Origin of Secondary Fault Structures in the Eastern Part of the Balkan Peninsula
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GEOLOGICA BALCANICA, 35. 1-2, Sofia, Jun. 2005, p. 19-38 Origin of secondary fault structures in the eastern part of the Balkan Peninsula Simeon Kalaidjiev 6 Prof N. Mihailov Str., 1000 Sofia (first submitted 03. 07.1998; revised version accepted September 2003; final version received December 2004) CuMeOH Ka;wuo:HCuee - Bmopu<moe pa3/lOMHOe cmpyK Abstract. The tectonic structures in the eastern part of the mypoo6pa3oeaHue eo eocmo<mou 'lacmu EaAKaHcKozo no Balkan Peninsula are formed in the zone of dynamic in Ayocmpoea. TeKTOHH"!eCKHe CT)JyKTyp&I BO BOCTO"'HOW "!aC fluence of the Kraishtid-Vardar lineament. The second TH EaJIKaHcKoro nonyocTpoBa !l>opMHpOBMHCb B 30He ,n:H ary structures are formed under conditions of predomi HaMH"!ecKoro BJIIDIHIDI KpamiiTH.lJ:HO- Bap.n:apcKoro JIHHea nating right-lateral strike-slip faulting along the linea MeHTa. BTopH"'H&re CTPYKTyp&r !l>opMHpoBaHHbi no ,n:JIHHe ment. They could be observed all over the Bulgarian ter JIHHeaMeHTa B ycJIOBHJI npeo6Jia,n:aJOw.ero Jiesoro c,n:BHra. ritory. There are 9 main fractures outside of the Kraishtid 0HH Ha6JIJO)laJOTCJI Ha BceH: TeppHTOpHH EoJirapHH. Ha6- structural zone which have an average strike of 150- JIJO,n:aJOTCJI 9 MarHCTpan&HbiX !l>paKTYP BHe KpamiiTH.D:HOW 1600. A large-scale secondary structure formation of CTJJYKTypHoil: 30H&r, HMeJOW.HX cpe,n:Hoe HanpaBJieHHe 150°- higher degree is related to them. A first-order cycle of 160°. C 3THMH !l>paKTypaMH CBJI3aHO o6pa30BaHHe MHO)J(eC ordering of the subgroup A2 structures is presented, TBa BTOpH"'HbiX cTpyKTYP 6oJiee BbiCOKoro nopJI)lKa. IloKa- which has in map view a fan-like shape that spreads to 3aHo HaJIH"!He H nepBOCTeneHHaJI IJ.HKJIH"'HOCTb rpynnHpO the north with a width of more than 500 km. As a rule, BaHJUI CT)JYKTYPbl cy6rpynn&I A , KOTOpble B nJiaHe HMeJOT the first-order structures A 1 change their orientation pa3IIIHpiDOUJ.YJOCJI K ceBepy Be·rtmJioo6pa3HYJO !l>opMy. Ee from 130-150° to 90° with increasing the distance from IIIHpOTa 6oJI&IIIe "!eM 500 KM. KaK npaBHJIO nepsoCTeneH the Kraishtid structural zone. Most of the fold struc H&re CTPYKTyp&r A MeHJIJOT csoJO opHeHTHpOBKY OT 130- tures in the region are genetically related to them. An 1500 .D:O 90° C yseJik"'eHHeM CBOero OTCTOJIHHJI OT KpaHIII idea that the fault net is formed by the stresses caused TH.lJ:HOW cTpyKTypHoil: 30Hbi. EoJI&IIIHHCTBO CKJia,n:"'aT&IX by the periodical changes of the axis spin velocity of our CTPYKTYP reHeTwleCKH CBJI3&rnaeTCJI c 3THMH cTpyKTypaMH. planet is based on the wave-cyclic ordering of the struc Ha OCHOBaHHe BOJIHOBOfO U.HKJIH"!eCKOfO rpynnHpOBaHJUI tures A (in map view) and A (in section). The faults ini 2 1 CTPYKTyp&r A (B nJiaHe) H A1 (s pa3pe3e) o6ocHOB&maeTcJI tiated during the Late Archean and the Early Proterozoic Te3a "'TO pa3fiOMHaJI CeTb lPOPMHpOBaHa Hanpe)J(eHHJIMH, cross through all the Bulgarian territory. Their kinemat nOJIBJIJIJOUJ.HMHCJI BCJie)lCTBHH nepHO.ll:H"'eCKOfO H3MeHeHHJI ics and morphological features are shown in this paper. cKopocTH ocosoro spaw.eHIDI Haiiieil: nJiaHeT&I. Pa3JIOM&I The specific role of the secondary structures about the HHHIJ.HHpOBaHHble BO BpeMJI n03.ll:HOfO apxeJI H paHHOfO geological evolution of the area is studied as well as their npoTepo3oJI, Ha6JIJO,n:aJOTCJI Ha sceH: EoJirapcKoil: TepHTO ore-controlling role. pHH. B HaCTOJIW.eil: CTaT&e BblJICHeH&I npHHa,n:Jie)J(aUJ.He HM KHHeMaTH"!ecKHe H Mop!l>oJiorH"!eCKHe xapaKTepHCTHKH. llccJie,n:oBaHHbi cneu,HlPH"'ecKaJI poJ!b BTOpocTeneHH&IX CTPYKTYP B reoJIOrH"!ecKoil: eBOJIJOU,HH pemoHa H HX py.n:o KOHTpOJIHPYJOW.ee 3Ha"!eHHe. Kalaidjiev, S. 2005. Origin of secondary fault structures in the eastern part of the Balkan Penin sula. -Geologica Bale., 35, 1-2; 19-38. Key words: secondary faults; eastern Balkan Peninsulil, Kraishtid - Vardar lineament, ore-control. Introduction fractures are designated as primary (principal) structures. The fractures formed within their In the present study all fractures that form ir dynamic field of influence are described as respectively of their size and rank secondary secondary (second-order, accompanying, sub- 19 ordinated, feathering). Each one secondary Kraishtid Zone are formed following the fracture can be considered as a primary one in mechanism occurring in the shear zones. respect to secondary fractures that are geneti Observing the regmatic network of the East cally related to it. ern part of the Balkan Peninsula, Bonchev Experimental data of Stoyanov (CTOSIHOB, (I>oHqeB, 1971) determined 6 main fault sets, 1977) confirm the origin of secondary fractures grouped into 3 orthogonal pairs. He con of the sub-groups A2 and A 1 and a group B ac cluded that the faults