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  • 1.
    Abdi, Amir
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Heinonen, Suvi
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Karinen, Tuomo
    Constraints on the geometry of the Suasselka post-glacial fault, northern Finland, based on reflection seismic imaging2015In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 649, p. 130-138Article in journal (Refereed)
    Abstract [en]

    Unloading of the ice during the last glacial period in northern Fennoscandia is believed to have generated major faulting. These faults, often referred to as post-glacial faults, typically have clear surface exposures, but their geometry at depth is poorly known. In order to better understand the geometry at depth of the Suasselka post-glacial fault in Finland, three high resolution 2D reflection seismic profiles over the fault were reprocessed. Their total profile length is about 60 km and they were acquired as part of a major effort in Finland to map the uppermost crust in mining areas. The reprocessing led to significantly improved images that could be used to map the fault at depth. Two approximately N-S striking profiles and one E-W striking profile were reprocessed. The different azimuths and the crooked nature of the profiles allowed the fault geometry to be relatively well constrained. Clear reflections from the fault, dipping towards the SE, can be traced from the shallow subsurface down to about 3 km. The strike and dip of two sets of dipping reflections in the stacked data along with geometrical constraints and cross-dip analysis give a consistent dip of about 35-45 degrees towards the SE for the fault. The strike and dip vary from N55E with a dip of 35 degrees in the east to a strike of N48E with a dip of 45 degrees in the west. Existence of the two sets of reflections indicates that the fault surface is non-planar. Aside from allowing the geometry of the fault to be determined, the seismic data show a complex reflectivity pattern in the area and indications of both reverse and normal movement along fault planes with similar orientation to the Suasselka post-glacial fault. These images can be used as a basis for better characterizing the 3D geology of the area.

  • 2.
    Abdollahi, Somayeh
    et al.
    Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Ardestani, Vahid Ebrahimzadeh
    Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Zeyen, Hermann
    Univ Paris Saclay, Univ Paris Sud, CNRS, GEOPS, F-91405 Orsay, France.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. Univ Tehran, Inst Geophys, POB 14155-6466, Tehran, Iran.
    Crustal and upper mantle structures of Makran subduction zone, SE Iran by combined surface wave velocity analysis and gravity modeling2018In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 747, p. 191-210Article in journal (Refereed)
    Abstract [en]

    The inversion of Rayleigh wave group velocity dispersion curves is challenging, because it is non-linear and multimodal. In this study, we develop and test a new Rayleigh wave dispersion curve inversion scheme using the Shuffled Complex Evolution (SCE) algorithm. Incorporating this optimization algorithm into the inverse procedure not only can effectively locate the promising areas in the solution space for a global minimum but also avoids its wandering near the global minimum in the final stage of search. In addition, our approach differs from others in the model parameterization: Instead of subdividing the model into a large number of thin layers, we invert for thickness, velocities and densities and their vertical gradients of four layers, sediments, upper-crust, lower-crust and upper mantle. The proposed inverse procedure is applied to non-linear inversion of fundamental mode Rayleigh wave group dispersion curves for shear and compressional wave velocities. At first, to determine the efficiency and stability of the SCE method, two noise-free and two noisy synthetic data sets are inverted. Then real data for Makran region in SE Iran are inverted to examine the usage and robustness of the proposed approach on real surface wave data. In a second step, we applied 3D Gravity Modeling based on surface wave analysis results to obtain the density structure and thickness of each layer. The reason for using both types of data sets, is that gravity anomaly has a bad vertical resolution and surface wave group velocities are good for placing layer limits at depth, but they are not very sensitive to densities. Therefore, using gravity data increases the overall resolution of density distribution. In a final step, we used again the SCE method to invert the fundamental mode Rayleigh wave group dispersion curves based on the gravity results. Gravity results like thicknesses and sediment densities have been used to constrain the limit of search space in the SCE method. Results show a high shear and compressional velocity under the Gulf of Oman which reduce to the North of the Makran region. The Moho depth of the Oman Gulf is about 18-28 km and it increases to 46-48 km under the Taftan-Bazman volcanic-arc. The density image shows an average crustal density with maximum values under the Gulf of Oman decreasing northward to the Makran.

  • 3. Alcalde, Juan
    et al.
    Marzan, Ignacio
    Saura, Eduard
    Marti, David
    Ayarza, Puy
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Perez-Estaun, Andres
    Carbonell, Ramon
    3D geological characterization of the Hontomin CO2 storage site, Spain: Multidisciplinary approach from seismic, well-log and regional data2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 627, p. 6-25Article in journal (Refereed)
    Abstract [en]

    The first Spanish Technological Development plant for CO2 storage is currently under development in Hontomin (Spain), in a fractured carbonate reservoir. The subsurface 3D geological structures of the Hontomin site were interpreted using well-log and 3D seismic reflection data. A shallow low velocity zone affects the wave propagation and decreases the coherency of the underlying seismic reflections, deteriorating the quality of the seismic data, and thus preventing a straightforward seismic interpretation. In order to provide a fully constrained model, a geologically supervised interpretation was carried out. In particular, a conceptual geological model was derived from an exhaustive well-logging analysis. This conceptual model was then improved throughout a detailed seismic facies analysis on selected seismic sections crossing the seismic wells and in consistency with the regional geology, leading to the interpretation of the entire 3D seismic volume. This procedure allowed characterizing nine main geological levels and four main fault sets. Thus, the stratigraphic sequence of the area and the geometries of the subsurface structures were defined. The resulting depth-converted 3D geological model allowed us to estimate a maximum CO2 storage capacity of 5.85 Mt. This work provides a 3D geological model of the Hontomin subsurface, which is a challenging case study of CO2 storage in a complex fractured carbonate reservoir. 

  • 4.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Henry, Bernard
    Jackson, Mike
    Werner, Tomasz
    Lagroix, France
    Methods and applications of magnetic anisotropy: A special issue in recognition of the career of Graham J. Borradaile2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 629, p. 1-5Article in journal (Refereed)
  • 5.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hirt, Ann
    Herwegh, Marco
    Ebert, Andreas
    Walter, Jens
    Leiss, Bernd
    Burlini, Luigi
    Seismic anisotropy in the Morcles nappe shear zone: Implications for seismic imaging of crustal scale shear zones2013In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 603, p. 162-178Article in journal (Refereed)
    Abstract [en]

    Microstructures and textures of calcite mylonites from the Morcles nappe large-scale shearzone in southwestern Switzerland develop principally as a function of 1) extrinsic physical parameters including temperature, stress, strain, strain rate and 2) intrinsic parameters, such as mineral composition. We collected rock samples at a single location from this shear zone, on which laboratory ultrasonic velocities, texture and microstructures were investigated and quantified. The samples had different concentration of secondary mineral phases (<5 up to 40 vol.%). Measured seismic P waveanisotropy ranges from 6.5% for polyphase mylonites (similar to 40 vol.%) to 18.4% in mylonites with <5 vol.% secondary phases. Texture strength of calcite is the main factor governing the seismic P wave anisotropy. Measured S wave splitting is generally highest in the foliation plane, but its origin is more difficult to explain solely by calcite texture. Additional texture measurements were made on calcite mylonites with low concentration of secondary phases (<= 10 vol.%) along the metamorphic gradient of the shear zone (15 km distance). A systematic increase in texture strength is observed moving from the frontal part of the shear zone (anchimetamorphism: 280 degrees C) to the higher temperature, basal part (greenschist facies: 350-400 degrees C). Calculated P wave velocities become increasingly anisotropic towards the high-strain part of the nappe, from an average of 5.8%in the frontal part to 13.2% in the root of the basal part. Secondary phases raise an additional complexity, and may act either to increase or decrease seismic anisotropy of shear zone mylonites. Inlight of our findings we reinterpret the origin of some seismically reflective layers in the Grone-Zweisimmen line in southwestern Switzerland (PNR20 Swiss National Research Program). We hypothesize that reflections originate in part from the lateral variation in textural and microstructural arrangement of calcite mylonites in shear zones. 

  • 6.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hirt, Ann
    Schmidt, Volkmar
    Dietrich, Dorothee
    Magnetic fabrics of the Morcles nappe complex2009In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 466, p. 89-100Article in journal (Refereed)
  • 7.
    Amini, Samar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Z. Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Roberts, Roland G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tomographic upper-mantle velocity structure beneath the Iranian Plateau2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 554-557, p. 42-49Article in journal (Refereed)
    Abstract [en]

    The Iranian plateau is one of the most structurally complex and tectonically inhomogeneous regions in the world. In this study, we analyze Pn arrival-times from regional seismicity in order to resolve lateral velocity variations within the uppermost-mantle under the Iranian Plateau. More than 48,000 Pn first arrival times selected from the EHB catalog were used with epicentral distances of 200 to 1600 km. We used regularized isotropic and anisotropic damped least-squares inversion to image lateral velocity variations in the upper mantle. Our velocity model, with high lateral resolution, shows positive anomalies in the Zagros mountain belt with a distinct transition approximately along the Main Zagros Thrust to the lower mantle velocity zone of Central Iran. Anomalously low velocities are observed predominantly beneath NW Iran and eastern Turkey, suggesting a zone of relatively weak mantle. Low velocity region under the Damavand volcano reveals the hot upper mantle beneath the central Alborz mountains.

