The Multiply Deformed Foreland Fold-Thrust Belt of the Balkan Orogen, Northern Bulgaria

Home , Arda (Maritsa tributary), Belogradchik, Berkovitsa, Etropole, Geology of Bulgaria, Geology of Greece

Multiply deformed foreland fold-thrust belt of the Balkan orogen The multiply deformed foreland fold-thrust belt of the Balkan orogen, northern Bulgaria

B.C. Burchﬁ el1 and Radoslav Nakov2 1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA 2Institute of Geology, Bulgarian Academy of Sciences, G. Bonchev str. Block 24, 1113 Soﬁ a, Bulgaria

ABSTRACT opment of extensional basins and abundant ation to the east in the Intrapontide zone, which magmatism due to trench rollback. The time contains the remnants of a complex assemblage The generally east-west–trending Balkan of the fi nal foreland fold-thrust belt defor- of Mesozoic and early Cenozoic oceanic frag- orogen (eastern Europe) consists of a north- mation was late Eocene extending into Oli- ments (Fig. 2; e.g., Okay et al., 2001a, 2001b; ern belt of folded and thrusted Mesozoic gocene or early Miocene, contemporaneous Robertson et al., 2004). The main part of the and Cenozoic strata that forms the external with the extension to the south. The deforma- Balkan orogen within Bulgaria consists of a fold-thrust belt of late Mesozoic and early tion within the fold-thrust belt was caused northern belt of folded and thrusted Mesozoic Cenozoic age, and a southern belt that con- by a transfer of transpressional right shear and Cenozoic strata that forms the external fold- sists of deformed igneous and metamorphic within north Bulgaria and the Southern thrust belt of late Mesozoic and early Cenozoic rocks overprinted by Cenozoic extensional Carpathians as crustal units were translated age and a southern part that consists of deformed basins. Unlike most foreland fold-thrust northward west of the Moesian foreland igneous and metamorphic rocks overprinted by belts, wherein deformation commonly crust and moved northeast and eastward into Cenozoic extensional basins (Figs. 2 and 3). The migrates toward the foreland, the fold-thrust the eastern Carpathian west-dipping sub- fold-thrust belt is exposed within the Forebalkan, belt within the Balkan orogen is marginal to duction zone. During the third event of defor- Stara Planina, and the northern part of the Sredna the Moesian Platform to the north, but was mation crustal units were molded around Gora topographic and tectonic units and is the deformed in at least three events related the Moesian foreland crust. The shortening main focus of this paper (Fig. 3). Although to three different dynamic systems caused ceased by early Miocene time and the right Stara Planina means the “old mountains,” it is a by changes in plate interactions. The earli- shear west of Moesian foreland crust was misnomer, as it is fl anked on the south by the est event of late-Early to early-Late Creta- manifested by discrete right-slip faults to late Cenozoic to active extensional Sub-Balkan ceous deformed strata deposited within the the present. During this third event southern graben system, which is mostly responsible for Moesian continental margin and within a Bulgaria was in an extensional regime that its elevation (Tzankov et al., 1996; Roy et al., continental rifted belt containing deep-water dominated the south- to southwest-vergent 1996). Within the Sredna Gora to the south are fl ysch of Late Jurassic–Early Cretaceous age, Hellenide orogen throughout the Cenozoic, the remnants of a Late Cretaceous backarc or a probable eastward extension of oceanic thus dividing the Balkan orogen into two dif- intraarc basin that has also been deformed; the troughs from the Southern Carpathians. The ferent deformational regions. structures are well exposed in the west, but are shortening was a consequence of south or largely covered by younger strata to the east. southwest synthetic subduction within the INTRODUCTION Although these rocks are folded and thrusted, Vardar zone along the southern margin of this belt of structures is generally not considered the Balkan orogen. In Late Cretaceous time The Balkan orogen within Bulgaria and to be part of the external fold-thrust belt; how- a backarc and/or intraarc rift zone developed northern Greece is the eastern continuation of ever, we regard it as part of external fold-thrust along the southern margin of the fold belt, the European Mesozoic and Cenozoic Alpide belt (discussed herein). Farther south the rocks terminating shortening. The backarc and/or folded chain. Within Bulgaria, northern Greece, within the Rhodope Mountains and their contin- intraarc basin closed in Late Cretaceous– and parts of Serbia and Macedonia to the west, uation into Greece to the south consist of a com- early Paleocene time, deforming the fold- the orogen consists of topographic units that plex of Precambrian(?), Paleozoic, Mesozoic, thrust belt for a second time, but antitheti- are in part a refl ection of their underlying geol- and early Cenozoic rocks metamorphosed and cally to north or northeast subduction in the ogy (Figs. 1–3; e.g., see Boyanov et al., 1989; intruded by abundant magmatic rocks of Meso- Vardar zone. North- and northwest-vergent Dabovski et al., 2002; Zagorchev et al., 2009). zoic and Cenozoic age (for a review see Burg, subduction within the Vardar zone caused The Balkan orogen is bounded on the north by 2012). They were deformed principally during magmatism, metamorphism, and deforma- the Moesian plain, which is underlain by a base- Mesozoic and early Cenozoic shortening events, tion within the Rhodope area of southern ment of Precambrian and Paleozoic rocks that and beginning in about middle to early-late Bulgaria south of the foreland thrust belt. In were largely undeformed during alpine time, Eocene time (Burchfi el et al., 2003), extensional Paleogene time the southern part of the Bal- and by the Vardar zone (sensu lato) on the west tectonism became the dominant mode of defor- kan orogen became extensional with devel- and south (Schmid et al., 2008) and its continu- mation within central and southern Bulgaria

Geosphere; April 2015; v. 11; no. 2; p. 463–490; doi:10.1130/GES01020.1; 17 ﬁ gures. Received 24 December 2013 ♦ Revision received 6 November 2014 ♦ Accepted 23 December 2014 ♦ Published online 27 February 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

ROMANIA

SERBIA Fore Black Moesian Plain Sea Forebalkan Stara SW Planina KOSOVO Black Sea

Mts Sredna Gora Va Strandja Bulgarian BULGARIA rdar West Mountains Rhodopian East MACEDONIA Mountains Zone Ver GREECE Thrace TURKEY Mountainstiskos ALBANIA Zone 0 100 km Intrapontide Aegean Sea

Figure 1. Topographic elements of the Balkan mountain chain in the southern Balkans. These topographic features are also an expression of the underlying geological units of the Balkan orogen shown in Figure 2. Dashed lines show the eastern and northern boundaries of the Vardar and Intrapontide zones, respectively.

with the formation of numerous extensional the tectonics of Bulgaria (Yovchev, 1971; geo- FORELAND FOLD-THRUST BELT basins accompanied by abundant magmatic logical maps of Bulgaria at scales of 1:100,000 OF THE BALKAN OROGEN activity (Ivanov, 1988; Bonev and Beccaletto, [Cheshitev, 1990–1995] and 1:500,000 [Cheshi- 2007; Burchfi el et al., 2008). tev and Kancev, 1989]). Our reconstructions The Mesozoic and Cenozoic foreland fold- The fi rst description of the tectonics of Bul- concerning Bulgarian territory are based on thrust belt of the Balkan orogen is best exposed garia was by Cvijic (1904) in his studies on the these works as well as our own fi eld work and within the Forebalkan and Stara Planina units structure of the Balkan Peninsula. From south to fi eld trips led by numerous Bulgarian geologists and to a lesser degree within the western part north Cvijic (1904) distinguished the Rhodope to many parts of the orogen. of the Sredna Gora unit (Fig. 3). Rocks form- Massif, Transitional zone, Balkan system, and The main focus of this paper is the fold-thrust ing the fold-thrust belt are of Mesozoic and Balkan plate (Moesian Platform in modern belt that is exposed within the Forebalkan, Stara Cenozoic age and were deposited along the terminology). St. Bončev (1936) introduced Planina, and part of the Sredna Gora topographic southern part of the Moesian shelf, the southern the Balkanides as an orogenic system and sub- and structural units (Fig. 3). This fold-thrust belt margin of the European continental crust. The divided it into three main units, from north to has the unusual characteristic of having been fold-thrust belt also involves rocks deformed, south, the Forebalkan, Balkan, and Srednogorie; deformed in at least three superposed different metamorphosed, and intruded by plutons in he assigned the Moesian Platform to the north events of different ages, and deformation did not pre-Mesozoic time that formed the crust below to the foreland of the orogen. The Srednogorie migrate from its internal to external parts, as in the Mesozoic Moesian shelf strata. Triassic to was accepted as the oldest tectonic element many fold-thrust belts. In addition, it is necessary Middle Jurassic shallow-water deposits form and in the strictest sense did not belong to the to try to relate these three deformational events to the base of the Moesian Alpine succession and Balkanides. The boundaries between the units orogen-wide processes. For at least the two older unconformably overlie pre-Mesozoic basement within the orogen were traced and interpreted in deformations (late-Early Cretaceous to early- rocks; both sequences are exposed within the different ways based on different criteria (e.g., Late Cretaceous and latest Cretaceous–early foreland fold-thrust belt and to the south in cen- see Yovchev, 1971; Bonchev, 1986; Gocev, Paleogene) the dynamics are related to activity tral Bulgaria (Fig. 4). 1986; Ivanov, 1988; Dabovski et al., 2002). The along the western and southern plate boundary The pre-alpine basement rocks assigned to differences in these interpretations refl ect the occupied by the Vardar zone, but for the younger the Moesian shelf form the exposed parts of the complexity and unusual character of the orogen. deformational event (middle Eocene to middle Moesian craton in the foreland fold-thrust belt Useful published works that contain extended Miocene) the dynamics are related to activity in Bulgaria and demonstrate that their overly- and detailed description of the structure include within the Carpathian orogen to the north. ing Triassic and Jurassic strata were deposited

464 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

Cenozoic CircumRhodope Vardar zone Figure 2. Generalized geologi- strata Allochthon cal map of the Balkan orogen and adjacent units in Serbia Paleogene Metamorphic rocks strata and some Mesozoic strata and Macedonia. Yellow—late volcanic rocks some volcanic rocks Cenozoic and Holocene sedimentary rocks; orange—Paleo- ‘Severin unit gene rocks; blue—Mesozoic rocks of the Moesian shelf and 20° 28° margin; red—rocks of Precam- YUGOSLAVIASERBIA brian to Mesozoic rocks meta- 44° ROMANIA 44° morphosed for the last time during Mesozoic to early Ceno- zoic time; green—Mesozoic rocks of the Vardar zone in the BULGARIA

west (interleaved with largely Black Sea older metamorphic and igneous rocks in red) and outcrops

of rocks in allochthonous posi- Adriatic Sea tion along the southern part of the orogen; purple—rocks of ALBANIA MACEDONIA the circum-Rhodope belt; lime green in northwestern Bulgaria TURKEY and Southern Carpathians— Vardar zone Cretaceous ﬂ ysch. Heavy blue GREECE zone lines follow thrust faults in Intrapontide Southern Carpathians and southeastern Serbia and along 40° 100 km 40° the eastern limit of the Vardar zone in Serbia, Macedonia, and Aegean Sea Greece and the Intrapontide zone in northwestern Turkey. 28° 20°

on continental crust (Fig. 4). Some Precam- been accreted in Mesozoic time (Fig. 4). Rocks the magnitude of accretionary shortening and brian metamorphic rocks are present, but most of the Rhodope Mountains underwent extensive Cenozoic extension. of the basement consists of a thick succession metamorphism and complex deformation in Nonmarine lower Triassic rocks transgress of metasedimentary and locally metavolcanic Mesozoic (and possibly Paleozoic) time, but the over the Permian and older basement rocks rocks of late Precambrian to Carboniferous age. regional relations of these events are still being along an unconformity widely exposed in north- They were intruded by large bodies of middle elucidated (e.g., see De Wet et al., 1989; Kilias west and central Bulgaria (Fig. 4). Shallow- to late Paleozoic igneous rocks and were meta- et al., 1999; Zagorchev, 2001; Burg, 2012). water marine conditions were established in late- morphosed from low to high grade. Locally they Some units contain evidence for ultrahigh-pres- Early Triassic time and extended through several are unconformably overlain by Late Carbonifer- sure metamorphism, and diamonds have been transgressive-regressive cycles into Late Triassic ous–Permian terrigenous sedimentary rocks and reported from some of the rocks (Kostopoulos time (Tronkov et al., 1965). Extension began in nonmarine volcanic and volcaniclastic rocks et al., 2000; Mposkos and Krohe, 2006; Bauer the Early Triassic and continued into the Juras- that have been intruded by their plutonic equiva- et al., 2007; Wawrzenitz and Mposkos, 1997; sic; extensional structures are clearly evident in lents (locally true for the volcanics but not for Liati et al., 2002). Some have suggested that the the subsurface of the main part of the foreland the sedimentary rocks). We regard all these rocks in the southern part of Rhodope Moun- fold-thrust belt (see seismic section in Georgiev rocks to be basement and parts of the Moesian tains are an assemblage of continental fragments et al., 2001; cross sections in Vangelov et al., craton before development of a passive margin accreted at various times during the Mesozoic, 2013). The faults show mainly down-to-the- during Triassic–Early Jurassic time. the last accretion having occurred in Late Cre- south displacement with thickening of Late Tri- The metamorphic rocks exposed south of taceous time (e.g., Turpaud and Reischmann, assic and Early Jurassic sedimentary units into the southern limit of known Mesozoic Moesian 2010; Burg, 2012); however, we interpret most the faults (Tronkov, 1963; Atanasov and Bokov, shelf strata probably mostly belong to the of the pre-Mesozoic rocks in Bulgaria as part 1983). The Triassic to Early Jurassic shallow- Moesian continental basement and possibly con- of the Moesian continental basement by Meso- water clastic and carbonate rocks are considered tain some metamorphosed strata of the Meosian zoic time. However, the width of the Moesian the earliest deposits of a south-facing passive shelf, but there are some rocks that may have shelf in the south remains uncertain because of margin in Bulgaria and began the Alpine period.

Geosphere, April 2015 465

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

LEGEND Folds 23° Thrust faults Normal faults 28° 44° 44°

Moesian Plain

ForebalkanFFo alkankan StaraStartaaraara n PlaninaPlPPlaninla Figure 3. Generalized Mesozoic aninnii a and Cenozoic structures of the Sredna SW a Balkan orogen. The narrowly W Gora spaced thrust faults and folds in the Forebalkan, Stara Planina, BulgarianBBu and parts of the Sredna Gora gag Rhodopianh p ri Mountains form the external fold-thrust iia t nsns a belt of the orogen. n

N 0 100km 28° 40° 23° Aegean Sea 40°

The position of the southern or western shelf the Moesian shelf exposed in southern Bulgaria by a thick upper Triassic (Carnian to Rheatian) edge for this continental margin is poorly known. (Fig. 4). Thus, while it is clear that the Triassic unit of black fl ysch that continues upward into In western Bulgaria is a small area of deep-water and Early Jurassic rocks of northwest and cen- a thick Middle Jurassic (Aalenian to Bathonian) Jurassic strata (the Trekljano Group; Zagorchev tral Bulgaria were deposited during extension, sequence black shale with numerous blocks and Tikhomirova, 1986; Fig. 5) that are above it is not clear how far these rocks were from the of Triassic carbonates (Georgiev et al., 2001; older shallow-water strata of the Moesian shelf shelf edge of the Moesian continental margin Tchoumatchenco et al., 2004), some of exotic and can be interpreted to be transitional into the to the south and west. Triassic deformation is stratigraphy. The interpretation of the Kotel zone oceanic rocks of the Vardar zone to the west (see known from rocks in the Strandja autochthon, rocks has been controversial. They have strati- following). All other rocks that are regarded as but its nature is unclear (Figs. 4 and 5; Sakar graphic similarities to the allochthonous rocks the deep-water equivalents to the shallow-water unit). Passive margin sedimentation continued in Strandja with which they are often correlated rocks of northwest and central Bulgaria are the during most of the Early and Middle Jurassic (Georgiev et al., 2001). The Kotel sequence is in allochthonous rocks in the Strandja Mountains and facies changes between different shallow- thrust contact with more normal Moesian shelf of southeastern Bulgaria and the thin sequences water environments can be determined through- deposits to the north, but are separated from the of chert, slate, and fi ne-grained clastic rocks out the area except in the southernmost part, rocks in Strandja by a wide belt of younger rocks in northern Greece (the Circum-Rhodope belt; where Jurassic rocks are rarely exposed or meta- (Figs. 5 and 6). The original tectonic position of Figs. 4 and 5). The original tectonic positions of morphosed (Sunal et al., 2011). the Kotel zone has been subject to several dif- these allochthonous deep-water Mesozoic rocks Beginning in the late Kimmeridgian and ferent interpretations that are critical to the tec- are generally interpreted to have been south of extending into the Hauterivian two areas within tonics of the Balkan orogen. Gočev (1986) inter- the Moesian shelf and south of the metamor- the Moesian shelf subsided rapidly and several preted the Kotel zone as deposited south of the phosed Mesozoic rocks, and the basement that kilometers of fl ysch were deposited in the Nis Moesian shelf and part of a far north-traveled underlies them that is also considered to be part and Trojan fl ysch troughs, which were later Strandja allochthon. Other interpretations were of the Moesian shelf (Georgiev et al., 2001; incorporated into the foreland fold-thrust belt proposed: Tchoumatchenko and Cernjvaska Okay et al., 2001a, 2001b). These autochtho- (Fig. 6). Along the southeastern margin of these (1990) suggested a turbidite succession fringing nous Mesozoic strata are poorly dated, but range fl ysch troughs is a distinctive narrow belt of the southern margin of the Moesian Platform; from Early Triassic to Middle Jurassic (Chata- lower Triassic to Jurassic shallow-water and Bonchev (1983, 1986) suggested a Moesian lov, 1990), and are the southernmost strata of deep-water strata, the Kotel zone, characterized marginal depression or a synkinematic mélange

