BIRTH OF SILICIC MAGMAS AT EYJAFJALLAJöKULL VOLCANO, ICELAND
The Eyjafjallajökull volcano is located in the S-Iceland off-rift zone that is characterized by a low geothermal gradient. During the first explosive phase of the 2010 eruption, mingled benmoreite tephra was produced. It is composed of basaltic, intermediate and silicic tephra grains having an alkali rhyolitic composition. The rhyolite has major- and trace-element compositions indistinguishable from the cryptotephra produced during the penultimate eruption (AD 1821-23). In-situ, laser ablation ICP-MS analyses reveal trace element characteristics that are fully compatible with an origin through fractional crystallization of the basaltic tephra. Isotope ratios measured in the mingled bulk 2010 tephra strongly suggest a silicic magma mixing end-member with identical isotope composition as the basaltic end-member. The small volume of silicic magma produced during post-glacial time at the off-rift Eyjafjallajökull volcano thus is readily explained by prolonged fractional crystallization alone.