Featured Application Because of the nearby baryte deposit located at the village of Eliseyna, the presented here geochemical and geochronological results have potential applications for targeting and exploration of additional base metals and other types of mineralization in the area studied.Abstract The Rzhanski granitoid pluton and Ignatitsa diorite porphyry bodies are considered Late Paleozoic in age, belonging to the Western Balkan Zone (WBZ) in Northwestern Bulgaria. Here, we provide U-Pb zircon geochronology of these magmatic bodies, together with their geochemistry complemented by the geochemistry of the overlying volcanic rocks. Geochemical data indicate that the intermediate to acid magmatic rocks are mostly peraluminous, calc-alkaline diorite/andesite to granite, that have an origin in a continental magmatic arc tectonic environment. All plutonic, subvolcanic and volcanic rocks exhibit uniform LILE- and LREE-enriched characteristics of an arc-related igneous suite. Zircons in the Ignatitsa diorite porphyry yield a magmatic crystallization age of 315 Ma, while the zircons in the Rzhanski aplitic metagranite pluton crystallize at 294 Ma. The record of the Variscan intrusive magmatism encompasses a region-wide, well-defined time interval 332-294 Ma in the WBZ, which coincides with those of the Central Balkan Zone and the adjacent Sredna Gora Zone. The age of the Variscan greenschist facies metamorphism using the metagranite and host greenschists relationships is limited between 294 Ma and the unpublished depositional age of 268 Ma for the overlying clastic formation in the studied part of the WBZ.

The Circum-Rhodope Belt is a major tectonic unit that surrounds both the Rhodope and the Serbo-Macedonian zones of the Alpine orogen in the northern Aegean region. The arc-related, supra-subduction zone Evros ophiolite represents the most important crustal element in the eastern part of the Circum-Rhodope Belt. A new U-Pb LA-ICP-MS zircon magmatic crystallization age of 174.6 ± 1.8 Ma obtained for the Agriani gabbro, together with the reviewed crystallization ages of other magmatic bodies reveal that the magmatic history of the Evros ophiolite spans 176 Ma to 169 Ma time interval. Reviewed ages of the medium to lowtemperature cooling history from 550 °C (40Ar/39Ar amphibole) down to 120 °C (fission-track apatite) show that it immediately followed the magmatic crystallization starting around 174 Ma and continued up to 140 Ma for the Evros ophiolite.

The Circum-Rhodope Belt fringes the Rhodope and Serbo-Macedonian zones in the Alpine orogen of the northern Aegean region. This belt contains Late Paleozoic and Mesozoic metasedimentary successions that record depositional history along the continental margin of Eurasia. Critical successions of the eastern Circum-Rhodope Belt, such as those exposed in the Fanari and Petrota areas, are studied here, integrating their structure, whole-rock geochemistry and U-Pb LA-ICP-MS zircon geochronological context. The Fanari turbiditic succession contains quartz arenite, while the Petrota succession consists of Fe-rich shale and sandstone, and both successions are distinguished by REE-depleted and REE-enriched characteristics and acidic and intermediate arc-related sedimentary sources, respectively. Detrital U-Pb zircon geochronology reveals a Late Carboniferous–Early Permian maximum depositional age of 301.2 ± 8.4 Ma for Fanari quartz arenite and a Late Jurassic maximum depositional age of 147.0 ± 2.0 Ma for Petrota Fe-shale. The results are interpreted in terms of Late Paleozoic continental slope deposition of the Fanari succession along the Eurasian margin and trench-arc sedimentation of the Petrota succession linked to the development of a Jurassic island arc system pertinent to the eastern Circum-Rhodope Belt. These tectonic settings and depositional environments can be used to restore an overall picture of a Late Paleozoic to Mid-Mesozoic sedimentation at the Rhodope–Serbo-Macedonian continental margin of Eurasia. Structures that developed in greenschist facies conditions and N-directed kinematics of the studied successions unequivocally relate them to other units of the eastern Circum-Rhodope Belt and its Late Jurassic tectonic evolution.

