ABSTRACT: Internal Deformation of Tilted Blocks in the Suez and Red Sea Rifts

MORETTI, ISABELLE, and BERNARD COLLETTA, Institut Francais du Petrole, Rueil Malmaison, France, and ENRICO RIVA, AGIP, Milano, Italy.

Two main types of deformation are generally considered in extensional terranes: (1) Faulted blocks are rigid and deformation consists of translations and rotations. (2) Blocks are pervasively deformed, by simple shear along closely spaced minor faults or by "flexural slip" parallel to bedding planes. To evaluate the amount of such pervasive deformation, field measurements were performed across three major tilted blocks of the Suez rift (Abu Durba and Araba-Qabeliat blocks) and Red Sea (Duwi block). They consist of narrow (150 to 20 km wide), elongated (30 to 60 km long) monoclines dipping to the northeast and bounded by major southwest-dipping faults that have vertical displacement of about 2 km. Tilt angles vary from 15 to 20 degrees. Secondary normal faults are scarce and widely spa ed, and their throw varies between 10 cm and 150 m. No pervasive and closely spaced faults with centimetric or metric throws have been observed. In the Abu Durba and Duwi blocks, the amount of extension caused by secondary faults is less than 7% while it is almost null across the Araba-Qabeliat block. Extensional models inducing pervasive deformation of blocks by vertical or oblique simple shear are not relevant when tilt angles do not exceed 20 degrees and rigid rotation can be applied to restore cross section. Moreover, most of the observed secondary normal faults have the same dip direction as major bounding faults. This arrangement suggests that tilting occurs over a ductile crustal layer that accommodates at depth the volume problems caused by rigid block rotation.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)