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  • 1.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Torklid Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Project: Development, Evaluation and Optimization of Measures to Reduce the Impact on the Environment from Mining Activities in Northern Regions2016Other (Other (popular science, discussion, etc.))
    Abstract [en]

    Min-North is a transnational project financed by the Interreg Nord program and coordinated by LTU. The project is a cooperation between Geological survey of Finland, GTK, Oulo University (Finland), The Arctic University of Norway, UiT and several (>17) small and large enterprises and mining companies in the northern region with expertise within geology, waste management, geophysics and geochemistry. The overall goal is to reduce the environmental impacts of mining in the northern regions by developing, evaluating, optimizing environmental techniques. In Sweden, geophysical and geochemical techniques will be integrated to develop a 4D model for tracing pollution transport in the mine waste, mine areas and in(to) the surroundings.

  • 2.
    Andersson, Christer
    Luleå tekniska universitet.
    Regional strukturgeologisk tolkning av fjärranalysdata1985Licentiate thesis, monograph (Other academic)
  • 3.
    Appel, Peter W.Uitterdijk
    et al.
    Geological Survey of Denmark and Greenland.
    Abrahamsen, Niels
    Geophysical Laboratory, Aarhus University.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Unusual features caused by lightning impact in West Greenland2006In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 143, no 5, p. 737-741Article in journal (Refereed)
    Abstract [en]

    Two lightning impacts are described from an area near the Inland Ice in West Greenland. The first lightning blasted an outcrop of metacherts. It subsequently split into two branches, which traversed rock outcrops and boulders, leaving behind two white almost straight lines, 30 m and 14 m long, respectively, where all lichens and plants were burned away. On the white lines the upper few millimetres of the traversed boulders were melted to a glass which subsequently peeled off by thermal expansion to leave a rough surface. Magnetic investigation of an amphibolite boulder found on the white line showed that a strong electric current indeed traversed the boulder. A few years later a second lightning impacted on a mountaintop close to the first impact. The second lightning left a trail on the rock surface covered by a thin layer of glass. The glass displays spectacular colours ranging from metallic blue to red, yellow and green.

  • 4.
    Ask, Daniel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Methodology for determination of the complete stress tensor and its variation versus depth based on overcoring rock stress data2017In: Rock Mechanics and Engineering: Volume 1: Principles, CRC Press, 2017, p. 245-265Chapter in book (Refereed)
    Abstract [en]

    This paper presents a methodology for evaluating the complete stress field and its variation versus depth. The validity of the protocol is visualized in the case study at the Äspö Hard Rock Laboratory (HRL), south-eastern Sweden, a site predominantly sampled using the overcoring method. Overcoring data involve explicit (measurementrelated) as well as implicit uncertainties. The former include for example uncertainties regarding determination of the location of the test sections in physical space and of the value of elastic parameters, as well as uncertainties in strain-/displacement measurements, etc. The explicit types of uncertainties are fairly straightforward to analyze and correct for during the stress calculation procedure. The implicit uncertainties, on the other hand, such as the assumption of homogeneity and linear-elasticity, are much more difficult to appreciate and correct for, if possible at all. Yet, as for explicit errors, they may render an individual test or a series of tests completely meaningless, and it is therefore crucial that both categories of uncertainties are identified, understood, and properly considered within the process of stress field determinations. The proposed methodology follows the directions outlined by ISRM for rock stress estimation using overcoring methods (Sjöberg et al., 2003; Sjöberg & Klasson, 2003). In addition, we pay particular attention on avoiding, identifying, and correcting for various potential sources of error, the sampling strategy, and considerations of the continuity hypothesis.

  • 5.
    Ask, Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ask, Daniel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rosberg, Jan Erik
    Lund University.
    Exploration for deep enhanced geothermal systems with Riksriggen and the LTU downhole stress measurement system2017In: 4th Sustainable Earth Sciences Conference and Exhibition 2017, Held at Near Surface Geoscience Conference and Exhibition 2017, European Association of Geoscientists and Engineers, 2017, p. 21-25Conference paper (Refereed)
    Abstract [en]

    Recent developments in drilling technology have resulted in about five to ten times faster penetration rates compared to penetration rates of conventional diamond drilling. The increased penetration rates open up for affordable drilling of deep boreholes in regions with cold crust, such as in Scandinavia, allowing for geothermal energy generation in enhanced geothermal systems. We present two infrastructures for downhole sampling and testing, Riksriggen and the LTU downhole stress measurement system. Riksriggen produces a borehole that allows in-situ sampling and testing to 2.5 km depth. Furthermore, highly relevant data for geothermal energy production is produced, for example fracture geometries and frequencies, as well as depth of zones with elevated transmissivity zones and their in-situ hydraulic conductivities. The LTU downhole stress measurement system allows determination of the three-dimensional stress tensor and its spatial variation with depth in a scientific unambiguously way. Thus, Riksriggen and the LTU downhole stress measurement system provide data needed for planning most stable borehole trajectory with depth and to determine optimal pattern of production and injection wells (e.g. hydraulic stimulation by fraccing), as well as for assessing the risk of induced seismicity.

  • 6.
    Autio, U.
    et al.
    Oulu Mining School, University of Oulu.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Savvaidis, Alexandros S.
    Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki.
    Suopios, Pantelis
    Department of Environmental and Natural Resources Engineering, Technological Educational Institute of Crete, Chania.
    Bastani, Mehrdad
    Geological Survey of Sweden.
    Combining electromagnetic measurements in the Mygdonian sedimentary basin, Greece2016In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 135, p. 261-269Article in journal (Refereed)
    Abstract [en]

    We present a novel approach where time-domain electromagnetic (TEM) data are transformed and subsequently used in two-dimensional (2-D) magnetotelluric inversion of the determinant of the impedance tensor. The main idea is to integrate TEM with magnetotelluric (MT) data to produce subsurface electrical resistivity models. Specifically, we show that 2-D MT data inversion of the determinant of the impedance tensor supported by inclusion of TEM–MT-transformed data has superior resolution at the near surface and at the same time static shift afflicting the MT data can be addressed. Thus, the approach allows for practical express integration of TEM data with MT measurements as opposed to a full combined 3-D inversion, which requires significant resources. The approach is successfully applied in the Mygdonian sedimentary basin located in Northern Greece. In addition to TEM and MT data, also controlled source — and radiomagnetotelluric data are available from the Mygdonian basin, which have been subjected to 2-D analysis previously. We have extended the analysis to a full 3-D inversion using ModEM code. All obtained models are analysed and are in a good agreement.

  • 7.
    Basokur, Ahmet Tuǧrul
    et al.
    Ankara Universitesi.
    Rasmussen, Thorkild Maack
    University of Uppsala, Solid Earth Physics.
    Kaya, Cemal
    MTA Genel Mudurlugu .
    Altun, Y.
    Demir Export A.S.
    Aktas, K.
    MTA Genel Mudurlugu .
    Comparison of induced polarization and controlled-source audio-magnetotellurics methods for massive chalcopyrite exploration in a volcanic area1997In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 62, no 4, p. 1087-1096Article in journal (Refereed)
    Abstract [en]

    In this paper, we compare and contrast the results of field experiments with the dipole-dipole-induced polarization (IP) and controlled-source audio-magnetotellurics (CSAMT) methods, along the same survey profiles, at a test area that was subject to extensive drilling and detailed geological investigation. The ore bodies are interbedded between two series of dacitic tuff. The depth and thickness of the massive chalcopyrite-pyritesphalerite body vary between 25 and 100 m and 0.5 and 16 m, respectively. Resistivity and IP phase measurements on the core samples collected from the test area provide some idea of the relative differences between the background rock units and the target. The resistivity of the chalcopyrite samples varies between 0.6 to 2 ohm-m and provides sufficient resistivity contrast with surrounding volcanic rock units for target detection. The results of dipole-dipole IP profiling with a 50-m dipole length conducted along two profiles are presented in the form of apparent resistivity and phase pseudosections. CSAMT measurements were made at 13 frequencies from 2 Hz to 8192 Hz along three profiles. The receiver dipole length was 25 m. The CSAMT data are presented in the form of pseudosections using conventional and new definitions of apparent resistivity. The elliptical contours of low apparent resistivity generated by the transition-field notch can be misleading with respect to the real anomaly of the ore body. These artificial anomaly patterns are suppressed by making use of an alternative apparent resistivity definition derived from the frequency-normalized impedance. The qualitative interpretation based on the IP and CSAMT pseudosections shows that the location and the extension of the ore body are indicated better in the CSAMT apparent resistivity data computed from the alternative definition. The qualitative interpretation of the IP data is difficult because of the 3-D effect arising from the neighboring thicker parts of the ore body and pyrite particles within the basement. At the final stage, the far-field range of the CSAMT apparent resistivity and phase data is identified by the visual inspection of the individual sounding diagrams. The models derived from the 2-D Occam inversion carried out on the far-field data are compared with the drill-hole information and are found to describe the actual geological situation.

