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Paleogene–Early Miocene deformations of Bukulja–Ven~ac crystalline(Vardar Zone, Serbia)

MILUN MAROVI]1, ILIJA \OKOVI]2, MARINKO TOLJI]3,JELENA MILIVOJEVI]4 & DARKO SPAHI]5

Abstract. Low-grade metamorphic rocks of the crystalline of Mts. Bukulja and Ven~ac, which are integralparts of the Vardar Zone, are of Late Cretaceous age. From the Middle Paleogene to the beginning of theMiocene, they were subjected to three phases of intensive deformations. In the first phase, during the MiddlePaleogene, these rocks were subjected to intense shortening (approximately in the E–W direction), regionalmetamorphism and deformations in the ductile and brittle domains, when first-generation folds with NNE–SSWstriking fold hinges were formed. In the second phase, during the Late Oligocene and up to the Early Miocene,extensional unroofing and exhumation of the crystalline occurred, which was followed by intrusion of the gran-itoid of Bukulja and refolding of the previously formed folds in a simple brachial form of Bukulja and Ven~acwith an ESE–WNW striking B-axis. The third phase was expressed in the Early lowermost Miocene (beforethe Ottnanghian), under conditions of NE–SW compression and NW–SE tension. It was characterized by wrench--tectonic activity, particularly by dextral movements along NNW–SSE striking faults.

Key words: Serbia, Vardar Zone, Bukulja–Ven~ac crystalline, structural analysis, tectonics, metamorphiccore-complex.

Apstrakt. Nisko metamorfne stene kristalina Bukuqe i Ven~aca, koje su sastavni deo Vardarskezone Srbije, su gorwokredne starosti. One su od sredine paleogena do po~etka miocena bile zahva}eneintenzivnim deformacijama tokom tri faze oblikovawa. U prvoj fazi, tokom sredweg paleogena, bilesu izloène jakom suèwu (pribli`no pravcem I–Z), regionalnom metamorfizmu i deformacijama uduktilnom i brittle domenu, kada su formirani nabori prve generacije sa B-osama pruàwa SSI–JJZ. Udrugoj fazi, tokom gorweg oligocena, do u dowi miocen do{lo je do ekstenzionog otkrivawa i ekshu-macije kristalina, {to je bilo pra}eno utiskivawem granitoida Bukuqe i prenabirawem prethodnoformiranih nabora u jednostavnu brahiformu Bukuqe i Ven~aca sa B-osom pruàwa IJI–ZSZ. Tre}ufazu, koja se ispoqila u ranom dowem miocenu (pre otnanga) u uslovima SI–JZ kompresije i SZ–JI, ten-zije karakteri{e wrench-tektonska aktivnost, posebno dekstralna kretawa du` raseda pruàwaSSZ–JJI.

Kqu~ne re~i: Srbija, Vardarska zona, bukuqsko-ven~a~ki kristalin, strukturna analiza, tektonika,metamorfni core-complex.

GEOLO[KI ANALI BALKANSKOGA POLUOSTRVA

ANNALES GÉOLOGIQUES DE LA PÉNINSULE BALKANIQUE68 9–20 BEOGRAD, decembar 2007

BELGRADE, December 2007

DOI: 10.2298/GABP0701009M

1 Faculty of Mining and Geology, Department of Geology, Belgrade University, Kameni~ka 6, 11000 Belgrade, Serbia.E-mail: [email protected]

2 Faculty of Mining and Geology, Department of Geology, Belgrade University, \u{ina 7, 11000 Belgrade, Serbia. E-mail:[email protected]

3 Faculty of Mining and Geology, Department of Geology, Belgrade University, \u{ina 7, 11000 Belgrade, Serbia. E-mail:[email protected]

4 Geological Institute of Serbia, Rovinjska 12, 11000 Belgrade, Serbia. E-mail: [email protected] Faculty of Mining and Geology, Department of Paleontology, Belgrade University, Kameni~ka 6, 11000 Belgrade, Serbia.