respectively called of cording to the theoretical model of Chinnery "Kraishtid", "Berkovitsa", "Tvurditsa" and (1966, 1966a; Chinnery, Petzak, 1968). In case "Yablanitsa" orientations are formed under "a of horizontal displacements to the opposite di unified stress field with maximum principal rection the same structures are respectively normal compression stresses in the meridian , called A 12 A22 and B1 (Kanaii.Il)KHeB, 1997). direction, and maximal extension, in the equa Stoyanov (CTOSIHOB, 1977) demonstrated that torial direction". the formation of the structures within the fault The Preboynitsa Fault in the Western Balkan zones, their kinematics and space-morphologi Mountains has been demonstrated as a natu cal peculiarities are predetermined by the spe ral model for secondary structure forming. cific local distribution of the deformations and Based on personal studies, mainly in areas the strain correspondent to the displacements with endogenic mineralizations, Kanaii.IJ;)lmeB along the faults. The formation of secondary (1997) concluded that all tectonic fractures fractures around an already existing or a pot en across the Bulgarian territory are formed ac tially existing primary fault plane is caused by cording to the model of structure-forming into the concentration of strains into the flanks of shear zones. After this model group A2 (320°- the faults. Their formation may be connected 600) includes. the faults of "Kraishtid", "Me also to the horizontal displacements into shear ridional" and "Tvurditsa" directions; sub zones. During deformation the main axes of ex group A 1 (90°-140 °), - the faults of "Balka tension may change their orientations as well as nide" and "Berkovitsa" directions, and group B the position of the two axes. Into the sectors of (60°-90 °), - of "Yablanitsa" direction. As compression the axis of the maximal principal shown by Kalaidjiev (KanaH.IJ;)l(HeB, 1988) the compressive stress remains horizontal. At the cyclic arrangement in plan of the secondary same time, depending on the weight of the cover faults depends on their distance from the pri and the magnitude of the transversal horizontal mary fault. Into the main dislocations of reaction, created by the surrounding environ "Kraishtid" orientation the secondary faults ment, the minimal principal compressive stress form fans, opened to the North or South, de may be vertical or horizontal. In the first case pending on their location, respectively on the strike-slip faults are formed, and in the second eastern or western fault block. one, secondary thrust structures. The situation in sectors of extension is similar, where the mini mal compressive stress remains horizontal. The Space distribution axes of the other principal stresses may have dif of the tectonic fractures ) ferent positions. Strike-slips (subgroup A2 are formed when the axis of the maximal shortening in the eastern part remains horizontal. However, in condition of of the Balkan Peninsula higher vertical loading (at deeper levels) the same stress may be in vertical position. The re The tectonic structures in the eastern part of spective secondary shears will be of normal the Balkan Peninsula are formed into the zone fault type. of dynamic influence of the "Krashtid-Vardar The so far studies of the author show, that in Lineament", which is supposed to extend to the real geological environment existing in the the south into the Red Sea Rift Zone (I>oHqeB, eastern part of the Balkan Peninsula the axes 1965, 1971). Zagorchev (1970) distinguished of the principal maximum and minimum com the Vardar and Strouma Rifts, and Gergelchev pressive stresses have inclinations of 45° and (reprenqeB et al., 1974, 1977) considered a 135°, forming respectively strike-slip faults "Strouma-Vardar Rift Belt". This is a primary with a normal component and strike-slip structure of planetary scale. The first-rank faults with a thrust component. All fractures secondary structures have been formed in a formed along the vertical component of the primary dominating dextral strike-slip dis , • placement along the lineament. They are stress field are defined as A2 A1 and B1 Stoyanov (CTOSIHOB, 1977) demonstrates for represented by sub-groups A2 and A 1 and the first time that some faults from the group B, being observed all over the country 20 Fig. I. Map of the first-order secondary fractures and the most important endogenic mineralizations in Bulgaria I - Faults (numbered in circles): I - Belogradchik - Mesta fault; 2 - Preboynitsa-Beglika fault; 3 - Kostalevo Mihalkovo fault; 4- Davidkovo-Ostritsa fault; 5 - Kobilyano-Kurdzhali fault; 6- Haskovo fault; 7- Merichleri fault; 8- Svilengrad- Nikopol fault; 9 -East Topolovgrad fault; I 0- Venelin - Tolbuhin fault; 11 - Trigora fault; 12- Balchik fault; 13- Rakovski- Gorun fault; 14- Balgarevo