Pseudo 3-D modeling of trishear fault-propagation folding

Basement structures, to which trishear fault-propagation models have most s uccessfully been applied, are commonly three-dimensional folds formed at th e tip-line of a fault. We present here a 'pseudo-3D' trishear model in whic h various parameters are permitted to vary along strike and oblique-slip ca n be modeled. These variations may be combined in an infinite number of way s, facilitating the simulation of many real structures. A thrust changing f rom blind to emergent can be produced by a change in the slip or propagatio n-to-slip (P/S) along strike. Folds with forelimbs changing from overturned to upright along strike can be modeled either by changing the slip, P/S or trishear angle. Also some minor folds perpendicular or oblique to the main structure can result from changes in the trishear angle or fault angle alo ng the strike, Models including growth strata show that it is practically i mpossible to distinguish between growth and pre-growth strata using the map patterns. As a field test, we have modeled the oblique slip East Kaibab mo nocline, demonstrating a good fit between the field observations and model predictions. (C) 2001 Elsevier Science Ltd. All rights reserved.