E-mail: [email protected]

Introduction

Crystalline of Bukulja and Ven~ac, with its non-me-tamorphosed Mesozoic–Cenozoic cover and Oligocene––Miocene granitoid, spatially belongs to the Vardar Zo-ne (Fig. 1). These are terrains with complex geologicalcompositions which have been discussed many times,often with controversial explanations.

There are dilemmas about the age of the crystallinein the first place, which directly influenced differentexplanations of the tectonics of these terrains. The crys-talline has most often been considered to be of Paleo-zoic age (SIMI] 1938; FILIPOVI] 1973; FILIPOVI] & RO-DIN 1980; \OKOVI] et al 1995; TRIVI] 1998). Such anopinion is mostly based on the fact that these are rocksof different metamorphic grade, while there are no reli-able paleontological proofs or even paleontologicalproofs of any kind. However, according to findings ofglobotruncana and other fauna and on the base of paly-nologic data from low-metamorphic rocks of Ven~ac,BRKOVI] et al. (1980) and MAROVI] et al. (2005), re-spectively, concluded that the Bukulja–Ven~ac crystal-line is of Late Cretaceous age.

According to its age, folding of the area has alsobeen explained in different ways. \OKOVI] & MAROVI]

(1985, 1986) separated three generations of folds inthese terrains. These authors related the first fold gene-ration to Hercynian deformation, which is marked byNE–SW striking fold axes. In the second phase, duringolder Alpine tectogenetic events, the Hercynian foldstructures were refolded into E–W striking folds. Thethird generation of folds is the consequence of a plu-ton intrusion and further refolding of all the existingfolds into large domes and brachial synclines.

TRIVI] (1998) separated three (? four) generations offolds. According to this author, axes of the oldest,Hercynian structures are oriented in the WNW–ESEdirection. These structures were refolded into folds withNNW–SSE striking axes during the first phase of Alpi-ne deformation in the Mesozoic. Later, during the laterAlpine phases, the geometry of such folds became morecomplex due to a pluton intrusion and strike-slip move-ments along E–W striking faults.

MAROVI] et al. (2005) considered the metamorphicrocks of Bukulja and Ven~ac to be of Late Cretaceousage and the authors are of the opinion that there areonly Alpine and no Hercynian folds in these rocks.

The relationship between the crystalline and the non-metamorphosed Cretaceous (prevailingly Late Cretaceous)deposits, including tectonically incorporated slices of ser-pentinite, is unclear and has been explained in differ-ent ways. Sedimentary deposits are widespread on thesurface, mostly north, east and southeast of the Buku-lja–Ven~ac crystalline, and they were also drilled outunder Neogene deposits of the Aran|elovac and Bela-novica Basin. There are also isolated and disconnectedportions of Cretaceous sediments on the southern rimof the crystalline. All this points to the possibility that

the crystalline was completely covered by Cretaceoussediments. The majority of authors is of the opinionthat the Cretaceous sediments transgressively overlie thecrystalline. According to TRIVI] (1998), metamorphicrocks were thrust over Cretaceous sediments in certainparts of the terrain in the South. BRKOVI] et al. (1980)and \OKOVI] & MAROVI] (1986) mentioned sectionswhere metamorphic rocks gradually transit into non-metamorphosed Upper Cretaceous deposits.

Finally, in accordance with different interpretationsof the geologic composition, the geotectonic position ofthe Bukulja–Ven~ac crystalline unit is also controver-sial. Its metamorphic content resembles the Drina–Iva-njica crystalline (\OKOVI] et al. 1995). The Bukulja––Ven~ac crystalline is located on the eastward exten-sion of the Jadar Block, which is made of Paleozoicrocks. This fact led FILIPOVI] (1995), FILIPOVI] & JO-VANOVI] (1998) and FILIPOVI] (2005) to include at leasta part of it (western part of Bukulja) into the Jadarentity. There is also the opinion that Bukulja–Ven~accrystalline is completely different from the metamor-phic rocks of both the Drina–Ivanjica and Jadar devel-opments and that it is made of metamorphosed Creta-ceous deposits belonging to the Vardar Zone (BRKOVI]

et al. 1980; MAROVI] et al. 2005).The above-cited problems concerning the geologic

composition of the Bukulja–Ven~ac crystalline are achallenge for further investigations directed toward newand better documented solutions. The results of one ofthese studies, which represent a contribution to a bet-ter understanding of the Paleogene–Early Miocene tec-tonics of these regions, are presented in this paper.