  • 8.
    Andersson, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Internal architecture of the Alnö alkaline and carbonatite complex (central Sweden) revealed using 3D models of gravity and magnetic data2018In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 740-741, p. 53-71Article in journal (Refereed)
    Abstract [en]

    The Alnö Complex in central Sweden is one of the largest alkaline and carbonatite ring-shaped intrusions in the world. Presented here is the 3D models of ground gravity and aeromagnetic data that confirm some of the previous ideas about the 3D geometry of the complex but also suggest that the complex may continue laterally further to north than previously expected. The data show the complex as (i) a strong positive Bouguer anomaly, around 20 mGal, and (ii) a strong positive magnetic anomaly, exceeding 2000 nT. Magnetic structures are clearly discernible within the complex and surrounding area. Both gravity and magnetic inversion models suggest that dense (> 2850 kg/m(3)) and magnetic ( > 0.05 SI) rocks extend down to about 3.5-4 km depth. Previous studies have suggested a solidified magma reservoir at this approximate depth. The inversion models further suggest that two apparently separate regions within the complex are likely connected at depth, starting from 800 to 1000 m, implying a common source for the rocks observed in these two regions. Modelling of the aeromagnetic data indicates that a > 3 km wide ring-shaped magnetic high situated in the sea north of Alnö Island may be a part of the complex. This could link a smaller satellite intrusion in Soraker on mainland to the larger intrusion on Alnö Island. While the rim of the ring must consist of highly magnetic rocks to support the anomaly, the centre has relatively low magnetisation and is probably made up of low-magnetic wall-rocks or metasomatised wall-rocks down to about 2 km depth. Below this depth the 3D susceptibility model suggests higher magnetic susceptibility values. Worldwide alkaline and carbonatite complexes are the main resources for rare earth elements (REEs), and owing to the size of the Alnö Complex, it can be highly prospective for REEs at depth.

  • 9. Ask, Maria
    et al.
    Beslier, Marie-Odile
    Boillot, Gilbert
    Ocean-continent boundary in the Iberia Abyssal Plain from multichannel seismic data1993In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 218, no 4, p. 383-393Article in journal (Refereed)
    Abstract [en]

    The Ocean-Continent Boundary of the West Iberia margin is marked by a basement ridge trending N-S. Four segments of this ridge are recognized, each of them being progressively offset westward from 40°N to 43°N. Because the setting and seismic character of the ridge in the Iberia Abyssal Plain are similar to those of the Galicia margin ridge, which is made of serpentinized peridotite, we think that the southern segments of the ridge are also made of the same mantle material. The segmentation of the ridge suggests that the northward propagation of the continental break-up during the North Atlantic opening in Early Cretaceous times was discontinuous, each segment possibly corresponding to a propagation step. East of the ridge, the basement of the whole Iberia Abyssal Plain consists of highly thinned continental crust locally resting on a seismic reflector that resembles the S reflector previously recognized off Galicia. By analogy with the Galicia margin, we propose that the tilted crustal blocks lay on serpentinized peridotite derived from the upper mantle, the S reflector corresponding to the contact between crustal rocks and serpentinite.

  • 10.
    Ask, Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Morgan, Julia K.
    Rice University, Houston.
    Projection of mechanical properties from shallow to greater depths seaward of the Nankai accretionary prism2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 482, no 1-4, p. 50-64Article in journal (Refereed)
    Abstract [en]

    Deformation processes in sediments at accretionary prisms are directly controlled by the state of in situ effective stresses, the mechanical, physical and geochemical properties of the materials of the fault zone and surrounding wall rocks, as well as time. Measurements of these properties and their evolution in space and time, are therefore needed for a full understanding of the process of earthquake generation within subduction zones.Reconsolidation tests have been carried out on Ocean Drilling Program cores collected from a reference site seaward of the active Nankai décollement zone off the southeast coast of Japan. The reconsolidation stress path subjects the samples to uniaxial strain deformation, which mimics their stress history, however at much higher loading rates than in the natural system. We have conducted two tests each from two mudstone samples within Lower Shikoku Basin. The samples were collected at 361 and 476 meter below seafloor, on either side of the protodécollement horizon.The objectives for mechanical testing are to probe the yield and failure surfaces of these shallow sediments (Considering their large scale behavior, our tests show that the samples collected above the protodécollement have higher strength than those below. We propose that cementation, microfabric and mineralogy of the sediments above the protodécollement result in a higher effective yield stress than predicted from in situ effective vertical stress at hydrostatic pore pressures. Sediments below the protodécollement, in contrast, are slightly underconsolidated, and provide an upper constraint on the magnitude of in situ effective vertical stress and pore-fluid pressure. We also used the test results to make initial predictions for the yield surface in 2D and 3D for subdécollement samples across the margin. The construction of the 2D yield surface is the first attempt to quantify the model of sediment deformation proposed by Morgan et al. (2007). These results hint that the presence of cement has a strong, and increasing, influence on sediment behavior. Further testing is needed to verify these findings.

  • 11.
    Bastida, F
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Aller, J
    Puchkov, VN
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Oslianski, A
    A cross-section through the Zilair Nappe (southern Urals)1997In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 276, no 1-4, p. 253-263Article in journal (Other academic)
    Abstract [en]

    A structural transect in the Zilair-Kugarchi area involves the western part of the Suvanyak Complex, the Zilair Nappe and the eastern part of the foreland thrust and fold belt. This section has been analyzed using field, microstructural and seismic data. The cross-section shows the transition from the hinterland to the foreland in the footwall to the suture of the southern Urals. The rocks involved range from early Palaeozoic to Permian in age. A characteristic of the Zilair Nappe is the dominance of a succession of volcanic greywackes and mudrocks of Late Devonian age (Zilair Formation). The metamorphic grade decreases from east to west, from greenschist facies to diagenetic conditions. The structure of the cross-section mainly comprises west-directed thrusts and thrust-related folds with an associated cleavage. Fold vergence changes along the section depending on of the distance to the associated thrust and its geometry. The Zilair thrust which separates the Zilair Nappe from the foreland thrust and fold belt accommodated ca. 10 km displacement and the characteristics of the deformation are similar on both sides of it. The contact between the Zilair Nappe and Suvanyak Complex is a west-dipping normal fault that does not represent a major tectonic boundary.

  • 12. Bauer, Friederike U.
    et al.
    Glasmacher, Ulrich A.
    Ring, Uwe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Karl, Markus
    Schumann, Andreas
    Nagudi, Betty
    Tracing the exhumation history of the Rwenzori Mountains, Albertine Rift, Uganda, using low-temperature thermochronology2013In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 599, p. 8-28Article in journal (Refereed)
    Abstract [en]

    The Rwenzori Mtns form a striking feature within the Albertine Rift of the East African Rift System. They are made up of a dissected Precambrian metamorphic basement block reaching heights of more than 5 km. Applying low-temperature therrnochronology a complex exhumation history becomes evident, where rock and surface uplift can be traced from Palaeozoic to Neogene times. Fission-track and (U-Th-Sm)/He cooling ages and derived cooling histories allow distinguishing different blocks in the Rwenzori Mtns. In the central part a northern and a southern block are separated by a putative NW-SE trending fault; with the northern block showing distinctly younger apatite fission-track ages (similar to 130 Ma) than the southern block (similar to 300 Ma). Cooling ages in both blocks do not vary significantly with elevation, despite considerable differences in elevation. Thermal history modelling reflects protracted cooling histories. Modelled t-T paths show decoupled blocks that were relocated separately along distinct fault planes, which reactivated pre-existing structures, inherited from Palaeozoic folding and thrusting. Initial cooling affected the Rwenzori area in Silurian to Devonian times, followed by Mesozoic and Cainozoic cooling events. Pre-Neogene evolution seems to be triggered by tectonic processes like the opening of the Indian Ocean and the south Atlantic. From thermochronological data the formation of a Mesozoic Albertine high is conceivable. In Cainozoic times the area was affected by rifting, resulting in differentiated surface uplift. Along the western flank of the Rwenzori Mtns, surface uplift was more pronounced. This is also reflected in their recent topography, formed by accelerated rock uplift in the near past (Pliocene to Pleistocene). Erosion could not compensate for this most recent uplift, resulting in apatite He ages of Oligocene to Miocene age or even older.