466 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

Figure 4. Outcrops of Triassic LEGEND and lower and middle Jurassic rock of the Moesian shelf (all Metamorphic rocks of Precambrian, Lower and Middle Jurassic rocks fi gures that show paleogeogra- Paleozoic, Mesozoic, Cenozoic Protolith phy show only the areas where Circum-Rhodope rocks rocks of a specifi c age crop Triassic rocks out). Pink shows the distribu- Kotel Zone rocks tion of Triassic strata and dark Triassic deformed rocks blue shows the distribution 232 Vardar zone rocks 28° of lower and middle Jurassic Romania strata. Dotted areas within the 44° Moesian Platform 44° Triassic rocks are areas where Serbia Triassic deformation has been identifi ed. The blue dashed line shows the southern and west- Moesian Shelf ern limit of exposures of these rocks (labeled Tr-J1/2, mean- Southern Kotel Zone ing Triassic and lower and mid- Stara dle Jurassic). The light purple Planina areas are variably metamorphosed rocks of Precambrian, limit Vardar Zone Moesian Bulgaria Strandja Paleozoic, and Mesozoic to Shelf J 1/2 Allochthon of - early Cenozoic age. Some rocks Tr z in these areas may belong to the Rhodope rocks Moesian shelf sequence. Green Macedonia areas in the west are underlain Turkey by rocks of the Vardar zone Greece of largely oceanic character. Yellow areas are underlain by N Triassic and Jurassic strata of the Circum-Rhodope belt, the paleogeographic position of which was largely offshelf 0 100 km to deep water south of the 40° 23° Rhodope Moesian shelf; the areas are Circum- 28° 40° allochthonous with respect to the shelf strata. In the eastern part of the fold-thrust belt is a belt of Triassic and Jurassic strata (orange), the Kotel zone, that are partly similar to rocks of the Moesian shelf and in many places contain olistoliths and are interpreted by some as allochthonous with respect to the shelf strata and by others as a rift sequence within the Moesian shelf (Kunchev et al., 1995; Georgiev et al., 2001; Tchoumatchenco et al., 2004). The dashed line shows the present-day boundary of the oceanic Vardar zone in the west (green) and the northern limit of Circum-Rhodope rocks (yellow). The Kotel allochthon (orange) may be the northern limit of Circum-Rhodope rocks, but other interpretations are possible.

thrust northward over the Moesian Platform of outcrops near the Serbian and Romanian bor- and Schmid, 2005). In fi gure 9 of Fügenschuh during the Mid-Cretaceous deformation; and ders (Figs. 6 and 7). These areas of subsidence and Schmid (2005), this peninsula is shown as Kanchev et al. (1995) proposed a rift basin and fl ysch deposition are now separated by a extending into the Southern Carpathians as the within the Moesian shelf because some of the large and structurally disrupted carbonate plat- Danubian unit (Fig. 6). The relations between olistoliths are similar to rocks of the Moesian form. The tectonic position of the Sinaja fl ysch the Kraina fl ysch unit and the Nis-Trojan fl ysch shelf. In the interpretations that the Kotel zone is (and Kraina subunit) is uncertain and has been basins to the south within Bulgaria remain far traveled, the rocks can be regarded as part of interpreted as either a far-traveled allochthonous uncertain (see following). Okay et al. (2001a) the Circum-Rhodope units. The interpretation fl ysch succession, like the Ceahlau unit of Roma- and Georgiev et al. (2001) interpreted the fl ysch of these rocks remains unresolved, but is impor- nia (Sandulescu, l975) formed along the western troughs to be a foredeep for the Strandja alloch- tant in the tectonic history of Balkan orogen (see continental margin of the Moesian Platform, thon, but there is little evidence that the alloch- following). or a fl ysch trough developed within basins that thon extended into western Bulgaria south of Another fl ysch succession, the Kraina sub- extend into the Moesian passive margin from the troughs, and they may also be interpreted unit in northern Bulgaria (and extending into the north at the northern end of a peninsula that as inverted rift basins that developed into basins Romania), contains Berriasian to Barremian terminates the Moesian unit within the South- related to the fi rst major deformation of the fore- Sinaja fl ysch and currently forms a narrow belt ern Car pathians (shown in fi g. 9 of Fügenschuh land fold-thrust belt in mid-Cretaceous time.

Geosphere, April 2015 467

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

Figure 5. Exposures of upper Juras- sic rocks deposited beyond the limit of exposures of Triassic and Juras- LEGEND sic rocks of the Moesian shelf. Some units shown are the Triassic rocks in the Sakar unit (dark purple) and Jurassic shallow water rocks below Meta- Triassic rocks of Sakar Unit Vardar zone strata below the Strandja unit in the south- Strandja and in Circum-Rhodope

east (pale purple). Kotel zone middle Kotel Zone Jurassic rocks Mafic and ultramafic rocks of Vardar zone Jurassic rocks are in blue and Triassic Strandja rocks and Circum-Rhodope units rocks are in purple, and deep-water 23° Kotel Zone Triassic rocks 28° rocks of the Treklyano Group (dark Triassic shelf rocks Granitic rocks of the Vardar zone green) may form a transition from 44° Southern 44° the Moesian shelf into the oceanic rocks of the Vardar zone. Lime green are rocks of the Circum-Rhodope

limit unit that in the southeast are associ-

ated with mafi c and ultramafi c rocks Kotel Zone (black) and form the Strandja alloch- of Trekljano Shelf thon in Bulgaria. Yellow areas are T Moesian R Group Circum-Rhodope rocks or displaced - exposed J roc rocks below the Circum-Rhodope 1/2 of ks and Strandja allochthons. Within Vardar MFZ Strandja the Vardar zone are numerous dif- Sakar Unit Allochthon ferent types of upper Jurassic rocks that include mafi c and ultramafi c Zone rocks (black), fl ysch-type sediments Rhodope (green), shallow-water rocks in yellow and orange, and granitic rocks rcum - Ci in red. Dashed green line is north- of ern limit of Circum-Rhodope rocks; dashed blue line is southern limit limit of Triassic and lower and middle Northern Jurassic rocks of the Moesian shelf; N 0 100km dashed black line is eastern limit of 40° Vardar zone rocks. MFZ—location 23° Aegean Sea 28° 40° of Maritsa fault zone that fi gures in the interpretation of the tectonic setting discussion; Tr-J1/2—Triassic and lower and middle Jurassic.

The now-separated fl ysch troughs appear to emplaced the Kraina unit and the Severin alloch- formity ranges from early Albian to Turonian have extended across northern Bulgaria to the thon, their probable northward continuation in (Tzankov et al., 1995; Figs. 7 and 8). The hia- Black Sea; their age and sedimentary faces are the Southern Carpathians, and strata broadly tus at the uncon formity broadens to the east to considered to be the continuation of the oceanic adjacent to these fl ysch basins (Figs. 7 and 8). include the Hauterivian to Cenomanian in the Severin and Ceahlau units of the Carpathians. This event is well documented and was often Tvarditsa area, the Hauterivian to Turonian in the There is no evidence in Bulgaria that they con- assigned to the Austo alpine phase of tectonism area southwest of Etropole, and the Hauterivian tained an oceanic crust, unlike the rocks in the in the literature [tectonic phases, a concept often to Santonian in the area of Gabrovo and Kalofer. Carpathians; however, the relations of these associated with the works of Hans Stille (1924) At Tvarditsa there is a second very well dated fl ysch troughs to sedimentary environments that and further developed by Alexander Tollmann late Santonian–early Campanian folding. The may have been deposited on oceanic crust within (1963, 1968), divided the geological record into distribution of the unconformity at the base of the Southern Carpathians remain unexplored. short periods of deformation, or phases, sepa- the lower-upper Cretaceous rocks that places rated by longer periods of general quiescence]. an upper limit on this deformational period is FIRST FOLDING EVENT WITHIN THE Although the terminology is now rarely used, it shown in Figure 7. BALKAN FOLD-THRUST BELT should be abandoned; our use of event applies The region deformed during this time period to a period of time bounded by unconformities, is characterized by generally east-west–trend- The fi rst deformation event within the Bal- and deformation within this period of time may ing structures that extend through the foreland kan fold-thrust belt was late-Early Cretaceous be diachronous. The deformation is most closely fold-thrust belt from the eastern part of the area to early-Late Cretaceous, and deformed the dated by unconformities in the area of Vratsa through Elena to Vratsa in the west. Deforma- fl ysch units within Nis-Trojan fl ysch basins, and Lukovit, where the hiatus at the uncon- tion also involved rocks farther south within the

468 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

LEGEND

Deep water flysch deposits of Late Jurassic - Early Cretaceous Kotel Zone rocks Allochthonous metmorphic rocks of the Southern Canpathians

Shallow water margins of Autochthonous rocks of the flysch basins Southern Carpathians Oceanic suture in Figure 6. Deep-water flysch South Carpathians deposits of latest Jurassic and Early Cretaceous age. The Supragetic Nis and Trojan fl ysch basins Units eahlau are interpreted as extensional C basins that formed within the Danubian Moseian shelf area. They were Getic displaced northward during the shortening of the foreland fold- Severin Romania thrust belt within Bulgaria, so Moesian Autochthon they do not overlie extensional structures within the basement rocks below. The Kraina unit Kraina unit in the northwestern part of Serbia Bulgaria is the southern extension of the deep-water depos- Vardar its (Severin unit: Ceahlau and Trojan Flysch Basin Sinaja fl ysch) within the South- ern Car pathians and are con- Nis sidered to have been deposited on a thin continental or oceanic Kotel zone crust. These fl ysch strata were thrust eastward and are alloch- Zone Bulgaria thonous, but how they correlate structurally with the Nis and Trojan units is unknown. Flysch and deep-water deposits Macedonia are present within the Vardar Turkey oceanic area and have no direct Greece connection with these other fl ysch units. N

0 100 km

Stara Planina unit from Tvarditsa, and south ments south of Trojan in the areas of Tvarditsa, strata (Tchoumatchenko and Cernjavska , l989). of Etropole, through Svoge and into Serbia Kalofer, Etropole, south of Etropole , and Svoge. They do not extend farther west than Tvarditsa. (Fig. 7). In the Trojan basin the structural ver- The younger of the two deformations present in In some regional tectonic schemes these rocks gence is generally to the north and Permian the Tvarditsa area formed recumbent folds with are interpreted to be far traveled and represent rocks are present in the cores of some of the overturned limbs of several kilometers. Areas the northern leading edge of thrust sheets now folds, but no older rocks are exposed, suggesting northwest and west of Vratsa were not affected preserved in Strandja and derived from the south that basement rocks are generally not involved by deformation during this event (Fig. 7). of the southern Meosian continental shelf edge in the deformation. Cleavage was formed in In the eastern part of the area north of (Gočev, 1986). these rocks, particularly in the southern parts of Tvarditsa , the westernmost and earliest struc- In northwesternmost Bulgaria, the Kraina the Nis and Trojan troughs. Farther south base- tures in the Kotel zone (Fig. 7), deep-water unit was deformed during this ﬁ rst event. The ment rocks were involved along the southern basinal facies of Triassic and Jurassic rocks, lower Cretaceous Sinaja ﬂ ysch, correlated with margin of the fold-thrust belt in tectonic ele- are unconformably overlapped by late Albian the Ceahlau and Severin units of the eastern

Geosphere, April 2015 469

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

LEGEND

TGTG 23° Allochthonous units of the Mafic and ultramafic Kotel Zone strata Treklyano Circum-Rhodope, Strandja rocks Group Severin and South Carpathian area Allochthon Unconformities that date the late Early to early Late Cretaceous structures. Kraina Unit Romania 28° 44° (Siniaja flysch) 44° Serbia

Morava Allochthon Forebalkan

0.0000 0.22 0.4 0.6 0.8 1.00 Vratsa Lukovit Berkovicaa Veliko Tarnovo Stara Sovge Planina Etropole Elena Sofiafia Tetevanetevan U Tvardiatsa Trojan GabrovoGa Kotel zone

Srednagora Kalofer Strandja TG Allochthon Bulgaria

Macedonia

Vardar Turkey Greece

Zone Circum-Rhodope N 0 100 km

Unit 28° 40° 23° 40°

Figure 7. Distribution of folds and faults of late-Early Cretaceous to early-Late Cretaceous age within the fold- thrust belt of Bulgaria. The unconformities that date structures of this age are shown in green and from these areas structures interpreted to be the same age are projected along the belt. The unconformities are folded; therefore the folds that fold them are from younger events, so the folds shown in the fi gure are in many cases also partly younger structures. The deformation of this age affected rocks in the Forebalkan, Stara Planina, and northern Sredna Gora units. The Kotel zone of uncertain structural position is shown in orange and was folded during this time. Other structures of probably the same age are the Moravian allochthon with the eastern thrust shown in Serbia and westernmost Bulgaria, overlying the Jurassic–lower Cretaceous Treklyano Group strata (TG— dark blue), and the Strandja allochthon (green) and their probable correlatives within the Circum-Rhodope unit (green; mafi c and ultramafi c shown in black), the northern limit of which is shown by the green dashed line. Struc- tures of this age within the Southern Carpathians (Severin allochthon and Kraina unit) are also shown in green.

and Southern Carpathians, respectively (see of the Kraina unit during this fi rst event is based Areas of Related Early Cretaceous to following), that makes up the Kraina subunit on regional relations with the Carpathians in Early-Late Cretaceous Convergent is strongly deformed and cleaved. The struc- Romania (Sandulescu, l975; Fügenschuh and Deformation tures in northwest Bulgaria are poorly dated Schmid, 2005). If the Sinaja fl ysch is correlative because they are overlain by Neogene sedimen- with the units in the Southern and eastern Car- In western Bulgaria and extending through tary rocks, were overthrust by the Belogradchik pathians, it may be far traveled from the west eastern Serbia and eastern Macedonia are struc- anticlinorium in middle Eocene time, and have and would be emplaced during this fi rst event; tures related to the Morava thrust belt (Zagor- obviously been reworked by younger deforma- however, newer interpretations may limit its dis- chev, 1996; Fig. 7). The Morava thrust belt is tion (see following). Assigning the deformation placement (see following). characterized by northeast-directed thrust faults

470 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen al . Tim- Miocene ion at the old-thrust belt

Weak folding followed by followed folding Weak extension -Q—latest Mio-

Folding and thrusting Folding

Folding SW of Sofia Folding Extension

Folding and thrusting in the Folding area of Trvarditsa Trvarditsa of area Folding and thrusting. Not significant and thrusting. Folding in the area of Vratsa and to west. west. and to Vratsa in ofthe area Intensive to the east. the east. to Intensive 3

Folding and thrusting without Folding sharp boundaries 1 —late Paleocene; 2

Eoc

? —Early to Late Triassic. —Early to Late

E of Tvarditsa S-SW of Tvarditsa Tvarditsa S-SW of Tvarditsa E of

? 1-3 —early and middle Eocene; Pal gures for end of deformation at that locality. Green Green end of deformation at that locality. for gures

? 1-2

e -sediments

Eoc

-Q

outhern type

Southern type -sediments

N —late Eocene; Eoc 3

Olig

ents —Early Jurassic to Early Cretaceous; T —Early Jurassic to Early Cretaceous; 1

Pal

Pal -K 1

Gabrovo NW of Kalofer SW-Etropole Tvarditsa Tvarditsa NW of KaloferGabrovo SW-Etropole

n type-se

orthern type-sedim

NoNorthern type-sediments

1-2

Eoc

- K 1-3

Eoc

1-3

- K —late-early Miocene–late Miocene; Eoc

Lukovit

1 2

-- Pal Pal

2 -N

K 2

2 1

- N

Vratsa

lochth

athian- —Late Cretaceous–early Paleocene; J —Late Cretaceous–early

(allochthon)(allochthon) 1 ed by the outcrops near the towns indicated. The upper limit of the three major hiatuses that mark the three major deformation major hiatuses that mark the three major limit of the three The upper the towns indicated. near ed by the outcrops

