Lvaylovgrad and Krumovgraj Area S, East Rhodope Mountains
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GEOLOGICA BALCANICA, 22.3, Sofia, Jun. 1992, 3-31, Lithostra tigraphic features and structure of the Precam brian of the Rhodopian Supergroup in the lvaylovgrad and Krumovgraj area s, East Rhodope Mountains Dimitar K ozhoukharov Geological Institute, Bulgarian Academy of Sciences, 1113 Sofia (Rec<: iued 22. 04. 1991 ; accepted 15. 11 . 1991) fl.. Ko:HCyxapoa - Jlumocmpamuzpai/Ju'ieCKUe oco6etmocmu u cmpoenue PoaonCKOU cynepzpynnbl ao Ke.M6pUJl a Jfaau/IOazpaacKo.M u Kpy,«oazpaactwAt pauonax, Bocmo'inble Poaonbl . 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The Rhodopian Supergrt?_up is represented in the l vaylovgrad and Krumovgrad areas by the rocks of the Rupcos Group: the Cepelare Varied Formation, Bogutevo Plagiogneiss formation, and Vaca Varied Formation. The three formations are distinguished for the first time in this part of the East Rhodope Mountains. The Cepelare 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: Yailadzik Member (mainly gneissose), Tumbata Mcmber(schists to gneiss-schists) and Kamilskido l Member (predominantly am phi bolitic). The members are introduced here for the first time. The rocks of the three members in- 3 tcdinger to the west and southwest of the village Popsko with the undivisiblc Cepelare Formation from the Avreil s yncline. The Bogutevo a nd Vii ca Formations (in incomplete sections) haye a compo sition and characteristi c fea tures similar to that in the type area, ar. d differ from the typical develop ment by the increased amount and dimensions of the ultrabasic bodies. The rocks of the Rhodopian Supergroup are pol ymetamorphi c prod uc!s which in their present shape are a result of multi phase s uperposition of metamor phic alterations (different in type and inten sity) during the Preca mbrian and the Phanerozoic stages of their deYelopment. With the exception of the low-temperature h yd rothermal meta morphi sm (serpentinization) ilnd the early hi gh-baric meta morphism proven for the meta ultrabcsics and eclogites , the metamorphic processes in all other rock varieties had the following sequence: Precambrian regional a mphibolite fa cies metamorphism; Pre cambrian (Riphean) regional migma tization; regional greenschi st facies diaphthoresis (at the Precam brian - Phanerozoic boundary); Early Alpine meta morphism (pregraniti c, pre-Upper Cretaceous); contact metamorphism rel ated to the Upper Cretaceous? graniti c intrusions; Late Alpine (Paleocene - Qua ternary) dynamomctamorphism. Introduction The Precambrian metamorphic rocks in the Ivaylovgrad and Krumovgrad areas of the East Rhodope Mts are di stinguished from the Paleozoic and Mesozoic low-grade to anchimetamorphic rocks by almost all geologists working in that part of the Rho dope Massif (5I p a 11 o B, 1960; YI BaH o B, 1961; Eo 51 HoB 11 .n.p., 1963,1969; Eo51HOB, JlHnMaH, 1973; Ko)Kyxapos, Ko)Kyxapoaa, 1984; Eo- 51 H o B, P y c e a a, 1984). The present paper deals with the metamorphic rocks of the Rhodopian Supergroup which are widespread within the scope of Kami !sk i do l syncline and along the northern periphery of the Bjala reka structure. The rocks of the Rhodopian Supergroup have been distinguished and mapped as a constituent of the so-called Proterozoic structural stage during the geological map ping on the scale 1:25 000 (Eo 5I HoB et al., 1963) in 1958 and 1960 without sub eli vision into smaller units. On the basis of the same mapping results, Yl B a 11 o B (1961) included these rocks into a formation designated as "upper varied formation M']" and showed its distribution on a geological map in 1:200 000. The boundaries of Rhoclopian Supergroup have been later corrected and defined more accurately during the compilation of a geological map of the East Rhodope Mts on the scale 1:50 000 (I. Boyanov, D. Kozhoukharov, A. Gora~ov, Z. Mazni kov, G . V a I eva, M. S pi r i dono v a, M. R use v a, Z . .S i 1 j a f o v a, unpub lished map, 1980). The present paper is based on a project (D. K o z h o u k h a r o v, E. K o z h o u k h a r ova, I. Boyan o v, I. Zag or c e v, unpublished re port, 1985) on the composition, structure and metamorphism of the Precambrian complexes of the East Rhodope block. The detailed subdivision of the Rupcos Group in the area studied was carried out by the present author within the scope of this project. Lithostratigraphic features of the Rupcos Group The Rhodopian Supergroup is represented in the East Rhodope Mts only by the rocks of the Rupcos Group (K o )K y x a p o B, 1986). Formerly, the same rocks have been referred to the so-called "lower metamorphic series - upper varied formation Mj" (Yl B a H o E, 196 1) , "Proterozoic structural stage" (Eo 51 H o B et a!., 1963), "Rho dope crystalline-schist series - upper varied stage R 4" (I van o v, 1965), "Protero zoic complex - lower varied formation Pt" (K o )K y x a p o a, 1968), "Upper Rhoda pian complex- varied suite Pt1" (K o z h o u k h a r o v et al., 1974), etc. Almost all researchers mentioned refer the metamorphic rocks from the Kami ! ski dol syncline to a single formation stating that the varied rock compos ition makes impossible a more detailed subdivision. This concept has not been changed also during later studi es when these rocks have been shown in the same sense and volume on the unpublished geological map of the East Rhodope Mts by I. Boyan o vet al. (1980). 4 A new geological map of the area on the scale 1:25 000 was made by the author in the period 1981-1988; the Precambrian metamorphic sequence was subdivided into forma tions, members and packets. These I ithostratigraphic units are the subject of the pre sent paper. The Rhodopian Supergroup and the Rupcos Group have been introduced by K o - )I{ y x a p o B (1984) with type region in the Central Rhodope Mts. The Rupcos Group consists in the type region of the C:epelare Varied Formation, Bogutevo Plagiogneiss Formation and Vaca Varied Formation; their presence in the Avren syncline (East Rhodope Mts) has been found later (K o )I{ y x a p o B, 1987). The investigated part of the Kamilski dol syncline and the northern periphery of the Bjala reka structure is a prolongation of the rocks of the Avren syncline towards east-northeast. All three forma tions have been distinguished for the first time also in that area between the villages Padalo and Huhta . Cepelare Varied Formation The C:epelare Formation is named by YI BaH o Bet a!. (1980) and defined with a more complete section by K o )I{ y x a p o B (1984). Both in the type region and in the other outcrops of the formation in the Rhodope Massif (K o z h o u k h a r o v, 1988), as well as in the Avren syncline (K o )I{ y x a p o B, 1987) the C:epelare Formation re- 0 , CJ2 ~3 § t.