Effects of mechanical layering of host rocks on dike growth and arrest

Many dikes intruding the layered host rock of Miyakejima and Piton de la Fournaise are arrested, segmented, and show variation in thickness. These geometric factors can be largely attributed to the mechanical layering of the host rocks that constitute these volcanoes. Some dikes are arrested at the base of stiff (high Young's modulus) rock layers, whereas others are segmented in the layers. We use finite-element models (FEM) to simulate a typical dike arrest at the base of a stiffer layer. The dike may become arrested when it reaches at the base of the stiffer layer for several reasons. First, the dike-induced tensile stress may not be high enough to break the rock. Second, the stiff layer may act as a “stress barrier”. Third, the material toughness of the layers may be unfavorable for vertical dike propagation and result either in dike arrest or dike deflection. When the magmatic overpressure (driving pressure) is sufficiently high dike can intrude into the overlying layer. Some deflected dikes resume their vertical propagation, thereby generating offset segments. The layering of a volcano thus commonly controls the dike propagation paths and if and where the dikes become arrested. Our measurements show that the dikes in these volcanoes tend to be comparatively thick where they dissect “soft” pyroclastic layers, and thin where they dissect stiff lava flows and sills. Numerical FEM simulations indicate that the variation of dike thickness observed in Miyakejima and Piton de la Fournaise can be broadly explained in terms of layer-stiffness differences of one or two orders of magnitude.

► We model dike arrest in the layered host rock based on our field observations.
► Arrested of dike depends on stiffness contrast between the layers of the host rock.
► We can forecast the onset site of fissure eruption from the host rock geology.
► Contrast of stiffness among the layers forms dike-thickness variations.
► Dike thickness variation can control the speed and flux of magma in dike conduit.