NW Bulgaria

Carpathian-type -Pal 2

periods within the fold-thrust belt are marked by colored lines that are shown on the ﬁ lines that are marked by colored periods within the fold-thrust belt are Eocene deformation deformation, orange line marks the end of Late Cretaceous–early line marks the end of mid-Cretaceous and by the middle beginning of extension locally shown by graben development in the central and eastern part Forebalkan ing of late-middle Eocene and late Eocene–early Miocene deformation is only marked by the end of deposition before the deformat ing of late-middle Eocene and late Eocene–early Miocene deformation is only marked by the end deposition before ages of units: N Cheshitev (1990–1995). Designations for from fold-thrust belt. Data are strata in the western Forebalkan identiﬁ Figure 8. Time-stratigraphic section along the Forebalkan fold-thrust belt. The sections are shown for different parts of the f different shown for The sections are fold-thrust belt. section along the Forebalkan Time-stratigraphic 8. Figure K cene–Quaternary; N

n ry ry

an n

vi an

i an

oni an

ach

arc

aeti

cian

emuri

ang

matia

bonian

ntonia

a al

rtonian

Albian

Aptian

arn

Baj

mme

Monian

Turonian Turonian

Berri

ei Oxford

Nori

D Meotian

Chattian Rupelia

Bath

Aal

Romania

Lutetian Lutetian

S Coniacian Coniacian

Berremi

Val

Ani

S Badenian Burdigalian Aquitanian Aquitanian

Yepresian Thanetian

Hauteri

Quaterna

Hettang

Lad

aastrichtian

Pria Ba

Campanian

Cenomanian

Scyth

e ocen Mi e Eocen Paleoc pper U Lower Middle Lower pe Upper Upper d

Plio

Oli

Low

Jurassic Jurassic Triassic Triassic Neogene Paleogene Cretaceous

Geosphere, April 2015 471

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

that involve metamorphic rocks as well as Tri- (2001a) presented evidence that the deforma- Danubian unit, sealed by Maastrichtian strata, assic to Kimmeridgian–Valanginian strata, tion and metamorphism of the Strandja rocks forming the large half-window in the Southern the uppermost Jurassic and lower Cretaceous occurred in Late Jurassic time (Sunal et al., Carpathians (Codarcea, 1940; Burchfi el, 1976; strata being characterized by turbidites (Trekly- 2011). The unconformably overlying strata are Sandulescu, 1984, 1994). We consider the fi rst ano Group, Fig. 7; Nachev and Nikolov, 1968; Cenomanian, and Okay et al. (2001a) assigned event to be the northwestern continuation of Zagorchev and Tikhomirova, 1986) represent- the deformation a Late Jurasssic–Early Creta- the mid-Cretaceous event within northwestern ing a western deep-water assemblage in the ceous age. Georgiev et al. (2001) regarded the Bulgaria, but the structures are greatly disrupted western part of the Moesian shelf. The thrusts deformation as mid-Cretaceous age. It is not by younger structures and traces of the oldest are overlapped by late Eocene strata, thus the diffi cult to interpret the deformation within the structures are diffi cult to correlate in detail (see timing based on stratigraphy is poorly known. foreland fold-thrust belt to be related to thrusting following). A third structural event took place Recent thermochronological data presented by along the continent-ocean boundary between in the late Paleocene and later, and is related to Kounov et al. (2010) indicated that the thrust- the Moesian shelf and the Vardar oceanic realm the third deformation in the Forebalkan zone ing occurred during late-Early Cretaceous time, that formed the Morava and Circum-Rhodope of Bulgaria (considered in more detail in the between 139 and 112 Ma, a little older than the tectonic units. The deformation within the fold- following). dated folding within the Forebalkan zone; how- thrust belt of central Bulgaria was partly local- ever, the uncertainties are such that the defor- ized within the Nis-Trojan fl ysch basins, but Early-Late Cretaceous to Latest mation within the two areas could be mostly also affected rocks beyond the margins of the Cretaceous–Paleocene Time contemporaneous. basins. The deformation extended west into Farther south in northern Greece on the the area east of Vratsa, as shown by the uncon- Between the end of the Early Cretaceous Chakadiki Peninsula are an imbricated assem- formity there, but farther west there is no evi- deformational period and the next younger blage of basement rocks and Triassic and Juras- dence for folding of this age, except in the Kraina deformational period of latest Cretaceous–ear- sic rocks with both shallow-water and deep- and southern Carpathians areas. In the area liest Cenozoic age, broad areas of northwest water sections that are mixed together by faults between Tetevan and Vratsa the deep Trojan and north-central Bulgaria were covered by and assigned to the Circum-Rhodope unit fl ysch basin grades into shelf deposits and the both shallow- and deep-water strata. However, (Fig. 7; Papanikolaou, 2009). There are mafi c deformation extended beyond the western limit sedimentary rocks of this age are not preserved and ultramafi c rocks within the faulted assem- of the basin to the east of Vratsa. Farther south above the folded rocks in the central part of the blage that were emplaced eastward in Late the deformation extended to east of Sofi a into Nis and Trojan troughs, e.g., in regions around Jurassic to Early Cretaceous time. Similar rocks the northern part of the Sredna Gora unit (Fig. 7). Teteven and Trojan (Figs. 7 and 9) where are present in small areas at the south end of Although there is no evidence for the west- Permian rocks are exposed in the cores of folds, the peninsula as well as in limited outcrops in ward continuation of these folds and thrust thus the age of the structures in this area must eastern Greece and in the Strandja allochthon faults in the western part of the Forebalkan be inferred by projecting the structures into this that are also assigned to the Circum-Rhodope zone, there was deformation within the Kraina area from surrounding areas where the younger unit (Fig. 7). unit in the northwestern part of Bulgaria during rocks are preserved and can be dated. In southeastern Bulgaria the low-grade the mid-Cretaceous event. The Kraina unit con- West of the folds east of Vratsa, deposition Triassic and Jurassic metasedimentary clas- tains Jurassic and Early Cretaceous fl ysch that of shallow-marine calcareous rocks with local tic sequences of the Strandja thrust sheets is correlated with the Sinaja fl ysch that occurs terrigenous interbeds took place paraconform- were emplaced to the north or northeast and in the Severin allochthon in the Southern Car- ably above lower Cretaceous rocks. Farther west are unconformably overlain by Cenomanian pathians (Fig. 6). The Severin allochthon tecton- subsidence was more rapid with the deposition strata (Chatalov, 1990). These rocks represent ically overlies the Danubian unit, which consists of the Kula fl ysch in northernmost Bulgaria a deep-water facies and were originally depos- of a metamorphic basement and an overlying and extending to eastern Serbia and southern ited south of the Moesian shelf on which they Triassic–Early Cretaceous shallow-water sec- Ro mania (Figs. 7 and 9). lie. The underlying basement is overlain by tion that is interpreted to be the western con- South of most of the foreland fold-thrust belt, metamorphosed marble and metaclastic rocks tinuation of the Moesian continental crust of during Late Cretaceous time, thick sections of assigned a Triassic to Middle Jurassic age. the Balkan foreland. Both the Danubian and volcanic and volcaniclastic rocks and fl ysch The Strandja allochthon is also assigned to the Severin units are overlain by the Getic-Supra- were deposited within an intraarc or backarc Circum-Rhodope unit; thus the unit appears to getic thrust faults, that consist mainly of a meta- extensional setting (Fig. 9; Boccaletti et al., be around the southern margin of the Rhodope morphic basement overlain by a shallow-water 1974; von Quadt et al., 2005; Burg, 2012), Mountains and continues in rocks along the Mesozoic section (Fig. 6). The Getic-Supragetic where they locally overlie Mesozoic sedimen- southeastern margin of the Vardar zone. The unit forms a huge half-window in the southern tary rocks and older basement rocks deformed thrusting of the Strandja rocks suggests that part of the Southern Carpathians and probably in the earlier deformational event. The main they may have formed by obduction of deep- tectonically overlapped both the Danubian and axis of igneous activity was south of the Stara water rocks from the margin of, or from within, Severin units, but was modifi ed by normal faults Planina, mostly within the Sredna Gora unit, oceanic areas that were around the southern in its eastern part in mid-Cenozoic time (see and formed a magmatic arc developed above a extent of the Moesian shelf (Papanikolaou, Fügenschuh and Schmid, 2005). The thrust- north-dipping subduction zone (Boccaletti et al., 2009; Bonev and Stampfl i, 2011). The thrust ing is from west to east and occurred in two 1974) located in northern Greece (present-day faults were emplaced on the Moesian shelf and events: the fi rst was mid-Cretaceous thrusting position) and continuing northward into the Var- may have extended as far north as the Kotel of the Getic-Supragetic above the Severin oce- dar zone of Macedonia and Serbia. Georgiev zone in the eastern part of the Forebalkan–Stara anic unit, sealed by Albian–Cenomanian strata, et al. (2012) studied these rocks in the eastern Planina area (Gočev, 1986; Figs. 6 and 7). followed by a second west to east thrusting of part of the Balkan orogen; they showed con- Dabovski and Savov (1988) and Okay et al. the Getic-Supragetic-Severin complex above the vincingly their intraarc and backarc position

472 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

LEGEND

Vardar zone strata Granitic rocks Volcanogenic Volcanic Non-volcanic Luda Kamchia strata rocks shallow-water strata flysch 23° Romania 28° 44° Kula basin 44°

0.0 0.2 0.4 0.6 0.8 Forebalkan Serbia 1.0 Vratsa West Berkovica Stara Pl Veliko Tarnovo anina

LudaL B Sofia Teteven Gabrovo lack Trojan Kamchia

Back SrednagoraBulgaria West Bulgarian

Sea Vardar Magmatic Arc Basin

fault Arc

Mountains Macedonia Rhodope

zone Turkey Greece Istanbul zone zone Intrapontide 0 100 km N 28° 23° 40° 40°

Figure 9. Paleogeographic elements. The gently arcuate belt of sedimentary and volcanic rocks (pink and purple) of Late Cretaceous age was deposited within the Sreda Gora unit of central Bulgaria. The well-defi ned belt of rocks was deposited within a backarc or intraarc basin and the arc is marked by Late Cretaceous plutons (red). The northern boundary was well defi ned; shallow-marine (blue) and fl ysch (Luda Kamchia fl ysch, light green) strata to the north are mainly devoid of volcanic material. The belt of magmatic rocks is interpreted to have formed by northward subduction from the Vardar zone (green) and it eastward extension in the Intrapontide zone. The extension that formed the backarc and intraarc basin extended eastward through the Black Sea area and into northern Turkey. East of Bulgaria is the west Black Sea fault along which the Istanbul zone moved south and was emplaced by early Eocene time.

and demonstrated that they were part of a mag- rich to the south and probably represent a more break between the fi rst and second convergent matic belt formed between 92 and 78 Ma. The northern part of the backarc–intraarc basin; they events within the fold-thrust belt. It also has northern margin of the backarc-intraarc basin are separated by younger thrust faults and were been suggested that the extension is related to is not well defi ned because transitions between deposited a considerable distance from con- the extensional opening of the Black Sea and volcani clastic rocks and the shallow-water strata temporaneous Late Cretaceous shallow-water to the formation of the West Black Sea fault, farther north are not preserved. In the eastern- sediments of the Moesian Platform to the north a right-slip fault that is along the eastern con- most part of the area, beginning near Gabrovo (Fig. 9). Their thickness and lack of transition tinental margin of Bulgaria (Okay et al., 1994). and extending to the Black Sea, is a thick to the shallow-water nonvolcanic rocks farther East of this fault the Istanbul zone moved south- sequence of largely nonvolcanic terrigenous north suggests that the backarc-intraarc basin ward to be emplaced in the western part of the sediments, much of it fl ysch (referred to as the had a sharply defi ned northern border formed by northern Pontides by early Eocene time (Okay Luda Kamchia trough) ranging in age from Late extension superimposed on the region affected et al., 1994; Fig. 9). The easternmost part of the Cretaceous to middle Eocene. Near the Black by the earlier shortening deformation. It has Srednogorie zone to the south has a very thick Sea there are some sediments of Eocene–Oligo- been suggested, but is diffi cult to prove, that the volcanic succession, as thick as 4 km, with cene age, but they are overlain structurally by northern margin of the backarc-intraarc basin abundant pillow lavas of high potassium com- strata of the Luda Kamchia trough. The upper may have been locally or regionally exposed position, suggesting an initial backarc rifting limit of the volcanic succession is pre–late dry land (Nachev, 1993). The extensional set- (Boccaletti et al., 1978; Georgiev et al., 2001) Campanian. These strata become more volcanic ting for these volcanic rocks forms a major that did not develop oceanic crust.

Geosphere, April 2015 473

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

SECOND PERIOD OF DEFORMATION: Lukovit and Vratsa it ranges from late Paleo- folding and thrusting of this age was widespread LATEST CRETACEOUS TO cene to early Eocene and from early Paleocene (Fig. 10) and the distribution of structures of lat- EARLY PALEOGENE to early Eocene, respectively. The hiatus also est Cretaceous to late Paleocene or early Eocene broadens to the south where it ranges from age overprints structures of the early-Late Cre- The second major period of deformation to early Paleocene to early Eocene near Kalofer taceous deformation. The structures consist of affect northwest and north-central Bulgaria and southwest of Etropole and to latest Cre- east-west–trending folds and thrust faults, gen- took place in latest Cretaceous and early Paleo- taceous to early Eocene near Tvarditsa (Figs. erally north vergent, from Varna in the east to gene time (Fig. 10). The broadest range for this 8 and 10). Vratsa in the west. It probably continues farther deformation is Maastrichtian to Thanetian time Throughout the region immediately in the west into the Southern Carpathians (see follow- and the evaluation of the hiatus that dates this southwestern part and south of the foreland ing), but the lack of Paleogene deposits in north- period of deformation is shown schematically fold-thrust belt, there is a general lack of Paleo- west Bulgaria does not permit the precise dat- (Figs. 8 and 10). It is most narrowly dated near gene strata (Fig. 11) and deformed upper Cre- ing of structures other than pre–late Neogene. Gabrovo, where the hiatus between deformed taceous rocks are overlain by Neogene rocks of South of the fold-thrust belt evidence for defor- and undeformed rocks is within the upper late Miocene or even Quaternary age. Thus it mation of this age is present near Kalofer and Paleocene, and a second deformation occurs a is impossible to assign the deformation of the Tvarditsa, where there are Paleogene rocks and little later very close to the Paleocene-Eocene upper Cretaceous rocks to a narrowly deﬁ ned structures, but the lack of extensive Paleogene boundary. The hiatus broadens to the west; near event, although based on more regional data, deposits makes it difﬁ cult to prove how wide-

LEGEND

Unconformities that date the Late Cretaceous - Paleocene structures. 23° Romania 28° 44° 44° BelogradchikBelo

VratsaVra

0.0 0.2 0.4

Serbia 0.6 0.8

Berkovicaer 1.0 U Lukovit

U U Varna Veliko Tarnovo Forebalkan Stara Planina Etropole Gabrovo Sofia Teteven U TrojanT

U Srednagora Kalofer Tvarditsa U West Bulgarian Bulgaria Vardar

Mountains Rhodope Macedonia

Zone Turkey

Greece

N 0 100 km 28° 23° 40° 40°

Figure 10. Structures formed during the Late Cretaceous–Paleocene shortening event. Thrust faults and folds are well developed through the Forebalkan, Stara Planina, and Sredna Gora units. The unconformity at the base of the early Eocene strata is shown by the orange lines; the distribution of these strata is shown in Figure 11. The blue lines show the boundaries of the major units as outlined in all of the ﬁ gures. Unit names are shown in the same color.

