Reconstruction of the Architecture of the Krafla Fissure Swarm (Northern Iceland), Through the Integration of Remote Sensing and Field Survey

The study of the architecture of an active rift, and of the geometry and kinematics of the structures composing it, is crucial for a better understanding of rifting processes. Due to its location at the boundary between two plates, Iceland represents an ideal site to shed light on this topic, offering the possibility to study an offshore sector of the Mid-Atlantic Ridge. In our work, we reconstructed the architecture of the Krafla Fissure Swarm (KFS), a rift situated in the Northern Volcanic Zone (NVZ) of Iceland, through the integration of remote sensing and field data. Along the rift, we recognized a total of 20,483 structures, classified as normal faults, extension fractures and eruptive fissures. We analyzed the geometry of the structures by collecting quantitative measurements of their strike and length, and we also calculated the variation of their density and spacing along the entire rift. In the field, we focused on three areas, in the northern, central and southern part of the rift, where we collected 4642 structural measurements at 1640 different sites, along extension fractures affecting Post-LGM units. For each site we measured the local strike, opening direction (wherever possible) and amount of opening for each extension fracture. Along normal faults, we measured 653 values of vertical offset, in order to calculate the stretch ratio along the rift, which is 1.003 in the central sector, and 1.001 and 1.002 in the northern and southern part, respectively. The distribution and geometry of all the classified fractures indicate that normal faults are longer south of the Krafla volcano with respect to faults located north of it, and that the number of extension fractures increases north of the volcano. We also recognized evidence of interaction with the termination of the transcurrent WNW-ESE Húsavík-Flatey Fault. Although we obtained an average opening direction (N99.5°E) that is mostly orthogonal to the N-S orientation of the rift, we also noticed the presence of right- and left-lateral components of motion along 67% of the rift fractures, which may have been produced by local perturbations due to shallow diking.