Evolution of Continental Plateaus: Insights From Thermal-Mechanical Modeling.
Medvedev S., C. Beaumont, O. Vanderhaeghe, P.  Fullsack, and R. A.  Jamieson

Departments of Oceanography and Earth Sciences, Dalhousie University, Halifax, Canada.
 

1. IIntroduction
 
          During prolonged thickening of the crust during orogenesis the radioactive heat-producing material that accumulates may cause significant heating and, as a result, weakening of the lower crust. In turn, this weakening can lead to mechanical decoupling of orogenic crust from underlying mantle and formation of a plateau. We test this hypothesis by modeling crustal thickening during continental collision driven by basal subduction.
 We focus on simple rheological models, depth dependent and temperature dependent linear viscosity  (Royden, 1996; Jamieson et al, submitted; Vanderhaeghe et al, in prep.) to allow first order comparisons with simplified analytical treatments of some physical problems.
         In the simple models we assume local isostatic equilibrium of the thickened crust and ignore the effect of erosion, the exponential dependence of viscosity on temperature, and any non-linear stress dependence of rheology.  Numerical calculations are, however, based on a fully coupled thermal-mechanical model, and they are supported and augmented by scaling and asymptotic analyses, and series of auxiliary models. By integrating several approaches to modeling, we demonstrate that there are three main phases during the precursor and plateau evolution. We show these phases and outline characteristic properties of each phase.

2. Model set-up (Initial and boundary conditions)

3. Evolution of Reference Model (RM) (Three stages of plateau evolution)
              deformation of Lagrangian grid (animation gif, 200 Kb)

4. Stage I: Wedge (Types of thermal behavior)

5. Stage II: Transition  (Types of mechanical and rheological boundaries)

6. Stage III: Plateau  (Influence of plateau type boundary conditions on the geometry of the plateau)

7. Conclusions
 
8. References

Appendix A. Scaling analysis of forces in wedge
Appendix B. Extended Thin Sheet Approximation (ETSA)

 



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