474 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

LEGEND

Shallow marine to Luda Kamchia Serbia 23° non-marine strata flysch Romania 28° 44° 44°

Rabishasha

0.0 0.2 0.4 0.6 0.8 1.0 Vratsa Lukovit BerkovicaBer Varna VelikokT Tarnovo Forebalkan Stara Planina Etropole Sofiafi Gabrovoabrovo Tetevanetevan TrojanTr

Srednagora Kalofer TvarditsaLuda Kamchia bbasin Macedonia West Bulgarian Bulgaria

Mountains Rhodope

Turkey Greece

0 100 km

Aegean Sea 28° 40° 23° 40°

Figure 11. Distribution of strata of early and middle Eocene shown in orange. These rocks rest unconformably on the structures that formed in Late Cretaceous–Paleocene time. They are mostly shallow-marine to nonmarine strata except for the ﬂ ysch-type strata that were deposited in the Luda Kamchia basin.

spread they are. The deformation of this time rocks, but it is impossible to separate events of the fold-thrust belt in northwest Bulgaria period was superimposed on the older structures from the mid-Cretaceous to Paleogene. At three (Codarcea, 1940; Burchﬁ el, 1976; Sandulescu, that were developed in pre-Turonian rocks of localities east and north of Rabisha (Fig. 11; see 1984, 1994). the eastern and central foreland fold-thrust belt Filipov and Cheshitiv, 1992) Paleogene (middle Where the two unconformities that date the and regions to the south of it. In the central part Eocene) rocks overlie folded upper Cretaceous mid-Cretaceous and Late Cretaceous–early of the foreland fold-thrust belt from Gabrovo to Carpathian-type strata dating the deformation as Paleogene events (Figs. 7 and 10) are close west of Teteven, there are no rocks younger than Late Cretaceous to middle Eocene. The middle together, such as east of Vratsa, north of Teteven , Early Cretaceous, and the relative effects of the Eocene is also folded, showing the effects of the near Gabrovo and north of Tvarditsa, the angu- two deformational events are very difﬁ cult to third period of deformation. By tracing struc- lar relations between beds at the unconformities separate. tures from east of Vratsa where they can be are highly variable. East of Vratsa and north West and northwest of Vratsa the age of dated westward, it is possible to interpret much of Teteven the angular relations below both the structures is not clear. Paleogene rocks of the structure in northwestern Bulgaria to have unconformities are moderate, a maximum of that would differentiate structures formed in formed during the middle Eocene, or perhaps ~30°–40°, suggesting the two events may be of this second event or younger time periods are in the earlier mid-Cretaceous. Early Paleogene about the same intensity; however, such relations largely missing. Neogene sedimentary rocks in and locally latest Cretaceous structures are pres- are not very substantive. These areas are near the area west of Vratsa unconformably overlie ent in the Southern Carpathians to the northwest the margins of the area deformed in mid-Cre- deformed Jurassic or locally lower Cretaceous and support the northwestward continuation taceous time. At Gabrovo rocks below the mid-

Geosphere, April 2015 475

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

Cretaceous unconformity are highly deformed, THIRD PERIOD OF DEFORMATION: but the upper limit for the third deformational isoclinally folded, and contain a well-developed MIDDLE EOCENE TO MIDDLE event or events is mostly provided by unconform- cleavage, whereas the Paleocene rocks above the MIOCENE ably overlying middle and upper Miocene, and unconformity are much less deformed and lack rarely lower Miocene, strata. Only in three areas cleavage. Similar relations are present north of Shortening deformation from middle Eocene can a strong, but circumstantial, case be made Tvarditsa and north of Kalofer. These relations to middle Miocene time is the third and fi nal con- for middle Eocene deformation in the fold-thrust yield only a preliminary picture of the relative vergent deformation in the foreland fold-thrust belt (Fig. 12). (1) South and west of Tvarditsa, importance of these two deformations, and much belt (Fig. 12). Structures formed during that deformed late middle and upper Eocene sedi- work needs to be done to unravel the relative time period are commonly assigned to middle mentary rocks overlie structures that are dated strengths of the two deformations throughout Eocene, Oligocene, or early Miocene deforma- as probable middle Eocene by projection from the area. tions. However, dating of these structures is not surrounding areas. (2) Likewise the thrust of On the regional scale, deformation occurring well constrained in many places because there crystalline rocks north and west of Kalofer over- in the latest Cretaceous to early Paleogene time is a widespread hiatus in the stratigraphic units rides middle Eocene rocks and is considered to period probably is related to the events leading from latest-middle Eocene to middle (locally be older than the late-middle Eocene rocks that to the fi nal closure of the Vardar ocean along the early) Miocene time (Figs. 8, 11, and 13), and are weakly folded near Tvarditsa (Bonchev, western and southern margins of the Moesian middle Miocene sedimentary rocks are the old- 1978). However, constraints on the timing of continental shelf (Burchfi el, l980; Roberson est rocks that unconformably overlie the struc- these structures are poor. (3) Major north-ver- and Dixon, l984; Dercourt et al., l986, Şengör tures in northwest Bulgaria (Figs. 12 and 13); gent thrusts and folds are present south and east and Yilmaz, l981). Postcollisional convergence however, in easternmost Bulgaria and trending of Gabrovo that extend eastward into the Black lasted into the middle Eocene, but the closure of into the Black Sea to the east there are more Sea. They carry rocks as young as early-middle the Vardar ocean is interpreted to be by north- complete sections that document deformation Eocene in their hanging walls, but concise upper ward subduction, in contrast to mid-Cretaceous that extends through that time period (Stuart limits on the deformation cannot be determined. subduction, which was southward (see follow- et al., 2011). Because the dating of the third Near the Black Sea coast these structures are ing). Northward polarity of subduction best period of deformation is poorly constrained, thrust over Oligocene rocks (Dachev et al., explains the geological relations at the time of it may have been a protracted or diachronous 1988), suggesting that at least the easternmost the second period of deformation, although not event, or may have consisted of more than one part of the belt was active during the Oligocene. all agree (for a discussion, see Burg, 2012). period of deformation, but at present that can- Much of the structure south and east of Gabrovo To the east, the fi nal displacement on the west not be resolved. Nevertheless, the deformation can interpreted as being part of this period of Black Sea fault ended in early Eocene time with occurred in a tectonic setting different from the deformation (Fig. 12). the emplacement of the Istanbul zone into the early two deformational events (see following). Recently published seismic and drilling data western Pontides (Okay et al., 1994; Fig. 9). From about late middle or late Eocene time to from the easternmost part of the fold-thrust belt the present most of area south of the fold-thrust where it extends into the Black Sea has docu- Latest Paleocene to Middle Eocene time belt in Bulgaria was dominated by extensional mented thrusts and associated folds that involve tectonism (see following; Marchev et al., 2004; early-middle Eocene rocks and are overlapped Following early Paleogene deformation, Bonev and Beccaletto, 2007; Burchfi el et al., unconformably by late-middle Eocene rocks, deposition of terrigenous strata with incursions 2008). Some evidence indicates that extension constraining the age of deformation there as of shallow-marine and brackish sediments took began during or between convergent deforma- middle Eocene (Stuart et al., 2011; Fig. 14). The place during latest Paleocene to (locally) early- tional events in Paleogene time, but widespread data from this area do not show a clear break middle Eocene time (Zagorchev et al., 1989; extension became dominant in about early-late between what we interpret to be the second and Goranov et al., 1992; Figs. 8 and 11). These Eocene time, marking the end of major regional third periods of deformation, and the data of strata are preserved in only a few places, mak- shortening within the Balkan orogen and most Stuart et al. (2011) show that deformation con- ing it diffi cult to prove the age and extent of of Bulgaria; however, shortening within the tinued into the Oligocene in the Black Sea area. either the preceding early Paleogene structures fold-thrust belt continued and is related to a In the western Black Sea, the structures curve to or the succeeding middle Eocene and younger different tectonic setting from the earlier two the south and are beneath the western Black Sea structures. Strata of this age are present within events (see following). In a few places deforma- continental margin, where they continue south- the fold-thrust belt southeast of Vratsa, south of tion can be constrained to be within the Eocene, east and may continue into the northern margin Lukovit, near Veliko Tarnovo, east of Gabrovo, but in other places deformation is younger; we of the Pontide belt of northern Turkey (Fig. 12). and in three small exposures near Rabisha (Fig. discuss each deformation herein. The relations of the structures to the west Black 11). Along the southern margin of the fold-thrust A distinct break between the second and third Sea fault and the Istanbul zone of the northern belt they are present north and west of Kalofer. shortening events within the foreland fold-thrust Pontides suggests that they are younger than In the eastern part of the belt along the Black belt is best constrained within the central part of the emplacement of Istanbul zone allochthon, Sea coast and in the offshore strata are numer- the belt, poorly documented in the western part interpreted to have been emplaced by the early ous unconformities within the early Paleogene of the belt, and does not obviously appear to be Eocene (Okay et al., l994), and their continua- strata, but there is no obvious break that sepa- present, as documented by Stuart et al. (2011), in tion should be north of the allochthon along the rates the second and third periods of deforma- the eastern part of the belt, where it trends into southwestern Black Sea margin. tion (Stuart et al., 2011). However, the defor- the Black Sea. Within the central part of the fold- The structural style within the fold-thrust mation in this area extends into the Oligocene, thrust belt early and middle Eocene and younger belt in northwest Bulgaria is different from the a time when the dynamic setting in the orogen sedimentary rocks that overlie structures of the central and eastern areas (Fig. 14). It contains changed between the second and third periods second deformational event are everywhere extensive involvement of pre-Mesozoic rocks, of deformation (see following). deformed, proving a third deformational event, in contrast to the central area, where there is

476 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

LEGEND

Folded unconformity at base Unconformity at base of Lower/Middle Eocene strata of Upper Eocene and Middle Miocee strata 23° Romania 28° 44° Kula basin folds 44° BA Moesian

0.0 0.2 0.4 0.6 Serbia 0.8 1.0 (Figure 14) BeA Vratsa Lukovit Autochthon

U Berkovitsa U Veliko Turnovo Forebalkan 4)

Stara Planina (Figure 14) SoA Sovge Teteven Etropole Trojan Gabrovo (Figure 1

U Sofia Elena SH U U Tvarditsa

BP Kalofer West Bulgarian Sredna Gora Pr Bulgaria Macedonia

Mountains Rhodope To Turkey

Greece TB

N 0 100 km

28° 40° 23° 40°

Figure 12. Structures formed during the middle–late Eocene to middle Miocene deformational event (shown in black). The orange line is the unconformity at the base of the early to middle Eocene strata that was folded during this deformational event; it provides the upper limit for the second deformation within the fold-thrust belt. The yellow line shows the unconformity at the base of the upper Eocene and middle Miocene strata that unconformably overlie folded rocks and provide a broad upper limit for the third deformation within the fold-thrust belt. South of Lukovit lower Miocene strata unconformably (yellow line) overlie folded lower and middle Eocene strata; this is one of the few places with an early Miocene upper limit on this deformational event. The structures shown in red formed within this time period, but are outside of the foreland fold-thrust belt and probably unrelated to the deformation of the fold-thrust belt. BA—Belogradchik anticlinorium, BeA—Berkovica anticlinorium, BP—Bobov dol-Persink, Pr—Pernik, SoA—Svoge anticlinorium, SH—Shipka thrust, TB—Thrace Basin, To— Tikvis-Oche basin.

only limited involvement of the pre-Mesozoic A more general argument can be proposed environment of deposition than that of early- rocks along its southern part and the eastern to suggest that middle Eocene deformation was middle Eocene strata (Fig. 13). These younger area, where only younger Mesozoic and Ceno- widespread and the beginning of last major rocks were deposited mainly in continental zoic rocks are exposed within the structures at shortening event to affect the Balkan fold-thrust and brackish environments in their basal parts, the surface. This change in structural style may belt. Most Paleogene sedimentary sequences locally contain coal, and in southern Bulgaria be related to the tectonic setting of the fold- end with lower-middle Eocene strata; upper they contain abundant volcanic rocks. They are thrust belt during late-middle Eocene to early Eocene rocks, although rare, begin a sedi- present mainly in southern Bulgaria and north- Miocene time and is discussed in more detail in mentary rock sequence that ranges from late ern Greece, where they were deposited in gra- the following. Eocene to early Miocene and has a different bens or half-grabens. Particularly in southern

Geosphere, April 2015 477

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

LEGEND

Middle Miocene strata Upper Eocene/Oligocene strata Upper Eocene strata Some Oligocene but mainly except in central Bulgaria where Middle and Upper Eocene mainly Oligocene-Miocene strata strata 23° Romania 28° 44° 44° Serbia m-M m-M

0.0 0.2 0.4 0.6 0.8 Vratsa1.0 Berkovica Lukovit Varna Veliko Tarnovo Forebalkan Stara Planina Bulgaria Etropole Gabrovo Sofia Teteven Tvarditsa Trojan Pomorie Srednagora Kalofer Burgas Black Sea

Macedonia Mountains Rhodope

Greece Turkey

N 0 100km

Aegean Sea 28° 40° TB 23° 40°

Figure 13. Outcrops of late Eocene–Oligocene and some middle Miocene (m-M) strata within the fold-thrust belt are limited and make it difﬁ cult to place an upper limit on the deformation of the third deformational event. Strata are more widespread in the southeast (pale orange), but are covered by younger deposits. Yellow areas are middle Miocene strata that unconformably overlie structures of the third deformational event. Blue area is some Oligo- cene but mainly middle and upper Miocene strata that become more widespread to the east beneath the Black Sea. Blue lines outline major tectonic units shown in Figure 1.

Bulgaria there is abundant evidence they were formably overlie deformed lower and middle Svoge anticlinoria also are considered to have deposited during active extension (Bonev and Eocene rocks south of Lukovit, and the struc- formed during middle Eocene time (Bonchev, Beccaletto, 2007; Burchﬁ el et al., 2008). These tures here are regarded as middle Eocene in age. 1971); however, in all these areas there is no regional relations have been interpreted to sug- Similar relations are present near Vratsa, but evidence for the middle Eocene age of defor- gest that the major shortening deformation may the two sequences are not in direct contact. The mation, and only an upper limit of locally early have begun in middle Eocene time but extended second folding of the upper Cretaceous Kula Miocene or more broadly middle Miocene can into Miocene time (see following). rocks in northwest Bulgaria, and the folding of be conﬁ rmed. Based on regional arguments structures in Eocene rocks at Veliko Tarnovo, are also consid- The intensity of middle Eocene deformation northwest and north-central Bulgaria are con- ered to have been deformed in middle Eocene increases toward the south across the fold-thrust sidered to belong to the middle Eocene defor- time (Fig. 12), although in these latter areas they belt. Structures near Vratsa, Lukovit, and Veliko mation and may have extended into Oligocene can only be dated as pre-Neogene. In northwest Tarnovo consist of generally east-west–trending time (Fig. 12). Lower Miocene rocks uncon- Bulgaria the large Belogradchik, Berkovica, and open folds, whereas at and east of Gabrovo the

478 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

rocks are more tightly folded and were involved Mesozoic metamorphic basement rocks and in tures are overridden by the generally horizontal in north-vergent thrusting. Northwest of Kalofer its footwall contain both Mesozoic sedimentary Shipka thrust north of Kalofer (SH in Fig. 12), (Fig. 12) at least 15 km of northward thrust- cover and their pre-Mesozoic metamorphic where basement rocks make up most of the ing of crystalline rocks took place; the basal basement. In the footwall of this structure are hanging wall. The thrust relationship is clear part of the thrust sheet contains well-developed not only Mesozoic strata, but also Paleogene where it overrides Mesozoic and lower Eocene mylonites and the footwall rocks contain a well- rocks of middle Eocene age. This is the so- rocks. Toward the south the thrust is folded with developed cleavage. The three major anticlinoria called Shipka overthrust or Stara Planina gran- a moderate (~30°) south dip and it is displaced by in northwest Bulgaria are north vergent and their ite thrust. In the area between Tvarditsa and normal faults that bound the north side of the late northern fl anks are marked by thrusts carrying Gabrovo this structure was formed in early-Late Cenozoic Sub-Balkan graben system (Tzankov pre-Mesozoic basement rocks and locally Meso- Cretaceous time; it is overlapped unconform- et al., 1996; Fig. 15). Within the region south, zoic rocks in their hanging walls and Mesozoic ably by late-Late Cretaceous to early Eocene west, and east of the Shipka allochthon are other rocks and only locally Cenozoic rocks in their sedimentary rocks (Kanchev, 1962; Kanchev thrust faults that carry only crystalline rocks in footwalls (Figs. 12 and 14). Rocks to the north et al., 1995). The structure involves Cenoma- their hanging walls and locally have Mesozoic and below the frontal thrusts are strongly folded nian and Turonian strata thrusted few kilome- rocks in their footwalls. These thrust faults are and commonly overturned. The anticlinoria con- ters to the north. The thrust is covered by late interpreted as forming part of a major allochthon sist of smaller folds and associated thrust faults. Senonian sediments. Kanchev (1962) assumed covering a large area to the south into the Sredna The Belogradchik anticlinorium (BA, Fig. 12) that this was a local event affecting only the Gora unit (Kockel, 1927; Vulchanov, 1971), but consists of two large north-vergent folds, thrust northern limbs of the Shipka (western part) and it has been disrupted and covered by the strata along their northern fl ank, that plunge eastward Tvarditsa (eastern part) anticlines. In a general of the Sub-Balkan graben system. The age of beneath folded Mesozoic rocks unconformably way this area is between Gabrovo and Tvarditsa. emplacement of this allochthon is interpreted to overlapped by mostly unfolded Neogene sedi- All thrusts are above Paleogene rocks, so the be post-middle Eocene, using the regional argu- mentary rocks; therefore the upper limit of their time of last deformation is the same. Toward ments presented here; however, its upper limit of age can be assigned to only early or middle Mio- the west this structural zone was last deformed deformation is poorly constrained. cene time. The Berkovica anticlinorium (BeA, at a later time, probably late Eocene, because Within the area of northwest and north-cen- Fig. 12) passes through a gentle axial depres- lower Eocene rocks are present below the north- tral Bulgaria, deformation that occurred from sion south of Vratsa, where its Mesozoic cover vergent thrust, marking the continuation of this the end of the late Eocene to early or middle is exposed, then reverses axial plunge and con- zone southeast of Vratsa. This thrust system Miocene time is very diffi cult to prove except tinues to the southeast to Etropole (Fig. 12). The therefore had a multiphase development. locally. Such structures would involve rocks Svoge anticlinorium (SoA, Fig. 12) has a gentle In the area where this structural zone is south deposited in late Eocene or Oligocene time; westward plunge west of Svoge and trends east of most of the folds of the fold-thrust belt, south sedimentary rocks of this age are very rare and from Svoge where it has been disrupted by Neo- of Trojan where the foreland fold-thrust belt crop out only near Tvarditsa and southwest of gene normal faults. Because it carries upper Cre- can be dated as mid-Cretaceous, diverse rocks, Sofi a (Fig. 13). Several other areas where short- taceous volcanic rocks in both its hanging wall including the Late Cretaceous to early Eocene ening occurred during this time period occur. (west of Sofi a) and footwall (near Etropole), and overlap assemblage mentioned here, the struc- (1) Along the northernmost thrust carrying because its basement and pre–Late Cretaceous Mesozoic cover is part of the Moesian shallow shelf sequence, it is considered to be related to the two other anticlinoria to the north. These Figure 14 (on following page). Cross sections of Bulgarian fold-thrust belt (lines of section anticlinoria are considered to have formed in are shown in Fig. 12). (A) Cross section from northwestern Bulgaria shows the extensive middle Eocene time, and probably are in the involvement of pre-Mesozoic rocks (Vratza Sheet D3; Tzankov, 1991). (B) Cross section hanging walls of major southwest-dipping thrust from central part of the thrust belt; cross section is incomplete because seismic data are faults; however, the timing of these structures is lacking from the area below the Stara Planina, and the structures are of three ages (see text), unknown with certainty. The structures are over- so surface geology is not suffi cient to understand ages of crosscutting relations at depth. The

