Tomographic filtering of high‐resolution mantle circulation models: Can seismic heterogeneity be explained by temperature alone?

[1] High-resolution mantle circulation models (MCMs) together with thermodynamic mineralogical models make it possible to construct 3-D elastic mantle heterogeneity based on geodynamic considerations. Recently, we have shown that in the presence of a strong thermal gradient across D 00 and corresponding large temperature variations in the lower mantle, the heterogeneity predicted from isochemical whole mantle flow agrees well with tomographic models in terms of magnitudes of S wave velocity (vs) variations. Here, we extend the comparison of geodynamic and tomographic structures by accounting explicitly for the limited resolving power of tomography. We focus on lateral variations in vs and use the resolution operator R associated with S20RTS to modify our geodynamic models so that they reflect the long-wavelength (>1000 km) nature and the effects of heterogeneous data coverage and damping inherent to the tomographic inversion. Prior to the multiplication with R, the geodynamic models need to be reparameterized onto the basis of S20RTS. The magnitude reduction introduced by this reparameterization is significant and needs careful assessment. We attempt a correction of the reparameterization effects and find that the inherent tomographic filtering alone then leads to a magnitude reduction by a factor of � 2 in the lower mantle. Our tomographically filtered models with strong core heating agree well with S20RTS, which resolves maximum negative anomalies of around � 1.5% in the lowermost mantle. Temperature variations on the order of +1000 K, corresponding to perturbations of around � 3% in vs in the unfiltered model, would be seen as � 1.5% when ‘‘imaged’’ with the data and damping of S20RTS. This supports our earlier finding that isochemical whole mantle flow with strong core heating and a pyrolite composition can be reconciled with tomography. In particular, the large lateral temperature variations associated with lower mantle plumes are able to account for the slow seismic anomalies in the large low-velocity zones under Africa and the Pacific. We also find that strong gradients in shear wave velocity of 2.25% per 50 km in our unfiltered models compare well with the sharp sides of the African superplume. Components: 5494 words, 7 figures.

[1]  Walter H. F. Smith,et al.  Free software helps map and display data , 1991 .

[2]  J. Trampert,et al.  Chemical versus thermal heterogeneity in the lower mantle: The most likely role of anelasticity , 2007 .

[3]  A. Dziewoński,et al.  Anisotropic shear‐wave velocity structure of the Earth's mantle: A global model , 2008 .

[4]  Anticorrelated Seismic Velocity Anomalies from Post-Perovskite in the Lowermost Mantle , 2008, Science.

[5]  Hans-Peter Bunge,et al.  Low plume excess temperature and high core heat flux inferred from non-adiabatic geotherms in internally heated mantle circulation models , 2005 .

[6]  G. Steinle‐Neumann,et al.  Thermal versus elastic heterogeneity in high‐resolution mantle circulation models with pyrolite composition: High plume excess temperatures in the lowermost mantle , 2009 .

[7]  Geoffrey D. Price,et al.  The influence of potassium on core and geodynamo evolution , 2003 .

[8]  Barbara Romanowicz,et al.  Global mantle shear velocity model developed using nonlinear asymptotic coupling theory , 1996 .

[9]  J. Tromp,et al.  Theoretical Global Seismology , 1998 .

[10]  C. R. Hagelberg,et al.  Mantle circulation models with variational data assimilation: inferring past mantle flow and structure from plate motion histories and seismic tomography , 2001 .

[11]  Mark A. Richards,et al.  Effect of depth-dependent viscosity on the planform of mantle convection , 1996, Nature.

[12]  B. Kennett,et al.  Joint seismic tomography for bulk sound and shear wave speed in the Earth's mantle , 1998 .

[13]  H. Bunge,et al.  Tomographic images of a mantle circulation model , 2001 .

[14]  D. Weidner,et al.  (ϖμ/ϖT)P of the lower mantle , 1996 .

[15]  Barbara Romanowicz,et al.  Comparison of global waveform inversions with and without considering cross-branch modal coupling , 1995 .

[16]  R. Hilst,et al.  Compositional heterogeneity in the bottom 1000 kilometers of Earth's mantle: toward a hybrid convection model , 1999, Science.

