27 research outputs found
The Quenast plug: a mega-porphyroclast during the Brabantian orogeny (Senne valley, Brabant massif)
No full textIn the fine-grained Ordovician siliciclastic deposit surrounding the Quenast plug, a variety of structural features demonstrate that the Quenast plug was emplaced prior to the Brabantian deformation event. These features include: a) a large-scale bending of the cleavage, mimicking the shape of the plug; b) a concomitant change in the orientation of the transverse fractures; c) a marked variation in cleavage intensity around the plug, with a high-strain zone along the NE-side of the plug and a low-strain zone along the NW-side of the plug; d) contractional and dilational kink bands. In combination with the ellipsoidal cross-section of the plug, these features indicate that the Quenast plug can be regarded as having acted as a mega-porphyroclast during the Brabantian deformation event. The different structural features are discussed and related to the geometry and deformation of the Quenast plug. Also the temporal and spatial relationships of the Quenast plug with respect to the Asquempont Detachment System and the Nieuwpoort-Asquempont Fault Zone are discussed. Finally, a preliminary attempt is made at estimating the shortening across the plug. Future work, concentrating on the magnetic fabric within the plug, will shed further light on the behaviour of the plug during the Brabantian deformation event.sponsorship: We kindly acknowledge L. Andre and J. Belliere for thoroughly reviewing the manuscript. We would like to express our gratitude to A. Vergari and M. Lauwers (Gralex), for the permission to access the quarry, their hospitality and enthousiasm. We Would also like to thank A. Herbosch for the helpful field discussions concerning the lithostratigraphical position of the Middle and Upper Ordovician units encountered. T.N. Debacker is a Postdoctoral Fellow of the Fund for Scientific Research-Flanders (F.W.O.-Vlaanderen) and M. Sintubin is a Research Associate of the "Onderzoeksfonds, K.U.Leuven". This work fits into the research projects G.0274.99, G.0094.01 and G.0271.05 of the F.W.O.-Vlaanderen. (F.W.O.-Vlaanderen|G.0274.99, F.W.O.-Vlaanderen|G.0094.01, F.W.O.-Vlaanderen|G.0271.05)status: Publishe
On the use of magnetic techniques for stratigraphic purposes: examples from the Lower Palaeozoic Anglo-Brabant Deformation Belt (Belgium)
No full textWithin the Lower Palaeozoic Anglo-Brabant Deformation Belt, magnetic susceptibility on its own does not allow for a straightforward distinction between different lithostratigraphic units, except for the high-susceptibility levels of the Lower Cambrian Tubize Formation. Moreover, the variation in magnetic susceptibility within individual lithostratigraphic units is often larger than that between different units, but at the same time, this internal variation in susceptibility may show no clear relationship to features obvious in outcrop or hand specimens. Hence, the applicability of magnetic susceptibility for stratigraphic purposes in the Anglo-Brabant Deformation Belt is low. Better results are obtained using the temperature-dependent variation in terms of percentage of magnetic susceptibility within the "room temperature interval". Also the anisotropy of magnetic susceptibility allows for a better distinction between different lithostratigraphic units than does magnetic susceptibility. The best results are obtained by a comparison of thermal demagnetisation curves of magnetic remanence, used for determining ferromagnetic mineralogy. This method even allows distinguishing lithostratigraphic units in which ferromagnetic carriers do not contribute to overall magnetic susceptibility and its anisotropy. Ideally, each magnetic technique should be used for stratigraphic purposes only in combination with other magnetic techniques. Moreover, knowledge about the magnetic carriers (s.l.) facilitates this use of magnetic techniques and strongly improves the accuracy of the interpretations.sponsorship: We would like to thank F. Martin-Hernandez and O. Averbush for thoroughly reviewing the manuscript. We are very grateful to A. Flirt (ETH, Zurich, Switzerland) for the additional magnetic analyses by means of the Curie Balance and to C. Aubourg for the stimulating discussions on ferromagnetic mineralogy. We would also like to acknowledge A. Herbosch for pointing out the unexpected lithology at Braine-le-Chateau. T.N. Debacker is a Postdoctoral Fellow of the Research Foundation-Flanders (F.W.O.-Vlaanderen). This work forms part of research project G.0271.05 of the F.W.O.-Vlaanderen. The handheld magnetic susceptibility meter was obtained by means of extra research funds given by the F.W.O.-Vlaanderen to T. Debacker. (F.W.O.-Vlaanderen|G.0271.05)status: Publishe
