黏滞分层地幔中密度异常驱动对流模型的研究
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摘要
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S12WM13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=5500kgm3,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.
A new model is employed to investigate the effects of viscous structures on the convection patterns in the mantle, which is driven by density anomaly and plate motions. We use the seismic tomography models of Grands and S12-WM13 to estimate the density anomaly distributions in the mantle and take the 660 km discontinuity as a boundary between the upper and lower mantle. We take ρ= 5500kg/m~3 as the average density of the mantle and μ=10~(21)Pa·s as the average viscosity of the upper mantle and calculate the convection patterns of the mantle with different viscous rations of 1, 10, 100 and 1000 between the lower and upper mantle, respectively. Computation results show that when the viscous ration between lower and upper mantle is more than 100 the flow speed in the lower mantle decreases obviously. But the convection patterns still exhibit a single cell style and not layered. This feature shows that there is a large-scale convection in the mantle. The relationship between convection patterns and global tectonics is also discussed in this paper.
A new model is employed to investigate the effects of viscous structures on the convection patterns in the mantle, which is driven by density anomaly and plate motions. We use the seismic tomography models of Grands and S12-WM13 to estimate the density anomaly distributions in the mantle and take the 660 km discontinuity as a boundary between the upper and lower mantle. We take ρ= 5500kg/m~3 as the average density of the mantle and μ=10~(21)Pa·s as the average viscosity of the upper mantle and calculate the convection patterns of the mantle with different viscous rations of 1, 10, 100 and 1000 between the lower and upper mantle, respectively. Computation results show that when the viscous ration between lower and upper mantle is more than 100 the flow speed in the lower mantle decreases obviously. But the convection patterns still exhibit a single cell style and not layered. This feature shows that there is a large-scale convection in the mantle. The relationship between convection patterns and global tectonics is also discussed in this paper.
引文
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[2]HagerBH,ClaytonRW,RichardsMA,etal.Lowermantle heterogeneity,dynamictopographyandthegeoid.Nature,1985,313:541～545
[3]CroughST.Hotspotsswells.Annu.Rev.EarthPlanet.Sci.1983,11:165～193
[4]HaxbyWF,WeisselJK.Evidenceforsmall_scalemantle convectionfromSEASATaltimeterdata.J.Geophys.Res.1986,91:3507～3520
[5]傅容珊.地幔热动力学模型.地球物理学进展,1993,8(2):13～26FuRS.Thermodynamicmodelofthemantle.ProgressinGeophysics(inChinese),1993,8(2):13～26
[6]傅容珊,陈 凌,黄建华等.全球地震层析地幔密度横向不均匀及大陆动力学.地球物理学进展,1995,10(3):51～62FuRS,ChenL,HuangJH,etal.Globalseismictomography,mantledensityheterogeneityofmantleandcontinentaldynamics.ProgressinGeophysics(inChinese),1995,10(3):51～62
[7]傅容珊,冷 伟,常筱华.地幔对流与深部物质运移研究的新进展.地球物理学进展,2005,20(1):170～179,FuRS,LengW,ChangXH.Advancementsinthestudyofmantle convectionandthematerialmovementsinthedeepEarthinterior.ProgressinGeophysics(inChinese),2005,20(1):170～179
[8]LoperDE.Asimplemodelofwholemantleconvection.J.Geophys.Res.,1985,90:1809～1836
[9]PeltierWR.Mantleconvectionandviscoelasticity.Ann.Rev.FluidMech.,1985,17:561～608
[10]PeltierWR.Mantleviscosity.In:PeltierWRed.Mantle Convection:PlateTectonicsandGlobalDynamics.NewYork:GordonandBreachSci.Publish,1989.389～475
