Variations of the magnetic properties of postglacial pillow lavas along the Reykjanes Ridge

Abstract

Systematic rare earth and minor element concentration variations occur in postglacial tholeiites which were extruded along the axial zone of the Reykjanes ridge. The northward increase in total Fe and Ti is partly responsible for an increase in the peak magnetic intensity of the lava flows between 60°N and 62°45′N. Three pillow lava types can be distinguished magnetically: high-remanence lavas which coagulated into small pillows, intermediate-remanence lavas, and low-remanence lavas which are made up of large pillows. From approximately 62°45′ latitude northward the peak magnetic intensity of the different pillow lava types decreases, despite a continued increase of the magnetic mineral content (as suggested by a further increase in total Fe and Ti). This can be explained by oxidation of the titanomagnetite, due to an increase in the degree of degassing and H2O dissociation of the tholeiites emplaced at a depth less than 400 m. Magnetic anomaly amplitudes over the axial zone of the ridge increase between 60°N and 62°45′N and decrease from the latter latitude northward. The amplitude pattern therefore closely resembles that obtained for the peak intensity variations of the tholeiites. This suggests that the ‘telechemical’ hypothesis may be basically correct.