lapped by middle Miocene rocks (Badenian) and upper Cretaceous (K2) is unconformable above the folded structures in pre–upper Creta- in only two places do they involve Eocene rocks; ceous strata that represent the Early Cretaceous deformation. The upper Cretaceous strata in the footwall of a thrust at the north ﬂ ank of the are in the lower plate of a thrust that carries pre-Permian metamorphic rocks that form the Belogradchik anticlinorium upper Eocene rocks crest of the Stara Planina at this longitude and were emplaced in early Paleogene deforma- are present northeast of Belogradchik (BA, Fig. tion. The thrust fault and related structures are downdropped by late Cenozoic normal faults 12), and ~20 km southeast of Vratsa the eastward at the southern side of the Stara Planina. The section shows that the Mesozoic strata of the continuation of the Berkovica anticlinorium is Forebalkan fold-thrust belt must pass below the pre-Permian rocks of the Stara Planina and structurally above lower-middle Eocene rocks. farther south, but how far south is unknown. A similar relation is also present in northwest On the basis of these two localities the structures Bulgaria, where the Forebalkan Mesozoic rocks must pass at depth below the pre-Permian are assigned a post-Eocene and pre-middle Mio- rocks that are part of the thrust belt, but how far is unknown. They may underlie the Sredna cene age (Bonchev, 1971). Gora unit in both. (C) Cross section from Stuart et al. (2011) along the Black Sea coast show- A major north-vergent thrust system that ing the tight dating of an early deformation of the second shortening event, where rocks as overrides strongly folded and overturned rocks young as early-middle Eocene are unconformably overlapped by late-middle Eocene rocks forms a continuous structural zone along the (E2). It also shows the folding of the upper Eocene and Oligocene strata (better expressed in southern margin of the fold-thrust belt and a section to the southeast, offshore ([not shown]) by the third event. On the south, it shows passes north of Kalofer (Fig. 12). Rocks in the normal faults of late Cenozoic age that displace the structures of the fold-thrust belt the hanging wall of this thrust zone carry pre- down to the south along the south side of the Stara Planina topographic front.

Geosphere, April 2015 479

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov 0 -1 km -2 km m 0 -1000 -2000 1000 J2-3 J3 T2 J1-2 T2-3 K1-1 K1-2

J3-K1 pP J1-2 T2-3 J3 T2 K2 K1 K/T E2 N4 N3 O4 O3 J2-3

1 Tr K1-4 K1-3 10 km K1-3

Detachment

1b K K1-3 Vratsa Vratsa K1-2 E1 K1-1 J3-K1

J2-3

1a K T2-3 PT1 T2 T1-2

P pP Vertical Exaggeration ~ 3X Vertical From Stuart et al., 2011 From PT1 Figure 14. Figure 5 km T1-2 P T3 T3 J2-3 K1-1

J3-K1

1b K PT1

Eastern Section 3 Central Section Central T1-2

T1-2 J J C B PT1 Northwest section K1 0 T1-2 A PT1 pC-C C O C-P1 O

O 1 O C K1

O Tr O C T1-2

O 1a

O K PT1

O 3 C O

CP J J V V

1-3 2 J Top Oligocene Top Top Upper Eocene Top

Top Middle to Lower Eocene Middle to Lower Top Eocene to Paleogene Lower Top Cretaceous (K/T) Top K Burgas Basin 1-3 T C

Crest of of Crest

Tr Stara Planina Stara O1/4

8 0 4 6

2 S 10

Depth (km) Depth pP O1/3 O1/2

01/4 pP pC-C 0 0 2000 1000 -2000 -1000 2 km 1 km -1 km

480 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

LEGEND

Late Miocene to Holocene strata 23° 28° Lom Romania 44° Fore 44° Serbia Black Moesian Sea Plain Forebalkan Stara SW SG Planina Sub-Balkan Graben System Black Sea Sredna Gora Mts Strandja Bulgarian Bulgaria Mountains Macedonia Rhodopian Mountains Turkey Greece Thrace Vertiskos

Mountains N 0 100km 28° Aegean Sea 40° 23° 40°

Figure 15. During the middle Miocene to Holocene the region in the southern part of the foreland fold-thrust belt was cut by mainly south- dipping normal faults forming the Sub-Balkan graben system. These listric normal faults displaced the generally south-dipping thrust faults so that their southern continuations are beneath the Sredna Gore lowlands and not exposed. Footwall uplifts along the Sub-Balkan graben system elevated the Stara Planina unit, creating a long gentle northward slope into the depositional area of the late Cenozoic strata along the Danube River above the Moesian Platform. SG—Soﬁ a graben. Tick marks are on the downthrown side of the normal faults. Light blue lines are outlines of major tectonic units shown in Figure 1.

rocks of the Luda Kamchia sedimentary strata, thus the deformation is early Miocene Eocene and even Oligocene time, and they are sequence east of Tvarditsa, upper Eocene rocks or latest Oligocene. (3) Rocks of Oligocene age deformed. The timing of this thrust is not well are present in the footwall (Fig. 13). (2) In the in the Tikvesh-Ovchepole basin of Macedonia constrained. Bobov dol-Persink and Pernik basins in west- were folded in latest Oligocene to early Mio- In the eastern continuation of the foreland, ern Bulgaria, Oligocene rocks unconformably cene time (Dumurdzanov et al., 2005). (4) In more Cenozoic strata are present as the fold- overlie weakly folded Eocene rocks and defor- the Thrace Basin of northwest Turkey folds thrust belt plunges to the east into the Black Sea. mation is dated as early Oligocene. These rocks are dated as late Oligocene to earliest Miocene Subsurface data show numerous unconformable are folded and cut by thrust faults of Oligocene (Perincek, 1991). The latter two areas are out- relations within the middle Cenozoic strata, and and/or early Miocene age (Zagorchev, 1998). side the fold-thrust belt of Bulgaria and their while there is a major middle and late Eocene However, the structural relations here were folding may be mainly unrelated to deforma- shortening with an unconformity at the base of reinterpreted by Kounov et al. (2011) to sug- tion of the fold-thrust belt. Although the north- the youngest upper Eocene strata, there is no gest that if thrusting had occurred it was the ern margin of the Luda Kamchia basin was obvious break between deformation of the sec- result of restraining bends in strike faults; this deformed and thrusted in post-middle Eocene ond and third deformational events. However, suggestion is in support of the hypothesis we time (see preceding discussion concerning important shortening took place in late Eocene present here for the dynamic setting of this third subsurface information along the Black Sea time and deformation continued throughout the event of deformation, i.e., that the thrust over- coast in Fig. 14), more southern parts of the Oligocene (Stuart et al., 2011, Fig. 14). Middle lies proven Oligocene–latest-early Miocene basin continued to receive sediments into late and upper Eocene rocks are folded with Oligo-

Geosphere, April 2015 481

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

cene rocks, but to a lesser degree, and this late younger than the last major deformation within DYNAMIC SETTING FOR folding and thrusting is late Oligocene (Dachev the fold-thrust belt, although younger shorten- DEVELOPMENT OF THE BALKAN et al., l988; Stuart et al., 2011; Fig. 14) and ing deformation extends into the Southern Car- FORELAND FOLD-THRUST BELT belongs to the third deformational event in pathians (Codarcea, 1940; Sandulescu, 1984, the fold-thrust belt. Although the younger two 1994). Some normal faults with small displace- Foreland fold-thrust belts in most mountain events cannot be separated in eastern Bulgaria, ment cut the late Cenozoic rocks. One of us ranges often show deformation that progresses the termination of the deformation is marked by (Nakov, 2009) suggested that some shortening from the inner to outer part of the orogen, and extensional faulting in the unconformably over- deformation occurred in post-Chersonian time are intimately related to the tectonic evolution of lying middle Miocene strata. (between 10 and 8.9 Ma), but if so, it was very the entire orogen. In contrast, the foreland belt These deformational structures we consider weak and unimportant in causing the distribution in the Balkan orogen was formed during three to be related to a different dynamic system from of late Cenozoic rocks. This weak shortening superposed shortening events that do not show the second event; however, the transition from was established northeast of Vratsa, but its extent the expected progressive development; the ques- the dynamic systems from the second to the and role further to the west and east is unknown. tion of why this happened is an orogen-wide third events remains unclear in the eastern part During the middle Miocene to Holocene, problem of the dynamics of the Balkan orogen. of the Bulgarian fold-thrust belt (see following). extensional tectonism was widespread through- The preceding discussion of the foreland From the interpreted distribution of middle- out much of southern Bulgaria and its wide- fold-thrust belt is almost entirely from surface late Eocene to middle Miocene structures it is spread effects reached the southern parts of the geology; few seismic lines are available, mak- likely that much of the foreland fold-thrust belt fold-thrust belt in late Miocene to Pliocene time ing an analysis of the geometry at depth and the was deformed in this time period. This is the last (Burchfi el et al., 2000, 2008). The grabens now magnitude of shortening structures uncertain. major deformation to affect northwestern Bul- fl anking the southern Stara Planina have mainly The vergence of the fold-thrust belt is gener- garia and was superposed on early Paleogene south-dipping normal faults on their north side ally northward for the Late Cretaceous and/or structures; and, even though it is it poorly dated, and considerable down-to-the-north rotation of early Paleogene and middle Eocene to Miocene it is clearly a younger event than the second hanging-wall blocks (Fig. 15). The rotation on deformations as determined by the sense of deformational event of early Paleogene age. It the graben fi ll is syntectonic and indicates that overturning of folds and dips on thrust faults; is very likely that the region between Vratsa and the faults are listric, the dip shallowing at depth for the mid-Cretaceous event it is less certain, Elena affected by a strong middle Cretaceous to the south (Tzankov et al., l996). An interpre- but is most likely also north vergent. How all deformation and possibly weaker Paleogene tation by Roy et al. (1996) indicates that dis- the structures of different ages interact at depth deformation was deformed for the third time placement on the south-dipping normal faults is unknown, but a simplistic analysis indicates during middle Eocene to middle Miocene time. unloaded the crust in their footwalls, causing it that the Moesian Platform currently dips gently All three unconformity-bounded sequences of to rise. Such unloading forms the highest topog- south to be below the Stara Planina unit; how sedimentary rocks that show the effects of all raphy, with a steep south-sloping gradient in the much farther south it continues is unknown. three superposed deformations are present in the footwall near the faults and a gentle northward That basement rocks are involved in the thrust- area near Vratsa and Lukovit. slope north of the topographic high explaining ing within the Stara Planina and in parts of the the present-day topography. The Sofi a graben, Sredna Gora units and some of youngest strata MIDDLE MIOCENE TO HOLOCENE which has a major fault along its south side, is to are present in the footwalls of the thrust faults the west of the Sub-Balkan graben system and suggest that the Mesozoic rocks continue far- During middle Miocene to Holocene time, also forms the south fl ank of the Stara Planina. ther south for at least tens of kilometers (Fig. southern Bulgaria was characterized by exten- Thus the present topography is the result of the 14). Tectonic overlaps of thrust hanging walls sional deformation, whereas northern Bulgaria two different types of Neogene sedimentary in the Gabrovo and Shipka areas are ~15–20 km was characterized by a broad area of deposi- basins in northern Bulgaria; extensional grabens where the thrust faults are nearly subhorizontal tion with slow subsidence except in the north- in the south and a broad northward-deepening and give a minimum displacement (central sec- west within the Moesian Platform, where more basin in the north separated by a topographically tion, Fig. 14). Tens of kilometers of displace- rapid subsidence occurred in the Lom depres- asymmetric mountain range formed by footwall ment on the foreland belt would suggest that at a sion (Fig. 15) and activity in the fold-thrust belt uplift. The faults of the Sub-Balkan graben sys- minimum, much of the crust in the Sredna Gora ceased. The present topography of Bulgaria tem are active, and so the elevation of the Stara unit is also allochthonous. Both of these thrust developed during middle Miocene to Holocene Planina probably continues today, indicating faults were emplaced during the youngest event time. North and south Bulgaria are separated by that the Stara Planina is one of the youngest and both thrusts are displaced by late Cenozoic the east-west–trending Stara Planina Mountains topographic features in Bulgaria. normal faults. through north-central Bulgaria (Fig. 1). The The normal faults of the Sub-Balkan graben Stara Planina is bounded on its south side by the system displace the south-dipping thrust faults TECTONIC SETTING FOR THE Sub-Balkan graben system formed by a system of the foreland fold-thrust belt (Figs. 14 and MID-CRETACEOUS SHORTENING of generally east-west–trending, southwest- 15) so that their southern continuations are not DEFORMATION dipping normal faults with the exception of the exposed, but are covered beneath the Sredna Sofi a graben, which has major normal faults on Gora lowlands. How far south the thrust faults The mid-Cretaceous folding within the fore- both sides (Fig. 15; Tzankov et al., l996). extend remains unknown, but because pre- land belt is within the Nis and Trojan fl ysch The middle Miocene (Badenian) and younger Mesozoic rocks are present within their hang- basins that formed prior to the shortening. The rocks of northern Bulgaria were deposited on ing walls from central Bulgaria to the west, it fl ysch basins shown in Figure 6 are in present- the Moesian Platform and extend south into the indicates that Mesozoic strata in their footwalls day positions, and they certainly moved north- northwestern and external part of the fold-thrust must extend an unknown, but considerable, dis- ward relative to the foreland during the two belt. They formed in a foredeep position, but are tance south of the Stara Planina. younger deformational events. Their narrow

