A rate- and state-dependent ductile flow law of polycrystalline halite under large shear strain and implications for transition to brittle deformation

• Published in: Geophysical research letters Vol. 37; no. 9; pp. np - n/a
• Main Authors: Noda, Hiroyuki, Shimamoto, Toshihiko
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01.05.2010; John Wiley & Sons, Inc
• Subjects: brittle-ductile transition; Brittleness; constitutive law; Deformation; Ductile brittle transition; Exponents; Filled plastics; Geology; Law; Physical properties; Rheology; Rocks; Shear strain; Stresses
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2010GL042512

We have conducted double‐shear biaxial deformation experiments in layers of NaCl within its fully‐plastic (FP) regime up to large shear strains (γ < 50) with velocity steps. From this, we have empirically formulated a rate‐ and state‐dependent flow law which explains the transient mechanical behavior. The steady state flow stress in the FP regime can be explained by a power‐law with a stress exponent ∼8.5 and an activation enthalpy of ∼1.3 eV, with the instantaneous response having a higher stress exponent (13 ± 8), although there is data scatter. The transition to brittle regime is associated with weakening from the ductile flow law. In FP regime, the mechanical response is characterized by a monotonic decay to a new steady state while in the transitional regime, by a peak‐decay behavior. The transient flow law obtained here is of considerable importance in the study of the brittle‐ductile transition in rocks.