1,720,989 research outputs found
Direct 40Ar/39Ar dating of Late Ordovician and Silurian brittle faulting in the southwestern Norwegian Caledonides
No full textStructural data as well as U–Pb zircon and 40Ar/39Ar biotite and muscovite ages were collected from the Rolvsnes granodiorite in western Norway. The granodiorite intruded at c. 466 Ma, cooled quickly and escaped later viscous deformation. Brittle top-to-the-NNW thrust faults (Set I) and WNW–ESE striking dextral strike-slip faults (Set II) formed in a NNW–SSE transpressional regime. 40Ar/39Ar dating of synkinematic mica from both sets reveals a c. 450 Ma (Late Ordovician) age of faulting, which constrains early-Caledonian brittle deformation. Set I and II faults are overprinted by a set of lower-grade, variably oriented chlorite- and epidote-coated faults (Set III) constraining WNW–ESE shortening. A lamprophyric dyke oriented compatibly with this stress field intruded at c. 435 Ma (Silurian), indicating that Set III formed at the onset of the Scandian Baltica–Laurentia collision. The preservation of Caledonian brittle structures indicates that the Rolvsnes granodiorite occupied a high tectonic level throughout the Caledonian orogeny
Manual extraction of bedrock lineaments from high-resolution LiDAR data: methodological bias and human perception
Full text linkManual extraction of topographic features from Light Detection and Ranging (LiDAR) images is a quick, cost effective and powerful tool to produce lineament maps of fractured basement areas. This commonly used technique, however, suffers from several biases. In this contribution, we present the influence of (1) scale, (2) illumination azimuth and (3) operator, which significantly affect results of remote sensing expressed as number, orientation and length of the mapped lineaments. Six operators (N1–N6) with differing experience in remote sensing and different Earth sciences backgrounds mapped the same LiDAR DEM of a fractured bedrock terrain located in western Norway at three different scales (1:20.000, 1:10.000, 1:5.000) and illuminated from three different azimuths (045°, 180°, 315°). The 54 lineament maps show considerable output variability depending on the three factors: (1) at larger scales, both the number and the orientation variability of picked lineaments increase, whereas the line lengths generally decrease. (2) Linear features oriented perpendicular to the source of illumination are preferentially enhanced. (3) Inter-operator result reproducibility is generally poor. Operators have different perceptions of what is a lineament. Ironically, this is particularly obvious for the results of the “most experienced” operators, seemingly reflecting a stronger conceptual bias of what lineaments are and an operational bias on how they should be mapped. Based on these results, we suggest guidelines aimed to improve the reliability of remote sensing lineament interpretations
Lithological and structural analysis of the Rødberget-Rørvika-Varpneset transect, Mid Norwegian Caledonides - Testing tectonostratigraphic correlations and structural models
No full textRemnants of the Caledonian orogen are visible through tectonostratigraphic and structural fingerprints in Central Norway, and the detailed study of key localities is important for the understanding of the overall evolution of this orogeny. In this study, a lithological and structural analysis of the Rødberget-Rørvika-Varpneset transect on Fosen peninsula, South-Trøndelag, is conducted. In earlier studies, several tectonostratigraphic hypotheses were proposed for this area: 1) the central amphibolites belong to the Støren Nappe, whereas the surrounding mica schists belong to the Gula Nappe, 2) Seve Nappe Complex, Gula and Støren nappes are represented in the area, and 3) the entire area can be correlated to the Seve Nappe Complex. In addition, it was proposed that the central amphibolites represent a larger synformal structure. With the help of lithological mapping, geochemical analysis of aplites and amphibolites, and U-Pb zircon dating, these earlier proposed tectonostratigraphic correlations and structural models are tested in this study. The study area is divided into four units: the Rødberget, Trongen, Rørvika and Varpneset units. The