引：1，自引：0，他引：1
Kari M. Cooper John M. Eiler Paul D. Asimow Charles H. Langmuir 《Earth and Planetary Science Letters》2004,220(3-4):297-316
Geochemical variations in mid-ocean ridge basalts have been attributed to differing proportions of compositionally distinct mantle components in their sources, some of which may be recycled crust. Oxygen isotopes are strongly fractionated by near-surface interactions of rocks with the hydrosphere, and thus provide a tracer of near-surface materials that have been recycled into the mantle. We present here oxygen isotope analyses of basaltic glasses from the mid-Atlantic ridge south of and across the Azores platform. Variations in δ18O in these samples are subtle (range of 0.47‰) and may partly reflect shallow fractional crystallization; we present a method to correct for these effects. Relatively high fractionation-corrected δ18O in these samples is associated with geochemical indices of enrichment, including high La/Sm, Ce/Pb, and 87Sr/86Sr and low 143Nd/144Nd. Our results suggest two first-order conclusions about these enriched materials: (1) they are derived (directly or indirectly) from recycled upper oceanic crustal rocks and/or sediments; and (2) these materials are present in the north Atlantic MORB sources in abundances of less than 10% (average 2–5%). Modeling of variations of δ18O with other geochemical variables further indicates that the enriched component is not derived from incorporation of sediment or bulk altered oceanic crust, from metasomatism of the mantle by hydrous or carbonate-rich fluids, or from partial melting of subducted sediment. Instead, the data appear to require a model in which the enriched component is depleted mantle that has been metasomatized by small-degree partial melts of subducted, dehydrated, altered oceanic crust. The age of this partial melting is broadly constrained to 250 Ma. Reconstructed plate motions suggest that the enriched component in the north Atlantic mantle may have originated by subduction along the western margin of Pangea. 相似文献
16.
This study considers two-dimensional mantle flow beneath a rigid lithosphere. The lithosphere which forms the upper boundary of a convecting region moves with a prescribed uniform horizontal velocity, and thickens with distance from the accreting plate boundary as it cools. Beneath the lithosphere, the mantle deforms viscously by diffusion creep and is heated radiogenically from within. Solutions for thermal convection beneath the lithosphere are obtained by finite-difference methods. Two important conclusions have resulted from this study: (1) convective patterns of large aspect ratio are stable beneath a rigid moving lithosphere; (2) even for a lithosphere velocity as small as 3 cm/yr. and a Rayleigh number as large as 106, mantle circulation with large aspect ratio is driven dominantly by the motion of the lithosphere rather than by temperature gradients within the flow. Gravity, topography and heat flow are determined and implications for convection in the upper mantle are discussed. 相似文献
17.
F.H. Busse 《Physics of the Earth and Planetary Interiors》1981,24(4):320-324
Some dynamic implications of separate convection systems in the upper and the lower mantle of the Earth are investigated. It is shown that the horizontal scale of convection cells in the lower mantle is likely to determine the scale of flow in the upper mantle. This does not preclude the nearly independent realization of convection cells with horizontal dimensions comparable to the depth of the upper mantle. 相似文献
18.
D.W. Graham L.M. Larsen B.B. Hanan M. Storey A.K. Pedersen J.E. Lupton 《Earth and Planetary Science Letters》1998,160(3-4):241-255
Picrites from the 61 million year old Vaigat Formation of the Nuussuaq Peninsula in West Greenland have 3He/4He ratios trapped in olivine phenocrysts which range up to 30 times the atmospheric ratio. These high values, measured during gas extraction by crushing in vacuum, are similar to the highest magmatic 3He/4He ratios found in young terrestrial volcanic rocks. By analogy with young basalts, in which crushing selectively extracts magmatic helium, any significant cosmogenic 3He appears to be absent in these picrites. Additional evidence for the absence of cosmogenic helium is provided by fusion results on the crushed olivine powders and by a single stepwise crushing experiment, in which only magmatic and radiogenic helium components are resolvable. The West Greenland picrites have Pb, Nd and Sr isotope compositions which overlap those found in picrites from Iceland and in basalts from Loihi Seamount, localities which today also have high 3He/4He ratios. Isotopic variations in He, Pb, Nd and Sr for the West Greenland picrites are interpreted to largely result from interaction of the early Iceland mantle plume with the upper mantle during plume ascent and dispersion beneath the continental lithosphere. The presence of high 3He/4He ratios in West Greenland, and the onset of magmatism across the North Atlantic Volcanic Province near 62 Ma, supports the hypothesis for very rapid dispersion (>1 m/year) of mantle plume head material during the earliest stages of plume impact, as predicted in recent numerical simulations of plume behavior during thermal mantle convection with non-Newtonian rheology. 相似文献
19.
186Os enrichments in volcanic rocks and peridotite-derived iridosmine grains have been attributed to contributions from Earth’s outer core to the mantle, and apparently constrain the scale of mantle convection and an early timing for inner–outer core segregation more than 3.5 Gyr ago. Here, we highlight that marine ferromanganese crusts and nodules are characterised by high Pt/Os ratios and Pt–Os contents that develop much larger 186Os excesses over geological time (≥0.2%/Gyr) than those hypothesised for Earth’s outer core (<0.005–0.01%/Gyr). 187Os/188Os ratios in ferromanganese crusts are radiogenic due to sequestering of continental Os from seawater. Similarly, ancient ferromanganese materials may have had 186Os excesses (>0.1%) as a result of high Pt/Os ratios in continental crust, even prior to in-growth of 186Os after formation due to their high Pt/Os ratios. Past recycling of small amounts of these materials into the Earth’s mantle will produce coupled 187Os–186Os excesses and little change in Re and platinum-group-element concentrations, as observed in Hawaiian picrites, and in contrast to the predicted result of outer core addition to the mantle. 187Os and 186Os enrichments in the Hawaiian mantle source are potentially consistent with it comprising recycled oceanic lithosphere, pelagic sediments and ferromanganese materials, and questions the notion that Os isotopes can be used to uniquely identify core–mantle interactions and the depth at which mantle sources for volcanism originate. 相似文献
20.
本文分别基于数值结果和地质学模型,在假定地球的上地幔存在稳定Rayleigh-Bénard对流的基础上,模拟了直径为10 km（陨石坑直径约180 km,以Chicxulub为例）和直径为100 km（陨石坑直径约1000 km）的小行星撞击对地球的上地幔对流格局的影响.本文将直径10 km小行星的撞击效果等效为热异常,将直径100 km小行星的撞击效果等效为热异常和速度异常（主要指陨石坑底部的回弹）的叠加.计算结果表明,当小行星的直径在10 km左右时,撞击对上地幔对流的影响十分微弱,热扰动时间仅2—3 Ma;而当小行星的直径达到100 km时,撞击就会对上地幔对流产生强烈影响.这时,对流从扰动到新的稳态有一定模式可循（依次为：调整、多个对流环、调整、稳定）,扰动的持续时间受黏度和撞击点位置影响,同时稳定后地幔热柱会向着撞击点的方向产生一定的位移. 相似文献