62 research outputs found
Linear to non-linear relationship between vein spacing and layer thickness in centimetre- to decimetre-scale siliciclastic multilayers from the High-Ardenne slate belt (Belgium, Germany)
No full textTypical spacing distributions have frequently been described for fractures in thin sedimentary layers ( 40 cm). Vein spacing tends to increase to a maximum value becoming more or less independent of layer thickness. The resemblance with fracture spacing suggests that in an unfractured rock vein saturation can occur. High-fluid pressures are responsible for vein nucleation but the stress state around the initial veins controls the spacing pattern. Subsequently, in a vein-saturated rock, or the existing veins will thicken by the process of crack-sealing, or a new cross-cutting vein generation will develop in case the regional stress field changes relatively with respect to the existing veins.sponsorship: The authors would like to acknowledge reviewers Julia Gale and Paul Gillespie for their helpful and incisive comments and Robert Holdsworth for editing the manuscript. We thank Herve Van Baelen and Carl Jacquemyn for the constructive discussions and Philippe Muchez for his contribution on fluid inclusions. Thorough reading of Richard Walker greatly improved the quality of the early manuscript. Koen Van Noten is a Research Assistant and Manuel Sintubin is a Research Professor of the 'Bijzonder Onderzoeksfonds' at the K.U.Leuven. This article frames in the research project KAN 1.5.128.05 of the Fonds voor Wetenschappelijk Onderzoek Vlaanderen. (Fonds voor Wetenschappelijk Onderzoek Vlaanderen|1.5.128.05)status: Publishe
Beeldspel: Ruimtelijk inzicht en beelddenken: Hints, noten, referenties, bronverwijzingen
No full textHints, noten, referenties, bronverwijzingen behoren bij de tekst en opgaven in het andere deel van Beeldspel.Delft University of Technolog
Periodized versus classic exercise therapy in Multiple Sclerosis: a randomized controlled trial
No full textBackground: Periodizing exercise interventions in Multiple Sclerosis (MS) shows good high intensity exercise training adherence. Whether this approach induces comparable training adaptations with respect to exercise capacity, body composition and muscle strength compared to conventional, linear progressive training programs however is not known. Methods: Thirty-one persons with MS (all phenotypes, mean EDSS 2.3?1.3) were randomized into a twelve-week periodized (MSPER, n=17) or a classic endurance (MSCLA, n=14) training program. At baseline (PRE), exercise capacity (maximal exercise test, VO2max), body composition (DEXA) and muscle strength (Biodex?) were assessed. Classic, moderate intensity endurance training (60-80% HRmax, 5 training sessions/2w, 60min/session) was performed on a stationary bicycle. Periodized exercise included 4 recurrent 3-week cycles of alternated endurance training (week 1: endurance training as described above), high intense exercise (week 2: 3 sessions/w, 3 ? 20s all-out sprints, 10min/session) and recovery weeks (week 3: one sprint session as described above). POST measurements were performed similar to baseline. Total exercise volume of both programs was expressed as total peak-effort training minutes. Results: For MSCLA, total exercise volume included 1728 total peak-effort training minutes, whereas MSPER included only 736. Despite this substantially reduced training volume, twelve weeks of periodized training significantly (p<0.05) improved VO2max (+14%, p=0.001), workload (+20%) and time until exhaustion (+25%). Classic training significantly (p<0.05) improved workload (+10%) and time until exhaustion (+17%), but not VO2max (+5%, p=0.131). Pre-post improvements for VO2max were significantly higher in MSPER compared to MSCLA (p=0.046). Conclusion: These data show that despite substantially lower training time (57% less peak-effort training minutes), 12 weeks of periodized exercise training in persons with MS seems to induce larger improvements in parameters of exercise capacity compared to classic endurance training. We therefore recommend to further investigate the effect of training periodization on various functional rehabilitation measures in MS.Keytsman, C (corresponding author), Hasselt Univ, REVAL Rehabil Ctr, Biomed Res Inst BIOMED, Agoralaan Bldg A, B-3590 Diepenbeek, Belgium.
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Spanningsevolutie van de brosse bovenkorst tijdens de vroeg-variscische tektonische inversie zoals gedefinieerd door opeenvolgende kwartsadertypes in de Hoge-Ardennenleisteengordel, Duitsland.
