Evolution of basaltic lavas of the Kverkfjöll volcanic system, Northern Volcanic Zone, Iceland : evidence from in-situ LA-ICP-MS analyses

Abstract

This study deals with the evolution of the basaltic lavas of the Kverkfjöll volcanic system, which is located at the eastern edge of the Northern Volcanic Zone in central Iceland. The aim of this study is to model the melt and mineral evolution of the collected basaltic sample series by utilizing major and trace element data. The sample set consists of separated glass shards and plagioclase, olivine and clinopyroxene macrocrystals (d>500 µm). In addition, the glass shards contain microcrystals (d1 in specific minerals. Incompatible elements are enriched in evolved glasses and in general show higher concentrations in microcrystals than in earlier crystallized macrocrystals. Partitioning of V between olivine microcrystals and adjacent glass were used to determine the oxygen fugacity at 0–1 log units above the NNO buffer. This together with the appearance of titanomagnetite suggests the melts of the sample series were moderately oxidized.

Stable ratios of incompatible element pairs analyzed from glass shards suggest that no remarkable contamination or magma mixing have disturbed the ratios between the most primitive and evolved samples. In the Zr/Y vs. Nb/Y diagram, the Kverkfjöll magmas plot in the high-ratio end of the Iceland array. This is consistent with the observed high incompatible element concentrations in the Kverkfjöll melts in comparison to the other volcanic centers nearby (i.e., Kistufell, Bárðarbunga and Grímsvötn). In addition, the volcanic rocks of Kverkfjöll are distinguishable from the other three volcanoes by its higher K₂O concentrations, resulting from a lower degree of partial melting.