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  • 101.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Moakhar, Mohsen Oveisy
    Razi University, Kermanshah.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A palaeomagnetic and geochemical study of basic intrusions in northern Sweden2004In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 126, no 2, p. 243-252Article in journal (Refereed)
    Abstract [en]

    A palaeomagnetic and geochemical study has been performed on basic dykes in northern Sweden. The dykes and a gabbro formation were sampled in 28 sites and characteristic magnetizations could be defined in 23 of them. The dykes form a part of a swarm that trends in NE-SW to E-W. From differences in palaeomagnetic signatures and composition it is concluded that this swarm is composed of two generations of dykes, group A and B, trending in similar directions. The dykes of group A have compositions that are similar to rapakivi related dykes, while those of group B are different from most rapakivi dykes in Fennoscandia. The calculated pole positions may suggest that the group B dykes are older than those of group A and both groups intruded within the time span 1.77 Ga to 1.50 Ga. The trend of the dykes is more or less parallell to a palaeo-compressional stress field that may be expected from the collisional tectonics related to the Gothian orogeny. The intrusion of the rapakivi formations in Fennoscandia has been suggested to be related with the Gothian orogeny and the intrusion of the dykes may thus be guided by the stress field generated by the collisional tectonics.

  • 102.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pesonen, L. J.
    Leino, M. A. H.
    Khramov, A. N.
    Mikhailova, N. P.
    Krasnova, A. F.
    Merlanen, S.
    Bylund, G.
    Terho, M.
    The drift of the Fennoscandian and Ukrainian Shields during the Precambrian: a Palaeomagnetic analysis1993In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 223, no 3-4, p. 177-198Article in journal (Refereed)
    Abstract [en]

    A revised Precambrian (2.85-0.6 Ga) Apparent Polar Wander Path (APWP) for the Fennoscandian Shield, based on a new compilation and analysis of data, is presented. In fitting the APW path to successive Grand Mean Palaeomagnetic poles (GMPs), we applied the spherical spline technique originally developed by Jupp and Kent in 1987. The position and orientation of the Fennoscandian Shield during 2.85-0.6 Ga was determined from the GMPs. Major palaeoclimatological findings are used to constrain the palaeomagnetic interpretation of palaeolatitudes. The general drift of Fennoscandia, from relatively high latitudes in the late Archaean-Early Proterozoic to nearly equatorial latitudes in the Middle Proterozoic, correlates with palaeoclimatological indications that a period of cold climate was followed by one of warm climate during this time interval. From the continuous APWP the APW velocities and latitudinal drift velocities of the shield were calculated. An accumulated APW curve was also calculated. The palaeomagnetic data are irregularly distributed and some periods are rather poorly represented. This means that the calculated velocities can sometimes be artifacts of sampling. Late Archaean and Early Proterozoic (2.85-1.90 Ga) data are too sparse to make these calculations meaningful and velocity calculations are therefore restricted to data of 1.90 Ga and younger ages. The accumulated APW curve shows a number of linear segments with varying slopes, indicating sudden changes in drift rate. During the Middle Proterozoic (1.90-1.35 Ga) there was a period when the rate of APW was constant and low and that of latitudinal drift also was low. This pattern changed at ca. 1.35 Ga, and the following Middle-Late Proterozoic period can be described by rapid APW and strongly fluctuating drift velocities. Jotnian rifting and the intrusion of numerous dyke swarms (at ca. 1.25 Ga) correlate with this shift in rate. These changes are attributed to changes in plate configuration. A new database for the Ukrainian Shield is also presented, and GMPs in the 2.32-1.20 Ga range are defined. The database is still inadequate and the comparison of the Ukrainian and Fennoscandian drift histories is therefore tentative. Similarities in position, latitudinal drift and rotation during the Early-Middle Proterozoic are, nevertheless, evident. A close relationship between the shields in this period is consistent with the low APW rate of Fennoscandia, indicating that Fennoscandia may have been part of a larger continent, including the Ukraine, at that time. At ca. 1.2 Ga, the latitudinal position of Ukraine differed significantly from that of Fennoscandia, suggesting that the large shield split up between ca. 1.35 and 1.2 Ga. This would explain the change in APW rate at 1.35 Ga. The subsequent increase in rate was due to a reduction in the size of the shield. The discrepancy in palaeopositions of Fennoscandia and Ukraine at 1.2 Ga led Mikhailova and Kravchenko to suggest a late Precambrian time (1.07-0.57 Ga) for the accreation of Fennoscandia to the East European Platform (EEP). This may be correct as the rate of APW for Fennoscandia decreased in the late Precambrian, reflecting such a consolidation.

  • 103.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pesonen, Lauri
    Division of Atmospheric Sciences and Geophysics, Department of Physics, University of Helsinki.
    Recent developments in paleomagnetism and geomagnetism2009In: EOS: Transactions, ISSN 0096-3941, E-ISSN 2324-9250, Vol. 90, no 51, p. 502-Article in journal (Other academic)
  • 104.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pesonen, L.J.
    Bylund, G.
    The continental drift of the Fennoscandian Shield during the Precambrian: a palaeomagnetic analysis1993In: Vol. 5, no Suppl. 1, p. 1-2Article in journal (Other academic)
  • 105.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pesonen, L.J.
    Mertanen, S.
    DÁgrella-Filho, M.
    Continental assemblies during the proterozoic and tectonic relations between Fennoscandia and Amazonia: a palaeomagnetic reconstruction2001In: Workshop on Geology of the SW Amazonian Craton: State-of- the-art. Abstracts, Instituto de Geociências-USP , 2001, p. 150-Conference paper (Other academic)
  • 106.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pisarevsky, Sergei A.
    Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtain University.
    Layer, Paul
    Geophysical Institute, University of Alaska, Fairbanks.
    Bylund, Göran
    Department of Geology, GeoBiosphere Science Centre, Lund University.
    A palaeomagnetic and 40Ar/39Ar study of mafic dykes in southern Sweden: A new Early Neoproterozoic key-pole for the Baltic Shield and implications for Sveconorwegian and Grenville loops2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 244, p. 192-206Article in journal (Refereed)
    Abstract [en]

    We present the results of palaeomagnetic and 40Ar/39Ar studies of the Proterozoic mafic dykes in the Norrköping and Falun areas of the southern Sweden. The primary remanence of two 939 ± 3 Ma dykes is supported by the rigorous baked contact test. The remanence direction of two other dykes, one of which was previously U-Pb dated at 946 ± 1 Ma is close to the reverse direction of 939 Ma dykes. Using these results together with previously published 935 ± 5 Ma palaeomagnetic data from the Göteborg-Slussen mafic dykes and some dykes from the Falun area we calculated the mean 946 -935 Ma palaeopole for Baltica (0.9°S, 240.7°E, A95 = 6.7), which can be qualified as the key pole. Using this pole together with other date we conclude that the Grenville and Sveconorwegian loops of Laurentian and Baltican Apparent Polar Wander Paths are temporary displaced by 100-150 m.y. We propose new palaeogeographic reconstructions of Baltica and Laurentia at ca. 940 Ma and ca. 850 Ma. We also present two new Mesoproterozoic non-key poles from 1410 Ma and 1595 Ma dykes.