Short Review of The LithostratigraphicCharacteristics of the Terrain

A wider area of the Bukulja–Ven~ac crystalline ismade of rocks of different composition and age (Fig. 1).Four large lithostratigraphic domains can be distin-guished: (1) Bukulja–Ven~ac crystalline, (2) serpenti-nite, Cretaceous clastics, carbonates and flysch, (3) Pa-leogene–Neogene granitoid and volcanic rocks and (4)Neogene–Quaternary sediments.

(1) The Bukulja–Ven~ac crystalline is made of rocksof different degrees of metamorphism, mostly low-grademetamorphics and, to a smaller extent, medium-to-high-grade metamorphics. These are mostly sedimentary rockswhich were subjected to regional metamorphism andalso to contact metamorphism in the vicinity of thegranitoid. The lowest structural position is occupied bygneisses (and also leptynolites in places), which are fol-lowed by: micaschists, sericite schists, meta-quartz con-glomerates, phyllites and sericite schists, marbles, calc-schists, metacalcarenites and metasiltstones. Also epi-dote-actinolite- and chlorite schists occur subordinatelyin the low-grade metamorphic complex. Rocks with ahigher grade of metamorphism are found in the vicin-

MILUN MAROVI], ILIJA \OKOVI], MARINKO TOLJI], DARKO SPAHI] & JELENA MILIVOJEVI]10

Paleogene–Early MIocene deformations of Bukulja–Ven~ac crystalline (Vardar Zone, Serbia) 11

Fig. 1. Geologic sketch of the wider area of Bukulja and Ven~ac.

ity of the granitoid, while going away from it – towardsthe Ven~ac, low-grade metamorphics predominate. TheBukulja–Ven~ac crystalline is of Late Cretaceous ormaybe partly even of Paleogene age. The second author(I.\.) is of the opinion that Ven~ac domain of the crys-talline is of Late Cretaceous age, while the rest of it isPaleozoic and resembles the Drina–Ivanjica Paleozoic.During these investigations, rich microfloral associa-tion, which indicates Late Cretaceous age, was foundin the calcschists and metacalcarenites of Ven~ac. Thisis in full agreement with the results on the crystallineage based on globotruncanas (BRKOVI] et al. 1980).However, this age most probably does not refer to thewhole crystalline. Based on a lithostratigraphic correla-tion, FILIPOVI] (2005) is of the opinion that the meta-morphic rocks west of Bukulja are similar to the JadarPaleozoic, thus that they are Devonian and Carboni-ferous in age.

(2) Cretaceous sequence of non-metamorphosed de-posits and serpentinite are exposed on the northern,eastern and southern slopes of the Bukulja–Ven~acmorphostructure. The Cretaceous sediments are repre-sented by reefal and stratified limestones, rarely also byEarly Cretaceous clastites and, for the largest part, byvarious types of carbonates, clastites and Late Creta-ceous flysch (BRKOVI] et al. 1980). Smaller tectonicslices of serpentinite of Jurassic age occur locally nearthe Cretaceous sediments.

(3) Oligocene–Early Miocene granitoid was intrudedinto the Bukulja crystalline (KARAMATA et al. 1994;KNE@EVI] et al. 1994). It induced also contact meta-morphism of the surrounding rocks. The granite intru-sion was followed by volcanic rocks, prevailingly phe-noandesites, latites and their pyroclastics.

(4) A Neogene–Quaternary cover is represented by lo-osely bound coarse-grained, gravely-sandy, clayey-sandyand clayey deposits. These are mostly fresh-water equi-valents of the Ottnangian–Karpatian and, to a lesserextent, also marine deposits of the Badenian and Sar-matian. The highest stratigraphic level is represented bydifferent types of Quaternary deposits.

Tectonic Setting

Methodology of research

Geologic mapping of the Bukulja–Ven~ac crystalline(including the granitoid) and its non-metamorphosedcover of Late Cretaceous age provided information re-levant for solving the tectonic setting of the area. Thesewere data on bedding, foliation, folds of different scaleand faults. They were analyzed within different scaleranges and homogeneous domains and the obtained datawere incorporated in a tectonic synthesis, together withknowledge on the lithostratigraphic units.

