The magmatic evolution of the Snæfell volcanic centre; an example of volcanism during incipient rifting in Iceland

Abstract

The Snæfell volcanic centre is situated in central-east Iceland, at the northern end of a short flank volcanic zone. Its products represent a typical suite of Icelandic volcanics and comprise a bimodal suite of alkalic lavas: a series from basaltic to mugearitic compositions and a small cluster of peralkaline rhyolites. Compositional variations across the whole series can be broadly explained by fractional crystallisation of a family of related parental/primary magmas in a magma chamber at mid-crustal (∼13 km) levels, that has been subject to periodic replenishment and periodic tapping, with sufficient repose times for extreme differentiation. Interaction with the crust appears minimal, although some crustal input into the rhyolites is indicated by their isotopic characteristics. The Snæfell volcanics therefore represent largely new additions to the Icelandic crust. The apparent depth of the magma chamber appears significant and sets Snæfell apart from the axial rift zones at centres such as Krafla, where seismic studies (e.g. Brandsdóttir, B., Menke, W., Einarsson, P., White, R.S., Staples, R.K., 1997. Faeroe–Iceland ridge experiment. 2. Crustal structure of Krafla central volcano. J. Geophys. Res. 102 (B4), 7867–7886) have detected the presence of magma bodies at depths of around 3 km beneath centres in the northern volcanic zone. Comparing Snæfell with volcanic centres in the propagating eastern volcanic zone suggests that, in terms of its stage of evolution, Snæfell is approximately equivalent to Torfajökull. Thus, the Öræfajökull–Snæfell volcanic zone may have represented a site of incipient rifting.