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  • 1.
    Eriksson, Per
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic properties of Neogene regional dikes from east Iceland with special reference to magma flow2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with rock magnetic measurements on Neogene dikes from the eastern fjords of Iceland. A vast amount of dikes generally striking north-north-east occur as swarms in the glacially eroded lava pile. They are considered as the underlying extensions of fissure swarms in active volcanic systems which like the dike swarms converge at central volcanoes. The dike swarms and associated central volcanoes are uncovered by ca. 1500 m of glacial erosion, leaving the upper parts of these igneous units bare. Two research papers have been prepared based on field studies and measurements of rock magnetism on carefully chosen occurrences of Icelandic dikes in order to test contradicting models of dike origin. The manuscripts are included in the thesis.The first is a detail study of a single composite dike, with a core of fine grained quartz-porphyry surrounded by dolerite margins. The core of the dike was sampled in three locations, separated by ~12 km and measured for magnetic remanence and anisotropy of magnetic susceptibility. Magma flow direction in this dike was interpreted using the mirror imbrication of the minor susceptibility axes from each margin of the quartz-porphyry core of the dike. The flow regime in all three locations showed a marked flow component from north to south, supported by field evidence in the form of parabolically aligned enclaves, and shear folds. Statistical procedures of bootstrapping was utilized to define the flow and handle imbrication in both the vertical and horizontal plane thus defining direction and inclination of flow. The main contribution of this paper was to prove that anisotropy of magnetic susceptibility used to infer flow direction may give consistent and reliable results, and to present new ways (to use old techniques) to define magma flow directions.The same technique used to infer flow in paper one has sub-sequentially been applied to a far larger set of mafic dikes, extending north-east from the exhumed Álftafjörður central volcano. The second paper documents that the flow regimes from the mafic dikes showed a predominantly horizontal flow from the central volcano, supporting tectonic models that suggest shallow magma chambers to be the source of the dikes. The thesis further discusses the results from these studies in comparison to other studies on Icelandic dikes where the magma flow is determined by the direction of the major susceptibility axis.

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  • 2.
    Eriksson, Per
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Riishuus, Morten S.
    Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland.
    Sigmundsson, Freysteinn
    Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magma flow directions inferred from field evidence and magnetic fabric studies of the Streitishvarf composite dike in east Iceland2011In: Journal of Volcanology and Geothermal Research, ISSN 0377-0273, E-ISSN 1872-6097, Vol. 206, no 1-2, p. 30-45Article in journal (Refereed)
    Abstract [en]

    Anisotropy of magnetic susceptibility (AMS) and rock magnetic studies have been made on three outcrops separated by 12 km along strike (NNE–SSW) on the Streitishvarf composite dike in east Iceland. Samples for this study have been collected from the inner quartz-porphyry part of the dike, which show clear field evidence of a lateral flow component from north to south at one of the sites. This flow component is consistent with margin AMS results from all three sites. The quartz-porphyry has a substantial bulk magnetic susceptibility (10-2 SI) mainly carried by magnetically soft titanium-poor titanomagnetite (MDF 15 mT). The ferrimagnetic grains yield a characteristic remanent magnetization in all three sites which gives a virtual geomagnetic pole at latitude 52:6°S and longitude 319:6°E. The degree of anisotropy is low (PJ = 1:033) and the magnetic fabrics shifts from oblate to prolate shapes depending on dike margin and outcrop. The magnetic fabric has been interpreted according to the imbrication model, using the minor susceptibility axis as shear plane indicator. The absolute directions given by the minor susceptibility are then quantified using vector algebra. The magma flow is indicated as an upward directed flow, flowing from north to south with an inclination between 30° – 64°, with a 95% confidence ellipse of 3° – 9°. A model for the intrusion of the Streitishvarf dike has been constructed where a magma pocket with felsic magma is punctured by a mafic dike, enabling the felsic magma to rise and extend to the south within the pathway created. The results of this study confirm the applicability of AMS in studies of magma flow directions in igneous dikes of felsic composition.

  • 3.
    Eriksson, Per
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Riishuus, M.S.
    Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magma flow and palaeo-stress deduced from magnetic fabric analysis of the Álftafjörður dyke swarm: implications for shallow crustal magma transport in Icelandic volcanic systems2015In: Geological Society Special Publication, ISSN 0305-8719, E-ISSN 2041-4927, Vol. 396, p. 107-132Article in journal (Refereed)
    Abstract [en]

    Neogene regional mafic dykes extending north of the Álftafjörður central volcano in east Iceland are studied to test models of dyke swarm emplacement at spreading ridges. This is accomplished by using anisotropy of magnetic susceptibility to define fossilized magma flow regimes. The imbrication of the foliation plane, defined by the minor susceptibility axis, is used as an indicator of the flow direction. Contemporaneous shear resolved on the dyke walls may modify a pure flow-induced fabric and such shear regimes are therefore retracted. The magma flow and palaeo-stress resolved on the dykes are determined in 13 of 24 dykes. The magma flow is interpreted as subhorizontal and northwards directed away from the central volcano for nine dykes, and found to be vertical in three cases. The preferentially subhorizontal magma flow in the Álftafjörður swarm suggests that dyke propagation in this type of Icelandic volcanic system originates in shallow crustal magma chambers. The regional tectonic palaeo-stress field is deduced to cause oblique spreading across the Álftafjörður dyke swarm and govern a subhorizontal dextral shear component on the dyke planes during propagation. This interpretation is not in conflict with the left-stepping en echelon trend distribution of individual dykes relative to the trend of the swarm

  • 4.
    Rüfenacht, R.
    et al.
    Institute of Applied Physics, University of Bern.
    Murk, A.
    Institute of Applied Physics, University of Bern.
    Kämpfer, N.
    Institute of Applied Physics, University of Bern.
    Eriksson, P.
    Chalmers University of Technology, Department of Earth and Space Sciences.
    Buehler, S. A.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Division of Space Technology, SRT, Luleä University of Technology.
    Middle-atmospheric zonal and meridional wind profiles from polar, tropical and midlatitudes with the ground-based microwave Doppler wind radiometer WIRA2014In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 7, p. 4491-4505Article in journal (Refereed)
    Abstract [en]

    WIRA is a ground-based microwave Doppler spectroradiometer specifically designed for the measurement of profiles of horizontal wind in the upper stratosphere and lower mesosphere region where no other continuously running measurement technique exists. A proof of principle has been delivered in a previous publication. A technical upgrade including a new high-frequency amplifier and sideband filter has improved the signal to noise ratio by a factor of 2.4. Since this upgrade the full horizontal wind field comprising zonal and meridional wind profiles is continuously measured. A completely new retrieval based on optimal estimation has been set up. Its characteristics are detailed in the present paper. Since the start of the routine operation of the first prototype in September 2010, WIRA has been measuring at four different locations at polar, mid- and tropical latitudes (67°22′ N/26°38′ E, 46°57′ N/7°26′ E, 43°56′ N/5°43′ E and 21°04′ S/55°23′ E) for time periods between 5.5 and 11 months. The data presented in this paper are daily average wind profiles with typical uncertainties and resolutions of 10 to 20 m s−1 and 10 to 16 km, respectively. A comparison between the data series from WIRA and European Centre for Medium-Range Weather Forecasts (ECMWF) model data revealed agreement within 10% in the stratospheric zonal wind. The meridional wind profiles agree within their error bars over the entire sensitive altitude range of WIRA. However, significant differences in the mesospheric zonal wind speed of up to 50% have been found.

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