Russian Journal of Earth Sciences
Vol. 6, No. 5, October 2004
Evolutionary models of floating continents
V. P. Trubitsyn
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences,
Moscow, Russia
Abstract
Processes lasting for milliseconds to some ten thousand years are described by a
viscoelastic model of the Earth that has been basically developed in the first
half of the 20th century. To describe longer processes, lasting for a few
hundreds of thousands to a few hundreds of millions of years, a mantle
convection model including a highly viscous oceanic lithosphere broken into
plates has been developed in the second half of the 20th century. Each continent
in this model is a part of and moves as a whole with its own rigid oceanic
plate. However, lithospheric oceanic plates are renewed over one hundred million
years, whereas continents drift on the mantle during a few billions of years.
Since strains of continents are much smaller than their displacements,
continents can be considered, in the first approximation, as solid bodies
floating on a convective mantle. Changes in the shape of continents produced by
their deformation, as well as changes in their number associated with breakups
and collisions, can be taken into account at each time step of their movement.
Therefore, global geological processes on time scales of tens of millions of
years to a few billions of years should be described in terms of mantle
convection models with continents floating among oceanic plates. The plates are
temporarily frozen with continents at their passive margins but, on average, in
a hundred million years, the plates become too heavy, break off from the
continents and sink into the mantle. The new model generalizes the theory of
mantle convection and plate tectonics by incorporating the effects of moving
continents and extends the applicability range of the model description to the
time scale of the Earth's geological history. The model is based on the
classical equations of mantle convection complemented with equations of motion
of a system of continents including their thermal and mechanical interaction
with the mantle and between each other. If the modern Earth is taken as an
initial state in the evolution of mantle flows with floating continents, the
initial temperature distribution can be found from tomography data with the use
of the temperature dependence of seismic velocities. The initial position and
shape of continents can be taken from geographic maps. These data are sufficient
in order to calculate from the equations the evolution of mantle flows and
global heat flux distribution and motions of continents. Because an average
description is only available as yet and several parameters of the mantle and
continents are known inaccurately, results of such modeling should be regarded
as preliminary, showing a basic possibility of calculating the history and the
future evolution of continents and islands.