Immature and mature transform zones near a hot spot: The South Iceland Seismic Zone and the Tjörnes Fracture Zone (Iceland)

• Published in: Tectonophysics Vol. 447; no. 1; pp. 142 - 154
• Main Authors: Bergerat, Françoise, Angelier, Jacques
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.02.2008; Elsevier
• Subjects: Earth Sciences; Iceland; Sciences of the Universe; Stress regimes; Transform Zone; Transform Zone; Stress regimes; Iceland
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2006.05.046

We describe and compare the two transform zones that connect the Icelandic rift segments and the mid-Atlantic Ridge close to the Icelandic hot spot, in terms of geometry of faulting and stress fields. The E–W trending South Iceland Seismic Zone is a diffuse shear zone with a Riedel fault pattern including N0°–N20°E trending right-lateral and N60°–N70°E trending left-lateral faults. The dominant stress field in this zone is characterised by NW–SE extension, in general agreement with left-lateral transform motion. The Tjörnes Fracture Zone includes three major lineaments at different stages of development. The most developed, the Húsavík–Flatey Fault, presents a relatively simple geometry with a major fault that trends ESE–WNW. The stress pattern is however complex, with two dominant directions of extension, E–W and NE–SW on average. Both these extensions are compatible with the right-lateral transform motion and reveal different behaviours in terms of coupling. Transform motion has unambiguous fault expression along a mature zone, a situation close to that of the Tjörnes Fracture Zone. In contrast, transform motion along the immature South Iceland Seismic Zone is expressed through a more complicate structural pattern. At the early stage of the transform process, relatively simple stress patterns prevail, with a single dominant stress field, whereas, when the transform zone is mature, moderate and low coupling situations may alternate, as a function of volcanic–tectonic crises and induce changes in stress orientation.