A gabbroic dyke of LREE-enriched and HREE-depleted geochemical characteristics that occurs along the Sandanska Bistritsa River Valley in the western Rhodope Massif of Bulgaria has been dated by U-Pb zircon LA-ICP-MS geochronology. In addition, the geochemical pattern with high LILE/HFSE ratio and a negative NbTa anomaly point to subduction-related petrogenesis of the mafic rock. Four zircons yielded a concordia age of 77.7 +/- 0.95 Ma, which is interpreted to date the magmatic crystallization of the protolith. This age further document, extend and confirm the presence of a Late Cretaceous basic magmatism in the western Rhodope Massif related to the Late Cretaceous Vardar Ocean northward subduction under the Eurasian plate margin.

The Sredogriv low-grade metamorphic rocks belongs to the Montana unit of the Western Balkan Zone in northwestern Bulgaria. The low-grade rocks mainly consist of metamorphosed greenschist facies clastic-marly-tuffaceous precursors and minor basic to acidic, presumably olistostromic magmatic rock bodies. Here, we present whole-rock geochemistry of metabasic dyke-like bodies in the Sredogriv metamorphic rocks. Field observations revealed that the dyke-like bodies are intruded into the Sredogriv sedimentary succession and do not represent olistostromic bodies, which is demonstrated by consistent elongation of the dykes that strike ESE-WNW to E-W. The dyke-like bodies demonstrate a weak metamorphic overprint. Major elements were analyzed by X-ray fluorescence facility at the Sofia University St. Kliment Ohridski, and the trace elements and rare-earth elements were determined by laser-ablation inductively coupled mass-spectrometry at the Geological Institute of the Bulgarian Academy of Sciences. Our recent study on the detrital zircons in the Sredogriv metaconglomerate yielded a maximum depositional age of 523 Ma, additionally maximum age of deposition is defined at 263 Ma for a conglomerate of the Smolyanovtsi Formation from the first unconformable sedimentary cover. Mostly continental detrital material from magmatic source built the sedimentary protolith of the Sredogriv metamorphic rocks, which are recycled in the clastic cover rocks. However, at present, the bulk chemical composition of the metabasic dyke-like bodies remains poorly understood. Our study shows that the dyke-like bodies represent enriched ocean-floor magmatic products, which are more likely crystallized in a back-arc tectonic setting.

The Sredogriv greenschist facies rocks belong to the Western Balkan Zone in northwestern Bulgaria. The low-grade rocks consist of clastic-tuffaceous precursors and presumably olistostromic magmatic bodies. We present U-Pb LA-ICP-MS zircon age constraints for the Sredogriv metaconglomerate, intruding metaalbitophyre and a breccia-conglomerate of the sedimentary cover. Detrital zircons in the Sredogriv metaconglomerate yield a maximum depositional age of 523 Ma, with a prominent NeoproterozoicEarly Cambrian detrital zircon age clusters derived from igneous sources. The metaalbitophyre crystallized at 308 Ma and contains the same age clusters of inherited zircons. A 263 Ma maximum age of deposition is defined for a breccia-conglomerate of the Smolyanovtsi Formation from the sedimentary cover that recycled material from the Sredogriv metamorphics and Carboniferous–Permian magmatic rocks. The depositional setting of the Sredogriv sedimentary succession is characterized by proximity to Cadomian island arc sources and provenance from the northern periphery of Gondwana. The timing of the Variscan greenschist facies metamorphism of the Sredogriv metamorphics is bracketed between 308 Ma and the depositional age of 272 Ma of another adjacent clastic formation. These results constrain the timing of the Cadomian sedimentary history and the Variscan magmatic and tectono-metamorphic evolution in this part of the Western Balkan Zone.

