2013 Annual Report - Jesus College - University of Cambridge

EARTH SCIENCES I Jesus College Annual Report 2013 29
Figure A
This deformation of rock is very much a
multi-scale problem: the mechanisms by
which plates deform, the mantle convects,
and melt migrates on length scales of
hundreds to thousands of kilometres are
defined by material properties and
deformation processes on a sub-millimetre
grain length scale. Combining these length
scales obviously poses great challenges for
numerical models. The only way to tackle
these challenges is with a concerted
interdisciplinary effort across the fields of
software engineering, numerical analysis,
mathematics, and geodynamics.
Within such a collaboration, I am
investigating with numerical models how
fluid magma interacts with its more
solid surroundings while undergoing
deformation.
In more detail, the models consist of a
high-viscosity porous matrix that can convect
as well as compact, and a lower-viscosity
fluid that fills the pores and convects along
with the matrix. When this two-phase
material is put under shear stress, narrow
lenses with higher porosity (i.e. more melt)
called shear bands develop. This shear
banding is a potential mechanism for melt
transport on a larger scale, and has been
observed in laboratory experiments (Figure
B). Comparisons between numerical models
and such laboratory experiments can help us
pin down details in material properties and
deformation mechanisms that are required to
create the observed shear band amplitudes,
periodicity, and angle.
Hopefully these models will give us clues
as to how small-scale deformation processes
can provide mechanisms for larger-scale melt
transport in subduction zones, and therefore
how the Earth’s mantle is coupled to its
surface. Understanding the coupling
between mantle convection and plate
tectonics would be a significant step towards
comprehending the origin and evolution of
tectonic deformation, the evolution of the
mantle, and ultimately the evolution of the
Earth as a whole.
Figure B