Thrust tectonics in the Strandja zone : new data from the Dervent Heights, SE Bulgaria

Dervent Heights are one of the least studied parts of the Strandja zone in Bulgaria. Our detailed field studies in the area of the villages of GoIiam and Valcha PoIiana show the need of revision of the earlier models for nappe tectonics in this pari of the Alpine orogenic belt. Two major units could be distinguished in the pre-Cenomanian basement - autochthon and allochthon. The autochthon is built by Variscan high-grade metamorphic rocks and not penetrativelly deformed granitoids. They are covered by low-grade Triassic metasediments. The allochthone consist of phyllite formation with early Paleozoic age, as well as the underlying carbonate and detrital metasediments. These metasediments form a mappable unit here designated as carbonate terrigeneous formation. Field data allow to reconsider the position of the abundant dolomites. It was suggested that they are forming the autochthon, but the field relations are consistent with interpreting them as a part of the carbonate-terigeneous formation. All studied rocks record very low-grade Early Alpine metamorphism (T<3OO-350'). The metasediments of the autochthon as well these of the allochthon display evidence for strong synmetamorphic deformations and because of that primary structures are not preserved. The timing of the emplacement of the allochthon is poorly constrained, but judging from the lack of localization of ductile as well as of brittle deformation along the major contacts it could be suggested that the emplacement was pre- to synmetamorphic

Two stages of Late Carboniferous to Triassicmagmatism in the Strandja Zone of Bulgaria and Turkey

Although Variscan terranes have been documented from the Balkans to the Caucasus, the southeastern portion of the Variscan Belt is not well understood. The Strandja Zone along the border between Bulgaria and Turkey encompasses one such terrane linking the Balkanides and the Pontides. However, the evolution of this terrane, and the Late Carboniferous to Triassic granitoids within it, is poorly resolved. Here we present laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb zircon ages, coupled with petrography and geochemistry from the Izvorovo Pluton within the Sakar Unit (Strandja Zone). This pluton is composed of variably metamorphosed and deformed granites which yield crystallization ages of c. 251–256 Ma. These ages are older than the previously assumed age of the Izvorovo Pluton based on a postulated genetic relationship between the Izvorovo Pluton and Late Jurassic to Early Cretaceous metamorphism. A better understanding of units across the Strandja Zone can now be achieved, revealing two age groups of plutons within it. An extensive magmatic episode occurred c. 312–295 Ma, and a longer-lived episode between c. 275 and 230 Ma. Intrusions associated with both magmatic events were emplaced into pre-Late Carboniferous basement, and were overprinted by Early Alpine metamorphism and deformation. These two stages of magmatism can likely be attributed to changes in tectonic setting in the Strandja Zone. Such a change in tectonic setting is likely related to the collision between Gondwana-derived terranes and Laurussia, followed by either subduction of the Palaeo-Tethys Ocean beneath Laurussia or rifting in the southern margin of Laurussia, with granitoids forming in different tectonic environments

Sulfide trace element signatures and S- and Pb-isotope geochemistry of porphyry copper and epithermal gold-base metal mineralization in the Elatsite–Chelopech ore field (Bulgaria)