U-Pb detrital zircon geochronology provides middle Permian-earliest Triassic (272-246 Ma) maximum depositional ages for the Zelenigrad and Vranska Formations of the Belogradchik Unit. These ages match the depositional span (305-249 Ma) of the sedimentary successions in the St. Iliya Heights of the Sakar-Strandzha Zone, in addition to their structural, textural and compositional similarities. The older zircon populations reveal erosion of Neoproterozoic basement, a feature characteristic for Gondwana-derived blocks. The gap between Cambrian and Carboniferous ages of the detrital zircon record of the Belogradchik Unit is ascribed to the Avalonia-type nature of the feeding provenance.

The eastern Rhodope Massif of Bulgaria concentrates meta-ophiolites of poorly known igneous ages, which offers the opportunity to examine the Tethyan oceanic floor and Eurasian plate margin interactions. MORB-type meta-mafic gabbro-basalt cross-cutting dykes and concordant layers to three meta- ultramafic bodies are enclosed in schist envelope. U-Pb zircon geochronology revealed crystallization ages of the dykes at 248 Ma and 245 Ma in one of the bodies, at 298 Ma for a layer at the contact of the second body and another layer at 160 Ma for the third body. Different Early Permian and Early Triassic crystallization ages of the bodies and another spatially close Late Devonian body, all witness for mantle lithosphere components that fall in the temporal range of the Paleotethys oceanic floor development and pre-Jurassic closure by subduction. As the different in age meta-ultramafic bodies are hosted by schists, this occurrence calls for a melange related to the subduction-accretion history. This melange telescoped during the subduction of the Paleotethys oceanic litho - sphere under the Eurasian plate margin, to which accreted as early as the Middle Triassic. The melange might well represent an element of the Paleotethys suture. The Late Jurassic crystallization age of a meta-gabbro at the contact of the third meta-ultramafic body in turn calls for the presence of Neotethys Ocean mantle lithosphere remnant, and is used to test the hypothesis for hidden mantle section of the Jurassic Evros ophiolite of the eastern Rhodope Massif. The answer is positive, and supported by the crystallization ages of the Evros ophiolite, the age of detrital zircons in the related Jurassic sedimentary successions, together with the Late Jurassic tectonic emplacement and the age of inherited Triassic-Jurassic zircons in the meta-gabbro. Thus, a Paleotethys and Neotethys oceanic floor mantle lithosphere interacted with the Eurasian plate margin and their remnants have been revealed in the eastern Rhodope Massif

The Circum-Rhodope Belt is a major tectonic unit that frames both the Rhodope and the Serbo-Macedonian zones of the Alpine orogen in the northern Aegean region. In the eastern part of the Circum-Rhodope Belt, the supra-subduction zone Evros ophiolite is an important crustal component that spans 176 Ma to 169 Ma magmatic activity, which cooled down to 550 °C around 164 Ma according to published radiometric dating. This incomplete ophiolite contains in its upper crustal section gabbroic complexes, to- gether with massive and pillow lavas and dykes. In this contribution, in one of these gabbroic complexes, namely the Petrota gabbroic complex, a cross-cutting basalt dyke was dated to refine the timing of the gabbro crystallization and the temporal spread of the magmatic evolution for the whole complex. The basalt dyke yielded magmatic crystallization age at 164.5±0.93 Ma as derived from U-Pb zircon geochronology. This new crystallization age confirms the previous age for the Petrota gabbro crystallization at 169±2 Ma, but extends the span of the magmatic evolution within 7–8 Myr-lasting time interval (including the analytical errors) for the complex. The latter time interval is comparable in span to the magmatic evolution of another Evros ophi- olite gabbro occurrence at the town of Didymotycho in northeastern Greece.

The petrological and geochemical data for the Sredogriv metamorphics determine protoliths of metaconglomerates and metasandstones with varying clay content and a significant amount of acidic igneous fragments. The geochemistry, geochronology, and mineralogy of these lithic clasts coincide with the exposed in the close vicinity allochthonous Neoproterozoic-Cambrian orthometamorphic bodies (Protopopintsi metagranite). The tectonic discrimination diagram defines a continental island arc tectonic setting simultaneously with the accretion of peri-Gondwanan fragments to the Balkan Ensemble followed by the development of the Early Silurian-Devonian epicontinental basin.