  • 107.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Danmarks og Grønlands Geologiske Undersøgelse, GEUS.
    Results of magnetotelluric and gravimetric measurements in western Nicaragua, central America1997In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 128, no 3, p. 647-58Article in journal (Refereed)
    Abstract [en]

    Studies a ca. 170 km long traverse running from the Pacific coast of Nicaragua in the west to the Nicaraguan Highland in the east. This part of Nicaragua is characterized by sedimentary rocks of the Pacific Coastal Plain, separated from the Tertiary volcanic rocks of the Highland by the NW-SE-trending Nicaraguan Depression. The purpose of this study is to provide electric conductivity and density constraints on geological crustal structures along the transect. This may then serve as a base for the understanding of the tectonic evolution of this part of Central America. Questions to be answered are: (1) is the Pacific coastal province an accreted terrane? (2) What is the character of the depression? Is this a hidden contact between an accreted terrane and the continental Chortis block? (3) If so, is there a different physical signature for the crust of the Pacific province compared to that of the Highlands?

  • 108.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Shumlyanskyy, Leonid
    Institute of Geochemistry, Mineralogy and Ore Formation, Kiev.
    Kravchenko, Svetlana
    Institute of Geophysics, National Academy of Sciences of Ukraine.
    New palaeomagnetic, age and geochemical data from basic dykes of the Ukrainian shield and the timing of accretion of Fennoscandia to the Ukrainian shield2008Conference paper (Other academic)
    Abstract [en]

    The east European craton (EEC) can be divided into three crustal segments, Sarmatia, Volgo-Uralia and Fennoscandia (Bogdanova, 1993). Lithological and age differences suggest that these segments have autonomous geological histories and various hypotheses have been presented for the time of formation of the EEC. Here we test a hypothesis of the Fennoscandian Shield being accreted to the Ukrainian Shield, which is a part of Sarmatia, for ca 1.8 Ga ago (Elming et al., 2001).This we do by palaeomagnetic, geochronological and geochemical studies of Palaeoproterozoic basic dykes in the Ukrainian Shield. We present palaeomagnetic results from 15 dykes and geochemical data from nine of them. The palaeomagnetic and geochemical data indicate at least three different generations of dykes and Ar39-Ar40 and U-Pb (zircon) age determinations have been done on dykes from two of these dyke generations.The calculated palaeomagnetic poles, some of the defined as key poles, are combined with poles calculated from anorthosites, gabbros and sedimentary rocks to form a ca 2.2 to 1.7 Ga sequence of apparent polar wander (APW) for the Ukrainian Shield. The tectonic reconstructions based on these palaeomagnetic data support the hypothesis that the Ukrainian Shield accreted to the Fennoscandian Shield at ca 1.8 Ga, however it later rotated into its present position relative Fennoscandia. This tectonic scenario is discussed with reference to geological data.

  • 109.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Shumlyanskyy, Leonid
    Institute of Geochemistry, Mineralogy and Ore Formation, Kiev.
    Kravchenko, Svetlana
    Institute of Geophysics, National Academy of Sciences of Ukraine.
    Layer, Paul
    Geophysical Institute, University of Alaska, Fairbanks.
    Söderlund, Ulf
    Department of Geology, GeoBiosphere Science Centre, Lund University.
    Proterozoic basic dykes in the Ukrainian shield: a palaeomagnetic, geochronologic and geochemical study – the accretion of the Ukrainian Shield to Fennoscandia2010In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 178, no 1-4, p. 119-135Article in journal (Refereed)
    Abstract [en]

    A palaeomagnetic, geochronologic and geochemical study of basic dykes in the Ukrainian Shield has been undertaken with the purpose of testing a hypothesis for timing of accretion of the Ukrainian Shield with Fennoscandia. On the basis of geological data it has been suggested that the two shields amalgamated at ca. 1900 to 1800 Ma. With this study of 11 basic dykes the palaeomagnetic database for the Ukrainian Shield is extended. The palaeomagnetic data indicate three generations of dykes. This is supported by the age data and the difference in geochemical compositions. Ages of two ca. 25 m wide dykes (Susly) in the North-Western Block of the shield have been determined, one for which a positive palaeomagnetic field test is demonstrated. The lower of the two 40Ar/39Ar hornblende ages of this dyke, 2061± 20 Ma, is similar to the U-Pb, zircon age of the granitic host rock (ca 2067 Ma, U-Pb, zircon), which suggests that the dyke intruded shortly after crystallization of the granite. Combined with the magnetization of the baked contact and that of another dyke a new ca 2060 Ma pole is presented (Plat. = 15.7o, Plon. = 182.9o, A95 = 13.7o), which may be regarded as a VGP. An U-Pb age of 1722 ± 12 Ma of baddeleyite from the Khmelnik dyke, which yields a well-defined VGP, is similar to the age of nearby anorthosite complexes. A new 1740–1770 Ma key pole for the Ukranian Shield is also presented (Plat. = 26.5o, Plon. = 169.1o, A95 = 3.9o). On the basis of palaeomagnetic and geochronological data a 2060 Ma to 1720 Ma apparent polar wander for the Ukrainian Shield is defined. This apparent polar wander is significantly different from that of Fennoscandia during the same time interval and indicates that the two shields were not in their present relative positions at ca. 1770 Ma. A scenario is here proposed where the Ukrainian Shield (and Sarmatia) collided with Fennoscandia at ca. 1900–1800 Ma and after that event, at ca. 1720–1660 Ma, it rotated approximately 43o into its present position.

  • 110.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Thunehed, Hans
    Luleå tekniska universitet.
    A seismic reflection investigation in the Skellefte District, northern Sweden1991In: Vol. 113, no 2-3, p. 258-Article in journal (Other academic)
  • 111.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Törne, Anders
    The blue road geotraverse: a magnetic ground survey and the interpretation of magnetic anomalies1976In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 98, p. 264-270Article in journal (Refereed)
    Abstract [en]

    Ground measurements of the magnetic field were carried out along a 20-km-wide zone along the Blue Road Geotraverse. In addition, a profile of high precision was measured. A large positive anomaly within the mountain area cannot be explained by anomalous magnetization of surface rocks. Optimization of theoretical models shows that it may have its origin at a depth of 30 km, indicating a rise of the Curie isothermal surface from the mountain area to the Baltic shield. The rise of the isotherm may be connected with the land uplift. Interpretation of smaller anomalies reveals the thickness of sedimentary layers

  • 112.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Widenfalk, LennartRodriguez, DionisioCentro de Investigaciones Geoscientificas, Universidad Nacional Autonoma de Nicaragua.
    Geoscientific research in Nicaragua: a Swedish-Nicaraguan joint project during the period 1981-19911998Collection (editor) (Other academic)
  • 113.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A palaeomagnetic and geochemical study of mafic dikes in northern Sweden1990In: Abstracts: Second Symposium on the Baltic Shield with Workshop on Correlation with Laurentia, Lund, Sweden June 5-7, 1990, Lund: International Geological Correlation Programme , 1990, p. 34-Conference paper (Other academic)
  • 114.
    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.

  • 115.
    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.

