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  • 1
    Electronic Resource
    Electronic Resource
    Power Spectra Analysis of Aeromagnetic Data and KTB Susceptibility Logs, and their Implication for Fractal Behavior of Crustal Magnetization (1998)
    Springer
    Pure and applied geophysics 151 (1998), S. 147-159 
    Details
    ISSN: 1420-9136
    Keywords: Key words: Magnetic anomaly, power spectrum, fractal parameter.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. —Power spectra analysis of aeromagnetic data from the southeast North Sea, where the depth to the top of the magnetic sources is reasonably well constrained, indicates that the scaling factor or spectral exponent (β) in an area with thick sediment cover is likely to be significantly different from the expected value of -3. This is consistent with the results from analyzing the KTB susceptibility data, which show that the magnetic scaling factor changes with burial depth. For sources shallower than about 1 km, a β value of -2.3 is roughly consistent with previous similar investigations. For sources deeper than a few kilometers, the β value could be as low as -1.0. Therefore, the depth estimation using power spectra analysis of magnetic data should be treated with caution, especially if there is no independent constraint on the source depth or the scaling factor (for instance from susceptibility logs in boreholes).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050109
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Deep Structure of the Swiss Alps: Results of NRP 20. O.A. Pfiffner, P. Lehner, P. Heitzmann, St. Mueller, and A. Steck (editors). (1998)
    Springer
    Surveys in geophysics 19 (1998), S. 207-209 
    Details
    ISSN: 1573-0956
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006582025632
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    Paper (German National Licenses)
    Fulltext
  • 3
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    The crustal structure in the transition zone between the western and eastern Barents Sea (2018)
    Wiley
    In:  Geophysical Journal International, 214 (1). pp. 315-330.
    Details
    Publication Date: 2021-02-08
    Description: We present a crustal-scale seismic profile in the Barents Sea based on new data. Wide-angle seismic data were recorded along a 600 km long profile at 38 ocean bottom seismometer and 52 onshore station locations. The modeling uses the joint refraction/reflection tomography approach where co-located multi-channel seismic reflection data constrain the sedimentary structure. Further, forward gravity modeling is based on the seismic model. We also calculate net regional erosion based on the calculated shallow velocity structure. Our model reveals a complex crustal structure of the Baltic Shield to Barents shelf transition zone, as well as strong structural variability on the shelf itself. We document large volumes of pre-Carboniferous sedimentary strata in the transition zone which reach a total thickness of 10 km. A high-velocity crustal domain found below the Varanger Peninsula likely represents an independent crustal block. Large lower crustal bodies with very high velocity and density below the Varanger Peninsula and the Fedynsky High are interpreted as underplated material that may have fed mafic dykes in the Devonian. We speculate that these lower crustal bodies are linked to the Devonian rifting processes in the East European Craton, or belonging to the integral part of the Timanides, as observed onshore in the Pechora Basin.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1093/gji/ggy139
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Seismic explosion sources on an ice cap – technical considerations (2015)
    Elsevier
    In:  Polar Science, 9 (1). pp. 107-118.
    Details
    Publication Date: 2017-05-01
    Description: Controlled source seismic investigation of crustal structure below ice covers is an emerging technique. We have recently conducted an explosive refraction/wide-angle reflection seismic experiment on the ice cap in east-central Greenland. The data-quality is high for all shot points and a full crustal model can be modelled. A crucial challenge for applying the technique is to control the sources. Here, we present data that describe the efficiency of explosive sources in the ice cover. Analysis of the data shows, that the ice cap traps a significant amount of energy, which is observed as a strong ice wave. The ice cap leads to low transmission of energy into the crust such that charges need be larger than in conventional onshore experiments to obtain reliable seismic signals. The strong reflection coefficient at the base of the ice generates strong multiples which may mask for secondary phases. This effect may be crucial for acquisition of reflection seismic profiles on ice caps. Our experience shows that it is essential to use optimum depth for the charges and to seal the boreholes carefully.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.polar.2014.11.002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Crustal structure across the Møre margin, mid-Norway, from wide-angle seismic and gravity data (2014)
    Elsevier
    In:  Tectonophysics, 626 . pp. 21-40.