[17]  L. Wen,et al.  Seismic evidence for a thermo-chemical boundary at the base of the Earth’s mantle , 2001 .

[18]  T. Becker,et al.  Predicting plate velocities with mantle circulation models , 2001 .

[19]  Andreas Fichtner,et al.  The adjoint method in seismology—: II. Applications: traveltimes and sensitivity functionals , 2006 .

[20]  P. Shearer,et al.  Shear and compressional velocity models of the mantle from cluster analysis of long‐period waveforms , 2008 .

[21]  S. Goes,et al.  Synthetic seismic signature of thermal mantle plumes , 2004 .

[22]  M. J. Gillan,et al.  Iron under Earth’s core conditions: Liquid-state thermodynamics and high-pressure melting curve from ab initio calculations , 2001, cond-mat/0107307.

[23]  Hans-Peter Bunge,et al.  Cluster Design in the Earth Sciences Tethys , 2006, HPCC.

[24]  Lars Stixrude,et al.  Thermodynamics of mantle minerals - II. Phase equilibria , 2011 .

[25]  L. Wen,et al.  Mapping the geometry and geographic distribution of a very low velocity province at the base of the Earth's mantle , 2004 .

[26]  Shijie Zhong,et al.  Thermochemical structures beneath Africa and the Pacific Ocean , 2005, Nature.

[27]  Andreas Fichtner,et al.  The adjoint method in seismology: I. Theory , 2006 .

[28]  P. Ma,et al.  Seismostratigraphy and Thermal Structure of Earth's Core-Mantle Boundary Region , 2007, Science.

[29]  J. Ritsema,et al.  Constraints on the correlation of P- and S-wave velocity heterogeneity in the mantle from P, PP, PPP and PKPab traveltimes , 2002 .

[30]  R. Holme,et al.  Mantle flow models with core‐mantle boundary constraints and chemical heterogeneities in the lowermost mantle , 2008 .

[31]  Gabi Laske,et al.  The Relative Behavior of Shear Velocity, Bulk Sound Speed, and Compressional Velocity in the Mantle: Implications for Chemical and Thermal Structure , 2013 .

[32]  Mark A. Richards,et al.  The origin of large scale structure in mantle convection: Effects of plate motions and viscosity stratification , 1996 .

[33]  T. Jordan,et al.  Comparisons Between Seismic Earth Structures and Mantle Flow Models Based on Radial Correlation Functions , 1993, Science.

[34]  Hans-Peter Bunge,et al.  A mineralogical model for density and elasticity of the Earth's mantle , 2007 .

[35]  B. Buffett.  Estimates of heat flow in the deep mantle based on the power requirements for the geodynamo , 2002 .

[36]  M. Richards,et al.  Large-scale mantle convection and the history of subduction , 1992, Nature.

[37]  L. Stixrude,et al.  Influence of phase transformations on lateral heterogeneity and dynamics in Earth's mantle , 2007 .

[38]  D. Helmberger,et al.  Evidence for strong shear velocity reductions and velocity gradients in the lower mantle beneath Africa , 1998 .

[39]  Y. Ohishi,et al.  Determination of post-perovskite phase transition boundary up to 4400 K and implications for thermal structure in D″ layer , 2009 .

[40]  Peter E. van Keken,et al.  Development of anisotropic structure in the Earth's lower mantle by solid-state convection , 2002, Nature.

[41]  Mark A. Richards,et al.  A sensitivity study of three-dimensional spherical mantle convection at 108 Rayleigh number: Effects of depth-dependent viscosity, heating mode, and an endothermic phase change , 1997 .

[42]  C. Conrad,et al.  How Mantle Slabs Drive Plate Tectonics , 2002, Science.

[43]  E. R. Engdahl,et al.  Evidence for deep mantle circulation from global tomography , 1997, Nature.

[44]  S. Zhong,et al.  The influence of thermochemical convection on the fixity of mantle plumes , 2004 .

[45]  H. Samuel,et al.  Beyond the thermal plume paradigm , 2005 .

