Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of left‐lateral transform motion between the African and Arabian plates since early Miocene (∼20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the μ m to the plate tectonic scale. We observe that under the DST a narrow, subvertical zone cuts through crust and lithosphere. First, from west to east the crustal thickness increases smoothly from 26 to 39 km, and a subhorizontal lower crustal reflector is detected east of the AF. Second, several faults exist in the upper crust in a 40 km wide zone centered on the AF, but none have kilometer‐size zones of decreased seismic velocities or zones of high electrical conductivities in the upper crust expected for large damage zones. Third, the AF is the main branch of the DST system, even though it has accommodated only a part (up to 60 km) of the overall 105 km of sinistral plate motion. Fourth, the AF acts as a barrier to fluids to a depth of 4 km, and the lithology changes abruptly across it. Fifth, in the top few hundred meters of the AF a locally transpressional regime is observed in a 100–300 m wide zone of deformed and displaced material, bordered by subparallel faults forming a positive flower structure. Other segments of the AF have a transtensional character with small pull‐aparts along them. The damage zones of the individual faults are only 5–20 m wide at this depth range. Sixth, two areas on the AF show mesoscale to microscale faulting and veining in limestone sequences with faulting depths between 2 and 5 km. Seventh, fluids in the AF are carried downward into the fault zone. Only a minor fraction of fluids is derived from ascending hydrothermal fluids. However, we found that on the kilometer scale the AF does not act as an important fluid conduit. Most of these findings are corroborated using thermomechanical modeling where shear deformation in the upper crust is localized in one or two major faults; at larger depth, shear deformation occurs in a 20–40 km wide zone with a mechanically weak decoupling zone extending subvertically through the entire lithosphere.
Geological and geochemical studies have been conducted on the Arava fault segment, which forms the major branch of the Dead Sea transform between the Dead Sea and the Gulf of Aqaba. Mesoscale to microscale faulting and veining related to this fault are described from limestone sequences of two locations (areas A and B) that represent different depth sections. In area A, pressure ridges expose the exhumed fault. Deformation mechanisms indicate that faulting took place at temperatures between 150°C and 300°C, which suggests faulting depths between 2 and 5 km with respect to published geothermal gradients. In area B, brittle fault damage forms a zone up to 150 m wide. The fault core is not exposed. Faulting took place at temperatures below 200°C (up to a 3‐km depth). In both areas, we found indications for a strong fault. Our kinematic analysis exhibits that the angle Ψ between δ1 and the strike of the Dead Sea transform immediately adjacent to the fault is ≤45°. The twin‐density technique yields differential stress values up to a peak stress of 200 MPa in fault rocks of area A. The strontium isotopic composition of vein fillings was used to demonstrate that the fluids were dominantly derived from stratigraphically younger carbonate units than the faulted rocks. Later generations of veins have more radiogenic 87Sr/86Sr, which is indicative for a derivation of fluids from stratigraphically increasingly higher levels as deformation progresses. For fluids expulsed by seismic pumping from marine carbonates, the variation of 87Sr/86Sr in vein calcites implies that (1) the expulsed fluids are replaced by fluids originating from stratigraphically higher reservoirs, (2) there was not enough time for isotopic strontium reequilibration between fluids and their new host rocks, requiring fractures to have been opened and closed within a geologically short interval, and (3) the most radiogenic 87Sr/86Sr, corresponding to the youngest fluid reservoir, yields a maximum age for the major activity along this fault. A 87Sr/86Sr value of 0.7081 for a fluid that equilibrated with marine carbonates corresponds to a maximum age at 30 Ma.
Integrated petrographic and chemostratigraphic studies have enabled the identification of sequence boundaries, sequence stratigraphy, and their system tracts for the Lower Cretaceous strata of the Kurnub Group (Jordan); the latter is underlain by the Jurassic (Callovian) strata and overlain by the Cretaceous (Cenomanian). Based on physical characteristics (sharp vertical facies changes) and geochemical parameters (SiO2/Al2O3, K2O/Al2O3, TiO2/Al2O3, Sr/Ca millimoles per mole, Mn parts per million, and the minor elements), 4 sequence boundaries are identified, associated with 11 facies types (from alluvial plain to the intertidal environment) and 9 system tracts, thus enabling the identification of record Lower Cretaceous sea-level fluctuations. The identified sequences mirror the Arabian plate sequences and suggest a eustatic origin. The siliciclastic Kurnub Group was derived mainly from felsic granite–gneiss and metasedimentary rocks (Arabian shield) and was deposited in a passive continental margin setting under semiarid-to-humid climatic conditions.
