Lockett, Jeremy Mark (1982) Theoretical models of thermo-mechanical ductile shear zone deformation in rocks. Doctoral thesis, Keele University.

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Abstract

Thermo-mechanical models of ductile shear zones have been constructed for both viscous and viscoelastic materials. The viscous model has been applied to both shear zones and ductile thrusts for constant velocity and constant shear stress boundary conditions. For the constant velocity boundary condition the viscous shear zone model provides an explanation for a number of geological structures. Constant velocity shears broaden with time and have a large temperature anomaly. The temperatures increase slowly with time but are insufficient for melting. The shears can be shown to broaden with increase in ambient temperature with depth. A minimum separation distance between pairs of shears is required for them to remain discrete. Constant velocity viscous shears have a near singularity in the shear stress at time t=o.
The viscoelastic model shows a more realistic initial stress evolution; with a zero initial stress. The viscoelastic constant velocity model predicts the occurrence of viscoelastic rebounds, under certain conditions, in which very large instantaneous shear velocities are developed. In viscoelastic rebounds large amounts of stored elastic stress are relaxed catastrophically in a localized region by viscous deformation. The rapid velocities generate large amounts of shear heating and give rise to localized thermal runaway and melting. The high temperatures generated rapidly decay to lower levels. With time the temperature and stress field solutions of the viscous and viscoelastic models converge.
For constant stress boundary conditions the viscous and viscoelastic models are identical except for the initial elastic strains in the viscoelastic model. At low values of temperature and stress,very small, geologically insignificant strains are developed. Higher temperatures and stresses give rise to thermal runaways and melting.
Thermo-mechanical stabilization .using a dislocation creep process explains many of the features seen in ductile shear zone. At lower ambient temperatures the models produce high stresses which would be limited by brittle failure.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QE Geology
Divisions: Faculty of Natural Sciences > School of Geography, Geology and the Environment
Contributors: Kusznir, Nick (Thesis advisor)
Depositing User: Lisa Bailey
Date Deposited: 04 Jun 2020 08:17
Last Modified: 04 Jun 2020 08:17
URI: https://eprints.keele.ac.uk/id/eprint/8112

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