1. Measurement of Dislocation Creep Based on: Low-Stress High-Temperature Creep in Olivine Single Crystals D.L. Kohlstedt and C. Goetze, 1974 Picture from Couvy et. al, 2004

2. I. The experiment II. A closer look at dislocation creep

3. Designing an experiment to model mantle flow processes Goal: produce a steady strain rate at a constant stress

4. Olivine single crystals High temperature (1450-1650°C) is needed for strain to occur fast enough to measure readily in the laboratory. Natural peridotite contains other phases, lowering the solidus below experimental temperatures Use of single crystal avoids grain boundary issues

5. San Carlos Peridot

6. Experimental setup Furnace Method of applying precise load Method of measuring strain

7. The Apparatus Molybdenum vs. graphite Gas inlet for H 2, CO 2, controls O 2 fugacity Crystals dry rapidly at >1000°C and Atmospheric pressure

8. Results 10 1 10 2 10 3 10 4 σ 1 – σ 3 (bars)

9. Microstructures

10. Dislocation Creep: A Mechanism for Plastic Flow

11. Edge dislocations and glide: the rug analogy

12. Screw dislocation

13. Slide on Burgers vectors? Slide on Power law creep equation?

14. Dislocation tangles & strain hardening

15. Edge dislocation pile-ups in olivine These sorts of dislocation tangles were commonly observed in crystals deformed at differential stresses above 1 kbar.

16. Climb and vacancy diffusion

17. Evidence for climb in olivine In samples deformed under lower stress, dislocation structures appear to have reached an equilibrium concentration, implying the existence of some annealing process such as climb.

18. Conlusions Basic laboratory experiments can be used to hypothesize flow laws for the mantle Dislocation creep is a viable mechanism for plastic flow at high temperature and low differential stress