Numerical simulation of magma pathways and vent distribution in rifts from the early stages to maturity

Continental rifting is the process by which the lithosphere is thinned in response to extensional forces resulting in the formation of large scale fault-bounded basins. Rifting can be accompanied by a large amount of volcanism which can occur both inside and outside the rift depression, usually through the propagation of magma-filled fractures, called dikes. Here I use a model of crustal unloading to explain the temporal evolution of in-rift and off-rift volcanism in terms of the geometrical development of rifted areas and the competition between unloading pressure and tectonic stretching. I find that the progressive deepening of a rift is accompanied by the formation of a stress barrier under the basin which deflects ascending dikes, causing a shift of surface volcanism from the center to the flanks. The intensification of the barrier due to further deepening of the basin also promotes the formation of lower crustal sill-like structures that can stack under the rift, shallowing the depth at which magma is injected. If combined with the widening of the rift due to stretching, the sedimentary loading and the eventual shallowing of the Moho due to mantle upwelling, this would result in a later stage where dikes are injected from above the stress barrier, moving surface volcanism back to the inside of the rift.