Oxygen Isotope Variations in Recent Magnesian Lavas from Iceland’s Northern Neovolcanic Zone

Abstract

Geochemical variations of Icelandic lavas reflect both differences in the compositions and conditions and extents of melting of their sources (e.g., Thirlwall, 1994) and magmatic differentiation and crustal contamination (e.g., Gee et al., 1996). Discriminating between these two processes is key to constructing models of the composition and dynamics of the Iceland plume. Recent efforts to do so have focused on relatively magnesian lavas from the northern and western neovolcanic zones; Theistareykir volcano has been of particular importance for this work because of its abundance of magnesian lavas, the absence of a well-developed central volcanic complex, and the fact that it's lavas include the 'depleted' extreme to the array of compositional variations in Icelandic lavas generally (e.g., Elliott et al., 1991). We report here a study of oxygen-isotope variations in phenocrysts from recent Theistareykir lavas, conducted to search for evidence for both crustal contamination and oxygen isotope variations in the sub-Icelandic mantle.