The western Mediterranean is composed by irregular troughs formed as back- arc basins in the hangingwall of the west-directed Apenninic subduction which retreated eastward during Neogene and Quaternary times. The basins are progressively younger toward the east aging from Late Oligocene-Early Miocene (Valencia, Provençal, Alboran and Algerian basins), to Late Miocene-Pleistocene (Tyrrhenian sea). The basins isolated boudins of continental lithosphere and the Sardinia-Corsica continental block represents the largest one. The boudinage has a range of 100-400 km of wavelength and it arrived to complete stretching of the continental lithosphere with formation of new oceanic crust in the Provençal, Algerian, Vavilov and Marsili basins. The boudins developed both in the earlier Alpine-Betic orogen (Alboran basin) and in its foreland (Provençal and Valencia troughs). The extension appears clearly asymmetric due to its eastward polarity, accommodated by east-dipping master low-angle normal faults. Moreover the thinning shows variations in the boudinage wavelength and it is also characterized by several along strike transfer zones and heterogeneities. The western Mediterranean back-arc setting is comparable with Atlantic and western Pacific back-arc basins associated with west-directed subduction zones that show similar large scale lithospheric boudinage.
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