Abstract: The Geometry and Kinematics of Duplex formation

Peter A. Geiser

Duplexing is one of the most widespread and important types of structures associated with faulting. It occurs across a scale spectrum extending across at least four orders of magnitude. Duplexing is found under all types of faulting, extensional, compressional and strike slip. There are four methods for forming duplexes. I refer to them as forward stepping, back stepping, out of sequence (OOS) and in situ. The forward stepping and OOS types originally described by Boyer and Elliott are created by footwall collapse, while backstepping and in situ, described here for the first time, are created by hanging wall collapse. In situ duplexes may also be created by footwall plucking. The geometry and kinematics of the four types are shown to form a wide variety of structures which may be grou ed into two broad classes, parautochthonous duplexes and allocthonous duplexes. Analysis of the geometry and kinematics of the four duplex mechanisms by structural forward modelling shows how a wide variety of complex assemblages, many not previously described, may be created by duplexing. Study of the geometry and deformation history of the four duplex types suggests criteria for distinguishing among them.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994