Rødberget unit represents Baltoscandian basement, whereas the Trongen, Rørvika and Varpneset units are correlated with the Seve Nappe Complex based on the following lines of evidence: 1) lithological similarities to Seve Nappe Complex rocks in Central Norway and Sweden, 2) penetrative at least amphibolite-facies metamorphism, 3) U-Pb zircon dating of an intermediate layer within the central amphibolites yielding an age of 435.4±3.3 Ma, interpreted to be the result of decompressional melting of amphibolites related to exhumation of the Seve Nappe Complex, and 4) the presence and geochemistry of aplites, which have intruded both mica schists and amphibolites, resembling similar intrusive rocks in the Seve Nappe Complex, which were emplaced at about 430 Ma. In addition, through a detailed structural analysis of foliations, lineations, fold axes and fold vergences it can be shown that the central Rørvika unit is not lying within a synform, but rather represents a wedge-shape structure where the vergence of the smaller folds reflects the movement of the lithologies in the area. Two large-scale models are proposed for the ductile structural evolution of the entire area: 1) an obstacle and buckling model, and 2) a rotation model. Both models are related to the evolution of antiformal basement windows and the Møre-Trøndelag Fault Complex (MTFC). Stress inversion of brittle structures shows that the study area has been affected by a NW-SE extensional event, reactivating the MTFC in Late Paleozoic to Late Mesozoic/Early Cenozoic. These results imply that the area of interest has experienced a different structural evolution than earlier proposed, with a different and more complex metamorphic and structural history. This has implications for tectonostratigraphic correlations across Trondheimsfjorden
Lithological and structural analysis of the Rødberget-Rørvika-Varpneset transect, Mid Norwegian Caledonides - Testing tectonostratigraphic correlations and structural models
Full text linkRemnants of the Caledonian orogen are visible through tectonostratigraphic and structural fingerprints in Central Norway, and the detailed study of key localities is important for the understanding of the overall evolution of this orogeny. In this study, a lithological and structural analysis of the Rødberget-Rørvika-Varpneset transect on Fosen peninsula, South-Trøndelag, is conducted. In earlier studies, several tectonostratigraphic hypotheses were proposed for this area: 1) the central amphibolites belong to the Støren Nappe, whereas the surrounding mica schists belong to the Gula Nappe, 2) Seve Nappe Complex, Gula and Støren nappes are represented in the area, and 3) the entire area can be correlated to the Seve Nappe Complex. In addition, it was proposed that the central amphibolites represent a larger synformal structure. With the help of lithological mapping, geochemical analysis of aplites and amphibolites, and U-Pb zircon dating, these earlier proposed tectonostratigraphic correlations and structural models are tested in this study. The study area is divided into four units: the Rødberget, Trongen, Rørvika and Varpneset units. The Rødberget unit represents Baltoscandian basement, whereas the Trongen, Rørvika and Varpneset units are correlated with the Seve Nappe Complex based on the following lines of evidence: 1) lithological similarities to Seve Nappe Complex rocks in Central Norway and Sweden, 2) penetrative at least amphibolite-facies metamorphism, 3) U-Pb zircon dating of an intermediate layer within the central amphibolites yielding an age of 435.4±3.3 Ma, interpreted to be the result of decompressional melting of amphibolites related to exhumation of the Seve Nappe Complex, and 4) the presence and geochemistry of aplites, which have intruded both mica schists and amphibolites, resembling similar intrusive rocks in the Seve Nappe Complex, which were emplaced at about 430 Ma. In addition, through a detailed structural analysis of foliations, lineations, fold axes and fold vergences it can be shown that the central Rørvika unit is not lying within a synform, but rather represents a wedge-shape structure where the vergence of the smaller folds reflects the movement of the lithologies in the area. Two large-scale