The Elatsite–Chelopech ore field in the northern part of the Panagyurishte district in Central Bulgaria comprises numerous spatially associated porphyry copper and epithermal gold deposits and prospects. In addition to the mineralization and alteration features, trace elements, lead and sulfur isotope signatures of sulfide minerals from porphyry copper, base metal and gold-base metal deposits/prospects have been studied. LA-ICP-MS analyses of pyrite, arsenopyrite and sulfosalt minerals validate them as major carriers for Au, Ag, Sb, Se and Co. Pyrite from the three types of mineralization has specific geochemical characteristics. Pyrite from the porphyry copper deposits/prospects has generally lower total trace element content compared to pyrite from the epithermal prospects, except for Se, Co and Ni. Pyrite from the base metal and gold-base metal veins is enriched in As, Au, Ag, Sb and Pb. In pyrite from the base metal deposits, Co and Ni have contents comparable to the pyrite from the porphyry copper deposits, while pyrite from the gold-base metal veins shows lower Co and Ni. Arsenopyrite from these deposits shows similar features. Similarly, sphalerite from the gold-base metal veins also has lower Co content compared to sphalerite from the base metal veins but higher In and Cu contents. In addition to the close spatial relationships between the Elatsite and Gorna Kamenitsa porphyry Cu deposits and Negarstitsa-West and Dolna Kamenitsa base metal prospects, as well as similarities in the mineralization and alteration styles, the lead isotopic (206Pb/204Pb = 18.61–18.68, 207Pb/204Pb = 15.64–15.65 for porphyry and 206Pb/204Pb = 18.55–18.67, 207Pb/204Pb = 15.64–15.68 for base metal) and sulfur isotopic (δ34S values of −3 to +1‰ for porphyry and δ34S values of −1.7 to +3.5‰ for base metal) signatures of sulfides support the idea of a genetic link between these two types of deposits. The porphyry and base-metal mineralization result from a common major ore-forming event during the Late Cretaceous, corresponding to deep/higher-temperature and shallower/distal/lower-temperature environments, respectively. In particular, more radiogenic lead (206Pb/204Pb = 18.41–18.47, 207Pb/204Pb = 15.67–15.76) and slightly different sulfur isotopic compositions (δ34S values of +3.5 to +10.6‰) of sulfides from the distal gold-base metal veins of Kordunsko Dere, Svishti Plaz and Shipkite might be a consequence of the interaction of the ore-forming fluids with an external older crustal and isotopically positive S source. Alternatively, a different fluid source/event for the formation of these gold-base metal veins may be suggested

The problems of the post-Cenomanian tectonic evolution of the central parts of the Sredna Gora Zone. The wrench tectonics - how real is real?

The Sredna Gora Zone holds a unique place in the tectonic subdivisions of the Balkanide orogen and its evolution is still a subject of debate. In the last twenty years, the idea of strike-slip-related evolution of the zone has been invoked. However, for the moment, the number of thorough studies where such a scenario is envisaged is limited, and substantial evidence based on detailed fieldwork is still missing. In this article, we discuss some of the major problems of the suggested wrench tectonic concept in the evolution of the central part of the Sredna Gora Zone. These are the character of some major shear zones in the area, to which strike-slip movements are attributed, and the transtension-transpression evolution scenario for the Chelopech and Panagyurishte basins. Despite refuting completely their wrench tectonic-related evolution, we confirm the presence of strike-slip and oblique slip structures cutting the sediments, whereas the time of their activity and role in the deformation of the basin fill are yet to be revealed. Finally, we present a model based on natural examples and analogue modeling, in which the long-lived dextral Maritsa shear zone represents a zone of localized strain partitioning, separating the opposite vergent thrust belts of the Rhodope to the south and the Sredna Gora and Balkan fold-thrust belt to the north, during oblique or possibly orthogonal convergence

Early alpine orogeny as recorded in metamorphic complexes of Southern Bulgaria

International audienc

Main fault zones controlling the late Alpine structure in the area east of Sofia (Srednogorie Zone, Western Bulgaria)

The northwestern narrow tip of the Upper Cretaceous Panagyurishte sedimentary strip is cropping out along the eastern-north-eastern margin of the Neogene Sofia graben. In this area the sedimentary strip is split in two parts separated by an uplifted pre-Upper Cretaceous basement block. Both parts show syncline geometries with cores built of Upper Cretaceous rocks. The synclines are striking NW-SE and are extremely asymmetrical with vertical to overturned southwestern limbs. Within the overturned limbs meso-scale structural features such as imbrications, folds and small-displacement faults indicate strong flattening of the rock volume under generally top-to-the-N shear. These features were observed along the Kamenitsa-Rakovishki and Negushevo fault zones. Due to the relatively poor outcrop conditions the precise dips of these fault zones are still poorly known and there are no data about the fault cores. Thus, the general north-vergent character of the both fault zones is assumed on the basis of the semi-penetrative small-scale structures within their immediate footwalls and field relations. Our new data suggest that the northward translations along the Negushevo fault zone resulted in formation of approx. 30 long and 2 km wide basement uplift

