To investigate the role of grain boundary sliding during dislocation creep of dunite, a series of deformation experiments were carried out under anhydrous conditions on fine-grained (~15 μm) samples synthesized from powdered San Carlos olivine and powdered San Carlos olivine+1.5 vol.% MORB. Triaxial compressive creep tests were conducted at a temperature of 1 473 K and confining pressures of 200 and 400 MPa using a high-resolution, gas-medium deformation apparatus. Each sample was deformed at several levels of differential stress between 100 and 250 MPa to yield strain rates in the range of 10-6 to 10-4 s-1. Under these conditions, the dominant creep mechanism involves the motion of dislocations, largely on the easy slip system (010), accommodated by grain boundary sliding (gbs). This grain size-sensitive creep regime is characterized by a stress exponent of n=3.4±0.2 and a grain size exponent of p=2.0±0.2. The activation volume for this gbs-accommodated dislocation creep regime is V*=(26±3)×10-6 m2·mol-1. Comparison of our flow law for gbs-accommodated dislocation creep with those for diffusion creep and for dislocation creep reveals that the present flow law is important for the flow of mantle rocks with grain sizes of <100 μm at differential stresses >20 MPa. Hence, gbs-accommodated dislocation creep is likely to be an important deformation mechanism in deep-rooted, highly localized shear zones in the lithospheric upper mantle.
Bibliographical noteFunding Information:
This study was supported by the National Science Foundation of USA (No. EAR-0910687), and the National Natural Science Foundation of China (No. 40874043). *Corresponding author: email@example.com © China University of Geosciences and Springer-Verlag Berlin Heidelberg 2010
- flow law
- grain boundary sliding