Particular attention was paid to the determination ofthe orientation of fault planes and associated slip direc-

tion, which was used for the reconstruction of pale-ostress and deformation phases manifested from themiddle Paleogene to the beginning of the Miocene.

Reconstruction of faulting succession and displace-ment was based on the criteria given by PETIT (1987)and GAMOND (1983, 1987). Reduced deviatoric paleo-stress tensors were computed for a cogenetic fault po-pulation which was separated from polyphase sets,based on field observations and kinematic compatibili-ty. The method of numerical and graphical inversionproposed by ANGELIER & MECHLER (1977), ANGELIER

(1979, 1989) and method of numerical dynamic analy-sis (NDA) by SPERNER et al. (1993) were used. Compu-tation of the data for paleostress analysis was perform-ed using Tectonic FP software (ORTNER et al. 2002).

Structural features

In a structural sense, three large homogeneous do-mains can be distinguished within the research area: (1)Bukulja–Ven~ac crystalline, (2) the thrust-fold sequenceof non-metamorphosed Cretaceous deposits with tecton-ically incorporated slices of serpentinite and (3) Neo-gene basins. The first two structural domains are dis-cussed in this paper, because they resulted from Paleo-gene–Early Miocene deformations, which were the sub-ject of the research.

The structural setting of the Bukulja–Ven~ac crys-talline is very complex with a polyphase-deformationhistory and at least two phases of folding. The area isdominated by a large (Dkm) brachial-antiform struc-ture, the hinge of which plunges toward ESE. The best-developed fabric element is foliation, which actuallymakes this antiform (Fig. 2A). Foliation is unevenlydeveloped: it is best-developed in gneisses and micas-chists, less present in phyllites, sericite schists and calc-schists, while it is poorly developed in metacalcarenite,metasiltstone and “massive” marble.

The foliation is probably the result of flattening per-pendicular to the foliation planes. Isoclinal intrafolialfolds of cm and dm scale are indicators of shearingalong foliation. They are particularly well-visible in themetacalcarenites of Ven~ac, and locally, also in quartz-sericite schists (Fig. 3). The Folds are mostly rootlessand represent thickened hinge zones, while their limbsare strongly flattened and sheared. These folds arewest–northwest-vergent with fold axes plunging towardNNE and SSW (Fig. 2B). Crenulations of foliation arenoticed locally. The crenulation axes plunge towardsouth–southeast to, southeast and northwest and theyare genetically related to the formation of the brachialantiform (Fig. 2C). Foliation and intrafolial rootlessfolds could have been formed in an almost horizontalposition. All this indicates refolding in the Bukulja––Ven~ac crystalline.

Foliation is developed in the granitoid as well. It hasa periclinal distribution (Fig. 2D) compatible with foli-



Fig. 2. Equal – area Lower hemisphere stereograms of: A, foliations in the crystalline; B, B-axis intrafolial folds; C, crenulationlineation; D, foliations in the granitoid; E, bedding in Cretaceous deposits north of Bukulja; F, bedding in Cretaceous depositsnorthwest of Ven~ac; G, bedding in Cretaceous deposits south of Ven~ac. Spheristat software was used for the analysis.

ation in the Bukulja–Ven~ac crystalline, which indi-cates their genetic relationship.

The thrust-fold stack of non-metamorphosed Creta-ceous sediments with tectonically incorporated slices ofserpentinite also have a very complex structure as well.Today, this unit is preserved within several small, moreor less homogeneous structural regions on the northern,eastern and southern rims of the Bukulja–Ven~ac anti-form. The structure is dominated by bedding and faults.The Bedding planes are well-exposed and penetrative.

Terrains on the northern slopes of Mt. Ven~ac arecomposed of non-metamorphosed deposits of Cretaceousage. Despite the fact that a large part of the area is cov-ered with deluvium, a lot of information was acquiredfor fault analyses.

