Surface Expression and Internal Structure of an Accommodation Zone, Gulf of Suez, Egypt
Dana Q. Coffield
Recent studies of rifts have shown that they are typically asymmetric, with much larger throw on one boundary fault system than on the other. In addition, the sense of rift asymmetry alternates along the axis of the rift, resulting in tilt-block domains of opposing dips to be juxtaposed against one another. The accommodation zones that separate the different domains strike perpendicular to the rift axis and accommodate the differential rotation between the tilt blocks. The problems presented by how the accommodation zones form, what controls their location, and the dynamics of their development are poorly understood.
The Morgan Hinge Accommodation zone is exposed at the surface in the southwestern Gulf of Suez. Here, a basement promontory extends eastward from the rift shoulder and separates the northeast-dipping blocks to the north from the southwest-dipping blocks to the south. A complete prerift and synrift stratigraphic succession is exposed around the margins of this promontory and effectively records the structural evolution of this feature.
The accommodation zone is approximately 10 km wide and consists of a complex fracturing and breaking up of the coherent blocks to the north and south into many small subblocks. Two fault trends dominate, one Gulf-parallel and the other Gulf-perpendicular. Fault spacing within the zone is on a kilometer scale, with most offsets showing normal displacements of tens to hundreds of meters. Strike-slip movement is negligible. These small-scale displacements between subblocks accommodate the large-scale displacements resulting from the opposing rotation between adjacent tilted blocks.
AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.