  • 116.
    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

  • 117.
    Ferrán, Carlos Cruz
    Luleå tekniska universitet.
    Paleomagnetic studies of Jurassic to Tertiary rocks in Jamaica and Cuba2000Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Paleomagnetic studies have been performed on Jurassic to Tertiary rocks in Cuba and Jamaica. Samples of predominantly volcanic and sedimentary rocks were collected at 73 sites and the study included 792 samples. High unblocking temperature components were identified in most samples and the NRMs are carried mainly by magnetite/titanomagnetite and hematite. For one Eocene rock formation in Cuba (the Sabaneta Formation) a positive fold test could be demonstrated and an improved precision of the mean direction after structureal correction could also be demonstrated for Palocene rocks in Jamaica (the More Town Shale Formation), however, the increased precision was not significant at a 95% confidence level. A mean pole position for the Cretaceous of Jamaica was defined from paleomagnetic data of the Summerfield and Guinea Corn Formations. From these data a paleolatitude of 20 degrees north was estimated for Jamaica with respect to the North American reference pole. The paleolatitudinal position of Jamaica was also calculated for the Paleocene (7degrees north; the More Town Shale Formation) and Eocene. (7,4 degrees north; the Richmond Formation), For Cuba a Jurassic-Cretaceous paleolatitudinal position was estimated at 9.6 degrees south (Gabbro of the ophiolite complex) and at the Eocene a latitudinal position was estimated at 21 degrees north (the Sabaneta Formation). Cuba and Jamaica rotated in a pattern that ca be explained by the eastward movement of the Caribbean Plate during the lower Cretaceous to Eocene. The latitudinal position calculated here for Cuba and Jamaica support various technique models presented on basis of geological data.

  • 118.
    Friborg, Johan
    Luleå tekniska universitet.
    Complex resistivity spectra on contaminated soils1993In: Abstracts of lectures and posters: 21:a Nordiska geologiska vintermötet 10-13 Januari 1994 Luleå / [ed] Jan-Anders Perdahl, Luleå: Högskolan i Luleå , 1993, p. 55-Conference paper (Other academic)
  • 119.
    Friborg, Johan
    Luleå tekniska universitet.
    Experimental and theoretical investigations into the streaming potential phenomenon with special reference to applications in glaciated terrain1997Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The occurrence of an electrical potential difference between the ends of a capillary tube when a fluid flows through is known as the streaming potential phenomenon. It was reported by Quincke in 1859 and was studied by Helmholtz, among others, in the nineteenth century. Its geophysical manifestation is the development of electrical potential differences in the ground when groundwater flows through porous rocks or soils. The phenomenon has been comparatively little studied in a geophysical context. The present thesis is the outcome of the author's experimental and theoretical research in the phenomenon. Natural streaming potentials, along with other electrical potentials in the ground that are present even in the absence of an artificially injected current, are also known as self-potentials (SP) or self-potential anomalies. Small-scale field measurements in the present work have demonstrated that SP observations within areas of size 0.5 m by 0.5 m appear to be approximately normally distributed. Hence a mean of such observations can be accepted as a representative value of the potential of the "point". The experimental work in the thesis was undertaken to simulate the natural phenomenon in the laboratory. An equipment to measure the streaming potentials developed across soil samples as a function of the applied pressure was designed. The total applied pressure could be varied between approximately 15 and 400 kPa. Pressure differences and electrical potential differences could be measured with an accuracy of about 0.1 kPa and 1 mV, respectively. The streaming potential developed across a sample is generally observed to be proportional to the pressure difference and the constant of proportionality is called the streaming potential coefficient C. This was determined for a number of sand and moraine samples. Two methods to estimate C from field observations of SP have been developed. The first can be regarded as a correction to observations of potentials due to water flow in slopes ("topographic SP") and the second is an active method where pumping from a well is used as a controlled source of streaming potentials. A comparison of values of C obtained from laboratory measurements and from estimates based on field observations showed that laboratory data can give reasonable estimates of the in situ value of C. Field observations of SP at several different sites have been used to illustrate the stability of the potentials over extended periods of time as long as conditions in the ground stay the same. When the appearance of an SP-anomaly changes this generally reflects significant changes in the conditions in the ground. It appears that anomalies with an amplitude exceeding about 10 mV, and probably even smaller ones, are significant. A case history illustrates the occurrence of streaming potentials in a practical field situation. It is shown that the removal of a topographic trend enhances the appearance of any local anomaly patterns present in the data. In the case under consideration these patterns reflect both variations in the electrical resistivity and presence of self-potentials not of a streaming origin. The apparent streaming potential coefficient can be obtained from a plot of SP versus elevation but it was found to vary with time due to variation in the near-surface resistivity. The streaming potential phenomenon can be described by means of the theory of coupled flows which expresses the flow (of, e.g., charge, matter or heat) as a linear combination of driving forces (gradients of , e.g., electric potential, pressure or temperature). The formulation is well suited to numerical modelling, and a detailed examination of the generation of sources of conduction current in the streaming potential problem has been made. A numerical study illustrates the calculation of conduction current source terms in a practical example. A qualitative discussion of the generation of sources of conduction current, by flow of ground water, for some simple geological models has been made to further illustrate the physical mechanisms behind the streaming potential phenomenon. Although not strictly a modelling tool, a method to estimate the limiting depth to a streaming potential source region has also been devised using the formal analogy between streaming potentials and magnetostatics and following Smith's analysis for the determination of the maximum depth to the top of a magnetised body.

  • 120.
    Friborg, Johan
    Luleå tekniska universitet.
    Laboratory investigation of the streaming potential properties of some soils from northern Sweden1997In: 3rd Nordic symposium on petrophysics: January 23-24, 1997, [Göteborg] : extended abstracts, Göteborg: Chalmers tekniska högskola , 1997, p. 16-19Conference paper (Refereed)
  • 121.
    Friborg, Johan
    Luleå tekniska universitet.
    Laboratory measurements of streaming potentials on soils at high pressure1995In: 57th EAGE conference and technical exhibition, Glasgow, United Kingdom, May 29-June 2, 1995, EAGE , 1995, p. D037-Conference paper (Other academic)
  • 122.
    Friborg, Johan
    Luleå tekniska universitet.
    Multifrequency IP-measurements and parametrization of ground impedance spectra1993Licentiate thesis, monograph (Other academic)
  • 123.
    Fyhn, Michael B.W.
    et al.
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Dahl-Jensen, Trine
    Geological Survey of Denmark and Greenland.
    Weng, Willy
    Geological Survey of Denmark and Greenland.
    Bojesen-Koefoed, Jørgen A.
    Geological Survey of Denmark and Greenland.
    Nielsen, Tove
    Geological Survey of Denmark and Greenland.
    Geological assessment of the East Greenland margin2012In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 26, p. 61-64Article in journal (Refereed)
  • 124.
    Gaina, Carmen
    et al.
    Geological Survey of Norway.
    Werner, Stephanie C.
    PGP, School of Geosciences, University of Oslo.
    Saltus, Richard W.
    USGS, Denver, CO.
    Maus, Stefan
    CIRES, University of Colorado, NOAA's National Geophysical Data Center, Boulder, CO.
    Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic2011In: Geological Society Memoir, ISSN 0435-4052, E-ISSN 2041-4722, Vol. 35, p. 39-48Article in journal (Refereed)
    Abstract [en]

    New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain.

