1,720,984 research outputs found
The role of strike-slip tectonics in the Leinetal Graben, Lower Saxony
No full textA detailed examination and interpretation of outcrop data in the northern part of the Leinetal Graben in Lower Saxony, Germany, suggests the graben is dissected and partly-bound by faults with a strong strike-slip history. We envisage a two-part tectonic evolution, which began in the Late Cretaceous to Early Cenozoic, with approximately N-S compression, which caused east-west extension (the bounding normal faults of the Leinetal Graben) and dextral strike-slip movement on the Ahlsburg Lineament. We postulate that the Ahlsburg Lineament was originally a relay ramp that developed in the early stages of the graben history. Later the major stress axes rotated anticlockwise, so that the maximum horizontal stress was oriented NW-SE. Because of this, the graben-bounding faults and the Ahlsburg Lineament were then subject to inversion under sinistral transpression, while new E-W striking dextral strike-slip faults were also initiated
Structure and kinematics of an outcrop-scale fold-cored triangle zone
No full textTriangle zones are widespread structural elements that link fold and thrust belts with their foreland basins. We present a structural analysis of an outcrop-scale (similar to 6 m [20 ft] wide) triangle zone that is exposed in the siliciclastic Carboniferous strata of the Harz Mountains in northern Germany. The geometry of the triangle zone is critically compared with larger outcrop and seismic-scale structures. The external form of the triangle zone is the same as that proposed for larger examples, with two bounding detachments that dip in opposing directions. However, the interior of the triangle zone is characterized by tight to isoclinal folds. We demonstrate how the triangle zone probably evolved from a fault-bend fold, which accreted further folds behind it. This is an alternative fold-based interpretation for a structure that is commonly modeled as a duplex stack. We present the resulting consequences for seismic interpretation and hydrocarbon reservoir evaluation
Mode of emplacement of the Slaufrudalur Pluton, Southeast Iceland inferred from three-dimensional GPS mapping and model building
No full textThe Slaufrudalur Pluton is a granitic pluton in the Tertiary lava pile of Southeast Iceland. Excellent exposures of its roof and walls made it possible to map the shape of the pluton with high-resolution GPS. Based on the GPS mapping and field observations, we reconstructed the three-dimensional shape of the Slaufrudalur Pluton with the aim to test which implications on the mechanisms of emplacement can be derived from this approach. The reconstructed pluton shape is characterised by steep walls and a flat roof at map-scale. This shape and the internal compositional layering indicate that the pluton was probably emplaced by cauldron subsidence along subvertical faults that are parallel with the strike of the regional fissure swarms. At the roof contact, the pluton exploited the original layering of the flood basalts. At outcrop-scale, however, the roof was modified by magmatic stoping, which resulted in a step-like pattern on a scale that cannot be resolved in the three-dimensional model. Hence, the reconstruction of the three-dimensional shape of the Slaufrudalur Pluton, combined with structural field studies, provided valuable information about the mechanism of its emplacement on pluton-scale. For a comprehensive understanding of all mechanisms involved in the emplacement of the Slaufrudalur Pluton, detailed structural field studies remain essential. (c) 2009 Elsevier B.V. All rights reserved
Multi-stage emplacement of the Götemar Pluton, SE Sweden: new evidence inferred from field observations and microfabric analysis, including cathodoluminescence microscopy
Full text linkThe emplacement of the Mesoproterozoic Götemar Pluton into Paleoproterozoic granitoid host rocks of the Transscandinavian Igneous Belt is re-examined by microfabric analysis, including cathodoluminescence microscopy. Field data on the pluton-host rock system are used to strengthen the model. The Götemar Pluton, situated on the Baltic Shield of SE Sweden, is a horizontally zoned tabular structure that was constructed by the intrusion of successive pulses of magma with different crystal/melt ratios, at an estimated crustal depth of 4–8 km. Initial pluton formation involved magma ascent along a vertical dike, which was arrested at a mechanical discontinuity within the granitoid host rocks; this led to the formation of an initial