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Sverre Planke - One of the best experts on this subject based on the ideXlab platform.
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u pb geochronology of cretaceous magmatism on svalbard and franz josef land barents sea large igneous province
Geological Magazine, 2013Co-Authors: Fernando Corfu, Henrik Svensen, Sverre Planke, Stephane Polteau, Jan Inge Faleide, Andrew Zayoncheck, Nikolay StolbovAbstract:The opening of the Arctic oceanic basins in the Mesozoic and Cenozoic proceeded in steps, with episodes of magmatism and sedimentation marking specific stages in this development. In addition to the stratigraphic record provided by sediments and fossils, the intrusive and extrusive rocks yield important information on this evolution. This study has determined the ages of mafic Sills and a felsic tuff in Svalbard and Franz Josef Land using the isotope dilution thermal ionization mass spectrometry (ID-TIMS) U–Pb method on zircon, baddeleyite, titanite and rutile. The results indicate crystallization of the Diabasodden Sill at 124.5 ± 0.2 Ma and the Linnevatn Sill at 124.7 ± 0.3 Ma, the latter also containing slightly younger secondary titanite with an age of 123.9 ± 0.3 Ma. A bentonite in the Helvetiafjellet Formation, also on Svalbard, has an age of 123.3 ± 0.2 Ma. Zircon in mafic Sills intersected by drill cores in Franz Josef Land indicate an age of 122.7 Ma for a thick Sill on Severnaya Island and a single grain age of ≥122.2 ± 1.1 Ma for a thinner Sill on Nagurskaya Island. These data emphasize the importance and relatively short-lived nature of the Cretaceous magmatic event in the region.
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3d relationships between Sills and their feeders evidence from the golden valley Sill complex karoo basin and experimental modelling
Journal of Volcanology and Geothermal Research, 2011Co-Authors: Christophe Y Galerne, Olivie Galland, Elseragnhild Neuma, Sverre PlankeAbstract:Abstract In this paper, we address Sill emplacement mechanisms through the three-dimensional relationships between Sills and their potential feeders (dykes or Sills) in the well-exposed Golden Valley Sill Complex (GVSC), Karoo Basin, South Africa. New field observations combined with existing chemical analyses show that: 1) the contacts between Sills in the GVSC are not Sill-feeding-Sill relationships, and 2) there are, however, close structural and geochemical relationships between one elliptical Sill, the Golden Valley Sill (GVS), and a small dyke (d4). Such relationships suggest that GVS is fed by d4 and that the linear shape of d4 may have controlled the elliptical development of the GVS. To test this hypothesis, we present preliminary results of experimental modelling of Sill emplacement, in which we vary the shape of the feeder. In the first experiment (E1) with a punctual feeder the Sill develops a sub-circular geometry, whereas in the second experiment (E2) with a long linear feeder the Sill develops an elliptical geometry. The geometrical relationships in E2 show that the elliptical shape of the Sill is controlled by the linear shape and the length of the linear feeder. The experiment E2 presents strong similarities with the GVS–d4 relationships and thus supports the proposition that d4 is the feeder of the GVS. Our experimental results also indicate that the feeders of the other elliptical Sills of the GVSC may be dykes.
