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Deformation Styles and Linkage of Salt Walls during Oblique Shortening

Dooley, Tim P.1; Jackson, Martin 1; Hudec, Michael R.1
1 Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX.

We built model arrays of elongated salt walls by diapiric downbuilding then shortened the model by a moving endwall. The arrays contained salt walls having a 90° range of orientations perpendicular, oblique and parallel to the direction of regional shortening. The complexity of shortening of the walls varied with their orientation.

Cross walls perpendicular to regional shortening deformed in a relatively simple fashion. Tear faults allowed greater shortening of the wall than of the surrounding overburden. As the originally parallel sides of cross walls converged, salt was driven to the ends of the walls, where it survived as a bulbous tip after advanced welding, creating an overall structure in planform resembling a Q-tip.

In contrast, walls oblique to regional shortening formed transpressional uplifts of their sedimentary roofs. During the early stages of shortening, transtensional crestal grabens accommodated differential slip on either side of the oblique salt walls. After oblique-slip ceased, the overburden between salt walls shortened along regional thrust faults, causing oblique walls to become sigmoidal.

Salt walls trending parallel to regional shortening had the most complex geometry. As these salt walls shortened parallel to their long axis, displaced salt bulged outward forming lateral wings. This lateral bulging contrasts with salt walls in all other orientations, which narrowed over time under compression. Extrusion from parallel-oriented walls was long lived because (1) the shortening required to fully weld the wall was much greater than for oblique and cross walls, and (2) an open conduit to the source layer survived even intense shortening.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009