No full textIn the recent decade, there is an increased interest in the processes active at the base of the seismogenic crust, with a particular focus on the evolution and characterisation of elevated fluid pressures that could possibly drive fault rupturing and initiate major earthquakes. The base of the seismogenic zone, however, is not directly accessible. One of the possibilities to overcome this research problem is the study of natural fossil analogues to pursue a better understanding of the formation and evolution of these overpressured fluids at relatively great depths. Within the broad framework of natural analogues, vein studies provide an important insight in the characterisation of fluids and the role of fluid pressure during a complete deformation cycle. In vein analysis, an extensive interdisciplinary approach is required in order to determine a fluid-assisted deformation during orogeny. This research project focuses on overpressured fluids that are generated in a sedimentary basin during late burial that is affected by an incipient tectonic shortening at the onset of orogeny. Quartz veins that result from the overpressures in sedimentary basins preserve valuable information on the metamorphic fluids which were present during burial and subsequent orogenic deformation. A detailed geometric and kinematic structural analysis of several successive quartz vein types has been performed to allow constraining a geometric evolutionary model of the emplacement of these different, successive veins with respect to structural features such as bedding, cleavage, folds and faults. This model is refined by means of a pervasive microstructural and microthermometric analysis of the vein infill in order to implement physico-chemical parameters such as formation temperature and pore-fluid pressure. Ultimately, this study aims at understanding why, how and when fluids become overpressured and how they subsequently evolve at the onset of orogeny. More specifically, the study focuses on Lower Devonian multilayer siliciclastic metasediments that were deposited in the Ardenne-Eifel basin. This basin formed part of the northern passive margin of the short-lived Rhenohercynian Ocean which was closed during the Variscan orogeny. These metasediments are currently exposed in the High-Ardenne slate belt (Belgium, France, Luxemburg & Germany), which belongs to the central part of the Rhenohercynian foreland fold-and-thrust belt in the northern extremity of the Central European Variscan belt. The rocks, in which quartz veins frequently occur, are studied in the north-eastern part of the High-Ardenne slate belt (Rursee, Urftsee; North Eifel; Germany) and are affected by a very low-grade metamorphism, which is considered to have a burial origin, pre- to early synkinematic with the prograding Variscan deformation. This metamorphism documents the peak of subsidence and sediment accumulation (at about 7 km) prior to the main Variscan contraction of the basin. The analysis focuses on two successive quartz vein types, oriented normal and parallel to bedding respectively, in which the very low-grade metamorphism is reflected. A first vein type consists of several generations of bedding-normal veins that remain perpendicular to bedding around the characteristic, NW-verging, upright to overturned folds of the North Eifel, thereby clearly predating the main Variscan contraction and fold-and-cleavage development of the slate belt. The planar to lensoid veins are mostly restricted to competent sandstone layers, although they sometimes continue into the adjacent incompetent layers, refracting at the competent-incompetent interface, similar to cleavage. The fabric of the bedding-normal veins predominantly shows a fibrous to elongate-blocky vein infill in which the fibres or the elongated crystals are oriented at high angle to the vein walls. Both syntaxial and ataxial growth morphologies are recognised. Repetition of host-rock inclusion bands internally in the vein quartz reflects episodic opening of the vein by the crack-seal mechanism. Pseudosecondary fluid-inclusion planes, oriented at high angle to the crystal fibre walls and reflecting intracrystal healed microcracks, confirm that crystal growth occurred by incremental crack-seal steps. The specific orientation of fluid-inclusion planes and host-rock inclusion bands indicate that the veins are extension veins which originally grew in Mode I fractures in a rock that was already significantly reduced in porosity during burial. The fluid-inclusion planes have been particularly useful as a microstructural marker to reconstruct the stress state in the basin at the time of vein formation. In this respect, the maximum principal stress (sigma 1) was still vertical, corresponding with load of the overburden (sigma V) and the veins opened perpendicular to the least principal stress (sigma 3), that roughly indicate the extension direction in the basin. The propagation of fractures during vein formation occured in the sigma1 - sigma2 plane. Secondary inclusion planes, corresponding to post-veining transcrystal microcracks oriented parallel to the vein walls, evidence that microcracks still developed after opening of the extension veins but still in a similar stress regime as the