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Study of the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust
Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere.
In areas of thrust tectonics two main styles are recognized; thin-skinned deformation and thick-skinned deformation. The distinction is important as attempts to structurally restore the deformation will give very different results depending on the assumed geometry.
Thin-skinned deformation refers to shortening that only involves the sedimentary cover. This style is typical of many fold and thrust belts developed in the foreland of a collisional zone. This is particularly the case where a good basal decollement exists such as salt or a zone of high pore fluid pressure.
Thick-skinned deformation refers to shortening that involves basement rocks rather than just the overlying cover. This type of geometry is typically found in the hinterland of a collisional zone. This style may also occur in the foreland where no effective decollement surface is present or where pre-existing extensional rift structures may be inverted.
Geological environments associated with thrust tectonics
Passive margins are characterised by large prisms of sedimentary material deposited since the original break-up of a continent associated with formation of a new spreading centre. This wedge of material will tend to spread under gravity and, where an effective detachment layer is present such as salt, the extensional faulting that forms at the landward side will be balanced at the front of the wedge by a series of toe-thrusts. Examples include the outboard part of the Niger delta (with an overpressured mudstone detachment) and the Angola margin (with a salt detachment).
Extensional tectonics – Study of the structures formed by, and the processes associated with, the stretching of a planetary body's crust
Strike-slip tectonics – Structure and processes associated with zones of lateral displacement in the Earth's crust