Effect of varying enstatite content on the deformation behavior of fine-grained synthetic peridotite under wet conditions

• Published in: Journal of Geophysical Research: Solid Earth 2000-06, Vol.105 (B6), p.13535-13553
• Main Authors: McDonnell, R. D., Peach, C. J., Roermund, H. L. M., Spiers, C. J.
• Format: Article
• Language: English
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Mineralogy; Silicates
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/1999JB900412

The effect of varying enstatite content on the deformation behavior of synthetic, fine‐grained (1 to 2 μm) forsterite‐enstatite rock with ∼0.5 wt% added water was investigated at temperatures of 900° to 1000°C, strain rates between 10−7 and 10−5 s−1, and a confining pressure of ∼600 MPa. The samples exhibited approached steady state flow at stresses ≤60 MPa. The results show that, at constant strain rate, increasing enstatite content is associated with a sharp decrease in flow strength in the range 0–2.5% vol% enstatite, with little further change up to 20 vol%. The observed power law n value of ∼1.7 and microstructures are similar to those obtained in previous work on material with 2.5 wt% enstatite and are consistent with a water‐enhanced grain boundary sliding (GBS) dominated deformation mechanism. Significantly, a negative correlation was found between grain size and enstatite content, indicating that enstatite content played a role in controlling the grain size of the starting materials. Moreover, a high correlation between measured flow strength and grain size was found, consistent with a grain size exponent of −3 in a conventional grain size sensitive flow equation. A water‐enhanced deformation mechanism involving GBS accommodated probably by grain boundary diffusion and/or dislocation activity is therefore implied, with the effect of enstatite content on flow strength being an indirect physical effect caused by grain size control. Other effects of second‐phase content, such as weakening caused by interphase boundary diffusion and/or migration processes, seem to be unimportant under the conditions investigated.