The rift-like structure and asymmetry of the Dead Sea Fault
Introduction
Together with the San Andreas Fault and the Alpine Fault of New Zealand, the Dead Sea Fault (DSF) (also known as Dead Sea Transform or Rift, Levant Fault, among others) (Fig. 1, Fig. 2) is one of the most prominent continental transform faults in the world (e.g. Quennell, 1959, Wilson, 1965, Niemi et al., 1997, Cloetingh & Ben-Avraham, 2002). It relates the opening of the Red Sea, to the south, to the Bitlis–Zagros collision, to the North, and has accommodated ca. 107 km of sinistral displacement between the Arabian and African plates since 13–18 Ma (e.g. Quennell, 1959, Freund, 1965, Freund et al., 1968, Dubertret, 1970, McKenzie et al., 1970, Garfunkel & Ben-Avraham, 2001, Ben-Avraham et al., 2008). The southern section of the DSF, from the Hula Basin to the Gulf of Aqaba, forms a 5 to 20 km wide morphological depression with a number of basins that are bordered by uplifted margins (Fig. 3, Fig. 4) (e.g. Quennell, 1958, Wdowinski & Zilberman, 1997). The resemblance of this morphology to rift valleys, in particular the East African rift, has caused a long-running debate concerning the formation of the rift valley along the already active transform fault. Subsidence of the valley, uplift of its shoulders and formation of the pull-apart basins initiated around 5 Ma ago, contemporaneous with a change in kinematics of the Arabian plate that added a small transtensional component to the ongoing strike-slip movement along the DSF.
The present paper aims to experimentally test the relation between this two-phase scenario and the structure and asymmetry of the DSF. For this purpose, we performed three dimensional analogue tectonic experiments using a layered brittle–ductile system. This method has been successfully applied to crustal- and lithosphere-scale tectonics for more than 20 years (see review in Brun, 2002). Previous particular applications to the Dead Sea Basin addressed the mechanics of pull-apart basin development including the formation of pull-apart basins in narrow transfer zones (Smit et al., 2008a, Smit et al., 2008b). The following summary of the DSF concentrates on the features that have been taken into account in the modelling study.
Section snippets
Rift-valley morphology
The southern segment of the DSF is marked by an almost continuous valley, with a series of deep pull-apart basins that are separated by less pronounced saddles. These structures are controlled by longitudinal en-echelon faults on which lateral motion takes place (e.g. Garfunkel, 1981, Garfunkel & Ben-Avraham, 2001). The so-called rift valley is bordered by steep faults along which the valley subsided and its flanks uplifted (Quennell, 1958, Quennell, 1959, Wdowinski & Zilberman, 1997) (Fig. 3).
Laboratory experiments
The aim of this experimental study is to provide an independent test whether the rift-like morphology of the Dead Sea Fault can be formed as the result of a late-stage transtension. We explicitly do not aim to rule out other hypotheses. Our 3D-laboratory experiments are complementary to recent 2.5D numerical experiments of the Dead Sea Fault (Sobolev et al., 2005, Petrunin & Sobolev, 2008). As pointed out by these authors, a fully 3D-modelling approach is required to study the effects of
Structural development and asymmetry
Successive stages of evolution of the model with intermediate brittle–ductile coupling are shown in Fig. 6. The fault zone develops similar to a classical Riedel shear-box experiment during phase 1 (e.g. Tchalenko, 1970). En-echelon Riedel shears (R) initiate at a 15° angle to the movement direction, followed by interconnecting P-shears in association to pop-up structures. As deformation continues, Y-shears parallel to the displacement form two nearly continuous fault zones defining a narrow
Application of experimental results to the Dead Sea Fault
During the first phase (ca. 13–5 Ma) the in total ca. 65 km strike-slip movement creates a faulted corridor with at the surface a width of ca. 10 km, which extends downward in the lithospheric mantle (Fig. 8A). The adopted kinematic change of the Arabian plate ca. 5 Ma ago, adds a small component of transverse extension (max. 4 km during 40 km of strike-slip displacement (Fig. 8B)). As a result, the lithospheric mantle undergoes a dominant strike-slip shear (Fig. 8C) causing the detected seismic
Conclusions
Laboratory experiments and their comparison with the most striking features of the DSF suggest that the rift-like morphology is a logical consequence of a change in plate kinematics ca. 5 Ma ago. The addition of even a minor component of transverse extension is sufficient to explain the rift-like morphology and structure of the DSF strike-slip fault zone, with a maximum strike-slip/extension displacement ratio of 0.1. The models indicate that the near vertical faults that delineate the rift
Acknowledgements
We thank J.-J Kermarrec, J. Vink and N. van Harlingen for their assistance in setting up experiments. L. Matenco and C. Gumiaux are thanked for their help in figure preparation. J.S acknowledges financial support from the Netherlands Research Centre for Integrated Solid Earth Sciences (ISES) and a Marie Curie Fellowship in the framework of the European Doctoral Training Centre for Sedimentary Basin Studies (Eurobasins). We benefitted from constructive criticism by two anonymous reviewers.
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