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• Study covering 95 % of the performed EP procedures in Bulgaria was performed. • EP procedures were divided in 2 groups-catheter ablations and diagnostic EP studies. • Detailed complexity classification is proposed for ablations (simple or complex) The implementation of diagnostic reference levels (DRLs) is an essential tool for optimisation of the routine practice, better management of patient exposure while maintaining sufficient image quality. National DRLs for electrophysiology (EP) procedures are not available in our country. The main purpose of the study was to propose, for first time in Bulgaria, national DRLs (NDRLs) for EP studies and ablation procedures of two different levels of complexity. The proposed DRLs can be later used to establish NDRLs by the national authority with regulatory functions related to medical exposure. A retrospective study was done with the three highest volume Bulgarian EP centers, where over 95 % of all cardiac ablations were performed. Data were extracted from the electronic registry for invasive electrophysiology BG-EPHY. Independently of the proposed NDRLs, we also compared the air kerma-area product (KAP) between the participating centers for procedures of the same level of complexity. The proposed NDRL in terms of KAP were: 5.2 Gy.cm2 for diagnostic EP studies, 25.5 Gy.cm2 for simple ablations, and 52.1 Gy.cm2 for complex ablations. There was a significant variation in KAP for procedures with the same degree of complexity within each center. This study is the first to propose NDLRs for EP studies and ablation procedures of two levels of complexity in Bulgaria. The results identified EP procedures requiring further optimization of patient protection and provided a basis for future comparisons and standardization with further investigations on the topic. The proposed NDRLs are recommended to be used for better management of radiation exposure during EP procedures of different levels of complexity. [ABSTRACT FROM AUTHOR]

Two platform-type carbonate successions of Berriasian to early Valanginian age are exposed in the eastern Circum-Rhodope belt which extends from the Chalkidiki Peninsula to the Thrace region in northern Greece. On the basis of new sedimentological and biostratigraphic results and analysis of published palaeomagnetic data, the Porto Koufos Limestones and Aliki Limestones are interpreted as deposits of a formerly unknown earliest Cretaceous carbonate platform in the Western Tethys realm. This Circum-Rhodope carbonate platform existed in tropical latitudes of the intra-Tethyan domain on the northern shelf area of the small Vardar oceanic basin. It was characterized by limited regional extent, remoteness from land, and short lateral transitions into deeper basin areas. Predominantly skeletal sediments with various microencrusters were produced along with variable amounts of lime mud, marine cements, peloids, intraclasts, aggregate grains, ooids and microbialites. The microfacies analysis of limestones formed around the Berriasian-Valanginian boundary indicates the configuration of a rimmed shelf with restricted lagoon, open lagoon, reef margin, fore-reef and upper slope depositional environments. During the early Valanginian a change from photozoan to heterozoan mode of carbonate production occurred mainly as a result of climate cooling. Deposition continued in protected lagoon, shoal and near-shoal settings implying a ramp-like morphology of the platform. Finally, a shift from skeletal to non-skeletal carbonate deposition took place as a consequence of high seawater carbonate saturation and possibly coeval increase of the marine trophic levels. A major sea level fall and climate cooling were the prime palaeoenvironmental controls that caused decline of the shallow-water carbonate factory and subsequent demise of the Circum-Rhodope carbonate platform in mid-Valanginian time that was followed by a long-term subaerial exposure and karstification which continued at least until the middle Eocene. The new results can be used for correlation with other shallow marine carbonates deposited in the intra-Tethyan domain during the earliest Cretaceous. Also, they appear to be of critical significance to decipher the Mesozoic geodynamic evolution of the Circum-Rhodope belt and adjacent tectonic zones. [ABSTRACT FROM AUTHOR]

In the Thrace region of NE Greece, the crystallization and post-solidification cooling below 600 °C of the intrusive suite of the Circum-Rhodope Belt arc-related Evros ophiolite span from 176.4 ± 0.93 to 163.5 ± 3.85 Ma. In the underlying Rhodope high-grade metamorphic basement, (ultra-) high-pressure metamafic rocks are cross-cut by orthogneisses with granitoid protoliths and crystallization ages between 160 ± 0.69 and 154 ± 1.5 Ma. This new U–Pb LA–ICP-MS zircon geochronological data provides evidence that the timing of the evolution of the Evros ophiolite coincides, within analytical error, with granitoid magmatism in the underlying high-grade basement. One of the dated metagranitoid rocks cross-cuts amphibolitized eclogite, indicating that the high-pressure conditions have a maximum age of 160 Ma postdating one of the proposed ages of ultra-high pressure conditions in the Rhodope Massif. The currently earliest recognised Rhodope high/ultra-high pressure metamorphic event is therefore related to the subduction setting which formed the Evros ophiolite. Based on these new temporal constraints and the regional tectonic–geochronologic framework, we discuss and update the geodynamic context connected to the Jurassic subduction–collisional setting at the Rhodope continental margin of Eurasia. [ABSTRACT FROM AUTHOR]