482 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

geometry and thick fl ysch strata that grade (Zagorchev and Tikhomirova, 1986; Zagorchev, belt may be a complex of different units from to both fl anks and along strike into shallow- 1986, 1996; Kounov et al., 2004, 2010; Schmid different tectonic positions. The tectonic set- water strata suggest that they were rifted basins et al., 2008) and with the emplacement of the ting is further complicated by the interpretation inverted during the mid-Cretaceous deforma- Strandja allochthon by northward thrusting of Naydenov et al. (2013) that the Maritsa fault tion, but if they involved basement rocks in in eastern Bulgaria from the eastern continua- zone (MFZ; Fig. 5) was a major right-slip shear their formation, the locations of the rift basins tion of Vardar zone (Fig. 7; e.g., Papanikolaou, zone during Late Jurassic–Early Cretaceous were in the southern part of the foreland belt 2009). In the footwall of the Strandja thrust are time; they suggested that the shortening within and their positions below the basal thrust of the metamorphic rocks of the Rhodope unit (sensu the southern Balkans was strongly obliquely foreland fold-thrust belt would now be even far- lato) that are probably the southernmost expo- convergent with north-vergent thrusting within ther south. What caused rifting of this age is not sures of the Moesian basement, but the Meso- the Strandja domain separated by right shear clear, but the positions of the basins relative to zoic cover rocks are poorly known and dated along the Maritsa shear zone from south-vergent exposed Mesozoic strata adjacent to the basins and were metamorphosed and deformed in thrust in the Rhodope domain to the south. The and late Paleozoic rocks within the folded basin Cretaceous time (e.g., Bonev and Boccaletto, nature of the Jurassic to early-Late Cretaceous strata indicate that they were within the Moesian 2007; Bonev et al., 2006). In the footwall of the tectonism still remains poorly understood (see shelf area. This is different from the fl ysch of Morava thrust are Jurassic to lower Cretaceous the discussion in Burg, 2012), but we inter- the Severin unit in the Southern Carpathians strata of the Trekljano Group that unconform- pret the complex Circum-Rhodope unit with of similar age to the northwest, regarded to be ably overlie upper Triassic rocks of the Moesian its deep-water strata and local ophiolitic rocks underlain by oceanic or very thin continental shelf (Zagorchev and Tikhomirova, 1986). The to have been thrust onto the southern extent of crust (Fig. 7). How these fl ysch basins relate basal unit of the group consists of polymictic the continental rocks of southern Bulgaria. It is to the oceanic area of the same age in the Car- sandstone and conglomerate of Early Jurassic somewhat irrelevant whether the rocks in the pathians is unclear and subject to considerable age that grade upward into a sequence of back Kotel zone are the leading edge of the Circum- interpretation. slates, siltstones, and radiolarites that range Rhodope unit, as they contain north-vergent In their study of the Southern Carpathians, in age from Middle to Late Jurassic (Kim- structures of mid-Cretaceous age (Georgiev Fügenschuh and Schmid (2005) suggested in meridgian); fl ysch deposits of middle Tithonian et al., 2001; Tchoumatchenco et al., 2004). We their fi gure 9E (but did not discuss in detail in to Berriasian age unconformably overlie these. suggest that the position far to the north of the their text), that the fl ysch of the Southern Car- Both sections are in the footwall of the Morava present position of the Strandza unit is because pathians (Severin fl ysch) formed two belts on thrust. These rocks are interpreted to be a deep- the Late Cretaceous and subsequent exten- either side of Moesian basement rocks that water succession transitional from the shallow- sion separated the Kotel zone from its original formed the basement for the Forebalkan fold- water strata to the north and east to the oceanic position. thrust belt in Bulgaria. The basement rocks strata of the Vardar zone to the west (Zagorchev In such a setting, the shortening within the would continue northward as the Danubian tec- and Tikhomirova, 1986; Zagorchev, l986). The Nis-Trojan basins is explained as a result of oro- tonic unit of the Southern Carpathians and end position of the Morava thrust is thus interpreted gen-wide deformation related to activity along farther north, thus forming a peninsula. Fügen- to have originated from the western edge of the the southern margin of the Moesian shelf where schuh and Schmid (2005, fi g. 9E therein) sug- Moesian continental crust. it passed southwest or south beneath rocks along gested that the fl ysch units overlying oceanic While the timing of the shortening within the eastern and northern margin of the Vardar crust pinch out southward and do not continue the foreland belt is reasonably well known zone. The fold-thrust belt would thus be syn- very far into Bulgaria. This interpretation is on the basis of stratigraphy (from ca. 110 to thetic to the thrusting and related to westward important because it suggests that the Moesian 90 Ma; Fig. 8), the events within the Rhodope and southward subduction in an oceanic domain basement east of where the fl ysch pinches out is are less well known and their contemporaneity either within or north of the Vardar zone. The part of basement rocks for the entire shelf area with shortening in the fold-thrust belt needs to geometry of structures within the present-day of Bulgaria. Such an interpretation has merit, in be better constrained. Burg (2012) presented a Rhodope crust (as shown in, e.g., Fig. 7) has that it could be suggested that the Nis-Trojan detailed discussion of deformation within the been greatly disrupted by younger Mesozoic basins are the easternmost extent of the fl ysch Rhodope region during that time, and pointed deformation that is dominantly south-vergent basins, but were rifts extending east from the out that the geology of the Rhodope is complex thrusting and later superposed Cenozoic exten- oceanic area of the Southern Carpathians into and remains controversial. Burg (2012) inter- sion (Burg, 2012). the Moesian continental crust? Thus the Bal- preted the Rhodope as a collage of thrusted units Between the mid-Cretaceous and latest Cre- kan crust in northern and central Bulgaria was that are mainly south vergent, units he suggested taceous–early Paleogene shortening events entirely continental crust (Fig. 4), and there is are related to northward subduction of oceanic within the foreland belt is when extensional rift- no good evidence that oceanic crust extended arc and thin continental crustal rocks. However, ing occurred within the Sredna Gora area with into Bulgaria. Such an interpretation needs the Circum-Rhodope rocks contain mafi c and the formation of a backarc or intraarc basin that further investigation because these connec- ultamafi c rocks that have been interpreted as probably extended eastward through the Black tions between Bulgaria and Romania have been remnants of oceanic crust (Papanikolaou, 2009). Sea area (Boccaletti et al., 1974; Burchfi el, strongly disrupted by younger shortening and Following Papanikolaou (2009), we inter- 1980; von Quadt et al., 2005; Fig. 9). This and strike-slip deformation. pret the emplacement of the Circum-Rhodope the abundance of magmatism of Late Cretaceous In Bulgaria the mid-Cretaceous deforma- allochthon to be the result of a mid-Cretaceous age are interpreted to be related to rollback along tional event caused shortening of the fl ysch period of south- and southwest-vergent subduc- a north-dipping subduction zone beneath the basins and affected rocks beyond the basin tion within an oceanic setting (see also Bonev Rhodope. This rift formed within the Moesian margins. Major northeast-vergent shortening and Stampfl i, 2011), a tectonic setting that continental crust, nonvolcanic Mesozoic rocks of similar age occurred along the eastern mar- remains controversial. Meinhold and Kostopou- of which are present within the foreland fold- gin of the Vardar zone on the Morava thrust los (2013) indicated that the Circum-Rhodope thrust belt to the north and within the northern

Geosphere, April 2015 483

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

part of the Rhodope area to the south. The width in the hanging wall of a south-dipping exten- to the south, making the dynamic setting for of the volcanic basin is unknown, but transitions sional detachment fault (Boyanov and Goranov, this third period of deformation different from of strata to the north are rare and the lack of vol- 2001; Bonev et al., 2006; Fig. 10). Although it the two previous deformational periods. The canic rocks to the north suggests that it had a is one of very few places where such evidence tectonic setting is based on regional consid- sharp northern boundary and/or was separated exists, it is unknown how widespread such Late erations that the southern part of the orogen in from the foreland fold-thrust belt rocks by some Cretaceous–Paleocene extension may be. Tim- the Rhodope and parts of the Sredna Gora units signifi cant distance. The fact that the rift was ing of such extension would be contempora- became an area of regional extension that began within or behind the volcanic arc indicates that neous with the second period of deformation in late-middle to late Eocene time and has domi- the vergence of subduction within the Vardar within the foreland fold-thrust belt (see Fig. 8). nated the region of southern Bulgaria until pres- zone had reversed, from southward during the If so, it remains to be determined how this ent (Burchfi el et al., 2008). However, because mid-Cretaceous deformation to northward sub- extension fi ts within the broader tectonic setting the timing of extension and the fi rst shortening duction during the Late Cretaceous magmatism of the orogen and to the retroarc setting of the deformation between southern and northern Bul- and rifting (see also Bonev and Stampfl i, 2011). fold-thrust belt, but extension contemporaneous garia, respectively, comes close to overlapping The formation of the backarc extension resulted with regional shortening has been recognized in with the second and third periods of shortening, in a pause in shortening deformation that caused many orogens (e.g., Burchfi el et al., 1992). it suggests a transition between the dynamics of a break between the mid-Cretaceous and latest The folds and thrust faults of the second event the second and third periods of deformation. The Cretaceous–Paleogene shortening. continued to the northwest into the Southern younger part of the third period of shortening Carpathians where Late Cretaceous structures deformation within the fold-thrust belt was in TECTONIC SETTING FOR THE are well known; however, their continuity has a tectonic setting that is contemporaneous with LATEST CRETACEOUS–PALEOCENE been greatly disrupted by Cenozoic strike-slip regional extension in the southern Balkans. SHORTENING DEFORMATION faulting and clockwise rotation (Fügenschuh Our favored interpretation is that the third and Schmid, 2005; see following discussion). period of deformation is related to a dynamic The second period of deformation occurred Deformation of this period and the following system that includes the northern part of the within the foreland fold-thrust belt at the same period also disrupted the Late Jurassic–Early foreland and thrust belt in Bulgaria and the time as the backarc or intraarc basin closed Cretaceous paleogeography and the mid-Creta- Southern and eastern Carpathians as these units and metamorphism and deformation occurred ceous structures, so their continuity is not clear. were molded around the western part of the within the Rhodope Mountains (Fig. 16). The However, there have been attempts to elucidate Moesian foreland crust. Tectonic analyses and timing of metamorphic and deformational the trans-border correlations (Tchoumatchenco paleomagnetic data indicate that the western part events within Rhodope is becoming clearer et al., 2011, and references therein; Kräutner of the Southern Carpathians moved northward (e.g., Bonev and Beccaletto, 2007; Bonev et al., and Krstić, 2003). into the eastern Carpathians by at least latest 2006; Burg, 2012; Silke et al., 2010). Much of Cretaceous time, shearing right laterally with the deformation and metamorphism is latest DYNAMIC SETTING FOR THE THIRD respect to the Moesian crust to the east (Fig. 17). Cretaceous to about middle Eocene and forms DEFORMATONAL EVENT: MIDDLE This crustal unit moved north and east, rotating the core of the Balkan orogen at the time the EOCENE TO EARLY MIOCENE clockwise, into the subduction zone within the second shortening deformation occurred within eastern Carpathians and was molded around the the foreland fold-thrust belt and during the clo- The third deformational event in the foreland western and northern part of the Moesian crust sure of the backarc-intraarc basin. The Rhodope thrust belt of middle Eocene to early Miocene (Fügenschuh and Schmid, 2005; van Hinsbergen deformation is related to northward subduction time took place when the tectonic setting of et al., 2008). During the early part of this motion, within the Vardar zone along the south margin southern Bulgaria and northern Greece became right shear along the western part of the Moesian of the Balkan orogen (Burg, 2012); therefore, an area of regional extension that has lasted to crust was transferred into shortening within Bul- the foreland fold-thrust belt is a retroarc or anti- the present, a major change from the preced- garia, molding rocks to the southern part of the thetic belt and has a dynamic setting different ing regional shortening environment. Thus the Moesian crust. The transfer of right shear into from that of the earlier mid-Cretaceous defor- dynamic setting for shortening within the fore- shortening ended by early Miocene time, but mation. There are suggestions that the Rhodope land fold-thrust belt of its third event is different the northward motion in the western part of the area was not a single continental unit at the time; from the two preceding shortening events. How- Southern Carpathians and Serbia continues to it may have contained ophiolitic rocks (e.g., see ever, the timing of the change is complex and its the present, manifested by localization of right Turpaud and Reischmann, 2010; Burg, 2012), transition is probably not contemporaneous or shear forming the discrete Cerna-Jiu and Timok so the details of this part of the orogen remain abrupt, and may have been protracted. faults, which have a minimum of 50 km of right to be determined. However, it appears that the The third period of deformation within the slip (see Kräutner and Krstić, 2003). The map of foreland fold-thrust belt formed the northern fold-thrust belt began in the late-middle Eocene, Kräutner and Krstić (2003) also showed geol- marginal tectonic element of the orogen that but the upper time limit for this deformation ogy indicating that units within the northwestern extends from the northward subduction within is poorly constrained because overlying strata Bulgarian fold-thrust belt were rotated clock- the Vardar zone that led to its closure by middle are not present across much of the belt. Where wise into the Southern Carpathians before they Eocene time, through a thickening Rhodope present the strata are locally middle Miocene were displaced by the younger discrete faults. metamorphic core in the south to the Moesian or younger, except in eastern Bulgaria, where The change in the regional tectonic setting Platform in the north. the structures trend into the Black Sea. Thus, during Paleogene time changed the nature of Within the metamorphic core there is local(?) whether some of the structures belong to this tectonic activity across the northern Balkan evidence for Maastrichtian–Paleocene extension period of deformation remains uncertain. It is orogen. The change from a convergent to exten- in the eastern Rhodope unit near Krumovgrad, clear that this period of shortening deformation sional orogen in southern Bulgaria and north- where coarse clastics appear to be back-rotated was contemporaneous with regional extension eastern Greece is related to the closure of the

484 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

LEGEND

23° Metamorphic rocks Domal cores of metamorphic rocks

Belogradchik

Vratsa Lukovit

U 0.0 0.2 0.4 0.6 0.8

Berkovica 1.0 Varna U Veliko Tarnovo Forebalkan Star a Pla nina Varna Etropole Gabrovo Sofia Tetevan U Trojan Tvarditsa

U Kalofer U Sredna Gora

W e s t

B u l g a r i Rhodope a n

o u n t a AD i n s

40° 23° 28° 40° N

Figure 16. Regional tectonic map for the Late Cretaceous–Paleocene deformation within the Balkan orogen. The structures of the fold- thrust belt are the same as those in Figure 10, accompanied by the regions in the Rhodope of Bulgaria and northeastern Greece, where shortening structures of the same age are shown in red. Large areas of the Rhodope and related metamorphic rocks are shown in gray, but structures of Late Cretaceous–Paleocene age (red) within this area are poorly constrained. This is the time when the oceanic region in Var- dar zone and its eastern continuation in the Intrapontide zone (IPS) were closing along a north-dipping subduction zone and the fold-thrust belt in northern Bulgaria was antithetic to the subduction. The Balkan orogen at this time was convergent, and shortening across its entire width. AD—Arda dome, KD—Kardamos dome, KeD—Kechros dome, N—Nestos thrust. Light blue are the outlines of major tectonic units as shown in Figure 1. Light green lines are the limits of the Vardar zone in Macedonia and Greece.

Vardar ocean and a change in location of sub- northward subduction and rollback in the Hel- North of the extensional region, shortening duction from the Vardar zone to west and south lenides and western Turkey, usually interpreted occurred within the foreland fold-thrust belt into the Hellenides and south into southwestern to be a backarc extensional tectonic setting, a in Bulgaria and continued westward into the Turkey (Papanikolaou, 2009). The beginning of relation discussed by many (e.g., Le Pichon and Southern Carpathians of Romania, where defor- extension within southern Balkan region began Angelier, 1981; Jolivet and Brun, 2010; Jolivet mation involved strike-slip faulting, shortening, an evolving Cenozoic tectonic setting related to et al., 2013) and not discussed further here. clockwise rotation, and orogen-parallel exten-

Geosphere, April 2015 485

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

sion (Fügenschuh and Schmid, 2005; van Hins- ern Carpathians (the Danubian unit) also caused By late Eocene time the shortening within the bergen et al., 2008). The Cenozoic deformation northeast extension along the eastern contact thrust belt of northern Bulgaria was contempo- of the arcuate Southern Carpathians mountain between the Getic and Danubian units, where a raneous with extension in the southern Balkans chain is the result of molding of deformed units detachment fault is along their contact (Fig. 17; and separated the Balkan orogen into two dif- against an arcuate foreland continental terrane Fügenschuh and Schmid, 2005). Additional step- ferent deformational provinces, a South Balkan as oceanic and/or thinned continental crust over transfer to extension farther south within extensional regime (Burchfi el et al., 2008) and was subducted westward and rolled back in western Bulgaria may also have contributed to a northern convergent area with the boundary the eastern Carpathians, closing from north to the extensional detachment with the Osogovo approximately along the Sub-Balkan graben south (Burchfi el, 1976, 1980; Fügenschuh and Mountains (Kounov et al., 2004, 2010). system (Tzankov et al., 1996; Figs. 12, 14, and Schmid, 2005). The westward extension of the The timing of the change from orogen-wide 17). Thus, this youngest period of shortening closure continues from the southern East Car- compression across the Balkan orogen from the in the Forebalkan fold-thrust belt is related to a pathian thrust belt into the Southern Car pathians; Vardar zone to the fold-thrust belt to the short- tectonic setting different from the previous two however, in northwest Bulgaria oceanic crust ening within the fold-thrust belt that is contem- deformational events. was lacking during the Cenozoic, and eastward poraneous with extension within the southern or northward thrusting around the increasingly Balkans and related to Carpathian tectonics is CONCLUSIONS convex-west curved belt was intracratonic and not well established. The oldest thrusting within associated with continued Cenozoic motion that the third period of deformation within the fold- The fold-thrust belt within Bulgaria formed developed discrete right-lateral strike-slip faults thrust belt is late-middle Eocene, and the fi nal in three separate events related to three different (Ratschbacher et al., 1993; Fügenschuh and closure of the Vardar zone was at about the same tectonic settings, thus making it a unique fore- Schmid, 2005; Fig. 17). time, thus it is unclear if this middle Eocene land fold-thrust belt. A mid-Cretaceous short- In early Cenozoic time convergence was east- deformation is the last event related to retroarc ening event was localized along extensional west within and west of the Moesian Platform antithetic deformation and older than the time fl ysch-fi lled troughs formed by rifting within the within continental crust in the Southern Car- when the regional extension began in the south- Moesian continental crust during latest Jurassic– pathians, forming thrusts and folds that extend ern Balkan area. By late Eocene time extension Early Cretaceous time. Folds and thrust faults into northwest Bulgaria during the third crustal was dominant in the southern Balkans. How, formed within and beyond the fl ysch troughs shortening event. By early Miocene time the and when, the change from the retroarc to trans- and were related to north- and northeast-vergent transfer of right shear to shortening ceased in fer tectonics occurred remains to be established; thrusting in southern part of the Moesian crust northwest Bulgaria. Kounov et al. (2011) inter- the transition may have been protracted and north of the Vardar ocean. We interpret the short- preted the southern extension of the strike-slip diachronous. Nevertheless, the third dynamic ening of the fold-thrust belt to be synthetic with faults to continue into western Bulgaria, where system that produced the youngest structures in respect to the southward subduction in the Var- they may merge into transpressional steep thrust the fold-thrust belt was active by late Eocene to dar zone (sensu lato). This shortening ceased faults (see also Gerdjikov and Georgiev, 2006), early Miocene time. when Late Cretaceous intraarc and/or backarc faults described by Zagorchev (1993) as thrust faults of Paleogene age. The thrust faults and folds within northwestern Bulgaria appear to end against the north-striking Cerna-Jiu and Timok Figure 17 (on following page). Regional tectonic map of the Balkan orogen, late Eocene to faults, but these are late Cenozoic faults and middle Miocene time. The Vardar and Intrapontide oceanic zones closed during Eocene whether the thrust faults in northwest Bulgaria time. The fi nal closure was about middle Eocene time, but poorly constrained, and may be had continuations in the Southern Carpathians or diachronous. Sediments in the Thermikos (ThB) and Tikvis-Ovchepole (TO) basins uncon- were terminated or merged into early Cenozoic formably overlie the Vardar zone structures where the oldest sediments in the basins are right shear zones remains to be investigated. middle and upper Eocene, respectively. Strata in the southern Thrace Basin (TB) that cover The transfer of strike slip to generally north- the Intrapontide zone are middle Eocene. Gray is metamorphic rocks in extensional core ward thrusting may explain the difference in complexes. In Eastern and Southern Carpathians, the green color indicates strata of Cre- structural style between structures in northwest taceous age deposited on oceanic or thin continual crust, purple indicates upper plate of Bulgaria and the remainder of the thrust belt to crystalline thrust sheets, and yellow indicates footwall rocks. Extension within the Rhodope the east. It is unclear how far east our postulated area begins in the late-middle Eocene in the Mesta graben (MG) of the western Rhodope transfer motion extends; it could extend across Mountains (WR) and the Osogovo Mountains (OM), and in late Eocene time in the eastern the entire fold-thrust belt, but with decreasing Rhodope (ER). P—Pernik graben. KD—Kardamos dome, KeD—Kechros dome, N—Nestos involvement of basement rocks and possibly dis- thrust. Arrows show the large clockwise rotation of the rocks of the eastern Carpathians placement, or it could begin to grade into rela- that started in the early Cenozoic and continued into the latest Cenozoic as the thrust belt tive southward motion of a combined Moesian– in the eastern Carpathians developed by rollback of the Carpathian subduction zone. The Black Sea crust, causing minor shortening along northward motion in the western part of the Southern Carpathians continued through the its southern boundary. This problem is unre- Cenozoic, but the transfer of shortening along the right shear in the Southern Carpathians solved. Nevertheless, the tectonic setting for the into thrusting in Bulgarian foreland fold-thrust belt occurred only in the third shortening third period of convergent deformation is clearly event and was completed by early or late Miocene time. The right shear continues in the different from the previous two periods where Southern Carpathians until the present day, with the formation of discrete right shear faults stresses cannot be transmitted from the south (Cerna-Jiu and Timok faults) in the later part of the Cenozoic. The extension in the north- through the South Balkan extensional system. east part of the Danubian unit in the Southern Carpathians is shown with the open arrow. The northward motion along the strike-slip Large black arrows in the southern Balkans show the direction of regional extension in the faults within the Moesian crust within the South- South Balkan extensional system.

