Author:
Macheva Lyubomirka,Machev Philip,Plotkina Julia,Salnikova Еkaterina,Stifeeva Maria
Abstract
The eclogites from Sredna Gora Mts. occur as small isolated bodies enclosed in amphibolites, two-mica schists and migmatized gneisses. They have tholeiitic composition and characteristics of MOR basalts. Three equilibrium mineral associations are distinguished in eclogites: (1) high-pressure (HP) – Grt+CPx(Omp)+Zo+Rt; (2) middle-pressure-high temperature (MP/HT) – Opx+CPx+Pl and middle pressure – middle temperature (MP/MT) presented by Amp+Pl+Qzt+Ep+Ilm+Ttn. The P-T conditions of HP stage reached values of 1.6–2.02 GPa and 650–690 °С. After the HP stage and CPx-Pl symplectite formation, the eclogites underwent a short-lived granulite facies overprint under temperatures similar to those of the HP event. The P-T conditions of the retrograde amphibolite facies overprint are in the range 620–650 °C and 0.6–0.8 GPa. The obtained age of 319±28 Ma by Sm-Nd garnet+whole rock method is interpreted as age of the final retrograde metamorphism under P-T conditions of high temperature amphibolite facies.
Publisher
Bulgarian Geological Society
Reference24 articles.
1. An, S.-C., S.-G. Li, Z. Liu. 2018. Modification of the Sm-Nd isotopic system in garnet induced by retrogressive fluids. – J. Metam. Geology, 36, 1039–1048; https://doi.org/10.1111/jmg.12426.
2. Antonov, M., S. Gerdjikov, L. Metodiev, Ch. Kiselinov, V. Sirakov, V. Valev. 2010. – Explanatory Note to the Geological Map of the Republic of Bulgaria in scale 1: 50 000. Map Sheet K-35-37-B (Pirdop). Sofia, Ministry of Environment and Water, Bulgarian Geological Survey, 99 p.
3. Blundy, J. D., T. J. B. Holland. 1990. Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer. – Contrib. Mineral. Petrol., 104, 208–224; https://doi.org/10.1007/BF00306444.
4. Bucher, K., M. Frey. 1994. Petrogenesis of Metamorphic Rocks. Berlin, Springer-Verlag, 317 p.
5. Carrigan, C. W., S. B. Mukasa, I. Haydoutov, K. Kolcheva. 2005. Age of Variscan magmatism from the Balkan sector of the orogen, central Bulgaria. – Lithos, 82, 125–147; https://doi.org/10.1016/j.lithos.2004.12.010.