The field relationships, biostratigraphic constraints and paleoenvironmental conditions of lowermost Cretaceous platform carbonates from the eastern part of the Vardar Zone and the Circum-Rhodope Belt are studied. Field data confirm the unconformable position of non-deformed and non-metamorphosed limestones over Upper Jurassic back-arc rift-spreading ridge Sithonia ophiolites of the Vardar Zone in the Chalikidiki Peninsula and deformed arc-related greenschists of the Circum-Rhodope Belt in Thrace region. The distinguished microfossil assemblages and foraminiferal morphogroups are compatible with deposition in a shallow-water environment adjacent to the continental margin of Eurasia. The morphogroup characteristics support such interpretation and newly discovered microfossils define the age of the limestones as Berriasian to early Valanginian. The microfossil data conform to available radiometric ages for the Late Jurassic ophiolite crystallization and time equivalent Circum-Rhodope Belt thrust tectonics. Hence, the obtained results provide sedimentary evidence for pre-Berriasian accretion of the eastern Vardar Zone ophiolites to the continental margin and completion of the Circum-Rhodope Belt tectono-metamorphic history. The earliest Cretaceous sedimentation extended along the whole length of the Circum-Rhodope Belt across the north Aegean region implying a region-wide development of a carbonate platform which postdated the imprint of an important tectonic event. The sedimentation seals the Late Jurassic-Early Cretaceous Balkan orogenic event in the internal Hellenides at the Eurasian plate margin. This conclusion has strong implications for the geodynamic evolution of the Alpine Belt of the North Aegean region. [ABSTRACT FROM AUTHOR]

We quantify the timing of the Tertiary crustal extension in the eastern Rhodope Massif of south Bulgaria using 40Аr/39Аr geochronology to constrain the temporal evolution of exhumation of the metamorphic domes. 40Аr/39Аr analyses of mineral phases with different closure temperatures extracted from metamorphic rocks collected in the footwall and the hanging wall of the extensional system reveal the low-temperature cooling history towards shallow crustal levels. The results reveal that subsequent to regional amphibolite facies metamorphism (i) the hanging wall gradually cooled between 500 and 300°C during the Paleocene to Late Eocene (64–34Ma), starting at a low rate of 25°C/Ma and increasing to 50–67°C/Ma during 38–34Ma, (ii) cooling below 400–300°C of the footwall beneath the extensional detachments occurred in the Middle–Late Eocene (39–35.5Ma) at an average rate of 35°C/Ma. 40Аr/39Аr data from the metamorphic basement has been combined with 40Аr/39Аr data from the volcanic and hydrothermal rocks in the vicinity to the extensional domes, to determine the temporal relationships between extensional tectonics, ore-forming and magmatic processes in the region. Extension of the high-grade basement, the ore-formation and volcanism overlaps within a 5Ma lasting time interval, especially during the cooling and exhumation of the footwall. The eastern Rhodope Massif records an early stage of Eocene extension within the Aegean extensional province, where distinct crustal-scale processes occurred simultaneously implying the presence of cause and effect processes, and thus represents a key example of coeval continental extension, magmatism and hydrothermal activity in the late-stage evolution of the orogens. [ABSTRACT FROM AUTHOR]

