Thermomechanical model reconciles contradictory geophysical observations at the Dead Sea Basin

Abstract

[1] The Dead Sea Transform (DST) comprises a boundary between the African and Arabian plates. During the last 15-20 m.y. more than 100 km of left lateral transform displacement has been accumulated on the DST and about 10 km thick Dead Sea Basin (DSB) was formed in the central part of the DST. Widespread igneous activity since some 20 Ma ago and especially in the last 5 m.y., thin (60-80 km) lithosphere constrained by seismic data and absence of seismicity below the Moho, seem to be quite natural for this tectonically active plate boundary. However, surface heat flow values of less than 50-60 mW/m 2 and deep seismicity in the lower crust (deeper than 20 km) reported for this region are apparently inconsistent with the tectonic settings specific for an active continental plate boundary and with the crustal structure of the DSB. To address these inconsistencies which comprise what we call the "DST heat-flow paradox," we have developed a numerical model that assumes an erosion of initially thick and cold lithosphere just before or during the active faulting at the DST. The optimal initial conditions for the model are defined using transient thermal analysis. From the results of our numerical experiments we conclude that the entire set of observations for the DSB can be explained within the classical pull-apart model assuming that the lithosphere has been thermally eroded at about 20 Ma and the uppermost mantle in the region have relatively weak rheology consistent with experimental data for wet olivine or pyroxenite.

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

“…Thermomechanic simulations also suggest that the DSB can be considered as a classical pull-apart basin, assuming that the lithosphere was thermally eroded at about 20 Myr. and an uppermost mantle with relatively weak rheology, which would be consistent with lab data for wet olivine or pyroxenite (Petrunin et al 2012). In addition, the low friction coefficients required to model the architecture of the DSB thermomechanically and the high subsidence rate of the basin sediments suggest the presence of hydrous minerals within the FZC.…”

“…Alteration of granitic rocks which include Feldspar to varieties of hydrous minerals including Muscovite have been observed at deeper levels in many fault zones (Etheridge et al 1983;Bruhn et al 1990). Based on thermomechanic modelling, Petrunin et al (2012) suggested that the state of the DSB as a classical pull-apart basin can be explained by thermal erosion of the lithosphere before approximately 20 Myr. As a consequence, we would expect relatively weak rheology of the uppermost mantle which would be consistent with the occurrence of wet olivine or pyroxenite (Petrunin et al 2012).…”

“…Based on thermomechanic modelling, Petrunin et al (2012) suggested that the state of the DSB as a classical pull-apart basin can be explained by thermal erosion of the lithosphere before approximately 20 Myr. As a consequence, we would expect relatively weak rheology of the uppermost mantle which would be consistent with the occurrence of wet olivine or pyroxenite (Petrunin et al 2012).…”

“…Thermomechanic modelling by Sobolev et al (2005) suggested that shear deformation is localized in a 20-40 km wide zone around the DST, with the resulting mechanically weak decoupling zone extending subvertically through the entire lithosphere. Petrunin et al (2012) showed that the DSB can be considered as a classical pullapart basin, assuming that the lithosphere was thermally eroded at about 20 Myr. and an uppermost mantle with relatively weak rheology, which would be consistent with lab data for wet olivine or pyroxenite.…”

Seismic structure beneath the Gulf of Aqaba and adjacent areas based on the tomographic inversion of regional earthquake data

“…Most scholars associate the origin of deep linear depressions along the DST, such as the Gulf of Aqaba and the Dead Sea, with the pullapart mechanism (Mann et al, 1983;Makovsky et al, 2008;Petrunin and Sobolev, 2008;Hartman et al, 2014). In this context, lateral displacements along a non-straight fault line should lead to the origin of compression and extension zones at the vicinity of the fault, and many studies have used both numerical modeling (Petrunin and Sobolev, 2008;Petrunin et al, 2012) and geological evidence (Ehrhardt et al, 2005) to demonstrate the possibility of such a scenario. Alternatively, the origin of the present depressions along the DST can be explained by the relative transform-normal extension (Ben-Avraham and Zoback, 1992;Smit et al, 2010) due to relocation of the pole of rotation for the DST at about 5 Ma (Garfunkel, 1981).…”