Basalts from the Centre of the Assumed Icelandic Mantle Plume

Abstract

Pleistocene to historic basalts in the northern part of the eastern volcanic zone in Iceland may have formed by partial melting over an extended depth range in the centre of the assumed Icelandic mantle plume. Practically all basalt types found on the ocean ridges are represented in this volcanic rift zone. Volume relations are, however, in favour of low degree partial melting products. The basalts differ from ocean ridge basalts in being undepleted in large trace ions, indicating a primary mantle source. The prevalence of low degree partial melting products in Iceland may explain the depleted nature of the astenosphere flowing away from the plume and along the northern part of the Mid-Atlantic Ridge. Volumes of lavas are found to correlate with degree of partial melting. Exceptions from this correlation are found locally and may be explained on the basis of volcano-tectonic implications. A simple model of thermal structure in the mantle plume-ocean ridge system is suggested which may explain some aspects of the compositional variations in basalts within the system.