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emplacement mechanisms of Sill complexes information from the geochemical architecture of the golden valley Sill complex south africa
Journal of Volcanology and Geothermal Research, 2008Co-Authors: Christophe Y Galerne, Elseragnhild Neuma, Sverre PlankeAbstract:Abstract The well-exposed Golden Valley Sill Complex, Karoo basin, South Africa, consists of four large Sills (ca. 100 m thick; long axes: 13–24 km), one small Sill (55–80 m thick; long axis: 4 km; forming an appendix to one of the large Sills), and two large dykes (15–20 m thick; 25 and 70 km long), plus some minor intrusions. Field mapping shows physical connections between the small Sill and one of the large Sills, but no other connection between the large Sills, or connections between the Sills and the large dykes. Geochemical variation diagrams for 327 dolerite samples from the different Sills and dykes in the Golden Valley Sill Complex showed similar compositional ranges for the dolerite bodies, but some differences in ratios between strongly incompatible elements. These differences were probed by Forward Stepwise-Discriminant Function Analysis using all major and trace elements as variables, and the height major Sills and dykes as populations. The Forward Stepwise-Discriminant Function Analysis identified six different geochemical signatures among the Sill-dyke populations. The six geochemical signatures were interpreted as representing six magma batches of distinct chemical characteristics that were involved in the formation of the Golden Valley Sill Complex. Four different magma batches gave rise to two of the large saucer-shaped Sills and the two dykes. The exposed large dykes thus do not represent feeders to the main Sills. A fifth magma batch gave rise to the two other large saucer-shaped Sills as well as the smaller one. The statistical analysis also gave information about the connection between different dolerite exposures that could not be obtained by field, and made it possible to reconstruct the different Sills through complex areas where several Sills meet, and through widely spaced exposures. On the basis the field mapping and statistical analysis of geochemical data the geochemical architecture of the complex was established. Our study gives support to both the main models proposed earlier to explain the emplacement of Sill complexes: (1) each Sill in a Sill complex is fed by different magma batches, and (2) the different Sills in a Sill complex feed one another, forming a group of nested Sills generated by one single batch of magma. Furthermore, our study indicates that the interconnected Sills in the Golden Valley Sill Complex are connected along their outermost edges through lateral overflow. The statistical analysis establishes a link between minor dolerite bodies and the main intrusion, thereby improving the geological mapping of the Sill complex. The different units in the Golden Valley Sill Complex show strong geochemical affinity to lavas in the Lesotho Formation, the younger of the two formations in the Lesotho lava remnant. This suggests that these Sills were emplaced at the same time as the Lesotho Formation, and that magmas with the same chemical characteristics as the Lesotho Formation were emplaced over a significantly larger area than covered by the remnants of the Lesotho Formation.
Abdelazim M Negm - One of the best experts on this subject based on the ideXlab platform.
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minimization of scour depth downstream radial stilling basins
2007Co-Authors: Abdelazim M NegmAbstract:In this research paper, the effect of the position of central symmetric Sill on the maximum scour depth downstream (DS) of radial stilling basin (RSB) was investigated experimentally. Central symmetric Sill of particular length (normal to the flow direction) were tested at different positions with reference to the position of the control gate. The flow pattern was observed and the scour pattern was measured for each test. The optimal position of the central symmetric Sill that minimizes the maximum depth of scour DS. radial stilling basin based on the analysis of the experimental measurements. Results were compared to the no Sill case. It was obtained that the scour is minimized if the Sill is installed within the middle third of the basin. The effect of using an end Sill combined with the central Sill at the optimal position was also investigated. It was found that the scour process were slightly reduced (in each of the three dimensions) when the central Sill at the optimal position was combined with the end Sill. A prediction model was developed using the multiple linear regression analysis to estimate the maximum scour depth. The other characteristics of the scour and deposition process were also presented and discussed.
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effect of end Sill on scour characteristics downstream of sudden expanding stilling basins
2004Co-Authors: Abdelazim M Negm, Noha G AhmadAbstract:Scour downstream of a hydraulic structure may endanger the whole structure after long or short run depending upon the extent of scouring processes. It is highly recommended to prevent the downstream bed from being scoured if possible or minimize the dimensions of the scour hole and force it to form away from the end of the stilling basin to increase the safety of the structure. It is believed that the end Sill when carefully designed- can have an important role to force the scour hole and reduce the extent of erosion. In this paper, the effects of using end Sills in the sudden expanding stilling basins are addressed experimentally. Stilling basins with different expansion ratios of 1.54, 2.0 and 2.5 are used to collect the scour information when a Sill is installed at the end of the basin. Sills of different dimensions are tested under wide range of flow conditions. The optimal Sill that reduces the extent of scour downstream of the most practical sudden expanding stilling basin is recommended.
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effect of asymmetric side Sill on scour characteristics downstream of sudden expanding stilling basins
2004Co-Authors: Osama K Saleh, Abdelazim M Negm, Noha G AhmadAbstract:Previous investigations proved that Scour downstream of Sudden Expanding Stilling Basins (SESB) are asymmetric due to the asymmetric flow conditions in the basin. Improving the flow pattern inside the basin by forcing it to be symmetric will improve the resulting scour pattern downstream of the basin. Different measures may be used to improve the flow pattern in the sudden expanding stilling basin. One of these measures is using one or more asymmetric side Sill at certain position with particular orientation. In this paper, the effect of asymmetric side Sill on the scour characteristics represented by the maximum scour depth downstream of SESB is investigated. Determination of the best position of the asymmetric side Sill is the main objective of the present research. The effects of such conditions on the flow patterns inside the basins are also discussed. It is concluded that using asymmetric side Sill reduces the maximum scour depth significantly, especially when two asymmetric side Sills are used. A simple prediction equation is developed for estimating the maximum depth of scour knowing the Froude number or the upstream head ratio and the relative position of the Sill.
