BACK-ARC EXTENSION AND DENUDATION OF MEDITERRANEAN ECLOGITES

Eclogite-facies rocks exposed in Mediterranean back arcs are delimited from above by low-angle normal faults and detachments. Nevertheless, our work demonstrates that these extensional structures associated wit h back arc extension played only a limited role in removing the overbu rden from above the eclogites. Extension in Mediterranean back arcs be gan in the late Oligocene or early Miocene, but the pressure - tempera ture - time (P-T-t) paths of eclogite-facies rocks exposed in these ar eas indicate that a major part of the overburden, several tens of kilo meters, has been removed from above these rocks prior to the Oligo-Mio cene. We show that the time period bracketed between the peak of eclog ite metamorphism (Eocene in the central Aegean, probably Upper Cretace ous in Corsica and the Betics) and the onset of back are extension in the Oligo-Miocene was characterized by thrust faulting. In the central Aegean, Corsica, and the Betics, eclogite-bearing units were partly u nroofed and then overthrusted lower-pressure units. We emphasize that, with one exception (Tinos island, Greece), the entire inventory of ex tensional contacts operated subsequently to the overthrusting of the e clogites above the lower-grade sequences. Thus Mediterranean back arc extension lags behind a major part of the denudation process, and is s uperposed on orogenic wedges that contain eclogite-facies rocks at rel atively shallow structural levels. We emphasize that the mode of occur rence of eclogites in Mediterranean back arc regions involves a contin uum of in - situ crustal accretion below the eclogites, widespread P-T paths that show cooling or isothermal decompression, and lower-grade rocks at the bottom of the structural pile. Thus instead of reflecting whole - crust back arc extension, the tectonic style associated with the denudation of Mediterranean eclogites better fits an active accret ionary-wedge setting. This is similar to the mode of occurrence of ecl ogite-facies rocks in mountain belts, such as the western Alps, where decompression was synorogenic and back arc extension played no role.