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Trondheim, Norway

Norwegian Geological Survey , abbr:NGU is a Norwegian government agency responsible for geologic mapping and research. The agency is located in Trondheim with an office in Tromsø, with about 225 employees. It is subordinate the Norwegian Ministry of Trade and Industry. Wikipedia.


Redfield T.F.,Geological Survey of Norway | Osmundsen P.T.,Geological Survey of Norway | Osmundsen P.T.,University Center in Svalbard
Bulletin of the Geological Society of America | Year: 2013

We present data that link Scandinavia's passive-margin domains under a unified system invoking isostatically driven, postextension phase vertical adjustments to severe crustal thinning. Topographic and geological data indicate that the relative location of the first landward occurrence of total crustal embrittlement or deformation coupling- the Taper Break-controlled and continues to control Scandinavia's post-thinning geomorphic evolution. Formed during Late Jurassic or Early Cretaceous thinning, yet marked today by seismicity, the Taper Break closely approximates the boundary between(1) less-stretched lithosphere that increases in rigidity both toward land and through postrifttime, and (2) the highlyattenuated, pervasively faulted, permanently weakened lithosphere of the distal margin. Following the stretching, thinning, and exhumation phases proposed by other workers, an accommodation phase is warranted. Commencing during quot;sagquot; basin time and continuing today, it is probably driven by thermal cooling and mass transfer from the escarpment to the basins offshore. The accommodation phase does not entirely coincide with the traditional postriftphase as the former may contain the latter. During accommodation, the original synriftescarpments can be eroded to very low base levels. Sharply tapered margin segments can undergo subsequent rejuvenation by out-of-sequence normal faulting and footwall uplift, probablyin response to tensile bending stresses engendered by lithosphericscale fl exure. Accommodation-phase upliftat passive margins is the inexorable and penultimate phase of hyperextension, and may perhaps be followed by the onset of subduction localized by the weakened lithosphere of the distal margin and the ocean-continent transition. © 2013 Geological Society of America. Source


Fabian K.,Geological Survey of Norway | McEnroe S.A.,Norwegian University of Science and Technology
Geochemistry, Geophysics, Geosystems | Year: 2013

Curie point temperatures (TC) of natural and synthetic magnetic materials are commonly determined in rock magnetism by several measurement methods that can be mutually incompatible and may lead to inconsistent results. Here the common evaluation routines for high-temperature magnetization and magnetic initial susceptibility curves are analyzed and revised based on Landau's theory of second-order phase transitions. It is confirmed that in high-field magnetization curves TC corresponds to the inflection point, below the temperature of maximum curvature or the double-tangent intersection point. At least four different physical processes contribute to the initial magnetic susceptibility near the ordering temperature. They include variation of saturation magnetization, superparamagnetic behavior, magnetization rotation, and magnetic domain wall motion. Because each of these processes may influence the apparent position of TC, initial susceptibility and high-field curves can yield deviating estimates of TC. A new procedure is proposed to efficiently determine the temperature variation of several magnetic parameters on a vibrating-sample magnetometer, by repeatedly measuring quarter-hysteresis loops during a single heating cycle. This procedure takes measurements during the inevitable waiting time necessary for thermal equilibration of the sample, whereby it is not slower than the commonly performed measurements on a Curie balance. However, it returns saturation magnetization, saturation remanence, high-field and low-field slopes, and other parameters as a function of temperature, which provide independent information about TC and other sample properties. © 2012. American Geophysical Union. All Rights Reserved. Source


Buiter S.J.H.,Geological Survey of Norway | Buiter S.J.H.,University of Oslo
Tectonophysics | Year: 2012

Fold-and-thrust belts and accretionary wedges form by compression of sedimentary sequences and basement rocks into forward and backward thrusts, folds, nappes, and duplexes. For over a century, models have been used to investigate the essential characteristics of such brittle wedges. Here I review model studies of brittle thrust wedges in orthogonal compression, focussing on critical taper theory, analogue and numerical techniques for modelling brittle behaviour, and the most commonly investigated variations in wedge model studies, those in basal dip, basal strength, internal strength, and surface processes. Many model results can be placed in the context of critical taper theory, which provides analytical solutions for wedge taper angle and slip line orientations for a homogeneous material on the verge of failure throughout. Dynamic forward models have confirmed critical taper predictions of decreasing surface dip for increasing basal dip, wider wedges with steeper forward thrusts and shallower backward thrusts for decreasing basal strength, narrower wedges and enhanced exhumation for surface erosion, and decreasing surface dip for increasing internal strength. But analogue and numerical models have been able to take these results a step further by investigating the evolution of non-critical thrust wedges and the effects of non-homogeneous materials with décollement layers and strain-weakening shear zones. These results have highlighted the strong impact of heterogeneous materials on the internal structures of thrust wedges and raise the question whether the complexity of structures that are observed in many natural fold-and-thrust belts requires that lithological layering, inherited faults, or a wide range of rheologies need to be included in forward models of brittle thrust wedges. © 2011 Elsevier B.V. Source


