Variscan ultra‐high‐pressure eclogite in the Upper Allochthon of the Rhodope Metamorphic Complex (Bulgaria)

Abstract

The Rhodope Metamorphic Complex (RMC) in Bulgaria has been established as a Mesozoic ultra‐high‐pressure metamorphic province by findings of microdiamond in gneisses. Additionally, Variscan ultra‐high‐pressure metamorphism has been proposed for the Ograzhden/Vertiskos Unit in the Upper Allochthon of the RMC, based on findings of coesite, graphite pseudomorphs after diamond and indirect age constraints. We confirm ultra‐high‐pressure metamorphism of eclogites in this unit using thermobarometry, phase‐equilibrium modelling and the Variscan age of metamorphism using Lu–Hf garnet–whole‐rock dating. In Belica (southern Rila Mountains), kyanite‐ and phengite‐bearing eclogite enclosed in high‐grade gneisses records P‐T conditions of 3.0–3.5 GPa and 700–750°C. Lu–Hf dating of eclogite samples from Belica and Gega (Ograzhden Mountain), where coesite was found, yielded ages of 334.1 ± 1.8 and 334.0 ± 2.2 Ma, respectively, interpreted as the age of garnet growth during post‐collisional subduction of continental crust after closure of the Rheic Ocean.