sill. Subsequent sill stacking and their constant inflation resulted in deformation and reheating of existing magma bodies, which also raised the pluton roof. This multi-stage emplacement scenario is indicated by complex dike relationships and the occurrence of several generations of quartz (Si-metasomatism). The sills were charged by different domains of a heterogeneous magma chamber with varying crystal/melt ratios. Ascent or emplacement of magma with a high crystal/melt ratio is indicated by syn-magmatic deformation of phenocrysts. Complex crystallization fabrics (e.g. oscillatory growth zoning caused by high crystal defect density, overgrowth and replacement features, resorbed and corroded crystal cores, rapakivi structure) are mostly related to processes within the main chamber, that is repeated magma mixing or water influx
Detailuntersuchungen zur Tektonik am ostlichen Rand der Leinetalgrabenstruktur bei Bovenden, Sudniedersachsen
No full textIm Leinetalgraben in Sudniedersachsen wurden im Bereich des ostlichen, N-S streichenden GrabenrandstOnmgssystems stratigraphische und strukturelle Detailaufuahmen im Keuper durchgefiihrt. Das generelle Einfallen der Keuperschichten mit ca. 25° gegen die GrabenrandstOrung weist auf ein listrisches StOrungssystem hin. Neben einer nachweisbaren NW-SE streichenden StOrung, muss aus den Schichtmachtigkeitsverhaltnissen auf weitere grabenrandparallele Abschiebungen geschlossen werden. Diese Ergebnisse gehen in die Planung und spatere Interpretation eines seismsichen Profils in diesem Bereich ein
From feeder dykes to scoria cones: the tectonically controlled plumbing system of the Rauðhólar volcanic chain, Northern Volcanic Zone, Iceland
No full textThe Rauoholar volcanic chain, located in the Northern Volcanic Zone of Iceland, has been variably eroded such that, in the northern part, the original scoria cones are preserved, while the central and southern parts expose their shallow feeders. The chain thus offers insight into the inner workings of the near-surface feeder system of scoria cones. The volcanic chain was mapped in 3D using GPS. The en echelon-arranged volcanic chain can be divided into three parts: The southernmost part contains only plugs and necks with a thin pyroclastic cover as well as multi-tiered lava flows. The central part combines partially eroded scoria cones, (feeder) dyke intersections, and welded scoria interbedded within rootless and clastogenic lava flows; the welded scoria is composed of different kinds of lithics and bombs. The northern part preserves almost intact, overlapping scoria cones with voluminous lapilli- sized scoriaceous deposits. The overall dyke trend is orthogonal but shows radial patterns in individual cone complexes. Feeder dykes observed to depths of about 200 m below the volcanic chain are up to 8 m thick and flare in to conduits in the uppermost 20-50 m. The exposed shallow plumbing system shows that magma pathways through the volcanic edifice are very complex with incremental, repeated intrusions. We interpret the arcuate shape to be the result of a local change in the orientation of the stress field because the Rauoholar volcanic chain is located within a major relay structure between volcanoes on the eastern Fremrinamur rift arm and a rift extension with grabens on the western periphery
Weibull-distributed dyke thickness reflects probabilistic character of host-rock strength
Full text linkMagmatic sheet intrusions (dykes) constitute the main form of magma transport in the Earth’s crust. The size distribution of dykes is a crucial parameter that controls volcanic surface deformation and eruption rates and is required to realistically model volcano deformation for eruption forecasting. Here we present statistical analyses of 3,676 dyke thickness measurements from different tectonic settings and show that dyke thickness consistently follows the Weibull distribution. Known from materials science, power law-distributed flaws in brittle materials lead to Weibull-distributed failure stress. We therefore propose a dynamic model in which dyke thickness is determined by variable magma pressure that exploits differently sized host-rock weaknesses. The observed dyke thickness distributions are thus site-specific because rock strength, rather than magma viscosity and composition, exerts the dominant control on dyke emplacement. Fundamentally, the strength of geomaterials is scale-dependent and should be approximated by a probability distribution
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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