Geochemistry and petrology of Holocene lavas in the Bárðardalur region, N-Iceland. Part I: Geochemical constraints on source provenance

Abstract

Because of extensive volcanic production in Iceland during the Holocene, many of the early postglacial large-volume fissure lavas cannot be unambiguously traced to their eruptive craters solely by observations in the field. For example, the Bárðarbunga volcanic system has been suggested as a likely source of the large Holocene lava flows found in Bárðardalur valley, but this idea mainly relies on petrographic observations. We conducted a chemical and isotopic study of the lavas in Bárðardalur. For comparative purposes, we also targeted basement rocks of the Bárðarbunga central volcano, as well as several eruptive units in the region north of Vatnajökull. Based on a comparison of chemical and radiogenic isotope data of lavas from the Bárðardalur region and the eruptive units north of Vatnajökull and the Bárðarbunga central volcano, it appears most likely that the lavas of Bárðardalur valley belong to the Bárðarbunga volcanic system. These new data, and a compiled dataset for other selected volcanic systems of the NRZ, shed light on possible limitations when assigning erupted material to its source volcano by means of chemical composition. Furthermore, this study demonstrates that our understanding of the relative importance of the different processes at play during the petrogenesis of Icelandic basalts is likely to be greatly improved by multi-parameter datasets for geologically well-characterized eruptive units.