NordVulk fellowships - Project list for the period 2020-2021

1. Volatiles in melt inclusions and glasses: assessing degassing processes and volatile budgets of recent Icelandic volcanic eruptions

The presence of dissolved volatiles in silicate melts strongly affects both the melt properties and the style of volcanic eruptions. Moreover, the reconstruction of volatile budgets of magmas feeding volcanic eruptions is fundamental for understanding mantle volatile systematics, as well as the potential impact on global climate (Edmonds and Wallace, 2017). Because of the strong pressure-dependent solubilities, volatile species are almost totally lost during volcanic eruptions, and therefore melt inclusions entrapped during crystal growth have mainly been used to study pre-eruptive volatile contents (e.g., Bali et al., 2018). Furthermore, volatile contents of melt inclusions can be used to estimate minimum pre-eruptive storage depths and to assess magma ascent rates.

The aim of the project is to use glasses and melt inclusions trapped in primitive crystals to gauge degassing processes, estimate pre- and syn-eruptive volatile contents (H2O, CO2, S, Cl, F) and constrain the volatile budget of selected Icelandic eruptions. The project will focus on the products of several recent eruptions from two volcanic rift zones in Iceland. Targeted samples are: (1) well-characterized Holocene sample set from the Veiðivötn fissure swarm segment of the Bárðarbunga volcanic system (Caracciolo et al., 2019); (2) from the poorly studied 13th century Fjallsendahraun (Frambruni) lava field, located north of the Vatnajökull ice cap, also associated with the Bárðarbunga volcanic system (Sigmarsson and Halldórsson, 2015); (3) from the ~950 A.D. Hallmundarhraun lava flow, located in West Iceland and originating from craters near Langjökull glacier (Sinton et al., 2005); (4) from the ~1800 B.P. Nesjahraun lava, southwest of Lake Þingvallavatn (Sinton et al., 2005). We are looking for a candidate with expertise in geochemistry, petrology and melt inclusion sample preparation. The successful applicant will perform a detailed petrographic and major element chemical characterization of the samples (both done in Reykjavík) and measure volatile contents of glasses using the ion-probe facility at the NordSIM laboratory in Stockholm, Sweden. In addition, fieldwork is required to collect samples in West Iceland.

NordVulk collaborators: Enikő Bali, Sæmundur A. Halldórsson and Guðmundur H. Guðfinnsson

Nordic collaborators: NordSIM laboratory, Stockholm, Sweden

For more information please contact: gudmhg@hi.is or eniko@hi.is

References

Bali, E., Hartley, M.E., Halldórsson, S.A., Gudfinnsson, G.H., Jakobsson, S., 2018. Melt inclusion constraints on volatile systematics and degassing history of the 2014–2015 Holuhraun eruption, Iceland. Contrib. to Mineral. Petrol. 173, 9. https://doi.org/10.1007/s00410-017-1435-0

Caracciolo, A., Bali, E., Gudfinnsson, G.H., Kahl, M., Halldórsson, S.A., Hartley, M.E., Gunnarsson, H., 2019. Temporal evolution of magma and crystal mush storage conditions in the Barðarbunga-Veiðivotn volcanic system, Iceland. LITHOS. https://doi.org/10.1016/j.lithos.2019.105234

Edmonds, M., Wallace, P.J., 2017. Volatiles and exsolved vapor in volcanic systems. Elements 13, 29–34. https://doi.org/10.2113/gselements.13.1.29

Sigmarsson, O., Halldórsson, S.A., 2015. Delimiting Bárðarbunga and Askja volcanic systems with Sr- and Nd-isotope ratios. Jökull 65, 17–27.