On the diagram F (Fig. 2), poles to bedding aremostly concentrated in the NW quadrant, marking amonoclinal dip toward southeast. However, field inves-tigations showed that the folds in this area are not sim-ple but that it is a folded unit with normal and over-turned limbs of NNW (NW) vergent folds, similar tothe folds of the first generation in the underlying Bu-kulja–Ven~ac crystalline, only less developed with lessstrain. Cretaceous deposits north of Bukulja are identi-cally deformed (Fig. 2E).

East of Ven~ac, there is an intensely tectonized zonein the Cretaceous deposits and serpentinite. Unfortuna-tely, this area is mostly covered, with no outcrops ofCretaceous deposits, thus a comprehensive measure-mant the of bedding attitude could not be performed.According to the data from the wider surroundings (BR-KOVI] et al. 1980), the area is characterized by a thrust-fold pattern marked by West-vergent recumbent foldsand reverse faults, developed under dextral transpressio.

Terrains made of non-metamorphosed Cretaceous de-posits on the southern and southwestern slopes of Ven-

~ac are mostly covered with deluvium and are unfavor-able for structural investigations. The scattering of thebedding data, presented on diagram G (Fig. 2) is prob-ably a consequence of the rotation of faulted blocks,but also of the small number of measurements which arestatistically not representative. Field observations show-ed that the Cretaceous deposits here are also intenselyfolded, with the occurrence of overturned west–north-west-vergent folds.

Results of paleostress analysis

Paleostress analysis in the area of the Bukulja–Ven-~ac crystalline, non-metamorphosed Cretaceous depositsand the granitoid show three kinematic stages, the firstprobably being of Middle Paleogene, the second of Oli-gocene to Oligocene–Miocene and the third of EarlyMiocene (Pre-Ottnangian to Karpatian) age. The rela-tive chronology of these events is deduced from cross-cutting map-scale faults in key outcrops.

Deformational event (D1) – E–W compression

This paleostress tensor group comprises a conjugatedpair of NW-trending sinistral and NE-trending dextralstrike-slip faults (Fig. 4). These faults are overprinted bymainly extensional structures on numerous outcrops.

Folds of the first generation with a NNE (NE)–SSW(SW) striking axes probably originated in such a stressfield. Today, they are exposed as intrafolial folds in theBukulja–Ven~ac crystalline, as well as in WNW (NW)vergent folds in non-metamorphosed Cretaceous deposits.

Deformational event (D2) – N–S-to-NE–SW extension

The second paleostress tensor group comprises WNWto NW and NE-trending normal faults (Fig. 5). Thesefaults are probably related to an Oligocene unroofingof the Bukulja–Ven~ac crystalline and the granitoidintrusion. In this case, WNW to NW trending normalfaults often form conjugate sets: synthetic, gently slop-ing northwards and antithetic, with steeper dips towardthe south. They were formed above the brittle-ductiledetachment zone along which the extensional unroofingoccurred.

Deformational event (D3) – wrench tectonic regime, NE–SW compression and NW–SE tension

The third paleostress tensor group comprises NNWto NW trending dextral and WNW trending sinistralstrike-slip faults (Fig. 6). Fault systems with these kine-matic characteristics, which originated in the stress fieldwith NE–SW compression and NW–SE tension, can be


Fig. 3. Isoclinal folds in metacalcarenites of Ven~ac (Ven~acquarry).


Fig. 4. Distribution of stress states related to a E–W compressional event. Stereographic projection of the meas-ured outcrop – scale faults and calculated stress axes. The circle, rectangle and triangle represent the orientationof the maximum, intermediate and minimum principal stress axes, respectively.

related to dextral wrenching. In this case, NNW to NWtrending faults could belong to the principal displace-ment zone (PDZ) with dextral characteristics (Y-faults),

while WNW-trending sinistral strike-slip faults couldrepresent X-faults. Such a stress field was generated atthe beginning of the Miocene (“Sava phase”).


Fig. 5. Distribution of stress states related to an extensional event with N–S to NE–SW trending �3. Explanation the sameas for Fig. 4.


Fig. 6. Distribution of stress states related to a dextral strike-slip regime with �1, trending NE–SW. Explanation the same asfor Figs. 4. and 5.

