Abstract
AbstractThe 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.
Highlights
Ultra-high-pressure (UHP) metamorphism records deep burial of crustal material during subduction and collision
The Rhodope Metamorphic Complex (RMC) in Bulgaria has been established as a Mesozoic ultra-high-pressure metamorphic province by findings of microdiamond in gneisses
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
Summary
Ultra-high-pressure (UHP) metamorphism records deep burial of crustal material during subduction and collision. Evidence for UHP metamorphism was found in the Eastern, Central and Western Rhodopes (Figure 1) and is probably Jurassic, between 200 and 150 Ma (Bauer et al, 2007; Liati et al, 2011; Nagel et al, 2011; Petrík et al, 2016). Zircons from two metagranites in this area yielded Ordovician protolith ages of 456.1 ± 1.8 and 452 ± 14 Ma and zircons from a metagabbro 454.1 ± 8.3 Ma (Peytcheva et al, 2009) Another Ograzhden outlier occurs near Belica (Figure 1) at the northern end of the Mesta Graben, on the southern slopes of the Rila Mountains. Kydonakis et al (2015) studied garnet-kyanite mica schists from the Vertiskos Unit and demonstrated eclogite-facies conditions They suggested the schists to originally represent the Mesozoic cover of the Vertiskos basement and that the eclogite-facies metamorphism is Mesozoic in age.
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