models are proposed for the ductile structural evolution of the entire area: 1) an obstacle and buckling model, and 2) a rotation model. Both models are related to the evolution of antiformal basement windows and the Møre-Trøndelag Fault Complex (MTFC). Stress inversion of brittle structures shows that the study area has been affected by a NW-SE extensional event, reactivating the MTFC in Late Paleozoic to Late Mesozoic/Early Cenozoic. These results imply that the area of interest has experienced a different structural evolution than earlier proposed, with a different and more complex metamorphic and structural history. This has implications for tectonostratigraphic correlations across Trondheimsfjorden
The Tectono‐Thermal Evolution of Western Norway – New Insights From Low‐Temperature Thermochronology
No full textAbstract The tectono‐thermal evolution of Western Norway's onshore rifted margin is debated. Previous studies suggest it does not exhibit a typical rifted margin cooling pattern. We present 29 new apatite fission track (AFT) ages and 54 new apatite single grain (U‐Th)/He ages from 14 samples, covering the onshore transition from the northern North Sea to the Norwegian Sea margin. AFT ages range from 323 ± 27 Ma to 140 ± 4 Ma, and (U‐Th)/He ages range from 228 ± 12 Ma to 57 ± 3 Ma. The samples show no clear age‐elevation correlation and large age offsets over short distances. Inverse thermal history modeling using HeFTy on 13 samples together with other geological constraints identifies four tectonic domains with distinct thermal and structural histories: (a) The inner Nordfjord subregion is dominated by N‐S striking faults, cooled to upper crustal levels (<8 km) in the Permian, remained stable until the Late Cretaceous, and experienced increased Cenozoic cooling. (b) The Sognefjord subregion cooled to upper crustal levels in the Carboniferous and offsets of AFT ages across fjords indicates Triassic/Jurassic reactivation of various faults. (c) The Hornelen subregion is dominated by prominent E‐W faults inherited from ductile precursors and shows the oldest AFT and (U‐Th)/He ages, reaching surface conditions already in the Jurassic with limited later reheating. (d) The Møre subregion shows rapid cooling in the Jurassic, likely due to footwall uplift accompanied by considerable topography. The new data set indicates a complex fragmentation of the onshore margin influenced by ductile precursor structures.Key Points A new apatite fission track and (U‐Th)/He data set from Western Norway shows no age‐elevation correlation and large horizontal age offsets The data set indicates a segmentation of the margin across ductile precursor structures inherited from the Caledonian orogeny Four subregions are identified with distinct thermal and structural historiesAbstract The tectono‐thermal evolution of Western Norway's onshore rifted margin is debated. Previous studies suggest it does not exhibit a typical rifted margin cooling pattern. We present 29 new apatite fission track (AFT) ages and 54 new apatite single grain (U‐Th)/He ages from 14 samples, covering the onshore transition from the northern North Sea to the Norwegian Sea margin. AFT ages range from 323 ± 27 Ma to 140 ± 4 Ma, and (U‐Th)/He ages range from 228 ± 12 Ma to 57 ± 3 Ma. The samples show no clear age‐elevation correlation and large age offsets over short distances. Inverse thermal history modeling using HeFTy on 13 samples together with other geological constraints identifies four tectonic domains with distinct thermal and structural histories: (a) The inner Nordfjord subregion is dominated by N‐S striking faults, cooled to upper crustal levels (<8 km) in the Permian, remained stable until the Late Cretaceous, and experienced increased Cenozoic cooling. (b) The Sognefjord subregion cooled to upper crustal levels in the Carboniferous and offsets of AFT ages across fjords indicates Triassic/Jurassic reactivation of various faults. (c) The Hornelen subregion is dominated by prominent E‐W faults inherited from ductile precursors and shows the oldest AFT and (U‐Th)/He ages, reaching surface conditions already in the Jurassic with limited later reheating. (d) The Møre subregion shows rapid cooling in the Jurassic, likely due to footwall uplift accompanied by considerable topography. The new data set indicates a complex fragmentation of the onshore margin influenced by ductile precursor structures.Key Points A new apatite fission track and (U‐Th)/He data set from Western Norway shows no age‐elevation correlation and large horizontal age offsets The data set indicates a segmentation of the margin across ductile precursor structures inherited from the Caledonian orogeny Four subregions are identified with distinct thermal and structural historiesEquinor https://doi.org/10.13039/10001681