Abstract: Deformation of the Circum-Rhodope Belt Mesozoic (Middle Triassic to earliest Lower Cretaceous) low-grade schists underneath an arc-related ophiolitic magmatic suite and associated sedimentary successions in the eastern Rhodope-Thrace region occurred as a two-episode tectonic process: (i) Late Jurassic deformation of arc to margin units resulting from the eastern Rhodope-Evros arc–Rhodope terrane continental margin collision and accretion to that margin, and (ii) Middle Eocene deformation related to the Tertiary crustal extension and final collision resulting in the closure of the Vardar ocean south of the Rhodope terrane. The first deformational event D1 is expressed by Late Jurassic NW-N vergent fold generations and the main and subsidiary planar-linear structures. Although overprinting, these structural elements depict uniform bulk north-directed thrust kinematics and are geometrically compatible with the increments of progressive deformation that develops in same greenschist-facies metamorphic grade. It followed the Early-Middle Jurassic magmatic evolution of the eastern Rhodope-Evros arc established on the upper plate of the southward subducting Maliac-Meliata oceanic lithosphere that established the Vardar Ocean in a supra-subduction back-arc setting. This first event resulted in the thrust-related tectonic emplacement of the Mesozoic schists in a supra-crustal level onto the Rhodope continental margin. This Late Jurassic-Early Cretaceous tectonic event related to N-vergent Balkan orogeny is well-constrained by geochronological data and traced at a regional-scale within distinct units of the Carpatho-Balkan Belt. Following subduction reversal towards the north whereby the Vardar Ocean was subducted beneath the Rhodope margin by latest Cretaceous times, the low-grade schists aquired a new position in the upper plate, and hence, the Mesozoic schists are lacking the Cretaceous S-directed tectono-metamorphic episode whose effects are widespread in the underlying high-grade basement. The subduction of the remnant Vardar Ocean located behind the colliding arc since the middle Cretaceous was responsible for its ultimate closure, Early Tertiary collision with the Pelagonian block and extension in the region caused the extensional collapse related to the second deformational event D2. This extensional episode was experienced passively by the Mesozoic schists located in the hanging wall of the extensional detachments in Eocene times. It resulted in NE-SW oriented open folds representing corrugation antiforms of the extensional detachment surfaces, brittle faulting and burial history beneath thick Eocene sediments as indicated by 42.1–39.7Ma 40Ar/39Ar mica plateau ages obtained in the study. The results provide structural constraints for the involvement components of Jurassic paleo-subduction zone in a Late Jurassic arc-continental margin collisional history that contributed to accretion-related crustal growth of the Rhodope terrane. [Copyright &y& Elsevier]

Abstract: In the northeastern Rhodope Massif, the Kulidzhik nappe exposes a unique juxtaposition of a high-grade basement allochthon onto a low-grade Mesozoic unit, and the counterpart Pelevun extensional allochthon belonging to the same unit. The Kulidzhik nappe tectonostratigraphy comprises structurally upward: (i) a lower unit consisting of high-grade basement orthogneisses; (ii) a low-grade greenschist-phyllite unit consisting of Jurassic extrusive rocks and metasedimentary rocks; (iii) the nappe allochthon built by the lower high-grade basement unit orthogneisses; and (iv) Eocene sedimentary rocks and Oligocene volcanic cover rocks. The Pelevun extensional allochthon is heterogeneous, and consists of Mesozoic low-grade unit marbles and greenschists and the upper high-grade basement unit. We have combined structure and kinematics, with lithological information and 40Аr/39Аr geochronology to constrain the tectonic evolution and regional significance of the Kulidzhik nappe and the Pelevun extensional allochthon. Mineral chemistry reveals igneous phases of the granitic protolith of the allochthonous orthogneisses with textures related to ductile deformation and metamorphism higher than 500°C. Their trace element patterns are indistinguishable from the high-grade basement orthogneisses in the eastern Rhodope. Mineral chemistry of the metamorphic assemblage in the underlying greenschists is consistent with medium-grade greenschist-facies metamorphism at temperatures well below 450°C, whose geochemistry defines transitional MORB to IAT affinities with a strong arc imprint. The greenschist''s composition is extremely similar to the composition of a supra-subduction zone Jurassic arc extrusive suite that occurs in the low-grade unit of the eastern Rhodope. The structural elements in all of the tectono-metamorphic units and the nappe surface indicate top-to-the NNE tectonic transport. Deformation evolved from ductile to brittle conditions coevally with a progressive decrease from lower amphibolite to weak greenschist-facies metamorphism towards the structural top. Two klippen gave plateau 40Аr/39Аr mica ages of 154.23±0.66Ma and 156.70±0.81Ma, respectively, which reflect cooling following the greenschist-facies event below ∼350°C, during shallow crustal level thrust emplacement and exhumation of the Kulidzhik allochthon. The hanging-wall Pelevun extensional allochthon preserves an internal NNE-directed ductile tectonic transport trend, but is underlain by a SSW-directed ductile–brittle extensional detachment and has experienced NE-SW brittle extension on high-angle normal faults. An amphibole 40Аr/39Аr inverse isochron age of 156.58±0.60Ma constrains a Late Jurassic upper greenschist-facies tectono-metamorphic event, whereas a white mica plateau age of 39.66±0.47Ma provides evidence for Middle Eocene cooling and exhumation of the Pelevun extensional allochthon in the hanging wall of the detachment. We relate the Kulidzhik nappe to Late Jurassic crustal deformation during arc-continental margin collision that involved NNE-directed nappe staking and metamorphism of continental margin basement and island arc units. The nappe shares a tectono-metamorphic history with the nappes of the adjacent Strandzha Massif, implying a region-wide early Alpine orogenic system. Our results reveal a record of early Alpine thrust tectonics and show the significance of crustal accretion-related assembly for the tectonic evolution of the Rhodope Massif. Both the Late Jurassic thrusting event and the subsequent Cretaceous thrusting event thickened the Rhodope crust creating crustal instability, which influenced Tertiary crustal extension. [Copyright &y& Elsevier]

