Understanding Circum-Pacific tectonics:
Numerical subduction modelling of variable density plates
Supervision: Saskia Goes (Imperial College)
Background: The main driving force for plate tectonics is provided by cold and dense
plates that subduct into the mantle, for example along the Pacific “Ring of Fire”.
Subduction zones control the formation of mountain chains like the Andes and new
ocean basins like the Philippine Sea and have shaped the Earth’s surface through
geologic time. They are also the site of the largest earthquakes and tsunamis, like the
2011 Tohoku event. Understanding the balance of forces that determine the observed
variability in subduction style through space and time is therefor crucial, but this has
been a challenging problem.
Rationale: The subduction balance of forces is a delicate one, and plates change their
motions and shape in response to variations in density and strength of the two
converging plates, as well to viscous resistance of the surrounding mantle. Only
recently have models been developed which are able to solve this dynamic interplay,
including by our group [e.g., Bellahsen et al., 2005; Capitanio et al., 2007; Morra et al.,
2006; Stegman et al., 2006]. The first set of models, where plates are treated as constant
density and strength bodies, have already yielded a wealth of new insights, for example
into why some subduction episodes have been very fast and what governs sea-ward
(basin-forming) or landward (collisional) plate boundary motions [Capitanio et al.,
2010; Goes et al., 2008; Schellart et al., 2007].
This project: Subducting plates are however not constant in density or strength, due to
lateral variations of plate age and the presence of submarine ridges or plateaus. Aim of
this project is to extend the previous models to a systematic investigation of the effect
of lateral variations in subducting plate strength and density on subduction motions and
geometry. The project makes use of a novel 3-D coupled solid-fluid (FEM/BEM)
subduction code that was developed in a previous project. The results will be compared
with the variable subduction behaviour found around the Pacific.
Figure 1. Example subduction model of a plate containing a buoyant ridge. The ridge hampers
subduction of the right-hand side of the plate. Colours represent stresses inside the slab, red for
high and blue for low stress (Fourel et al., in preparation, 2013).
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Our Team: The work would be supervised by Saskia Goes, who has studied subduction
numerically and observationally for over 20 years. The student would join the Imperial
Plates & Mantle group consisting of 5 academic staff, 9 other PhD students and 2
postdocs, working on shallow and deep geophysical imaging, geochemistry and mantle
dynamics. We will also closely collaborate with Dr. Loic Fourel, at IPG Paris, and Dr.
Gabriele Morra, University of Louisiana, who built the model, and Prof. Richard
Craster in Mathematics who has expertise in plate bending for various rheologies. In
addition, the student would become part of our multi-institutional subduction initiative,
which involves besides Imperial, also the Universities of Durham and Cardiff, and ANU
in Australia.
Student Profile We are seeking a highly motivated individual with a background in
geophysics, physics, or geology with a strong quantitative foundation. The successful
candidate will be able to work independently, and have a keen interest to do
interdisciplinary work on the dynamics of the deep Earth. Previous experience with
numerical (fluid dynamic and/or solid-mechanic) modelling is highly desirable.
Application information can be found on the departmental web site. For more
information on this project please contact Saskia Goes ([email protected]).
References and further reading
Bellahsen, N., C. Faccenna, and F. Funiciello (2005), Dynamics of subduction and plate
motion in laboratory experiments: Insights into the ‘‘plate tectonics’’ behavior of the
Earth, J. Geophys. Res., 110(B1), 1-15.
Capitanio, F. A., G. Morra, and S. Goes (2007), Dynamic models of downgoing plate
buoyancy driven subduction: subduction motions and energy dissipation, Earth
Planet. Sci. Lett., 262, 284-297.
Capitanio, F. A., G. Morra, S. Goes, R. F. Weinberg, and L. Moresi (2010), India-Asia
convergence driven by the subduction of the Greater Indian continent, Nature
Geosci., 3(2), 136-139.
Goes, S., F. A. Capitanio, and G. Morra (2008), Evidence for lower mantle slab
penetration phases in plate motions, Nature, 451, 981-984.
Morra, G., K. Regenauer-Lieb, and D. Giardini (2006), On the curvature of oceanic
arcs, Geology, 34, 877-880.
Schellart, W. P., J. Freeman, D. R. Stegman, L. Moresi, and D. May (2007), Evolution
and diversity of subduction zones controlled by slab width, Nature, 446, 308-311.
Stegman, D. R., J. Freeman, W. P. Schellart, L. Moresi, and D. May (2006), Influence
of trench width on subduction hinge retreat rates in 3-D models of slab rollback,
Geochem. Geophys. Geosys., 7, Q03012, doi03010.01029/02005GC001056.
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