СПИСАНИЕ НА БЪЛГАРСКОТО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, год. 79, кн. 3, 2018, с. 75–76 REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 79, part 3, 2018, p. 75–76 National Conference with international participation “GEOSCIENCES 2018”

The Plakalnitsa Fault Zone characteristics in the area of Dragoybalkan ridge, West Характеристика на Плакалнишката разломна зона в района на Драгойбалканския рид, Западна България Zornitsa Dotseva, Dian Vangelov, Ianko Gerdjikov Зорница Доцева, Диан Вангелов, Янко Герджиков

Sofia University “St. Kliment Ohridski”, Faculty of Geology and Geography, 1000 ; E-mail: [email protected]

Keywords: Plakalnitsa fault zone, Dragoybalkan ridge, polyphasal deformation.

The Plakalnitsa Fault Zone (PFZ) is one of the most facies volcano-sedimentary complex (Cambrian–Or­ prominent tectonic boundaries on the territory of dovician?) and intruded into them syn- to post-meta­ Bulgaria along the front of the Balkanide orogen. It morphic small granitoid intrusions. In this domain can be traced for over than 300 km from the Timok these rocks are thrusted toward southwest, over the river valley in Eastern Serbia (Timok fault) to central Upper Carboniferous and Permian sedimentary and parts of Stara Planina Mountain as single fault plain or volcanic rocks (back thrust). Northeastward the few kilometer wide fault zone. It was first character- metamorphites overrides more than 3 km wide sub- ized by Bonchev (1910) under the name “Plakalnitsa thrust zone including slices of Triassic to Paleogene fault” in the region of Balkan. According to sedimentary rocks, with dying-out and shallowing Kockel (1927), this is the most important and large toward the foot wall intensity of deformation. There fault structure in Western Bulgaria, comparable to the are numerous orthogonal or oblique dextral and sin- “Chudnite Skali” Dislocation and the Shipka- istral srike-slip faults combined with normal fault- zone to the east. Later Janichevsky (1935) proves the ing displacements in the volume of the zone, but also compressive character of the structure. The variable back thrusts, triangular zones and flower structures. characteristics and segmentation of deformation are This domain is limited to the east by a right-lateral the main reasons to be known and described under nu- strike-slip/normal fault surface, and to the east of it merous of names (Bonchev, 1971) but not well char- the thickness of the zone to the next domain is only a acterized in regional aspects yet. few tens of meters. The orientation of the PFZ varies from 135° to In the Temush-Urvich domain the PFZ hanging 120° in the area of Dragoybalkan ridge. Its width is wall is presented by Ribaritsa type metamorphosed from several tens of meters up to 2 km. The zone has granitoids (Angelov et al., 2010) thrusted by low- a imbricate structure and the dip of the frontal fault grade volcano-sedimentary complex and intruded into surfaces (often overlapping) varies from sub-vertical them granitoids. They are transgressively overlaid by to 70° in the valley of Malak River, to 65–40° Permian and Triassic clastic rocks, later involved in by Praveshka Lakavitsa and Tseritsa, and below 20° transpressional deformations, located mainly along at the village of Skravena (according to drilling data). the zone roots. The faults in the zone core are ori- In the northwest direction, sub-horizontal shearings ented obliquely to the main zone trend and combined are also located at the frontal parts of the zone, but with the right-lateral displacements. The sinistral and with sub-vertical in its internal parts also, often with a dextral strike-slip orthogonal fault system is devel- strike-slip component. op mainly in the central part of the domain and not The well exposed outcrops along the Dragoybalkan documented in the sub-thrust zone. The sub-thrust ridge in vicinity are good example for the zone itself is missing or very narrow, represented heterogeneity and fast lateral changes in the PFZ in by Lower–Middle Triassic or Jurassic sediments. short distances. In the area the field data allow to In front of this domain and in its frames were docu- be characterized two domains with contrast com- mented Upper Cretaceous magmatic activity, local- position, which we named Lyutidol-Lipnitsa and ized in its southeastern part. In the northwestern part Temush-Urvich (Fig. 1, 2). In the first domain the was established not described so far brittle-ductile hanging wall of the zone is composed of metamor- shear zone with most probably Early Alpine аge. phosed during the Variscan orogeny in green-schist This segment ends in the valley of the Malak Iskar

75 Fig. 1. Schematic Geological Map of the Plakalni­ tsa Fault Zone in the area of Dragoybalkan ridge (modified after Geological Map of R. Bulgaria on Scale 1:50 000)

Fig. 2. Schematic fault map of the studied area: 1a, Lyutidol-Lipnitsa domain, 1b, Temush-Urvich domain; 2, Dragoybalkan fault. Stereo-plot dia- gram (lower hemisphere) of the measured fault plains: A, in the zone hanging wall; B, in the sub- thrust zone.

River, where the area is only a few tens of meters References wide, south of the village of Laga. Angelov, V., M. Antonov, S. Gerdzhikov, S. Tanatsiev, H. Zh. Ivanov et al. (2004, unpublished report) and Kiselinov, P. Petrov, V. Valev. 2010. Explanatory Note Petrov (2005) interpreted the PFZ as Late Alpine neg- to the Geological Map of the Republic of Bulgaria. Scale ative flower structure. The Dragoybalkan fault is ac- 1:50 000. Map Sheet K-34-48-B (Botevgrad). Sofia, Min­ istry of Environment and Water, Bulgarian National Geo­ cepted as roots of the zone, extensionally reactivated logical Survey, 19 p. during the Late Pliocene. The low-grade metamorphic Bonchev, S. 1910. Die Leitlinien der geologischen Bau des overprint on the Paleozoic rocks, the syn- to post- westlichen Balkans. – Rev. Bulg. Geol. Soc., 4, 1–59 (in metamorphic granitoids and especially the “Ribaritsa Bulgarian with a German abstract). type” granite developed only in the frames of the zone Bonchev, E. (Ed.). 1971. Problems of Bulgarian Geotectonics. Sofia, Tehnika, 204 p. (in Bulgarian). are evidences for the Variscan activity of the PFZ. All Janichevsky, A. 1935. Note sur le gisement minier de Pla­ these facts are evidences for the polyphasal reactiva- kalnica–Medna planina. – Geologica Balc., 1, 2, 78–84. tion and evolution of the PFZ and its significant role Кockel, С. 1927. Die Grundzuge des Baues von Bulgarien. – as a major tectonic boundary. The characteristics of Ztschr. Dtsch. Geol. Ges., 79, 8–10, 192–193. Petrov, N. 2005. Emplacement mechanisms of Upper Creta­ the zone east and westward differs from in the studied ceous magmatic bodies in the area of Elatsite porphyry area, which confirm the heterogeneity of the deforma- copper deposits. – Ann. Sofia Univ., Fac. Geol. and Geogr., tion style along the trace of the PFZ. 98, 1–Geol., 43–64 (in Bulgarian with an English abstract).

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