Ph.D position available at Université de Strasbourg, autumn 2013
From: HEAP Michael (EOT) <heap@xxxxxxxxxx>
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Projet “contrats doctoraux” Initiative d’Excellence (IdEx) 2013
Ph.D position available at Université de Strasbourg, autumn 2013
Permeability evolution through the brittle-ductile transition in volcanic rocks
Principal supervisor: Prof. Patrick BAUD
Co-supervisor: Dr. Michael HEAP
A comprehensive description of the microstructural, physical, and mechanical properties of edifice-forming rocks represents essential input for the development of effective and robust volcanic unrest models (Sparks, 2003). In the assessment of the structural response of a volcanic edifice to stress perturbations, details of the mechanical response of the rocks (the breadth of the probable failure modes, the operative micromechanical processes) become central to the question of ascribing the permissible mechanistic sources behind geophysical, geodetic, and geochemical signals of unrest (Gottsmann et al., 2011). An improved understanding of the relationships between rock microstructure (microcracks, vesicles), rock physical properties (e.g., porosity, bulk density, ultrasonic wave velocities, permeability), and rock mechanical properties (e.g., strength) of representative materials, and how they evolve during deformation, should allow us to construct a better scheme to assess t
he structural stability of the volcano (Voight, 2000), as well as an improved imaging of subsurface activity (e.g., Manconi et al., 2007).
Unfortunately, few data exist on the deformation of volcanic rocks at high temperature, most data are restricted to the shear faulting regime, and little is known as to their permeability at high temperature. Pertinently, the switch from dilatancy and/or dilatant modes of failure (axial splitting, shear faulting) to compaction and/or compactive modes of failure (compactive shear bands), and the resultant impact on permeability, is not well understood for volcanic materials (even at ambient temperatures). Volcanic rocks are certainly prone to this switch in failure mode within the depth interval of the edifice due to their often high porosity (usually within the range 10-40%). This failure mode switch has important ramifications for volcano dynamics (host rock permeability can control the efficiency by which ascending magma can degas, thus dictating eruption characteristics, Mueller et al., 2008) since the formation of compactive shear bands could drastically influence the way
fluids and gases are transported within the edifice (Baud et al., 2012).
This Ph.D project aims to tackle this problem by conducting a systematic experimental study on the mechanical behaviour of volcanic rocks (focusing, in particular, on andesitic rocks from Volcán de Colima, Mexico) at high temperature over a pressure range representative of those within a volcanic edifice. In particular, the project will produce failure envelopes, mapping out the change in failure modes, and study the influence of failure mode on permeability evolution during deformation. The output of acoustic emissions (AE) and the evolution of ultrasonic wave velocities will also be monitored during deformation. The project will use the newly-acquired, state-of-the-art high-pressure, high temperature triaxial deformation apparatus at IPG Strasbourg. Training will be provided in conducting rock deformation experiments and in analysing the results. A successful candidate should have a familiarity with quantitative analysis and be confident about working both in the laborator
y and the field for sample collection.
For more information and details on how to apply: email heap@xxxxxxxxxx
Deadline for application: 15 May 2013
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