Segmentation, volcanism and deformation of oblique spreading centres: A quantitative study of the Reykjanes Ridge

New multi-beam swath bathymetry charts and high-resolution side-scan sonar imagery provide detailed evidence for volcanic and magmatic segmentation along the Reykjanes Ridge. By combining these data sets, we have quantified some relationships between different orders of segmentation, various characteristics of volcanism, and changes in tectonism along the ridge axis. Three orders of segmentation along the Reykjanes Ridge have been recognised: (1) A long-wavelength depth variation, or swell, that is related to the shoaling of the ridge towards Iceland; (2) Intermediate-wavelength rises of the order of 40-120 km; and (3) A short-wavelength, volcanic segmentation of the order of 5-30 km. The long-wavelength depth variation, which is probably controlled by the temperature of the underlying asthenosphere, has a maximum positive deviation from a predicted depth curve that forms a break in slope at 59-60°N. This feature migrated southward along the ridge at between 5 and 10 cm/yr at least four times in the past 10 Ma. The intermediate-wavelength rises, which are also temporally and spatially unstable, are probably related to local Rayleigh-Taylor style asthenospheric instabilities. The short-wavelength segments have an evolutionary life-cycle, starting with eruption via fissure volcanoes, and progressing by increasing magma flux to the formation of conical, and then shield-like, volcanoes. These segments are tectonically dismembered by extensional faulting, following a rapid decrease in magma supply. We propose a model for the construction of the volcanic layer of the Reykjanes Ridge which involves a cyclicity of magmatic and tectonic activity.