Contractional kink bands formed by stress deflection along pre-existing anisotropies? Examples from the Anglo-Brabant Deformation Belt (Belgium) and the North Dobrogea Orogen (Romania)
No full textKink bands within two slate belts, the Anglo-Brabant Deformation Belt (Belgium) and the North Dobrogea Orogen (Romania), reveal similar problems with respect to linking kink band geometries to expected palaeostress directions. In the North Dobrogea Orogen, the two opposite kink band sets of two different systems of conjugate kink bands develop for a wide variety of cleavage orientations. In the Anglo-Brabant Deformation Belt, the occurrence of the two opposite kink band sets of a conjugate kink band system opposes the expected occurrence. In both cases, this can be attributed to stress deflection along a pre-existing anisotropy. Moreover, the presence of kink bands in the North Dobrogea Orogen with curving kink axes (and curving kink band boundaries) also puts doubt on the direct relationship between kink band geometry and stress. The idea of stress deflection along a pre-existing anisotropy and the strong control of the pre-existing anisotropy on the kink band geometry and orientation has important implications for the use of kink bands as regional palaeostress indicators. Depending on the relative intensity and relative orientation of the pre-existing fabrics (here bedding and cleavage), different mechanisms of kink band development may operate. Depending on the mechanism, different solutions in terms of inferred palaeostress direction may exist. © 2008 Elsevier Ltd. All rights reserved.sponsorship: The authors wish to acknowledge B. Goscombe, D. Srivastava and T. Blenkinsop for their constructive remarks on the manuscript, and are grateful to G. Oaie and M. Vaida for the support during the fieldwork in North Dobrogea (Romania). T.N. Debacker is a Post-doctoral Fellow of the Fund for Scientific Research-Flanders (F.W.O.-Vlaanderen) and M. Sintubin a Research Associate of the "Onderzoeksfonds, K.U.Leuven". This work, resulting from fieldwork when T. Debacker was at the Katholieke Universiteit Leuven (2002-2005), forms part of research projects G.0274.99, G.0094.01 and C.0271.05 of the F.W.O.-Vlaanderen. The research in Romania benefited from the International scientific and technological cooperation program from the Science, Innovation and Media Department of the Ministry of the Flemish Community (BIL01/34). (Science, Innovation and Media Department of the Ministry of the Flemish Community|BIL01/34)status: Publishe
Transitional geometries between gently plunging and steeply plunging folds: an example from the Lower Palaeozoic Brabant Massif, Anglo-Brabant deformation belt, Belgium
No full textThe anisotropy of magnetic susceptibility (AMS) in low-grade cleaved mudstone: the common influence of composite magnetic fabrics
No full textCleavage/fold relationships in the Silurian metapelites, southeastern Anglo-Brabant fold belt (Ronquieres, Belgium)
No full textThe presence of convergent cleavage fans in folded Silurian pelitic deposits along the southern extremity of the Brabant Massif has commonly been considered as an indication for a polyphase deformation history. Recent field work on the classic section at Ronquières shows, however, that all the structural elements can be explained by a single progressive deformation, taking place at gradually higher structural levels. This deformation is considered to have occurred at the time of the Acadian orogeny. The section under study contains a fold train of five gentle to open first-order folds, unconformably overlain by gently S-dipping Givetian rocks. Although the Silurian turbidite deposits are predominantly pelitic, the folds are characterized by convergent cleavage fans. The trend of the cleavage fan axes remains constant in the various folds throughout the section. In contrast, the trend of the fold hinge lines gradually changes along the section from a clockwise relation with the cleavage fan axis in the northern part (anticlockwise cleavage transection) towards an anticlockwise relation in the southern part (clockwise cleavage transection). Individual fault/fault intersections have a constant trend throughout the section, parallel to the cleavage fan axes and the mean fold hinge line. Small kink bands and small transverse joints reflect the same structural trend. The coaxial disposition of the structural elements seems at first sight incompatible with the presence of both clockwise and anticlockwise cleavage-transected folds. This disposition may, however, be explained by an en-echelon periclinal nature of the fold train, possibly formed in a slightly constrictional deformation environment.status: Publishe
How do current policies support a transition towards a circular economy in the built environment?
