Chemistry of basalts from the Icelandic Rift Zone

The chemistry of basalts from the Icelandic Rift Zone is discussed on the basis of 34 analysis, both new and previously published. It is concluded that a distinct chemical grouping is present between alkalibasalts and tholeiitic basalts.The tholeiitic basalts can furthermore be grouped into batches with slightly different primitive chemistry but identical differentiation trends.The chemical variation within a group of basalts from the same volcanic center can be related to a time scale in such a way, that the youngest (historic) lavas all show advanched differentiation, but the lavas known to be oldest have the most primitive chemistry.The possibility is suggested, that the volcanic activity along the Icelandic Rift Zone represents an independent cycle of chemical differentiation, distinct from the Tertiary volcanic activity along the Wyville Thompson Ridge.Attention is drawn to a fairly well defined grouping of basalts from different parts of the Midatlantic Ridge using the plot combined iron against magnesia.