    Details
    Publication Date: 2018-01-05
    Description: The Møre Margin in the NE Atlantic represents a dominantly passive margin with an unusual abrupt transition from alpine morphology onshore to a deep sedimentary basin offshore. In order to study this transition in detail, three ocean bottom seismometer profiles with deep seismic reflection and refraction data were acquired in 2009; two dip-profiles which were extended by land stations, and one tie-profile parallel to the strike of the Møre–Trøndelag Fault Complex. The modeling of the wide-angle seismic data was performed with a combined inversion and forward modeling approach and validated with a 3D-density model. Modeling of the geophysical data indicates the presence of a 12–15 km thick accumulation of sedimentary rocks in the Møre Basin. The modeling of the strike profile located closer to land shows a decrease in crustal velocity from north to south. Near the coast we observe an intra-crustal reflector under the Trøndelag Platform, but not under the Slørebotn Sub-basin. Furthermore, two lower crustal high-velocity bodies are modeled, one located near the Møre Marginal High and one beneath the Slørebotn Sub-basin. While the outer lower crustal body is modeled with a density allowing an interpretation as magmatic underplating, the inner body has a density close to mantle density which might suggest an origin as an eclogized body, formed by metamorphosis of lower crustal gabbro during the Caledonian orogeny. The difference in velocity and extent of the lower crustal bodies seems to be controlled by the Jan Mayen Lineament, suggesting that the lineament represents a pre-Caledonian structural feature in the basement.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.tecto.2014.03.021
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Stochastic velocity inversion of seismic reflection/refraction traveltime data for rift structure of the southwest Barents Sea (2013)
    Elsevier
    In:  Tectonophysics, 593 . pp. 135-150.
    Details
    Publication Date: 2019-09-23
    Description: We present results from an active-source, onshore–offshore seismic reflection/refraction transect acquired as part of the PETROBAR project (Petroleum-related studies of the Barents Sea region). The 700 km-long profile is oriented NW–SE, coincident with previously published multichannel seismic reflection profiles. We utilize layer-based raytracing in a Markov Chain Monte Carlo (MCMC) inversion to determine a probabilistic velocity model constraining the sedimentary rocks, crystalline crust, and uppermost mantle in a complex tectonic regime. The profile images a wide range of crustal types and ages, fromProterozoic craton to Paleozoic to early Cenozoic rift basins; and volcanics related to Eocene continental breakupwith Greenland. Our analyses indicate a complex architecture of the crystalline crust along the profile,with crystalline crustal thicknesses ranging from43 kmbeneath the Varanger Peninsula to 12 kmbeneath the Bjørnøya Basin. Assuming an original, post-Caledonide crustal thickness of 35 km in the offshore area, we calculate the cumulative thinning (β) factors along the entire profile. The average β factor along the profile is 1.7 ± 0.1, suggesting 211–243 km of extension, consistent with the amount of overlap derived from published plate reconstructions. Local β factors approach 3, where Bjørnøya Basin reaches a depth of more than 13 km. Volcanics, carbonates, salt, diagenesis and metamorphism make deep sedimentary basin fill difficult to distinguish from original, pre-rift crystalline crust, and thus actual stretching may in places exceed our estimates.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.tecto.2013.02.033
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Crustal composition of the Møre Margin and compilation of a conjugate Atlantic margin transect (2016)
    Elsevier
    In:  Tectonophysics, 666 . pp. 144-157.
    Details
    Publication Date: 2019-09-24
    Description: Highlights • The basement at the mid-Norwegian Møre Margin is dominantly felsic in composition. • A lower crustal body is interpreted as a mixture of continental blocks and eclogite. • The thickness of the outer lower crustal body is twice as thick on the East Greenland Margin. • The thinning during this first phase of post-Caledonian extension was highest for proto Norway. Abstract The inner part of the volcanic, passive Møre Margin, mid-Norway, expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust. Previous P-wave modeling of wide-angle seismic data revealed the presence of a high-velocity (7.7–8.0 km/s) body in the lower crust in this transitional region. These velocities are too high to be readily interpreted as Early Cenozoic intrusions, a model often invoked to explain lower crustal high-velocity bodies in the region. We present a Vp/Vs model, derived from the modeling of wide-angle seismic data, acquired by use of Ocean Bottom Seismograph horizontal components. The modeling suggests dominantly felsic composition of the crust. An average Vp/Vs value for the lower crustal body is modeled at 1.77, which is compatible with a mixture of continental blocks and Caledonian eclogites. The results are compiled with earlier results into a transect extending from onshore Norway to onshore Greenland. Back-stripping of the transect to Early Cenozoic indicates asymmetric conjugate magmatism related to the continental break-up. Further back-stripping to the time when most of the Caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25% higher for proto Norway than proto Greenland.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.tecto.2015.11.002
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Velocity model of the crust and upper mantle at the southern margin of the East European Craton (Azov Sea-Crimea-Black Sea area), DOBRE-2 & DOBRE'99 transect (2013)
    In:  [Poster] In: EGU General Assembly 2013, 07.-12.04.2013, Vienna, Austria .
