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.