Evolution of the Chugach Metamorphic Complex of Southern Alaska in space and time
No full textMetamorphe Komplexe werden weltweit durch verschiedenste Prozesse in verschiedenen tektonischen Umgebungen geformt. Um in einem bestimmten Fall eines metamorphen Komplexes zwischen den verschiedenen Prozessen zu unterscheiden, müssen die räumliche Geometrie und die zeitliche Entwicklung des Komplexes verstanden sein. Die vorliegende Arbeit enthält die Resultate einer interdisziplinären Studie welche sich mit der räumlichen und zeitlichen Entwicklung des Chugach Metamorphen Komplexes (CMC) befasst hat, mit dem Ziel, die Prozesse zu verstehen welche zur Bildung des Komplexes geführt haben. Der CMC ist ein ~10-50 km breiter und ~350 km langer metamorpher Komplex, makroskopisch bestehend aus zwei verschiedenen Zonen: einer inneren migmatitischen Gneis-Zone und einer äusseren Schiefer-Zone. Der Komplex bildete sich im Akkretionskeil des Chugach terranes, welches auf ~2200 km entlang des südlichen Kontinentalrandes von Alaska aufgeschlossen ist. Im ersten Kapitel wird die regionale Geologie des Untersuchungsgebietes zusammengefasst. Im zweiten Kapitel wird das maximale Ablagerungsalter der Sedimente in welchen sich der CMC bildete, durch LA-ICP-MS Datierung von detritären Zirkonen auf Paleozän-Späte Kreide bestimmt. Im dritten Kapitel wird getestet, ob die Minerale Granat, Monazit, Allanit und Xenotim für die Datierung des prograden Metamorphose-Pfades herangezogen werden können. Im vierten Kapitel wird der Metamorphose-Höhepunkt mit Hilfe von U-Pb SHRIMP Datierung von metamorphen Zirkonen auf ~55-52 Ma datiert. Im fünften Kapitel wird die strukturelle Geometrie des Komplexes entlang dreier Profile durch den Komplex beschrieben, und die Abkühlgeschichte verschiedener Bereiche des Komplexes wird durch 40Ar/39Ar Datierung von Muskovit und Biotit, Rb/Sr Isochronen-Datierung und Zirkon Spaltspuren-Datierung bestimmt. Schliesslich wird eine mögliche tektonische Entwicklung des Komplexes präsentiert und mit bestehenden Modellen verglichen.Metamorphic complexes form by various different processes in many different tectonic settings all over the world. In order to distinguish in one particular case between different processes which formed the complex, an understanding of the spatial geometry and the temporal evolution of the complex is needed. This thesis contains the results of an interdisciplinary study conducted on the Chugach Metamorphic Complex (CMC) of southern Alaska, which aimed at constraining the evolution of the complex in space and time, in order to distinguish between different processes which formed the complex. The CMC is a ~10-50 km wide and ~350 km long upper amphibolite facies metamorphic complex, which consists of two macroscopically different zones: an inner migmatitic gneiss zone and an outer schist zone. The complex developed in the Late Cretaceous accretionary prism of the Chugach terrane, which is exposed along the southern Alaskan margin on ~2200 km along strike.In the first chapter, the regional geology of the study area is reviewed and summarized. In the second chapter, the maximum depositional age of the sediments is constrained by LA-ICP-MS dating of detrital zircons to Paleocene-Late Cretaceous. In the third chapter, the applicability of garnet, monazite, allanite and xenotime as prograde geochronometers is tested. In the fourth chapter, the timing of peak metamorphism is constrained by U-Pb SHRIMP dating of metamorphic zircon rims to ~55-52 Ma. In the fifth chapter, the structural geometry of the complex along three composite transects is described, and the cooling history of the complex based on 40Ar/39Ar dating of biotite and muscovite, Rb/Sr isochron dating and zircon fission track dating is revealed. Finally, a possible tectonic evolution of the complex is presented and is compared to previous models.Deta GasserZsfassung in dt. SpracheGraz, Univ., Diss., 201
