Experimental deformation of olivine single crystals at mantle pressures and temperatures

• Published in: Physics of the earth and planetary interiors 2009-01, Vol.172 (1), p.74-83
• Main Authors: Raterron, Paul, Amiguet, Elodie, Chen, Jiuhua, Li, Li, Cordier, Patrick
• Format: Article
• Language: English
• Subjects: Activation volume; COMPRESSION; CREEP; DEFORMATION; DIFFRACTION; Dislocation creep; DISLOCATIONS; ENSTATITE; High pressure; MONOCRYSTALS; national synchrotron light source; OLIVINE; OXYGEN; PARTICLE ACCELERATORS; Rheological law; San Carlos olivine; SLIP; Slip systems; STABILITY; STRAIN RATE; SYNCHROTRONS; TRANSMISSION ELECTRON MICROSCOPY; Upper mantle; WATER
• ISSN: 0031-9201; 1872-7395; 0031-9201
• DOI: 10.1016/j.pepi.2008.07.026

Deformation experiments were carried out in a deformation-DIA high-pressure apparatus (D-DIA) on oriented San Carlos olivine single crystals, at pressure ( P) ranging from 3.5 to 8.5 GPa, temperature ( T) from 1373 to 1673 K, and in poor water condition. Oxygen fugacity ( fO 2) was maintained within the olivine stability field and contact with enstatite powder ensured an orthopyroxene activity a opx = 1. Two compression directions were tested, promoting either [1 0 0] slip alone or [0 0 1] slip alone in (0 1 0) crystallographic plane, here called, respectively, a-slip and c-slip. Constant applied stress ( σ) and specimen strain rates ( ε ˙ ) were monitored in situ using time-resolved X-ray synchrotron diffraction and radiography, respectively. Transmission electron microscopy (TEM) investigation of run products revealed that dislocation creep was responsible for sample deformation. Comparison of the obtained high- P deformation data with the data obtained at room- P by Bai et al. [Bai, Q., Mackwell, S.L., Kohlstedt D.L., 1991, High-temperature creep of olivine single crystals. 1. Mechanical results for buffered samples, Journal of Geophysical Research, 96, 2441–2463] – on identical materials deformed at comparable T– σ– fO 2– a opx conditions – allowed quantifying the P effect on a-slip and c-slip rheological laws. A slip transition with increasing pressure, from dominant a-slip to dominant c-slip, is documented. a-slip appears sensitive to pressure, which translates into the high activation volume V a * = 12 ± 4   c m 3 /mol in the corresponding rheological law, while pressure has little effect on c-slip with V c * = 3 ± 4   c m 3 /mol . These results may explain the discrepancy between olivine low- P and high- P deformation data which has been debated in the literature for more than a decade.