Late Cretaceous eclogite in the Eastern Rhodopes (Bulgaria): evidence for subduction under the Sredna Gora magmatic arc

The Rhodopes in Bulgaria and Greece represent a nappe stack of high-grade units with polymetamorphic history. Constraining the time of metamorphism in individual subunits is essential for unraveling the controversial framework of subduction, exhumation and nappe stacking. Here we present new evidence for Late Cretaceous high-pressure metamorphism in the Eastern Rhodopes. In eclogite from the Byala Reka-Kechros Dome (Kazak eclogite), garnet growth is dated at 81.6 +/- 3.5 Ma by Lu-Hf chronometry, indicating that prograde eclogite-facies metamorphism occurred during the Late Cretaceous. Petrological data and modeling suggest peak-pressure conditions of 1.2-1.6 GPa, 570-620 A degrees C. We propose that metamorphism took place in a subduction zone dipping towards north under the Sredna Gora section of the Apuseni-Banat-Timok-Sredna Gora continental magmatic arc. Eclogite-facies metamorphism coincides with the main phase of granitoid intrusions in the Sredna Gora Zone. The site of magmatic activity in this area shifted southward during the Late Cretaceous and arrived in the Eastern Rhodopes at similar to 69 Ma, as shown by granite intrusions of that age only 4 km north of the locality of the dated eclogite sample. This proximity may be explained by south-directed rollback of the subduction zone, although also post-69 Ma tectonic displacement has to be considered. Together with published age data from other parts of the Rhodopes, the new data confirm that multiple subduction events took place between similar to 200 and similar to 40 Ma along this section of the southern European plate boundary