1. Constraining post-glacial eruption rates of Icelandic lavas using palaeomagnetic secular variation
The post-glacial volcanism of Iceland is dominated by mafic effusive eruptions, with ~500 lavas emplaced over the past 11,000 years. The ages of the majority of these lavas are poorly constrained or unknown and this hinders our understanding of postglacial eruption rates. Although radiocarbon or other isotopic dating methods have been applied to Icelandic lavas, they are not appropriate in all cases and they are additionally time consuming and expensive. An alternative approach is to use palaeomagnetic dating. As lavas cool the magnetic moments of the iron oxides within them align with the direction of Earth’s magnetic field and acquire a moment (intensity) that is proportional to the strength of the field. Earth’s magnetic field varies in both direction and strength on timescales of centuries to millennia and these variations can be recorded by lavas. By determining the directions and intensities recorded by lavas of unknown ages and matching them to temporally continuous reference curves, the ages of the lavas can be estimated. However, the first step in this process is to develop reliable reference curves of direction and intensity for Iceland. This one year post-doc project focusses on obtaining new palaeodirectional and palaeointensity data from lavas that have good age control, with the overall aim of developing the first palaeomagnetic reference curve for Iceland.
This project will be primarily conducted at the Institute of Earth Sciences, University of Iceland, with the majority of palaeodirectional and palaeointensity analyses being made in the institute’s newly refurbished palaeomagnetism laboratory. More detailed rock magnetic analyses will be performed during visits to the palaeomagnetic laboratory in Lund, Sweden. Additional palaeointensity experiments using the microwave method will be made by the post-doc during a visit to the University of Liverpool Geomagnetism Laboratory.
Main NordVulk collaborator: Maxwell Brown
Nordic collaborator: Andreas Nilsson, Lund University, Sweden
Other collaborators: Þorvaldur Þórðarson, University of Iceland and Mimi Hill, University of Liverpool, UK.
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2. Oxygen fugacity of primitive basalt magmas in Iceland
Oxygen fugacity is an important physicochemical parameter for magma evolution. For example, it affects the crystallisation sequence of minerals, and hence compositional trends, the solubility and degassing behaviour of volatiles (e.g. that of sulphur) and the value of diffusion coefficients in common silicate systems. This important parameter is, however, poorly constrained for Icelandic magmas. Generally, it has been estimated on the basis of determination of Fe3+/SFe of glasses (e.g.: Breddam, 2002, JPet 43/2, 345–373; Shorttle et al., 2015, EPSL 427, 272-285; Hartley et al., 2017, EPSL 479, 192-205), and has been shown to be variable between different localities.
In this project, a different approach will be followed. Many primitive magmas, both from the rift zone and the off-rift regions of Iceland, contain olivine with spinel inclusions. This enables determinations of oxygen fugacity in the magmatic systems based on the composition of olivine-spinel pairs (e.g.: Ballhaus et al., 1991, CMP 107/1, 27-40; Nikolaev et al., 2016, GeochemInt 54/4, 301-320). The main advantage of this method is that following the crystallisation of these mineral pairs, the information about oxygen fugacity at the time of crystallisation is frozen into the minerals and is largely unaffected by subsequent processes. Furthermore, olivine and spinel compositions can be determined in a relatively easy, fast and cost-effective way with the use of an electron microprobe.
This project mainly involves petrographic observations and electron microprobe analyses. In order to map the spatial variation of this physicochemical parameter within Iceland, the candidate will work on a selected set of samples from the active rift zone and off-rift zones in Iceland.
Main NordVulk collaborators: Enikő Bali, Maren Kahl and Guðmundur H. Guðfinnsson, University of Iceland.
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3. Petrography and geochemistry of hydrothermally altered drill cores from Hoffell, Southeast Iceland
Southeast Iceland has experienced more erosion than other parts of Iceland, leading to exposures of volcanic rocks and intrusions from greater depths than elsewhere in the country. Hoffell is in this area near the edge of Vatnajökull glacier, where erosion has removed over 2000 meters of overburden and exposed highly altered rocks in the lower greenschist facies at the flanks of Geitafell central volcano. A number of background studies are available from the field, several PhD and MSc studies, and most recently a mineralogical study within the EU-FP7 supported IMAGE project. As a part of an exploration effort to find hot water for domestic use, a number of wells have been drilled in the vicinity of Hoffell farmhouse, including two where 102 m and 140 m of drill cores were recovered. The cores are exceptionally continuous, but have not been properly studied. They show well-developed structural and mineralogical features, including secondary mineral assemblages of greenschist facies alteration, and possibly some contact metamorphism, and superimposition of zeolite facies mineralogy. The successful applicant is expected to perform a detailed petrographic study of the cores and do some geochemical analyses, an appealing and challenging study for an interested researcher. In addition to facilities provided at the University of Iceland, the applicant will have access to the drill core research lab at the Reykjanes geothermal power plant. This study is especially timely in light of the recent successful drilling of a 4.65 km deep geothermal well into amphibolite grade rocks at Reykjanes by the IDDP consortium.
Main NordVulk collaborators: Enikő Bali and Guðmundur H. Guðfinnsson, University of Iceland.
Nordic collaborators: Guðmundur Ómar Friðleifsson at HS Orka, Iceland and Magnús Ólafsson at Iceland GeoSurvey, Iceland.