High-grade metamorphic complexes in Bulgaria

Various in age, metamorphic overprint and rock compositions high-grade metamorphic complexes are exposed in the southern parts of the Balkan Peninsula. Until recently all the complexes were presumed to be Precambrian in age. Despite of this groundless assumption, the current geochronological data have shown that the Precambrian age clusters are quite rare and concern mainly the protoliths. To avoid the controversial views about the evolution of the high-grade complexes in Bulgaria we propound a new scheme of their subdivision based on both field and geochronological data. The main difference from the other available schemes is that we use only the ages of the metamorphic overprint and not of the protolithic age. Isolated Cadomian crustal fragments are distinguished only in low-grade metamorphic complex of Krayshte and Stara Planina Mountain. Carboniferous high-grade metamorphics are exposed in Southwestern Bulgaria and Srеdna Gora. Rocks building up the core of the Alpine Orogen of the Balkans suffered Jurassic, Cretaceous and Tertiary high-grade metamorphic overprints. The metamorphics in Sakar and Osogovo are Early Alpine in age. The Rhodope metamorphic complex is a composite unit with polymetamorphic evolution comprising both pre-Mesozoic and Mesozoic protoliths affected by Mesozoic and Tertiary orogenic events. The tectonic structre of the Rhodopes has resulted from the processes of syn-metamorphic thrusting as well as syn- to post-metamorphic extension. Fragments of high-grade complexes with well constrained pre-Mesozoic ages are distinguished only in the uppermost parts of the Rhodopian metamorphic section. В южните части на Балканския полуостров се разкриват разнообразни по състав, степен на наложени изменения и възраст високостепенни метаморфни комплекси. До скоро всички те по презумпция се считаха за докамбрийски, но публикуваните в последните години геохроноложки данни показаха, че доказаните прекамбрийски възрасти са твърде малко и се отнасят главно за протолити. Основавайки се на собствени теренни наблюдения, в съчетание с геохроноложките данни, предлагаме нова схема за подялба на високометаморфния фундамент на територията на България. За разлика от предишни схеми, тази подялба е базирана на възрастта на високостепенните метаморфни изменения, запечатани от скалите, а не на данни за протолитните възрасти. Малки по площ, кадомски корови фрагменти са установени единствено в херцинските нискостепенни метаморфни комплекси, разкриващи се в Краището и Старопланинската област. В югозападна България и Средногорието широко разпространени са мигматизирани гнайси, запечатали метаморфизъм с карбонска възраст. Ядрените части на Алпийския ороген на Балканите са засегнати от юрски, креден и терциерен метаморфизъм. С ранноалпийска възраст са метаморфните комплекси в Сакар и Осогово. Родопският метаморфен комплекс е сложна полиметаморфна единица включваща до-мезозойски и мезозойски протолити, засегнати от мезозойски и терциерни динамо-термални събития. Тектонското разслояване в Родопите е резултат от синметаморфни навличания и син- до постметаморфна екстензия. Фрагменти от домезозойски високометаморфни комплекси в Родопите уверено се установяват само в най-високо разположените в разреза единици

Two partial melting events as recorded by the U-Th-Pb chronometer in monazite: LA-ICPMS in situ dating in metapelites from the Bulgarian Central Rhodopes

International audienc

Timok fault and Tertiary strike-slip tectonics in part of western Bulgaria

The existence of NW-SE and NNW-SSE trending, regional-scale faults is well-known feature in the area of Tran and Breznik (West Bulgaria). Despite the numerous studies in the area, there is a lack of direct data about the kinematics of the main fault zones. Our investigations allow to define three groups of faults and also demonstrate the dominant dextral strike-slip kinematics of the faults from Pernik fault zone, as well as of several segments of Tran-Kosharevo fault. The field data, together with analysis of the existing maps, suggest the existence of another main strike-slip fault zone with almost N-S strike – the Timok fault. This fault is well-documented in Eastern Serbia, as its continuation in the area of Tran (Kraishte zone) was already suggested by Karaguleva et al. (1980) and Krautner and Krstic (2003). In the westernmost parts of Bulgaria, the Timok fault is traced along the fault segments, previously interpreted as parts of Tran-Kosharevo fault. To the Southward the zone is following the Serkirna fault. Unlike the northeast Serbia the translations along the Timok fault in western Bulgaria are much smaller – probably of not more than few kilometers. Additionally, our new data do not support the idea that these fault zones are part of Maritsa fault zone, well-defined southeast from Sofia