Megadyke propagation down dynamic topography

Timothy Davis , Yuan Li, Adina E Pusok , Richard Katz

Magmatic dykes that align vertically and extend laterally for hundreds to thousands of kilometres are known as megadykes. Observations of solidified megadyke swarms indicate that they have a common magma source and a characteristic run-out length. There is no consensus on what determines this length. We develop quantitative predictions to test the hypothesis that run-out length is set by the dimensions of the topographic swell above a mantle plume.

Our model describes lateral dyke propagation from a constant-pressure magma source by fluid-driven fracturing of an elastic crust. The dyke is confined at its level of neutral buoyancy, which is warped by the dynamic topography of the plume swell. This gives the dyke gravitational potential energy that drives lateral magmatic flow. Solidification blocks the fracture perimeter when advance of the fracture's tip slows below a critical value. 

When assisted by dynamic topography, dykes in this model propagate to lengths approximately twice the underlying plume-head radius. Hence our model links the characteristic dyke length of a megadyke swarm to the size of the ancient plume that created it. Furthermore, the model predicts a sensitivity to source pressure, explaining the existence of dykes that are far longer than others in a swarm.