Description
Exceptionally preserved dykes, lava flows and welded tuffs in eastern Iceland provide an ideal opportunity for interdisciplinary studies attempting to achieve a deeper understanding of the surface dynamics of volcanic processes at oceanic spreading ridges. The goal of project is a study of Neogene welded tuffs will provide valuable analogue data to recent and future eruptions of pyroclastic density currents in Iceland. Paleomagnetic and anisotropy of magnetic susceptibility (rock fabric) studies will be applied to determine flow direction and vent sources for specific volcanic deposits. The project is sequentially planned: Fieldwork in eastern Iceland to collect oriented drill cores from igneous rocks, laboratory treatment and statistical analysis and collaboration on interpretations of results. The combined expertise in rock magnetism of the project promoter (Complutense University of Madrid) and the knowledge of the geodynamics and geology of East Iceland of the donor partner (University of Iceland) maximize the outcome and ensure a high probability for success. The main beneficiaries of the project will be the scientific community.
Summary of project results
The anisotropy of the magnetic susceptibility (AMS) is a relatively fast method to measure rock fabrics. AMS studies have proven useful to determine intrusive and eruptive transport and depositional processes. Recent volcanic events in Iceland (2010 Eyjafjallajökull and 2014-2015 Bardarbunga eruptions) have impacted on the public awareness towards the need for advancement of our knowledge on many aspects of volcanic hazards. The project aimed at contributing to this knowledge by attempting to related rock fabrics of pyroclastic density currents and lava flows in the Neogene archives of eastern Iceland to eruptive transport and depositional processes. During the project, some fieldwork was performed: in Eastern Iceland, a total of 213 cores were drilled, individually oriented, and retrieved from 24 sites, including sites from all targeted geological units. Analysis of such samples was performed at the Paleomagnetic laboratory of the Complutense University of Madrid (Spain): anisotropy of magnetic susceptibility measurement (408 speciments; KLY-3 AMS rotatory, AGICO) and hysteresis runs (48 curves -2 representative samples per site-; Coercitivity-Spectrometer, Kazan University). As a result, magnetic fabric of Skessa and Bjólfur tuffs showed the higher grouping of the principal axes of the AMS ellipsoid, characterized by a markedly oblate shape, a minimum axis k3) very close to the vertical, and a foliation plane –near the horizontal- where the lineation (maximum axis, k1) is well developed with its azimuth close to that of the minimum axis k3, which indicates the sense of the pyroclastic density peleocurrent. These senses, inferred by the magnetic fabric, are generally compatible with the available geological information (except 1 of the 6 sites). In the lavas (basaltic groups Holmar and Gjrjóta), AMS ellipsoids display different degrees of clustering, with bothe prolate and oblate shape parameters, and lineations (k1 axis) dipping variably. The analysis of how paleoflow directions are recorded in different levels of these lavas was in progress at the end of the NILS period. This information will help to identify the presence of the “inverse fabrics” related to monodomain grains, characterized by paleoflow indicators orthogonal to those recorded in pseudo- and multidomain grains. Once the data interpreted, partners shall publish a scientific paper showing its results.
Summary of bilateral results
Partners worked closely together performing the fieldwork in Iceland, and carrying out the laboratory analysis in Spain. Besides, Morten Schiordan Riishus gave a talk at the University Complutense of Madrid entitled “The 2014-2015 tectonic-volcanic episode of the Bardarbunga volcanic syste,, Iceland: lateral dyke growth, fissure eruption and lava field construction”, in a seminar series of the “Meteorology and Geophysics “Master at the UCM, addressed to graduate students at the Faculty of Physics. Researchers from the IGN – National Georaphical Institute were also present. At the time of the closure of the NILS programme funding, data reduction and interpretation was still in progress. The first publication will be related to the results of volcanic tuffs (Skessa and Bjólfur). Prof. Riishus is now involved in a project by Prof. Ruiz resaerarch students Miguel García Castaño (AMS applied to a big, ~200 Ma-aged African dyke) and Julio José Costales (AMS in Miocene basalts from the Alboran Domain, northern Morocco). Potential further collaborations include working on AMS applied to the ~90 Ma granites emplacement in western Mexico. Prof. Ruiz is now also involved with prof. Riishus former Phd student Birgir V. Óskarsson (Miocene Bjólvur tuff, Eastern Iceland9.
http://pc213fis.fis.ucm.es/vcruiz_nils_project.html