Broekmans M.A.T.M.,Geological Survey of Norway
Reviews in Mineralogy and Geochemistry | Year: 2012

More than seventy years have gone since the first recognition of deleterious alkali-aggregate reaction by Stanton in 1940, and a tremendous lot of research has been committed since, a small part of which is described above, summarized in below list: 1. deleterious AAR is a worldwide problem occurring on all continents, and new countries/regions are still added to the list as additional structures are being diagnosed with the damage mechanism. The irreparable character of AAR as a concrete property inherited from its main constituents, renders it an expensive one especially for large infrastructural works or any other type of structure designed with a long service life in mind; 2. alkalis Na and K are a natural part of the concrete composition, either inherited from the raw materials used for clinkering of the Portland cement, or infiltrated from seawater or deicers or other alkali-containing chemicals, or occasionally released from the aggregate upon exposure to the concrete interior; 3. several types of deleterious AAR are known. The most common and widespread is alkali-silica reaction ASR, less abundant is the alkali-carbonate reaction ACR that may either be 'cryptic ASR' from finely dispersed silica in carbonate rock which is deleterious, or a true reaction with carbonate which is non-deleterious. Both ACR and cryptic-ASR may occur in a given aggregate material; 4. the most abundant silica polymorph in the supracrustal rocks used for concrete aggregate is quartz, α-SiO 2. Additional alkali-reactive silica species include chert/flint, chalcedony and opal in sedimentary rocks, in volcanic rocks also cristobalite or tridymite, that may be important constituents in certain regions. Alkali-reactivity is affected by silica grain size, accessibility (e.g., internal porosity, permeability), and a range of properties and qualities known to govern the dissolution of quartz under geological conditions; 5. the alkali-silica reaction mechanism is very complicated and affected by the type of alkali-reactive silica and pore solution chemistry. Alkalis are regenerated by subsequent reactions rather than consolidated with the reaction products, and are thus available for further reaction; 6. alkali-silica reaction products have variable optical properties in thin section, morphology and chemical composition, related to position (inside the alkali-reactive particle, or in the paste), age, and natural variation in locally available 'starting materials' aggregate and cement. Inconsistent analytical setup as well as of reporting results complicates direct comparison of data from different sources; 7. the crystalline structure of ASR gel can be represented as consisting of kanemite domains of ∼10 Å, without long-range order between adjacent domains. The structure of the interstitial space between domains is presently unknown, but is assumed capable of accommodating additional water contributing to gel expansion; 8. alternative alkali-reactive species comprise natural and industrial glasses, as well as a range of common rock-forming silicate minerals and carbonates (also see point 3); 9. routine assessment of AAR concrete in a laboratory involves petrography on cores extracted from a damaged structure. Rigorous procedures are essential to minimize introduction of artifacts during extraction, handling, storage and assessment; 10. cracks and internal porosity can be visualized by impregnating plane and thin sections with fluorescent epoxy. The amount of AAR damage (and its progress over time) can be quantified with a number of alternative methods, the most accurate being time-robbing and hence costly, the quick-and-dirty alternatives being less expensive but less accurate; 11. assessment of bulk deleterious aggregate in set concrete is complicated by imperfect liberation, whether using chemical or mechanical procedures; 12. in situ analysis of ASR gel in thin section is complicated by a range of factors, most of which can be compensated for by rigorous specimen preparation procedures, fine-tuning instrument settings and operating conditions, and by critical post-processing of acquired data; 13. the crystallinity index for quartz QCI by Murata and Norman (1976) is a meaningless concept in its current form, and should be abandoned for the assessment of alkali-silica reactivity potential of concrete aggregate. Copyright © Mineralogical Society of America. Source


Fabian K.,Geological Survey of Norway | Leonhardt R.,Zentralanstalt fur Meteorologie und Geodynamik
Earth and Planetary Science Letters | Year: 2010

A recent proposal of a multiple-specimen technique promises to be a viable alternative to the classical Thellier-Thellier method of absolute paleointensity determination. However, to exploit the full potential of the multiple-specimen approach, a thorough understanding of its theoretical foundation, and a detailed experimental verification of its implicit assumptions is required. Here, the validity of the multiple-specimen technique is studied on a collection of synthetic samples covering grain sizes ranging from single domain (SD) over intermediate pseudo-single domain (PSD), to multidomain (MD). The experimental data indicate that the multiple-specimen method in its present form systematically overestimates paleointensity for intermediate PSD to MD particle sizes. This finding is investigated theoretically by a statistical theory of weak-field thermoremanence, and quantified by a phenomenological thermoremanence model. Based on this theoretical framework, and on the new experimental evidence, an extended version of the multiple-specimen technique is designed, which is more reliable in the critical domain-state range. The new measurement scheme improves normalization, and quantifies the PSD and MD overestimate, which then can even be corrected for. Furthermore, the proposed measurement scheme includes a thermal repeat measurement to assess the effect of alteration upon the accuracy of the final paleointensity result. The new technique is verified experimentally for the synthetic samples investigated. © 2010 Elsevier B.V. Source

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