Evolution and Geodynamics of Transform Zones Between Icelandic Rift Zones and Reykjanes and Kolbeinsey Spreading Ridges

ABSTRACT Tjörnes Transform Zone (TTZ) and Reykjanes Rift Zone (RRZ) are two transform zones connecting Icelandic rift zones with Reykjanes and Kolbeinsey spreading ridges, respectively. They are strikingly different from the majority of transform zones that develop under the strong influence of the Icelandic plume. TTZ has a complicated pattern comprising several active and inactive rift and transtensive structures. RRZ has a relatively simple structure including several en‐echelon volcanic systems. The transform zones have a similar position between the spreading ridges and the Icelandic rift zones within a large igneous province, but a very different structure. We have used physical modelling with lithospheric accretion to reproduce the conditions for the evolution of the present‐day structure of the TTZ and RRZ. The modelling results show that the main conditions for the TTZ include the presence of a crustal thickness gradient, the interaction of overlapping structures, structural inheritance, and the magmatic pulses of the Icelandic plume. The specific feature of TTZ is Húsavík‐Flatey Fracture Zone with a transtensive pattern. We rely on it could onset from Northern Rift Zone and predefine the whole pattern of the TTZ western branch. The main conditions for the RRZ are crustal thickness and its variation with distance from the centre of the Icelandic plume, and structural control of the Reykjanes Ridge. Nowadays, its active part is an analogue of a small part of TTZ. Another method, morphometric analysis of fault scarps, has been used to reflect the current structure and activity of the transform zones. Within the TTZ, the western branch shows decreasing tectonic activity, while the eastern branch shows increasing activity. In the RRZ, the most active volcanic systems are those adjacent to the Western Rift Zone and the Reykjanes Ridge. There is currently a southward displacement of all extension centres. The current evolution trend of both transform zones supposes their structural simplification.