Mechanism for three types of mafic dyke swarms

This study proposes three models to explain the mechanism of the three major types of mafic dyke swarms.Parallel dyke swarms form in response to a regional stress field,e.g.the mafic dyke swarms in the North China Craton,whereas small radiating dyke swarm forms due to stress constructions around a plutonic or volcanic edifice,such as the dyke swarm at Spanish Peak,USA.The third type of radiating dyke swarm is giant fan-shaped dyke swarm such as the Mackenzie dyke swarm.Fractures that formed prior to magmatism may play a vital role in dictating the dyke swarm geometry.In most of the cases,the pre-existing fractures are induced by tectonic stresses and not by magma injection though magma injection can increase the fracture size by propagation at the dyke tip.