Global modelling of the lithosphere and mantle and explaning geoid signal by merging of tomography derived mantle flow models with full thermal convection models including lateral viscosity variations

Joint project of

  • GeoForschungsZentrum Potsdam (GFZ): Dr. M.K. Kaban (principal investigator) and Dr. A. Petrunin
  • J. W. Goethe University, Frankfurt/M: Prof. H. Schmeling (principal investigator) and M. Shahraki

Duration: January 2007 – December 2012

Summary

We continue the development of a new-generation global dynamic model of the crust and mantle, which is based on an integrative analysis of the gravity, GPS and other geophysical data. Based on the results obtained during the previous stages we focus on the following aspects.

  1. Development of an integrative model of the lithosphere (including a rheological model).
  2. Modelling of the effect of lateral viscosity variations in the mantle on the global geoid and surface plate velocities.

The new “satellite-based” gravity models form a basis for this study. Most global inversions of geoid signals use tomographic data to model an instantaneous mantle flow field (snap shot) and invert for radial viscosity variations. Now, such data will be incorporated into a fully 3D spherical thermal convection code with temperature, pressure and stress dependent rheology, to consistently include heat advection and conduction, i.e. thermal boundary layers of the earth, and investigate the 3D effect of rheology on the geoid.

Main results and perspectives

A key characteristic of this study is that we try to combine nearly all geophysical fields and methods in a joint analysis with the observed gravity and geoid to produce an integrated global dynamic model of the Earth. Several methods and data-sets have been employed before in separate studies. However, it was always unclear how the non-considered parameters might affect the final result. In the present study we integrate these features in one self-consistent model and extend it to a full mantle convection model.

During the first stage of the project several principal problems have been solved.

  1. A new integrative global model of the lithosphere has been constructed. Different to all previous models the present one combines main physical parameters, which are consistently determined using unified data sets and modelling techniques. This model includes position of the main lithospheric boundaries and physical properties of the main layers (primarily seismic velocities, density and temperature).
  2. Using these results, we have determined the gravity field component induced by thermal and compositional variations in the upper mantle. After removing of the effect of the isostatically compensated lithosphere from the observed geoid, the residual field chiefly reflects the effect of deep mantle structure and dynamics. This residual geoid is used as the principal constraint in global dynamic modelling.
  3. We continue development of a new generation global dynamic model of the mantle. Several principal steps have been made in this direction:
  • A new global dynamic model (instantaneous) includes for the first time a comprehensive effect of the transition zone boundaries (410 and 660).
  • A fast and precise method for modelling of lateral viscosity variations in a convecting mantle has been further developed.
  • A new parameterization formulation of the Arrhenius type of viscosity law has been formulated to be applied to variable viscosity convection models

In the 3d stage of the project we are going to complete two interrelated principal tasks developed during the previous stages. First, we are going to complete a global rheological model of the lithosphere. Second, it should be completed a new generation 3D dynamic model of the mantle, which includes all principal features of the Earth structure and fits to the observed fields (primarily to the observed gravity field, geoid, plate velocities, and total heat flow).

We continue the development of a new-generation global dynamic model of the crust and mantle, which is based on an integrative analysis of the gravity, GPS and other geophysical data. Based on the results obtained during the previous stages we focus on the following aspects.

  1. Development of an integrative model of the lithosphere (including a rheological model).
  2. Modelling of the effect of lateral viscosity variations in the mantle on the global geoid and surface plate velocities.