Presentation on theme: "Measurement of Dislocation Creep Based on: Low-Stress High-Temperature Creep in Olivine Single Crystals D.L. Kohlstedt and C. Goetze, 1974 Picture from."— Presentation transcript:
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
I. The experiment II. A closer look at dislocation creep
Designing an experiment to model mantle flow processes Goal: produce a steady strain rate at a constant stress
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
San Carlos Peridot
Experimental setup Furnace Method of applying precise load Method of measuring strain
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
Results 10 1 10 2 10 3 10 4 σ 1 – σ 3 (bars)
Dislocation Creep: A Mechanism for Plastic Flow
Edge dislocations and glide: the rug analogy
Slide on Burgers vectors? Slide on Power law creep equation?
Dislocation tangles & strain hardening
Edge dislocation pile-ups in olivine These sorts of dislocation tangles were commonly observed in crystals deformed at differential stresses above 1 kbar.
Climb and vacancy diffusion
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.
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