  • 13.
    Behrens, K.
    et al.
    Institute of Geophysics, University of Hamburg.
    Goldflam, S.
    Institute of Geophysics, University of Hamburg.
    Heikkinen, P.
    Institute of Seismology, University of Helsinki.
    Hirschleber, H.
    Institute of Geophysics, University of Hamburg.
    Lindqvist, Gustaf
    Luleå tekniska universitet.
    Lund, C-E-
    Department of Geophysics, University of Uppsala.
    Reflection seismic measurements across the Granulite Belt of the POLAR Profile in the northern Baltic Shield, Northern Finland1989In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 162, no 1-2, p. 101-111Article in journal (Refereed)
    Abstract [en]

    Reflection seismic measurements were carried out in 1985 on the central part of the POLAR refraction seismic profile in Northern Finland. The survey was planned and executed jointly by the Universities of Helsinki, Uppsala and Hamburg, using digital equipment with a total of 144 channels. By repeating the shots and moving the geophone spreads every day we were able to observe a 42-50 km recording spread. Referred to reflection elements, a line of 84 km total length through the source-receiver midpoints was recorded. We processed the results up to normal moveout-corrected time sections.A number of reflectors dipping 8°-15° to the northeast were recorded in the Lapland Granulite Belt range. These represent a system of sheared granulites which were observed on the surface in the southern part of the profile. From gravity modelling, the bottom of the dipping layers coincides with the lower boundary of the granulites. Between the depths of 22 and 35 km the crust in this area seems to be transparent to seismic signals. This leads to the assumption that the middle part of the crust is characterized by gentle velocity and density gradients. The crust-mantle boundary seems to be a layered Moho with good reflectors lying at depths between 40 and 44 km.

  • 14.
    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.

  • 15.
    Bergman, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Palm, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    High-resolution reflection seismic imaging of the upper crust at Laxemar, southeastern Sweden2002In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 355, no 1-4, p. 201-213Article in journal (Refereed)
    Abstract [en]

    A major cost in exploring the upper 1–2 km of crystalline crust with reflection seismics is the drilling required for explosive sources. By reducing the charge size to a minimum, shallow inexpensive shotholes can be drilled with handheld equipment. Here, we present results from a full-scale test using small charges for high-resolution seismic surveying over a nuclear waste disposal study site (not an actual site). Two 2–2.5-km-long crossing profiles were acquired in December 1999 with 10-m shot and geophone spacing in the Laxemar area, near Oskarshamn in southeastern Sweden. After standard processing, including dip moveout (DMO), several subhorizontal to moderately dipping reflections are imaged. Many of the dipping ones can be correlated to fracture zones observed in a ca. 1700-m-deep borehole where the profiles cross and/or to fracture zones mapped on the surface. The imaged fracture zones form a complex 3D pattern illustrating the necessity of having 3D control before interpreting seismic reflection data. Analyses of sonic and density logs from the borehole show that greenstones have significantly higher impedances than the more dominant granite found in the borehole (granite/greenstone reflection coefficient is +0.065). These greenstones may contribute to the reflectivity when associated with fracture zones. In some cases, where they are present as larger subhorizontal lenses, they may be the dominant source of reflectivity. A set of north-dipping (10°) reflectors at 3–3.5-km depth can be correlated to a similar set observed below the island of Ävrö about 3 km to the east.

  • 16.
    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.

  • 17. Brown, D.
    et al.
    Zhang, X.
    Palomeras, I.
    Simancas, F.
    Carbonell, R.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Salisbury, M.
    Petrophysical analysis of a mid-crustal reflector in the IBERSEIS profile, SW Spain2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 550, p. 35-46Article in journal (Refereed)
    Abstract [en]

    The origin of strong crustal reflectors in vertical incidence reflection seismic data is generally attributed to either rock layering, deformation fabrics in shear zones, fluids, or igneous intrusions. The IBERSEIS normal incidence reflection and wide-angle seismic profiles in SW Spain imaged a large, high velocity, subhorizontal reflector in the middle crust (the IBERSEIS Reflective Body) whose origin has been attributed to a mafic intrusion. In order to test this hypothesis, in this paper we present laboratory measurements of Vp, Vs, and density from 17 samples of mafic igneous and metamorphic rocks, and metasediments that are thought to be equivalent to the proposed IBERSEIS Reflective Body. These measurements are then corrected to 400 degrees C at 600 MPa and used to calculate Poisson's ratio and to compare it, Vp, and Vs to values measured in situ by wide-angle data. Finally, normal incidence reflection coefficients are calculated to test if the measured lithologies could reproduce the reflectivity imaged in the vertical incidence reflection seismic data for the IBERSEIS Reflective Body. Our physical property measurements are very similar to those modeled from the wide-angle data, and our reflection coefficients are sufficiently high to cause strong mid-crustal reflectivity. Our data indicate, therefore, that previous interpretations of the IBERSEIS Reflective Body as a mafic sill are quite reasonable.

  • 18.
    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.

  • 19.
    Burchardt, Steffi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Tanner, David Colin
    Krumbholz, Michael
    Mode of emplacement of the Slaufrudalur Pluton, Southeast Iceland inferred from three-dimensional GPS mapping and model building2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 480, p. 232-240Article in journal (Refereed)
  • 20. Carracedo, J. C.
    et al.
    Fernandez-Turiel, J. L.
    Gimeno, D.
    Guillou, H.
    Kluegel, A.
    Krastel, S.
    Paris, R.
    Perez-Torrado, F. J.
    Rodriguez-Badiola, E.
    Rodriguez-Gonzalez, A.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Walter, T. R.
    Wiesmaier, S.
    Comment on "The distribution of basaltic volcanism on Tenerife, Canary Islands: Implications on the origin and dynamics of the rift systems" by A. Geyer and J. Marti. Tectonophysics 483 (2010) 310-3262011In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 503, no 3-4, p. 239-241Article in journal (Other academic)
  • 21.
    Chemia, Z.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Schmeling, H.
    Institute of Earth Sciences, Section Geophysics J. W. Goethe-University, Frankfurt am Main, Germany.
    Koyi, H.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    The effect of the salt viscosity on future evolution of the Gorleben salt diapir, Germany2009In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 473, no 3-4, p. 446-456Article in journal (Refereed)
    Abstract [en]

    The Gorleben diapir, which has been targeted for radioactive waste disposal, contains large blocks of anhydrite. Numerical models that   depict the geometrical configuration of the Gorleben diapir are used to understand internal structure of diapir caused by movement of the anhydrite blocks for various salt rheologies. It is shown that the   theology of the salt plays a significant role in how and at which rate   the anhydrite blocks sink within the diapir. The mobility of anhydrite   blocks depends on the effective viscosity of salt which has to be lower   than threshold value of around 10(18)-10(19) Pa s. Decreasing salt   viscosity allows the previously "stationary" anhydrite blocks to sink.   If the effective viscosity of salt in post-depositional stage of the Gorleben diapir falls below this threshold value, induced internal flow   due to the present anhydrite layer might disturb any repository within the diapir.

  • 22.
    Chen, Lin
    et al.
    Chinese Academy of Sciences, Beijing, China.
    Berntsson, Fredrik
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, The Institute of Technology.
    Zhang, Zhongjie
    Chinese Academy of Sciences, Beijing, China.
    Wang, Peng
    Chinese Academy of Sciences, Guangzhou, China; University of Chinese Academy of Sciences, Beijing, China.
    Wu, Jing
    Chinese Academy of Sciences, Beijing, China.
    Xu, Tao
    Chinese Academy of Sciences, Beijing, China.
    Seismically constrained thermo-rheological structure of the eastern Tibetan margin: Implication for lithospheric delamination2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 627, p. 122-134Article in journal (Refereed)
    Abstract [en]

    The eastern Tibetan margin bordered by the Longmen Shan range exhibits significant lateral differences in the lithospheric structure and thermal state. To investigate the roles of these differences in mountain building, we construct a thermo-rheological model along a wide-angle seismic profile across the eastern Tibetan margin based on recent seismic and thermal observations. The thermal modeling is constrained by the surface heat flow data and crustal P wave velocity model. The construction of the theological envelopes is based on rock mechanics results, and involves two types of rheology: a weak case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite, and a strong case where the lower crust is mafic granulite and the lithospheric mantle is dry peridotite. The results demonstrate: (1) one high-temperature anomaly exists within the uppermost mantle beneath eastern Tibet, indicating that the crust in eastern Tibet is remarkably warmer than that in the Sichuan basin, and (2) the rheological strength of the lithospheric mantle beneath eastern Tibet is considerably weaker than that beneath the Sichuan basin. The rheological profiles are in accord with seismicity distribution. By combining these results with the observed crustal/lithospheric architecture, Pn velocity distribution and magmatism in the eastern Tibetan margin, we suggest that the delamination of a thickened lithospheric mantle root beneath eastern Tibet is responsible for the growth of the eastern Tibetan margin.