  • 125.
    Gong, Zheng
    et al.
    Department of Geology and Geophysics, Yale University.
    Evans, David A.D.
    Department of Geology and Geophysics, Yale University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Söderlund, Ulf
    Department of Geology, Lund University.
    Salminen, Johanna M.
    Department of Geosciences and Geography, University of Helsinki.
    Corrigendum to "Paleomagnetism, magnetic anisotropy and U-Pb baddeleyite geochronology of the early Neoproterozoic Blekinge-Dalarna dolerite dykes, Sweden" [Precambrian Res. 317 (2018) 14-32]2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 320, p. 484-485Article in journal (Refereed)
    Abstract [en]

    The authors regret that the incorrect version of Table 3 Fig. 12 appeared in the paper. The corrected Table 3 and Fig. 12 are presented below. In Table 2, Group A mean direction should be Dec = 128.8° Inc = 39.6° α95 = 6.5° and Group B mean direction should be Dec = 127.6° Inc = 65.4° α95 = 9.7°. These changes do not affect any main conclusion of the paper. The authors would like to apologize for any inconvenience caused.

  • 126.
    Gong, Zheng
    et al.
    Department of Geology and Geophysics, Yale University.
    Evans, David A.D.
    Department of Geology and Geophysics, Yale University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Söderlund, Ulf
    Department of Geology, Lund University.
    Salminen, Johanna M.
    Department of Geosciences and Geography, University of Helsinki.
    Paleomagnetism, magnetic anisotropy and U-Pb baddeleyite geochronology of the early Neoproterozoic Blekinge-Dalarna dolerite dykes, Sweden2018In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 317, p. 14-32Article in journal (Refereed)
    Abstract [en]

    Paleogeographic proximity of Baltica and Laurentia in the supercontinent Rodinia has been widely accepted. However, robust paleomagnetic poles are still scarce, hampering quantitative tests of proposed relative positions of the two cratons. A recent paleomagnetic study of the early Neoproterozoic Blekinge-Dalarna dolerite (BDD) dykes in Sweden provided a 946-935 Ma key pole for Baltica, but earlier studies on other BDD dykes discerned large variances in paleomagnetic directions that appeared to indicate more complicated motion of Baltica, or alternatively, unusual geodynamo behavior in early Neoproterozoic time. We present combined paleomagnetic, rock magnetic, magnetic fabric and geochronological studies on BDD dykes in the Dalarna region, southern Sweden. Positive baked-contact and paleosecular variation tests support the reliability of the 951-935 Ma key pole (Paleolatitude = -2.6°N, Paleolongitude = 239.6°E, A95 = 5.8°, N = 12 dykes); and the ancient magnetic field was likely a stable geocentric axial dipole at that time, based on a positive reversal test. Detailed analysis of the 947 Ma Nornäs dyke, one of the dykes previously showing anomalous directions, suggests a partial viscous remagnetization. Therefore, the observed large variances in nearly coeval BDD dykes are suspected to result from present-day overprints that were not adequately removed in earlier studies. In addition, we obtained a 971 Ma virtual geomagnetic pole (Paleolatitude = -27.0°N, Paleolongitude = 230.4°E, A95 = 14.9°, N = 4 dykes) for Baltica. Comparing similar-aged poles from Laurentia, we suggest that Baltica and Laurentia drifted together from high to low latitude between 970-960 Ma and 950-935 Ma, and returned back to high latitude by 920-870 Ma. In this scenario, the apparent polar wander paths of Baltica and Laurentia may be more complicated than the previously proposed, solitary Sveconorwegian and Grenville loops. The new U-Pb baddeleyite ages do not support BDD dykes as a giant circumferential swarm generated by a mantle plume, and the prolonged timespan of dyke intrusion is likely associated with the plate boundary forces as causing gravitational extension at the waning stage of the Sveconorwegian orogeny.

  • 127.
    Gonzalez, Gustavo A
    Luleå tekniska universitet.
    Geological modelling based on gravity and magnetic measurements in the Northern Part of the Nicaraguan depression1991Licentiate thesis, monograph (Other academic)
  • 128.
    Granlund, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Estimation of snow wetness using multi-offset ground penetrating radar: towards more accurate estimates of snow water equivalent2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Measurements of snow water equivalent (SWE) constitute an important input to hydrological models used to predict snowmelt runoffs. The new generation of such models use distributed snow data, including distribution of SWE, as input, and rely on it for calibration and validation. Using ground penetrating radar (GPR) from snowmobiles or helicopters is one of the methods to estimate SWE, and it allows for covering large areas in a short period of time. However, the accuracy offered by GPR is detrimentally affected by the presence of liquid water in the snow. This is a problem since when a snowpack is at its peak, and therefore of the largest interest, it has quite often started to melt so there might be liquid water in the snowpack. The present work is an attempt to solve this problem for SWE estimates made by multi-offset GPR operated from a snowmobile. The main idea is to use radar data already available, and to utilize, in addition to two-way travel time, radar wave attenuation, which both depend on snow wetness. Thus obtained liquid water content of a snowpack can be used to get more accurate estimates of SWE.Using radar wave attenuation to obtain liquid water content requires the relationship between liquid water content and electrical conductivity, which has to be established experimentally. The results of several series of experiments, first establishing this relationship for a specific salt content, and then confirming that variation in salt content does not significantly affect it, are presented in this work.However, there remains another problem to be solved. Attenuation caused by energy dissipation in the snow can only be determined from measured radar wave amplitude if losses due to reflection at the snow/ground interface are known. Since a multi-offset GPR system is in fact an array of antennas, several measurements can be made at each point with radar waves reflecting from the ground with different angles of incidence. It should therefore be possible to calculate angle-dependent reflectivity from radar wave amplitudes using Snell's law and one of Fresnel equations. However, applicability of this method in the presence of measurement errors has to be verified. Initial experiments point to problems due to antenna ring-down from the direct wave interfering with the reflected wave, so further tests of the method should be conducted, or ultimately another method to determine reflectivity of the snow/ground interface should be found. Theoretical and experimental results presented in this thesis lead to the conclusion that when SWE is estimated with a multi-offset GPR system, radar wave amplitudes, available in radar data, can be used to establish liquid water content of a snowpack and hence improve the accuracy of SWE estimates, provided that the problem with establishing reflectivity of the snow/ground interface is solved.

  • 129.
    Guarnieri, Pierpaolo
    et al.
    GEUS, Geological Survey of Denmark and Greenland, Copenhagen.
    Brethes, Anaïs
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geometry and kinematics of the Triassic rift basin in Jameson Land (East Greenland)2017In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 36, no 4, p. 602-614Article in journal (Refereed)
    Abstract [en]

    The Triassic rift basin along the east Greenland margin described in this paper is represented by NE-SW trending basins and highs segmented by NW-SE trending transfer zones. Coarse-grained sediments along the eastern side of Jameson Land are shown to be hosted in half-graben structures belonging to the Carlsberg Fjord Basin that is bounded by NW dipping normal faults mapped and described after fieldwork in the Klitdal area in Liverpool Land. New aeromagnetic and electromagnetic data together with new drill cores allow the reinterpretation of available seismic lines showing the continuation of the Triassic rift basin toward the SW where it is buried under the Upper Triassic postrift sediments and the Jurassic successions of the Jameson Land Basin. The N-S trending Liverpool Land, interpreted as the boundary block of the Triassic basin, is shown to represent a structural high inherited from the Late Carboniferous tectonics and faulted during the Triassic rifting. The Carlsberg Fjord Basin and the Klitdal Fault System described in this paper should be seen as analogues to the Helgeland Basin in the Norwegian offshore that is bounded by the Ylvingen Fault Zone and to the Papa and West of Shetlands Basins that are bounded by the Spine Fault. The Triassic rift zone and transfer faults on both conjugate margins show a straightforward correlation with the trends of the initial spreading line and fracture zones of the northeast Atlantic indicating a possible inheritance of the Triassic rifting

