Tectonics and magma dynamics coupling in a dyke swarm of Iceland
Résumé
To study the dynamics of dyke and fissure swarms in Iceland, we analyse the distribution of the dykes across the Tertiary Alftafjördur dyke swarm and that of open fissures and faults across the active Krafla fissure swarm. Within these narrow (5 to 10 km wide) and long (length/width ratio >10) swarms, deformation is accommodated both by tectonics and magmatism. The dyke swarm built during the westward regional tilting of the host-rock lava pile. The populations of dykes suggest that a characteristic thickness at about 3 m is involved during dyking. Dykes show a quasi-periodic distribution across the swarm and form clusters spaced by about 2.5 km. The analysis of the fissure distribution in the Krafla volcanic system reveals a cluster spacing of about half of that of the dyke clusters. We discuss the potential origins of these features as a result of magma dynamics, host-rock properties and tectonics. Clustering possibly reflects the intrinsic mechanical response to stretching of the upper levels of the brittle crust. We propose a three-dimensional model of dyke swarms in which magma likely migrates laterally within the upper crust from igneous centres where high magmatic supply rates locally perturb the regional stress field.