  • 23.
    Cheraghi, Saeid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bellefleur, Gilles
    Crustal-scale reflection seismic investigations in the Bathurst Mining Camp, New Brunswick, Canada2011In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 506, no 1-4, p. 55-72Article in journal (Refereed)
    Abstract [en]

    The Bathurst Mining Camp, northern New Brunswick, Canada contains the super giant Brunswick No. 12 massive sulphide deposit and the smaller, now abandoned, Brunswick No. 6 deposit. Discoveries of additional base metal deposits in the camp require a better understanding of geological structures at depth. To this end, reflection seismic data in the Brunswick No. 6 area were acquired along three 2D profiles in 1999, with a total length of about 30 km. We have recovered, processed and interpreted these seismic data in conjunction with petrophysical and geological data from the study area. The seismic data and the borehole geophysical data allow a better understanding of both the shallow and deep structures (to 9 km depth) in the area. The seismic data show steeply dipping structures of the Brunswick No. 6 area, many of which reach the surface and allow for correlation with the surface and borehole geological information. Finite-difference modeling of major geological formations constrained with borehole petrophysical measurements indicates good correlation between the observed seismic and the synthetic data. A sequence of seismically reflective and transparent zones indicates a thrust stack in the Brunswick No. 6 area. The contact between the reflective and transparent zones is a series of faults bringing the two units over each other. A reflective package is observed in all three profiles and correlates well with the Brunswick horizon, the key mineralized zone in the study area. The Brunswick horizon extends down to depth greater than 3 km, increasing the hope for discovery of deeper base metal deposits. Two other sets of reflections are also observed in all three profiles in the depth range of about 5-8 km. We interpret them as two sets of thrusted sheets, which could be an indication that the Brunswick belt extends down to a maximum depth of 8 km.

  • 24.
    Cheraghi, Saeid
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bellefleur, Gilles
    Geological Survey of Canada.
    Crustal-scale reflection seismic investigations in the Bathurst Mining Camp, New Brunswick, Canada2011In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 506, no 1-4, p. 55-72Article in journal (Refereed)
  • 25. Cherevatova, M.
    et al.
    Smirnov, M.
    Korja, T.
    Kaikkonen, P.
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hubert, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kamm, Jochen
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Kalscheuer, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Crustal structure beneath southern Norway imaged by magnetotellurics2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 628, p. 55-70Article in journal (Refereed)
    Abstract [en]

    We use data from two magnetotelluric profiles, ToSca10 and ToSca'09, over the Scandinavian Mountains to study the crustal structure in southern Norway. The profiles cross the major tectonic structures of the Caledonian orogen as well as the western margin of the Precambrian Baltica. Dimensionality and strike analyses indicate generally 3-D behavior of the data. However, the majority of the used data distinguishes a preferable strike direction, which is supported by the geology of the region. Hence, we employ 2-D inversion and choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Magnetotelluric data from both profiles are inverted using a damped least squares solution based on a singular value decomposition. We improved the solution by defining the inverse model covariance matrix through gradient or Laplacian smoothing operators. The two-dimensional inversion models of the ToSca'09 and ToSca'10 field data from southern Norway derived from the damped least squares scheme with the Laplacian inverse model covariance matrix are presented. Resistive rocks, extending to the surface, image the autochthonous Southwest Scandinavian Domain and the allochthonous Western Gneiss Region. Near-surface conductors, which are located between the resistive Caledonian nappes and Precambrian basement, delineate highly conductive shallow-sea sediments, so called alum shales. They exhibit a decollement along which the Caledonian nappes were overthrust. A deeper, upper to midcrustal conducting layer in the Southwest Scandinavian Domain may depict the remnants of closed ocean basins formed during the accretions and collisions of various Sveconorwegian terranes. In ToSca'10, the Caledonian nappes, the conducting alum shales and the deeper conductor are terminated in the west by the Faltungsgraben shear complex which represents a crustal scale boundary between the Western Gneiss Region in the west and the Southwest Scandinavian Domain in the east.  

  • 26. Cherevatova, M.
    et al.
    Smirnov, M. Yu.
    Jones, A. G.
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Becken, M.
    Biolik, M.
    Ebbing, J.
    Gradmann, S.
    Gurk, M.
    Huebert, J.
    Junge, A.
    Kamm, Jochen
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Korja, T.
    Lahti, I.
    Lower, A.
    Nittinger, C.
    Savvaidis, A.
    Smirnov, M.
    Magnetotelluric array data analysis from north-west Fennoscandia2015In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 653, p. 1-19Article in journal (Refereed)
    Abstract [en]

    New magnetotelluric (MT) data in north-west Fennoscandia were acquired within the framework of the project "Magnetotellurics in the Scandes" (MaSca). The project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia. An array of 59 synchronous long period and 220 broad-band MT sites was occupied in the summers of 2011 to 2013. We estimated MT transfer functions in the period range from 0.003 to 10(5) s. The Q-function multi-site multi-frequency analysis and the phase tensor were used to estimate strike and dimensionality of MT data. Dimensionality and strike analyses indicate generally 2-D behaviour of the data with 3-D effects at some sites and period bands. In this paper we present 2-D inversion of the data, 3-D inversion models are shown in the parallel paper. We choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Seven crustal-scale and four lithospheric-scale 2-D models are presented. The resistive regions are images of the Archaean and Proterozoic basement in the east and thin Caledonian nappes in the west. The middle and lower crust of the Svecofennian province is conductive. The southern end of the Kittila Greenstone Belt is seen in the models as a strong upper to middle crustal conductor. In the Caledonides, the highly conductive alum shales are observed along the Caledonian Thrust Front. The thickest lithosphere is in the Palaeoproterozioc Svecofennian Domain, not in the Archaean. The thickness of the lithosphere is around 200 km in the north and 300 km in the south-west.

  • 27. Cherevatova, M.
    et al.
    Smirnov, M. Yu.
    Korja, T.
    Pedersen, Laust Börsting
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Ebbing, J.
    Gradmann, S.
    Becken, M.
    Electrical conductivity structure of north-west Fennoscandia from three-dimensional inversion of magnetotelluric data2015In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 653, p. 20-32Article in journal (Refereed)
    Abstract [en]

    New magnetotelluric (MT) data in north-west Fennoscandia were acquired within the framework of the project "Magnetotellurics in the Scandes" (MaSca). The project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia. An array of 59 simultaneous long period and 220 broad-band MT sites were occupied in the summers of 2011 to 2013. The 3-D inversion of the MaSca data was obtained using the ModEM 3-D code. The full impedance and tipper data were used for the inversion. The rocks of Archaean and Proterozoic basement towards east and the Caledonian nappes towards west are modelled as resistive structures. In the central and southern parts, the whole crust is resistive and reflects the Trans-Scandinavian Igneous Belt granitoids. The middle to lower crust of the Svecofennian province is conductive. An uppermost crustal conductor is revealed in the Skelleftea Ore District. The south end of the Kittila Greenstone Belt is seen in the models as a strong upper to middle crustal conductor. In the Caledonides, the highly conductive alum shales are observed along the Caledonian Thrust Front. A map of the crustal conductance for the north-west Fennoscandian Shield is presented.

  • 28.
    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.

  • 29. Corti, Giacomo
    et al.
    Ranalli, Giorgio
    Mulugeta, Genene
    Uppsala University, Disciplinary Domain of Science and Technology, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Uppsala Centre for Sustainable Development.
    Agostini, Andrea
    Sani, Federico
    Zugu, Alessandro
    Control of the rheological structure of the lithosphere on the inward migration of tectonic activity during continental rifting2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 490, no 3-4, p. 165-172Article in journal (Refereed)
    Abstract [en]

    Analogue models are used to analyse the parameters controlling the evolution of extensional deformation in continental rifts. Models are deformed in a centrifuge and simulate the continental lithosphere floating and extending above a low-viscosity asthenosphere. Model results reproduce the typical evolution of deformation during continental narrow rifting, with early activation of large boundary faults and basin subsidence, followed by their abandonment and localization of tectonic activity in internal faults near the centre of the rift. The experiments document the strong influence exerted by the thickness of both brittle and ductile crustal layers and syn-rift sediment accumulation on the evolution of deformation, namely on the amount of bulk extension preceding inward fault migration. Thin upper and/or lower crust and absent or low syn-rift sedimentation promote a rapid abandonment of boundary faults and a transition to in-rift fault development for low amounts of extension; conversely, thick upper and/or lower crust and high syn-rift sediment accumulation favour prolonged slip on boundary faults and delayed development of internal faulting. The experimental results suggest that the inward migration of faulting during extension of continental lithosphere results from the interplay between the ductile stresses acting at the base of the upper crust and the total resistance of this brittle layer.

