Lithostratigraphic features and structure of the Precambrian of the Rhodopian Supergroup in the Ivaylovgrad and Krumovgrad areas, East Rhodope Mountains

Abstract

The Rhodopian Supergroup is represented in the lvaylovgrad and Krumovgrad areas by the rocks of the Rupčos Group: the Čepelare Varied Formation, Bogutevo Plagiogneiss formation, and Vâča Varied Formation. The three formations are distinguished for the first time in this part of the East Rhodope Mountains. The Čepelare Formation occurs here in a more specific manner. Three members are gradually outlined from the west to the east between the villages Padalo and Kamilski Dol. They have also a varied composition, but each of them is dominated by a particular rock variety: Yailadžik Member (mainly gneissose), Tumbata Mcmber (schists to gneiss-schists) and Kamilskidol Member (predominantly am phibolitic). The members are introduced here for the first time. The rocks of the three members interfinger to the west and so uthwest of the village Popsko with the undivisible Čepelare Formation from the Avren syncline. The Bogutevo and Vâča Formations (in incomplete sections) have a composition and characteristic features similar to that in the type area, and differ from the typical development by the increased amount and dimensions of the ultrabasic bodies. The rocks of the Rhodopian Supergroup are polymetamorphic products which in their present shape are a result of multiphase superposition of metamorphic alterations (different in type and intensity) during the Precambrian and the Phanerozoic stages of their development. With the except ion of the low-temperature hydrothermal metamorphism (serpentinization) and the early high-baric metamorphism proven for the metaultrabasics and eclogites, the metamorphic processes in all other rock varieties had the following sequence: Precambrian regional amphibolite facies metamorphism; Precambrian (Riphean) regional migma tization; regional greenschist facies diaphthoresis (at the Precambrian – Phanerozoic bound ary); Early Alpine metamorphism (pregranitic, pre-Upper Cretaceous); contact metamorphism related to the Upper Cretaceous granitic intrusions; Late Alpine (Paleocene – Quaternary) dynamomctamorphism.