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The structure normally develops further by successive activations of horse units in the frontal part of the bowing imbricate structure. Occasionally, reactivation of more internal units can lead to so-called out of sequence thrusts. The normal type of duplex activity leads to a transfer of slip along a glide surface at low tectonic level to higher level. One especially important geometrical feature of this progression is that different parts of the main thrust are active at different times during the forward transport of overlying thrust sheet, and in consequence the same plane will have differing amounts of displacement at different positions in the overall structure. In this type of duplex development the overall dip of the imbricate splay faults and the internal bedding of the horses is away from the overall movement direction sense of the thrust sheet and the duplex is termed a hinterland dipping duplex. If, however; the slip on individual horses beoomes larger, and about the same as the length of the individual horses, each successively activating horse provides an uplift to the previously formed and deactivated horses and

develops an overall antiformal structure in the imbricate zone and in the overlying thrust sheet. Such antiformal imbricate stacks show a progressively decreasing downward amplitude of their elements, and the antiformal structure dies to zero in the decollcment along the floor thrust. A further type of imbricate 

 structure develops where the slip on individual horses is greater than the length of the horse. Where this is true, the successive uplifts of the roof thrust and previously formed horses occur behind the early formed and forward horses. This rearward uplift changes the dip of the imbricate faults and the overall dips of their contained strata and the imbricate structure now forms a

foreland dipping duplex. It should be clear from the discussion above that the movements of fauIt blocks over irregularly oriented flats and ramps sets up folds in the moving block, and that the axial surfaces of these folds will be controlled by locations of the changes of orientation of the fault trace, Although most geometric analysis of these folds has been undertaken in studies of thrust faulting, such features are characteristic of all types of faults showing non planar surfaces. In the case of reverse or thrust faults a special nomenclature has been developed to describe different types ramp and flat geometry and each type has its own special effect in terms of fold development . Ramps which form perpendicular to the main direction of overaII lransport direction are known as frontal ramps. A frontal ramp can occur anywhere within a thrust sheet and

need not occur in the most forward part of the sheet. Ramps at angle to the transport direction are known as lateral or sidewall ramps, those

inclined at other angles are oblique ramps, When a thrust

moves over a surface with a complex interconnecting

surface of different types of ramps the thrust sheet geometry on an "inside-out" form of the underlying thrust. Forward movements of an , initially shaped trough-like thrust sheet with an advanced frontal ramp and two lateral ramps leads to the transIation of this thrust sheet into a flat roofed dome-like structure. This is just one way of forming a culmination in dome in a thrust sheet.

Foot wall Hanging wall morphology

Influence of the geometry of the thrust foot wall on the moving thrust sheet of the hanging wall

is to produce a duplex structure on splay faults which have forms of frontal and sidewall ramps. In this case not only do we have a possibility of producing an anticlinal stack with uplift controlled by the direction of the frontal ramps, but the antiformal stack will be bowed into a culmination by the movement on the sidewall ramps of the imbricate structure.