pseudosecondary inclusion planes. The consistent pre-folding orientation of bedding-normal veins in the North Eifel corresponds to the pre-folding orientation of intermullion quartz veins in the central part of the High-Ardenne slate belt (Ardennes, Belgium) highlighting that this veining event occurred regionally. The (micro)structural analysis of bedding-normal veins eventually shows that these veins developed at low differential stress during the lateststage of the extensional stress regime and reflect a regional NW-SE opening of the Ardenne-Eifel basin. A structural change of the pre-folding vein orientation from NW-SE (Ardennes) to NNW-SSE (Eifel) is probably related to a post-veining oroclinal bending of the slate belt during the main Variscan contraction due to the presence of the rigid Brabant basement in the north. Apart from the orientation analysis, the spatial distribution of these bedding-normal quartz veins in the High-Ardenne slate belt is investigated in order to determine the effect of the layer thickness to vein spacing. The results show a quasi linear relationship between vein spacing and layer thickness in thin (<40 cm) competent sandstone layers and a non-linear relationship in thicker sandstone layers (>40 cm). Vein spacing tends to increase to a maximum value becoming more or less independent of layer thickness. The resemblance of vein spacing with regularly spaced fractures that result from saturation during fracture development, suggests that in an unfractured rock, the host rock can get saturated by the presence of initial veins in which the veins subsequently either grow by progressive extension or that new cross-cutting veins develop in case the regional stress field changes relatively with respect to the existing veins. In the North Eifel, bedding-parallel quartz veins cross-cut, truncate and offset the bedding-normal veins and are continuously present around fold hinges. Bedding-parallel veins occur interbedded between two contrasting lithologies, as well as intrabedded in the competent and incompetent sequences. Macroscopically, the veins show a composite internal fabric consisting of several distinct generations of quartz laminae, often marked by slickenlines, intercalated with thin pelitic wall-rock inclusion seams. Microscopically, the variety in microstructures is indicative of different combined mechanisms of vein growth and mineral infill, reflecting a complex vein formation. Repeated crack-seal inclusion bands that are oriented parallel to the vein wall, and thus parallel to bedding, reflect bedding-normal opening of crack-seal quartz laminae. This mechanism also is also evidenced by the alignment of pseudosecondary fluid-inclusion planes internally in the fibres. The presence of blocky laminae reflects crystal growth in an open cavity during bedding-normal uplift. Bedding-parallel stylolites in often occur in these blocky laminae and represent pressure-dissolution during bedding-normal collapse. The occurrence of shear laminae, in which small quartz crystals are dynamically recrystallised during the main phase of the Variscan contraction, has, on the other hand, been used as indicator of bedding-parallel shear events. The pronounced bedding-parallel fabric is interpreted to form during several alternating phases of bedding-normal uplift and bedding-parallel shearing taking place at the onset of folding. Based on the microstructural analysis, the bedding-parallel veins are classified as extension veins to extensional-shear veins that formed at low differential stress. This vein type is the brittle expression of the first phases of the compressional stress regime affecting the siliciclastic metasediments of the Ardenne-Eifel basin at the onset of Variscan shortening. In this configuration, the bedding-parallel veins demonstrate a particular stress-state in the basin at the time of vein formation in which the maximum principal stress (sigma1) was oriented parallel to a NW-SE-oriented tectonic compression (sigmaT) and the minimum principal stress (sigma3) corresponded to the vertical load of the overburden. The succession of bedding-normal to bedding-parallel extension quartz veins thus materialises the transition from extension to compression at the onset of Variscan orogeny and is interpreted to have formed during early orogenic compressional tectonic inversion. A petrographic and micro-thermometric analysis of fluid inclusions within the vein quartz has further helped to constrain the kinematic and pressure-temperature trapping conditions of both vein types, allowing the reconstruction of the fluid pressure and stress-state evolution during tectonic inversion. The method used for defining the trapping conditions involves cross-cutting isochores, calculated from the salinity and homogenisation temperatures representative of both vein types, with an independent vitrinite reflectance geothermometer that defines the maximum temperature of 250degrees°C at the time of vein formation. The results demonstrate that the bedding-normal extension veins are trapped from a low salinity (3.5-8 eq.wt.% NaCl) H2O-NaCl fluid at near-lithostatic fluid pressures prior to inversion. After the tectonic inversion, bedding-parallel veins formed from a low salinity (4-7 eq.wt.