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We report on the isotopic compositions of the intermediate rocks from Middle-Late Jurassic Chortiatis arc (160-173 Ma) and Kassandra-Sithonia backarc 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. [ABSTRACT FROM AUTHOR]

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 metaultramafic 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 mélange related to the subduction-accretion history. This mélange telescoped during the subduction of the Paleotethys oceanic lithosphere under the Eurasian plate margin, to which accreted as early as the Middle Triassic. The mélange 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The incomplete Evros ophiolites in NE Greece form a NE-SW-oriented discontinuous belt in the Alpine orogen of the north Aegean. Field data, petrology and geochemistry are presented here for the intrusive section and associated mafic dykes of these ophiolites. Bodies of high-level isotropic gabbro and plagiogranite in the ophiolite suite are cross-cut by NE SW-trending boninitic and tholeiitic-boninitic affinity dykes, respectively. The dykes fill tensile fractures or faults, which implies dyke emplacement in an extensional tectonic regime. The tholeiitic-transitional boninitic gabbro is REE- and HFS-depleted relative to N-MORB, indicating derivation from melting of a refractory mantle peridotite source. Associated boninitic dykes are slightly LREE-enriched, showing mineral and wholerock geochemistry similar to the gabbro. The plagiogranite is a strongly REE-enriched high-silica trondhjemite, with textures and composition typical for an oceanic crust differentiate. Plagiogranite-hosted tholeiitic and transitional boninitic dykes are variably REE-enriched. Geochemical modelling indicates origin of the plagiogranite by up to 75% fractional crystallization of basaltic magma similar to that producing the associated tholeiitic dykes. All mafic rocks have high LILE/HFSE ratios and negative Ta-Nb-Ti and Ce anomalies, typical for subduction zone-related settings. The mafic rocks show a similar trace-element character to the mafic lavas of an extrusive section in Bulgaria, suggesting they both form genetically related intrusive and extrusive suites of the Evros ophiolites. The field occurrence, the structural context, the petrology and geochemical signature of the studied magmatic assemblage provide evidence for its origin in a proto-arc (fore-arc) tectonic setting, thus tracing the early stages of the tectono-magmatic evolution of Jurassic arc-marginal basin system that has generated the supra-subduction type Evros ophiolites. Keywords: isotropic gabbro, plagiogranite, tholeiitic-oninitic dykes, Evros ophiolites, Greece.

In NW Turkey, the medium-grade Kemer micaschists of the Biga Peninsula record NE-directed extension related to ductile to brittle-ductile shearing during the Palaeogene period: a lower limit for their exhumation is given by the Late Maastrichtian age of the HP-LT metamorphism of a similar nearby area(Camlica micaschists); an upper limit is given by the Early Eocene intrusion age of the post-kinematic Karabiga granitoid, dated as 52.7 [+ or -] 1.9 Ma using the U-Pb LA-ICP MS method on xenotime. Correlations with the northeasterly Rhodope region and integration into the geodynamic regional frame indicate that the Kemer micaschists experienced an extensional deformation connected to a collisional context in latest Cretaceous-early Tertiary times. The Kemer micaschists therefore represent a new area (the first in Turkey), which suffered synorogenic extension in the north Aegean domain at the very beginning of Tertiary times. Keywords: ductile shear, metamorphism, extension, north Aegean, U-Pb (LA-ICP-MS) geochronology, xenotime.

Late Palaeozoic granitoids, meta-granitoids and meta-volcanic rocks predominate in the metamorphic basement of the northern and western parts of the Sakar-Strandzha Zone (SASTZ) in southeast Bulgaria, together with the subsidiary Triassic meta-granitoids and meta-volcanic rocks. Generally, igneous minerals and textures are preserved, except in the meta-granitoids and meta-volcanic rocks that experienced a low- to high-grade metamorphic overprint. The volcanic rocks have a peraluminous and high-K calc-alkaline composition, and the granitoids range between I- to S-type compositions, typical of volcanic arcs and syn-collisional settings. LILE and LREE-enrichment and Nb-Ta anomalies characterize the intrusive and extrusive rock suites. U-Pb zircon geochronology has yielded crystallization ages between 245 and 237 Ma for the majority of the studied igneous rocks, and between 297 and 295 Ma for a small group of igneous rocks. Early Permian and Middle Triassic igneous suites of the northern and western SASTZ have similar compositions and a similar tectonic setting when compared to Late Carboniferous-Early Permian intrusive and extrusive suites of the adjacent Sakar unit of the SASTZ, confirming a common regional late Palaeozoic-early Mesozoic tectono-magmatic event. As the Late Carboniferous-Permian to Middle Triassic magmatic arc components extend across the SASTZ, they trace the time-correspondent active continental margin along the Eurasian plate during subduction of the Paleotethys oceanic lithosphere. The late Palaeozoic Eurasian active continental margin magmatic arc evolution of the SASTZ can be linked with the Serbo-Macedonian-Rhodope zones to the southwest, where coeval meta-granitoids document the same geodynamic context. By contrast, the Triassic igneous suite of the SASTZ is unrelated to the Serbo-Macedonian-Rhodope zones, where Triassic meta-ophiolite and meta-granitoids record Neotethys rifting. [ABSTRACT FROM AUTHOR]

We investigated the Sakar unit metamorphic rocks of the Sakar–Strandzha zone in Bulgaria, using 40Ar/39Ar dating of amphibole from the polymetamorphic basement and white mica in the overlying upper Permian metasedimentary rocks of the Paleokastro Formation. The amphibole and white mica revealed plateau ages of 140.50 ± 1.75 Ma and 126.19 ± 1.29 Ma, respectively, indicating an Early Cretaceous cooling history of the regional amphibolite-facies metamorphism to greenschist-facies conditions. Similar metamorphic grades and cooling histories of the Sakar unit share evidence with the nearby Rhodope Massif for the northern Aegean region-wide early Alpine tectonometamorphic event. [ABSTRACT FROM AUTHOR]