Abstract: The work by Koglin et al. (Koglin, N., Kostopoulos, D., Reichmann, T., 2009. Geochemistry, petrogenesis and tectonic setting of the Samothraki mafic suite, NE Greece: Trace-element, isotopic and zircon age constraints. Tectonophysics 473, 53–68. doi:10.1016/j.tecto.2008.10.028), where the authors have proposed to nullify the scenario presented by Bonev and Stampfli (Bonev, N., Stampfli, G., 2008. Petrology, geochemistry and geodynamic implications of Jurassic island arc magmatism as revealed by mafic volcanic rocks in the Mesozoic low-grade sequence, eastern Rhodope, Bulgaria. Lithos 100, 210–233) is here put under discussion. The arguments for this proposal are reviewed in the light of available stratigraphic and radiometric age constraints, geochemical signature and tectonics of highly relevant Jurassic ophiolitic suites occurring immediately north of the Samothraki mafic suite. Our conclusion is that the weak arguments and the lack of knowledge on the relevant constraints from the regional geologic information make inconsistent the proposal and the model of these authors. [Copyright &y& Elsevier]

Abstract: The Kazdağ Massif exposes an extensional metamorphic dome in the Biga Peninsula of northwest Turkey, bounded on both flanks by detachments and/or shear zones. The northern flank is marked by the extensional Alakeçi shear zone (ASZ), with poorly known P–T–t path. We therefore focus on metamorphic conditions and temporal history of the ASZ to determine its tectono-metamorphic evolution. ASZ mylonites were derived from both the footwall Kazdağ Massif core metamorphic rocks and the hanging wall Çetmi mélange lithologies. The mylonitic fabrics in the ASZ depict a top-to-the NNE shearing, parallel to the NNE-plunging stretching lineation and NNW-dipping mylonitic foliation. This geometry implies normal sense movement i.e. north-side down-dip extensional displacement along this flank of the Kazdağ Massif. The northward transition from ductile to brittle–ductile shear regime through the ASZ shows that the non-coaxial deformation occurred at decreasing temperatures and degree of metamorphism. The paragenesis in equilibrium of the mylonitic gneisses and schists contains quartz+feldspar+muscovite+biotite+garnet±staurolite, with late retrogressive chlorite after biotite and garnet. Calculated thermo-barometric conditions for ASZ rocks yielded pressures between 6.9 and 5.7 kbar and temperatures between 706 and 587 °C, which constrain the peak metamorphism. The mylonitic rocks supplied isochron 39Ar/40Ar mica ages between 26.97 and 24.19 Ma, which we interpret to date the cooling of the mylonites following the P–T decrease across the ASZ. The metamorphic data support the structural record and strengthen the extensional character of the ASZ. The transition from sillimanite-bearing footwall Kazdağ Massif core gneisses in the deeper structural levels to chlorite schists towards the shallow structural levels at the top of the ASZ, is consistent with an extensional exhumation of the metamorphic pile. These data allow us to determine the peak P–T conditions and the temporal evolution in the northern flank of the Kazdağ Massif, where Late Oligocene extensional exhumation was assisted by NNE-directed ductile–brittle ASZ, which had operated from amphibolite to greenschist facies. The ASZ, together with similar time-constrained ductile–brittle activity of SW-directed detachment along the southern flank of the massif, collectively indicates a bivergent mode of extension in the western Kazdağ Massif. The latter is likely influenced by magmatic activity spatially and temporally related to these extensional zones. At the regional scale, the bivergent tectono-metamorphic pattern of the Kazdağ Massif is similar to those observed on other places of the north-central Aegean domain. [Copyright &y& Elsevier]