The eastern Circum-Rhodope belt (CRB) is a major unit that surrounds both the Serbo-Macedonian and the Rhodope zones in the Alpine orogen of the northern Aegean region. This belt contains Triassic-Jurassic metasedimentary successions and Middle Jurassic (176-165 Ma) supra-subduction zone Evros ophiolite. The latter has experienced ocean-floor hydrothermal metamorphism or very-low to low-grade metamorphism. We report on mineral compositions of rock-forming minerals in schist and mafic rocks from the eastern CRB. Our goal is to use the mineral compositions to assess the metamorphic conditions suffered by the rocks. The studied minerals include amphibole, garnet and mica. The electron probe microanalyzer was used to obtain the mineral chemistry recalculated into the mineral structural formula. The amphiboles in the mafic rocks have the compositions from magnesio-hornblende to edenite hornblende, which includes also actinolite-hornblende to actinolite and ferro-tschermakite in the greenschists. In the mica schist, the amphibole is magnesian-hastingsite, which is associated with almandine garnet, muscovite and biotite. The mineral assemblage studied, and its composition, reflects unequivocally greenschist facies metamorphic conditions experienced by the rocks. These conditions are further confirmed by the abundant chlorite and epidote observed in the metasedimentary and metamafic rocks. Thus, our study extends quantitively the metamorphic grade and conditions pertinent to the eastern CRB rocks.

The eastern Rhodope Massif of Bulgaria concentrates meta-ophiolites of poorly known igneous ages, which offers the opportunity to examine the Tethyan oceanic floor and Eurasian plate margin interactions. MORB-type meta-mafic gabbro-basalt cross-cutting dykes and concordant layers to three meta- ultramafic bodies are enclosed in schist envelope. U-Pb zircon geochronology revealed crystallization ages of the dykes at 248 Ma and 245 Ma in one of the bodies, at 298 Ma for a layer at the contact of the second body and another layer at 160 Ma for the third body. Different Early Permian and Early Triassic crystallization ages of the bodies and another spatially close Late Devonian body, all witness for mantle lithosphere components that fall in the temporal range of the Paleotethys oceanic floor development and pre-Jurassic closure by subduction. As the different in age meta-ultramafic bodies are hosted by schists, this occurrence calls for a melange related to the subduction-accretion history. This melange telescoped during the subduction of the Paleotethys oceanic lithosphere under the Eurasian plate margin, to which accreted as early as the Middle Triassic. The melange might well represent an element of the Paleotethys suture. The Late Jurassic crystallization age of a meta-gabbro at the contact of the third meta-ultramafic body in turn calls for the presence of Neotethys Ocean mantle lithosphere remnant, and is used to test the hypothesis for hidden mantle section of the Jurassic Evros ophiolite of the eastern Rhodope Massif. The answer is positive, and supported by the crystallization ages of the Evros ophiolite, the age of detrital zircons in the related Jurassic sedimentary successions, together with the Late Jurassic tectonic emplacement and the age of inherited Triassic-Jurassic zircons in the meta-gabbro. Thus, a Paleotethys and Neotethys oceanic floor mantle lithosphere interacted with the Eurasian plate margin and their remnants have been revealed in the eastern Rhodope Massif.

The Sredogriv low-grade metamorphic rocks belongs to the Montana Unit of the Western Balkan Zone in Northwestern Bulgaria. The low-grade rocks predominantly consist of metamorphosed in greenschist facies clastic and clastic-marly precursors and minor basic to acidic extrusive and intrusive presumably olistostromic rock bodies. Here, we present detrital zircon age constraint for clastic rock of the Sredogriv metamorphics of unknown till now depositional timing, together with an age of the clastic rock unconformably overlying these metamorphics. Detrital zircons in the Sredogriv metaconglomerate yielded a maximum depositional age of 523 Ma, additionally maximum age of deposition is defined at 263 Ma for a conglomerate of the Smolyanovtsi Formation from the first unconformable sedimentary cover. Mostly continental detrital material from magmatic source built the protolith of the Sredogriv metamorphics, which are recycled in the clastic cover rocks. Hence, the greenschist facies metamorphism of the Sredogriv metamorphics took place between 523 Ma and 263 Ma.

