Thrust Fault - Tectonic Environment

Tectonic Environment

Large overthrust faults occur in areas that have undergone great compressional forces.

These conditions exist in the orogenic belts that result from either two continental tectonic collisions or from subduction zone accretion.

The resultant compressional forces produce mountain ranges. The Himalayas, the Alps, and the Appalachians are prominent examples of compressional orogenies with numerous overthrust faults.

Thrust faults occur in the foreland basin which occur marginal to orogenic belts. Here, compression does not result in appreciable mountain building, which is mostly accommodated by folding and stacking of thrusts. Instead thrust faults generally cause a thickening of the stratigraphic section.

Foreland basin thrusts also usually observe the ramp-flat geometry, with thrusts propagating within units at a very low angle "flats" (at 1-5 degrees) and then moving up-section in steeper ramps (at 5-20 degrees) where they offset stratigraphic units. Identifying ramps where they occur within units is usually problematic.

Thrusts and duplexes are also found in accretionary wedges in the ocean trench margin of subduction zones, where oceanic sediments are scraped off the subducted plate and accumulate. Here, the accretionary wedge must thicken by up to 200% and this is achieved by stacking thrust fault upon thrust fault in a melange of disrupted rock, often with chaotic folding. Here, ramp flat geometries are not usually observed because the compressional force is at a steep angle to the sedimentary layering.