Sinton, J., Grönvold, K., Sæmundsson, K., 2005. Postglacial eruptive history of the Western Volcanic Zone, Iceland. Geochemistry, Geophys. Geosystems 6, 1–34. https://doi.org/10.1029/2005GC001021

 

2. Using geophysical data for an intercorrelated study of marine Ikka Fjord and the Grønnedal-Íka alkaline complex, SW Greenland

The 1325±6 Ma intrusive complex of Grønnedal-Íka in SW Greenland comprises rocks of mainly nepheline syenites and carbonatites associated with continental rifting during the Gardar rifting episode at 1.3–1.1 Ga. It forms the 500 m high mountains on the northern shore of the inner part of the marine Ikka Fjord, and is also exposed along its southern shore. Thus, the bedrock underlying inner Ikka Fjord most likely consists of nepheline syenites. In direct correlation to the outcrops of the Grønnedal-Íka complex are close to a thousand submarine columns built up by the mineral ikaite (CaCO3Ÿ6H2O) found growing over groundwater springs issuing from the bottom of the fjord. The theory is that groundwater percolating through the old and fractured Grønnedal-Íka complex dissolves minerals that lead to a sodium carbonate-enriched fluid seeping up through fractures in the seabed. When this fluid mixes with seawater, ikaite precipitates and grows upwards as the groundwater fluid has a lower density than seawater. The tallest columns grow up to 20 m to a few meters below sea surface, most likely limited by the ice coverage during wintertime and by a freshwater layer at the top of the water column. Ikka Fjord is the only place on Earth where these ikaite columns are found.

Data collected during fieldwork in Ikka Fjord in 2018 and 2019, included drone-acquired aerial photographs recorded at low tide, high-resolution multibeam echosounder bathymetry data, bedrock mapping and rock, ikaite and fluvial water samples. Fieldwork planned for 2020, includes sub-bottom profiling, hydrographic water column profiling and further drone surveys to supplement the present data sets. We are looking for a candidate with a background in marine geophysics, who can work on the data collected 2018-2019. The successful candidate will take part in the fieldwork to Ikka Fjord in June 2020.

Examples of research question to be addressed are:

- How are the distribution and size of the ikaite columns related to bedrock, structures and ground water seeps?

- How is the fjord sediment stratigraphy manifested? Does it show signs of residual carbonate from previously broken down ikaite columns?

- How is the formation of present ikaite columns related to substrate sediment cover?

Main NordVulk collaborator: Gabrielle Stockmann, Assistant Professor in Geochemistry, University of Iceland

Nordic collaborators: Richard Gyllencreutz, University Lecturer in Marine Geophysics, Stockholm University, Sweden and Erik Sturkell, Professor in Applied Geophysics, University of Gothenburg, Sweden

Other collaborators: Paul Seaman, independent geophysicist, UK

For more information please contact: gabrielle@hi.is
 

3. Geochemical and petrological variability of the Fjallgarðar volcanic ridge: constraints on the spatial and temporal evolution of off-axis Quaternary basalt formation in Central East Iceland

The Fjallgarðar Volcanic Ridge (FVR) in Central East Iceland stretches for almost 190 km from the northern border of Vatnajökull to the Slétta peninsula in the North. FVR consists of a series of interglacial and subglacially erupted volcanic strata, likely formed during dyke-fed fissure eruptions over the last 0.8 Ma. Volcanic glasses occur in pillow lavas and hyaloclastites of the glacial units. The stratigraphic evolution of flow series from individual eruptive centres, as well as the chemical and petrological variability of the dyke systems, however, remain largely unknown. A previous petrochemical study based on XRF data, suggested a temporal change from low-K basalts to high-K basalts along the entire FVR that may reflect changing magma source compositions (Helgason, 1989).

Through fieldwork and by using available samples, we propose to stratigraphically sample several sections at different locations along the entire length of FVR to elucidate its magmatic evolution by means of trace elements and radiogenic isotopes. We will test whether the stratigraphic evolution of a single fissure swam displays variations in magma sources and degrees of partial melting and the potential relation of these to jumps of the ridge axis to its current position at the Northern Rift Zone (NRZ). We will test if the along-dyke variability shows decreasing influence of enriched mantle plume material with increasing distance from the plume centre close to Vatnajökull. We will also compare these data to those available from the Kverkfjöll volcanic system which display a unique geochemical fingerprint for NRZ magmas but may not sample the same plume component as indicated by their He isotope ratios. We also suggest testing the compositional variation of basalts erupted during glacial and interglacial conditions in order to test the model of suppressed partial melting during glacial times (Jull and McKenzie, 1996; Hjartardóttir and Einarsson, 2012).