  • 130.
    Hammarsten, Michael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    A statistical study of incoherent scatter plasma line enhancements during the International Polar Year ’07-’08 in Svalbard2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There was a large radar campaign during 2007 and 2008, the International Polar Year (IPY),and at that time the EISCAT Svalbard Radar was operated and measured the ionosphere continuouslyat most times. This report presents statistical results from an electron enhancementpoint of view. Until now there has been some research into the field and results based on theions in the ionosphere, and the enhancements we refer to as Naturally enhanced ion acousticlines (NEIALs). Plasma line data from May 2007 to February 2008 has been analysed inorder to find and classify enhancements as NEIALs have been classified but with respect tothe electron distribution instead of the ion distribution. A method of detection was developedin order to differentiate the enhancements from the background with a relation between theminimum and maximum power of each measured dump. Results show that there is a largedifference between the downshifted plasma lines and the upshifted plasma lines, both has arange distribution peak at 180 km and the upshifted plasma line has another peak at 230 kmwhich the downshifted plasma line does not. The occurrence rate of the enhancements was1.64 % for the downshifted plasma line and 4.69 % for the upshifted plasma line. Threedifferent types of enhancements are classified using the variance distribution for the peakfrequency of that detected dump, Single, Profile, and Diffuse. The Single enhancements havea bit different spectral, range, and time of day distributions than of the Profile and Diffusedistributions. The Diffuse classifications are mostly wrong classifications and aliasing and itis very similar to Profile enhancements as seen by its distribution.

  • 131.
    Ingri, Johan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Suteerasak, Thongchai
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Widerlund, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Sequestering of phosphorus during freshening of a silled marine basin: Role of manganese2011Conference paper (Other academic)
  • 132.
    Ingri, Johan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Widerlund, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Suteerasak, Thongchai
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Susanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Changes in trace metal sedimentation during freshening of a coastal basin2014In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 167, p. 2-12Article in journal (Refereed)
    Abstract [en]

    Holocene freshening has turned the Bothnian Bay, northern Baltic Sea into an oligotrophic basin. Sequestering of trace elements has changed significantly during the oligotrophication process. In principle, trace metals have been transferred from permanently buried sulfides to Fe–Mn-oxyhydroxides in the top layers of the sediment. The oxyhydroxide layers restrict the flux of trace metals from the sediment to the oxic bottom water. Hence, Fe–Mn cycling in the suboxic sediment enriches a number of trace metals in the surface sediment. Arsenic, Sn, Ge and Bi show enrichment in the Fe-oxyhydroxide layer, whereas Mo, Cd, Ni, Co, Cu, and Sb are enriched in the uppermost Mn-oxyhydroxide layer. This natural redox cycling in the sediment obscures pollution effects.The oligotrophication process started approximately 3500 years ago, reflected in decreasing deposition of Zn, a proxy for phytoplankton production, and formation of Mn oxyhydroxide layers. Similarly, Ba/Al data indicate a decrease in the pelagic input of plankton. Barium data also suggest that dissolved sulfide in the sediment never reached high concentrations. Germanium is closely related to Ba, suggesting that Ge can be used as a proxy for phytoplankton production. Vanadium, U, Re, and Mo all indicate that the bottom water never has been significantly sulfidic during the last 5500 years. Rhenium data indicate that the organic carbon oxidation rate has decreased during the last 5500 years. Cadmium follows the organic matter distribution, but started to increase 1000 YBP (years before present). The reason for this enhanced input of Cd is unclear.

  • 133.
    Jensen, Mai-Britt Mose
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geophysical tools for prognosis of deformation in hardrock environments2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Underground mining of the Kiirunavaara iron mineralization is causing large-scale deformation of the hangingwall of the orebody. To understand and possibly predict future deformation, a structural model of the hanging wall and a good understanding of the petrophysical and mechanical properties of the constituent rocks is necessary. This thesis presents results from the study of Anisotropy of Magnetic Susceptibility (AMS), magneto-mineralogy, fracture frequency (F/m), rock quality (RQD), rock strength (Point Load) and P-wave velocity and anisotropy of the rocks from the hanging wall, as well as seismic reflection surveying and gravity modelling. The results are combined into a structural model of the hanging wall and further used for analysis of the correlation between petrophysical and rock mechanical parameters.In total, 76 samples from 12 outcrops and 295 samples from three drillcores in the hanging wall have been included in the AMS study. Axial and diametrical P-wave velocity was measured on 25 water-saturated samples and 156 samples were used for the Point Load tests. F/m and RQD data for the drillcores already existed. The drillcores are located along the eastern end of the seismic profiles and consist of both crystalline and sedimentary rocks.A high degree of magnetic anisotropy observed in the crystalline rocks indicates a low degree of metamorphism. AMS data also indicates the presence of a magnetic foliation in the rocks. The dip of the magnetic foliation plane (F) and the degree of magnetic anisotropy (Pj) measured in samples from outcrops was plotted as iso-maps and shows that both F and Pj decreases towards the east, which was confirmed by data from the drillcores. The decrease in both parameters is primarily a reflection of a change in rock type, but is also changing within the crystalline rock sequence.A good correlation (r > 0.6) between Pj, and F and RQD, and F and F/m was observed in one drillcore for both crystalline and sedimentary rocks; and between the shape parameter (T) and F/m in crystalline rock in another drillcore. This suggests the AMS parameter may be used as an indicator of rock mechanical properties. AMS data was also correlated to joint strike orientations and it was concluded that AMS can also be used to predict joint orientation.Two parallel reflection seismic profiles were shot within the town of Kiruna i order to locate deformation zones and lithological boundaries in the hangingwall. No deformation zones were found, but five seismic reflectors corresponding to five lithological boundaries were located, and their strike and dip calculated. The result of the seismic survey was used to constrain the gravity model, as was density measurements of 230 samples from the drillcores. The gravity model has a depth of three km, and indicates that the crystalline rock in the hanging wall can be separated into two parallel N-S trending blocks.

