Russian Journal of Earth Sciences
Vol 1, No. 2, December 1998
3-D Spherical models for mantle convection, continental
drift, and the formation and disintegration of
supercontinents
V. P. Trubitsyn and V. V. Rykov
Abstract
One of the most important problems of geoscience is to
explain the drift mechanism of continents uniting
periodically to form supercontinents similar to Pangea. This
work presents for the first time a numerical model of mantle
convection in a 3-D spherical mantle with drifting
continents. The mantle is modeled by a viscous fluid
developing thermal convection upon heating. When the
drifting continents are placed into the mantle, they start
drifting under the effect of the forces of viscous coupling
with mantle convection flows. Subject to numerical solution
is the set of mass, heat, and momentum transfer equations
for convection in the viscous mantle and the associated set
of Euler equations for the movement of the solid continents.
The mantle and continents interact with one another
mechanically in the course of heat exchange. In order to
better understand the mantle-continent interaction
processes, we have analyzed two models, one with a single
continent and a weak thermal convection with a Rayleigh
number of 104 and the other with five continents and an
intense thermal convection with a Rayleigh number of 106.
In the case of weak convection, there form in the mantle but
a few ascending and descending flows. The drifting continent
is pulled into one of the descending flows. As the size and
shape of the continent differ from those of the descending
flow zones, its position proves unstable, so that it drifts
constantly. In the absence of other continents and any
external forces, the continent moves along the descending
flow system. At higher Rayleigh numbers, convection becomes
nonstationary, in which case the number, shape, and position
of mantle convection flows vary constantly. What is more, if
there are several continents, the motion of each one of them
becomes bound and more complex. The continents can collide
directly, as well as interact with one another through the
intermediary of the mantle and thus change the structure of
its convection. The numerical experiments performed
demonstrate the possibility of both a partial uniting of
several continents and the formation of a single
supercontinent like Pangea upon the uniting of all the
continents.