The Dead Sea Transform: Evidence for a Strong Fault?

DEAD Sea (Israel & Jordan); GULF of Aqaba; ISRAEL; JORDAN; MIDDLE East

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 &delta1 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. [ABSTRACT FROM AUTHOR]

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