Physical Modeling of Salt Tectonics in the Eastern Nile Deep-Sea Fan

By

 Bruno C. Vendeville¹, Lies Loncke², Virginie Gaullier³, Jean Mascle⁴

(1) University of Texas at Austin, Austin, TX (2) Géosciences Azur, 06235 Villefranche-sur-mer, France (3) LSM, Perpignan, France (4) Geosciences Azur, 06235 Villefranche-sur-Mer, France

 The present-day setting of the eastern Mediterranean includes the combined influences of thick-skinned, crustal-scale tectonics and thin-skinned, gravity-driven spreading of the Messinian evaporites and their Plio-Pleistocene overburden. The west and north parts of the Nile deep-sea fan show salt-related structures typical of those found on other salt-bearing passive margins. In contrast, the structural pattern of the east part of the fan is drastically different. The eastern part comprises a long (>200 km) NW-SE deformation corridor trending obliquely with respect to the slope direction. Along dip, the corridor exhibits a structural progression typical of salt-bearing passive margins, including small distal buckle folds, midslope minibasins surrounded by salt ridges, and proximal normal growth faults. Less typical is the corridor’s being bounded by narrow, NW-SE fault zones underlain by narrow salt ridges. We used physical models to test whether such pattern was caused by the presence of NW-SE dormant or active subsalt relief or of a bathymetric high (the Eratosthenes seamount) acting as a buttress during spreading. Model results clearly indicate that the presence of a passive subsalt relief and/or of a buttress, rather than that of an active subsalt relief, has caused this peculiar structural pattern. Early gravity spreading caused radial thin-skinned extension and the formation of minibasins and NW-SE and ENE-WSW salt ridges, a pattern also enhanced if basement steps are present. Later, buttressing by the seamount opposed further northeastward extension. The salt and overburden spread northwestward, reactivating the NW-SE salt ridges as strike-slip zones bounding the corridor.