We report on the isotopic compositions of the intermediate rocks from Middle-Late Jurassic Chortiatis arc (160-173 Ma) and Kassandra-Sithonia back- arc ophiolites of Late Jurassic age (150-160 Ma), both exposed in the eastern Vardar Zone-western Circum-Rhodope belt transect of northeastern Greece. The Kassandra-Sithonia ophiolites consist of dunites, gabbros, basalts, and rhyolites, whose Nd-Sr-Pb isotopes are compatible with a dominant mantle-derived MORB component mixed with a detectable amount of crustal material and/or sediment entrained in their mantle source in a subduction zone. Their isotopic features are consistent with the origin of the studied rocks within the coupled Chortiatis arc/Kassandra-Sithonia back-arc system outboard the Eurasian continental margin (Serbo-Macedonian Massif). In both elements of the above-mentioned system, the documented Nd-Sr-Pb isotopes are comparable to those from the Middle Jurassic arc-related Evros ophiolites (164-176 Ma) in the eastern Circum-Rhodope belt of Bulgaria and Greece. This implies the presence of regionwide Vardarian Jurassic arc/back-arc systems connected with both western and the eastern Circum-Rhodope belts. A rhyolite dated at 149 Ma that intrudes the Sithonia ophiolite displays distinct Nd-Sr-Pb isotopic features suggesting an origin connected to a Late Jurassic-Early Cretaceous north-directed flat subduction zone within the Kassandra-Sithonia back-arc region, beneath the Eurasian continental margin. This subduction zone explains the granitoid magmatism (138-155 Ma) recorded along that margin to the north.

We focused on the eastern Circum-Rhodope belt (CRB) low-grade sequence along the Mareshnitsa River Valley in Bulgaria. U-Pb detrital zircon geochronology revealed latest Late Jurassic maximum depositional age of a metasandstone. A major Jurassic zircon cluster in the metasandstone is consistent with a provenance from the CRB-related Evros arc, whereas the minor cluster of Triassic zircons come from the high-grade basement. The results indicate mostly latest Late Jurasic sedimentation proximal to the Evros arc (CRB) and minor detrital input from the continental margin of Eurasia (Rhodope). The results further support the presence of Mesozoic (Jurassic) oceanic lithosphere mantle remnants within the metamorphic basement of the eastern Rhodope Massif.

AbstractWe report on the isotopic compositions of the Jurassic supra-subduction zone Evros ophiolite mafic rocks exposed in the eastern Circum-Rhodope Belt of northeastern Greece. These mafic units consist of low-Ti gabbroic and basaltic rocks, whose Nd–Sr–Pb isotopes are compatible with dominant mantle-derived MORB component mixed with a detectable amount of crustal material and/or sediment invoved in their melt source in the subduction zone. These isotopic features are consistent with an intra-oceanic arc origin of the mafic ophiolite rocks, and the Evros ophiolite Nd and Pb isotopes are comparable to those of the counterpart mafic rocks from the Mandritsa unit in Bulgaria.

