Tensile fracture of rock at high confining pressure: implications for dike propagation

Field observations indicate that zones of inelastic deformation produced at the tips of propagating dikes can be much larger than those produced at the tips of tensile cracks in laboratory experiments. This is in direct conflict with the concept that fracture toughness and fracture energy are rock properties, independent of crack size and loading configuration. For a propagating dike, the near-tip stress field is dominated by the large suction acting within a small (~several meter) cavity at the tip generated by viscous flow of magma within the dike. Perturbations to the ambient stress are on the order of the cavity suction and act over regions on the order of the cavity length. The tip cavity pressure may be maintained be exsolution of magmatic volatiles or by influx of host rock pore fluids; inelastic deformation is enhanced by the latter. Shear stresses scale with the cavity suction and may produce shear failure off the dike plane. -from Author