Growth of Continental Plateaux:
Channel Injection or Tectonic Thickening?
 

Sergei Medvedev and Chris Beaumont
Dalhousie University, Halifax, Canada
 

1.  Summary: Statement of Problem

How do continental plateaux grow?
What is the nature of crustal thickening in the transition zone at the plateau margins?
Does widening and thickening occur by:
 (1) basal accretion associated with channel flow;
 (2) frontal accretion associated with tectonic thickening; or
 (3) combination of those two?

2. Introduction

3. General Channel Injection Model

4. Tectonic Thickening Model

5. Channel Injection Model I: Transition Zone with Uniform Property Channel

6. Tectonic Thickening Model for Transition Zone

     6a. Tectonic Thickening vs. Channel Injection Model I

7. Channel Injection Model II: Constant Thickness, Variable Viscosity Channel

     7a. Channel Injection Model I vs. Channel Injection Model II

8. Channel Injection Model III: Channel Properties Defined by Temperature Field

     8a. Channel Injection Model II vs. Channel Injection Model II

9. The Associated Thermal Model

10. General Conclusions:
 

• The models presented represent successively more complete approximations to the evolution of a continental plateau and adjacent transition zone
• Channel Injection Model I is incomplete (Panel 5)
• Channel Injection Model II completes the connection between plateau and transition by assuming channel viscosity decrease when the channel burial exceeds the critical depth D* (Panel 7)
• Channel Injection Model III includes the associated thermal evolution and demonstrates self-consistent plateau widening if the channel viscosity decreases when its temperature exceeds the critical value T* (Panel 8)
• Tectonic Thickening and Channel injection are end member modes of plateau growth which may be preferred according to the crustal temperature in the transition zone
• Estimates of crustal viscosity vary dramatically according to the model chosen to approximate the topography of the plateau and transition zone (Panels 6a, 7a, 8a)

References

• C. Beaumont, R.A. Jamieson, M.H. Nguyen and B. Lee, 2001. Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface denudation, Nature, 414, 738-742.
• Clark M. K. and L. H. Royden,  2000. Topographic ooze: Building the eastern margin of Tibet by lower crustal flow, Geology, 28, 703-706.
• Medvedev S.,  Mechanics of viscous wedges: modeling by analytical and numerical approaches, J. Geophys. Res., in press.
• Medvedev S., Beaumont C., O. Vanderhaeghe, P. Fullsack, and R.A. Jamieson, 2000. Evolution of Continental Plateaus: Insights from Thermal-Mechanical Modeling (abstract), AGU Fall Meet. 1094.
• Royden, L., 1996. Coupling and decoupling of crust and mantle in convergent orogens: Implications for strain partitioning in the crust, J. Geophys. Res., 101, 17679-17705.