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Dead sea, kinematic analysis, Gulf of Aqaba, Arava fault segment
DDC:
550 - Earth sciences
Abstract:
Geological and geochemical studies have been conducted on the Arava Fault segment, which forms the major branch of the Dead Sea Transform fault between the Dead Sea and the Gulf of Aqaba. Meso- to micro-scale faulting and veining related to this large-scale deformation is described from limestone sequences of two locations (area A and B) that represent different depth-sections. In both areas, we found indications for a strong fault. Our kinematic analysis exhibits a 1 axis that is around 45° to the fault plane and high shear stress magnitudes (up to 100 MPa) were derived from microstructures. In area A, pressure ridges expose the exhumed fault. Deformation mechanisms indicate that faulting took place at temperatures between 150 and 300°C 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. Cross-cutting relations between veins and fractures, different cathodoluminescence colors in vein cements and sedimentary matrix allow the tracing of the temporal evolution of the fault. All these features reflect the multiple reactivation of the fault and the cyclic nature of earthquake faulting processes. 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 (i) the expulsed fluids are replaced by fluids origi nating from stratigraphically higher reservoirs, (ii) there was not enough time for isotopic Sr-reequilibration between fluids and their new host-rocks, requiring fractures to have been opened and closed within a geologically short interval, and (iii) 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 of 30 Ma.
