Earth, Planets and Space, 56(11), 1019-1033, 2004
Influence of two major phase transitions on mantle convection
with moving and subducting plates
Masaki Yoshida
Abstract
A series of numerical simulation has been carried out to explore the influence
of two major phase transitions
at 410 km and 660 km phase boundaries on mantle convection with self-consistently
moving and subducting plates, that is, on the ``plate-like regime''
of mantle convection. The degree of Clausius-Clapeyron slope at the
660 km phase boundary is systematically changed within the range estimated
by high pressure experiments.
On the plate-like regime where moving plates continuously subduct,
as the Clausius-Clapeyron slope is steepened,
the upwelling plumes originating from the bottom thermal boundary layer
are less buoyant owing to the increase
of average mantle temperature, so that the upwelling plumes
are hard to penetrate through the 660 km phase boundary.
Investigations reveal that three types of small upwelling plumes
in the upper mantle are found on the plate-like regime:
(1) The secondary plumes directly derived from the upwelling plumes from the lower mantle,
(2) the passive upwellings from the shallow parts of the lower mantle due to the diffused
return flow by continuously subducting plates, and
(3) the secondary plumes originating from the 660 km phase boundary
caused by the development of the small-scale convection cells confined in the upper mantle.