Abstract: Tectonic episodicity and convective feedback mechanisms
U. Walzer and R. Hendel. Tectonic episodicity and convective feed-back mechanisms. Phys. Earth Planet. Int., 100:167-188, 1997b.
Tectonic episodicity and convective feedback mechanisms
Uwe Walzer1, Roland Hendel1,
1 Institut für Geowissenschaften, Friedrich-Schiller-Universität, Burgweg 11, 07749 Jena, Germany
Abstract.
The evolution of the Earth is characterized by irreversible processes; radioactive decay of the major heat-producing elements, thermal convection and chemical segregation. The prevailing heat from within and the temperature dependence of the viscosity are essential for thermal convection. In the present paper, the chemical and thermal evolution of the mantle and the generation of the continent material are represented by a two-dimensional and finite-difference Boussinesq convection model. We have introduced the above-mentioned principal features in this model, a geochemical paper by Hofmann (1988, Earth Planet. Sci. Lett., 90: 297-314) constituting our starting point for the distribution of the radionuclides. The concentration of the radionuclides and the viscosity are functions of the location and time developing according to our system of differential equations. Although the real Earth is a much more complex system, we have dared to make a comparison with observed geological data; we obtain a depleted upper mantle and acceptable values for the heat flow on the surface of the Earth as well as for the distribution of temperature, viscosity and of the velocity of creep in the mantle. The ups and downs of the convective vigour of the model roughly resemble the supercontinent cycles, the world-wide distribution of mineral dates in time, the sea-level variations and the variations of a number of geochemical parameters.
Key words: Earth, mantle, convection, mantle convection, evolution, episodicity, tectonic episodicity, heat-producing elements, supercontinent, continent, earth evolution, chemical segregation, chemical differentiation, fractionation, Wilson cycle, sea level, Phanerozoic, Archaic, Proterozoic, viscosity.