Structural style variations along the Ionian fold and thrust belt

Abstract

The Hellenides of Western Greece is a salt detached fold and thrust belt which resulted from the inversion of the previous southern Neo-Tethys margin. Before the Paleogene and Neogene contractional deformation, the Ionian basin was formed during the Triassic to early Jurassic rifting, bounded by the Apulian and Gabrovo platforms to the west and to the east respectively. The structural style of Western Greece is largely controlled by the presence of Triassic evaporites flooring the sedimentary succession of the Ionian basin, while previous models invoked the existence of extensional faults affecting the Triassic to Jurassic succession as one of the main structural controls. Understanding the present contractional structure mainly depends on unraveling the geometry of the Mesozoic extensional system, the distribution of the salt horizon and the presence and geometry of salt structures preceding the contractional deformation. Based on an extensive field study carried out along the Ionian fold and thrust belt, we present several regional and local balanced cross-sections and define several characteristic structural templates resulting from of this area.Despite inversion tectonics and reactivated salt structures are common features in many salt-detached fold and thrust belts but no evidence for the presence of inherited (and inverted) Jurassic extensional faults was found. However, the deformational style was strongly controlled by significant changes in thicknesses involving the pre-contractional stratigraphic package, and suggesting the presence of pre-existing salt structures. The pre-shortening configuration was dominated by salt pillows and salt plateaus formed during the Triassic to early Jurassic rifting. As a result, we observe a significative change in the deformation style, from remarkable detachment folds, box-folds or inclined folds, to more wide and far-travelled thrust sheets formed in the areas with a thicker stratigraphy. Despite the stratigraphic thickness is reduced to few hundreds of meters in some cases,  diapirism is just related with the contractional stage, as a result of the squeezing of former salt pillows, and no evidence of precursor passive diapirs has been found.