LITHOSPHERIC BOUDINAGE IN THE WESTERN MEDITERRANEAN BACK-ARC BASIN

The western Mediterranean is composed of irregular troughs formed as b ack-are basins in the hanging wall of the W-directed Apenninic subduct ion which retreated eastward during Neogene and Quaternary times. The basins are progressively younger toward the east, ageing from late Oli gocene-early Miocene (Valencia, Provencal, Alboran and Algerian basins ), to middle Miocene-Pleistocene (Tyrrhenian Sea). The basins isolated boudins of continental lithosphere, the Sardinia-Corsica block repres enting the largest. The boudinage has a wavelength of 100-400 km and f acilitated stretching of the continental lithosphere with formation of new oceanic crust in the Provencal, Algerian, Vavilov and Marsili bas ins. The boudins developed both in the earlier Alpine-Betic orogen (Al boran basin) and in its foreland (Provencal and Valencia troughs). The extension appears clearly asymmetric due to its eastward polarity, ac commodated by E-dipping master low-angle normal faults. Moreover the t hinning shows variations in boudinage wavelength and is characterized by several along-strike transfer zones and heterogeneities. The wester n Mediterranean back-are setting is comparable with Atlantic and weste rn Pacific back-are basins associated with W-directed subduction zones that show similar large-scale lithospheric boudinage.