  • 30.
    Cruciani, F.
    et al.
    Univ Perugia, Dept Phys & Geol, I-06123 Perugia, Italy..
    Barchi, M. R.
    Univ Perugia, Dept Phys & Geol, I-06123 Perugia, Italy..
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Porreca, M.
    Univ Perugia, Dept Phys & Geol, I-06123 Perugia, Italy..
    Kinematic evolution of a regional-scale gravity-driven deepwater fold-and-thrust belt: The Lamu Basin case-history (East Africa)2017In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 712-713, p. 30-44Article in journal (Refereed)
    Abstract [en]

    The deepwater fold-and-thrust belts (DWFTBs) are geological structures recently explored thanks to advances in offshore seismic imaging by oil industry. In this study we present a kinematic analysis based on three balanced cross-sections of depth-converted, 2-D seismic profiles along the offshore Lamu Basin (East African passive margin). This margin is characterized by a regional-scale DWFTB (>450 km long), which is the product of gravity-driven contraction on the shelf that exhibits complex structural styles and differing amount of shortening along strike. Net shortening is up to 48 km in the northern wider part of the fold-and-thrust belt (approximate to 180 km), diminishing to <15 km toward the south, where the belt is markedly narrower (approximate to 50 km). The three balanced profiles show a shortening percentage around 20% (comparable with the maximum values documented in other gravity-driven DWFTBs), with a significant variability along dip: higher values are achieved in the outer (i.e. down-dip) portion of the system, dominated by basinward-verging, imbricate thrust sheets. Fold wavelength increases landward, where doubly-verging structures and symmetric detachment folds accommodate a lower amount of shortening. Similar to other cases, a linear and systematic relationship between sedimentary thickness and fold wavelength is observed. Reconstruction of the rate of shortening through time within a fold-and-thrust belt shows that after an early phase of slow activation (Late Cretaceous), >95% of net shortening was produced in <10 Myr (during Paleocene). During this acme phase, which followed a period of high sedimentation rate, thrusts were largely synchronous and the shortening rate reached a maximum value of 5 mm/yr. The kinematic evolution reconstructed in this study suggests that the structural evolution of gravity-driven fold-and-thrust belts differs from the accretionary wedges and the collisional fold-and-thrust belts, where thrusts propagate in-sequence and shortening is uniformly accommodated along dip.

  • 31.
    Dehghannejad, Mahdieh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bauer, Tobias E.
    Division of Geosciences, Luleå University of Technology, Sweden.
    Malehmir, Alireza
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Weihed, Pär
    Division of Geosciences, Luleå University of Technology, Sweden.
    Crustal geometry of the central Skellefte district, northern Sweden – constraints from reflection seismic investigations2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 524, p. 87-99Article in journal (Refereed)
    Abstract [en]

    The Palaeoproterozoic Skellefte mining district in Sweden is one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, three new sub-parallel reflection seismic profiles, with a total length of about 95 km, were acquired in the central part of the district. Processed seismic data reveal a series of gentle- to steeply- dipping reflections and a series of diffraction packages. The majority of reflections that extend to the surface can be correlated with geological features either observed in the field or interpreted from the aeromagnetic map. A set of south-dipping reflections represent inferred syn-extensional listric extensional faults that were inverted during subsequent crustal-shortening. Cross-cutting northdipping reflections are correlated to late-compressional break-back faults. Flat-lying reflections in the central parts of the study area could represent lithological contacts within the Skellefte Group, or the contact between Skellefte Group rocks and their unknown basement. Flat-lying reflections occurring further north are inferred to originate from the top of the Jörn intrusive complex or an intrusive contact within it. So far unknown south- and north-dipping faults have been identified in the vicinity of the Maurliden deposit. Based on the seismic results, a preliminary 3D-model has been created in order to visualize the fault pattern and to provide a base for future 3D/4D modeling in the Skellefte district.

  • 32.
    Dehghannejad, Mahdieh
    et al.
    Department of Earth Sciences, Uppsala University.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Malehmir, Alireza
    Department of Earth Sciences, Uppsala University.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Crustal geometry of the central Skellefte district, northern Sweden: constraints from reflection seismic investigations2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 524-525, p. 87-99Article in journal (Refereed)
    Abstract [en]

    The Palaeoproterozoic Skellefte mining district in Sweden is one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, three new sub-parallel reflection seismic profiles, with a total length of about 95 km, were acquired in the central part of the district. Processed seismic data reveal a series of gentle- to steeply- dipping reflections and a series of diffraction packages. The majority of reflections that extend to the surface can be correlated with geological features either observed in the field or interpreted from the aeromagnetic map. A set of south-dipping reflections represent inferred syn-extensional listric extensional faults that were inverted during subsequent crustal-shortening. Cross-cutting north-dipping reflections are correlated to late-compressional break-back faults. Flat-lying reflections in the central parts of the study area could represent lithological contacts within the Skellefte Group, or the contact between Skellefte Group rocks and their unknown basement. Flat-lying reflections occurring further north are inferred to originate from the top of the Jörn intrusive complex or an intrusive contact within it. So far unknown south- and north-dipping faults have been identified in the vicinity of the Maurliden deposit. Based on the seismic results, a preliminary 3D-model has been created in order to visualize the fault pattern and to provide a base for future 3D/4D modeling in the Skellefte district.

  • 33. Delcamp, A.
    et al.
    Petronis, M. S.
    Troll, Valentine
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Carracedo, J. C.
    de Vries, B. van Wyk
    Perez-Torrado, F. J.
    Vertical axis rotation of the upper portions of the north-east rift of Tenerife Island inferred from paleomagnetic data2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 492, no 1-4, p. 40-59Article in journal (Refereed)
    Abstract [en]

    Paleomagnetic sampling sites were established in 82 dykes along an 8 km long section of the north-east rift-zone (NERZ) of Tenerife, Canary Islands, Spain. Of the 70 interpretable sites, 16 are of normal polarity and 54 of reversed polarity. Four normal polarity sites and fifteen reverse polarity sites were excluded from the grand mean calculation for statistical reasons. After inverting the reverse polarity sites through the origin, the in-situ grand mean yields a declination (D) = 023.8 degrees, an inclination (I) = 42.3 degrees, alpha(95) = 3.2 degrees, kappa = 39.0, N = 51 that is discordant to the expected late Miocene to Pleistocene field direction (D = 357.6 degrees, I = 38.8 degrees, alpha(95) = 4.7 degrees). This discordance can be explained as either a 26 degrees clockwise vertical axis rotation or a 28 degrees WNW-side-down-tilt about an average 009 degrees horizontal tilt axis. The sampled section is composed of numerous semi-vertical dykes cutting mainly lava flow units that are sub-horizontal and cross-cut by steeply dipping faults (70 degrees-90 degrees). Field evidence is therefore more compatible with a vertical-axis rotation rather than a horizontal axis tilt of the drilled units. We argue that this clockwise vertical-axis rotation is likely related to strike-slip movements that occurred along the edges of the collapse scars and accommodate the emplacement and growth of the underlying intrusive core and associated dykes. Six new Ar-40/Ar-39 age determinations constrain the main interval of dyke emplacement within the NERZ between 0.99 Ma and 0.56 Ma. The intrusive activity in the sampled section of the rift appears to have been almost continuous, with several intrusion pulses that are probably related to flank destabilisation event(s) during the mid Pleistocene. Our study thus demonstrates a long-lived, multi-faceted history that shaped the NERZ.