  • 134.
    Jensen, Mai-Britt Mose
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The Kirunavaara hangingwall: a geophysical and petrophysical analysis2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Underground mining of the Kirunavaara iron mineralization is causing large-scale deformation of the hangingwall of the orebody. To understand and possibly even predict this deformation, a good understanding of the elastic and mechanical properties of the rocks in the hangingwall is necessary. This thesis presents results from the study of Anisotropy of magnetic susceptibility (AMS), magneto-mineralogy, fracture frequency (FF), and rock quality (RQD). If a link can be found between AMS and the rock mechanical parameters FF and RQD, AMS may serve as a cheap tool for a rough indicator of rock mechanical properties. Two parallel reflection seismic profiles were shot within the town of Kiruna in order to locate deformation zones and lithological boundaries in the hangingwall. This work was done in cooperation with Uppsala University. AMS, FF and RQD data was obtained from three drillcores in the hangingwall and 13 outcrops. The drillcores are located along the southernmost of the seismic profiles. The AMS study showed that the magnetic fabric varies very much between rock types, and even within what has previously been thought of as homogeneous porphyry. Based on the magnetic fabric, 5 sub-groups of porphyries (group I-V) were identified. Results of the magneto-mineralogy study further indicate that magnetite controls the magnetic susceptibility of not just the porphyries, but all the rock types in the Kirunavaara hangingwall. The only exception is the paramagnetic type IV porphyry. Data from outcrops show a decrease in the dip of the magnetic foliation plane (F) and the degree of magnetic anisotropy (Pj) towards the east, and this was confirmed by data from drillcores. The decrease in dip also corresponds to previous studies of the structural geology in the area. For the porphyries, a qualitative correlation was found between the FF and the magnetic shape parameter (T), but no solid correlation could be established between the RQD and Pj, F or T. The magnetic data suggests that the rocks in the uppermost part of the Kirunavaara hangingwall (down to 151-185m) have been subjected to shearing while deeper rocks (below 151-185m) show signs of folding. This sub-horizontal layering is also observed in the magneto-mineralogy and RQD-data. A possible explanation is that the porphyries of the Kirunavaara hangingwall originate from (at least) two different lava-flows, the resultant rocks having a different mineralogical composition and thus different magnetic and rock mechanical properties. Five seismic reflectors, corresponding to five lithological boundaries, were located, and their strike and dip calculated. What appears to be the upper part of the Kirunavaara mineralization was also mapped, as a bonus. Tomographic modelling of first arrivals indicates the position of low velocity (deformation) zones in the near-surface, down to 200m.

  • 135.
    Jensen, Mai-Britt Mose
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic, seismic and mechanical properties of porphyritic meta-rhyolites: The effect of microscopic foliation on rock strength and P-wave velocity in drillcores2013In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 157, p. 93-102Article in journal (Refereed)
    Abstract [en]

    Seismic velocity and rock strength in drillcores has previously been shown to vary depending on the angle between the measuring direction and the macroscopic foliation plane, but very little research has been performed on samples with a microscopic foliation. In this study, we use the anisotropy of magnetic susceptibility (AMS) to identify a foliation in what has been assumed to be isotropic rhyolites. We then use scatterplots and simple linear regression analysis to identify and quantify the relationships between AMS, diametrical P-wave velocity and point load (PL) strength in the ferromagnetic samples. Our study suggests that the PL strength increases with 56% when the angle between the foliation plane and the measuring direction is increased from 14° (close to the foliation plane) to 65°. Such a high change in rock strength with direction, in rocks with no macroscopic foliation, could have serious implication e.g. in rock mechanical modeling, and AMS can thus be used as a tool predict fracturing

  • 136.
    Jensen, Mai-Britt Mose
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kashubin, A.
    Department of Earth Sciences, Uppsala University.
    Juhlin, C.
    Department of Earth Sciences, Uppsala University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tomographic modelling and petrophysical measurements for locating weakness zones in bedrock, Kiruna, Sweden2011Conference paper (Refereed)
  • 137.
    Jensen, Mai-Britt Mose
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kashubin, Artem S.
    Department of Earth Sciences, Uppsala University.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Multidisciplinary study of the hanging wall of the Kiirunavaara iron ore deposit, northern Sweden2012In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 6, p. B269-B285Article in journal (Refereed)
    Abstract [en]

    Potential weakness zones due to mining-related fracture development under the town of Kiruna, Sweden, have been investigated by integration of seismic, gravity, and petrophysical data. Reflection seismic data were acquired along two subparallel 2D profiles within the residential area of the town. The profiles of ~3.5 km, each oriented approximately east-west, nearly perpendicular to the general strike of the local geology, crossed several contact zones between quartz-bearing porphyries, a sequence of interchanging sedimentary rocks (siltstone, sandstone, conglomerate, and agglomerate), and metabasalt. The resulting reflection seismic sections revealed a strong east-dipping reflectivity that is imaged down to approximately 1.5 km. The location and orientation of major features agree well between the profiles and with the surface geology and known contact zones between the different rock types. Our imaging results, supported by traveltime modelling, indicate that the contact zones dip 40°-50° to the east. The deepest and the weakest reflections are associated with a ~60° dipping structure that is presumably related to the Kiirunavaara iron mineralization. Tomographic inversion of refracted arrivals revealed a more detailed image of the velocity distribution in the upper 100-200 m along the profiles, enabling us to identify near-surface low velocity zones. These could be possible weakness zones developed along the lithological contacts and within the geologic units. The structural image obtained from the seismic data was used to constrain data inversion along a 28 km long east-northeast to west-southwest-oriented gravity profile. The resulting density model indicates that the quartz-bearing porphyry in the hanging wall of the Kiirunavaara mineralization can be separated into two blocks oriented parallel to the ore body. One block has an unexpected low density, which could be an indication of extensive fracturing and deformation.

  • 138.
    Johansson, Linnéa
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Modelling and interpretation of VTEM data from Soppero, Sweden2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The geological and geophysical knowledge about the northernmost part of Sweden has recently increased due to the Barents project, which includes acquisition of modern geophysical and geological information on behalf of the Swedish Geological Survey (SGU). During August 2013, a helicopter-borne versatile time domain electromagnetic (VTEM) survey was performed by Geotech Ltd, in the Soppero area northeast of Kiruna. From the VTEM measurements, a number of TEM anomalous zones have been identified and two of them are located south and southeast of the Lannavaara village. The main conductive features in the Lannavaara area can be explained by the presence of graphitic schist, which is spatially associated with a number of sulphide and iron oxide mineralisation occurrences. In this project, Maxwell thin sheet modelling and EM Flow conductivity-depth-imaging (CDI) software have been applied to selected anomalies in the Lannavaara area, for the purpose of extracting geometrical parameters of conductive features. This information has been used in order to confirm the structural framework of the area and evaluate the utility of VTEM measurements in this geological environment. In general, Maxwell thin sheet models of anomalies with small amplitudes show a better correlation with existing drill holes than models of anomalies with large amplitudes. The use of small amplitudes managed to confirm the structural model in the central part of the investigated area, which is an anticline. However, the use of different models and their distribution across the area is limited. Compared with Maxwell, CDIs from EM Flow provided a better way of confirming the general structural model in the area, although they include artefacts due to strong lateral gradients in conductivity. The Lannavaara area has also been investigated by VLF, Slingram and magnetic measurements and based on these data, multivariate analysis in SiroSOM reveals a strong correlation between VTEM and Slingram data, while VLF data appears to have much less or more complicated correlation with the other data sets. In summary, the results from the various software raise a question about the geological complexity in parts of the Lannavaara area, which may include multiple layers of graphitic schist, possibly expressed as smooth transitions in conductivity when represented by data from electromagnetic methods.

