A Long Postglacial Rhyolitic Activity of the Icelandic Krafla Volcano During the Eemian in Iceland : Implications

The use of tephrostratigraphy in marine cores is an important tool for dating sedimentary sequences along the North Atlantic and Western Europe. Most analyzed marine tephra were produced by Icelandic volcanoes, albeit rarely from the Krafla volcano, and require land-based records for validation. Two series of rhyolitic tephra emitted to the east of the Krafla volcano were recorded in the Eemian Rangá Formation in Northern Iceland, with the two series separated by the Grímvötn 1 tephra known as “5e low-bas IV” in marine cores (~127 ka). These rhyolitic deposits were seemingly ejected from the Hágangnahali paleocrater row (North of the Hágöng) and overlay the older Halarauður Ignimbrite. This rhyolitic activity persisted for ~10 ka to the end of the Eemian thermal optimum. This rhyolitic series was initiated by deglaciation (MIS 6a/5e) but postdates the Halarauður ignimbrite. The ignimbrite and caldera formation were correlated with an ODP907 tephra, yielding a possible ~207 ka age, but possibly more. These results constrain the main rhyolitic activity of Krafla to after the mid-Pleistocene transition, as observed for other “two-magma” volcanoes. Rhyolitic activity is non-systematically triggered by deglaciation, at least as analyzed during the period 80–400 ka, but is possibly valid from the late Pliocene of Iceland.