Evolution of the Chugach Metamorphic Complex of Southern Alaska in space and time
No full textMetamorphe Komplexe werden weltweit durch verschiedenste Prozesse in verschiedenen tektonischen Umgebungen geformt. Um in einem bestimmten Fall eines metamorphen Komplexes zwischen den verschiedenen Prozessen zu unterscheiden, müssen die räumliche Geometrie und die zeitliche Entwicklung des Komplexes verstanden sein. Die vorliegende Arbeit enthält die Resultate einer interdisziplinären Studie welche sich mit der räumlichen und zeitlichen Entwicklung des Chugach Metamorphen Komplexes (CMC) befasst hat, mit dem Ziel, die Prozesse zu verstehen welche zur Bildung des Komplexes geführt haben. Der CMC ist ein ~10-50 km breiter und ~350 km langer metamorpher Komplex, makroskopisch bestehend aus zwei verschiedenen Zonen: einer inneren migmatitischen Gneis-Zone und einer äusseren Schiefer-Zone. Der Komplex bildete sich im Akkretionskeil des Chugach terranes, welches auf ~2200 km entlang des südlichen Kontinentalrandes von Alaska aufgeschlossen ist. Im ersten Kapitel wird die regionale Geologie des Untersuchungsgebietes zusammengefasst. Im zweiten Kapitel wird das maximale Ablagerungsalter der Sedimente in welchen sich der CMC bildete, durch LA-ICP-MS Datierung von detritären Zirkonen auf Paleozän-Späte Kreide bestimmt. Im dritten Kapitel wird getestet, ob die Minerale Granat, Monazit, Allanit und Xenotim für die Datierung des prograden Metamorphose-Pfades herangezogen werden können. Im vierten Kapitel wird der Metamorphose-Höhepunkt mit Hilfe von U-Pb SHRIMP Datierung von metamorphen Zirkonen auf ~55-52 Ma datiert. Im fünften Kapitel wird die strukturelle Geometrie des Komplexes entlang dreier Profile durch den Komplex beschrieben, und die Abkühlgeschichte verschiedener Bereiche des Komplexes wird durch 40Ar/39Ar Datierung von Muskovit und Biotit, Rb/Sr Isochronen-Datierung und Zirkon Spaltspuren-Datierung bestimmt. Schliesslich wird eine mögliche tektonische Entwicklung des Komplexes präsentiert und mit bestehenden Modellen verglichen.Metamorphic complexes form by various different processes in many different tectonic settings all over the world. In order to distinguish in one particular case between different processes which formed the complex, an understanding of the spatial geometry and the temporal evolution of the complex is needed. This thesis contains the results of an interdisciplinary study conducted on the Chugach Metamorphic Complex (CMC) of southern Alaska, which aimed at constraining the evolution of the complex in space and time, in order to distinguish between different processes which formed the complex. The CMC is a ~10-50 km wide and ~350 km long upper amphibolite facies metamorphic complex, which consists of two macroscopically different zones: an inner migmatitic gneiss zone and an outer schist zone. The complex developed in the Late Cretaceous accretionary prism of the Chugach terrane, which is exposed along the southern Alaskan margin on ~2200 km along strike.In the first chapter, the regional geology of the study area is reviewed and summarized. In the second chapter, the maximum depositional age of the sediments is constrained by LA-ICP-MS dating of detrital zircons to Paleocene-Late Cretaceous. In the third chapter, the applicability of garnet, monazite, allanite and xenotime as prograde geochronometers is tested. In the fourth chapter, the timing of peak metamorphism is constrained by U-Pb SHRIMP dating of metamorphic zircon rims to ~55-52 Ma. In the fifth chapter, the structural geometry of the complex along three composite transects is described, and the cooling history of the complex based on 40Ar/39Ar dating of biotite and muscovite, Rb/Sr isochron dating and zircon fission track dating is revealed. Finally, a possible tectonic evolution of the complex is presented and is compared to previous models.Deta GasserZsfassung in dt. SpracheGraz, Univ., Diss., 201
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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