  • 139.
    Jokat, Wilfried
    et al.
    Ayred Wegener Institute for Polar and Marine Research.
    Uenzelmann-Neben, Gabriele
    Ayred Wegener Institute for Polar and Marine Research.
    Kristoffersen, Yngve
    Ayred Wegener Institute for Polar and Marine Research.
    Rasmussen, Thorkild Maack
    Ayred Wegener Institute for Polar and Marine Research.
    Lomonosov Ridge: a double-sided continental margin1992In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 20, no 10, p. 887-890Article in journal (Refereed)
    Abstract [en]

    The first two traverses of marine multichannel seismic data across the Lomonosov Ridge (central Arctic), by the German research icebreaker Polarstern and the Swedish icebreaker Oden, demonstrate a prograded margin toward the Amerasian side and fault-bounded half grabens toward the Eurasian side of the ridge. Nearly 450m of undisturbed flat-lying strata have been deposited on top of the peneplaned ridge since it rifted from the Barents-Kara Sea margin and subsided below sea level in early Tertiary time (64-56 Ma) .

  • 140.
    Jokat, Wilfried
    et al.
    Ayred Wegener Institute for Polar and Marine Research.
    Weigelt, Estella
    Ayred Wegener Institute for Polar and Marine Research.
    Kristoffersen, Yngve
    University of Bergen, Institut for Solid Earth Physics.
    Rasmussen, Thorkild Maack
    University of Uppsala.
    Schöne, Tilo
    University of Uppsala.
    New geophysical results from the south‐western Eurasian Basin (Morris Jesup Rise, Gakkel Ridge, Yermak Plateau) and the Fram Strait1995In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 123, no 2, p. 601-610Article in journal (Refereed)
  • 141.
    Jokat, Wilfried
    et al.
    Ayred Wegener Institute for Polar and Marine Research.
    Weigelt, Estella
    Ayred Wegener Institute for Polar and Marine Research.
    Kristoffersen, Yngve
    University of Bergen, Institut for Solid Earth Physics.
    Rasmussen, Thorkild Maack
    University of Uppsala.
    Schöne, Tilo
    University of Uppsala.
    New insights into the evolution of the Lomonosov Ridge and the Eurasian Basin1995In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 122, no 2, p. 378--392Article in journal (Refereed)
  • 142.
    Juhlin, C.
    et al.
    Uppsala University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mellqvist, C.
    SGAB Analytica.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Wikström, A.
    Geological Survey of Sweden.
    Crustal reflectivity near the Archean-Proterozoic boundary in northern Sweden and implications for the tectonic evolution of the area2002In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 150, no 1, p. 180-197Article in journal (Refereed)
    Abstract [en]

    Sm–Nd isotope ratios of 1.9–1.8 Ga granitoids delineate the Archaean–Proterozoic boundary in northern Sweden, an important feature in the Fennoscandian Shield. The boundary strikes approximately WNW–ESE and is defined as a c. 20 km wide zone with juvenile Palaeoproterozoic rocks to the SSW and Archaean and Proterozoic rocks, derived to a large extent from Archaean sources, to the NNE. It therefore constitutes the strongly reworked margin of the old Archaean craton. Extrapolation of the boundary offshore into the Bothnian Bay and correlation with the marine reflection seismic BABEL Lines 2 and 3/4 indicates that the boundary dips to the south-southwest, consistent with interpretation of the Sm–Nd data. In order to tie the BABEL results with onshore surface geology and obtain detailed images of the uppermost crust a short (30 km of subsurface coverage) pilot profile was acquired in the Luleå area of northern Sweden during August 1999. The profile consisted of a high-resolution shallow component (1 kg shots) and a lower-resolution deep component (12 kg shots). Both components image most of the reflective crust, with the deep component providing a better image below 10 s. Comparison of signal penetration curves with data acquired over the Trans-Scandinavian Igneous Belt (a large batholith) indicate the transparent nature of the crust there to be caused by geological factors, not acquisition parameters. Lower crustal reflectivity patterns on the Luleå test profile are similar to those observed on the BABEL lines, suggesting the same lower crust onshore as offshore. Interpreted Archaean reflective upper crust in the NE extends below more transparent Proterozoic crust in the SW. This transparent crust contains a number of high-amplitude reflectors that may represent shear zones and/or mafic rock within granite intrusions. A marked boundary in the magnetic field in the SW has been interpreted as being the result of a gently west-dipping contact zone between meta-sediments and felsic volcanic rocks, however, the seismic data indicate a near-vertical structure in this area. By correlating the onshore and offshore seismic data we have better defined the location of the Archaean–Proterozoic boundary on the BABEL profiles. Our new interpretation of the crustal structure along the northern part of the BABEL Line 2 shows a more bi-vergent geometry than previous interpretations. Comparison of the re-interpreted crustal structure in northern Sweden with that found in the Middle Urals shows several similarities, in particular the accretion of a series of arcs to a stable craton. Based on this similarity and geological data, we deduce that a continental arc accreted to the southwestern margin of the Archaean craton at c. 1.87 Ga. Shortly thereafter, the Skellefte island arc underthrust the continental arc owing to a collision further to the southwest resulting in the bi-vergent crustal structure observed today.

  • 143.
    Korja, Toivo
    et al.
    Department of Geophysics, University of Oulu.
    Hjelt, Sven-Erik
    Department of Geophysics, University of Oulu.
    Koivukoski, K.
    Department of Geophysics, University of Oulu.
    Rasmussen, Thorkild Maack
    Department of Geophysics, University of Uppsala.
    Roberts, Roland G.
    bDepartment of Geophysics, University of Uppsala.
    The geoelectric model of the POLAR Profile, Northern Finland1989In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 162, no 1-2, p. 113-133Article in journal (Refereed)
    Abstract [en]

    Electromagnetic soundings have been made in order to construct a geoelectrical (conductivity) model of the crust along the European Geotraverse (EGT) POLAR Profile. Forty magnetotelluric (MT) soundings, eighteen audiomagnetotelluric (AMT) soundings and ten magnetohydrodynamic (MHD) soundings were made on the main POLAR Profile (POLAR I) and ten more MT soundings on a parallel profile (POLAR II), 40 km to the southeast of the main profile. Analysis of simultaneous recordings by the EISCAT magnetometer chain, and thin-sheet modelling of the effect of the Barents Sea, indicate that neither the source field effects nor the presence of the ocean are significant at periods below 200 s in the measurement area. The magnetotelluric data have been modelled with two-dimensional models representing the regional structure along the profiles. In addition to the regional structure, a thin inhomogeneous surface layer is included in the models in order to explain some local features of the measured response functions. Although details of the surface electrical structures are poorly resolved, the gross features of the geoelectrical cross section are considered to be reliable. The results divide the POLAR Profile into three different blocks. The better conducting Karasjok-Kittilä Greenstone Belt in the south has an average resistivity of less than 10 Ωm. The more resistant Lapland Granulite Belt, with a resistivity between 100 and 200 Ωm, is underlain by conductive (< 5 Ωm), N-dipping layers. The depth for the uppermost conductive layer varies from a few kilometres in the southwestern part of the granulite belt to 13 km in the northeastern part, from where it rises steeply towards the surface close to the boundary between the Lapland Granulite Belt and the Inari Terrain. These features appear to be continuous between the two parallel MT profiles. Within the Inari Terrain a conductive zone at an approximate depth of 10 km and with a resistivity of about 20 Ωm was identified in a resistive upper crust. The geoelectric cross section agrees, in gross detail, with the corresponding gravity, refraction seismic and reflection seismic cross sections of the POLAR Profile. All methods indicated a similar shape for the southwestern part of the Lapland Granulite Belt i.e., granulites have a gently NE-dipping boundary against the underlying Karelian Province. In the northeastern part of the granulite belt the geoelectric model and the gravimetric model show a rather steep S-dipping boundary against the Inari Terrain northeast of the granulite belt.

