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.

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 yielded a maximum depositional age of 523 Ma, with a prominent Neoproterozoic-Early 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 maximum age of deposition is defined at 263 Ma for a breccia-conglomerate of the Smolyanovtsi Formation from the sedimentary cover that recycled material from the Sredogriv metamorphics and Carboniferous-Permian magmatic rocks. Proximity to Cadomian island arc sources and provenance from the northern periphery of Gondwana outline the depositional setting of the Sredogriv sedimentary succession. 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. The results obtained allow us to identify the timing of the Cadomian sedimentary history and the Variscan magmatic and tectono-metamorphic evolution in part of the Western Balkan Zone.

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.

This study investigates the Terrigenous-carbonate Sakar-type Triassic (TCSTT) and Sakar-type Triassic (STT) metasedimentary successions in the Sakar Unit, SE Bulgaria. Both share lithological similarities (alternation of carbonate-silicate schists, mica schists, marbles, and impure marbles) and are affected by post-Triassic metamorphism, but exhibit differences in metamorphic grade and provenance. The STT displays a higher metamorphic grade (low amphibolite facies) compared to the TCSTT (low greenschist facies). Petrographic observations and geochemical analyses indicate protoliths composed of arkosic sandstones, shales, and limestones, derived from a quartz-dominated source with minor contributions from intermediate magmatic sources. U-Pb geochronology of detrital zircons reveals a dominant Carboniferous age, supplemented by early Ordovician ages, consistent with the presence of Carboniferous-Permian magmatic rocks in the basement. The presence of Early Paleozoic and Cambrian-Neoproterozoic zircons in the detrital zircon populations suggests that older rocks in the basement of the Sakar Unit and Srednogorie zone are also sources of the sedimentary material. Based on immobile trace elements contents and discrimination diagrams, the siliciclastic component comes from rocks formed in a continental arc tectonic setting. REE patterns exhibit a negative Eu anomaly, inherited from the granitic source rocks.

The geochemistry of Triassic metacarbonate rocks from the Sakar unit, Sakar-Strandzha zone recorded condition on deposition environments and primary (protoliths) composition. The metacarbonate yielded trace element distribution that conform seawater condition on shallow shelves under oxic conditions and coincide interpretation of Chatalov (1990). The REE pattern determines low to moderate contamination of terrigenous material. The significant variation of Sr can be efficient for distinguish the metacarbonates in SE Bulgaria.

This study investigates the metasedimentary sequences of terrigenous–carbonate Sakar-type Triassic (TCSTT) and Sakar-type Triassic (STT) in the Sakar Unit, southeastern Bulgaria. Both share lithological similarities (alternation of carbonate–silicate schists, mica schists, marbles, and impure marbles) and are affected by post-Triassic metamorphism, but with differences in metamorphic grade and partly in the variation of potential sources of the sedimentary material. STT shows a higher metamorphic grade (lower amphibolite facies) when compared to TCSTT (lower greenschist facies). Petrographic observations and geochemical analyses indicate protoliths composed of arkosic sandstones, shales, and limestones derived from a quartz-dominated source with minor contributions from intermediate magmatic sources. The U-Pb geochronology of the detrital zircons reveals a dominant Carboniferous age complemented by an Early Ordovician age, which is consistent with the presence of Carboniferous–Permian igneous rocks in the basement. The presence of Early Paleozoic and Cambrian–Neoproterozoic zircons in the detrital zircon populations suggests that older rocks of the basement of the Sakar Unit and the Srednogorie Zone are also sources of the sedimentary material. Based on the immobile trace element content and discrimination diagrams, the siliciclastic component originates from rocks formed in a continental-arc setting. REE patterns indicate a negative Eu anomaly inherited from granitic-source rocks.