| 1. |
- Koyi, Hemin, et al.
(författare)
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Salt diapirs of the southwest Nordkapp Basin : analogue modelling
- 1993
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 228:3-4, s. 167-187
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Tidskriftsartikel (refereegranskat)abstract
- The geometry and evolution of the salt diapirs in the southwestern segment of the Nordkapp Basin (SW NKB) were interpreted on reflection seismic data. Reflection seismic profiles were used to build a dynamically scaled model analogue to study salt tectonics of the basin. The model was prepared using lengths, densities, and sedimentary histories obtained from seismic and well data. Model results suggest that the salt structures in the SW NKB were influenced by basement faults that horizontally stretched and faulted their overburden and induced salt flow by differential loading. Model diapirs rose only where the overburden was faulted. The salt structures are aligned in two NE-SW rows that parallel the major basement faults that outline the basin. Carboniferous salt in the SW NKB formed conformable pillows in the Early Triassic (Scythian), which became diapiric during the late Early and Middle Triassic. The salt diapirs spread to form asymmetric broad overhangs at superficial levels during slow sedimentation in Late Triassic and/or Jurassic. Diapir overhangs were later reactivated because of burial by Cretaceous and Tertiary sediments. Basement faults were mapped by comparing thickness of the sediments and/or level of the reflectors on either side of the diapirs that had relatively narrow overhangs. Depth conversion and restoration of velocity pull-up of reflectors beneath salt diapirs suggest that the salt diapirs of the SW NKB have broad overhangs above narrow stems.
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| 3. |
- Talbot, Christopher J., et al.
(författare)
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Diapiric spokes pattern
- 1991
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 188:1-2, s. 187-201
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Tidskriftsartikel (refereegranskat)abstract
- Not all finger-like diapirs evolve from or into linear walls as previously supposed. That would imply that all contemporaneous finger diapirs lie in rows and many do not. Physical models demonstrate that diapiric linear walls or rows of fingers have to be forced by lateral forces, lateral boundaries, or internal edge effects. By contrast, the kinematics of the simplest isothermal gravity overturns responsible for finger-like diapirs are geometrically, kinematically and dynamically similar to the “spoke patterns” of vigorous thermal convection. This is because Rayleigh-Taylor (RT) diapirism and Rayleigh-Bènard (RB) thermal convection are end members of a continuous dynamic spectrum due to any combination of compositional or thermally induced density inversions. All simple RT overturns are dynamically similar, but the vigour of thermal convection varies with the heat flow.The kinematics of spoke patterns are difficult to study in rapid, multiple overturns of thermal convection in low viscosity fluids. However, spoke patterns in slow, isothermal diapiric analogues can be analysed at any stage during their single overturn. Such studies indicate that two sets of spokes conduct fluids of different densities horizontally along the top and bottom boundaries to finger-like diapiric stems or plumes where they rise or sink to spread in polygonal bulbs at the opposite boundary. Spokes converge to hubs at the bottom boundary beneath stems feeding diapiric bulbs at the top boundary and vice versa. If the movement cells are considered centred on rising plumes, the cell corners are mapped by sinking plumes.The differences between spoke patterns and previously understood diapiric patterns are illustrated by geological examples with emphasis on relevance to the search for oil and gas. Physical arguments suggest that spoke patterns are probably the most common geometries of gravity-driven overturns in layered rocks of both the crust and the mantle.
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