Origin of coast-perpendicular extensional faults, western Gulf of Mexico: The relationship between an early-stage ridge and a late-stage fault

Abstract

An area near Corpus Christi, Texas, comprises two large, coast-parallel, listric-normal growth faults detached on mobilized shale. Like with most large Gulf of Mexico listric-normal (i.e., growth) faults, fault planes dip basinward, accommodate large amounts of extension, and link along strike with other growth faults. Less characteristically, the hanging wall of the growth-fault system comprises an elongate ridge whose strike is coast-perpendicular and, hence, orthogonal to the growth faults. A high-angle, coast-perpendicular normal fault orthogonal to the growth faults nucleates on the roof of the ridge. A model for the concomitant development of coast-parallel and coast-perpendicular ridges and faults is proposed to explain the development of the orthogonal fault. First, the early development of coast-parallel and coast-perpendicular ridges could have been related to convergent thin-skinned shortening, differential loading, or a combination of the two. Second, when large seaward translation occurred, ridges having different orientations evolved differently. Those oriented parallel to the direction of maximum extension (coast perpendicular) were subjected to little or no extension; conditions were thus set for a later nucleation of the orthogonal fault above the coast-perpendicular ridge during a much later stage of extension. In contrast, ridges striking perpendicular to the direction of maximum extension (coast parallel) underwent collapse and acted as nucleation points for coast-parallel growth faulting.