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effect of Sill arrangement on maximum scour depth downstream of abruptly enlarged stilling basins
2004Co-Authors: Abdelazim M NegmAbstract:Scour downstream (DS) of hydraulic structures (HS) may endanger the safety of the structures if the necessary precuations are not considered during the design stage. Normally, different measures produce different effects on reducing the maximum scour depth DS of HS. One of the important HSs is the abruptly enlarged (or sudden expanding) stilling basins. In this paper, the effects of different arrangements of Sills inside an abruptly enlarged stilling basin will be discussed. An experimental program was conducted to investigate the effects of continuous end Sill, one asymmetric side side, double staggered asymmetric side Sills, symmetric side Sills, central Sill and continuous central Sill. The flow patterns were observed and the maximum scour depths were recorded. The results revealed that in most of the cases the flow patterns are asymmetric resulting in asymmetric scours. The reduction in the maximum scour depth depends on the type of arrangement of the used Sill and on the flow conditions represented by Froude number. Both of the central Sill with limited width and continuous central Sill improved the flow patterns towards symmetric type and yielded minimized maaximum scour depth with preference to the continuous Sill.
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theoretical modeling of hydraulic jumps in radial stilling basins ended with Sills
2003Co-Authors: A A Habib, G M Abdelaal, Abdelazim M Negm, T. M. OwaisAbstract:The use of end Sill is one of the common methods that have been used to optimize the hydraulic jump length. Extensive studies have been conducted to investigate the effect Sills or end Sills on the hydraulic jumps in rectangular basins but not yet in radial basins. The complete design of stilling basins needs the accurate estimation of the depth ratio of the formed hydraulic jump in the basin. In the present paper, a theoretical model is developed to predict the depth ratio of the radial hydraulic jump when a basin is ended with a Sill. Both the momentum and continuity equation in one dimension are applied to the control volume where the basin begins and ends. Also, the energy equation is used to develop a theoretical model to evaluate the energy loss by the radial hydraulic jump when a Sill exists at the end of the basin. An experimental program is conducted to collect experimental data to enable verification of the developed theoretical models. Good agreement between theoretical and experimental results is obtained. The developed models could be used safely to compute both the depth ratio of the jump and the energy loss by the jump formed in radial basin with an end Sill.
Janine Kavanagh - One of the best experts on this subject based on the ideXlab platform.
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the mechanics of Sill inception propagation and growth experimental evidence for rapid reduction in magmatic overpressure
Earth and Planetary Science Letters, 2015Co-Authors: Janine Kavanagh, David Outelie, Alexande R CrudeAbstract:Abstract A model of magma propagation in the crust is presented using a series of analogue experiments, where dyed water is injected at a constant flux into layers of solidified gelatine. The gelatine layers are transparent and, when intruded, deform in an almost ideal-elastic manner under the experimental conditions (low gelatine concentration: 2.5 or 3 wt%, and low temperature: 5–10 °C). The upper gelatine layer was 1.0 to 1.5 times stiffer than the lower layer, with either a ‘weak’ or ‘strong’ interface strength between the gelatine layers. The gelatine is seeded with 20 – 50 μm -diameter PMMA-RhB neutrally buoyant particles that are fluoresced by a pulsed, vertical laser sheet centred on the injection point. Digital image correlation (DIC) is used to calculate incremental strain and finite strain in the deforming host material as it is intruded. This is mapped in 2D for the developing experimental volcanic plumbing system that comprises a feeder dyke and Sill. Since the gelatine deforms elastically, strain measurements correlate with stress. Our results indicate that, for constant magma flux, the moment of Sill inception is characterised by a significant magmatic pressure decrease of up to ∼ 60 % . This is evidenced by the rapid contraction of the feeder dyke at the moment the Sill forms. Sill propagation is then controlled by the fracture properties of the weak interface, with fluid from the feeder dyke extracted to help grow the Sill. Pressure drops during Sill inception and growth are likely to be important in volcanic systems, where destabilisation of the magmatic plumbing system could trigger an eruption.