  • 34.
    Delcamp, Audray
    et al.
    Department of Geology, Trinity College, Dublin, Dublin 2, Ireland.
    Petronis, M. S.
    Environmental Geology Natural Resource Management Department, New Mexico Highlands University, Las Vegas, New Mexico, 87 701, USA.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Carracedo, Juan Carlos
    Estación Volcanológica de Canarias, IPNA-Consejo Superior de Investigaciones Científicas (CSIC), La Laguna, 38206, Tenerife, Spain.
    van Wyk de Vries, B.
    Laboratoire Magmas et Volcans CNRS-UMR 6524, Observatoire du Physique du Globe de Clermont Université Blaise Pascal, Clermont-Ferrand, France.
    Pérez-Torrado, Francisco José
    Departamento de Física-Geología, Universidad de Las Palmas de Gran Canaria, 35017 Las Palmas de Gran Canaria, Spain.
    Vertical axis rotation of the upper portions of the north-east rift of Tenerife Island inferred from paleomagnetic data2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 492, no 1-4, p. 40-59Article in journal (Refereed)
    Abstract [en]

    Paleomagnetic sampling sites were established in 82 dykes along an 8 km long section of the north-east rift-zone (NERZ) of Tenerife, Canary Islands, Spain. Of the 70 interpretable sites, 16 are of normal polarity and 54 of reversed polarity. Four normal polarity sites and fifteen reverse polarity sites were excluded from the grand mean calculation for statistical reasons. After inverting the reverse polarity sites through the origin, the in-situ grand mean yields a declination (D) = 023.8°, an inclination (I) = 42.3°, α95 = 3.2°, ĸ = 39.0, N = 51 that is discordant to the expected late Miocene to Pleistocene field direction (D = 357.6°, I = 38.8°, α95 = 4.7°). This discordance can be explained as either a 26° clockwise vertical axis rotation or a 28° WNW-side-down-tilt about an average 009° horizontal tilt axis. The sampled section is composed of numerous semi-vertical dykes cutting mainly lava flow units that are sub-horizontal and cross-cut by steeply dipping faults (70°–90°). Field evidence is therefore more compatible with a vertical-axis rotation rather than a horizontal axis tilt of the drilled units. We argue that this clockwise vertical-axis rotation is likely related to strike-slip movements that occurred along the edges of the collapse scars and accommodate the emplacement and growth of the underlying intrusive core and associated dykes. Six new 40Ar/39Ar age determinations constrain the main interval of dyke emplacement within the NERZ between 0.99 Ma and 0.56 Ma. The intrusive activity in the sampled section of the rift appears to have been almost continuous, with several intrusion pulses that are probably related to flank destabilisation event(s) during the mid Pleistocene. Our study thus demonstrates a long-lived, multi-faceted history that shaped the NERZ.

  • 35. Dörr, N.
    et al.
    Lisker, F.
    Clift, P. D.
    Carter, A.
    Gee, David G.
    Uppsala universitet, Geofysik.
    Tebenkov, A. M.
    Spiegel, C.
    Late Mesozoic-Cenozoic exhumation history of northern Svalbard and its regional significance: Constraints from apatite fission track analysis2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 514, p. 81-92Article in journal (Refereed)
    Abstract [en]

    The late Mesozoic-Cenozoic was a time of profound tectonic activity in the Arctic, with incipient spreading in the Arctic Ocean, Baffin Bay-Labrador Sea and North Atlantic, as well as the northward movement of the Greenland microplate leading to collision and deformation in Greenland, Arctic Canada and Svalbard (Eurekan Orogeny). It is, however, still unclear, how northern Svalbard, situated at the northwestern edge of the Barents Shelf, was affected by these processes. Furthermore, northern Svalbard has been proposed to have been a Cretaceous-Cenozoic sediment source to surrounding regions because it lacks a post-Devonian sedimentary cover. When erosion took place and how that related to the tectonic history of the Arctic, is yet unresolved. In order to reconstruct the erosion history of northern Svalbard, we constrained its thermal evolution using apatite fission track (AFT) thermochronology. Our data reveal AFT ages between 62 +/- 5 and 214 +/- 10 Ma, recording late Mesozoic-early Paleogene exhumation. Our data show that northern Svalbard was emergent and experienced erosion from the Early Jurassic and presumably through the Cenozoic, although total exhumation was restricted to similar to 6 km. Pronounced exhumation took place during Jurassic-Cretaceous time, probably linked to the extensional tectonics during the opening of the Amerasian Basin (Arctic Ocean). In contrast, Cenozoic ocean basin formation and the Eurekan deformation did not cause significant erosion of northem Svalbard. Nonetheless, AFT data show that Late Cretaceous-Early Paleocene fault-related exhumation affected some parts of northern Svalbard. Fault zones were reactivated due to the reorganization of Arctic landmasses during an early phase of the Eurekan deformation, which implies that this episode commenced similar to 20 m.y. earlier in Svalbard than previously understood.

  • 36. Dörr, N.
    et al.
    Lisker, F.
    Clift, P. D.
    Carter, A.
    Gee, David G.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tebenkov, A. M.
    Spiegel, C.
    Late Mesozoic-Cenozoic exhumation history of northern Svalbard and its regional significance: Constraints from apatite fission track analysis2012In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 514, p. 81-92Article in journal (Refereed)
    Abstract [en]

    The late Mesozoic-Cenozoic was a time of profound tectonic activity in the Arctic, with incipient spreading in the Arctic Ocean, Baffin Bay-Labrador Sea and North Atlantic, as well as the northward movement of the Greenland microplate leading to collision and deformation in Greenland, Arctic Canada and Svalbard (Eurekan Orogeny). It is, however, still unclear, how northern Svalbard, situated at the northwestern edge of the Barents Shelf, was affected by these processes. Furthermore, northern Svalbard has been proposed to have been a Cretaceous-Cenozoic sediment source to surrounding regions because it lacks a post-Devonian sedimentary cover. When erosion took place and how that related to the tectonic history of the Arctic, is yet unresolved. In order to reconstruct the erosion history of northern Svalbard, we constrained its thermal evolution using apatite fission track (AFT) thermochronology. Our data reveal AFT ages between 62 +/- 5 and 214 +/- 10 Ma, recording late Mesozoic-early Paleogene exhumation. Our data show that northern Svalbard was emergent and experienced erosion from the Early Jurassic and presumably through the Cenozoic, although total exhumation was restricted to similar to 6 km. Pronounced exhumation took place during Jurassic-Cretaceous time, probably linked to the extensional tectonics during the opening of the Amerasian Basin (Arctic Ocean). In contrast, Cenozoic ocean basin formation and the Eurekan deformation did not cause significant erosion of northem Svalbard. Nonetheless, AFT data show that Late Cretaceous-Early Paleocene fault-related exhumation affected some parts of northern Svalbard. Fault zones were reactivated due to the reorganization of Arctic landmasses during an early phase of the Eurekan deformation, which implies that this episode commenced similar to 20 m.y. earlier in Svalbard than previously understood.

  • 37.
    Eaton, David W.S.
    et al.
    Department of Earth Sciences, University of Western Ontario.
    Dineva, Savka
    Mereu, Robert F.
    Department of Earth Sciences, University of Western Ontario.
    Crustal thickness and V P/V S variations in the Grenville orogen (Ontario, Canada) from analysis of teleseismic receiver functions2006In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 420, no 1-2, p. 223-238Article in journal (Refereed)
    Abstract [en]

    We have developed a simple semblance-weighted stacking technique to estimate crustal thickness and average V P/V S ratio using teleseismic receiver functions. We have applied our method to data from 32 broadband seismograph stations that cover a 700 × 400 km 2 region of the Grenville orogen, a 1.2-0.98 Ga Himalayan-scale collisional belt in eastern North America. Our seismograph network partly overlaps with Lithoprobe and other crustal refraction surveys. In 8 out of 9 cases where a crustal-refraction profile passes within 30 km of a seismograph station, the two independent crustal thickness estimates agree to within 7%. Our regional crustal-thickness model, constructed using both teleseismic and refraction observations, ranges between 34.0 and 52.4 km. Crustal-thickness trends show a strong correlation with geological belts, but do not correlate with surface topography and are far in excess of relief required to maintain local isostatic equilibrium. The thickest crust (52.4 ± 1.7 km) was found at a station located within the 1.1 Ga mid-continent (failed) rift. The Central Gneiss Belt, which contains rocks exhumed from deep levels of the crust, is characterized by V P/V S ranging from 1.78 to 1.85. In other parts of the Grenville orogen, V P/V S is found to be generally less than 1.80. The thinnest crust (34.5-37.0 km) occurs northeast of the 0.7 Ga Ottawa-Bonnechere graben and correlates with areas of high intraplate seismicity

  • 38.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Plomerová, Jaroslava
    Geophysical Institute, Czech Acad. Sci..
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Vecsey, Ludek
    Geophysical Institute, Czech Acad. Sci..
    Babuška, Vladislav
    Geophysical Institute, Czech Acad. Sci..
    Shomali, Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bodvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Seismic anisotropy of the mantle lithosphere beneath the Swedish National Seismological Network (SNSN)2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 480, no 1-4, p. 241-258Article in journal (Refereed)
    Abstract [en]

    Body-wave analysis – shear-wave splitting and P-travel time residuals - detect anisotropic structure of the upper mantle beneath the Swedish part of Fennoscandia. Geographic variations of both the splitting measurements and the P-residual spheres map regions of different fabrics of the mantle lithosphere. The fabric of individual mantle domains is internally consistent, usually with sudden changes at their boundaries. Distinct back-azimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Based upon joint inversion of body-wave anisotropic parameters we instead propose 3D self-consistent anisotropic models of well-defined mantle lithosphere domains with differently oriented fabrics approximated by hexagonal aggregates with plunging symmetry axes. The domain-like structure of the Precambrian mantle lithosphere, most probably retaining fossil fabric since the domains’ origin, supports the idea of the existence of an early form of plate tectonics during formation of continental cratons already in the Archean. Similarly to different geochemical and geological constraints, the 3D anisotropy modelling and mapping of fabrics of the lithosphere domains contribute to tracking plate tectonics regimes back in time.

