Abstract: Generation of Plate-Tectonic Behavior and a New Viscosity Profile of the Earth's Mantle
U. Walzer, R. Hendel, and J. Baumgardner. Generation of plate-tectonic behavior and a new viscosity profile of the Earth's mantle. In D. Wolf, G. Münster, and M. Kremer, editors, NIC Symposium, volume 20 in NIC Series, pages 419-428, Jülich, 2003b.
Generation of Plate-Tectonic Behavior and a New Viscosity Profile of the Earth's Mantle
Uwe Walzer1, Roland Hendel1, John Baumgardner2
1 Institut für Geowissenschaften, Friedrich-Schiller-Universität, Burgweg 11, 07749 Jena, Germany
2 Los Alamos National Laboratory, MS B216 T-3, Los Alamos, NM 87545, USA
Abstract. This paper reports a series of compressible spherical-shell convection calculations with a new viscosity profile, called eta3 , that is derived from PREM and mineral physics. The viscosity profile displays not only a high-viscosity lithosphere and a viscosity hill in the central region of the lower mantle of the Earth but also a prominent high-viscosity transition layer inferred to arise from a high garnet content. Moreover, there is not only the usual asthenosphere but also a second low-viscosity zone just below the 660-km discontinuity. We introduced a viscoplastic yield stress and obtained plate-like movements near the surface. A variation of the parameters revealed a Rayleigh-number-yield-stress area where the plate-tectonic character of the solution is stable and pronounced. Runs with eta3 but without any yield stress show networks of reticularly connected very thin sheet-like downwellings but, of course, no plates. For calculations with eta3 plus yield stress, the distributions of the downwellings are more Earth-like.
The newly derived viscosity profile (Fig. 2) shows a certain similarity with the frequency distribution of earthquakes as a function of depth (Fig. 3). For the results regarding plate tectonics see Walzer et al. (2004a)pdf, 29 mb · en.
Key words: Earth, mantle, convection, mantle convection, spherical shell, viscosity, viscosity profile, transition layer, lower mantle, downwelling, downwelling slab, lithospheric plates, plate tectonics, Rayleigh number, Urey number, orogenetic activity, Karato, PREM.