Monocline

Abstract: Field data from the Oligocene–Miocene Gulf of Suez rift demonstrate that coeval growth faults, folds, and transfer zones exerted a major control on synrift stratigraphic sequence development. Growth folds in the Suez rift are related to steeply dipping normal faults that propagated upward, resulting in broad, upward-widening monoclines in overlying strata. Folding during fault propagation was accommodated by layer-parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault. The eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall. This evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments. Synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults, whereas they diverge into broadly synclinal expanded sections away from the growth monocline. Continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments, each successively younger sequence dipping basinward at a shallower angle than the previous one. The resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults. Along-strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low-relief transfer zones. Data from other rift basins indicate that fault-propagation folds are not unique to the Gulf of Suez.

Abstract: The Etna volcano is located in an apparently anomalous position on the hinge zone of the Apennines subduction and its Na-alkaline geochemistry does not favour a magma source from the deep slab as indicated for the Aeolian K-alkaline magmatism. The steeper dip of the regional foreland monocline at the front of the Apennines in the Ionian Sea than in Sicily, implies a larger rollback of the subduction hinge in the Ionian Sea. Moreover, the lengthening of the Apennines arc needs extension parallel to the arc. Therefore, the larger southeastward subduction rollback of the Ionian lithosphere with respect to the Hyblean plateau in Sicily, should kinematically produce right-lateral transtension and a sort of vertical ‘slab window’ which might explain (i) the Plio-Pleistocene alkaline magmatism of eastern Sicily (e.g. the Etna volcano) and (ii) the late Pliocene to present right lateral transtensional tectonics and seismicity of eastern Sicily. The area of transfer of different dip and rollback occurs along the inherited Mesozoic passive continental margin between Sicily and the oceanic Ionian Sea, i.e. the Malta escarpment.