  • 144.
    Korstgård, John A.
    et al.
    Department of Earth Sciences, University of Aarhus.
    Stensgaard, Bo Møller
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland2006In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 11, p. 179-184Article in journal (Refereed)
    Abstract [en]

    Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Archaean and Palaeoproterozoic ages occur with metamorphic grade varying from low amphibolite facies to granulite facies. The determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 Ga Kangâmiut dyke swarm along a NNE trend. In Archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. Along Itilleq strong shearing in an E-W-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. Within this Itivdleq shear zone Kangâmiut dykes follow the E-W shear fabrics giving the impression that dykes were reoriented by the shearing. However, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. Metamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern Nagssugtoqidian orogen. Here a zone of strong deformation, the Ikertôq thrust zone, coincides roughly with the amphibolite-granulite facies transition. Total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. Even the nature of facies transitions is apparent. Static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt.

  • 145.
    Legchenko, Anatoly V.
    et al.
    IRD Institut de Recherche pour le Developpement, Paris.
    Girard, Jean François
    BRGM, Orleans.
    Perttu, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Vouillamoz, Jean Michel
    IRD/UJF-Grenoble-1/CNRS/G-INP-UMR LTHE, Grenoble.
    Baltassat, Jean Michel
    BRGM, Orleans.
    Morlighem, S.
    VALE.
    Experimental verification of advanced SNMR modeling2014Conference paper (Refereed)
    Abstract [en]

    Whatever would be the practical implementation of Surface Nuclear Magnetic Resonance (SNMR) survey, inversion is based on forward modeling of the magnetic resonance response. Consequently, the mathematical model is a crucial point for inversion. We have developed advanced mathematical model that allows computing magnetic resonance signal from 3D targets both in FID (free induction decay) and SE (spin echo) modes. This model takes into account both time and lateral variations of the earth's magnetic field, water temperature and electrical resistivity of the subsurface but also the effect of magnetic rocks on MRS signal. For experimental verification of the modeling routine we used two bulk water reservoirs. One-dimensional (1-D) measurements were performed in winter from the ice surface in the Baltic Sea (Sweden) and 3-D verification was made using an artificial water pool located in the southern part of the New Caledonia Island. Modeling was carried out taking into account reservoir geometry and local conditions obtained from independent measurements. We have found a good correspondence between observed and theoretical signals for both FID and SE measurements. At our knowledge, SNMR modeling was never compared with field data obtained under all mentioned above conditions

  • 146.
    Leytón, Brenda
    Luleå tekniska universitet.
    Geophysical studies and image analysis in Northeastern Nicaragua, Central America1994Licentiate thesis, monograph (Other academic)
  • 147.
    Leytón, Brenda
    Luleå tekniska universitet.
    Geophysical studies and image analysis of a mining region in Nicaragua1993In: Abstracts of lectures and posters: 21:a Nordiska geologiska vintermötet 10-13 Januari 1994 Luleå / [ed] Jan-Anders Perdahl, Luleå: Högskolan i Luleå , 1993, p. 112-Conference paper (Other academic)
  • 148.
    Lindqvist, Gustaf
    Luleå tekniska universitet.
    Applied Geophysics in Norden1985In: The Leading Edge, ISSN 1070-485X, E-ISSN 1938-3789, no 4, p. 68-69Article in journal (Refereed)
    Abstract [en]

    The five countries comprising the area now known as Norden are Denmark, Finland, Iceland, Norway, and Sweden. Scandinavia is a part of Norden and it includes Norway, Sweden and Denmark. Associated with Denmark are the Faroe Islands and Greenland. The population of Denmark and Finland is around 5 million each, Norway is 4 million, and Sweden 8 million. The outlying islands have small populations: Iceland 200,000, Greenland 50,000, and the Faroe Islands, 10,000. The use of geophysics in Scandinavia and Greenland is associated with ore prospecting, engineering activities, and oil exploration. Geophysical work in Iceland is dominated by geothermal and volcanological investigations

  • 149.
    Lohawijarn, Warawutti
    Luleå tekniska universitet.
    Regional gravity and auxiliary geophysical measurements in the Songkhla, Yala and Pattani provinces in the peninsular Thailand and their geological interpretation1992Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A regional gravity survey and VES measurements were carried out in Songkla-Yala-Pattani provinces of Peninsular Thailand, an area between latitudes 6º 15'N and 7º 15'N and longitudes 100º 15'E and 101º 30'E. In addition the aeromagnetic maps of the area have been analyzed qualitatively as well as quantitatively in this thesis, an analysis that has not been undertaken before this. Peninsular Thailand is the long, north-south trending, narrow strip of about 1000 km joining mainland Southeast Asia in the north and the Malay peninsula in the south. The objective of this study is to add to the geological information in the area, for example, the extents of geological formations, the depths of sedimentary basins. Little about the geological picture of the area has been known because of sparsity and deep weathering and lateritising of exposures. Altogether, more than 600 gravity points and some 620 linekilometres with station spacings of 0.5 km and 2.0 km were measured. The VES measurements comprised 27 sounding points with maximum AB/2 of 1 km in 2 subareas (Saba Yoi basin and Chana basin). In addition to these, density measurement on rocks from 26 sites and the field determination of alluvium density on one selected site were carried out. An absolute Bouguer anomaly map was prepared. It shows a strike of the gravity anomaly (N20E) that agrees with the geological map. However the gravity results show high Bouguer anomalies in many places where on the geological map there is Quaternary rock and Triassic rock. These anomalies have been interpreted as due to very shallow granitic basement which has not been known before. The extent of sedimentary basins, determined from low anomaly areas, I.e. the Saba Yoi basin. Hat Yai basin, Chana basin and Yarang basin were found to be smaller than the ones drawn on the geological map. The Triassic mountain range on the west of Saba Yoi appears as low anomaly region and was interpreted as a Triassic/Carboniferous basin with a depth extent of 10 km. The limestone outcrops to the southwest of Saba Yoi and west of Changwat Yala appear to follow trends of faults defined by closely spaced gravity contours. There are limited regions of granitic basement, here assumed to be slabs at about 12.6 km depth and confined to the northern part of the area. in which the magnetic content (<0.5 vol.%) seems to be locally higher than normal in the basement. Vertical electrical sounding has been proved to be a viable for determining shallow sedimentary sequences about 100 m to 300 m deep within a sedimentary basin. Geoelectrical stratification has been derived for the Chana and Saba Yoi basins.

  • 150.
    Lyngsie, Stig B.
    et al.
    Geological Institute, University of Copenhagen.
    Thybo, H.
    Geological Institute, University of Copenhagen.
    Rasmussen, Thorkild Maack
    bGeological Survey of Denmark and Greenland.
    Erratum to "Regional geological and tectonic structures of the North Sea area from potential field modelling" [Tectonophysics Volume 413/3-4 (2006) 147-170] (DOI:10.1016/j.tecto.2005.10.045)(2006In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 413, no 3-4, p. 303-306Article in journal (Refereed)
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