SEGMENTATION, VOLCANISM AND DEFORMATION OF OBLIQUE SPREADING CENTERS - A QUANTITATIVE STUDY OF THE REYKJANES RIDGE

New multi-beam swath bathymetry charts and high-resolution side-scan s onar imagery provide detailed evidence for volcanic and magmatic segme ntation along the Reykjanes Ridge. By combining these data sets, we ha ve quantified some relationships between different orders of segmentat ion, various characteristics of volcanism, and changes in tectonism al ong the ridge axis. Three orders of segmentation along the Reykjanes R idge have been recognised: (1) A long-wavelength depth variation, or s well, 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 s hort-wavelength, volcanic segmentation of the order of 5-30 km. The lo ng-wavelength depth variation, which is probably controlled by the tem perature of the underlying asthenosphere, has a maximum positive devia tion from a predicted depth curve that forms a break in slope at 59-60 -degrees-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 intermediat e-wavelength rises, which are also temporally and spatially unstable, are probably related to local Rayleigh-Taylor style asthenospheric ins tabilities. The short-wavelength segments have an evolutionary life-cy cle, starting with eruption via fissure volcanoes, and progressing by increasing magma flux to the formation of conical, and then shield-lik e, volcanoes. These segments are tectonically dismembered by extension al faulting, following a rapid decrease in magma supply. We propose a model for the construction of the volcanic layer of the Reykjanes Ridg e which involves a cyclicity of magmatic and tectonic activity.