486 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

LEGEND

Metamorphic rock of Domal cores of Exposed and covered mainly Extensional volcanic rocks Rhodope area metamorphic rocks non-volcanic strata in southern Balkans

Extensional volcanogenic strata Cretaceous Flysch of East Allochthonous metamorphic Autochthonous basement in southern Balkans and South Carpathians rocks in South Carpathians in South Carpathians

28°

Cenozoic

Peceneaga subduction - Camena fault Late fault Ceahlau Dobrogea Jiu

Capadava Cerna

Romania fault- Ovidia

44° fault Moesian Autochthon 28° 44°

Serbia Timok

U U

Forebalkan

Stara Planina

U U U U Black Sea

r ofe OM Kal Srednagora Bulgaria MG Rhodope P WR TO ER Macedonia VardarV Zone a r TB d N KeD a r KD Z Greece o Turkey n I P S e Aegean 28° N Sea 40° ThB 40° 100 km

Figure 17. 28°

Geosphere, April 2015 487

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

extension occurred through central Bulgaria in that from National Science Foundation (NSF) grants detachment system, Himalayan orogen: Extension the Sredna Gora unit related to northward sub- EAR-9903021 and EAR-9628225. Final support was contemporaneous with and parallel to shortening in a from a grant for the Medusa Project by NSF Conti- collisional mountain belt: Geological Society of Amer- duction and rollback of the subducted slab. nental Dynamics Program grant EAR-0409373. The ica Special Paper 269, 41 p., doi: 10 .1130 /SPE269 -p1 . The second period of shortening within the Burchfi el, B.C., Nakov, R., Tzankov, T., and Royden, L.H., Schlum berger Chair and the Department of Earth, 2000, Cenozoic extension in Bulgaria and northern fold-thrust belt developed during closure of Atmospheric and Planetary Sciences at the Massachu- Greece: The northern part of the Aegean extensional the intraarc or backarc rifts during Late Creta- setts Institute of Technology supported the develop- regime, in Bozkurt, E., et al., eds., Tectonics and mag- ceous–Paleocene time, but the basal décolle- ment of the manuscript and illustrations. This work matism in Turkey and the surrounding area: Geological could not have been done without the close coopera- Society of London Special Publication 173, p. 325– ment below the belt probably extended south tion and continued support of the Geological Insti- 352, doi: 10 .1144 /GSL .SP .2000 .173 .01 .16 . below the Sredna Gora. Deformation in the fold- tute of the Bulgarian Academy of Sciences (Sofi a). Burchfi el, B.C., Nakov., R., and Tzankov, T., 2003, Evidence We thank A.M.C. Şengör, W. Frisch, and Alexandre from the Mesta half-graben, SW Bulgaria, for the late thrust belt was part of orogen-wide shortening Eocene beginning of Aegean extension in the Central related to northward subduction within the Var- Kounov for reviews of the manuscript. Balkan Peninsula: Tectonophysics, v. 375, p. 61–76, dar oceanic zone, a reversal of subduction from doi: 10 .1016 /j .tecto .2003 .09 .001 . REFERENCES CITED Burchfi el, B.C., Nakov, R., Dumurdzanov, N., Papanikolaou, the earlier shortening event: the fold-thrust belt D., Tzankov, T., Serafi movski, T., King, R.W., Kotzev, formed in an antithetic, retroarc tectonic setting Atanasov, A., and Bokov, P., 1983, Geology and oil-gas V., Todosov, A., and Nurce, B., 2008, Evolution and and was contemporaneous with metamorphism prospective of the Moesian Platform in central north dynamics of the Cenozoic tectonics of the South Bal- Bulgaria: Sofi a, Bulgaria, Technika Publishing House, kan extensional system: Geosphere, v. 4, p. 919–938, and shortening within the Rhodope area. 287 p. doi: 10 .1130 /GES00169 .1 . The third and fi nal shortening event within Bauer, C., Rubatto, D., Krenn, K., Proyer, A., and Hoinkes, Boyanov I., and Goranov, A., 2001, Late Alpine (Palaeo- G., 2007, A zircon study from the Rhodope metamor- gene) superimposed depressions in parts of southeast the fold-thrust belt began in late-middle to late phic complex, N-Greece: Time record of a multistage Bulgaria: Geologica Balcanica, v. 31, no. 3–4, p. 3–36. Eocene time, and may have continued to early evolution: Lithos, v. 99, p. 207–228, doi:10 .1016 /j Boyanov, I., Dabovski, C., Gochev, P., Harkovska, A., Miocene time. We relate this event to transfer .lithos .2007 .05 .003 . Kostadinov, V., Tzankov, T., and Zagorchev, I., 1989, A Boccaletti, M., Manetti, P., and Peccerillo, A., 1974, The new view of the Alpine tectonic evolution of Bulgaria: of transpressive right shear within northwest- Balkanids as an instance of back-arc thrust belt. Pos- Geologica Rhodopica, v. 1, p. 107–119. ern Bulgaria, eastern Serbia, and the Southern sible relation with the Hellenids: Geological Society Burg, J.-P., 2012, Rhodope: From Mesozoic convergence to Carpathians into shortening within the fold- of America Bulletin, v. 85, p. 1077–1084, doi:10 .1130 Cenozoic extension. Review of petro-structural data /0016 -7606 (1974)85 <1077: TBAAIO>2 .0 .CO;2 . in the geochronological frame, in Skourtsos, E., and thrust belt in northwest Bulgaria. The right Boccaletti, M., Manetti, P., Peccerillo, A., and Stanisheva- Lister, G.S., eds., The geology of Greece: Journal of shear continues to the present, but the transfer Vassileva, G., 1978, Late Cretaceous high potassium the Virtual Explorer, v. 42, Paper 1, p. 1–44. volcanism in eastern Srednogorie, Bulgaria: Geological Chatalov, G.A., 1990, Geology of the Strandza Zone in Bul- into shortening in northwest Bulgaria ceased in Society of America Bulletin, v. 89, p. 439–447, doi: 10 garia: Geologica Balacanica, ser. Operum Singulorum early Miocene time. Late Cenozoic right shear .1130 /0016 -7606 (1978)89 <439: LCHVIE>2 .0 .CO;2 . 4: Sofi a, Bulgarian Academy of Sciences, 272 p. became localized within the Southern Carpath- Bončev, S., 1936, Geologische skizze Bulgariens: Congres Cheshitev, G., ed., 1990–1995, Geological map of Bulgaria: des Geographes Slave, Sofi a, IV, p. 29–47. Sofi a, Bulgari, Committee for Geology and Mineral ians, forming the Cerna-Jiu and Timok faults. Bonchev, E., ed., 1971, Tectonics of the fore-Balkan: Sofi a, Resources, Department of Geophysical Prospecting The deformation is part of the complex Ceno- Bulgarina Academy of Sciences, 584 p. and Geological Mapping, scale 1:100,000. zoic deformations within the Southern Car- Bonchev, E., 1978, The post-Lutetian turning point in the Cheshitev, G., and Kancev, Il., eds., 1989, Geological map evolution of the Balkanide mobile area: Geologica Bal- of Bulgaria: Sofi a, Bulgaria, Committee for Geology pathians, where deformation is a consequence kanica, v. 8, no. 3, p. 25–36. and Mineral Resources, Department of Geophysical of northward and convergent motion causing Bonchev, E., 1983, The Kotel olistostrom formation—is it Prospecting and Geological Mapping, scale 1:500,000. existing?: The Jurassic in East Stara Planina: Geologi- Civijc, J., 1904, Die tectonic der Balkanhalbinsel mit Beruck- molding of tectonic units around the Moesian cal Balcanica, v. 13, no. 4, p. 81–83 (in Russian with sichtigung der neueren Forschritte in der Kenntniede continental crust. Late Eocene to early Mio- English abstract). Geologie von Bulgarien, Serbien and Makedonien: cene shortening in the fold-thrust belt was con- Bonchev, E., 1986, The Balkanides, geotectonic position and Compte Rendue, IX International Congress Vienne development: Sofi a, Bulgarina Academy of Sciences, 1903, Wien, p. 1–54. temporaneous with and separated tectonically 273 p. (in Bulgarian with Russian and English sum- Cordarcea, A., 1940, Vues nouvelles sur las Tectonicque from regional extension in the southern part mary). du Banat meridional et du Plateau de Mehedinti: of the Balkan orogen, the former site of major Bonev, N., and Beccaletto, L., 2007, From syn- to post-oro- Annuales of the Romanian Institute of Geology, v. 20, genic Tertiary extension in the north Aegean region: p. 1–74. shortening, metamorphism, and plutonism. The Constraints on the kinematics in the eastern Rhodope- Dabovski, C., Boyanov, I., Khrischev, K., Nikolov, T., Sapu- change from retroarc shortening to shortening Thrace, Bulgaria-Greece and the Biga Peninsula, NW nov, I., Yanev, Y., and Zagorchev, I., 2002, Structure Turkey, in Taymaz, T., et al., eds., The geodynamics of and Alpine evolution of Bulgaria: Geologica Balcanica, related to molding of tectonic elements around the Aegean and Anatolia: Geological Society of Lon- v. 32, no. 2–4, p. 5–9. the Moesian crust began in the middle Eocene; don Special Publication 291, p. 113–142, doi:10 .1144 Dabovski, C.N., and Savov, S.S., 1988, Structural studies the change may have taken place during the /SP291 .6 . in the nappes of southeast Strandzha: Geologica Bal- Bonev, N., and Stampfl i, G., 2011, Alpine tectonic evolution cancia, v. 18, no. 2, p. 19–36. earliest deformation in the third deformational of a Jurassic subduction-accretionary complex: Defor- Dachev, C., Stanev, V., and Bokov, P., 1988, Structure of event, but this is unknown due to poor tim- mation kinematics and 40Ar/39Ar age constraints on the the Bulgarian Black Sea area: Bollettino de Geofi zica ing constraints. Nevertheless, the third defor- Mesozoic low-grade schists of the Circum-Rhodope Teorica et Applicata, v. 30, p. 79–107. Belt in the eastern Rhodope-Thrace region, Bulgaria- De Wet, A.P., Miller, J.A., Bickle, M.J., and Chapman, H.J., mational event is related to a dynamic system Greece: Journal of Geodynamics, v. 52, p. 143–167, 1989, Geology and geochronology of the Arnea, Sitho- distinct from the older two, and occurred when doi: 10 .1016 /j .jog .2010 .12 .006 . nia and Ouranopolis intrusions, Chalkidiki Peninsula, Bonev, N., Burg, J.-P., and Ivanov, Z., 2006, Mesozoic– northern Greece: Tectonophysics, v. 161, p. 65–79, doi: the orogen in Bulgaria was separated into two Tertiary structural evolution of an extensional gneiss 10 .1016 /0040 -1951 (89) 90303-X . distinct parts: a northern part characterized by dome—The Kesebir-Kardamos dome, eastern Rho- Dumurdzanov, N., Serafi movski, T., and Burchfi el, B.C., shortening and a southern part characterized dope (Bulgaria-Greece): International Journal of Earth 2005, Cenozoic tectonics of Macedonia and its relation Sciences, v. 95, p. 318–340, doi: 10 .1007 /s00531 -005 to the South Balkan extensional regime: Geosphere, by regional extension. -0025 -y . v. 1, p. 1–22, doi: 10 .1130 /GES00006 .1 . Burchfi el, B.C., 1976, Geology of Romania: Geological Fügenschuh, B., and Schmid, S.M., 2005, Age and sig- ACKNOWLEDGMENTS Society of America Special Paper 158, 82 p., doi: 10 nifi cance of core complex formation in a very curved .1130 /SPE158 -p1 . orogen: Evidence from fission track studies in the Our work in Bulgaria has taken place for more Burchfi el, B.C., 1980, The eastern Alpine orogen of the South Carpathians (Romania): Tectonophysics, v. 404, Mediterranean: An example of collision tectonics: Tec- p. 33–53, doi: 10 .1016 /j .tecto .2005 .03 .019 . than two decades and has been supported by several tonophysics, v. 63, p. 31–61, doi: 10 .1016 /0040 -1951 Filipov, L., and Cheshitiv, G., eds., 1992, Vidin Map Sheet: different sources. The work began with support from (80)90106 -7 . Sofi a, Bulgaria, Committee for Geology and Mineral Maxus Energy Corporation, but the company was Burchfi el, B.C., Chen, Z., Hodges, K.V., Liu, Y., Royden, Resources, Department of Geophysical Prospecting sold in the l990s; their support was concurrent with L.H., Deng, C., and Xu, J., 1992, The South Tibetan and Geological Mapping, scale 1:100,000.

