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.