Brittle-viscous deformation cycles in quartz veins at the base of the seismogenic zone

Applications are invited for a three-year PhD studentship. The studentship will start on 1 January 2017.

Crustal deformation near the brittle-viscous transition involves the competition between cracking and viscous flow. A prominent role of variations in fluid pressure is often invoked to explain the mechanics of fault zones at depth. High fluid pressures are also invoked to explain characteristic fault slip behaviours observed for seismogenic faults, such as non-volcanic tremors and slow-slip events. Yet, a micromechanical model for the cyclic interplay between fracturing and viscous flow as a function of oscillating fluid pressures and evolving rock microstructure has not been proposed.

This project will use a network of quartz veins emplaced along fault zones in the Baltic Shield near the brittle-viscous transition. Quartz shows evidence of cyclic switches from brittle to viscous deformation processes, presumably determined by oscillations in fluid pressure. The material comes from a site chosen for the disposal of radioactive waste (Onkalo, Finland). The project will be conducted in collaboration with Posiva Oy, the Finnish expert organisation in radioactive waste management. The samples and the related industrial implications make this project a unique opportunity to constrain the mechanical behaviour of quartz at the brittle-viscous transition, and the role of fluid pressure.

The project aims are: (i) to determine the mechanical evolution of long-lived brittle-viscous shear zones active at the base of the seismogenic crust, (ii) to determine the fluid pressure responsible for the cyclic brittle-viscous transitions by means of fluid inclusion studies, and (iii) to characterise the multi-scale fluid pathways of a fault system by means of field studies, microstructural observations and 3D microtomography. Lab work will make extensive use of electron backscatter diffraction (EBSD) to determine the dominant deformation mechanism in the brittle-viscous shear zones. The cumulative dataset will provide a holistic model of the contribution of the cyclical interaction between fast fracture and slow creep to the mechanical evolution of faults at the brittle-viscous transition, and of the role played by fluids.

Eligiblity:

Applicants should have (at least) a first or upper second class honours degree in an appropriate subject and preferably a relevant MSc or MRes qualification.

General information about stipends eligibility for a research degree is available at: https://www.plymouth.ac.uk/student-life/your-studies/the-graduate-school/applicants-and-enquirers

You can apply via the online application form which can be found at: https://www.plymouth.ac.uk/study/postgraduate and select ‘Apply’.

Please mark it FAO Sharon Healy and clearly state that you are applying for a PhD studentship within the School of Geography, Earth and Environmental Science. Please attach a covering letter detailing your suitability for the studentship, a CV and two academic references.

For more information on the admissions process please contact Sharon Healy ([Email Address Removed] or [Email Address Removed]).

The closing date for applications is 12 noon (UK time) on 16 November 2016. Shortlisted candidates will be invited for interview on the 30 November. We regret that we may not be able to respond to all applications. Applicants who have not received an offer of a place by 24 November should consider their application has been unsuccessful on this occasion.