Basalts from the Centre of the Assumed Icelandic Mantle Plume

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