The Transition Zone SlabsPurgatory - CIDER过渡区板炼狱-苹果酒

TheTransitionZone:

Slabs’PurgatoryCIDER,2006-GroupAGarrettLeahy,VedLekic,UrskaManners,ChristineReif,JoostvanSummeren,Tai-LinTseng,MagaliBillen,Wang-PingChen,AdamDziewonskiTongaSeismicityPredictedSlabPositionsDegree45and24sphericalharmonicexpansionsoflocationsofslabsbasedonplatehistoryreconstructionsassumingnostagnationintransitionzone.TomographicModelsHarvardBerkeleyPreliminaryConclusionsTomographyrevealslargerfastregionsinthewesternPacifictransitionzone.Deepearthquakestressaxesshowevidenceofresistancetocrossingthe660kmdiscontinuity.Structurebelowandabove660kmdiscontinuityhasdifferentspectralcharacter.Implication:slabsstagnateinthetransitionzoneforsomelengthoftime.ASimpleForceBalanceforslabsintheTransitionZoneFb=∫

gdxdz

xzConstraintsonDrandClapeyronslopesDensitycontrastsSeismicconstraintsLabexperimentsonmantleminerals/rocksLatticedynamicssimulationClapeyronslopesLabexperimentsonphasetransformationCalorimatricCalculationsSummaryPhaseTransitionData

SeismicConstrainsCalculations(Pyrolite)Simulations(MgSiO3)Dr4105%to6%About3%

Dr6607%to9%6%to7%About8%

LabExperimentsCalorimatricCalculationdP/dT410(Mpa/K)a

to

b2.5to4dP/dT660(Mpa/K)g

toMw+Pv–3to–1About-3dP/dT660(Mpa/K)Pyrolite-0.5

DensityContrastClapeyronSlopeForClapeyronSlopeofOlivinePolymorphs:Duffy,T.,SynchrotronfacilitiesandthestudyoftheEarth'sdeepinterior.Rep.Prog.Phys.68(2005)1811-1859.SlabThermalAnomalyGaussianCross-slabProfileExponentialDecreaseInPeakAnomalyMax.SlabDepth:1000kmMax.SlabDepth:500kmPhaseTransitionAnomalyTemperatureAnomalyTransitionHeight(km)410:

=3.0MPa/K

=3-6%660:

=-1.3MPa/K

=7-9%410:=

4.0MPa/K

=4%660:

=-2MPa/K

=3%EffectofDiponSumofThermalAndPhaseChangeForces010---Dip(degrees)--8090TotalForce(x1012N/m)1612840EffectofDensityChangeatPhaseBoundariesChangeinDensityat660(%)ChangeinDensityat410(%)66.577.588.5965.43EffectofClapeyronSlopeClapeyronSlopeat660Mpa/KClapeyronSlopeat410Mpa/K-3-2-1-0.55432.5EffectofShearForcesMajorslowingoccursuponenteringlowermantleLowermantleviscositygreaterthan1022PascanstronglyhinderSlab.

um=1019Pas

tran=1020PasMetastableOlivineGrowthRate:

G(T)=A*k*T*exp[-H/(RT)](1-exp[

G/(RT)]) k=exp(10)Growthconstant A=1e-3 Extrapolationparameterfor lowTinslab.DepthofMetastableOlivineinSlab

z~v*ln(1-f)/(-2*S*G) v Slabvelocity S=1/d GrainboundarySurfaceArea/Volume f=0.95Volumefractionofwadsleyiteat completionoftransformation.CoolerTemperaturestronglyinhibitstransformation.WhataboutaMetastableOlivineWedge?ConclusionsBuoyancyfromtemperaturecanbeorderofmagnitudelargerthanotherforces.Needdynamicmodeloftemperature.Extrabuoyancyfrom410phasechangemaybemuchlargerthanresistingbuoyancyfrom660.Shearforcesbeneath660maysignificantlyhinderslabsinkingintolowermantle.Ifphaseparametersat410and660arecomparable,thenamo