  • 8.
    Bauer, Tobias
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Skyttä, Pietari
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dehghannejad, Mahdieh
    Uppsala University.
    Tavakoli, Saman
    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.
    Geological multi-scale modelling as a tool for modern ore exploration in the Skellefte mining district, Sweden2011In: Proceedings IAMG 2011 Salzburg: Mathematical Geosciences at the crossroads of theory and practice, 2011, p. 759-Conference paper (Other academic)
    Abstract [en]

    The Palaeoproterozoic Skellefte Mining District is host to abundant ore deposits. Geological 3Dmodelling was performed using the gOcad software platform. Geological methods such as field mapping, structural analysis and facies analysis combined with geophysical techniques such as reflection seismic investigations, resistivity, magnetic, electromagnetic and gravimetric studies and analysis of potential field data provide a framework for the reconstruction of the crustal geometry and geological history of the district as a tool for modern ore exploration. Results will be furthermore utilized for kinematic 4-dimensional modelling

  • 9.
    Bauer, Tobias
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Skyttä, Pietari
    Hermansson, Tobias
    Boliden Mineral AB, Luleå tekniska universitet.
    Dehghannejad, Mahdieh
    Uppsala University, Uppsala universitet, Department of Earth Sciences, Uppsala University.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The Skellefte District2015In: 3D, 4D and Predictive Modelling of Major Mineral Belts in Europe, Encyclopedia of Global Archaeology/Springer Verlag, 2015, p. 93-121Chapter in book (Refereed)
    Abstract [en]

    Four-dimensional geological modelling has been conducted in the Palaeoproterozoic Skellefte mining district. 3D-modelling of volcanic-hosted massive sulphide deposits and associated host-rocks has been carried out in multiple scales from deposit to regional scale and is based on a combination of geological and geophysical investigations. A conceptual model founded on unravelling the structural control on sedimentation, volcanism and mineralization and the subsequent deformation patterns, acts as a base for geological modelling. The final 3D-model provides a structural framework in which the mineralizations can be studied by improved understanding of the structural evolution in the mine areas, and by comparing the regional structural patterns versus the form and attitude of ore deposits. Additionally, uncertainty and prospectivity models were constructed showing the distribution of data and the potential of discovering new ore deposits. Subsequent 4D-modelling adds the time aspect to the 3D-models and aims at visualizing and understanding the geological history in the district and as a support for ore targeting. Moreover, adding geological time to the modelling helps gaining confidence about both the conceptual models and the 3D-models. The final 3D- and 4D-models provide a regional three-dimensional context for both industrial and academic activities in the Skellefte district, and aid the understanding of large-scale tectonic processes.

  • 10.
    Bauer, Tobias
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Skyttä, Pietari
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dehghannejad, Mahdieh
    Uppsala University, Uppsala universitet, Department of Earth Sciences, Uppsala University.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    From deposit to regional scale: 4-dimensional geological modelling in the Skellefte Mining District, Sweden2011Conference paper (Refereed)
  • 11.
    Bauer, Tobias
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Skyttä, Pietari
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hermansson, Tobias
    Boliden Mineral AB.
    Dehghannejad, Mahdieh
    Uppsala University.
    Juanatey, Maria Garcia
    Uppsala University.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Juhlin, Christopher
    Uppsala University.
    A regional scale 3D-model of the Skellefte mining district, northern Sweden2013In: Mineral depostits for a high-tech world: Proceedings of the 12th SGA Biennial Meeting 2013, 12-15 August 2013, Uppsala, Sweden, Uppsala: Sveriges Geologiska Undersökning , 2013, Vol. 1, p. 62-65Conference paper (Refereed)
  • 12.
    Bauer, Tobias
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Dehghannejad, Mahdieh
    Department of Earth Sciences, Uppsala University.
    Garcia, Maria
    Department of Earth Sciences, Uppsala University.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    4-dimensional geological modelling of the Skellefte district, Sweden2010In: The international archives of the photogrammetry, remote sensing and spatial information sciences, ISPRS Commission IV - Working Group 8 , 2010, Vol. XXXVIII-4, p. 93-96Conference paper (Other academic)
  • 13.
    Bedini, Enton
    et al.
    Federal Institute for Geosciences and Natural Resources (BGR), Hannover; Geological Survey of Denmark and Greenland (GEUS) Copenhagen K, Denmark.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark.
    Use of airborne hyperspectral and gamma-ray spectroscopy data for mineral exploration at the Sarfartoq carbonatite complex, southern West Greenland2018In: Geosciences Journal, ISSN 1226-4806, Vol. 22, no 4, p. 641-651Article in journal (Refereed)
    Abstract [en]

    The Sarfartoq carbonatite complex occurs in the transition zone between Archaean and Paleoproterozoic gneisses in southern West Greenland. The Sarfartoq carbonatite complex hosts ore deposits and occurrences of rare earth elements and niobium. In this study, airborne HyMap hyperspectral imagery and coincident airborne gamma-ray spectroscopy data were analysed for mineral exploration of Sarfartoq carbonatite complex. The study area included the carbonatite core zone and a hydrothermally altered shear zone prospective for rare earth elements mineralization in the southern margin of the carbonatite complex. The analysis of the hyperspectral imagery was focused on the mapping of the spatial distribution of carbonatite, fenite and limonite. Significant anomalies of uranium, thorium and potassium were outlined from the gamma-ray spectroscopy data. Decision trees were used to combine the results from the hyperspectral image analysis and airborne gamma-ray spectroscopy. Significant anomalies of thorium at the hydrothermally altered shear zone coinciding with the presence of carbonatite rocks are generally indicative of outcropping rare earth element mineralization. The study indicates the benefits of coincident airborne hyperspectral and gamma-ray spectroscopy surveys for the mineral exploration of carbonatite complexes.

  • 14.
    Beka, Thomas I.
    et al.
    Faculty of Science and Technology, UiT-The Arctic University of Norway.
    Bergh, Steffen G.
    Department of Geology, UiT-The Arctic University of Norway, N-9037 Tromsø.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Birkelund, Yngve
    Department of Physics and Technology, UiT-The Arctic University of Norway.
    Magnetotelluric signatures of the complex tertiary fold-thrust belt and extensional fault architecture beneath Broggerhalvoya, Svalbard2017In: Polar Research, ISSN 0800-0395, E-ISSN 1751-8369, Vol. 36, article id 1409586Article in journal (Refereed)
    Abstract [en]

    Magnetotelluric (MT) data were recently collected on Broggerhalvoya, Svalbard, in a 0.003-1000 s period range along a curved WNW-ESE profile. The collected data manifested strong three-dimensional (3D) effects. We modelled the full impedance tensor with tipper and bathymetry included in 3D, and benchmarked the result with determinant data two-dimensional (2D) inversion. The final inversion results indicated striking similarity with known surface bedrock geology and well reflected the tectonic history of the region. The most convincing contribution of the MT data is perhaps the elegantly imaged interplay between repeated basement-involved fold-thrust belt structures and successive down-dropped strata along steeply dipping oblique-normal faults (e.g., the Scheteligfjellet Fault) that created a horst/ridge and graben/depression system. Peculiarly, the MT result suggests that the Paleocene-Eocene fold-thrust belt structures dominate the shallow crustal level, while later normal faults in the area can be traced deeper into the pre-Devonian basement formations strongly affecting fluid and heat migration towards the surface. Near the sub-vertical Scheteligfjellet Fault, the MT model indicates aquifers within the upraised horsts of the pre-Devonian system at 2-5 km depth, sandwiched between the down-faulted resistive (ca. 500-3000 Om) Carboniferous and Permian successions. The section west of the Ny-Alesund settlement has signatures of lateral and subvertical cap-rock sealings, surrounding a steep and deep-seated major fault and aquifer systems. This section of the peninsula therefore requires closer investigation to evaluate the deep geothermal resource prospect.