    Details
    Publication Date: 2013-03-05
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Poster
  • 9
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    Continent size revisited: Geophysical evidence for West Antarctica as a back-arc system (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Antarctica has traditionally been considered continental inside the coastline of ice and bedrock since Press and Dewart (1959). Sixty years later, we reconsider the conventional extent of this sixth continent. Geochemical observations show that subduction was active along the whole western coast of West Antarctica until the mid-Cretaceous after which it gradually ceased towards the tip of the Antarctic Peninsula. We propose that the entire West Antarctica formed as a back-arc basin system flanked by a volcanic arc, similar to e.g. the Japan Sea, instead of a continental rift system as conventionally interpreted. Globally, the fundamental difference between oceanic and continental lithosphere is reflected in hypsometry, largely controlled by lithosphere buoyancy. The equivalent hypsometry in West Antarctica (−580 ± 335 m on average, extending down to −1.6 km) is much deeper than in any continent, but corresponds to back-arc basins and oceans proper. This first order observation questions the conventional interpretation of West Antarctica as continental, since even continental shelves do not extend deeper than −200 m in equivalent hypsometry. We present a suite of geophysical observations that supports our geodynamic interpretation: a linear belt of seismicity sub-parallel to the volcanic arc along the Pacific margin of West Antarctica; a pattern of free air gravity anomalies typical of subduction systems; and extremely thin crystalline crust typical of back-arc basins. We calculate residual mantle gravity anomalies and demonstrate that they require the presence of (1) a thick sedimentary sequence of up to ca. 50% of the total crustal thickness or (2) extremely low density mantle below the deep basins of West Antarctica and, possibly, the Wilkes Basin in East Antarctica. Case (2) requires the presence of anomalously hot mantle below the entire West Antarctica with a size much larger than around continental rifts. We propose, by analogy with back-arc basins in the Western Pacific, the existence of rotated back-arc basins caused by differential slab roll-back during subduction of the Phoenix plate under the West Antarctica margin. Our finding reduces the continental lithosphere in Antarctica to 2/3 of its traditional area. It has significant implications for global models of lithosphere-mantle dynamics and models of the ice sheet evolution.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    A new tectonic map of the Iranian plateau based on aeromagnetic identification of magmatic arcs and ophiolite belts (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights • The Radially averaged power spectrum method is applied to calculate average magnetic susceptibility in Iran. • The results demonstrate that known occurrences of Magmatic-Ophiolite Arcs (MOA) correlate with high average susceptibility areas. • We interpret two parallel, hitherto unknown, MOAs in eastern Iran which developed in a steeply dipping (〉60° dip) subduction zone. • Neo-Tethys subduction angle was shallow (〈20° dip) of in NW Iran and steep (〉60° dip) in SE Iran which indicates slab tearing. • We define a new outline of the economically important Tabas sedimentary basin. Abstract The Iranian plateau is one of the most complex geodynamic settings within the Alpine-Himalayan belt. The Paleo-Tethys and Neo-Tethys ocean subduction is responsible for the formation of several magmatic arcs and sedimentary basins within the plateau. These zones mostly are separated by thrust faults related to paleo-suture zones, which are highlighted by ophiolites. Sediment cover and overprint of a different magmatic phase from late Triassic to the Quaternary impede identification of some magmatic arcs and ophiolite belts. We track the known magmatic arcs, such as the Urmia-Dokhtar Magmatic Arc (UDMA), and unknown, sediment covered magmatic arcs by aeromagnetic data. We present a new map of average susceptibility calculated by the radially averaged power spectrum method. High average susceptibility values indicate the presence of a number of lineaments that correlate with known occurrences of Magmatic-Ophiolite Arcs (MOA), and low average susceptibility coincides with known sedimentary basins like Zagros, Makran, Kopeh-Dagh, and Tabas. In analogy to Zagros, low average susceptibility values indicate sedimentary basins to the south of the Darouneh fault and in the northern part of the Lut, Tabas and Yazd blocks. We interpret the Tabas basin as a pull-apart or back-arc basin. We identify hitherto unknown parallel MOAs in eastern Iran and the SE part of UDMA which both indicate steeply dipping (〉60° dip) paleo-subduction zones. In contrast, we interpret shallow subduction (〈20° dip) of Neo-Tethys in the NW part of UDMA as well as in the Sabzevar-Kavir MOA.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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