488 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Multiply deformed foreland fold-thrust belt of the Balkan orogen

Filipov, L., and Cheshitiv, G., eds., 1995, Vidin Map Sheet, Bulgaria: Journal of Structural Geology, v. 33, p. 859– Robertson, A.R., Ustaomer, T., Pikett, E.A., Collins, A.S., Explanatory note: Sofia, Bulgaria, Committee for 874, doi: 10 .1016 /j .jsg .2011 .03 .006 . Andrew, T., and Dixon, J.E., 2004, Testing modes of Geology and Mineral Resources, “Geologia i Geo- Kräutner, H.G., and Krstić, B.P., 2003, Geological map of late Palaeozoic–early Mesozoic orogeny in western fi zika” AD, 60 p., scale 1:100,000. the Carpatho-Balkanides between Mehadia, Oravita, Turkey: Support for an evolving open-Tethys model: Georgiev, G., Dabovski, C., and Stanisheva-Vassileva, G., Niš and Sofi a: Belgrade, Geological Institute of Serbia, Geological Society of London Journal, v. 161, p. 501– 2001, East Srednogorie–Balkan Rift Zone, in Ziegler, scale 1:300,000. 511, doi: 10 .1144 /0016 -764903 -080 . P.A., et al., eds., Stratigraphy and evolution of Peri- Le Pichon, X., and Angelier, J., 1981, The Hellenic arc and Roy, M., Royden, L.H., Burchfi el, B.C., Tzankov, T., and Tethyan platforms: Peri-Tethys Memoir 6: Paris, trench system: A key to the neotectonic evolution of the Nakov, R., 1996, Flexural uplift of the Stara Planina Memoires du Museum National d’Histoire Naturelle, eastern Mediterranean sea: Royal Society of London Range, central Bulgaria: Basin Research, v. 8, p. 143– v. 186, p. 259–293. Philosophical Transactions, v. 300, p. 357–372, doi:10 156, doi: 10 .1046 /j .1365 -2117 .1996 .01513 .x . Georgiev, S., von Quadt, A., Heinrich, C.A., Peytcheva, I., .1098 /rsta .1981 .0069 . Sandulescu, M., 1984, Geotectonica Romaniei: Bucharest, and Marchev, P., 2012, Time evolution of a rifted conti- Liati, A., Gebauer, D., and Wysoczanski, R., 2002, U-Pb Editura Tehnica, 450 p. nental arc: Integrated ID-TIMS and LA-ICPMS study SHRIMP dating of zircon domains from UHP garnet- Sandulescu, M., 1994, Overview on Romanian geology. of magmatic zircons from the Eastern Srednogorie, rich mafi c rocks and late pegmatoids in the Rhodope ALCAPA II Field Guidebook: Romanian Journal of Bulgaria: Lithos, v. 154, p. 53–67, doi: 10 .1016 /j .lithos zone (N Greece); evidence for Early Cretaceous crys- Tectonics and Regional Geology, v. 75, no. 2, p. 3–15. .2012 .06 .020 . tallization and Late Cretaceous metamorphism: Chem- Schmid, S.M., Bernoulli, D., Fügenschuh, B., Matenco, L., Gerdjikov, I., and Georgiev, N., 2006, The Maritsa fault ical Geology, v. 184, p. 281–299, doi: 10 .1016 /S0009 Schefer, S., Tischler, R., and Ustaszewski, K., 2008, system—A strike-slip zone along the northern margin -2541 (01)00367 -9 . The Alpine-Carpathian-Dinaridic orogenic system: of the Rhodopes: St. Ivan Rilski University of Mining Marchev, P., Raicheva, R., Downes, H., Vaselli, O., Chiara- Correlation and evolution of tectonic units: Swiss Jour- and Geology Annual, v. 49, p. 33–39 (in Bulgarian with dia, M., and Moritz, R., 2004, Compositional diversity nal of Geoscience, v. 101, p. 139–183, doi:10 .1007 English abs). of Eocene–Oligocene basaltic magmatism in the East- /s00015 -008 -1247 -3 . Gočev, P.M., 1986, Modèle pour une nouvelle synthèse ern Rhodopes, SE Bulgaria: Implications for genesis Şengör, A.M.C., and Yilmaz, Y., 1981, Tethyan evolution téctonique de la Bulgarie: Ministerul Geologiei, Institu- and tectonic setting: Tectonophysics, v. 393, p. 301– of Turkey: A plate tectonic approach: Tectonophysics, tul de Geologie si Geofi zica, Dari de Seama, Bucuresti , 328, doi: 10 .1016 /j .tecto .2004 .07 .045 . v. 75, p. 181–241, doi: 10 .1016 /0040 -1951 (81)90275 -4 . v. 70-71, no. 5, Tectonica si geologie regionala, Meinhold, G., and Kostopoulos, D.K., 2013, The Circum- Silke, J.-A., Froitzheim, N., Nagel, T.N., Frei, D., Georgiev, p. 97–107. Rhodope Belt, northern Greece: Age, provenance, and N., and Jan, P., 2010, Structural and geochronological Goranov, A., Boyanev, I., and Atanasov, G., 1992, tectonic setting: Tectonophysics, v. 595–596, p. 55–68, evidence for Paleogene thrusting in the western Rho- Lithostratigraphic subdivision of the Paleogene in doi: 10 .1016 /j .tecto .2012 .03 .034 . dopes, SW Bulgarian: Elements for a new tectonic the East Rhodopes and its correlation with Paleogene Mposkos, E., and Krohe, A., 2006, Pressure-temperature model of the Rhodope metamorphic province: Tecton- and Neogene in upper Thracia: University of Sofi a deformation paths of closely associated ultra-highpres- ics, v. 29, TC3008, doi: 10 .1029 /2009TC002558 . “St. Kliment Ohridski” Annals, 1—Geology, v. 182, sure (diamond-bearing) crustal and mantle rocks of the Stille, H., 1924, Grundfragen der Vergleichenden Tektonik: p. 169–182. Kimi complex: Implications for the tectonic history of Berlin, Gebruder Borntraeger, 443 p. Ivanov, Z., 1988, Aperçu general sur l’évolution géologique the Rhodope Mountains, northern Greece: Canadian Stuart, C.J., Nemcok, M., Vangelov, D., Higgins, E.R., et structurale du massif des Rhodopes dans lae cadre Journal of Earth Sciences, v. 43, p. 1755–1776, doi: Welker, C., and Meaux, D.P., 2011, Structural and depo- des Balkanides: Société Géologique de France, Bulle- 10 .1139 /e06 -064 . sitional evolution of the East Balkan thrust belt, Bul- tin, v. 8, p. 227–240. Nachev, I., 1993, Late Cretaceous Paleogeodynamics of Bul- garia: American Association of Petroleum Geologists Jolivet, L., and Brun, J.-P., 2010, Cenozoic geodynamic garia: Geologica Balcanica, v. 23.4, p. 3–23. Bulletin, v. 95, p. 649–673, doi: 10 .1306 /08181008061 . evolution of the Aegean: International Journal of Earth Nachev, I., and Nikolov, T., 1968, On the lower Cretaceous Sunal, G., Satir, M., Natal’in, B.A., Topuz, G., and Vonder- Sciences, v. 99, p. 109–138, doi: 10 .1007 /s00531 -008 in the Kraishte: Review of the Bulgarian Geological schmidt, O., 2011, Metamorphism and diachronous -0366 -4 . Society, v. XXIX, no. 3, p. 330–333 (in Bulgarian with cooling in the contractional orogen: The Strandja Mas- Jolivet, L., and 22 others, 2013, Aegean tectonics: Strain summary in English). sif, NW Turkey: Geological Magazine, v. 148, p. 580– localization, slab tearing and trench retreat: Tectono- Nakov, R., 2009, The northern boundary of the Fore-Balkan 596, doi: 10 .1017 /S0016756810001020 . physics, v. 597–598, p. 1–33, doi:10 .1016 /j .tecto .2012 between Ogosta and Iskar Rivers—Post-Cretaceous Tchoumatchenko, P., and Cernjvaska, S., 1990, The Jurassic .06 .011 . tectonics: Bulgarian Geological Society Proceedings, system in East Stara Planina, II, Palaeogeographic and Kanchev, I., 1962, The tectonics of the region Elena- Geosciences 2009, p. 87–88. paleotectonic evolution: Geologica Balcanica, v. 20, Tvarditsa-Triavna of the Stara Planina: Contributions Naydenov, K., Peytcheva, I., von Quadt, A., Sarov, S., Kol- no. 3, p. 17–58 (in Russian with English abstract). to Geology of Bulgaria. v. 1, p. 329–408 (in Bulgarian cheva, K., and Dimov, D., 2013, The Maritza strike- Tchoumatchenco, P., Yaneva, M., Budurov, K., Ivanova, with Russian and French summary). slip shear zone between Kostenets and Krichim D., Koleva-Rekalova, E., Petrunova, L., and Zago- Kanchev, I., Nikolov, T., Ruskova, N., and Milanova, V., towns, South Bulgaria—Structural, petrographic rcev, I., 2004, Late Cimmerian tectonics of the Trias- 1995, Explanatory note to map sheet “Tvarditsa” 1:100 and isotope geochronology study: Tectonophysics, sic and Jurassic rocks in Louda Kamcia, East Stara 000: Sofi a, Bulgaria, Committee of Geology, Geology v. 595–596, p. 69–89, doi: 10 .1016 /j .tecto .2012 .08 Planina Mts. (Bulgaria): Bulgarian Geological Society and Geophysics, AD, 139 p. (in Bulgarian). .005 . Annual Scientifi c Conference Proceedings, “Geology Kilias, A., Falalakis, G., and Mountrakis, D., 1999, Creta- Okay, A.I., Şengör, A.M.C., and Gorur, N., 1994, Kine- 2004”, 3 p. ceous–Tertiary structure and kinematics of the Serbo- matic history of the opening of the Black Sea and its Tchoumatchenco, P., Rabrenovic, D., Radulovic, V., and macedonian metamorphic rocks and their relation to effects on the surrounding regions: Geology, v. 22, Malesevic, N., 2011, Trans-border east Serbia/west the exhumation of the Hellenic hinterland (Macedonia, p. 267–270, doi: 10 .1130 /0091 -7613 (1994)022 <0267: Bulgaria) correlation of the morpho-tectonic structures: Greece): International Journal of Earth Sciences, v. 88, KHOTOO>2 .3 .CO;2 . Annales Geologiques de la Peninsule Balkanique, p. 513–531, doi: 10 .1007 /s005310050282 . Okay, A.I., Satõr, M., Tüysüz, O., Akyüz, S., and Chen, F., v. 72, p. 21–27, doi: 10 .2298 /GABP1172021T . Kockel, C.W., 1927, Zur Stratigraphie und Tektonik Bul- 2001a, The tectonics of the Strandja Massif: Late- Tronkov, D., 1963, Character of the Old Cimmerian struc- gariens. Mit einem Beitrag von F. Kossmat: Das Variscan and mid-Mesozoic deformation and meta- tural stage, type and time of the Old Cimmerian tec- Grenzgebiet zwischen ostlichem und zentralen Balkan: morphism in the northern Aegean: International Jour- tonic movements in northwestern Bulgaria: Proceed- Geologische Rundschau, v. 18, p. 349–395. nal of Earth Sciences, v. 90, p. 217–233, doi: 10 .1007 ings on the Geology of Bulgaria: Stratigraphy and Kostopoulos, D.K., Ioannidis, N.M., and Sklavounos, /s005310000104 . Tectonics, v. 5, p. 171–196 (in Bulgarian with sum- S.A., 2000, A new occurrence of ultrahigh-pressure Okay, A.I., Tansel, I., and Tüysüz, O., 2001b, Obduction, mary in Russian and German). metamorphism, central Macedonia, northern Greece: subduction and collision as refl ected in the Upper Cre- Tronkov, D., Encheva, M., and Trifonova, E., 1965, Stra- Evidence from graphitized diamonds?: International taceous–Lower Eocene sedimentary record of western tigraphy of the Triassic system in northwest Bulgaria: Geology Review, v. 42, p. 545–554, doi:10 .1080 Turkey: Geological Magazine, v. 138, p. 117–142, doi: Bulgarian Academy of Sciences, Bulletin of the Insti- /00206810009465098 . 10 .1017 /S0016756801005088 . tute of Geology, v. 14, p. 261–292. Kounov, A., Seward, D., Bernouli, D., Burg, J.-P., and Iva- Papanikolaou, D., 2009, Timing of tectonic emplacement Turpaud, P., and Reischmann, T., 2010, Characterisation nov, Z., 2004, Thermotectonic evolution of an exten- of the ophiolites and terrane paleogeography in the of igneous terranes by zircon dating: Implications for sional dome: the Cenozoic Osogovo-Lisets core com- Hellenides: Lithos, v. 108, p. 262–280, doi:10 .1016 /j UHP occurrences and suture identifi cation in the Cen- plex (Kriashte zone, western Bulgaria): International .lithos .2008 .08 .003 . tral Rhodope, northern Greece: International Journal of Journal of Earth Sciences, v. 93, p. 1008–1024, doi: 10 Perincek, D., l991, Possible strand of the North Anatolian Earth Sciences, v. 99, p. 567–591, doi:10 .1007 /s00531 .1007 /s00531 -004 -0435 -2 . fault in the Thrace Basin, Turkey—An interpretation: -008 -0409 -x . Kounov, A., Seward, D., Burg, J.-P., Bernouli, D., Ivanov, American Association of Petroleum Geologists Bulle- Tzankov, T., Angelova, D., Nakov, R., Burchfi el, B.C., and Z., and Handler, R., 2010, Geochronological and struc- tin, v. 75, p. 241–257. Royden, L.H., 1996, The sub-Balkan graben system of tural constraints on the Cretaceous thermotectonic evo- Ratschbacher, L., Linzer, H.-G., Moser, F., Strusievicz, central Bulgaria: Basin Research, v. 8, p. 125–142, doi: lution of the Kraishte zone, western Bulgaria: Tecton- R.-O., Bedelean, H., Har, N., and Mogoş, P.-A., 1993, 10 .1046 /j .1365 -2117 .1996 .01452 .x . ics, v. 29, TC2002, doi: 10 .1029 /2009TC002509 . Cretaceous to Miocene thrusting and wrenching along Tzankov, Tz., Nedyalkova, L., Angelov, V., Aladjova- Kounov, A., Burg, J.-P., Bernoulli, D., Seward, D., Ivanov, the central south Carpathians due to a corner effect dur- Hrischeva, K., Yaney, S., Haydutov, I., Sapunov, I., and Z., Dimov, D., and Gerdjikov, I., 2011, Paleostress ing collision and orocline formation: Tectonics, v. 12, Chumachenco, P., 1991, Geological map of Bulgaria, analysis of Cenozoic faulting in the Kraishte area, SW p. 855–873, doi: 10 .1029 /93TC00232 . sheet Vratsa: Sofi a, Bulgaria, Committee for Geology

Geosphere, April 2015 489

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021 Burchﬁ el and Nakov

and Mineral Resources, Department of Geophysical taceous magmatism and Cu-Au mineralization in the Zagorchev, I., 1996, Pre-Paleogene Alpine tectonic units Prospecting and Geological Mapping, scale 1:100,000. Panagyurishte region of the Apuseni-Banat-Timok- and terranes in the border area of SW Bulgaria and Tzankov, Tz., Aladjova-Hrischeva, K., Yanev, S., Haydutov, Srednogorie belt, Bulgaria: Ore Geology Reviews, Yugoslavia, in Knezevic, V., and Krstić, B., eds., I., Sapunov, I., Chumachenco, P., Nedyalkova, L., and v. 27, p. 95–126, doi: 10 .1016 /j .oregeorev .2005 .07 .024 . Terranes of Serbia: The formation of the geologic Angelov, V., 1995, Explanatory note to the geological Vulchanov, A., 1971, Content, origine and relation of the framework of Serbia and the adjacent regions: Uni- map of Bulgaria, scale 1:100,000, map sheet Vratsa: “Sredna Gora Allochthon” to the neighboring mor- versity of Belgrade Faculty of Mining and Geology, Sofi a, Bulgaria, Committee for Geology and Mineral photectonic units: Sophia, Bulgaria, Annual of the p. 81–86. Resources, “Geologia i Geofi zika,” AD, 102 p. State Company “Geological Investigations,” v. XX, Zagorchev, I., l998, Pre-Priabonian Paleogene forma- Tollmann, A., 1963, Ostalpensynthese: Vienna, Austria, p. 99–110 (in Bulgarian with abs. in Russian and tions in southwestern Bulgaria and northern Greece: Franz Deuticke, 256 p. French). Stratigraphy and tectonic implications: Geo- Tollmann, A., 1968, Die alpidischen Gebirgsbildung– Wawrzenitz, N., and Mposkos, E., 1997, First evidence for logical Magazine, v. 35, p. 101–119, doi:10 .1017 Phasen in den Ostalpen und Westkarpaten: Geotek- Lower Cretaceous HP/HT-metamorphism in the east- /S0016756897008285 . tonic Forscherungen, v. 21, 156 p. ern Rhodope, north Aegean region, north-east Greece: Zagorchev, I., 2001, Introduction to the geology of SW Bul- Vangelov, D., Kiselinov, H., Andreeva, P., and Vangelova, V., European Journal of Mineralogy, v. 9, p. 659–664, doi: garia: Geologica Balcanica, v. 31, no. 1–2, p. 3–52. 2013, Structural characteristics for a part of the East- 10 .1127 /ejm /9 /3 /0659 . Zagorchev, I., and Tikhomirova, L.B., 1986, Stratigraphy ern Fore-Balkan: Review of the Bulgarian Geological Yovchev, Y., ed., 1971, Tectonic structure of Bulgaria: Sofi a, of the Jurassic Trekljano Group (SW Bulgaria): Geo- Society, v. 74, part 1-3, p. 21–39. Publishing House Technica, 558 p. (in Bulgarian with logica Balcanica, v. 16, no. 3, p. 23–44. van Hinsbergen, D.J.J., Dupont-Nivet, G., Nakov, R., Oud, K., English summary). Zagorchev, I., Popov, N., and Ruseva, M., 1989, Paleogene and Panaiotu, C., 2008, No signifi cant post-Eocene rota- Zagorchev, I., 1986, Jurassic paleogeography of a part of stratigraphy in a part of SW Bulgaria: Geologica Bal- tion of the Moesian Platform and Rhodope (Bulgaria): south-west Bulgaria in the light of new stratigraphic canica, v. 19, no. 6, p. 41–69. Implications for the kinematic evolution of the Carpath- data: Geologica Balcanica, v. 16, no. 5, p. 3–20. Zagorchev, I., Dabovski, C., and Nikolov, T., 2009, Meso- ian and Aegean arcs: Earth and Planetary Science Let- Zagorchev, I., 1993, Bosilegrad and Radomir map sheet, zoic geology, in Zagorchev, I., et al., eds., Geology of ters, v. 273, p. 345–358, doi: 10 .1016 /j .epsl .2008 .06 .051 . scale 1:100,000, and explanatory note: Sofi a, Bulgaria, Bulgaria, Volume II, Part 5: Sofi a, Prof. Marin Drinov von Quadt, A., Moritz, R., Peytcheva, I., and Heinrich, C.A., Committee for Geology and Mineral Resources, “Geo- Academic Publishing House, p. 15–37 (in Bulgarian 2005, Geochronology and geodynamics of Late Cre- logia I Geofi zika” AD, (explanatory note, 77 p.). with English summary).

490 Geosphere, April 2015

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/11/2/463/3336828/463.pdf by guest on 02 October 2021