This project will be aiming at detailed sampling of the volcanic strata over the entire length of the FVR axis. The major element, trace element and Sr-Nd-Hf-Pb isotope geochemistry of whole rocks, glasses and glass inclusions from subaerial- and subglacially-erupted material will be used to determine the sources and processes of melting and melt ascent. If suitable samples are found, we will also aim at analysing He isotopes. We plan to use mineral-melt thermo-barometry to develop a model of magma stagnation in the crust and explore how changes in the melting regime may impact storage and ascent of melts through the crust.

The analytical work of the project will be performed at NordVulk (major elements, trace elements, Sr-Nd-Hf-Pb isotopes) and in Helsinki (in-situ trace element analysis of glass and glass inclusions). This project has the potential of being developed into a full PhD research project but may also suite as a one to two-year postdoctoral project.

NordVulk collaborator: Sæmundur A. Halldórsson

Nordic collaborator: Christoph Beier, professor of geochemistry, University of Helsinki, Finland

Other collaborators: Karsten Haase, professor of endogenous geodynamics, Friedrich-Alexander Universität Erlangen-Nürnberg, Germany, Jóhann Helgason, Iceland Geodetic Survey

References

Hjartardóttir, Á.R. and Einarsson, P. (2012). The Kverkfjöll fissure swarm and the eastern boundary of the Northern Volcanic Rift Zone, Iceland. Bulletin of Volcanology 74(1), 143-162. DOI: 10.1007/s00445-011-0496-6.

Helgason, J. (1989). The Fjallgardar volcanic ridge in NE Iceland: an aborted early stage plate boundary or a volcanically dormant zone? Geological Society, London, Special Publications 42, 201.

Helgason, J. (1984). Frequent shifts of the volcanic zone in Iceland. Geology 12 (4), 212-216.

Jull, M. & McKenzie, D. (1996). The effect of deglaciation on mantle melting beneath Iceland. Journal of Geophysical Research-Solid Earth 101, 21815-21828.
 

4. Graben subsidence in western Öxarfjörður

Graben subsidence often occurs as a result of shallow dike intrusions, such as the one from Bárðarbunga in 2014. However, it is unclear whether that is always the case, or whether some grabens form amagmatically.

The main aim of this project is to study the fault offsets in Öxarfjörður by using 3D bathymetric data and chirp seismic reflection data, both of which have already been acquired. The data will be processed using GIS applications. The characteristics of the faults and the accompanying graben structures will be studied and compared with grabens formed in rifting events on land in order to see whether they share similar characteristics.

NordVulk collaborators: Ásta Rut Hjartardóttir, Bryndís Brandsdóttir and Páll Einarsson

For more information please contact: astahj@hi.is or bryndis@hi.is

 

5. Magma bodies in roots of active volcanoes

One of the challenges of volcanology is to identify and improve understanding of magma bodies in roots of active volcanoes.  The project uses volcano geodesy observations in Iceland to address the nature of magma bodies in roots of active volcanoes, in combination with other data sets. These other data sets may include other types of observations at active volcanoes, observations at eroded volcanic settings, or laboratory findings.  The project will be focused towards the interest of the applicant and is expected to be carried out in international cooperation. 

NordVulk collaborator: Freysteinn Sigmundsson

For more information and further definition of project scope, please contact fs@hi.is.

 

6. The solid Earth response to climate change

Retreating ice caps cause glacial isostatic adjustment, with the resulting ground uplift depending on the viscosity structure of the Earth. Extensive observations of ongoing uplift in Iceland open the possibility for improved models of the glacial isostatic adjustment process and crustal properties, as well as a comparison of ground deformation in Iceland due to surface load changes to other areas of the world where similar changes are occurring.  The project will be focused towards the interest of applicant and is expected to be carried out in international cooperation.

NordVulk collaborator: Freysteinn Sigmundsson

For more information and further definition of project scope, please contact fs@hi.is.

 

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