The energetics of steady state heterogeneous shear in mylonitic rock

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1994-02, Vol.175 (1), p.261-272
• Main Author: Handy, Mark R.
• Format: Article
• Language: English
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Tectonics. Structural geology. Plate tectonics
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/0921-5093(94)91065-0

Deformation of Earth's lithosphere below about 5–10 km depth is accommodated heterogeneously in mylonitic shear zones. The persistance of heterogenous mylonitic deformation to very high strains is a manifestation either of slow transient rheological instability or of heterogeneous steady state creep. The latter possibility may be explained with the following hypothesis: rock deforms at heterogeneous steady state when it acquires a structure that minimizes the overall rate of strain energy dissipation, and when the effective ( i.e. volume-weighted) rate of strain energy dissipated within this structure is uniform and constant. Thus small volumes of weak anastomozing shear zone deforming at high strain rate dissipate the same amount of viscous strain energy per unit time as do much larger volumes of strong country rock deforming at lower strain rate. The relative magnitude of differential creep stresses in the shear zone and country rock during heterogeneous shear depends on the relative creep parameters of weak and strong rock. Strain localization leads to a modest reduction in the bulk strength of the whole rock at steady state.