БЪЛГАРСКО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, Национална конференция с международно участие „ГЕОНАУКИ 2017“ BULGARIAN GEOLOGICAL SOCIETY, National Conference with international participation “GEOSCIENCES 2017”

Deep seismic profile in the Rhodopes (S. ) and its conceptual significance Дълбочинен сеизмичен профил в Родопите (Ю. България) и неговото концептуално значение Khrischo Khrischev1, Stefan Shanov1, Stefka Pristavova2, Yotzo Yanev1 Хрисчо Хрисчев1, Стефaн Шанов1, Стефкa Приставова2, Йоцо Янев1

1 Bulgarian Geological Society; Acad. G. Bonchev str., bl. 24, 1113 ; E-mails: [email protected]; [email protected] 2 University of Mining and Geology “St Ivan Rilski”, 1 Prof. B. Kamenov str., 1700 Sofia; E-mail: [email protected]

Kеywords: deep seismic profile, оbduction, Rhodopes.

The most informative profile from deep seismic pro- testify to the sub-oceanic character of the crust. Four filing in the Rhodopes (Velev, 1996) is geologically plates are distinguished based on the patterns of seis- reinterpreted after complete processing and trans- mic reflections, as well as inner “discordances” and formation of time scale to metric one (Khrischev, surfaces of shearing, plus one upper plate with more Shanov, 2017). Thus, it is closer to the real struc- local distribution. tural pattern defining its conceptual significance. Surface outcrops, and the resulting dating of them The profile covers a small part of the Central have 4 plates (1st, 3rd, 4th, and 5th). The first three Rhodopes (east of Ardino), mainly crossing the of them are represented by high-grade metamorphites Eastern Rhodopes in East-West direction (Fig. 1). with radioisotopic ages of the protolites from Late The two tectonic units are highly distinguished by Proterozoic to Late Paleozoic: 1st plate, mel- their structure and by the nature of the Earth’s crust ange; 3rd plate, Byala Reka and Startsevo litho-tec- – continental or sub-oceanic, respectively, which tonic units; 4th plate, Krumovitsa litho-tectonic unit are clearly separated in the seismic record by the (Geological Map of Bulgaria, scale 1:50 000). The top degree of stratification and reflection of boundaries. plate is of anhimetamorphic volcanogenic sedimen- Both units are related by obduction (Kozhuharova, tary rocks of Triassic–Jurassic age. 1984; Velev, 1996). The plates 1, 2 and 3 have a community in their Interpretation. The Central Rhodopes, with a configuration, representing a common obduction phe- wide development of the granite-gneisses, have sig- nomenon. The lowest of them has the largest thickness nificant seismic transparency, marking the granitiza- (up to 7 km) and a complex internal structure with du- tion (mainly Hercynian according to the radioisotope rable sub-horizontal shear zones. Plate 4th is extreme- data – Geological Map of Bulgaria, scale 1:50 000 and ly different in position (horizontal, spatially sustained references therein). In the eastern direction, reflection and expressively discontinuous), thickness (several surfaces become more precise and expressive, indi- times less, ~1 km) and specific seismic record, testi- cating the probable framework of granite protoliths. fying to a complex rock structure (undefined reflec- Their convergence and wedging to the east suggests tion sites). This is a Later Alpine thrusting structure belonging to a continental margin. with a South thrusting direction (Geological Map of In the Eastern Rhodopes, the Earth’s crust beneath Bulgaria, scale 1:50 000). the Paleogene cover is dominated by metamorphic Other features identified by the seismic record are: rocks and has a complex internal structure. Almost • The nature of the obduction boundary – obliq