Abstract

Large displacement on a low-angle normal fault results in isostatic uplift of the lower plate in response to tectonic denudation. Simple models of the denudation process predict warping of the lower plate into a broad antiform, or antiform-synform pair, with axes perpendicular to the direction of extension. The amount of warping is strongly influenced by initial fault geometry, surface topography, the amount of extension, and the distribution of extension within the upper plate. Late-stage processes that augment antiform growth include one-sided denudation of the antiform, reverse faulting due to concave-upward flexure, and wholesale detachment and reverse-drag folding of the antiform. Antiformal uplifts, now exhumed by erosion, form mountain ranges in the southwestern United States where conditions were favorable for warping during mid-Tertiary crustal extension. Four major structural domains are apparent in transects across these uplifts and adjacent areas: (1) unextended area, (2) synformal upper plate, (3) antiformal uplift, and (4) wedge-shaped upper plate. Each domain is separated from adjacent domains by the traces of a master low-angle normal fault.

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