[11]HagerB,ClaytonRW.Constraintsonthestructureofmantle convectionusingseismicobservations,flowmodels,andthegeoid.In:PeltierWRed.MantleConvection:PlateTectonicsandGlobal Dynamics.NewYork:GordonandBreachSci.Publish,1989.657～763
[12]StaceyFD,FuRS,SpiliopoulosS.Viscositystructureimpliedby mantleconvection.Phys.EarthPlanet.Inter.1989,55:1～9
[13]PariG,PeltierWR.Theheatflowconstraintonmantle tomography_basedconvectionmodels:towardsageodynamicallyself_consistentinferenceofmantleviscosity.J.Geophys.Res.,1995,
100:12731～12751
[14]Cserepes,Laszlo,YuenDA,etal.Effectofthemid_mantle viscosityandphase_transitionstructureon3Dmantleconvection.Phys.EarthPlanet.Inter.2000,118:135～148
[15]BungeHP,RichardsMA,BaumgardnerJR.Asensitivitystudyof three_dimensionalsphericalmantleconvectionat108Rayleigh number:effectsofdepth_dependentviscosity,heatingmode,andan endothermicphasechange.J.Geophy.Res.,1997,102:11991～12007
[16]ZhongSJ,ZuberMT,MoresiL,GurnisM.Roleoftemperature-dependentviscosityandsurfaceplatesinsphericalshellmodelsof mantleconvection.J.Geophys.Res.,2000,105:11063～11082
[17]ShuxiaZ,YuanDA.Theinfluencesoflowermantleviscosity stratificationon3Dspherical_shellmantleconvectionEarth.Planet.Sci.Lett.,1995,132:157～166
[18]叶正仁.地幔对流、大地水准面异常和板块运动.见:现今地球动力学问题讨论会论文集.北京:地震出版社,1994.72～80YeZR.Mantleconvectiongeoidanomalyandplatemotions.In:ProblemsofPresentGeodynamics(inChinese).Beijing:SeismologicalPress,1994.72～80
[19]叶正仁,王 建.上地幔变黏度小尺度对流的数值研究.地球物理学报,2003,46(3):335～339YeZR,WangJ.Anumericalresearchonthesmall_scale convectionwithvariableviscosityintheuppermantle.ChineseJ.Geophys.(inChinese),2003,46(3):335～339
[20]傅容珊,黄建华.刘文忠.利用地球物理观测反演地幔对流模型.地球物理学报,1993,36(3):298～307FuRS,HuangJH,LiuWZ.Inversionofmantleconvectionmodel usingseveralgeophysicaldata.ChineseJ.Geophys.(inChinese),1993,36(3):298～307
[21]王 建,叶正仁.地幔对流对全球岩石圈应力产生与分布的作用.地球物理学报,2005,48(3):584～590WangJ,YeZR.Effectsofmantleflowongenerationand distributionofgloballithosphericstressfield.ChineseJ.Geophys.(inChinese),2005,48(3):584～590
[22]CizkovaH,CadekO,YuenDA,ZhouH.Geoidslopespectrum andconstraintsonmantleviscositystratification.Geophys.Res.Lett.1996,23:3063～3066
[23]KidoM,CadekO.Inferencesofviscosityfromtheoceanicgeoid:Indicationofalowviscosityzonebelowthe660_kmdiscontinuity.EarthPlanet.Sci.Lett.,2003,151:125～137
[24]KidoM,YuenDA,CadekO,NakakukiT.Mantleviscosity derivedbygeneticalgorithmusingoceanicgeoidandseismic tomographyforwhole-mantleversusblocked_flowsituations.Phys.EarthPlanet.Inter.,1998,107:307～326
[25]傅容珊,黄建华,常筱华.地震层析成像之密度异常驱动地幔对流模型.大地测量与地球动力学,2003,23(1):6～11FuRS,HuangJH,ChangXH.Amantleconvectionmodeldrived bydensityanomaliesinmantle.J.GeodesyandGeodynamics,2003,23(1):6～11
[26]GrandSP,vanderHilstRD,WidiyantoroS.Globalseismic tomography:asnapshotofconvectionintheEarth.GSAToday,1997,7:1～7
[27]SuWJ,WoodwardRL,DziwonskiAM.Degree12modelofshear velocityheterogeneityinthemantle.J.Geophys.Res.,1994,99:6945～6980
[28]ChandrasekharV.HydrodynamicandHydromagneticStability.Oxford:ClarendonPress,1961.652
[29]BirchF.Thevelocityofcompressionalwavesinrocksto10kilobars.Part2.J.Geophys.Res.,1961,66:2199～2224
[30]AndersonOL,SchreiberE,LiebermanRC,SogaN.Someelastic constantdataonmineralsrelevanttogeophysics.Rew.Geophys.Space.Phys.,1968,6:491～524
[31]AstersG,JordanTH,SilverPG,GilbertF.Asphericalearth structurefromfundamentalspherical_modedata.Nature,1982,298:609～613
[32]DeMetsC,GordonRG,ArgusDFSteinS.Currentplatemotions.Geophys.J.Int.,1990,101:425～478
[33]GrippAE,GordonRG.Currentvelocitiesrelativetothehotspots incorporatingthenuvel_1globalplatemotionmodel.Geophysical ResearchLetters,1990,17(8):1109～1102
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