Francine Entwistle

Postgraduate Student

Telephone number: +44(0) 113 34 35658
Email address: eefe@leeds.ac.uk
Room: 8.152

Qualifications

2005-2009, MSci Geology, University of Manchester

Project details

Project title

How do geothermal fields relate to contact aureoles?

Supervisors

Pro. B Yardley, University of Leeds Dr D Morgan, University of Leeds Dr C Rochelle, BGS T Milodowski, BGS

Funding

BUFI studentship in association with the BGS

Start date

01/09/2009

Project outline

Volcanic activity is accompanied by two very different types of metamorphic processes in the country rocks: the development of contact aureoles around the underlying magma chamber that fed the volcanism, and the development of groundwater circulation systems or geothermal fields at higher levels, with extensive hydrothermal metamorphism. Geothermal fields have been successfully exploited for electricity generation for over a century, and provide a natural way of mining heat from young igneous rock. There is now growing interest in extracting heat from the hotter rocks beneath geothermal fields, which might provide a source of supercritical water. Key questions for any attempt to extract heat from rocks at temperatures above the critical point of water are whether they are sufficiently permeable for water to be able to penetrate, and whether the P-T regime permits water of sufficient density to be present.

Previous investigations in Greenland (Bird et al. 1988, Manning et al. 1991) and in Skye (Ferry et al. 1987) have investigated metamorphic effects in basalts and associated gabbro intrusions, and have documented evidence for both extensive hydrothermal alteration associated with greenschist facies assemblages - the signature of the former geothermal field - and higher tempreature metamorphic zones with less infiltration. What is not clear is whether this behaviour arises because in natural systems the permeability does not remain open at higher temperatures, or whether it arises because the density of water is sufficiently small at high temperatures (Figure 1) that reaction is effectively inhibited by a reduced mass flux and the reduced solubility of minerals. The challenge for this project is to understand the processes that modify permeability under extreme conditions of high temperatures at shallow depths.