  • 15.
    Beka, Thomas I.
    et al.
    Faculty of Science and Technology, UiT-The Arctic University of Norway.
    Senger, Kim
    Department of Arctic Geology, The University Centre in Svalbard.
    Autio, Uula A
    Oulu Mining School, Geophysics, University of Oulu.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Birkelund, Yngve
    Faculty of Science and Technology, UiT-The Arctic University of Norway.
    Integrated electromagnetic data investigation of a Mesozoic CO2 storage target reservoir-cap-rock succession, Svalbard2017In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 136, p. 417-430Article in journal (Refereed)
    Abstract [en]

    Recently acquired time-domain electromagnetic (TEM) and magnetotelluric (MT) data sets are utilized in the first electromagnetic (EM) characterization of a geological CO2 storage target site in Adventdalen, Arctic Norway. Combining the two EM data sets enabled to resolve the electrical resistivity structure of the target site better than either of the methods alone. 2D inverting the MT data in the audio period interval (0.003–1 s) with supporting input derived from the TEM data (0.01–10 ms) provided a geologically meaningful resistivity model that included information not previously evident from existing seismic and borehole data. The ca. 1.8 × 1 km 2D resistivity model displays a laterally constrained highly conductive anomaly (ca. 10 Ω m) at about 400–500 m depth, where reflectors of a parallel seismic section are concealed and core samples indicate a highly fractured décollement zone formed during Paleogene compression. The base of the permafrost is imaged at ca. 200 m depth. Synthetic inversion tests, however, suggest that this may be exaggerated by tens of meters, due to a thin conductive layer present approximately between 10 and 25 m depth. The resistivity model does not give indication for a fluid pathway we can connect to leakage, in line with water injection and leak-off tests in the reservoir and cap-rock, both of which indicate a sealing shale-dominated cap-rock separating an over-pressured compartment above the sealing shale from a severely under-pressured reservoir interval. The results we present indicate the advantage of integrating EM exploration techniques in a CO2 reservoir-cap-rock study to obtain a more complete picture.

  • 16.
    Beka, Thomas I.
    et al.
    Department of Physics and Technology, UiT-The Arctic University of Norway.
    Smirnov, Maxim
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Birkelund, Yngve
    Department of Physics and Technology, UiT-The Arctic University of Norway.
    Senger, Kim
    The University Centre in Svalbard.
    Bergh, Steffen G.
    Department of Geology, UiT-The Arctic University of Norway, N-9037 Tromsø.
    Analysis and 3D inversion of magnetotelluric crooked profile data from central Svalbard for geothermal application2016In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 686, p. 98-115Article in journal (Refereed)
    Abstract [en]

    Broadband (0.001–1000 s) magnetotelluric (MT) data along a crooked profile collected to investigate the geothermal potential on Spitsbergen could not be fully explained by two-dimensional (2D) models; hence we interpret the data with three-dimensional (3D) inversion herein. To better accommodate 3D features and nearby off profile resistivity structures, the full MT impedance tensor data together with the tipper were inverted. As a model control, a detailed bathymetry is systematically incorporated in the inversion. Our results from testing different inversion settings emphasised that appropriately choosing and tuning the starting model, data error floor and the model regularization together are crucial to obtain optimum benefit from MT field data. Through the 3D inversion, we reproduced out of quadrant impedance components and obtained an overall satisfactory data fit (RMS = 1.05). The final 3D resistivity model displays a complex geology of the near surface region (< 1.5 km), which suggests fractures, localized and regional fault systems and igneous intrusions in the Mesozoic platform cover deposits. The Billefjorden fault zone is revealed as a consistent and deep rooted (> 2 km) conductive anomaly, confirming the regional nature of the fault. The fault zone is positioned between two uplifted basement blocks (> 1000 Ωm) of presumably pre-Devonian (Caledonian) metamorphic rocks, and the fault may have been responsible for deformation in the overlying Paleozoic-Mesozoic unit. Upper crustal conductive anomalies (< 10 Ωm) below the Paleozoic-Mesozoic succession in the western part of the 3D model are interpreted as part of a Devonian basin fill. These conductors are laterally and vertically bounded by resistive rocks, suggesting a conducive environment for deep geothermal heat storage. Having this scenario in an area of a known high heat-flow, deep faults and a thinned lithosphere makes the hypothesis on finding a technologically exploitable geothermal resource close to human settlement in the area stronger.

  • 17.
    Belay, R.
    et al.
    University of Uppsala, Department of Geophysics.
    Rasmussen, Thorkild Maack
    University of Uppsala, Department of Geophysics.
    One‐dimensional non‐linear inversion of magnetotelluric data: the importance of data errorrs1995In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 43, no 7, p. 905-918Article in journal (Refereed)
    Abstract [en]

    Inversion of noisy magnetotelluric data over a horizontally stratified earth has no unique solution. Instead, the resistivities and thicknesses of the layers can only be specified to lie within certain bounds at a particular confidence level. The significance of having correctly estimated data errors when calculating the parameters and parameter bounds is discussed. Emphasis is put on the very corrunon problem of not being able to obtain models which can be considered acceptable with a reasonable certainty from a statistical point of view. A method is presented to obtain a pragmatic data error description by adjustment of wrongly estimated data errors while keeping the suppression of 1D data features at a minimum. A comparison is made between calculation of the parameter bounds based on approximating the confidence surface by hyperellipsoids and a calculation based on a full non‐linear most‐squares analysis. In general it is found that the approximation works very well when the confidence limit is small. However, significant deviations are found in some cases.

  • 18. Berggren, Robert
    et al.
    Sandrin, Alessandro
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Physical properties of rocks and geophysical data as tools for targeting Fe-oxide Cu-Au mineralisations in northern Sweden2004In: EOS: Transactions, ISSN 0096-3941, E-ISSN 2324-9250, Vol. 85, no 47Article in journal (Other academic)
  • 19.
    Bergström, Jörgen
    Luleå tekniska universitet.
    Geophysical methods for investigating and monitoring the integrity of sealing layers on mining waste deposits1998Licentiate thesis, monograph (Other academic)
  • 20.
    Berube, Andrew P.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A graphical 3D finite element program for modelling self-potentials generated by flow through a porous medium2007In: Journal of Environmental & Engineering Geophysics, ISSN 1083-1363, E-ISSN 1943-2658, Vol. 12, no 2, p. 185-197Article in journal (Refereed)
    Abstract [en]

    In order to provide a better understanding of the self-potentials generated by groundwater flow through real in-situ geological conditions and a tool for assisting in the interpretation of SP measurements obtained from such domains, a three-dimensional finite element computer program was written to model self-potentials generated by the flow of liquid through a porous medium. Using the program, a finite element domain is defined and each element can be assigned separate anisotropic hydraulic, electric and cross-coupling conductivity values. The hydraulic flow is defined by boundary conditions and the hydraulic conductivity distribution and is related to the electric flow through the thermodynamic theory of coupled flows.The program first determines the hydraulic potential distribution, and then calculates the electric current sources before solving for the electric potential distribution. The program was made to be quite user-friendly, versatile and fully graphical. The program was used to model seepage flow through an earth embankment dam and the results were compared to actual self-potential field measurements. It was found that the results obtained by the program were comparable with field measurements provided that sufficient knowledge of the conductive properties within the dam was available for modelling. The program successfully provides the hydraulic and electric potential distributions throughout the domain based on the input model parameters.

  • 21.
    Bhongsuwan, Tribop
    Luleå tekniska universitet.
    Research in rock magnetism and palaeomagnetism of recent sediments and palaeozoic to tertiary rocks in Thailand2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Rock magnetic and palaeomagnetic studies have been performed on sediments and Palaeozoic to Tertiary rocks in Thailand. The first part of the thesis includes an environmantal study based on the magnetic properties of recent sediments in one of southern Thailands largest water reservoirs, the Songkla Lake. Sediment from 21 cores collected from different parts of the lake were investigated. From the correlation with age determinations of the sediments, the sedimentation velocities could be determined and related to different parts of the lake. In an attempt to put Thailand and its geological evolution into a plate tectonic context rock magnetic and palaeomagnetic studies were performed on rock from different blocks in southern and northern Thailand. The results show that large parts of Thailand have been remagnetized due to the intrusions of Permian-Triassic granites, and that rock have been deformed in relation with a collition between Asia and India. The plate tectonic analysis shows a clear tectonic contrast between the Shan Thai and Indochina Blocks, a difference that can be related to a collition between Asia and India during the Cenozoic. The study also demonstrates that northeast Thailand, which forms a part of the Indochina Block, has been attached to the South China Block during late Jurrasic time. The presented model of the tectonic evolution for this part of Thailand supports to a large extent earlier presented geological models.

  • 22.
    Bhongsuwan, Tripob
    Luleå tekniska universitet.
    Palaeomagnetic investigations in Thailand1993Licentiate thesis, monograph (Other academic)
  • 23.
    Bispo-Santos, F.
    et al.
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    D'Agrella-Filho,, M S
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Paleomagnetism of paleoproterozoic mafic and felsic volcanic rocks of the Rio Negro-Juruena Province, Southwestern Amazonian Craton, Brazil2007Conference paper (Other academic)
    Abstract [en]

    Several paleogeographic configurations for the Amazonian Craton have been suggested along its geological history. Paleomagnetic tests for suggested configurations are however restricted due to very sparce and low quality paleomagnetic data, especially for Paleoproterozoic. In an attempt to improve our understanding of the geodynamic evolution, a paleomagnetic study was performed on felsic volcanic rocks of the Colider Suite, and associated mafic rocks in the Rio Negro-Juruena Province, southwestern Amazonian Craton. These rocks have well dated zircon U-Pb ages between 1.80-1.78 Ga. Very stable northern (southern) directions with moderate to steep negative (positive) inclinations were isolated during AF and thermal demagnetization. Rock magnetism experiments show that the magnetization, which is probably of primary origin, in the felsic rocks is carried by hematite and in the mafic rocks by Ti-poor titanomagnetite. A preliminary mean direction (D=187.4°, I=50.9°, N=16, A95=11.3°, K=11.7) yield a paleomagnetic pole located at 289.4°E, 65.4°S (A95=12.9°), which is classified with quality factor of Q=5. Paleogeographic reconstructions using key Paleoproterozoic poles suggest that Laurentia, Baltica, North China, and Amazonian Craton were located in laterally contiguous positions forming a large continental mass at 1.83-1.77 Ga ago.

  • 24. Bispo-Santos, F.
    et al.
    DÁgrella-Filho, M.S.
    Perillo, B.M.
    Tohver, E.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Janikian, L.
    Trinidade, R.I.
    Pacca, I.I.G.
    Silva, J.A.
    Barros, M.A
    Pinho, F.E.C.
    Preliminary paleomagnetic results from the Guadalupe intrusives, Amazonian craton: tectonic implications2009Conference paper (Refereed)
  • 25.
    Bispo-Santos, Franklin
    et al.
    Universidade de São Paulo.
    D’Agrella-Filho, Manoel S.
    Universidade de São Paulo.
    Pacca, Igor I.G.
    Universidade de São Paulo.
    Janikian, Liliane
    Universidade de São Paulo.
    Trindade, Ricardo I.F.
    Universidade de São Paulo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Silva, Jesué A.
    METAMAT.
    Barros, Márcia A.S.
    Department of Mineral Resources, UFMT.
    Pinho, Francisco E.C.
    Department of Mineral Resources, UFMT.
    Columbia revisited: paleomagnetic results from the 1790 Ma colider volcanics (SW Amazonian Craton, Brazil)2008In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 164, no 1-2, p. 40-49Article in journal (Refereed)
    Abstract [en]

    In an attempt to improve our understanding of the Paleoproterozoic geodynamic evolution, a paleomagnetic study was performed on 10 sites of acid volcanic rocks of the Colider Suite, southwestern Amazonian Craton. These rocks have a well-dated zircon U-Pb mean age of 1789 +/- 7 Ma. Alternating field and thermal demagnetization revealed northern (southern) directions with moderate to high upward (downward) inclinations. Rock magnetism experiments and magnetic mineralogy show that this characteristic magnetization is carried by Ti-poor magnetite or by hematite that replaces magnetite by late-magmatic cleuteric alteration. Both magnetite and hematite carry the same characteristic component. The mean direction (Dm = 183.0 degrees, Im = 53.5 degrees, N = 10, alpha(95) = 9.8 degrees, K = 25.2) yielded a paleomagnetic pole located at 298.8 degrees E, 63.3 degrees S (alpha(95) = 10.2 degrees, K = 23.6), which is classified with a quality factor Q = 5. Paleogeographic reconstructions using this pole and other reliable Paleoproterozoic poles suggest that Laurentia, Baltica, North China Craton and Amazonian Craton were located in laterally contiguous positions forming a large continental mass at 1790 Ma ago. This is reinforced by geological evidence which support the existence of the supercontinent Columbia in Paleoproterozoic times.

  • 26.
    Bispo-Santos, Franklin
    et al.
    Universidade de São Paulo.
    D’Agrella-Filho, Manoel S.
    Universidade de São Paulo.
    Trindade, Ricardo I.F.
    Universidade de São Paulo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Janikian, Liliane
    Universidade de São Paulo.
    Vasconcelos, Paulo M.
    University of Queensland.
    Perillo, Bruno M.
    Universidade de São Paulo.
    Pacca, Igor I.G.
    Universidade de São Paulo.
    Silva, Jesué A. da
    Companhia Matogrossense de Mineração–METAMAT.
    Barros, Márcia A.S.
    Universidade Federal de Mato Grosso.
    Tectonic implications of the 1419 Ma Nova Guarita mafic intrusives paleomagnetic pole (Amazonian Craton) on the longevity of Nuna2012In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 196-197, p. 1-22Article in journal (Refereed)
    Abstract [en]

    The Nuna supercontinent was probably assembled in the Paleoproterozoic, but its paleogeography and the timing for its demise are still a matter of debate. A paleomagnetic and geochronological study carried out on the Mesoproterozoic Nova Guarita dyke swarm (northern Mato Grosso State, SW Amazonian Craton) provides additional constraints on the duration of this supercontinent. Paleomagnetic AF and thermal treatment revealed south/southwest (northeast) magnetic directions with downward (upward) inclinations for nineteen analyzed sites. These directions are carried by PSD magnetite with high unblocking temperatures as indicated by additional magnetic tests, including thermomagnetic curves, hysteresis loops and the progressive acquisition of isothermal remanence in selected samples. A positive contact test with the host granite in one of the studied dykes further attests to the primary origin of the characteristic magnetic component. A mean site direction was calculated at Dm = 220.5°, Im = 45.9° (α95 = 6.5°, K = 27.7), which yielded a paleomagnetic pole located at 245.9°E, 47.9°S (A95 = 7.0°). 40Ar/39Ar dating carried out on biotites from four analyzed dykes yielded well-defined plateau ages with a mean of 1418.5 ± 3.5 Ma. The Nova Guarita pole precludes a long-lived Nuna configuration in which Laurentia, Baltica, North China, and Amazonia formed a long and continuous block as previously proposed for the Paleoproterozoic. It is nevertheless fully compatible with a SAMBA (Amazonia-Baltica) link at Mesoproterozoic times.

  • 27.
    Boldreel, Lars Ole
    Luleå tekniska universitet.
    An attempt based on an interpretation of multichannel reflection seismic data to delineate sedimentary sequences, structures and evolution in the part of the Western Barents Sea 72° - 74°N and 10° - 17°E1988Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is an attempt to throw further light on the structural development of the passive continental margin of the Western Barents Sea in the area from 72000'N to 74000'N and from 17000'E to 10000'E. It is based mainly on multichannel reflection seismics but available aeromagnetic, shipborne magnetic and free-air gravimetric data have also been analyzed. It seems from the results that the area between what is generally called the Senja fracture zone and the possible southernmost part of the Hornsund fault zone consists of a nonoceanic basement. The transition between the oceanic and the continental basement is placed adjacent to the Senja fracture zone and its northern continuation up to 740 N. The transition zone to the east of the Senja Fracture Zone in the area 720 50'N to 74000'N suggested in earlier works is here correlated with the development of a listric fault complex rooted in a detachment zone. The non-oceanic basement to the east of the Senja Fracture Zone is also examined and it is suggested that this basement is a stretched continental crust. A chronology for the sequences chosen has been established using the wells 711719-1 and 711719-2 located to the south of the area studied. The structural development of the margin has been dated on the basis of seven depth maps and four isopach maps of the sequences representing the time from the onset of the Tertiary to the end of the Oligocene. The main result is that the end of a major rifting phase corresponds to the beginning of the Paleocene while the onset of the sea floor spreading corresponds to the time interval from Early Eocene to Late Eocene. It appears from backstripping studies that the free-air gravity anomaly associated with the Senja Fracture Zone is probably due to the sediments loading an oceanic plate. This would mean that the Senja "Fracture Zone" is not really a fracture zone. It also seems that the seafloor spreading took place in an oblique northwards manner and that the oceanic basement closest to the Senja "Fracture Zone" and its northern continuation up to 740N is of Eocene age. If this interpretation is correct it would call for a modification of the 2-stage opening model of this area proposed in earlier works.

  • 28.
    Boldreel, Lars Ole
    Luleå tekniska universitet.
    On the structural development of the salt dome province in NW Jutland, Denmark, based on seismic studies1985In: First Break, ISSN 0263-5046, E-ISSN 1365-2397, Vol. 3, no 8, p. 15-21Article in journal (Refereed)
  • 29.
    Boldreel, Lars Ole
    Luleå tekniska universitet.
    Structural development of the salt dome province in NW-Jutland, Denmark, based on seismic studies1985In: Vol. 23, no 3, p. 424-Article in journal (Other academic)
  • 30.
    Brethes, Anais
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Geological Survey of Denmark and Greenland (GEUS), Department of Petrology and Economic Geology, Denmark.
    Guarnieri, Pierpaolo
    Geological Survey of Denmark and Greenland (GEUS), Department of Petrology and Economic Geology.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias Erich
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Interpretation of aeromagnetic data in the Jameson Land Basin, central East Greenland: Structures and related mineralized systems2018In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 724-725, p. 116-136Article in journal (Refereed)
    Abstract [en]

    This paper provides a detailed interpretation of several aeromagnetic datasets over the Jameson Land Basin in central East Greenland. The interpretation is based on texture and lineament analysis of magnetic data and derivatives of these, in combination with geological field observations. Numerous faults and Cenozoic intrusions were identified and a chronological interpretation of the events responsible for the magnetic features is proposed built on crosscutting relationships and correlated with absolute ages. Lineaments identified in enhanced magnetic data are compared with structures controlling the mineralized systems occurring in the area and form the basis for the interpretations presented in this paper. Several structures associated with base metal mineralization systems that were known at a local scale are here delineated at a larger scale; allowing the identification of areas displaying favorable geological settings for mineralization. This study demonstrates the usefulness of high-resolution airborne magnetic data for detailed structural interpretation and mineral exploration in geological contexts such as the Jameson Land Basin.

  • 31.
    Brethes, Anais
    et al.
    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.
    Guarnieri, Pierpolo
    GEUS.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    3D modelling of the base-metal mineralized Jameson Land Basin (central East Greenland) using geologically constrained inversion of magnetic data2015Conference paper (Other academic)
  • 32.
    Brethes, Anaïs
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    An integrated study of geological, magnetic and electromagnetic data for mineral exploration in the Jameson Land Basin, central East Greenland2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Jameson Land Basin, located in central East Greenland, initiated in Devonian time with the collapse of the over-thickened Caledonian Orogen. The basin developed during different phases of rifting from the late Paleozoic to the Mesozoic and has accumulated between 16-18 km of sediments. In Paleogene time, the basin was affected by intense magmatism due to the opening of the North Atlantic Ocean c. 55 Ma ago. Due to a significant uplift in Miocene time, the sedimentary sequence is well exposed along the basin margins, revealing numerous mineral occurrences hosted within almost the entire stratigraphic succession. The major types of mineralization comprise: (1) intrusion-related Mo (± Pb, Zn, Cu, Ag) mineralization associated with Paleogene intrusive complexes; (2) stratabound and/or stratiform Cu, Pb, Zn, (Ag) within Upper Permian and Triassic clastic and marine sedimentary formations; (3) stratabound and structurally controlled Pb-Zn, Cu, Ba, (Sr) mineralization in Upper Permian carbonates; and (4) structurally-controlled Pb, Zn, Cu (±Sb, Bi, Ag, Au) vein-type mineralization within Caledonian and Paleozoic rocks.

    It is well acknowledged that structures such as faults, thrusts, detachments, shear zones and associated fracture systems play an important role as fluid conduits connecting metal sources and sites of mineral precipitation. In particular, previous studies showed that mineral occurrences within the East Greenland Caledonides are closely related to lineaments and intrusions. In this context, the Crusmid-3D project was initiated in 2014, aiming at establishing the links between the crustal structures and the mineral occurrences in the Jameson Land Basin using a combination of geological and geophysical data. The interest for mineral exploration in the area led exploration companies and institutions to carry out magnetic and electromagnetic surveys, and the data derived from these constitute the base of this study.

    This thesis provides a detailed structural interpretation of aeromagnetic data in the Jameson Land Basin where several magnetic trends associated with Tertiary dikes and sills as well as with reactivated Paleozoic and Triassic faults were delineated. These data, in combination with a literature review and compilation of the mineral occurrences in the Jameson Land Basin, allowed highlighting seven prospective areas for structurally-controlled base metal mineralization.

    New structural data from geological fieldwork, drilling results and geophysical data (magnetic, electromagnetic and seismic data) along the eastern margin of the basin allowed a new interpretation of the geometry of the Triassic rift in East Greenland, represented by NE-SW-trending basins and highs segmented by NW-SE-trending transfer zones. It can be correlated with its European conjugate margin, displaying analogies with the Triassic Froan and Helgeland Basins in the Norwegian offshore and with the Papa and West Shetlands Basins north of the Shetland Islands.

    The proposed structural model of the Triassic rift was further investigated using 3D-geologically-constrained inversion of magnetic data in order to refine the architecture of the eastern margin of the Jameson Land Basin. Modelling results confirmed the presence of a shallow westward dipping peneplained crystalline basement in the southern part of the area while the northern part is characterized by faulted blocks, which accommodated relatively thick red bed sedimentary sequences, thereby representing a good potential source of base metals.

    Furthermore, Induced Polarization (IP) effects observed in airborne time-domain electromagnetic data acquired in the eastern margin of the basin were investigated using Self-Organizing Maps (SOM). The analysis of the shape and amplitude of the transient response curves using the SOM allowed identifying four areas where the transient curve patterns exhibit strong IP effects. These are shown to be collocated with Tertiary sills and dikes, clay-altered rocks as well as with a sulfide-bearing brecciated granite and with Triassic stratigraphic horizons hosting disseminated base metal sulfides.

  • 33.
    Brethes, Anaïs
    et al.
    Geological Survey of Denmark and Greenland.
    Guarnieri, Pierpaolo
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Integrating 3D photogeology with aeromagnetic data as a tool for base-metal exploration in East Greenland2014In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 31, p. 71-74Article in journal (Refereed)
  • 34.
    Brethes, Anaïs
    et al.
    Geological Survey of Denmark and Greenland.
    Guarnieri, Pierpaolo
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    3D-Modelling of the Early Triassic Base-Metal Mineralized Syn-Rift Sequence in the Jameson Land Basin (East Greenland)2015In: Mineral Resources in a Sustainable World / [ed] A.S. Andre-Mayer; M. Cathelineau; P. Muchez; E. Pirard; S. Sindern, 2015, p. 1701-1704Conference paper (Refereed)
    Abstract [en]

    The Jameson Land Basin in central East Greenland is mineralized in Pb, Zn and Cu. Mineralization occurs in several stratigraphic horizons and along structures in Upper Permian and Triassic sediments. A good understanding of the basin architecture and evolution is therefore essential for mineral exploration in this area. 3D-Photomapping from high resolution aerial photos along with a structural interpretation of aeromagnetic data, electromagnetic data, and results from fieldwork and drilling were integrated into a 3D-structural model. This data integration allowed modelling the rift architecture in the eastern margin of the Jameson Land Basin.

  • 35.
    Brethes, Anaïs
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Guarnieri, Pierpaolo
    GEUS.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geological Analysis of Aeromagnetic Data over the Blyklippen Lead-zinc Mine at Mesters Vig, Central East Greenland2016In: First Conference on Geophysics for Mineral Exploration and Mining: Near Surface Geoscience 2016, Barcelona, Spain, 4-8 September 2016, Houten, 2016, article id Mo MIN 05Conference paper (Refereed)
    Abstract [en]

    In the Mesters Vig area epithermal Pb-Zn sulphide-bearing quartz veins are associated with the border faults of a NNW-SSE elongated graben down-faulting Carboniferous to Lower Triassic sediments. The analysis of the total magnetic field, tilt derivative, vertical derivative and analytic signal allowed to define subcropping magnetic domains and identify structural trends. Doleritic dykes, sills and faults were mapped and structural relationships were established between them. Finally, aeromagnetic data allowed here to delineate structural trends along and in the vicinity of which mineralized quartz veins are mapped.

  • 36.
    Brethes, Anaïs
    et al.
    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.
    Guarnieri, Pierpaolo
    GEUS.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mapping and characterization of Induced Polarization in airborne TEM data from central East Greenland: application of a Self-Organizing Map procedure2016Conference paper (Refereed)
    Abstract [en]

    nduced Polarization (IP) effects were observed in airborne Time Domain EM (TEM) data acquired in central East Greenland in the context of exploration for disseminated sulphides in a sedimentary basin. Some of the IP anomalies were targeted by drilling which revealed the absence of mineralization. In order to understand the possible causes of the IP effects we first identified them in the TEM data. IP indicators were extracted from the shape of the transient curves at every measurement location and were analysed by using a Self-Organizing Map (SOM) procedure. Results from K-mean clustering of the SOM are visualized on a geographical map showing the transient curves’ characteristics. Some of the clusters are clearly correlated with the geology whereas others merely reflect recordings below the noise level. In order to interpret the cause of the IP anomalies the airborne TEM data were inverted for the Cole-Cole parameters.

  • 37.
    Buchan, K. L.
    et al.
    Geological Survey of Canada.
    Mertanen, S.
    Geological Survey of Finland.
    Park, R. G.
    Department of Earth Sciences, Keele University.
    Pesonen, L. J.
    Geological Survey of Finland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Abrahamsen, N.
    University of Aarhus.
    Bylund, G.
    Lunds universitet.
    Comparing the drift of Laurentia and baltica in the Proterozoic: the importance of key palaeomagnetic poles2000In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 319, no 3, p. 167-198Article in journal (Refereed)
    Abstract [en]

    Key palaeomagnetic poles are defined as those which pass basic reliability criteria and are precisely and accurately dated. They allow a more rigorous analysis of Precambrian continental drift and continental reconstructions than the traditional apparent polar wander path (APWP) approach using mostly non-key poles. Between ca. 2.45 and 2.00 Ga in the early Palaeoproterozoic, key poles define the drift of the Archaean Superior craton of Laurentia, yielding a result that is quite unlike the drift interpreted in earlier studies using the APWP method. There are no early Palaeoproterozoic key poles for the other Archaean cratons that amalgamated to form Laurentia and Baltica prior to 1.8 Ga, so that a rigorous test of early Palaeoproterozoic reconstruction models is not possible. Key poles from Laurentia between ca. 1.46 and 1.267 Ga and Baltica between 1.63 and 1.265 Ga help to define, in a preliminary fashion, the early Mesoproterozoic drift of the two shields. The key pole age match at ca. 1.265 Ga is consistent with Baltica located adjacent to eastern Greenland, and geological considerations suggest that the most reasonable fit aligns the Labradorian belt of Laurentia with the Gothian belt of Baltica. Although there is limited support from non-key poles and key poles that are not matched in age for such a fit as early as ca. 1.8 Ga, no rigorous assessment will be possible until a match in key pole ages is achieved. In the late Mesoproterozoic to Neoproterozoic, Laurentia's drift is reasonably well documented by seven key poles between 1.235 and 0.73 Ga. There are no key poles in this period from Baltica, however, so that a ≈90° clockwise rotation of Baltica relative to Laurentia between 1.265 and 1.0 Ga, widely used in the literature, cannot be confirmed.

  • 38.
    Buchan, Kenneth
    et al.
    Geological Survey of Canada.
    Ernst, Richard
    Geological Survey of Canada.
    Hamilton, Mike A.
    Geological Survey of Canada.
    Mertanen, Satu
    Geological Survey of Finland.
    Pesonen, Lauri J.
    Geological Survey of Finland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The 1.7-0.7 Ga paleomagnetic record for Laurentia, Baltica and Siberia and its application to Rodinia reconstructions1999In: Vol. 4, no 1, p. 114-Article in journal (Other academic)
  • 39. Buchan, Kenneth L.
    et al.
    Ernst, Richard E.
    Hamilton, Michael A.
    Mertanen, Satu
    Pesonen, Lauri J.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rodinia: the evidence from integrated palaeomagnetism and U-Pb geochronology2001In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 110, no 1-4, p. 9-32Article in journal (Refereed)
    Abstract [en]

    Of many hundreds of well-defined palaeomagnetic poles that have been reported from cratons around the world in the 1700-500 Ma period, only a few are precisely dated. However, such ‘key' palaeopoles are a prerequisite for establishing rigorous palaeomagnetic reconstructions in order to chart the assembly, drift and breakup of the postulated late Precambrian supercontinent of Rodinia. Most key palaeopoles are derived from mafic dykes and sills that have been dated by U-Pb techniques. Most are from Laurentia, the largest and best studied of the continental fragments that are thought to have comprised Rodinia. Thirteen key Laurentia palaeopoles form an incomplete reference set that can be used for comparison with key palaeopoles from other cratons as they become available. Currently, there are four key palaeopoles for Baltica between 1700 and 500 Ma, although only one allows a direct comparison with a similar aged pole from Laurentia. The 1265 Ma match between Baltica and Laurentia is consistent with reconstructions in which Baltica is adjacent to present-day east Greenland, with the ca. 1700-1500 Ma Gothian and Labradorian belts aligned. Few key palaeopoles are yet available from other cratons. However, recent U-Pb dating of dykes, sills, or volcanic rocks in the Siberian, Australian and Kalahari cratons and in Coats Land of Antarctica constrains the ages of individual palaeopoles from each of these areas. Most of these are not key palaeopoles because they have not been conclusively demonstrated to be primary, or local tectonic rotations have not been ruled out. Nevertheless, they are useful in testing Rodinia reconstructions. In this paper, a U-Pb baddeleyite age is reported from the late Gardar magmatic rocks of southwest Greenland. Along with the previously published palaeopole for this unit, this age helps constrain the Mesoproterozoic location of southwest Greenland relative to North America.

  • 40. Bylund, G.
    et al.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Från Söderhavet till Arktis2000In: Har du tid?, Stockholm: Naturvetenskapliga forskningsrådet (NFR) , 2000, p. 61-74Chapter in book (Other (popular science, discussion, etc.))
  • 41. Bylund, Göran
    et al.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The Dala dolerites, central Sweden, and their palaeomagnetic signature1992In: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 14, no 1, p. 143-153Article in journal (Refereed)
    Abstract [en]

    New palaeomagnetic results are presented from nine dolerites from central Sweden. Data are also presented from four porphyry sites and one granite site. The data obtained are compared with previously published data from the area. Based on the directions of the characteristic magnetizations isolated in the various rock units a division into five groups, A-E, has been made. Group A consists of dolerites of late Sveconorwegian (c. 1050-850 Ma) age and group B comprises dolerites belonging to the Central Scandinavian Dolerite Group (c. 1250-1150 Ma). Groups C and D are less clearly defined. Group C, with a shallow negative northerly remanence inclination represents the Tuna dykes (c. 1370 Ma). The D direction, with a shallow positive northerly inclination, may represent an older generation of dolerites. The border between groups C and D is diffuse and may be the result of a prolonged mid-Proterozoic period with dolerite intrusions in Dalarna during which significant apparent polar wander occurred. Group E comprises dolerites with a steep positive inclination close to the direction of the Earth's present field. The porphyries and the granite studied carry group D and E remanence directions. This strengthens the evidence for a D-group generation of dolerites contemporary with the porphyries and the granite, c.1650 Ma ago.

  • 42.
    Bérube, Andrew Patrick
    Luleå tekniska universitet.
    Investigating the streaming potential phenomenon using electric measurements and numerical modelling with special reference to seepage monitoring in embankment dams2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A three-dimensional finite element computer program has been developed to numerically model the streaming potential phenomenon. The program can in fact calculate and display the primary and secondary potential distributions for any two coupled flows in a three dimensional domain. For streaming potentials, the primary flow is hydraulic and the secondary flow is electrical. The program operates in three separate stages. The program first determines the hydraulic potential distribution in the ground based on hydraulic conductivity values and the hydraulic driving forces, such as the pressure drop through an embankment dam. The program then calculates the geometry and magnitude of the electric current sources based on the fluid flow and cross-coupling conductivity values. Finally the electric potential distribution is solved for using these current sources and the electric conductivity distribution. Additionally, the program can incorporate external current sources, which can be used to simulate resistivity measurements in a model. The model domain can take any three-dimensional shape and can be divided into elements as desired. The individual elements can be assigned separate hydraulic, electric and cross-coupling conductivity values, creating an inhomogeneous anisotropic domain with three separate conductivity distributions. Four different types of finite element are available to choose from; two- and three-dimensional versions of isoparametric elements with either linear or quadratic interpolating polynomials. The program has been made fully graphical, allowing the user quick and easy access to information at any particular point of the domain. In order to provide a better picture of the streaming potentials in earth dams and the potential of the SP method for dam safety monitoring, SP investigations were performed on a number of embankment dams. Electric resistivity measurements were also performed on some of the dams to compliment the SP data. The resistivity data was found to be of considerable assistance for interpreting the SP measurements as well as for simulating real dam conditions with the modelling program. Three hydro-electric dams of different size on the Luleå River in northern Sweden were studied together with several dams built by mining companies for containing mine tailing reservoirs. A number of potential seepage areas were identified in several of the investigated dams.

  • 43.
    Bérubé, Andrew Patrick
    Luleå tekniska universitet.
    Geophysical methods for the investigation of subsurface flows2002Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Geophysical methods of investigating the substratum have been proven to provide quality data for a variety of applications. Despite this fact, such methods are not used in some fields to the degree that they could be. Reasons for this can include the complexity of the required measurements, the difficulties in interpreting the results, and a simple ignorance of the full potential of the various methods. One method that requires only very simple measurements with very little equipment is the self-potential or SP method, which can provide invaluable information concerning subsurface heat or liquid flows. This information could be used for example to track contaminants or to identify problem areas in or under an earth dam before they became serious. One difficulty with the SP method can be interpreting the results when the subsurface geology is complex. The first part of this thesis addresses this problem by creating a finite element computer program to model the streaming potential phenomenon for a complex domain with varying hydraulic, thermal and electrical conductivities. The second part of this thesis deals with a geophysical investigation of mining waste impoundments. Relatively simple electrical and electromagnetic methods are used to provide a thorough assessment of the impoundments' condition. Modern technological advances in both the measuring equipment and processing computers are seen to make the measurements faster and interpreting the results much easier.

  • 44.
    Cherevatova, M.
    et al.
    Institute for Geophysics, University of Münster, 48149 Münster, Germany.
    Egbert, G. D.
    College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA.
    Smirnov, M. Yu
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A multi-resolution approach to electromagnetic modelling2018In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 214, no 1, p. 656-671Article in journal (Refereed)
    Abstract [en]

    We present a multi-resolution approach for 3-D magnetotelluric forward modelling. Our approach is motivated by the fact that fine-grid resolution is typically required at shallow levels to adequately represent near surface inhomogeneities, topography and bathymetry, while a much coarser grid may be adequate at depth where the diffusively propagating electromagnetic fields are much smoother. With a conventional structured finite difference grid, the fine discretization required to adequately represent rapid variations near the surface is continued to all depths, resulting in higher computational costs. Increasing the computational efficiency of the forward modelling is especially important for solving regularized inversion problems. We implement a multi-resolution finite difference scheme that allows us to decrease the horizontal grid resolution with depth, as is done with vertical discretization. In our implementation, the multi-resolution grid is represented as a vertical stack of subgrids, with each subgrid being a standard Cartesian tensor product staggered grid. Thus, our approach is similar to the octree discretization previously used for electromagnetic modelling, but simpler in that we allow refinement only with depth. The major difficulty arose in deriving the forward modelling operators on interfaces between adjacent subgrids. We considered three ways of handling the interface layers and suggest a preferable one, which results in similar accuracy as the staggered grid solution, while retaining the symmetry of coefficient matrix. A comparison between multi-resolution and staggered solvers for various models shows that multi-resolution approach improves on computational efficiency without compromising the accuracy of the solution.

  • 45.
    Chirindja, F.J.
    et al.
    Geology Department, Eduardo Mondlane University, Maputo.
    Dahlin, Torleif
    LTH, Lund, Department of Engineering Geology, Lund University.
    Perttu, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Steinbrusch, F.
    Indian Institute of Technology Madras, Chennai.
    Owen, R.
    University of Zimbabwe, Harare.
    Combined electrical resistivity tomography and magnetic resonance sounding investigation of the surface-water/groundwater interaction in the Urema Graben, Mozambique2016In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 24, no 6, p. 1583-1592Article in journal (Refereed)
    Abstract [en]

    This study focusses on the hydrogeology of Urema Graben, especially possible interactions between surface water and groundwater around Lake Urema, in Gorongosa National Park (GNP). Lake Urema is the only permanent water source for wildlife inside GNP, and there are concerns that it will disappear due to interferences in surface-water/groundwater interactions as a result of changes in the hydraulic environment. As the lake is the only permanent water source, this would be a disaster for the ecosystem of the park. The sub-surface geology in Urema Graben was investigated by 20 km of electrical resistivity tomography (ERT) and three magnetic resonance sounding (MRS) surveys. The average depth penetration was 60 and 100 m, respectively. The location of the ERT lines was decided based on general rift morphology and therefore orientated perpendicular to Urema Graben, from the transitional areas of the margins of the Barue platform in the west to the Cheringoma plateau escarpments in the east. ERT and MRS both indicate a second aquifer, where Urema Lake is a window of the first upper semi-confined aquifer, while the lower aquifer is confined by a clay layer 30–40 m thick. The location and depth of this aquifer suggest that it is probably linked to the Pungwe River which could be a main source of recharge during the dry season. If a dam or any other infra-structure is constructed in Pungwe River upstream of GNP, the groundwater level will decrease which could lead to drying out of Urema Lake.

