Why is wet olivine weak?
Abstract
The hydrolytic weakening of a range of natural minerals has been the subject of much study in rock deformation for many years. Natural olivine single crystals deformed under hydrous conditions show significant weakening relative to those deformed dry. This weakening effect can be understood in terms of changes in the populations of the majority point defect species that control diffusion on the three sublattices in olivine. Constraints on such behavior are provided by diffusion, deformation and electrical conductivity experiments. The results of recent hydrothermal experiments in which water-derived species diffuse into iron-free and iron-bearing olivines provide indications of the hydrous defect speciation in the olivine. They also provide information on the rates of transport of the various defect species, both intrinsic and hydrogen-bearing, within the olivine structure. As deformation within the dislocation creep regime is controlled by diffusion of intrinsic defect species, notably oxygen and silicon defects, changes in the concentrations of these defects will directly affect creep rates. While the concentrations of these defects in olivine under dry conditions are likely only at the atomic ppb level, hydrogen stabilization of silicon vacancies may raise the concentration of these defects into the ppm level. This enhancement of silicon defect concentrations under hydrous conditions in olivine may change the rate-limiting species for creep from silicon vacancies to oxygen interstitials. Such hydrated silicon defects at the ppm level should be detectable using infrared spectroscopy. Our current research is aimed at testing this hypothesis.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.T21C..08M
- Keywords:
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- 3902 Creep and deformation;
- 3904 Defects;
- 5104 Fracture and flow;
- 5120 Plasticity;
- diffusion;
- and creep