Discussion and Conclusions

Investigations in the area of the Bukulja–Ven~accrystalline showed the following:

• The Bukulja–Ven~ac crystalline is of Late Creta-ceous age, maybe even partly Early Paleogene. It wasintruded by an Early Miocene granitoid.

• The crystalline is overlain mostly by Late Creta-ceous non-metamorphosed clastic-carbonate rocks andflysch.

• Metamorphic grade in the crystalline decreasesfrom the granitoid to the periphery and toward the up-per structural levels, where there is a gradual transitioninto non-metamorphosed members of the Late Creta-ceous.

• There is a similar manner of folding (fold shape,vergences) in both sequences of Cretaceous deposits:the metamorphosed and the non-metamorphosed ones,but deformations in the crystalline is more intense andoccurred in the ductile domain. Two phases of foldingare noticed.

• Reconstruction of paleostress fields points to threemajor phases of brittle formation : in the middle of thePaleogene, in the Oligocene–Early Miocene and in theEarly Miocene.

The above presented facts point to a unique tecton-ic-sedimentary environment in this area during the LateCretaceous (maybe also in the ?Early Paleogene), whichwas inverted in the middle of the Paleogene. Such anenvironment is consistent with the model elaborated byPAMI} (1993), PAMI} et al. (2000, 2002), according towhich the northern part of the Vardar Zone (Vardar––Sava) is the result of obliteration in the Upper Creta-ceous–Paleogene active continental margin of SouthernEurope, with well-defined island arc and back-arc ba-sins. This sedimentation area was inverted and includ-ed into the Dinaridic orogene by collisional processesin the Eocene. According to PAMI} et al. (2000, 2002),this phase was followed by intense deformation of theJurassic ophiolitic mélange, metamorphism and magma-tism.

The Bukulja–Ven~ac sedimentation and deformationarea (Fig. 7) was probably generated in a similar tec-tonic setting. In the middle of the Paleogene, the Bu-kulja–Ven~ac area was subjected to shortening in theapproximate E–W direction, when a thick WNW ver-gent thrust-fold sequence was formed. The secondauthor (I.\.) is of the opinion that these structures wereformed only in the Ven~ac domain of the crystalline,while, in its other parts, the Hercynian structures wererefolded by a Mesozoic–Cenozoic tectonic event. Thelower parts of the sequence reached the zone of duc-tile deformations and underwent regional low- to medi-um-grade metamorphism. The whole process was fol-lowed by the formation of tight and isoclinal folds withhinges striking NNE (NE)–SSW (SW) with strong axialplane cleavage, and subsequent transposition of beddingalong the cleavage, the formation of foliation. Rem-

nants of these folds are preserved today as intrafolialfolds.

In the brittle-ductile and brittle domain, above themetamorphites, this phase of tectogenesis resulted inthe formation of distinctly WNW (NW) vergent over-turned, sometimes also recumbent, folds with axesstriking NNE (NE)–SSW (SW) and the formation ofconjugated NW trending sinistral and NE trending dex-tral strike slip faults.

Extension, probably ductile, followed by intrusion ofgranitoid, volcanism and exhumation of the Late Creta-ceous metamorphics (metamorphic core complex) ischaracteristic for the second phase, which that wasexpressed in the Late Oligocene and up into the EarlyMiocene.

The process of exhumation metamorphism and em-placement of the granitoid was marked by refolding ofthe foliation and the previously formed folds, when thedistinct brachial-antiform of the Mts. Bukulja and Ven-~ac (with an ESE plunging axis) was formed. There arecertain indications that a shallow synform), rim synform,which is presently mostly burried with Neogene–Qua-ternary deposits, was formed northeast of the antiform.

Unfortunately, the detachment zone along which theductile extension occurred has not been defined, whichcertainly does not mean that it does not exist. Furtherdetailed investigations are necessary for its determina-tion.

In the brittle domain in the area of extensional allo-chthon, WNW to NW and NE trending normal faultswere activated, often as pairs of synthetic and antithet-ic sets.

