A long postglacial rhyolitic activity of the Icelandic Krafla volcano during the Eemian: limited impact of glacio-isostasy

Tephrostratigraphy in marine cores is an important tool for dating sedimentary sequences along the North Atlantic and in Western Europe. Most previously 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, the two series being separated by the Grímsvötn 1 tephra known as “5e low bas IV” in marine core (∼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 ∼20 ka to the end of the Eemian last thermal optimum. probably initiated by deglaciation (MIS 6a/5e). It postdated the Halarauður ignimbrite. The ignimbrite and caldera formation were correlated with an ODP907 tephra, yielding a possible 207 ka age, but possibly older. 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 analysed during the period 80–400 ka, but this genetic link is possibly valid for the late Pliocene of Iceland.