No full textBuilding and construction industry consumes huge quantities of materials in an unsustainable way. As a result of a linear design approach and economic model, at the end of use, but also throughout the cycle, buildings or parts of buildings are demolished and remnants treated as waste or –best case– down-cycled. This creation of waste as well as the use of virgin resources leads to an important environmental, economic and societal impact. To create a sustainable build environment, the building sector needs to move towards a circular economy in which circular and dynamic buildings as well as their component and materials preserve value. Policies and regulations in member states and across the EU will influence the ability to transition to a circular economy – positively and negatively. Within the H2020 Buildings As Materials Banks (BAMB) Project work is underway to understand where the opportunities and barriers lie in a complex and, sometimes contradictory, regulatory landscape. This paper presents an overview of the current policy instruments that are considered to have relevance in relation to promoting, or possibly hindering, the adoption of circular economy opportunities in the built environment. The analysis of the current policy instruments has been done on a European level and on a member state level for 4 different countries being: Belgium, Portugal, Sweden and UK. The paper will mainly focus on the European Level and Belgium
Spectral properties in a class of operators and group representations in nested Hilbert spaces
No full textThe author characterizes the spectrum of the elements of some operator algebras acting in a nested Hilbert space. In one of those algebras he proves the spectral theorem for Hermitian operators and the SNAG theorem for unitary representations of locally compact Abelian groups. Then extends the SNAG theorem to representations in three more general classes of operators.Anglai
Large-scale slumping deduced from structural and sedimentary features in the Lower Palaeozoic Anglo-Brabant fold belt, Belgium
No full textDistinguishing slump folds from tectonic folds in poorly exposed areas can be difficult, especially when the scale of the slump folds exceeds outcrop scale. In the southeastern part of the single-phase deformed, Lower Palaeozoic Anglo-Brabant fold belt a comparison of cleavage/fold relationships and stratigraphic polarity shows that a 200 m thick interval of middle Caradoc fine-grained turbidites in the core of a large synform was overturned prior to tectonic deformation. This overturning is attributed to large-scale slumping, which was most likely a result of middle Caradoc seismic activity.
The exposed portion of the large slump sheet contains only a few small slump folds and intraformational breccias, making up less than 5% of the exposed thickness. If the beds were not overturned, large-scale slumping would never be suspected and the small slump folds would probably be interpreted as localized features in an overall ‘stable’ sedimentary pile. This may explain why so few ancient large-scale slides and slumps have been reported: the small amount of internal deformation makes them very difficult to recognize, especially when dealing with poorly exposed areas. As such, large ancient slides and slumps may be more common than suggested by the geological literature.</jats:p
Transitional geometries between gently plunging and steeply plunging folds: an example from the Lower Palaeozoic Brabant Massif, Anglo-Brabant deformation belt, Belgium
No full textAlthough many studies have dealt with markedly different fold orientations and associated cleavage–fold relationships within
individual, single-phase deformed fold belts, there are very few descriptions of possible gradual, transitional fold geometries.
The Lower Cambrian steep core of the single-phase deformed Brabant Massif contains steeply plunging, west-facing folds with
a Z-shaped asymmetry, whereas the Ordovician–Silurian southern rim consists of gently plunging, upward facing folds. A gradual
transition is observed between these end-member orientations, in a NW–SE-trending zone 1–1.5 km wide, in which the folds appear
to be strongly curvilinear and locally downward facing. The structural geometries within this transition zone are described
in detail and the geometric changes analysed in the light of the fold transition. The strongly variable fold orientations
are tentatively attributed to a bulk oblate tectonic strain. The transition zone overlies an aeromagnetic lineament, classically
interpreted as a dextral shear zone. The steeply plunging folds, the transition zone and the aeromagnetic lineaments are all
attributed to a local dextral transpression, in which deformation is partitioned both vertically and laterally. The results
indicate that within zones of heterogeneous transpression, the different deformation domains are not necessarily always fault
bounded.
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