  • 39.
    Eken, Tuna
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Roberts, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hieronymus, Christoph F.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bödvarsson, Reynir
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    S and P velocity heterogeneities within the upper mantle below the Baltic Shield2008In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 462, no 1-4, p. 109-124Article in journal (Refereed)
    Abstract [en]

    Upper mantle structure beneath the Baltic (Fennoscandian) Shield is investigated using non-linear tomographic inversion of relative arrival-time residuals. 52 selected teleseismic earthquakes recorded by 45 broadband stations of the Swedish National Seismological Network (SNSN) provide 1532 good quality S-wave relative arrival times. SV and SH arrival-time residuals were initially analyzed independently, providing two separate models. These reveal several consistent major features, many of which are also consistent with P-wave results. Lateral velocity variations of ± 3–4% are observed to depths of at least 470 km. The correlation between the SH and SV models is investigated and shows a pattern of minor but significant differences down to around 150–200 km depth, below which the models are essentially similar. Direct cell by cell comparison of the model velocities reveals a similar pattern, with velocity differences between the models of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially attributed to noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. One of the significant and sharp discrepancies between the S models coincides with a presumed boundary between Archean and Proterozic domains, suggesting different anisotropic characteristics in the two regions.

  • 40.
    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.

  • 41.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pesonen, L. J.
    Leino, M. A. H.
    Khramov, A. N.
    Mikhailova, N. P.
    Krasnova, A. F.
    Merlanen, S.
    Bylund, G.
    Terho, M.
    The drift of the Fennoscandian and Ukrainian Shields during the Precambrian: a Palaeomagnetic analysis1993In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 223, no 3-4, p. 177-198Article in journal (Refereed)
    Abstract [en]

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

  • 42.
    Eshagh, Mehdi
    et al.
    University West, Department of Engineering Science, Division of Computer, Electrical and Surveying Engineering.
    Hussain, Mutloob
    Department of Earth Sciences, Quad-i-Azam University, Islamabad 45320, Pakistan.
    An approach to Moho discontinuity recovery from on-orbit GOCE data with application over Indo-Pak region2016In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. Part B, p. 253-262Article in journal (Refereed)
    Abstract [en]

    In this research, a modified form of Vening Meinesz-Moritz (VMM) theory of isostasy for the second-order radial derivative of gravitational potential, measured from the Gravity field and steady-state Ocean Circulation Explorer (GOCE), is developed for local Moho depth recovery. An integral equation is organised for inverting the GOCE data to compute a Moho model in combination with topographic/bathymetric heights of SRTM30, sediment and consolidated crystalline basement and the laterally-varying density contrast model of CRUST1.0. A Moho model from EGM2008 to degree and order 180 is also computed based on the same principle for the purpose of comparison. In addition, we compare both of them with the 3 available seismic Moho models; two global and one regional over the Indo-Pak region. Numerical results show that our GOCE-based Moho model is closer to the all seismic models than that of EGM2008. The model is closest to the regional one with a standard deviation of 5.5 km and a root mean squares error of 7.8 km, which is 2.3 km smaller than the corresponding one based on EGM2008.

  • 43.
    Eshagh, Mehdi
    et al.
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering. K. N. Toosi University of Technology, Department of Geodesy, Tehran, Iran; Islamic Azad University, Department of Geology, Karaj branch, Iran.
    Tenzer, Robert
    Hong Kong Polytechnic University,Department of Land Surveying and Geo-Informatics, Hong Kong.
    Elastic thickness of the Iranian lithosphere from gravity and seismic data2020In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 774, article id 228186Article in journal (Refereed)
    Abstract [en]

    We estimate the (effective) elastic thickness of the Iranian lithosphere (and adjoining tectonic plates) by using the approach that combines the Vening Meinesz-Moritz's (VMM) regional isostatic principle with the isostatic flexural model formulated based on solving a flexural differential equation for a thin elastic shell. To model the response on a load more realistically, we also consider the lithospheric density structure. The resulting expression describes a functional relation that links gravity field and mechanical properties of the lithosphere. The Young modulus and the Poisson ratio are computed from seismic velocity data in prior of estimating the lithospheric elastic thickness. The presented results reveal that the estimated elastic thickness closely resembles a regional tectonic configuration associated with the extensional tectonism along the Red Sea-Gulf Rift System, the continental collision of the Arabian and Eurasian plates, and the subduction along the Makran Subduction Zone. Seismically and volcanically active convergent tectonic margins of the Zagros and Kopeh Dagh Fold and Thrust Belts further extending along the Makran Accretionary Complex are characterised by a low lithospheric strength, with the elastic thickness typically less than ∼30 km. These small values of the elastic thickness are in a striking contrast to much larger values within most of the Central Iranian Blocks. According to our estimate, local maxima there reach ∼70 km in the Tabas micro-block. The elastic thickness of the Turan and Arabian Platforms reaches maxima of ∼100 km. These results generally support the hypothesis that tectonically active zones and orogens have a relatively low strength, resulting in a significant response of the lithosphere on various tectonic loads, compared to a significant strength of old cratonic formations. Interestingly, however, we observe a striking contrast between a low strength of the Arabian Shield compared to a high strength of the Arabian Platform. A possible explanation of this finding could be given by a different thermal regime of the Arabian lithosphere, controlled mainly by a mantle upwelling and a consequent extensional tectonism along the Red Sea-Gulf Rift System. © 2019

  • 44.
    Farzipour-Saein, Ali
    et al.
    Univ Isfahan, Fac Sci, Dept Geol, PO Code 81746-73441, Esfahan, Iran..
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Intermediate decollement activation in response to the basal friction variation and its effect on folding style in the Zagros fold-thrust belt, an analogue modeling approach2016In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 687, p. 56-65Article in journal (Refereed)
    Abstract [en]

    Although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains, the interaction between basal and intermediate decollements is poorly constrained. This study uses results of two scaled sand-box models shortened from one end to study the variation in structural development in response to varying basal friction and its consequent interaction with intermediate decollement horizons. Two models with similar incompetent intermediate decollement, but with different basal friction (with and without a thick basal decollement), were prepared analogous for the eastern and the western parts of the Razak basement fault in the Fars Region of the eastern part of the Zagros fold thrust belt (ZFTB). Combined results of scaled models with geological observations are used to argue that the basal decollement friction characteristics govern propagation of deformation front. In addition, model results, analogues to north-south direction, show that deformation complexity and disharmonic folding exist in the section where the intermediate decollement has been activated in response to the shortening without the basal decollement (throughout the western part of the Razak basement fault where less thickness of the Hormuz series as the basal decollement has been documented compared to its eastern part). In other words, the complexity in deformation is less portrayed along sections where basal friction beneath the model decreases (e.g. the eastern part of the Razak basement fault). We argue here that, in addition to other parameters (not presented in this study) interaction of intermediate decollement levels with basal decollement friction characteristics could explain decoupling between structures within the sedimentary column of the Fars Region of the eastern part of the Zagros fold thrust belt.

  • 45.
    Frenje, L
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Scattering of seismic waves simulated by finite difference modelling in random media: application to the Gravberg-1 well, Sweden1998In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 293, no 1-2, p. 61-68Article in journal (Refereed)
    Abstract [en]

    We generate surface and VSP synthetic seismograms using finite difference modelling of the elastic wave equation in self-similar media. The elastic model is determined by analyses of the sonic log from the deep Gravberg-1 borehole in central Sweden. The upper 1200 m is highly fractured and the velocities are best described by a log-normal distribution rather than a Gaussian distribution. Analyses of this interval after removing the deterministic trend and assuming a self-similar Gaussian distribution of the random component give a standard deviation of 370 m/s, a correlation distance of 45 m and a Hurst number of 0.18. These values and others from deeper levels are used to generate the 2-D elastic model and the synthetic seismograms are compared with real data. Synthetic surface seismic data show a poor qualitative match when compared to real data. Synthetic VSP data match the real VSP better qualitatively. In general, the synthetic data show considerably more scattering effects than the real data. Possible explanations for this discrepancy include: (1) intrinsic attenuation has been ignored; (2) a Gaussian distribution of the random component was assumed; or (3) the heterogeneities have a preferred orientation. The poor match implies that the method for extracting the 2-D or 3-D velocity variations in the uppermost crust from 1-D sonic log data need to be studied further.