% NaCl) H2O-NaCl fluid at lithostatic to supra-lithostatic fluid pressures during the early stages of the compressional stress regime. Subsequently, during progressive Variscan contraction both vein types were passively folded within characteristic, NW-verging, upright to overturned folds of the North Eifel. In contrast to both extensive veining events that characterise the tectonic inversion, quartz veining occurred rather occasionally during the main compression stage of orogeny. This kinematic history eventually shows a clear relationship between fluid-pressure evolution and the stress-state changes in the basin and exemplifies that (supra‑)lithostatic overpressures are easier to maintain during compressional tectonic inversion at the onset of orogeny, than during the main phase of compression. This intimate relationship during the stress-state evolution from extension to compression is illustrated by plotting the changing differential stress (sigma1-sigma3) against the vertical effective stress and the fluid-pressure evolution in a 2D brittle failure mode plot. The results show that the two vein types, which are induced at elevated to (supra‑)lithostatic fluid pressures, can only form at low differential stress closely related in time to the tectonic switch. The tectonic setting and the localised stress state in the basin are thus both crucial to determine whether the lithostatic fluid overpressure can be sustained by a rock prior to failure at depth. These 2D brittle failure mode plots are moreover very useful to visualisethe influence of rock parameters such as the tensile strength of rock on the maximum overpressures that can be built up during the transition between two stress regimes. This regional aspect of fluid redistribution within overpressured fluid reservoirs contrasts with the more localised fluid flow along fault systems caused by fault-valving. The 3D aspect of stress transitions during tectonic inversion of a crust is, however, much more complex than represented in a 2D brittle failure mode plot. The tectonic switch, illustrated in these brittle failure mode plots, occurs at a specific isotropic stress state in which the three principal stresses are equal and sigma1 - sigma3 = 0. The chance that a stress state in the Earths crust equals an isotropic pressure state is, however, highly improbable. The 2D stress-state evolution visualised in the brittle failure mode plots is therefore an oversimplification of the actual 3D stress-state evolution in the Earths crust. To discuss the 3D aspects of stress transitions and to illustrate the complexity of triaxial stress transitions during inversion of Andersonian stress regimes, possible 3D stress-state evolutions are reconstructed based on the bedding-normal and bedding-parallel veins reflecting the early Variscan tectonic inversion. From these 3D stress-state reconstructions is concluded that, no matter what orientation of basin geometry or shortening, a transitional wrench tectonic regime should always occur between extension and compression. This transitional stage should contribute to the permeability enhancement during tectonic inversion, although structures that are related to this transitional stage have not yet been reported in a shortened basin affected by tectonic inversion at low differential stress. Ideally, a transitional wrench tectonic regime should be implemented in brittle mode plots at the tectonic inversion. It has been concluded from this research that the naturally fractured Ardenne-Eifel basin can serve a possible analogue to the present upper crust by its regional extent of overpressuring, but more importantly by demonstrating that a tectonic inversion from extension to compression at the onset of orogeny is the crucial timing during which maximum (lithostatic) overpressures can be sustained.status: Publishe
Data en Gebiedsontwikkeling: Innovaties, strategieën en reflecties
No full textGebiedsontwikkelingen worden steeds complexer waardoor gebruik van data en slimme toepassingen een must is. Toch gebeurt dit nog op beperkte schaal. Wat houdt dit tegen, welke gevaren liggen op de loer, en welke voorbeelden kunnen voor inspiratie zorgen? Daarover vertellen experts in deze uitgave van de Kring van Adviseurs Gebiedsontwikkeling. Zij presenteren pakkende en innovatieve voorbeelden van hoe data wordt gebruikt, zoals voor gebouwen, mobiliteit, water, winkelstraten en publieke ruimte. Ook gaan zij in op de drijvende krachten achter en de beperking van de huidige toepassingen. De auteurs geven daarbij praktische adviezen voor het goed benutten van data, maar temperen ook verwachtingen en kraken kritische noten. Zodoende biedt deze publicatie een evenwichtig en inspirerend hulpmiddel voor eenieder die wordt geconfronteerd met datatoepassing in gebiedsontwikkeling, of daarmee aan de slag wil gaan.Urban Development ManagementPractice Chair Urban Area Developmen
Supplemental materials for preprint: Unfolding Veined Fold Limbs to Deduce a Basin's Prefolding Stress State
No full textChapter 9 - Unfolding Veined Fold Limbs to Deduce a Basin's Prefolding Stress State
