Constraints on Magma Pressure Distribution During Long Range Lateral Propagation of Giant Radial Dyke Swarms

Giant dyke swarms are important but enigmatic components of magma transport in the Earth and terrestrial planets. Although widely documented on Earth, Venus, and Mars as extending laterally for 100–1,000 s of kilometers from their magma sources, the reasons for this extraordinary lateral propagation are not known. A critical parameter in dyke propagation is magma pressure, but this is generally unknown. This uncertainty is a barrier to improve physical modeling and prediction of volcanic hazards. Here, we combined rock mechanical analyses with geological constraints from the largest dykes of the giant Mull Dyke Swarm to reconstruct magma pressures using a Monte Carlo framework at six locations along the 660 km long trajectory of the dykes. Our results show that in the most conservative of our scenarios the magma pressures were sufficiently high for the dykes to erupt 100 s km from the magma source. Moreover, we show that magma depressurization over distance is crudely exponential and not linear as previously thought. We also argue that the concept of the level of neutral buoyancy fails to predict the upper termination depth of Mull dykes by several kilometers. We argue that near‐surface cooling played a crucial role in maintaining dyke tips beneath the surface hence promoting long range propagation.