  • 46.
    Fuchs, Lukas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Schmeling, Harro
    Goethe-University, Institute of Geoscience, Frankfurt am Main, Germany.
    Numerical modeling of the effect of composite rheology on internal deformation in down-built diapirs.2015In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 646, p. 79-95Article in journal (Refereed)
    Abstract [en]

    A two-dimensional finite difference code (FDCON) is used to estimate the progressive deformation and the effect of a composite rheology, i.e., Newtonian combined with non-Newtonian, on finite deformation patterns within a down-built diapir. The geometry of the diapir is fixed using two rigid rectangular overburden units which sink into a source layer of a certain viscosity. We have analyzed the progressive deformation within the entire salt layer for a composite rheology and compared them to a standard model with Newtonian rheology (ηs = 1018 Pa s). The composite rheology models show a more complex deformation patterns in comparison to the standard model. Deformation is more localized within the source layer, leaving a broader less deformed zone within the middle of the source layer. In comparison to the standard model, ellipticity (R) of the strain ellipse is amplified by a factor of up to three in high deformation regions with a finite deformation f larger than two (f = log10(R)). Initially vertical and horizontal passive marker-lines within the salt layer, are folded during salt movement. Initially horizontally-oriented marker-lines in the source layer show upright folds within the middle of the stem. Within the source layer, initially vertical marker-lines form recumbent folds, which are refolded during their flow from the source layer into the stem. During their refolding, the hinge of the fold migrates outward towards the flank of the diapir. A temporal and spatial hinge migration is observed for sub-horizontal folds that originated in the source layer as they are refolded. We have also studied both the effect of curved versus sharp corners between the source layer and the stem on strain evolution within both the feeding source layer and the down-built diapir. Strain evolution and hinge migration are strongly influenced by the geometry of the corner between the source layer and the stem.

  • 47.
    Fuchs, Lukas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Koyi, Hemin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Schmeling, Harro
    Goethe-University, Institute of Geoscience, Frankfurt am Main, Germany.
    Numerical modeling on progressive internal deformation indown-built diapirs2014In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 632, p. 111-122Article in journal (Refereed)
    Abstract [en]

    A two-dimensional finite difference code (FDCON) is used to estimate the finite deformationwithin a down-builtdiapir. The geometry of the down-built diapir is fixed by using two rigid rectangular overburden unitswhich sinkinto a source layer of a constant viscosity. Thus, the model refers to diapirs consisting of a source layerfeeding a vertical stem, and not to other salt structures (e.g. salt sheets or pillows). With this setup westudy the progressive strain in three different deformation regimes within the “salt” material: (I) a squeezedchannel-flow deformation regime and (II) a corner-flow deformation regime within the source layer, and(III) a pure channel-flow deformation regime within the stem. We analyze the evolution of finite deformationin each regime individually, progressive strain for particles passing all three regimes, and total 2Dfinite deformationwithin the salt layer. Model results show that the material which enters the stem bears inherited strainaccumulated from the other two domains. Therefore, finite deformation in the stem differs from the expectedchannel-flow deformation, due to the deformation accumulated within the source layer. The stem displays ahigh deformation zone within its center and areas of decreasing progressive strain between its center and itsboundaries.High deformation zoneswithin the stemcould also be observedwithin natural diapirs (e.g. Klodowa,Polen). The location and structure of the high deformation zone (e.g. symmetric or asymmetric) could revealinformation about different rates of salt supplies from the source layer. Thus, deformation pattern could directlybe correlated to the evolution of the diapir.

  • 48.
    García Juanatey, María de los Angeles
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Hübert, Juliane
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Tryggvason, Ari
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Pedersen, Laust B.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bauer, Tobias E.
    Luleå University of Technology.
    Dehghannejad, Mahdieh
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    2D and 3D MT in the central Skellefte Ore District, northern Sweden2019In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 764, p. 124-138Article in journal (Refereed)
    Abstract [en]

    New broadband magnetotelluric (MT) data have been acquired along two parallel profiles in the central part of the metallogenic Skellefte district in northern Sweden. The data were recorded as part of the Swedish 4D modelling of mineral belts project and cover an area with several economical and sub-economical deposits. The dimensionality and quality of the data were carefully analyzed and new error floors were systematically determined prior to inverse modelling in 2D and 3D. The algorithms used were EMILIA and WSINV3DMT. For the 2D inversion, only the determinant of the impedance tensor was used, while for the 3D inversion all elements were considered. The obtained models fit the inverted data, and image the main regional features. A detailed comparison reveals the superiority of the 3D model, both in model structures and data fit. After assessing the main features in the model, an interpretation is proposed and refined with the support of previous geophysical studies. The most interesting features are large and medium-sized conductors associated with crustal-scale shear zones and faults within the Skellefte Group rocks. These may be depicting a network of fossil pathways for hydrothermal fluid transport and as such, provide new insight into past processes in the area.

    The full text will be freely available from 2021-04-13 15:31
  • 49. Gregersen, S.
    et al.
    Voss, P.
    Nielsen, L. V.
    Achauer, U.
    Busche, H.
    Rabbel, W.
    Shomali, Zaher Hossein
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Uniqueness of modeling results from teleseismic P-Wave tomography in Project Tor2010In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 481, no 1-4, p. 99-107Article in journal (Refereed)
    Abstract [en]

    Within Project Tor. which is about Teleseismic Tomography across the Tomquist Zone in Germany-Denmark-Sweden, we have confirmed very significant deep lithosphere differences And modeling is substantiated via completely independent methods. In 1996-1997 our 130 seismographs constituted the largest seismic antenna ever in Europe. The Tor area was chosen along a well studied crustal profile of an earlier project, and the modeling efforts were concentrated on the deep lithosphere and asthenosphere differences to depths around 300 km The Tor data have been subjected to P-wave travel time tomography. surface wave and receiver function analysis as well as anisotropy and scattering measurements An important goal of the project was to make several independent inversions of the tomography data. and compare the results in an attempt to evaluate uniqueness, resolution and accuracy of these inversions. The comparisons of this paper involve more diversity in methods than any previous comparison. The geological outcome is a substantiation of earlier statements that, "The transition is interpreted to be sharp and steep in two places It goes all through the lithosphere at the northern rim of the Tornquist Zone near the border between Sweden and Denmark, and here the lithosphere difference is large to depths more than 200 km. The other lithosphere difference. of smaller scale, is found near the southern edge of the Ringkobing-Fyn High near the border between Denmark and Germany Also this transition is sharp and steep. and goes all through the lithosphere to depths around 120 km. These two sharp transitions divide the Tor region into 3 different lithosphere structures distinguishable in P-wave travel time tomography. surface wave dispersion. P- and S-wave anisotropy and partly in P-wave scattering" The mentioned broad-scale features are judged to be unambiguously determined, with well-described resolution and accuracy Unfortunately a detail like the slope of the subcrustal lithosphere transition right under the Tronquist Zone cannot be constrained even if this is where the resolution is best. and the curiosity largest.

  • 50. Gutscher, M.-A.
    et al.
    Klingelhoefer, F.
    Theunissen, T.
    Spakman, W.
    Berthet, Théo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Wang, T.K.
    Lee, C.-S.
    Thermal modeling of the SW Ryukyu forearc (Taiwan): Implications for the seismogenic zone and the age of the subducting Philippine Sea Plate (Huatung Basin)2016In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 692, no Part B, p. 131-142Article in journal (Refereed)
    Abstract [en]

    Subduction mega-thrust earthquakes in the SW Ryukyu trench pose a seismic and tsunami hazard. One of the objectives of this study is to estimate the downdip width of the seismogenic zone using numerical modeling to determine the temperature distribution along the plate interface. However, this approach depends strongly on the thermal parameters of the subducting slab. While the Philippine Sea plate (PSP) subducting beneath the central and eastern Ryukyu arc is of Eocene age (35–50 Ma), its age west of the Gagua Ridge is uncertain, with proposed ages ranging from Lower Cretaceous (140 Ma) to Upper Eocene (35 Ma). Since the sparse available heat flow data are insufficient to resolve this debate, both end-member hypotheses are tested as input parameters. We examined two transects at 122.5°E and 123.5°E on either side of the N-S trending, 4-km high, Gagua Ridge. The shallow forearc geometry is obtained from wide-angle seismic data. The deep slab geometry was obtained from hypocenter distribution and tomography. For an Eocene slab age, we obtain a 100 km and 110 km wide seismogenic zone (between the 150 °C and 350 °C isotherms) west and east of Gagua Ridge, respectively. This is in good agreement with the observed distribution of hypocenters. Using a Cretaceous slab west of Gagua Ridge predicts a deep seismogenic zone (25 km–60 km depth), inconsistent with observed thrust earthquakes. Tomographic images at 122.5°E and 123.5°E show a similar slab thickness of 70–80 km suggesting that the oceanic lithosphere has a young (Eocene) thermal age. The westernmost PSP (Huatung Basin) may have been thermally rejuvenated by mantle convection near the slab corner. The tectonic history since 6 Ma (transition from subduction to collision beneath Taiwan) may have also perturbed the thermal structure.

123 1 - 50 of 121
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