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an experimental investigation of Sill formation and propagation in layered elastic media
Earth and Planetary Science Letters, 2006Co-Authors: Janine Kavanagh, Thierry Menand, Stephe R J SparksAbstract:A series of experiments are described where dyed water (a magma analogue) was intruded into solid gelatine (a crustal analogue) to investigate the formation of Sills. We considered a layered gelatine system with contrasting adjacent layers. By varying the density and rigidity of the gelatine we found that experimental Sills form when the upper layer is more rigid than the lower layer, with intrusion occurring in a plane directly below the interface. Experimental dykes were observed to propagate to the surface when the Young's Modulus ratio of upper to lower gelatine layers was less than one. Experimental dyke arrest occurred when the upper layer was more rigid and the interface was strong. Two varieties of experimental Sill formed when the upper layer was more rigid than the lower layer and the interface was sufficiently weak. The form of the intrusion depends on the balance of driving pressures and the Young's Modulus ratio of contrasting adjacent layers. When the rigidity ratio is high and there is a large driving pressure the experimental feeder dyke completely converts to propagate as a Sill. However, when the rigidity ratio and driving pressure are both close to one a dyke–Sill hybrid forms. Under these conditions the experimental Sill formation is accompanied by contemporaneous dyke intrusion into the overlying more rigid layer. During Sill propagation deformation structures such as faults and en echelon fractures are formed into the lower layer. Experimental Sill propagation dynamics are controlled by viscous dissipation along the length of the Sill; causing acceleration with increasing length. Our study suggests that rigidity contrasts may play a major role in the location of Sills and development of igneous complexes. In ancient cratonic areas the Moho is a suitable site for the preferential formation of Sills with higher rigidity continental crust overlying weaker mantle. Mantle plumes impacting ancient continents provide a situation in which large Sills can form to fractionate prior to eruption of flood basalts. The boundary between the upper and lower crust (Conrad discontinuity) may provide a preferential focus for the emplacement of sheets of silicic magma at continental arcs where the lower crust is weakened by prolonged heating and possible hydration.
Christophe Y Galerne - One of the best experts on this subject based on the ideXlab platform.
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3d relationships between Sills and their feeders evidence from the golden valley Sill complex karoo basin and experimental modelling
Journal of Volcanology and Geothermal Research, 2011Co-Authors: Christophe Y Galerne, Olivie Galland, Elseragnhild Neuma, Sverre PlankeAbstract:Abstract In this paper, we address Sill emplacement mechanisms through the three-dimensional relationships between Sills and their potential feeders (dykes or Sills) in the well-exposed Golden Valley Sill Complex (GVSC), Karoo Basin, South Africa. New field observations combined with existing chemical analyses show that: 1) the contacts between Sills in the GVSC are not Sill-feeding-Sill relationships, and 2) there are, however, close structural and geochemical relationships between one elliptical Sill, the Golden Valley Sill (GVS), and a small dyke (d4). Such relationships suggest that GVS is fed by d4 and that the linear shape of d4 may have controlled the elliptical development of the GVS. To test this hypothesis, we present preliminary results of experimental modelling of Sill emplacement, in which we vary the shape of the feeder. In the first experiment (E1) with a punctual feeder the Sill develops a sub-circular geometry, whereas in the second experiment (E2) with a long linear feeder the Sill develops an elliptical geometry. The geometrical relationships in E2 show that the elliptical shape of the Sill is controlled by the linear shape and the length of the linear feeder. The experiment E2 presents strong similarities with the GVS–d4 relationships and thus supports the proposition that d4 is the feeder of the GVS. Our experimental results also indicate that the feeders of the other elliptical Sills of the GVSC may be dykes.
