1. Dynamic elevation of the Cordillera, western United States Anthony R. Lowry, Neil M. Ribe and Robert B. Smith Presentation by Doug Jones

2. Purpose of this Paper?

3. To better understand the relative importance of the contributions of different sources to elevation of the western USA Isolate topographic expression of each process that influences elevation

5. First Step? Remove topographic effects of near surface processes

6. First Step? Remove topographic effects of near surface processes – Erosion – Deposition – Volcanic construction – Fault displacement – Strain

7. Removing near/subsurface processes?

8. Comparing elevations with gravitational potential then removing the undercompensated parts of the topography

12. Crustal Mass Variations?

13. Found by relating crustal refraction seismic velocities to density

15. Conductive Thermal Variations?

16. First order approximation from surface heat flow measurements

18. Dynamic Elevation?

19. Subtract previous estimates of topographic effects of near surface processes

21. Yellowstone plume buoyancy?

22. Used a 3D numerical convection model – Calculations of both temperature and material properties vary spatially

23. Material Properties Expressed in terms of mantle activation energy (H* m )

24. Lithospheric Thickness

25. Swell Topography

26. Thermal Structure

27. Types of Mantle Buoyancy Thermal boundary layer buoyancy Hotspot swell buoyancy Magmagenic buoyancy Others

28. Thermal Boundary Layer Buoyancy?

29. Thermal Boundary Layer Buoyancy Thinning of thermal boundary layer contributes to raised elevation 15% of total isostatic response to mantle buoyancy Not sufficient to offset effects of crustal thinning

30. Hot Spot Swell Buoyancy 25% of estimated dynamic elevation

31. Magmagenic Buoyancy?

32. When partially melted, both the melt and residuum are less dense than the original aggregate Aggregate density change after %5 partially melted same as 500K change in temperature Dynamic elevation is dynamic, not compositional – Partial melt only contributes slightly to elevation

34. Other Sources of Dynamic Buoyancy? Superadiabatic upwelling Phase boundary deflections Deeper buoyancy

35. Superadiabatic Upwelling?

36. Upwelling in Basin-Range as passive response to rifting If isentropic (no change in entropy) no thermal anomaly would be produced If upwelling material was anomalously hot, then anomaly would be produced

37. Phase Boundary Deflection?

38. Latent heat of recrystalization Deflection at the 410 & 60 km phase boundary could have uplifts of 2 and.5 km respectively

39. Deeper Buoyancy The small scale anomalies studied in this paper would not be affected significantly by deeper buoyancy sources

40. Conclusions 95% confidence mantle buoyancy largely contributes (~2 km) to dynamic uplift Little insight into relative contributions of different mechanisms for dynamic uplift