[46]  N. Simmons,et al.  Thermochemical structure and dynamics of the African superplume , 2007 .

[47]  Paul H. Roberts,et al.  A three-dimensional self-consistent computer simulation of a geomagnetic field reversal , 1995, Nature.

[48]  B. Romanowicz,et al.  A Three-Dimensional Radially-Anisotropic Model of Shear Velocity in the Whole Mantle , 2006 .

[49]  M. Gillan,et al.  Gross thermodynamics of two-component core convection , 2004 .

[50]  D. L. Anderson,et al.  Preliminary reference earth model , 1981 .

[51]  F. A. Dahlen,et al.  Resolution limit of traveltime tomography , 2004 .

[52]  John Hernlund,et al.  On the statistical distribution of seismic velocities in Earth's deep mantle , 2008 .

[53]  D. Helmberger,et al.  Sharp Sides to the African Superplume , 2002, Science.

[54]  R. Boehler.  High‐pressure experiments and the phase diagram of lower mantle and core materials , 2000 .

[55]  M. Richards,et al.  The dynamics of Cenozoic and Mesozoic plate motions , 1998 .

[56]  Wei-jia Su,et al.  Degree 12 model of shear velocity heterogeneity in the mantle , 1994 .

[57]  H. Bunge,et al.  Seismically ”Fast” Geodynamic Mantle Models , 2001 .

[58]  Wei-jia Su,et al.  Simultaneous inversion for 3-D variations in shear and bulk velocity in the mantle , 1997 .

[59]  J. Tromp,et al.  Even‐degree lateral variations in the Earth's mantle constrained by free oscillations and the free‐air gravity anomaly , 2001 .

[60]  McSween Hy,et al.  Evidence for Life in a Martian Meteorite , 1997 .

[61]  Jeroen Ritsema,et al.  Tomographic filtering of geodynamic models: Implications for model interpretation and large‐scale mantle structure , 2007 .

[62]  H. Bunge,et al.  Heterogeneity and time dependence in 3D spherical mantle convection models with continental drift , 2005 .

[63]  W. DeGrado,et al.  Seismostratigraphy and Thermal Structure of Earth ’ s Core-Mantle Boundary Region , 2007 .

[64]  J. Woodhouse,et al.  Evidence for proportionality of P and S heterogeneity in the lower mantle , 1995 .

[65]  D. L. Anderson.  Hotspots, polar wander, Mesozoic convection and the geoid , 1982, Nature.

[66]  Guust Nolet,et al.  A catalogue of deep mantle plumes: New results from finite‐frequency tomography , 2006 .

[67]  Guust Nolet,et al.  Two-stage subduction history under North America inferred from multiple-frequency tomography , 2008 .

[68]  R. Cohen,et al.  Elasticity of iron at the temperature of the Earth's inner core , 2001, Nature.

[69]  G. Nolet,et al.  Measuring finite‐frequency body‐wave amplitudes and traveltimes , 2006 .

[70]  Barbara Romanowicz,et al.  Imaging 3‐D spherical convection models: What can seismic tomography tell us about mantle dynamics? , 1997 .

[71]  Lars Stixrude,et al.  Thermodynamics of mantle minerals – I. Physical properties , 2005 .

[72]  Richards,et al.  Time scales and heterogeneous structure in geodynamic earth models , 1998, Science.

[73]  M. Gillan,et al.  Temperature and composition of the Earth's core , 2007 .

[74]  M. Richards,et al.  Mantle–circulation models with sequential data assimilation: inferring present–day mantle structure from plate–motion histories , 2002, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[75]  Hendrik Jan van Heijst,et al.  Global transition zone tomography , 2004 .

[76]  Bradford H. Hager,et al.  Large‐scale heterogeneities in the lower mantle , 1977 .

[77]  Jeremy Bloxham,et al.  An Earth-like numerical dynamo model , 1997, Nature.

[78]  G. Nolet,et al.  Plume fluxes from seismic tomography , 2006 .

[79]  Joseph S. Resovsky,et al.  Probabilistic Tomography Maps Chemical Heterogeneities Throughout the Lower Mantle , 2004, Science.