Three different styles of plane-or nearly plane-roofed duplexes have been obtained using a computerized kinematic model of thrust-ramp anticlines. A thrust duplex consists of a group of fault-bounded slices (horses) with common lower (floor) and upper (roof) fault boundaries. The model assumes constant bed thickness and bed length parallel to the thrust ramp, in the forelimb of the anticline and everywhere that bedding is horizontal. Fault horse formation is accompanied by shear parallel to the new fault ramp. The model has been used to generate three different styles of plane-or nearly plane-roofed duplexes. In the only style having a perfectly planar roof, the fault horses are emplaced on the footwall upper flat and dip toward the foreland. The two hinterland-dipping duplex styles obtained do not have perfectly planar roofs. The first style has nearly planar faults within the duplex and can be developed with a minimum of two horses of intermediate spacing. The second style has faults that curve asymptotically into the roof and floor thrusts in a snakehead geometry and requires a minimum of four or more relatively closely spaced horses. Widely spaced horses having a common upper detachment result in a bumpy-roofed duplex with a roof deformed into anticlines and synclines.

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