HR: 13:55h
AN: V32E-02 INVITED     [PDF]
TI: Joint Modelling of Seismic, Geodynamic and Mineral Physics Data: Implications for the Origin of 3-D Density and Seismic Velocity Anomalies in the Mantle.
AU: * Forte, A M
EM: forte.alessandro@uqam.ca
AF: GEOTOP, Universit\'e de Qu\'ebec \`a Montr\'eal, D\'epartement des Sciences de la Terre, C.P. 8888, Succ. Centre-Ville, Montr\'eal, QC H3C 3P8 Canada
AU: Mitrovica, J X
EM: jxm@physics.utoronto.ca
AF: University of Toronto, Department of Physics, 60 St George Street, Toronto, ON M5S 1A7 Canada
AU: Grand, S P
EM: steveg@maestro.geo.utexas.edu
AF: University of Texas, Department of Geological Sciences, Austin, TX 78712 United States
AB: Models of instantaneous (present-day) mantle dynamics provide strong constraints on the distribution and amplitude of 3-D density anomalies. In recent work [Forte, Mitrovica \& Espesset, Phil. Trans., 2002], we developed models of 3-D mantle flow based on high-resolution tomographic models of global seismic shear velocity heterogeneity [e.g., Grand, Phil. Trans., 2002] which reconcile a wide variety of surface manifestations of mantle convection which include global gravity anomalies, plate tectonic motions, dynamic surface topography and the dynamic ellipticity of the core-mantle boundary. These diverse geodynamic observables provide direct constraints on the mantle density anomalies which are the driving force of the convective flow field. These density anomalies may be inferred by carrying out joint inversions of the geodynamic data sets, in which we assume a correlation between mantle density anomalies and the seismic velocity anomalies in a given tomography model. Neither the sign of the correlation (which may be positive or negative), nor the amplitude of the density anomalies is constrained to a-priori values in these inversions but are instead allowed to vary in order to provide optimal fits to the surface geodynamic data sets. The relationship between the geodynamically inferred density anomalies and seismic anomalies, when taken in conjunction with the separate mineral physical constraints on thermal and compositional derivatives [e.g., Karato, 1993; Wang \& Weidner, 1996; Stacey, 1998], provide direct insights on the relative importance of thermal and chemical contributions to mantle heterogeneity [e.g., Forte \& Mitrovica, Nature, 2001]. We will present the results of new density inversions employing mantle flow models based on the most recent mantle viscosity profiles derived by jointly inverting an updated and enlarged set of glacial isostatic adjustment data and mantle convection data sets [Mitrovica \& Forte, 2003]. We have also devised a new and independent test of the origin of mantle heterogeneity by carrying out joint global inversions of seismic and geodynamic data [Grand \& Forte, this meeting] assuming different scalings between density and seismic velocity which may be derived from mineral physics data. These hypothesis tests, as well as the direct inversions for mantle density, show a simple positive correlation between seismic shear velocity and density which is in accord with a dominant thermal origin for this heterogeneity.
DE: 3900 MINERAL PHYSICS
DE: 8105 Continental margins and sedimentary basins
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8180 Tomography
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting