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  • 51.
    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.

  • 52.
    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.

  • 53.
    D'Agrella-Filho, Manoel Souza
    et al.
    Sao Paulo University.
    Trindade, Ricardo I. Ferreira
    Sao Paulo University.
    Tohver, Eric
    University of Western Australia.
    Bispo-Santos, Franklin
    Sao Paulo University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pacca, Igor I. Gil
    Sao Paulo University.
    Proterozoic paleogeographic evolution of South American cratons2008Conference paper (Other academic)
    Abstract [en]

    The South American platform is composed of four major cratons (Amazonian, São Francisco, Rio de la Plata and São Luis) and other smaller continental blocks and terrains that may have taken part in supercontinental assemblages. Here, paleogeographic configurations from the Paleoproterozoic up to the Cambrian are tested by means of an updated paleomagnetic and geochronologic record of South America, including new high-quality poles from the Amazonian and São Francisco cratons. These poles are compared to those of other cratons thought to have interacted with South American units in the Proterozoic, such as Baltica and Laurentia. The oldest assemblage of continents to be addressed is the Paleoproterozoic Columbia (~1800 Ma), for which our data support a configuration aligning Laurentia, Baltica, North China and Amazonia through their Paleo-Mesoproterozoic belts. For Neoproterozoic times (~1200-1000 Ma) a connection between Laurentia and the Amazonian craton in an evolving configuration (with relative movement between the two units) is supported by a pole-to-pole comparison. In contrast, striking differences in Laurentia's drift history compared to São Francisco, São Luis (=West Africa) and Kalahari rule-out the effective participation of these cratons in Rodinia. The assembly of Gondwana has probably occurred in different steps, comprising first (~630 Ma) the connection between Sao Francisco, Rio de la Plata, other minor blocks and the African cratons, followed by the collision of these central Gondwanan blocks with the Amazonian craton and adjoining blocks by mid-Cambrian times (~530 Ma), after the opening of the Iapetus ocean basin between Laurentia and the Amazonian craton. In this scenario, the West Gondwana was not a coherent tectonic unit before the end of Precambrian times.

  • 54.
    d'Agrella-Filho, M.S.
    et al.
    University of Sao Paolo.
    Pacca, I I G
    University of Sao Paolo.
    Sigueira, R.
    University of Sao Paolo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Teixeira, W.
    University of Sao Paolo.
    Bettencourt, J.S.
    Geraldes, M.C.
    Amazonian Proterozoic poles: implications to Rodinia paleogeography2001In: From basins to mountains: Rodinia at the turn of the century / Chris Powell Memorial Symposium / [ed] K.N. Sircombe; Z.X. Li, University of Western Australia , 2001, p. 27-30Conference paper (Other academic)
  • 55.
    D'Agrella-Filho, M.S.
    et al.
    University of Sao Paolo.
    Pacca, Igor Gal
    University of Sao Paolo.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Trinidade, R.I.F.
    University of Sao Paolo.
    Paleomagnetic evidence for oblique collision between Amazonia and Laurentia at about 1.1 Ga2004In: International Geological Congress, Abstracts: 32nd international geological congress, Florence, Italy, Aug. 20-28, 2004, 2004, p. 1089-Conference paper (Other academic)
    Abstract [en]

    The connection between Amazonia and Laurentia at late Meso- proterozoic times through the Grenville/Sunsas-Aguapei collisional belts is a key feature of Rodinia paleogeography.However, at least three different geometries are proposed for such connection, mainly due to the paucity of paleomagnetic data for Amazonia.Connections along Greenland and Labrador were initially proposed based on the fit of geological provinces and scarse virtual geomagnetic poles.More recently, a connection through the Llano belt in Texas was proposed based on a single well dated 1.2 Ga paleopole obtained in mafic rocks from the Nova Floresta Formation. We present a series of poles obtained on sedimentary rocks of the Aguapei Group (western Matto Grosso State-Amazonian Craton) and intrusive mafic rocks, whose evolution is related to the Meso-Neoproterozoic Aguapei-Sunsas orogeny (1.3-0.9 Ga).Together with the 1.2 Ga Nova Floresta pole, they define a straight apparent polar wander path which matches the Laurentia APWP by 1.1 Ga for a connection along the (present day) Labrador region. The pole's trajectories imply a high degree of obliquity for such a collision in agreement with tectonic models put forward for the southwestern margin of Amazonia, the southeastern margin of Laurentia and the southwestern margin of Baltica.

  • 56.
    Darwesh, Ali
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Parameters optimization of oil well drilling operations2019Doctoral thesis, comprehensive summary (Other academic)
  • 57.
    Darwesh, Ali K.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maack Rasmussen, Thorkild
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Kicks controlling techniques efficiency in term of time2017In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 5, p. 482-492Article in journal (Refereed)
    Abstract [en]

    Kicks are the result of under balance drilling operation. Time consumed to control the kicks will be different in depending on the controlling technique. Drilling fluid considered as a first barrier to control formation pressure and well kicks. Any advance in drilling fluids leads to more controlled operation in term of time. This paper will follow the general increasing profile of pressure before entering the reservoir. Both methods of well controlling technique; circulating techniques and non-circulating have been implemented in many oil blocks. The process of designing and casing selection, setting depth and many other issues is predominately dependent on the utilization of accurate values of formation pressure. Formation pressures used to design safe mud weights to overcome fracturing the formation and prevent well kicks. Hence the emphasis has been placed on the practical utilization of kicks pressure near the reservoir. The presented relationships will help the engineer to better understand lithological columns and reduce potential hole problems during the kick appearance. Selecting the best well controlling practical method can lead to not harming the reservoir and more production later. Changes in some drilling fluid properties have been proposed with increasing the depth without damaging the reservoir. Suggestions in relation to the casing setting point of the intermediate section are also proposed. Standard equations with proper modification for gases and safety margin have been proposed for the future drilling operation in oil fields above the reservoir.

  • 58.
    Darwesh, Ali K.
    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.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Time Optimizing near the Pay Zone2017In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 10, p. 848-858Article in journal (Refereed)
    Abstract [en]

    Well control techniques are used in oil and gas drilling operations to control bottom hole pressure and avoid any fluid influx from formation to the well. These techniques are highly important near the pay zone in term of time. Controlling formation fluid pressure and thereby the formations behavior in a predictable fashion will help toward more optimized environmental friendly drilling operation. Time consumed to control the formation fluid pressure will range between few hours to many days. This paper discusses hydrostatic pressure distribution and changes near the pay zone for one oil blocks in Kur- distan, in the northern part of Iraq. Obtaining homogeneous increase in some drilling fluid properties will help the engineer to better interpret sampling of the lithological columns and reduce potential hole problems and operationtime.

  • 59.
    Darwesh, Ali
    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.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Evaluation of Limestone Interval in the Drilled Surface Section of Bn-1 Oil Well2016In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 8, no 8, p. 515-524Article in journal (Refereed)
    Abstract [en]

    The first exploration oil well in any oil block consumes in general more time and cost than the other wells in the same block. Evaluating the drilled wells serves to improve the future operations. This paper evaluates the drilled surface section through real field data for the first exploration oil well drilled in one of the oil blocks, in Kurdistan north of Iraq. The surface section of the well was drilled with the conventional method to penetrate many different geological formations with tight intervals. Drilling efficiency and the difficulties encountered are discussed and explained using various data sources. All daily drilling reports concerning a specific interval were studied. This includes weight on bit, string rotation, mud pump flow and penetration rate. Evaluation was carried out by analyzing the used controllable drilling parameters with the formations features. Penetration of the Pila Spi formation (Middle Eocene) was the most difficult formation in the drilled section. Microsoft Office 365 Pro Plus used in making graphs and Excel tables. Evaluations showed that the conventional technology used left many negative effects, like increase in None Productive Time NPT, cost and ground water pollution. Simultaneous Casing Drilling method proposed as an alternative method for the future campaign.

  • 60.
    Darwesh, Ali
    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.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods2018In: Open Petroleum Engineering Journal, ISSN 1874-8341, Vol. 11, p. 14-28Article in journal (Refereed)
    Abstract [en]

    Background: This paper discusses the wiper trip effects on well instability in shale formations.Objectives: Problematic shale interval sections have been studied for the time spent on the wiper trip operations. Lifting efficiency and well wall instability change with the time analyzed. Detailed drilling operation, formation heterogeneity, rheological and filtration characteristics of polymer water-based mud are discussed. Physical and chemical properties of the drilled formation and drilling fluid are also studied.Materials and Methods: Wiper trips are analyzed using a typical drawing program to find the relations between the most controllable parameters. For that, two calculation models have been implemented to find the net rising cutting particles velocity in the annular. The relation between the net rising velocity and wiper trips is analyzed. Laboratory works have been done to support the findings of field work.Results: Strong relations have been found between the wiper trip impacts and lithology types of the penetrated shale.Conclusion: A modified drilling program is proposed in relation to changes in casing setting depth and drilling fluid properties that make the operations more efficient in cost and time.

  • 61. Das, U.C.
    et al.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Resistivity and induced polarization responses of arbitarily shaped 3-D bodies in a two-layered Earth1987In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 35, no 1, p. 98-109Article in journal (Refereed)
  • 62.
    Donadini, Fabio
    et al.
    Scripps Institution of Oceanography, La Jolla, United States of America.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tauxe, Lisa
    Scripps Institution of Oceanography, La Jolla, United States of America.
    Paleointensity results from the 1.7 GA old hoting Gabbro, Sweden2009Conference paper (Other academic)
    Abstract [en]

    Complete text of publication follows. The Hoting Gabbro is located in the western part of the Central Svecofennian Subprovince, and dates about 1.786+-0.010 Ga. In the Hoting area, dykes intruded at around 1.6 Ga, and partly remagnetized the gabbros. Previous paleomagnetic and geochemical studies indicated that the stable characteristic remanent magnetization was acquired at about 1.7 Ga, when the slow cooling of the gabbro is taken into account. Preliminary palaeointensity studies from gabbros in the Hoting area suggested a very low field of about 5.8+-1.9 muT. Unfortunately, at that stage, only two sites out of nine yielded results. During 2008, we sampled seven sites from the Hoting area in order to perform new palaeointensity experiments. At Scripps, we applied the IZZI method on 60 specimens, and 39 yielded reliable results varying between 3 and 20 muT, and confirm the previous low results. Low field values have been associated with oxyexolution processes that might bias the palaeointensity result towards low values, and so we are currently investigating the mineralogy of the samples with SEM analyses. We will present the details of the palaeointensity and mineralogical results, and infer the evolution of the geomagnetic field during Precambrian.

  • 63.
    Donadini, Fabio
    et al.
    Institut für Geophysik, ETH Zürich.
    Elming, Sten-Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tauxe, Lisa
    Scripps Institution of Oceanography, University of California, San Diego.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Mineralogy.
    Paleointensity determination on a 1.786 Ga old gabbro from Hoting, Central Sweden2011In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 309, no 3-4, p. 234-248Article in journal (Refereed)
    Abstract [en]

    Paleointensities from Precambrian rocks are rare and might be biased by remagnetization processes. Here we present new analyses of samples from a 1.786 Ga gabbro near Hoting, Central Sweden. Rock magnetic and mineralogical analyses indicate that one of the sites (site 5) may be pristine, whereas the others exhibit evidence of alteration. Characteristic remanent magnetization was determined using principal component analysis for each sample and was compared with results obtained in a previous study of Elming et al. (2009). Intensity measurements from site 5 show higher values compared to those of the other sites, suggesting that alteration processes may lead to underestimation of the field intensity. After cooling rate and anisotropy correction, the field moment at 1.786 Ga was estimated to be 25.6 ± 3.3 ZAm2 and 15.2 ± 6.1 ZAm2 from site 5 only and from all sites respectively. We consider the result from site 5 to be more accurate owing to the lack of evidence for alteration; our estimates agree well with the Proterozoic VDM values suggested by Biggin et al. (2009).

  • 64. Dyrelius, D.
    et al.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bergarters fysik1985In: Geofysik, Uppsala: Svenska fysikersamfundet , 1985Chapter in book (Other (popular science, discussion, etc.))
  • 65.
    Døssing, Arne
    et al.
    DTU Space, National Space Institute, Technical University of Denmark.
    Hopper, John R.
    Geological Survey of Denmark and Greenland (GEUS), Copenhagen.
    Olesen, Arne Vestergaard
    DTU Space, National Space Institute, Technical University of Denmark.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland (GEUS), Copenhagen.
    Halpenny, John F.
    Natural Resources Canada, Ottawa, ON.
    New aero-gravity results from the Arctic: Linking the latest Cretaceous-early Cenozoic plate kinematics of the North Atlantic and Arctic Ocean2013In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 14, no 10, p. 4044-4065Article in journal (Refereed)
    Abstract [en]

    The tectonic history of the Arctic Ocean remains poorly resolved and highly controversial. Details regarding break up of the Lomonosov Ridge from the Barents-Kara shelf margins and the establishment of seafloor spreading in the Cenozoic Eurasia Basin are unresolved. Significantly, the plate tectonic evolution of the Mesozoic Amerasia Basin is essentially unknown. The Arctic Ocean north of Greenland is at a critical juncture that formed at the locus of a Mesozoic three-plate setting between the Lomonosov Ridge, Greenland, and North America. In addition, the area is close to the European plate, resulting in complicated interactions between all these areas that are difficult to resolve. In 2009, the 550,000 km2 LOMGRAV aero-geophysical survey produced the first collocated gravity and magnetic measurements over the area, significantly increasing the data coverage. We present an interpretation of a new free-air gravity compilation, which reveals a regionally consistent structural grain across the Lomonosov Ridge, the Ellesmere and Lincoln Sea shelves, and the Alpha Ridge. We interpret the grain as evidence of latest Cretaceous (∼80 Ma) regional extension in response to the northward propagation of Atlantic and Labrador Sea opening into the Arctic, west of Greenland. This interpretation is consistent with coincident alkaline volcanic activity evident in the borderlands of the Lincoln Sea. We further suggest that Eurekan crustal shortening contributed to the formation of the distinct Lomonosov Ridge plateau against an important fault zone north of Greenland. Our results provide new constraints for Cretaceous-Cenozoic plate reconstructions of the Arctic. Key Points Presentation of the largest aero-gravity survey acquired over the Arctic Ocean Plate tectonic link between Atlantic and Arctic spreading west of Greenland New plate reconstruction models are presented for the area north of Greenland

  • 66.
    Døssing, Arne
    et al.
    DTU Space, National Space Institute, Technical University of Denmark.
    Jackson, H. Ruth
    Geological Survey of Canada Atlantic (GSCA), Halifax.
    Matzka, Jürgen
    National Space Institute, DTU Space.
    Einarsson, Indridi
    National Space Institute, DTU Space.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland (GEUS) .
    Brozena, John M.
    Naval Research Laboratory.
    On the origin of the Amerasia Basin and the High Arctic Large Igneous Province-Results of new aeromagnetic data2013In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 363, p. 219-230Article in journal (Refereed)
    Abstract [en]

    The history of the 2.5 million km2 Amerasia Basin (sensu lato) is in many ways the least known in the global tectonic system. Radically different hypotheses proposed to explain its origin are supported only by inconclusive and/or indirect observations and several outstanding issues on the origin of the Basin remain unaddressed. The difficulty lies in the geodynamic evolution and signature of the Basin being overprinted by excess volcanism of the Alpha-Mendeleev Ridge complex, part of the High Arctic Large Igneous Province (HALIP) and one of the largest (>1 million km2) and most intense magmatic and magnetic complexes on Earth. Here, we present the results of a 550,000km2 aerogeophysical survey over the poorly explored Lomonosov Ridge (near Greenland) and adjoining Amerasia and Eurasia Basins that provides the first direct evidence for consistent linear magnetic features between the Alpha and Lomonosov Ridges, enabling the tectonic origin of both the Amerasia Basin and the HALIP to be constrained. A landward Lower Cretaceous ( ~ 138 - 125(120) Ma) giant dyke swarm (minimum 350×800km2) and tentative oceanward Barremian (or alternatively lower Valanginian-Barremian) seafloor spreading anomalies are revealed. Prior to Cenozoic opening of the Eurasia Basin the giant dyke swarm stretched from Franz Josef Land to the southern Alpha Ridge and possibly further to Queen Elisabeth Islands, Canada. The swarm points towards a 250-km-wide donut-shaped anomaly on the southern Alpha Ridge, which we propose was the centre of the HALIP mantle plume, suggesting that pronounced intrusive activity, associated with an Alpha Ridge mantle plume, took place well before the Late Cretaceous Superchron and caused continental breakup in the northern Amerasia Basin. Our results imply that at least the southern Alpha Ridge as well as large parts of the area between the Lomonosov and southern Alpha Ridges are highly attenuated continental crust formed by poly-phase breakup with LIP volcanic addition. Significantly, our results are consistent with an early ( ~ pre-120 Ma) overall continental scale rotational opening of the Amerasia Basin in which the Eurasian continental margin is rifted from the Canadian-southern Alpha Ridge margin about one or more poles in the Mackenzie Delta (Alaska). The findings provide a key to resolving Arctic plate reconstructions and LIPs in the Mesozoic.

  • 67. Edfelt, Åsa
    et al.
    Sandrin, Alessandro
    Luleå tekniska universitet.
    Evins, Paul
    EGRU, School of Earth Sciences, James Cook University.
    Jeffries, Teresa
    Natural History Museum, London.
    Storey, Craig
    Open University, Walton Hall, Milton Keynes.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Stratigraphy and tectonic setting of the host rocks to the Tjårrojåkka Fe-oxide Cu-Au deposits, Kiruna area, northern Sweden2006In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 128, no 3, p. 221-232Article in journal (Refereed)
    Abstract [en]

    The Tjårrojåkka area is located about 50 km WSW of Kiruna, northern Sweden, and hosts one of the best examples of spatially and possibly genetically related Fe-oxide and Cu-Au occurrences in the area. The bedrock is dominated by intermediate and basic extrusive and intrusive rocks. An andesite constrains the ages of these rocks with a U-Pb LA-ICPMS age of 1878±7 Ma. They are cut by dolerites, which acted as feeder dykes for the overlying basalts. Based on geochemistry and the obtained age the andesites and basaltic andesites can be correlated with the 1.9 Ga intermediate volcanic rocks of the Svecofennian Porphyrite Group in northern Sweden. They formed during subduction-related magmatism in a volcanic arc environment on the Archaean continental margin above the Kiruna Greenstone Group. Chemically the basalts and associated dolerites have the same signature, but cannot directly be related to any known basaltic unit in northern Sweden. The basalts show only minor contamination of continental crust and may represent a local extensional event in a subaquatic back arc setting with extrusion of mantle derived magma. The intrusive rocks range from gabbro to quartz-monzodiorite in composition. The area is metamorphosed at epidote-amphibolite facies and has been affected by scapolite, K-feldspar, epidote, and albite alteration that is more intense in the vicinity of deformation zones and mineral deposits. Three events of deformation have been distinguished in the area. D1 brittle-ductile deformation created NE-SW-striking steep foliation corresponding with the strike of the Tjårrojåkka-Fe and Cu deposits and was followed by the development of an E-W deformation zone (D2). A compressional event (D3), possible involving thrusting from the SW, produced folds in the central part of the area and a NNW-SSE striking deformation zone in NE.

  • 68.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A palaeomagnetic study and K-Ar age determinations of tertiary rocks in Nicaragua1998In: Geoscientific research in Nicaragua: a Swedish-Nicaraguan joint project during the period 1981-1991, Luleå: Luleå tekniska universitet, 1998, p. 1-19Chapter in book (Other academic)
  • 69.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A palaeomagnetic study of Svecokarelian basic rocks from northern Sweden1985In: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 107, no 1, p. 17-35Article in journal (Refereed)
    Abstract [en]

    This palaeomagnetic investigation comprises basic rocks from six localities from the Svecokarelian zone in northern Sweden. Most of the pole positions in this study and other reported poles of Svecokarelian and post-Svecokarelian rocks fall within an approximately 12 degrees wide band running from east to west representing ages of magnetizations from 1880-1700 to ∼ 1530 Ma. Thermal demagnetizations of specimens of the probably oldest massifs indicate a possible backward continuation of the polar wandering path. Mineralogical studies of thin sections of the rocks show ore symplectites and myrmekitic textures indicating a slow rate of cooling at least at the end of the rock formation. Signs of metamorphism are demonstrated by the existence of secondary minerals, including magnetite, not related to late magmatic alterations. The distribution of site means as well as the change of directions of the remanence vectors during thermal demagnetization can be explained by a slow rate of cooling and where signs of metamorphism exist by partial remagnetization of the rock. This study has, apart from the palaeomagnetic results, demonstrated the difficulty of correlating radiometric ages with ages of magnetization

  • 70.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Basic dykes and dyke swarms in central and northern Sweden and the plate tectonic evolution of Fennoscandia: palaeomagnetic and Ar39/Ar40 studies2005In: "Dyke swarms - time markers of crustal evolution": Fifth International Dyke Conference, Pohtimolampi Wilderness Hotel, Polar Circle, Rovaniemi, Finland, 31 June - 3 August 2005 ; abstracts and programme / [ed] Jouni Vuollo; Satu Mertanen, Espoo: Geological Survey of Finland , 2005, p. 11-Conference paper (Other academic)
    Abstract [en]

    Palaeomagnetic and Ar39/Ar40 studies have been performed on basic dykes and dyke swarms in central and northern Sweden. At least five different generations of dykes have been defined and will be discussed in a plate tectonic context. Reliable palaeomagnetic data have been obtained from a big gabbro diabase and a geographically related dyke swarm in the northern part of Sweden from which poles similar to those calculated from Svecofennian gabbros (ca 1.86 Ga) are defined. In another swarm of palaeomagnetically similar age, just north of the Skellefte district, partially remagnetized dykes indicate a possible Subjotnian or Caledonian regional remagnetization. The dykes are younger when moving towards the south and in the central part there is a significant dyke swarm with at least two generations of dykes (ca. 1.7 and 1.6 Ga, respectively), one of which is related with rapakivi magmatism. Palaeomagnetic and anisotropy of magnetic susceptibility (AMS) data from the huge ca 1.25 Ga sill complexes in central Sweden and western Finland and from basic intrusions in Greenland suggest that Baltica and Laurentia were joined at that time. The similar stress field as indicated by the AMS data and the tensional regime reflected by the sill complexes is interpreted related to the break up of Baltica from Laurentia. New data from ca 1.1 Ga dykes in central Sweden confirms a clockwise rotation of Fennoscandia between 1.25 and 1.1 Ga, a rotation that is not seen for Laurentia.

  • 71.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Density and magnetic properties of rocks in the Caledonides of Jämtland, Sweden1980In: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 102, no 4, p. 439-453Article in journal (Refereed)
    Abstract [en]

    Density and magnetic properties were determined on some 1350 rock samples, taken from the different lithologies in the Caledonides of Jmtland, Sweden. The density determinations showed a strong trend of increasing density when moving from east to west in the investigated area. There was also a general increase in density upwards in the tectono-stratigraphy from the autochthon to the Seve of the Seve-Kli Nappe Complex. The determination of magnetic properties showed that east of the Caledonian Front the dominating high-susceptibility rock was the Rtan granite. In the Eastern Complex, west of the Caledonian Front, high-susceptibility rocks were found in the parautochthonous and allochthonous crystalline basement, whereas in the Western Complex the Ottfjllet dolerite in the Srv Nappe was the dominating high-susceptibility rock.

  • 72.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Evidence for early Proterozoic plate tectonics from seismic reflection profiles in the Baltic Shield1990In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 348, p. 34-38Article in journal (Refereed)
    Abstract [en]

    Plate tectonics provides the linking framework for all tectonic and magmatic activity seen today, but it is not known when plate tectonics first developed on Earth. New deep seismic reflection and coincident refraction profiles across an exposed, 1.89-Gyr-old volcanic arc complex show a 10-km-thick offset in the Moho and bivergent reflectors in the crust, which were most probably created by plate convergence, subduction and accretion during the Early Proterozoic. Hence, plate tectonic models seem to be applicable for at least the second half of Earth's history.

  • 73.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geological modelling based on gravity data from the central part of the Swedish caledonides1988In: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 110, no 4, p. 317-327Article in journal (Refereed)
    Abstract [en]

    Gravimetric measurements have been carried out within a c. 500 km2 area of western Jämtland in the Swedish Caledonides. Using different types of regional-residual gravity field separations, various geological models have been tested to fit the measured gravity data. Information on the geology and density of the rocks have reduced the number of possible models which are presented along two profiles. These models confirm the existence of antiforms and synforms running approximately parallel to the mountain range. The main profile crosses the two synforms over which positive anomalies are identified. Both in the western Tnnfors Synform and the eastern re Synform this is explained by the presence of high density Seve rocks, in the former case occurring beneath a cover of Kli Nappes. The depth to the base of the Seve Nappe units in the Tnnfors Synform is calculated at 4.5 km and in the re Synform at 3 km. The maximum depth to the interface between Kli and Seve rocks in the Tnnfors district is 3.2 km. Gravimetric models of the basement rocks in the windows, and difference in physical properties between the crystalline rocks of the windows and those of the autochthonous basement east of the Caledonian thrust front, imply that the basement exposed in the antiforms is allochthonous. A gravity minimum east of the re Synform is interpreted as a southern continuation of low density granites related to the Olden Complex. The inferred thickness of these low density rocks suggests that it may be a part of the autochthonous basement.

  • 74.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geological modelling based on gravity data from the central part of the Swedish Caledonides1991In: Vol. 113, no 2-3, p. 257-258Article in journal (Other academic)
  • 75.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Integrated seismic studies of the Baltic shield using data in the Gulf of Bothnia region1993In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 112, no 3, p. 305-324Article in journal (Refereed)
    Abstract [en]

    In the autumn of 1989 a co-operative experiment involving 12 research institutions in northwestern Europe collected 2268 km of deep seismic reflection profiles in the Gulf of Bothnia and the Baltic Sea. the 121 litre airgun array used for this profiling was also recorded by 62 muiticomponent land stations to provide coincident refraction surveys, fan-spreads, and 3-D seismic coverage of much of the Gulf of Bothnia. We thus have potentially both high-resolution impedance contrast images as well as more regional 3-D velocity models in both P- and S-waves. In the Bothnian Bay a south-dipping, non-reflective zone coincides with the conductive Archaean-Proterozoic boundary onshore in Finland. Between the Bothnian Bay and Bothnian Sea observed reflectivity geometries and velocity models at Moho depths suggest structures inherited from a 1.9Ga subduction zone; the upper crust here appears to have anomalously low velocity. Within the Bothnian Sea, reflectivity varies considerably beneath the metasedimentary/granitoid rocks of the Central Svecofennian Province (CSP) and the surrounding metavolcanic-arc rocks. Numerous dipping reflectors appear throughout the metavolcanic crust, whereas the CSP has little reflectivity. Wide-angle reflections indicate that the metasedimentary crust of the Bothnian Basin is 10 km thicker than the neighbouring Svecofennian subprovinces. Near the Åland archipelago Rapakivi granite plutons exhibit bright reflections, a contrast to the usual non-reflective plutons elsewhere in western Europe. Additional dipping reflections deep in the crust of this area may support models of rifting and crustal thinning during emplacement of the 1.70-1.54 Ga Rapakivi granites. Coeval gabbroic/anorthositic magmatism may explain the high reflectivity and high velocity of these plutons. the c. 1.25 Ga mafic sills and feeder dykes of the Central Scandinavian Dolerite Group also produce clear reflections on both near- and far-offset seismic sections. Continued modelling will produce better velocity models of the crust and better constrained contour maps of crustal thickness in this part of the Baltic shield.

  • 76.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic properties of pyrrhotite1981In: Vol. 19, no 2, p. 144-Article in journal (Other academic)
  • 77.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Palaeomagnetism of Precambrian rocks in northern Sweden and its correlation to radiometric data1994In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 69, no 1-4, p. 61-79Article in journal (Refereed)
    Abstract [en]

    A palaeomagnetic study has been performed on Palaeo- to Mesoproterozoic basic intrusions and volcanic rocks from the Fennoscandian shield in northern Sweden. Three, possibly four, different generations of magnetizations were identified, the oldest assigned to a Svecofennian age (1.86-1.89 Ga). A second generation is related to the intrusion of granitoids of 1.80-1.76 Ga. In this geological event probably also the third group of directions has its origin. These different magnetizations may indicate that there are at least two different generations of basic intrusions in northern Sweden. A fourth group of directions is isolated as overprints. This magnetization is interpreted to be a Subjotnian magnetization, reflecting a previously unrecognized regional Subjotnian metamorphic event in the northwestern part of the Fennoscandian shield. The drift history for the Fennoscandian shield during the period 1.88-1.50 Ga has been defined based on these new palaeomagnetic data

  • 78.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Recording marine airgun shots at offsets between 300 and 700 km1991In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 18, no 4, p. 645-648Article in journal (Refereed)
    Abstract [en]

    This paper demonstrates that - under favorable conditions - by using multichannel recording and subsequent stacking of adjacent records marine airgun shots have been detected at offset distances up to 700 km, the maximum offset at which the authors attempted to record data.^Besides a powerful airgun array, a low noise environment at the recording site and the elimination of static shifts are the prerequisites to obtain refracted and reflected arrivals from the crust and upper mantle at such large offsets.^Primary arrivals detected at offsets between 400 and 700 km image the upper mantle from 70 to about 120 km depth.^Stacking of neighboring shots and/or receivers successfully increases the signal-to-noise ratio, if the traces have been corrected for offset differences, which requires knowledge of the apparent phase velocities.^The data presented here were collected in autumn 1989 during the BABEL Project on the Baltic Shield.

  • 79.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Research in rock magnetism and palaeomagnetism with reference to Caledonian and Precambrian rocks in Sweden1982Doctoral thesis, comprehensive summary (Other academic)
  • 80.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Subjotnian metamorphism in northern Sweden: a palaeomagnetic analysis of rocks from the northern svecofennian province and the Skellefte district1993In: 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. 44-Conference paper (Other academic)
  • 81.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    The definition of the southern extension of the Chortis block: a palaeomagnetic and regional geophysical study 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. 45-Conference paper (Other academic)
  • 82.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bylund, Göran
    Palaeomagnetism and the Siljan impact structure, central Sweden1991In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 105, no 3, p. 757-770Article in journal (Refereed)
    Abstract [en]

    A palaeomagnetic study of rocks, from inside and outside the impact structure has been carried out, with the aim of identifying natural remanent magnetizations (NRMs) related to the impact event. Three different directions of magnetizations, not recognized elsewhere, were identified within the central part of the structure. These three magnetizations are defined in terms of coercivity and blocking temperature. The implications of the results are discussed in relation to ages obtained from Ar-Ar dating of impact melt

  • 83.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bylund, Göran
    Lund University.
    Paleomagnetism and the Siljan impact structure, central Sweden1990In: Programme and abstracts: symposium Fennoscandian impact structures, may 29-31, 1990, Espoo and Lappajärvi, Finland / [ed] L.J. Pesonen; H. Niemisara, Geological Survey of Finland , 1990, p. 25-Conference paper (Other academic)
  • 84.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bylund, göran
    Lund University.
    Paleomagnetism and the Siljan impact structure, Central Sweden1992In: Vol. 114, no 1, p. 158-Article in journal (Other academic)
  • 85.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    D'Agrella-Filho, M.S.
    Universidade de São Paulo.
    Page, L.M.
    University of Lund.
    Tohver, E.
    School of Earth and Geographical Sciences, University of Western Australia, Crawley.
    Trindade, R. I. F.
    Universidade de São Paulo.
    Pacca, I.I.G.
    Universidade de São Paulo.
    Geraldes, M.C.
    Faculdade de Geologia, Universidade do Estado do Rio de Janeiro.
    Teixeira, W.
    Instituto de Geociências, Universidade de São Paulo.
    A palaeomagnetic and Ar-40/Ar-39 study of late precambrian sills in the SW part of the Amazonian craton: Amazonia in the Rodinia reconstruction2009In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 178, no 1, p. 106-122Article in journal (Refereed)
    Abstract [en]

    A new key palaeomagnetic pole (Plat. = 64.3°S, Plon. = 271.0°E, N = 14, A95= 9.2°; Q = 5) is calculated from a primary magnetization isolated in early Neoproterozoic Aguapei basic sills and dykes hosted by 1.3-1.0 Ga sedimentary rocks from the southwestern part of the Amazon craton. The characteristic remanence carried by stable, pseudo-single domain titanomagnetite shows two antipodal polarities that pass a reversals test. Magnetic anisotropy for most sites shows fabric orientations that are typical of sills, with horizontal magnetic foliations concordant to the flat-lying bedding of the host sedimentary rocks. 40Ar/39Ar analyses for one of the sills reveal a well-defined plateau age at 981 ± 2 Myr. A tectonic reconstruction for Amazonia relative Laurentia based on this new pole 'is consistent with' a position of the present northwestern part of Amazonia attached with eastern Laurentia close to Greenland at ca. 981 Ma. On basis of palaeomagnetic and geological data, we propose a scenario where Amazonia moved northeastwards along the present southeast coast of Laurentia from ca. 1200 to 980 Ma. By 980 Ma, Amazonia is placed alongside Laurentia and Baltica, in a position similar to other reconstructions of Rodinia but with a significantly different orientation.

  • 86.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Enmark, Thomas
    Widenfalk, Lennart
    A combined geological petrophysical and geophysical investigation of the Notträsk gabbro, northern Sweden1983In: Vol. 105, no 4, p. 386-387Article in journal (Refereed)
  • 87.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jensen, Mai-Britt Mose
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    A correlation of AMS and rock quality in crystalline and sedimentary rocks in the Kiirunavaara hanging wall2012In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 86, p. 54-69Article in journal (Refereed)
    Abstract [en]

    A study of the magnetic fabric and rock quality has been performed on crystalline and sedimentary rocks from the hanging wall of the Kiirunavaara iron ore deposit, northern Sweden. The rock samples were taken from 12 outcrops and three oriented drillcores and consist of quartzite, siltstone, conglomerate, porphyritic basalts, quartz-bearing porphyry and mylonite.Anisotropy of magnetic susceptibility (AMS) was used to determine the texture of the rocks by defining the shape of the magnetic susceptibility ellipsoids, the orientation of the magnetic foliation planes and the degree of magnetic anisotropy. AMS data from the outcrops as well as data from the uppermost part of two of the drillcores was used to produce a surface contour map which indicates that both the dip of the magnetic foliation plane and the degree of magnetic anisotropy decreases towards the east. These two parameters thus generally follow the major structural features of the Kiruna region.Two classical rock mechanical parameters, RQD (Rock Quality Designation) and F/m (fractures pr. meter), were used to quantify the amount of discontinuities and fractures in the drill cores. RQD and F/m was subsequently correlated with the AMS data, and a correlation was observed, with the correlation coefficient r varying between 0.6142-0.7557. The correlation was limited to just one of the drillcores however it could be traced across rock type boundaries. The correlation indicates that AMS may be used as an indicator tool of the rock mechanical properties in both crystalline and sedimentary rocks.

  • 88.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kravchenko, S. N.
    National Academy of Sciences of Ukraine.
    Layer, P.
    University of Alaska.
    Rusakov, O. M.
    National Academy of Sciences of Ukraine.
    Glevasskaya, A. M.
    National Academy of Sciences of Ukraine.
    Mikhailova, N. P.
    National Academy of Sciences of Ukraine.
    Bachhtadse, V.
    Ludwig-Maximilians-University.
    Palaeomagnetism and AR-40/AR-39 age determinations of the Ediacaran traps from the southwestern margin of the East European Craton, Ukraine: relevance to the Rodinia break-up2007In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 164, no 5, p. 969-982Article in journal (Refereed)
    Abstract [en]

    A palaeomagnetic study and age determinations have been performed on Ediacaran basalts from the northwestern Ukraine. Whole-rock ^sup 40^Ar/^sup 39^Ar age determination revealed plateau ages at 590-560 Ma and 393 Ma, the latter probably reflecting a resetting of the radiometric system. Palaeomagnetic poles have been calculated from five basalt flows, two of which (A poles) are considered reliable with ages that range from 580 to 560 Ma. Tentative poles (B poles), calculated from most probably primary magnetizations, have ages estimated at 580-545 Ma. Secondary magnetizations, possibly of late Ediacaran or Devonian age, have also been isolated (C poles). Based on the new poles, Baltica drifted together with Laurentia from an equatorial position at c. 750 Ma to occupy high southern latitude positions at c. 580 Ma. Baltica during that time period was joined to Laurentia in a similar relative position to that at 750 Ma. The two shields then split up from each other and from c. 550 Ma Baltica drifted at moderately high latitudes and rotated some 180° during the final opening of the Iapetus ocean. This reconstruction suggests that during the Ediacaran glaciation Baltica occupied high-latitude positions, which contradicts the high-obliquity model to explain low-latitude Neoproterozoic glaciations

  • 89.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kravchenko, Svetlana
    Geophysical Institute, Academy of Sciences of Ukraine, Kiev.
    A palaeomagnetic study of Mesoproterozoic basic dykes from the Ukrainian Shield and the amalgamation of the shield with Fennoscandia2005In: "Dyke swarms - time markers of crustal evolution": Fifth International Dyke Conference, Pohtimolampi Wilderness Hotel, Polar Circle, Rovaniemi, Finland, 31 June - 3 August 2005 ; abstracts and programme / [ed] Jouni Vuollo; Satu Mertanen, Espoo: Geological Survey of Finland , 2005, p. 12-Conference paper (Other academic)
    Abstract [en]

    A palaeomagnetic study has been performed on Palaeo-Mesoproterozoic basic intrusions from three crustal blocks of the Ukrainian Shield. At least three different generations of dykes has been identified and positive field tests can be demonstrated for some of them. A sequence of 2.1 to 1.72 Ga apparent polar wander has been defined on basis of the new palaeomagnetic and Ar/Ar data presented here and on basis of old data from anorthosites. The calculated poles are significantly different from poles of similar age from the Fennoscandian Shield. Although the poles are not perfectly coeval the tectonic reconstructions demonstrate that the Ukrainian Shield collided with Fennoscandia at 1.80-1.85 Ga and then rotated some 45° into its present relative position.

  • 90.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Kravchenko, Svetlana
    Institute of Geophysics, Acadamy of Science, Kiev.
    Mikhailova, Ninel
    Geophysical Institute, Academy of Sciences of Ukraine, Kiev.
    The consolidation of the East European Craton: a palaeomagnetic analysis of Proterozoic rocks from the Ukrainian and Fennoscandian shields1999In: Vol. 4, no 1, p. 151-Article in journal (Other academic)
  • 91.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Layer, P.
    Geophysical Institute, University of Alaska.
    Ubieta, K.
    Centro de Investigaciones Geoscientificas (CIGEO), the Autonomous University of Nicaragua (UNAN), Managua.
    A palaeomagnetic study and age determinations of Tertiary rocks in Nicaragua, Central America2001In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 147, no 2, p. 294-309Article in journal (Refereed)
    Abstract [en]

    Palaeomagnetic, K-Ar and Ar40/Ar39 measurements have been made to elucidate Nicaragua's plate tectonic history. These show that the Nicaraguan Highland rotated 90° counterclockwise between 30 and 18 Myr ago, but the Pacific Coastal Plain has not rotated.A lack of data has prevented a direct comparison with the tectonic history of adjacent areas, in particular, the Chortis Block, which is the part of the Caribbean Plate that is geologically most closely related to the Nicaraguan Highland. However, our data suggest that the Caribbean Plate in this part of Central America was not consolidated until c. 15 Ma.

  • 92.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Layer, Paul
    Geophysical Institute, University of Alaska Fairbanks.
    Söderlund, Ulf
    Department of Geology, Lund University.
    Cooling history and age of magnetization of a deep intrusion: A new 1.7 Ga key pole and Svecofennian-post Svecofennian APWP for Baltica2019In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 329, p. 182-194Article in journal (Refereed)
    Abstract [en]

    A paleomagnetic and chronogical study has been performed on the Turinge gabbro-diabase formation and on a cross cutting basic dyke in central Sweden and on the Joulovaara gabbro intrusion in northern Sweden in the Fennoscandian Shield. U-Pb age of baddeleyite and 40Ar/ 39Ar ages of hornblende and biotite reveal a cooling history of the deep gabbro-diabase intrusion in Turinge. The cooling is suggested to have taken place in two stages, one related to the time of intrusion in temperature down to ca 500 °C with a cooling rate up to 46 - 59°/Ma and another at a lower rate of ca 2.9 °C/Ma, which is suggested to be related with uplift. From this cooling history it can be concluded that the magnetization age of the diabase, ca 1695 – 1700 Ma is close to the crystallization age and the 40Ar/39Ar age of hornblende. Applying a similar cooling history for the other studied deep intrusion, the ca 1800 Ma gabbro of Joulovaara gabbro, it is estimated that the magnetization age of the gabbro should be close to that of the U-Pb age of the formation, although the pole of the Joulovaara gabbro is less reliable.

    The cooling history presented here for the Turinge gabbro-diabase has implications for estimations of magnetization ages also for other deep intrusions.

    The new pole (Plat. = 51.6°, Plon. = 220.2°; A95= 4.8°) of the Turinge gabbro-diabase passes most of the reliability criteria and is considered a new key pole for Fennoscandia.

    The Basic dyke that cuts the Turinge gabbro-diabase was here dated at ca 1200 Ma (whole rock, 40Ar/ 39Ar) and the virtual geomagnetic pole calculated from its primary magnetization falls into the expected trend of APWP for Baltica.

    The new Turinge key pole prolong the time of overlapping poles for Fennoscandia, indicating only small movements of the shield between ca. 1870 to 1700 Ma.

  • 93.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Leino, M.A.H.
    Pesonen, L.J.
    Khramov, A.N.
    Bylund, G.
    Mertanen, S.
    Krasnova, A.F.
    Terho, M.
    Drift history of Fennoscandia2009In: A continent revealed: the European geotraverse, Cambridge: Cambridge University Press, 2009Chapter in book (Other academic)
  • 94.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maokhar, M.O.
    Razi University, Department of Physics, Faculty of Basic Sciences.
    Layer, P.
    University of Alaska, Institute for Geophysics, Fairbanks.
    Donadini, F.
    Scripps Institution of Oceanography, La Jolla, United States of America.
    Uplift deduced from remanent magnetization of a proterozoic basic dyke and the baked country rock in the Hoting area, central Sweden: a palaeomagnetic and Ar-40/Ar-39 study2009In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 179, no 1, p. 59-78Article in journal (Refereed)
    Abstract [en]

    Remanent magnetization in dyke contact zones in the Hoting area of the Fennoscandian Shield in the central part of Sweden has been studied in order to establish the ambient temperature of the host rock and the depth of burial of the present erosion surface at the time of intrusion. A positive baked contact test for two Subjotnian dykes demonstrates the primary nature of the dyke magnetization. From the magnetic properties and the palaeomagnetic data, it can be concluded that the overprinting in the hybrid zone of one of the basic dykes is a partial thermoremanent magnetization. Reliable results were also obtained from a palaeointensity study of samples from the hybrid zone in the baked host rock. The study was performed in the laboratories at Luleå and at Scripps and a mean intensity of the Earth's magnetic field of 5.8 ± 1.9 μT was determined. The maximum temperature due to the dyke intrusion in the hybrid zone has been defined and from that an ambient temperature of 375 °C in the host rock at the time of intrusion has been calculated. This calculated temperature is not contradicted by the 40Ar/39Ar data. A palaeothermal gradient in the crust at ca. 1.6 Ga is calculated at ca. 34 °C km-1 and yields a depth of burial of the present erosion surface at ca. 10.4 km. This implies an uplift rate of 0.65 km (100 Ma)-1. A slow cooling of the gabbroic host rock (ca. 3.5 °C Ma-1) has been calculated from the difference in the U-Pb age of zircon (1.786 ± 0.010 Ga) and the 40Ar/39Ar biotite ages (1.648 ± 0.012 Ga; 1614 ± 0.024 Ga) of this study. This slow cooling resulted in a palaeomagnetic age of ca. 1.7 Ga for the gabbro, which is also the age of the determined palaeointensity. The calculated ca. 1.614 Ga palaeomagnetic pole from the basic dykes fulfils most of the criteria for a reliable pole and may be regarded as a new key-pole for Fennoscandia.

  • 95.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mattsson, Håkan
    Luleå tekniska universitet.
    Post Jotnian basic intrusions in the Fennoscandian Shield, and the break up of baltica from Laurentia: a palaeomagnetic and AMS study2001In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 108, no 3-4, p. 215-236Article in journal (Refereed)
    Abstract [en]

    A palaeomagnetic and anisotropy of magnetic susceptibility (AMS) study has been performed on dolerite sills of the Central Scandinavian Dolerite Group (CSDG) in the Fennoscandian Shield. The dolerites occur in four previously known complexes in central Sweden and Finland and from the results of this palaeomagnetic study another complex has been identified in northern Sweden. These complexes cover an area of at least 100 000 km2 and the palaeomagnetic data suggest a small difference in time between the intrusion of the dolerites. The measurements of anisotropy of magnetic susceptibility reveal a magnetic fabric with almost horizontal foliation planes and lineations that indicate fairly uniform ca NW or SE directed magma flows. The dolerites of the CSDG are geochemically rather uniform and have compositions typical of mantle derived melts formed in continental tensional settings. In a palaeomagnetic reconstruction of Baltica versus Laurentia at ca 1.27 Ga the two continents were joined, with NE Greenland attached to NW Baltica. AMS data from a few dolerites and a basalt in NE Greenland indicate magma flow directions that in the tectonic reconstruction are more or less parallel to the flow of the dolerites in Sweden. This may suggest a common magma source located at the reconstructed contact between Baltica and Laurentia. Both the dolerites in Greenland and those in Sweden are of tholeitic composition indicating an intraplate origin, which supports the interpretation of joined continents at that time. The tensional regime, that is reflected by the huge sill complexes, is in our interpretation related to the break up of Baltica from Laurentia at ca 1.27 Ga ago.

  • 96.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mattsson, Håkan J.
    Luleå tekniska universitet.
    A paleomagnetic and AMS study of the Rätan granite of the Transscandinavian Igneous Belt, central Sweden2001In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 123, no 4, p. 205-215Article in journal (Refereed)
    Abstract [en]

    The 1.85-1.67 Ga Transscandinavian Igneous Belt (TIB) forms a major Paleoproterozoic igneous complex in the western part of the Fennoscandian Shield. Different tectonic models propose that the TIB was formed in a tectonic regime governed either by compression or by extension. This paper presents an analysis of anisotropy of magnetic susceptibility (AMS) and paleomagnetic data from the Rätan granite (1.70 Ga), which forms a large pluton in the central part of the TIB. The major aim of the study is to test the existing tectonic models and to define a paleomagnetic pole position for the Rätan granite. Three contrasting magnetic fabric domains are identified. In the eastern and western domains the AMS fabric is characterized by NW-SE to N-S trending subvertical foliation planes and a girdle distribution of the maximum and intermediate anisotropy axes. The central domain is characterized by subhorizontal magnetic foliation planes and lineations that cluster in a NW-SE trending direction. We suggest that the Rätan granite was emplaced in a tectonic regime governed by NW-SE directed extension and that the pluton was fed obliquely with a magma source situated to the present northwest. A positive baked contact test is demonstrated for a basic dyke suggesting that the Rätan granite has not been remagnetized since c. 1.6 Ga. A paleomagnetic formation mean direction is defined for the granite (decl. = 2°, incl. = 59°) that yields a paleopole position of Plat = 67° and Plon = 190°.

  • 97.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mikhailnova, N.P.
    Ukrainian Academy of Sciences.
    Kravchenko, S.
    Ukrainian Academy of Sciences.
    Palaeomagnetism of Proterozoic rocks from the Ukrainian Shield and the consolidation of the East European Craton1998In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 16, no Suppl. 1, p. 103-Article in journal (Other academic)
  • 98.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mikhailova, N. P.
    Geophysical Institute, Academy of Sciences of Ukraine, Kiev.
    Kravchenko, S.
    Geophysical Institute, Academy of Sciences of Ukraine, Kiev.
    Palaeomagnetism of Proterozoic rocks from the Ukrainian shield: new tectonic reconstructions of the Ukrainian and Fennoscandian shields2001In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 339, no 1-2, p. 19-38Article in journal (Refereed)
    Abstract [en]

    A palaeomagnetic study has been performed on Palaeo-Mesoproterozoic rocks from three crustal blocks of the Ukrainian Shield, southern Sarmatia. Primary remanent magnetizations have been isolated in 2.0 Ga monzonite, 2.0-1.8 Ga sandstone, 1.77-1.72 Ga anorthosite and from mafic dykes of probably Palaeo-Mesoproterozoic ages. On basis of these results a sequence of 2.0-1.72 Ga apparent polar wander has for the first time been defined for the Ukrainian Shield. Palaeomagnetic and geological data indicate that there has probably not been any large scale tectonic movements within Sarmatia since the Mesoproterozoic. This suggests that tectonic reconstructions for the Ukrainian Shield may also include Sarmatia. The calculated pole positions for the Ukrainian Shield are significantly different from poles of similar age from the Fennoscandian Shield. The tectonic reconstructions demonstrate that the relative position and orientation of the Ukrainian Shield as a part of Sarmatia in the time interval 2.0-1.78 Ga was different from its present position relative to Fennoscandia. One pole from the Ukrainian Shield falls on the ca. 1.6 or 1.3 Ga part of the Fennoscandian APWP. This pole may represent a time when Fennoscandia was already accreted to Ukrainia. Contemporaneous rifting of the two cratons at ca. 1.35 Ga indicates that they were already joined to each other at that time, which means that the final accretion should have taken place sometimes after ca. 1.8 Ga ago.

  • 99.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mikhailova, N. P.
    Institute of Geophysics, Acadamy of Science, Kiev.
    Kravchenko, S. N.
    Geophysical Institute, Academy of Sciences of Ukraine, Kiev.
    Consolidation of the East European craton: a paleomagnetic analysis of proterozoic rocks from the Ukrainian shield and tectonic reconstructions versus fennoscandia1998In: Geophysical Journal, ISSN 0275-9128, Vol. 20, no 4, p. 71-74Article in journal (Refereed)
  • 100.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Moakhar, Mohsen Oveisy
    Luleå University of Technology.
    A palaeomagnetic analysis of rapakivi intrusions and related dykes in the Fennoscandian Shield1999In: Vol. 4, no 1, p. 686-Article in journal (Other academic)
123456 51 - 100 of 283
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