Abstract: 3-D Strike-Slip Pull-Apart Basins: Geometries Determined from Scaled Analogue Models

Ken R. McClay, T. Dooley

The 3-D evolution of strike-slip pull-apart basin systems have been modelled using scaled sandbox analogues. This paper presents models of straight and offset strike-slip systems and compares the results with structures found in natural strike-slip fault terranes. Particular attention was focused upon the progressive development of pull-apart basin geometries and their bounding faults. Homogeneous sandpacks were used to simulate isotropic conditions and wet clay models were used to simulate more competent pre-kinematic strata. Syn-kinematic layers were added incrementally during progressive deformation in order to simulate syn-offset sedimentation. The deformation geometries were controlled by offset strike-slip faults in rigid basement plates with the offsets varying from 30° un erlapping geometries to 150° overlapping geometries. Completed models were sectioned both vertically and horizontally and the structures were then digitised and displayed using a 3-D graphics workstation. The strike-slip models are characterized by asymmetric half grabens in rhombic pull-apart structures. The pull-aparts are bounded on two sides by continuations of the principal displacement zones and by two steep, planar sidewall faults generated by rotation of early formed Riedel shears at the tips of the offset principal displacement bones. The pull-apart geometries vary from lazy Z shapes to box-like rhomboids depending upon the degree of offset of the principal displacement zones. At large displacements the pull-apart basins are transected by basin floor shortcut faults that pr duce a throughgoing and smoother main fault system. Syn-kinematic strata within the pull-apart basins show complex fault patterns with flower structures developed along the principal displacement zones and steep extensional fault geometries along the side-wall faults. Volumetric analysis demonstrates that the pull-aparts typically have depth-length ratios typically between 1:2 to 1:3. Geometric and kinematic models for pull-apart basin geometries and their progressive evolution in 3-D are presented and compared with examples from the Gulf of Aqaba, the Dead Sea and strike-slip terranes from SW USA.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994