The decompressional release of magma at continental triple-rift break-up, large igneous province (LIP) centres, above mantle plume stems, results in highly magmatic settings. As a particularly well-exposed example, it is proposed that the East Greenland coastal dyke swarm preserves a structural record of how dyke dilations v. tectonic extension increased upon approaching its Kangerlussuaq triple rift centre. Such more magmatic break-up is reflected by how abruptly its volcanic rifted margin transitions into 100% dykes, and, in this case, up to 100 km further inland than its geophysically determined continent–ocean boundary. Correspondingly high magma flux through an igneous Kap Edward Holm centre sustained the lateral injection of up to 150 km-long dykes, evidenced by increased cut-off dyke thicknesses, below which there is an anomalously low abundance of thinner dykes, that conform to the cube root of their thermal arrest distance. Only the thickest and, thereby, longest dyke injections linked up with a more southerly located igneous Imilik centre of an en echelon offset dyke swarm, the complex transition into which is also addressed. This highly magmatic central plumbing system is further compared to similar volcanic zones across Iceland and other post-Paleozoic break-up LIPs in order to contextualize its importance.