  • 46.
    Chouliaras, Gerassimos
    et al.
    Department of Seismology, University of Uppsala.
    Rasmussen, Thorkild Maack
    Department of Solid Earth Physics, University of Uppsala.
    The application of the magnetotelluric impedance tensor to earthquake prediction research in Greece1988In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 152, no 1-2, p. 119-135Article in journal (Refereed)
    Abstract [en]

    Continuous short period (0.1-3600 s) measurements of the magnetotelluric field components were conducted simultaneously at two sites in Greece for a period of 5 weeks. The estimation of the impedance tensor elements from 8-hr windows of recorded data, at each station, is found to describe the local electromagnetic induction with great accuracy. The computation of the residual electric field, obtained as the difference between the observed and estimated inductive part of the electric fields, clearly improves the detection of any local electric field anomaly. This method was used in an attempt to detect precursory Sci smic electrical signals (SES) that have been reported to precede earthquakes in Greece. The results indicate the success of this method in resolving ambiguities about the nature of the reported SES, i.e. whether it has an external or internal source. Although during the recording period no large earthquake occurred, five with a magnitude of between ML = 4.0 and ML = 4.3 occurred within a radius of 150 km from one of the stations. The magnetotelluric recordings and the computed residual electric fields for the time intervals reported to contain the SES precursors to these events were analysed in some detail. In two of the cases it was found that the sources could not be related to earthquake processes. In the other three cases the nature of the source of the suspected SES, although electric, could not be established with certainty. These results indicate that for earthquakes of small magnitude (ML ≤ 4.3) or of large epicentral distance (r ≥ 100 km), the detection of a SES is extremely difficult.

  • 47. D´Agrella-Filho, Mabuel S.
    et al.
    Pacca, Igor I. P.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Teixeira, Wilson
    Bettencourt, Jorge Silva
    Geraldes, M.C.
    Preliminary paleomagnetic results from metabasic and sedimentary rocks from the Amazonian craton: tectonic implications for the Rodinia supercontinent2001In: Workshop on Geology of the SW Amazonian Craton: State-of- the-art. Abstracts, Instituto de Geociências-USP , 2001, p. 155-158Conference paper (Other academic)
  • 48.
    D'Agrella-Filho, Manoel S.
    et al.
    Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Tohver, Eric
    School of Earth and Geographical Sciences, University of Western Australia, Crawley.
    Santos, João O.S.
    Redstone Resources Limited, Perth.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Trinidade, Ricardo I.F.
    Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Pacca, Igor I.G.
    Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Geraldes, Mauro C.
    Faculdade de Geologia, Universidade do Estado do Rio de Janeiro.
    Direct dating of paleomagnetic results from Precambrian sediments in the Amazon craton: Evidence for Grenvillian emplacement of exotic crust in SE Appalachians of North America2008In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 267, no 1-2, p. 188-199Article in journal (Refereed)
    Abstract [en]

    We apply a new diagenetic dating technique to determine the age of magnetization for Precambrian sedimentary rocks in the SW Amazon craton. Two new palcomagnetic poles are reported from the rocks of the Aguapei Gp.: red beds of the Fortuna Fm. (P-lat = 59.8 degrees N, P-lon = 155.9 degrees E, A(95)=9.5, K= 14, 18 sites, N/n 128/115, Q=5) and the reverse-polarity mudstones of the overlying Vale da Promissao Formation (P-lat=49.5 degrees N, P-lon = 89.3 degrees E, A(95) = 12.5, K=30, 6 sites, N/n=94/80, Q=4). The Fortuna Fm. magnetization is hosted by massive, interstitial hematite cement and constitutes a post-depositional remanence. The age of diagenesis of the red beds is well-constrained by the 1149 +/- 7 Ma U-Pb age of authigenic xenotime rims on detrital zircons determined by SHRIMP analysis. The magnetite-hosted remanence of the Vale da Promissao Fm. may be detrital in origin, but the age of deposition is poorly constrained. The reliable and precisely-dated Fortuna Fun. pateomagnetic pole fixes the paleogeographic position of the Amazon craton near the SE Appalachians portion of North America at 1.15 Ga. These data demonstrate a mobile Grenvillian link between these two cratons, and support the recent identification of Amazon crust in the Blue Ridge province region of North America

  • 49.
    D'Agrella-Filho, Manoel S.
    et al.
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Trindade, Ricardo I.F.
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Teixeira, Wilson
    Instituto de Geociências, Universidade de São Paulo.
    Yokoyama, Elder
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Tohver, Eric
    School of Earth and Geographical Sciences, University of Western Australia, Crawley.
    Geraldes, Mauro C.
    Faculdade de Geologia, Universidade do Estado do Rio de Janeiro.
    Pacca, Igor I.G.
    Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo.
    Barros, Marcia A.S.
    Instituto de Ciências Exatas e da Terra, Departamento de Geologia, Universidade Federal de Mato Grosso.
    Ruiz, Amarildo S.
    Instituto de Ciências Exatas e da Terra, Departamento de Geologia, Universidade Federal de Mato Grosso.
    The 1420 Ma Indiavaí Mafic Intrusion (SW Amazonian Craton): Paleomagnetic results and implications for the Columbia supercontinent2012In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 22, no 3-4, p. 956-973Article in journal (Refereed)
    Abstract [en]

    The configuration and the timing of assembly and break-up of Columbia are still matter of debate. In order to improve our knowledge about the Mesoproterozoic evolution of Columbia, a paleomagnetic study was carried out on the 1420 Ma Indiavaí mafic intrusive rocks that crosscut the polycyclic Proterozoic basement of the SW Amazonian Craton, in southwestern Mato Grosso State (Brazil). Alternating field and thermal demagnetization revealed south/southwest ChRM directions with downward inclinations for sixteen analyzed sites. These directions are probably carried by SD/PSD magnetite with high coercivities and high unblocking temperatures as indicated by additional rock magnetic tests, including thermomagnetic data, hysteresis data and the progressive acquisition of isothermal remanent magnetization. Different stable magnetization components isolated in host rocks from the basement 10 km NW away to the Indiavaí intrusion, further support the primary origin of the ChRM. A mean of the site mean directions was calculated at Dm = 209.8°, Im = 50.7° (α95 = 8.0°, K = 22.1), which yielded a paleomagnetic pole located at 249.7°E, -57.0°N (A95 = 8.6°). The similarity of this pole with the recently published 1420 Ma pole from the Nova Guarita dykes in northern Mato Grosso State suggests a similar tectonic framework for these two sites located 600 km apart, implying the bulk rigidity of the Rondonian-San Ignacio crust at that time. Furthermore these data provide new insights on the tectonic significance of the 1100-1000 Ma Nova Brasilândia belt –a major EW feature that cuts across the basement rocks of this province, which can now be interpreted as intracratonic, in contrast to previous interpretation. From a global perspective, a new Mesoproterozoic paleogeography of Columbia has been proposed based on comparison of these 1420 Ma poles and a 1780 Ma pole from Amazonia with other paleomagnetic poles of similar age from Baltica and Laurentia, a reconstruction in agreement with geological correlations.

  • 50.
    D’Agrella-Filho, Manoel S.
    et al.
    Universidade de São Paulo.
    Trindade, Ricardo I.F.
    Universidade de São Paulo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Yokoyama, Eder
    Universidade de São Paulo.
    Bispo-Santos, Franklin
    Universidade de São Paulo.
    A new 1.42 GA paleomagnetic pole from the Amazonian craton: implications for the Columbia supercontinent configuration2011In: Proceedings of Second Biennial Meeting of Latinmag: Tandil Argentina, November 2011, 2011Conference paper (Other academic)
    Abstract [en]

    Paleomagnetic studies carried out on the 1.42 Ga Indiavaí mafic intrusive rocks, that crop out in the SW Mato Grosso State provides a great opportunity to test the proposed paleogeographic models for Columbia. Paleomagnetic AF and thermal treatment revealed south/southwest magnetic directions with downward inclinations for sixteen analyzed sites. These directions are probably carried by SD/PSD magnetite with high coercivities and high unblocking temperatures as indicated by additional magnetic tests, including thermomagnetic curves, hysteresis loops and the IRM acquisition curves. A different magnetization obtained for host mafic rocks from the basement ca. 10 km NW away from the Indiavaí intrusive, further attests to the primary origin of the characteristic magnetic component. A mean site direction was calculated at Dm=209.8°, Im=50.7° (α95=8.0°, K=22.1), which yielded a paleomagnetic pole located at 249.7°E, -57.0°N (A95=8.6°). Comparison of this pole with other paleomagnetic poles of similar age from Baltica and Laurentia provides evidence for a link of north-northeastern Amazonian craton, southwestern Baltica and Laurentia, as previously suggested from the similar Mesoproterozoic geological evolution of their margins.

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