The Mallorca stranded and extended foreland thrust belt, its missing hinterland and the tectonic evolution of the Western Mediterranean

The Mallorca Foreland Thrust Belt (FTB) is stranded in the Western Mediterranean, isolated among deep basins from its corresponding hinterland domain. Here we integrate new structural data from Mallorca with preliminary detrital zircon data and previously published stratigraphic, paleontological, biogeographic and tectonic constraints, to provide a new tectonic evolutionary model for the Western Mediterranean. Mallorca underwent two Cenozoic rifting phases in the Oligocene and Serravallian, before and after the development of its FTB structure. The first Cenozoic extensional event produced Oligocene to Early Miocene semigrabens coeval to felsic volcanism in Mallorca and the Valencia trough (»29-19 Ma). The Oligocene extension affected a major part of the Western Mediterranean, opening the Liguro-Provençal and other back-arc basins after the collapse of the Palaeogene AlKaPeCa orogen, and Mallorca, its former hinterland. Continued plate convergence inverted the Oligocene back-arc basin, and onshore grabens during the Early-Middle Miocene (19-14 Ma), producing the Mallorca FTB and nucleating a new subduction system in the Westernmost Mediterranean. Renewed subduction probably initiated through the collapse of a NW-SE trending transform fault, inherited from the Mesozoic opening of the Tethys ocean. Development of the Mallorca WNW-directed FTB and subduction of the South-East Iberian passive margin occurred at this stage, individualizing the Betic-Rif slab that initiated its westward retreat. Moreover, detrital zircon age-population data show that the Betic and Mallorca foreland basins shared the same hinterland, equivalent to rocks of the Malaguide complex, located at the top of the AlKa orogenic domain. A later, second rifting event produced the extensional collapse of the Mallorca FTB during the Serravallian (»14-11 Ma), coeval to topographic uplift of the Island. This later rifting was polyphasic, with two orthogonal extensional systems, producing first NE-SW, and then NW-SE extension that favored the development of continental internal drainage basins. These basins shared common insular fauna with those overlying the Alboran domain in the Internal Betics, probably forming part of the same emerged archipelago, which is further supported by biogeographic data indicating a Middle Miocene common ancestry for several taxa now present in the Betics and Mallorca. Serravallian extension occurred at the northern edge of the subduction system coeval to the Algero-Balearic basin opening. Extension initiated towards the SW direction of slab tearing or detachment, and later rotated to a NW-SE direction, probably in response to flexural and isostatic rebound. This tectonic response propagated to the Betics between the Late Tortonian and Present. By these tectonic mechanisms, including slab retreat, edge delamination under continental FTB areas of the orogen and slab tearing, the Mallorca hinterland was driven towards the southwest, contributing to the present isolation of Mallorca from its Betic hinterland.