Review articleSalt tectonics in pull-apart basins with application to the Dead Sea Basin
Introduction
Since the seventies, the development of structures within pull-apart basins has been extensively described in great detail from numerous field examples (see reviews by Crowell, 1974, Sylvester, 1988) and laboratory experiments or theoretical studies (e.g. Wilcox et al., 1973, Rodgers, 1980). In contrast, the case of pull-apart basins involving a salt layer has never been specifically considered. At the same time, salt tectonics has been studied mostly in large salt basins and in particular passive margins like those of the Gulf of Mexico (e.g. Diegel et al., 1995, Rowan et al., 2004,) or Southern Atlantic (e.g. Mohriak et al., 1995, Marton et al., 2000, Fort et al., 2004). During the two last decades, the analogue modelling of salt tectonic processes in various tectonic environments, generated mechanically-based data bases for the interpretation of salt structures, either extensional (Vendeville and Jackson, 1992, Jackson and Vendeville, 1994, Mauduit and Brun, 1998) or contractional (Brun and Fort, 2004). The Dead Sea Basin provides a well-studied example of pull-apart basins that displays a broad variety of salt structures rather well documented by field and seismic studies (Neev and Hall, 1979, Ben-Avraham et al., 1993, Ten Brink and Ben-Avraham, 1989, Ben-Avraham, 1997, Gardosh et al., 1997, Al-Zoubi and Ten Brink, 2001, Larsen et al., 2002, Weinberger et al., 2006a, Weinberger et al., 2006b).
In the present paper, we address the nature and mechanics of salt tectonics in pull-apart basins. We begin with a review of salt-related structures in the Dead Sea Basin. Subsequently, we present specifically designed laboratory experiments to provide a general analysis of salt tectonics in pull-apart basins. We demonstrate that when the basin fill is decoupled from the underlying basement by a salt layer in an elongated pull-apart basin, it remains frictionally coupled to the boundary blocks. The basin fill, therefore, undergoes a strike-slip shear couple that simultaneously generates en échelon fold trains and oblique normal faults, trending mutually perpendicular. These findings confirm that salt tectonics of the Dead Sea Basin is a direct consequence of sinistral strike-slip shear.
Section snippets
Tectonic framework
The Dead Sea Transform (DST) relates the opening of the Red Sea to the Taurus–Zagros collision, to the North. Since ca. 13 Ma, it has accommodated an amount of 107 km of sinistral displacement between the Arabian and African plates (e.g. Quennell, 1958, Quennell, 1959, McKenzie et al., 1970, Le Pichon and Gaulier, 1988). Coeval with the onset of oceanic accretion in the Red Sea and the initiation of the East and North Anatolian faults, a number of pull-apart basins initiate along the DST, among
Salt structures in the Dead Sea Basin
Characteristic structures related to salt tectonics in the Dead Sea Basin fall into four main categories: Salt diapirs that cut through the sedimentary layers, salt walls that drape some faults, low-amplitude salt ridges and rollovers associated with growth faults.
Experimental procedure
The modelling presented here simulates a pull-apart basin with syn-kinematic sedimentation during which ductile material is deposited into the basin to represent a salt layer. As in many previous studies of pull-apart basin development (e.g. Faugère et al., 1986, Jolivet et al., 1991, Basile and Brun, 1999, Sims et al., 1999) the present experiments are carried out using a classical Riedel shear box in which deformation is induced at the base of an 8-cm-thick sand layer by the displacement of a
Discussion of experimental results
The above models display three main types of structures related to interactions between sedimentation and deformation during the evolution of a pull-apart salt basin: en échelon folding that can almost evolve into diapirs, normal faulting and strike-slip faulting with a dip-slip component. To explain the synchronous development of this large variety of structures, two types of boundary conditions must be taken into account (Fig. 13).
First, in the central part of an elongated pull-apart
Implications for salt tectonics in the Dead Sea
As pointed out above, salt structures in the Dead Sea Basin are salt diapirs, in particular the large Sedom and Lisan diapirs, salt walls, en échelon salt ridges, and rollovers associated with oblique normal faults inside the basin. Most of these structures compare well to the experiments presented in this paper.
In the southern part of the basin, where the salt layer is thick (> 1 km.; Larsen et al., 2003), the Sedom diapir is an extensional diapir elongated parallel to the western border fault
Conclusions
Laboratory models that have been carried out to simulate salt tectonics within a pull-apart basin lead to the following guidelines:
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In the central part of an elongated pull-apart structure the basin fill is decoupled from the underlying basement by a salt layers but frictionally coupled to the boundary blocks. Consequently, the cover undergoes a strike-slip shear couple that can simultaneously generate en échelon fold trains and normal faults, trending mutually perpendicular. Extreme stretching
Acknowledgements
We thank J.-J Kermarrec for his help in setting up experiments. J.S acknowledges the financial support from the Netherlands Research Centre for Integrated Solid Earth Sciences (ISES) anda Marie Curie Fellowship in the framework of the European Doctoral Training Centre for Sedimentary Basin Studies (Eurobasins). JPB acknowledges financial support from The Institut Universitaire de France.
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