After the exhumation of the metamorphic core com-plex of Bukulja and Ven~ac, tectonic shortening affect-ed the area. It is expressed through dextral transpressionwith NE–SW compression and NW–SE tension. Acti-vation of the NNW–NW trending dextral and WNWtrending sinistral strike-slip faults is characteristic for thisphase. In the domain of the first system, small NE-trend-ing normal faults (probably “pinnate” faults) were acti-vated. Under transpressional conditions, west-vergentfolds and thrusts were formed, particularly on the east-ern periphery of Ven~ac. This transpressional event af-fected the Vardar Zone, the Serbian–Macedonian Unitand the Carpatho-Balkanides, all the way to the MoesianPlate (wrench corridor, MAROVI] et al. 2001).

The process of destruction of the previously formedstructures, related to the shaping of the Pannonian Ba-sin and its periphery, commenced after the transpres-sional events, already from the Ottnangian.

The performed investigations stress the problemwhich demands more detailed research and applicationof new methods in order to obtain more reliable andprecise solutions. This refers, in the first place, to thenecessity of performing detailed structural investiga-tions and registering kinematic indicators of extension-al processes and stress fields in general. Particularattention should also, be paid to an explanation of the


manner of extensional unroofing, transpressional tecton-ics and related phenomena.

In order to date the tectonic events, it will be nec-essary to apply methods of thermogeochronology, e.g.,Ar/Ar on mica and fission-track analyses.

Acknowledgements

The work was funded by the Ministry of Science ofSerbia, project No. 146009b. We owe special gratitude to\OR\E GRUJI] (Stanford University) for his detailed reviewand constructive suggestions for improvements of the work.We are also thankful to LUKA PE[I] (Belgrade University)for his most helpful and useful suggestions.

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Rezime

Paleogeno-dowomiocenske deformacijeBukuqsko-ven~a~kog kristalina(Vardarska zona, Srbija)

Niskometamorfni kristalin Bukuqe i Ven~acasa svojim nemetamorfisanim mezozojsko-kenozo-jskim pokrovom je deo Vardarske zone. Sloène jegeolo{ke gra|e, posebno tektonskog sklopa, koji jerezultat vi{efaznog oblikovawa. Predmet ovograda su paleogeno-dowomiocenske deformacijekoje su najodgovornije za formirawe najmarkant-nijih struktura u ovom regionu.

O geolo{koj gra|i bukuqsko-ven~a~kog krista-lina postoje brojne kontroverze, po~ev od wegovestarosti, nabornog sklopa, odnosa prema nemeta-morfisanim krednim tvorevinama, sve do geotek-tonske pripadnosti.

Ova istraìvawa su pokazala, odnosno potvrdi-la, da je kristalin gorwokredne (mo`da delom ipaleogene? ) starosti. Saglasno tome ne posedujehercinske nabore, ve} samo alpske, koji su rezul-tat paleogeno-dowomiocenskih oblikovawa. Utvr-|ene su tri glavne faze formirawa paleogeno-do-womiocenskog sklopa.

U prvoj fazi, sredinom paleogena, u naponskompoqu I–Z kompresija, stene bukuqsko-ven~a~kogpodru~ja bile su izloène jakom saìmawu, regio-nalnom metamorfizmu i deformacijama u duktil-nom i brittle domenu (formirani su izrazito ZSZ-vergentni nabori koji su u duktilnom domenu pret-peli jo{ i transpoziciju, formirawe folijacije ishearing).

U drugoj fazi, tokom gorweg oligocena do udowi miocen obavqeno je ekstenziono raskrov-qavawe i ekshumacija kristalina, {to je bilopra}eno utiskivawem granitoida i prenabirawemprethodno formiranog nabornog sklopa u jednos-tavnu brahi-antiformu Bukuqe i Ven~aca.

Za posledwu fazu ispoqenu u dowem miocenu(pre otnanga), u uslovima SI–JZ kompresije iSZ–JI tenzije, karakteristi~na je wrench-tektons-ka aktivnost.

Tokom sve tri tektonske faze, aktivirani surasedi koji su imali kinematska obele`ja saglasnonaponskom poqu u kome su formirani.


paleogene–early miocene deformations of bukulja–ven~ac crystalline … · 2008-01-18 · nisko...

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