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The multi-component Hekla Ö Tephra,Iceland: a complex widespread mid-Holocene tephra layer |
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| Authors: | Daníel Freyr Jónsson Esther Ruth Gudmundsdóttir Gudrún Larsen Bergrún Arna Óladóttir Egill Erlendsson Sigrún Dögg Eddudóttir Olgeir Sigmarsson |
| Institution: | 1. Institute of Earth Sciences, Nordic Volcanological Center, University of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland
Environment Agency of Iceland, Suðurlandsbraut 24, IS-108 Reykjavík, Iceland;2. Institute of Earth Sciences, Nordic Volcanological Center, University of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland;3. Institute of Life and Environmental Sciences, University of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland;4. Department of Archaeology and Ancient History, Uppsala University, Thunbergsvägen 3H, 752 38, Uppsala, Sweden;5. Institute of Earth Sciences, Nordic Volcanological Center, University of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland Laboratoire Magmas et Volcans, CNRS – Université Clermont Auvergne, Campus Universitaire des Cézeaux, 63178 Aubière, France |
| Abstract: | Large Plinian eruptions from Hekla volcano, Iceland, produce compositionally zoned tephra used as key markers in tephrochronology. However, spatial variations in chemical composition of a tephra layer may complicate its identification. An example is the 5950–6180 cal a bp Hekla Ö tephra layer, which shows compositional spread from rhyolite, dacite and andesite to basalt. In soil sections north of Hekla, the SiO2 content of the tephra glass reaches 76 wt% in the lowest unit of the Hekla Ö deposit and decreases to 62–63 wt% in the uppermost unit. Intermingled within the whole deposit are basalt tephra grains having 46–47 wt% SiO2. The composition of the basalt glass includes primitive basalt and a more evolved basalt (MgO >6 and <6 wt%, respectively). Together with literature data, the Hekla Ö tephra and the so-called T-Tephra/Hekla-T are most likely from contemporaneous eruptions of different vents on the Hekla volcanic system, forming a single important marker tephra (Hekla ÖT) deposited over 80% of Iceland. Identification is complicated by its spatial compositional heterogeneity, such as systematic decrease in SiO2 content from the east to the west of Hekla volcano. Consequently, an individual tephra layer from a large explosive eruption can have different composition at different locations. © 2020 John Wiley & Sons, Ltd. |
| Keywords: | Hekla Iceland mid-Holocene tephrochronology zoned tephra layer |