Tecronophysics, 215 (1992) 209-220 Elsevier Science Publishers B.V., Amsterdam 209 ~~v~~oprn~nt of asymmetric basins along Continental transform faults Zvi Bun-Avraha~ Department of Geophysics and Planetary Sciences Tel Acir Unkersity, Tel .4rir 69978, Israel (Received June 15, 1991; revised version accepted November 28, 1991) ABSTRACT Ben-Avraham, Z., 1992. Development of asymmetric basins aiong continent~i transform faults. In: P.A. Ziegler (Editor), Geodynamics of Rifting, Volume III. Thematic Discussions. Tecronop!~ys~cs, 215: 209-220. Many basins associated with wrench or transform faults are asymmetrical, both longitudinally and laterally; the sense of basin asymmetry changes along the strike of transform faults. Geophysical data from the Dead Sea rift and other transforms indicate that wrench-induced asymmetric basins are bounded on only one side by a transform fault. This implies that, during the evolution of such basins, maximum compression was parallel to the transform. The direction of extension can change during the geologic evolution of a basin. A possible explanation of this observation takes the strength of the fault into into consideration. In the case of a weak fault in a strong crust, the horizontal principal stresses would probably rotate to orientations parallel and perpendicular to the fault, thus minimizing the shear stress on the main fault. Basins formed by regional extension, such as in the East African rift system, sometimes show similar features. Recent studies have shown that these basins often undergo oblique extension. This suggests that the asymmet~ in these basins may result from simultaneous strike-slip motion and fault-no~ai extension, similar to the way as~rnet~ is produced in large transform basins. Periods of oblique extension can alternate with periods of orthogonal extension. The asymmetry formed during periods of oblique extension is often preserved in the stratigraphic record. Transform faults are often associated with sed- imentary basins of various sizes (e.g. Freund et al., 1970; Aydin and Nur, 1982; Mann et al., 1983). A large number of models have been de- veloped to explain the structural evolution of such basins. The most widely accepted are the stepover or pull-apart models. These modeIs sug- gest that basins are formed at places where bends or stepovers occur along the trace of the strike-slip faults, leading to en echelon segmentation of the faults. The models therefore predict that the two longitudinal sides of such basins would be Carres~~de~ce to: Z. Ben-Avraham, department of Geo- physics and Planetary Sciences Tel Aviv University, Tel Aviv 59978, Israel. bounded by strike-slip faults, while the transverse faults, which trend diagonally to the strike-slip faults, are predominantly normal faults (Aydin and Nur, 1985). According to these models, which are based on simple geometrical considerations, the transverse faults are somewhat secondary fea- tures, forming the complemental sides of a bend or a stepover across which the basin was ex- tended. An extensive review of the literature on pull- apart models is given by Christie-Blick and Bid- dle (1985). They classify them into theoretical and empirical models. The theoretical models are based on assumptions on the thermal and me- chanical properties of the lithosphere, while the empirical models are based on geological and geophysical data from different basins. The vari- ous models of pull-apart basins suggest that the bounding blocks are torsionally rigid and deform ~~-1951/92/$05.~ 0 1992 - Elsevier Science Publishers B.V. All rights reserved