The mechanics of continental deformation in Asia and California

Thesis

The failure of plate tectonic theory to explain the deformation observed across continental plate boundary zones has led to the development of continuum models of lithospheric deformation in which the lithosphere is treated as a layer of viscous material governed by the equation for creeping viscous flow,

ϑσji	= ρ9i
ϑxj

where the left hand side represents spatial gradients of stress that are balanced by differences in gravitational potential energy on the right hand side.

Strain rates and an assumed power law rheology are used as a proxy for stress,

τij = BΕ(1/n)-1εij

where B is a strength parameter that represents the depth-averaged temperature dependence of the lithospheric rheology, E is the second invariant of the strain rate tensor, and n is the power law exponent in the stress-strain rate relationship. Finite element methods are used to solve the thin viscous sheet equations (England & McKenzie, 1982), yielding a velocity field that may be compared to observations from regions of continental deformation.

In this study I investigate the deformation of the lithosphere in two regions of active deformation: south-east Asia and the western North America plate boundary zone. Particular attention is paid to the degree to which the deformation fields reflect the driving forces, and the effect of lateral variations in effective viscosity and lithospheric strength upon the deformation field.

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Authors: Whitehouse, P

• DOI: 10.5287/ora-vmagqbarj
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford