Journal of Conference Abstracts

Dyke Propagation and Damage

Catherine Meriaux (meriaux@esc.cam.ac.uk)¹, John R. Lister (lister@esc.cam.ac.uk)¹, Vladimir Lyakhovsky (vladi@cc.huji.ac.il)² & Amotz Agnon (amotz@pangea.Stanford.EDU)³

¹DAMTP, ITG, Silver Street, CB39EW Cambridge, U.K.

²The Institute of Earth Sciences, The Hebrew University of Jerusalem, Givat Ram, 91904, Jerusalem, Israel

³Departement of geological and environmental Sciences, Stanford University, CA 943052115, U.S.A.

Observations of off-plane inelastic deformation around dykes motivate consideration of models of fluid-driven crack propagation in a solid which can undergo material degradation or damage. The application to dyke propagation of a recently proposed damage rheology (Lyakhovsky et al., 1997) based on thermodynamical principles and experimental measurements is discussed.

The rheological model predicts that the rate of accumulation of damage is the product of a material-dependent parameter c_d and the squared strain. For geological values, a dimensionless parameter c_d / P characterizing the ratio of a damage timescale to a flow timescale is very small, where is the magmatic viscosity and P the driving pressure. As a result, significant rates of damage are confined to a small region near the dyke tip where strains are large. Consideration of possible singularities in near-tip solutions, shows that the rate of propagation is governed by the viscous fluid-mechanics and, to a good approximation, has a value equal to that given by the zero-stress-intensity solutions of previous models based on linear elastic fracture mechanics. Both predictions of a narrow damage zone and of the rate of propagation are in good agreement with observations.