Professor, Physics and Geology Departments, University of
Physical processes and geodynamics of the deep crust;
B.Sc., Dalhousie (1965); Ph.D., Cambridge (1970).
Postdoctoral, Leicester (1971-72); Postdoctoral, Toronto
(1973-74); Lecturer, Toronto (1974-79); Assistant Professor,
Toronto (1979-82); Associate Professor, Toronto (1982-1989),
Professor, Toronto (1989-present).
The spontaneous symmetry breaking manifested by the Earth as a division into continents and oceans is elegantly explained to first order by the theory of plate tectonics driven by convection in the Earth's mantle. Plate tectonics explains, via the interaction of plates at their mutual boundaries, many of the important geological processes which have formed the Earth's crust as we see it today. There are many equally important observed geological features of the Earth's crust which are not explained by the theory of plate tectonics as such. One example of this is continental mountain building which occurs far from plate boundaries. It is also not clear whether the simple effects of accumulated deformation on very old continental crust is sufficient to account for its observed differences in character from modern continental crust. In the several decades since the acceptance of the plate tectonic paradigm, considerable evidence has accumulated to demonstrate that the continental crust is not simply a passive geochemical blemish riding as a rigid passenger on tectonic plates. In particular, many recent experimental studies by a number of groups suggest that the viscosity of the deep continental crust appears to be very low (presumably because of high temperatures); low enough, in fact, that the crust in many areas acts dynamically as a relatively thin elastic surface layer riding on an a lower "fluid" layer which is inviscid over geological time scales, or nearly so. This relatively simple model can be used to quantitatively predict the thresholds and rates for a number of geologically important intraplate processes: metamorphic core complex formation, gravitationally induced thrust faulting via hydraulic uplift; gravitationally induced continental "overflow" onto ocean basins, giant isostatic amplification of sedimentary basins being examples.
Some of the main features of such processes such as thresholds for activation are and have been examined theoretically. However, detailed visualization requires detailed modelling. Using the commercial FEMLAB code as a base, we have developed a finite-element moving-mesh solver ("Thermax2d") which handles realistic crustal conditions: compressible thermally activated viscoelastic deformation coupled to a thermal diffusion with heat source, and the thermal and mechanical effects of magmatic injection. Arbitrary combinations of stress, velocity, temperature and heat flux boundary conditions are possible. Boundaries can also have arbitrary erosion functions specified. We are currently looking at:
a) thermal weakening of elastic crust and the consequences for
flexurally supported loads.
Preprints, figures and movies of latest research:
Preprint detailing the basis of Thermax2D: finite element modelling code for coupled viscoelastic (Maxwell) flow and thermal diffusion
A frivolous test case with Thermax2d: softened butter on a hotplate.
figures illustrating load shedding from thermally thinned elastic crust: a
mechanism for crustal density stratification and a potential contributor to
core complex formation
Selected Publications of Interest:
"Topography of the crust-mantle interface under the
Western Superior craton from gravity data", B
Nitescu, AR Cruden, RC Bailey, Can. J. Earth Sci. 40, 1307-1320
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