Figure 3: Conceptual model of dyke emplacement.

(a) Conceptual model of the host rock above a magma chamber. The rock contains weaknesses that follow a power law size distribution. New dykes that nucleate at the roof of the magma chamber utilize these weaknesses. (b) Dykes of varying size form at times t₁, t₂ and t₃ due to different overpressures p₁, p₂ and p₃, respectively. Large weaknesses require only low overpressure for magma intrusion, while small weaknesses require greater overpressure. High overpressure generally leads to thicker dykes because more excess magma is available in the inflated chamber, while large weaknesses result in overall thinner dykes. (c) Pressure increases in the magma chamber due to magma inflow and degassing until the rock strength is overcome and a new dyke forms. Excess magma from the chamber then enters the dyke, and the pressure is reset. Consequently, failure stress and dyke thickness follow a Weibull distribution (see text for details), provided that the magma chamber is in steady state during the formation of a genetically related set of dykes. The pressure evolution between dyking events (sketched as linear) depends on numerous variables but does not affect our model.