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emplacement mechanisms of Sill complexes information from the geochemical architecture of the golden valley Sill complex south africa
Journal of Volcanology and Geothermal Research, 2008Co-Authors: Christophe Y Galerne, Elseragnhild Neuma, Sverre PlankeAbstract:Abstract The well-exposed Golden Valley Sill Complex, Karoo basin, South Africa, consists of four large Sills (ca. 100 m thick; long axes: 13–24 km), one small Sill (55–80 m thick; long axis: 4 km; forming an appendix to one of the large Sills), and two large dykes (15–20 m thick; 25 and 70 km long), plus some minor intrusions. Field mapping shows physical connections between the small Sill and one of the large Sills, but no other connection between the large Sills, or connections between the Sills and the large dykes. Geochemical variation diagrams for 327 dolerite samples from the different Sills and dykes in the Golden Valley Sill Complex showed similar compositional ranges for the dolerite bodies, but some differences in ratios between strongly incompatible elements. These differences were probed by Forward Stepwise-Discriminant Function Analysis using all major and trace elements as variables, and the height major Sills and dykes as populations. The Forward Stepwise-Discriminant Function Analysis identified six different geochemical signatures among the Sill-dyke populations. The six geochemical signatures were interpreted as representing six magma batches of distinct chemical characteristics that were involved in the formation of the Golden Valley Sill Complex. Four different magma batches gave rise to two of the large saucer-shaped Sills and the two dykes. The exposed large dykes thus do not represent feeders to the main Sills. A fifth magma batch gave rise to the two other large saucer-shaped Sills as well as the smaller one. The statistical analysis also gave information about the connection between different dolerite exposures that could not be obtained by field, and made it possible to reconstruct the different Sills through complex areas where several Sills meet, and through widely spaced exposures. On the basis the field mapping and statistical analysis of geochemical data the geochemical architecture of the complex was established. Our study gives support to both the main models proposed earlier to explain the emplacement of Sill complexes: (1) each Sill in a Sill complex is fed by different magma batches, and (2) the different Sills in a Sill complex feed one another, forming a group of nested Sills generated by one single batch of magma. Furthermore, our study indicates that the interconnected Sills in the Golden Valley Sill Complex are connected along their outermost edges through lateral overflow. The statistical analysis establishes a link between minor dolerite bodies and the main intrusion, thereby improving the geological mapping of the Sill complex. The different units in the Golden Valley Sill Complex show strong geochemical affinity to lavas in the Lesotho Formation, the younger of the two formations in the Lesotho lava remnant. This suggests that these Sills were emplaced at the same time as the Lesotho Formation, and that magmas with the same chemical characteristics as the Lesotho Formation were emplaced over a significantly larger area than covered by the remnants of the Lesotho Formation.
Noha G Ahmad - One of the best experts on this subject based on the ideXlab platform.
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effect of end Sill on scour characteristics downstream of sudden expanding stilling basins
2004Co-Authors: Abdelazim M Negm, Noha G AhmadAbstract:Scour downstream of a hydraulic structure may endanger the whole structure after long or short run depending upon the extent of scouring processes. It is highly recommended to prevent the downstream bed from being scoured if possible or minimize the dimensions of the scour hole and force it to form away from the end of the stilling basin to increase the safety of the structure. It is believed that the end Sill when carefully designed- can have an important role to force the scour hole and reduce the extent of erosion. In this paper, the effects of using end Sills in the sudden expanding stilling basins are addressed experimentally. Stilling basins with different expansion ratios of 1.54, 2.0 and 2.5 are used to collect the scour information when a Sill is installed at the end of the basin. Sills of different dimensions are tested under wide range of flow conditions. The optimal Sill that reduces the extent of scour downstream of the most practical sudden expanding stilling basin is recommended.
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effect of asymmetric side Sill on scour characteristics downstream of sudden expanding stilling basins
2004Co-Authors: Osama K Saleh, Abdelazim M Negm, Noha G AhmadAbstract:Previous investigations proved that Scour downstream of Sudden Expanding Stilling Basins (SESB) are asymmetric due to the asymmetric flow conditions in the basin. Improving the flow pattern inside the basin by forcing it to be symmetric will improve the resulting scour pattern downstream of the basin. Different measures may be used to improve the flow pattern in the sudden expanding stilling basin. One of these measures is using one or more asymmetric side Sill at certain position with particular orientation. In this paper, the effect of asymmetric side Sill on the scour characteristics represented by the maximum scour depth downstream of SESB is investigated. Determination of the best position of the asymmetric side Sill is the main objective of the present research. The effects of such conditions on the flow patterns inside the basins are also discussed. It is concluded that using asymmetric side Sill reduces the maximum scour depth significantly, especially when two asymmetric side Sills are used. A simple prediction equation is developed for estimating the maximum depth of scour knowing the Froude number or the upstream head ratio and the relative position of the Sill.