Metamorphosed mafic ophiolitic rocks in the metamorphic section of the eastern Rhodope Massif in Bulgaria and Greece are important for understanding the oceanic lithosphere fragments, which have been involved in Alpine tectonic-metamorphic processes. Petrography and mineral compositions of the meta-mafic rocks (mostly gabbro-basalt to minor diorite-andesite) point to main amphibolite-facies overprint, which strongly obliterated the primary textures, and the original igneous grain-sizes are partly preserved only of the plagioclase. The meta-mafic rocks are classified as low-K and low-to high-Ti tholeiitic affinity igneous protoliths of basaltic to andesitic compositions, in which high-Ti and low-Ti groups are identified on the basis of Ti concentrations. They also differ with respect to trace element and REE characteristics. A complex chemistry of high-Ti group indicates an origin primarily from MORB mantle source, subsequently modified by subduction-zone derived LILE-and REE-enriched melts and contribution of HFSE-enriched component that produce the oceanic island tholeiites. The low-Ti group displays IAT affinity, with clearly defined subduction-related component demonstrated by LILE enrichment, HFSE and HREE depletion relative to N-MORB and negative Nb and Ti anomalies, all indicative for an island arc petrogenesis. A single dunite sample studied also displays geochemical characteristics of the low-Ti group meta-mafic rocks. Geochemical diversity of the meta-basic rocks with MORB, transitional MORB/IAT and IAT affinities hints their supra-subduction zone (SSZ) origin in an island arc/ back-arc system, with identifiable arc-related and rifting/sea-floor spreading magmatic products represented by the low-Ti and high-Ti groups, respectively. At present, the available Middle-Late Paleozoic/Early Triassic radiometric ages of the meta-mafic rocks protoliths predominate over the Early Paleozoic ages, which suggests that the development of the inferred arc/back-arc system relates mostly to the ocean-floor magmatic evolution of the Paleotethyan realm.

We focused on the eastern Circum-Rhodope belt (CRB) low-grade sedimentary sequences in Bulgaria, in which clastic rocks are presented. U-Pb detrital zircon geochronology indicates the latest Late Jurassic maximum depositional ages of two samples from two distinct locations. Prominent Jurassic zircon cluster in the first sample is consistent with provenance from CRB-related Evros arc, whereas the Triassic zircons come from the high-grade basement. In the second sample, the main Permian and Carboniferous zircon populations, minor Triassic clusters and two Jurassic zircons reflect a provenance mainly from the high-grade basement and to a lesser extent from the Evros arc. These new results indicate latest Late Jurasic sedimentation proximal to the Evros arc (CRB) and along the continental margin of Eurasia (Rhodope), respectively for the studied first and second sample. The results further support the presence of Mesozoic (Jurassic) oceanic lithosphere mantle remnants within the metamorphic basement of the eastern Rhodope Massif. The results obtained shed new light and could open a discussion on the Late Jurassic clastic sedimentation along the transect from the continental margin of Eurasia (Rhodope) towards the Evros arc system of the eastern CRB.

The Circum-Rhodope belt is a major tectonic unit in the Alpine orogen of northern Aegean region, which consists of metasedimentary rocks and unmetamorphosed arc-related Jurassic Evros ophiolite. Here, we review the biostratigraphic and detrital zircon ages available for the distinct units of the eastern Circum-Rhodope belt in Bulgaria and Greece. Both, biostratigraphic and radiometric ages consistently reveal a Middle Triassic to latest Late Jurassic timing of the sedimentation. Most importantly, the continuous depositional record sketches sedimentary sources from the continental margin (Rhodope) and the Jurassic arc system (Evros ophiolite) as documented mostly by the detrital zircons in clastic successions.

We focused on the Sakar-Strandzha Zone (SASTZ) carbonate sequences in Bulgaria, where the Sakar, Subbalkanide and Strandzha Triassic facies types are presented. Strontium isotopic compositions of carbonate samples from the Triassic type section of the Sakar unit confirm an Early-Middle Triassic age of sedimentation consistent with biostratigraphic data, whereas the strontium isotopic compositions of other Sakar-type inferred Triassic sections suggest an Early Permian depositional age. The strontium isotopic compositions of a Strandzha-type Triassic carbonate sample are in agreement with Middle Triassic sedimentation. A few Subbalkanide-type Triassic carbonate samples from the northern and western SASTZ yielded strontium isotopic compositions indicating an Early Devonian sedimentation. The new results indicate late Paleozoic-early Mesozoic sedimentation, and require most of the Subbalkanide-type Triassic and some of the Sakar-type inferred Triassic carbonate sequences in the SASTZ to be revisited.