Russian Journal of Earth Sciences
Vol. 6, No. 1, February 2004
Numerical analysis of geodynamic evolution of the Earth based on
a
thermochemical model of the mantle convection
L. I. Lobkovsky and V. D. Kotelkin
Abstract
Full-scale numerical modeling of the geodynamic evolution of the Earth
throughout its existence is performed in terms of the thermochemical model of
mantle convection proposed by the authors. Numerical modelling results are
visualized in color and their detailed videorecord is presented. The global
geodynamic process is clearly characterized by the presence of cycles of
different lengths. Hydrodynamic pulsations associated with reorganizations of
convective cells in the upper mantle correlate well with the geological cycles
of Stille (~30 Myr). Moreover, the numerical experiments have shown that large
avalanche-like flows of substance from the upper mantle into the lower mantle
through their endothermic interface took place during the geodynamic evolution
of the Earth; these impulsive downward flows significantly differ both
quantitatively and qualitatively. In particular, impulsive flows of upper mantle
substance into the lower mantle on a continental or regional scale (the so-called
avalanches), also observable in our model, correspond in our
interpretation to the geological cycles of Bertrand (~170 Myr). In addition,
numerical experiments revealed the presence of basically new impulsive flows of
upper mantle substance into the lower mantle on a planetary (global) scale that
are referred to as overturns; about half of the upper mantle material is
replaced by the material of the lower mantle over a relatively short time of the
development of such an overturn. In our interpretation, the mantle overturns
correlate with the Wilson cycles (700-900 Myr), which is evidence of their
geodynamic nature and accounts for such major geological events as periodic
assemblages and breakups of continent, the asymmetric structure of the Earth,
and others. As the mantle cools during the evolution of the Earth, mantle
overturns gradually attenuate and degenerate into mantle avalanches.