No full textTectonic structures that developed prior to folding, such as pre- and early-kinematic veins, hold valuable information on the stress state of the paleobasin in which these early structures formed. To derive the parental orientation of these prefolding brittle structures, folds need to “unfold.” A fold restoration methodology is presented in which fold limbs, and the structures they contain, are rotated back to their depositional horizontal position by removing the tilt of the fold hinge line and the dip of individual fold limbs. The method is applied on quartz veins emplaced in folded Lower Devonian sandstones from the High-Ardenne slate belt (Belgium, Germany) and allowed deducing NW-SE opening when the Ardenne-Eifel Basin was at maximum burial depth (early Carboniferous). This exercise can be used in structural geology classes to teach how to rotate data using stereonet techniques, thereby encouraging students in applying an unfolding strategy to derive information from prefolding structures.status: Published onlin
Spatial distribution of quartz veins in alternating siliciclastic sequences and its relationship to bed thickness
No full textstatus: Publishe
Unfolding Veined Fold Limbs to Deduce a Basin's Prefolding Stress State
No full textTectonic structures that developed prior to folding, such as pre- and early-kinematic veins, hold valuable information on the stress state of the paleobasin in which these early structures formed. To derive the parental orientation of these prefolding brittle structures, folds need to “unfold.” A fold restoration methodology is presented in which fold limbs, and the structures they contain, are rotated back to their depositional horizontal position by removing the tilt of the fold hinge line and the dip of individual fold limbs. The method is applied on quartz veins emplaced in folded Lower Devonian sandstones from the High-Ardenne slate belt (Belgium, Germany) and allowed deducing NW-SE opening when the Ardenne-Eifel Basin was at maximum burial depth (early Carboniferous). This exercise can be used in structural geology classes to teach how to rotate data using stereonet techniques, thereby encouraging students in applying an unfolding strategy to derive information from prefolding structures
Fracture networks and strike–slip deformation along reactivated normal faults in Quaternary travertine deposits, Denizli Basin, western Turkey
No full textThe Denizli Basin in the West Anatolian Extensional Province in western Turkey is known for its numerous
Quaternary travertine occurrences. Travertine morphology is often dependant on the relative position of the deposition with respect to basin-bounding faults. The travertine occurrences examined in this study are situated at the intersection of the locally E–W oriented Denizli Basin and the adjacent NE–SW oriented Baklan Graben in the NE. Based on an extensive field campaign, including LIDAR scanning, several high-resolution fault/fracture maps of five large quarries (>300 m in length and >60 m in height) are
constructed in which this world-class travertine deposit is currently excavated. A structural analysis is performed in order to determine the tectonic overprinting of the travertine body and to derive the stress states of the basin after travertine deposition. The mostly open, non-stratabound joints are several tens of metres long and often bifurcate creating a dense fracture network. Minor infill of the joints resulted in the presence of a few colour-banded calcite veins. Based on the E–W, NE–SW and NW–SE orientation of three dominant joint sets it is concluded that the joint network is caused by local N-S extension, alternated by NW–SE and NE–SW extension exemplifying the presence of stress permutations in the Quaternary. High angle E–W to WNW–ESE faults cross-cut the quarries. Faults are filled with travertine debris and clastic infill of above lying sedimentary units indicative of the open nature of the faults. The specific E–Wfault orientation in the locally E–Wtrending Denizli Basin indicates that they initiated as normal faults. A paleostress inversion analysis performed on kinematic indicators such as striations on the clayey fault infill and the sinistral displacement of paleosols shows that some of the normal faults were reactivated causing left-lateral deformation in a transient strike–slip stress field with a NE–SW oriented σ1.sponsorship: The authors would like to acknowledge the quarry owners of the Cakmak, Ilik, Alimoglu, Faber and Ece quarries for their willingness to cooperate and their hospitality during field work. LIDAR scanning of the different quarries was performed by the Geospatial Research Ltd. (Durham University). We are very grateful to Mehmet Oruc Baykara who kindly provided all the logistic help, to Benjamin Lopez and Wim Vandewijngaerde for field assistance and to Carl Jacquemyn for his help with the GPS measurements. Reviewers Andrea Brogi and Andrea Billi are thanked for their comments and for sharing their knowledge on travertine deposits. Fabrizio Storti edited the manuscript. This work was undertaken during a postdoctoral project of Koen Van Noten which frames in a Joint Industry Project (JIP) focusing on the architecture of travertine geobodies. Financial support was provided by Eni, Petrobras, Total and KULeuven R&D. (Eni, Petrobras, Total, KULeuven RD)status: Publishe
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