Snæfellsnes—off-axis volcanism in Western Iceland: inferences on mantle lithology and temperature

Abstract

Volcanism in Iceland can be compositionally and spatially divided into two broad groups: tholeiitic basalts erupted from the active rift and smaller degree alkaline, to transitional-tholeiitic basalts erupted in off-axis areas. Investigating the melt generation processes for off-axis volcanism requires constraining parameters including, melt-source material, temperature, and pressure. Here, we utilize trace elements in olivine macrocrysts and Al-in-olivine thermometry to independently constrain melt source lithology, and maximum crystallization temperatures from post-glacial melts on the Snæfellsnes Peninsula. High-precision trace element (Ni, Fe, and Mn) analyses of olivine, from 20 Snæfellsnes lava flows, have similar concentrations to rift olivines, this indicates similar melt source lithologies for Snæfellsnes and rift lavas, most likely peridotite. Al-in-olivine geothermometry data from 17 lava flows from primitive (Fo > 85%) olivine macrocrysts show consistent maximum crystallization temperatures ~1300 °C for Snæfellsnes, lower than the rift zone but higher than MORB.