1. Upper Mantle Viscous Drag on the Lithosphere David Terrell Warner Pacific College March 2006

2. Historical Background Continental Drift. Ocean Floor Spreading Plate Tectonics. 1957/8 international Geophysical year. 1961-8 papers on world seismology and paleo-magnetism Vine 1966 Science “Spreading of the Ocean Floor” Isaks, Oliver, and Sykes 1968 J. G. R. “Seismology and the New Global Tectonics.”

3. Seismic Analysis/Geomorphology Isostacy –(explains mountain gravity anomalies) Global earthquake distribution –Follows definite patterns Earthquake Depth –Relative to some continental margins

4. Subduction Locality/Depth of Earthquakes.

5. Volcanism Friction/Phase change

6. Ocean Floor Spreading Ocean Floor Magnetic Anomalies

7. Earth’s configuration Lithosphere (0 – 100 km) –Crust Asthenosphere (Soft) Mantle (100 – 2890 km) –Upper –Lower Nucleus/Core (2890 – 5378 km) –Outer –Inner... **

8. Layer boundaries Mohorovicic discontinuity –Physical – chemical changes –About 5 km under mid-oceanic ridges –About 75 km under continents Gutenberg discontinuity –Between silicate mantle/iron nickel core Lehman discontinuity –Between “liquid” outer and “solid” inner core

9. Mantle Convection

10. Internally Generated Heat Asymmetric Equations of Fluid-Dynamics –Mass conservation –Continuity

11. Normal Convection

12. Thermal Convection Symmetric Asymmetric FOR MORE INFO... Butler and Peltier 2002 J.G.R. Thermal Evolution of The Earth: Models with time-dependent layering of mantle convection which satisfy the Urey ratio constraint. www.gps.caltech.edu/~gurnis/Movies/movies-more.html

13. Internally Heated Convection

14. Upper mantle convection Heat generated during accretion Heat generated by Radioactivity – 40 K –U –Th –Others now in smaller amounts (Rb, Sm, etc.)

15. Stress-Strain Mantle deformation –Fluid dynamics –Elastic modulus FOR MORE INFO... Non-linear rheology: http://www.geo.ucalgary.ca/~wu/Goph681/Rheology.pdf

16. Equations of Motion Fluid Dynamics Equations that govern motion Equation of mass conservation  is density;  i is normal unitary vector defining integration surface; and v i is 1 st order tensor defining velocity Equation of continuity Mass conservation http://www.navier-stokes.net/nsfield.htm

17. Heat Equation Cp is the heat capacity and  is the expansion coefficient

18. Rayleigh’s number Convection occurs if R > 1100 - 1700

19. Stress A first approximation: Density ρ is about 3.4x10 3 kg/m 3 and viscosity ν is about 10 24 poises (1 poise = 10 -1 Pa·s)

20. Accumulated stress Using estimated values for heat generated and the current estimates for the movement of some plates –Say speeds of ~2-3 cm/y Values for accumulated stress in about 200 Ma of about 300-400 bars can be calculated These values are well below values calculated for isostacy in some places but big enough to break a thin (<10 km) crust.

21. Current Status Even though this is an old problem new computing (modeling) technologies as well as experimental data have opened this area to new research.

22. Thanks so much for listening! Some useful web sites: www.warnerpacific.edu/personal/dterrell http://anquetil.colorado.edu/VE/convecti on2.shtml http://anquetil.colorado.edu/VE/convecti on2.shtml http://www.gps.caltech.edu/~gurnis/Movi es/movies-more.html http://www.gps.caltech.edu/~gurnis/Movi es/movies-more.html http://www.mantleplumes.org/Convectio n.html http://www.mantleplumes.org/Convectio n.html