Cadomian and post-cadomian tectonics west of the Rhodope Massif – The Frolosh greenstone belt and the Ograzhdenian metamorphic supercomplex

The Frolosh Greenstone Belt (FGB) is traced at a distance of more than 200 km in the territories of Bulgaria, Macedonia and Serbia. It consists of various greenschist-facies rocks (actinolite schists, phyllites, calcareous schists, impure marbles, metasandstones, metadiabases, massive green rocks, etc.) of the Frolosh metamorphic complex with bodies of metabasites (including lherzolites), and inliers (retrogressed mica gneisses and migmatites) from the Ograzhdenian supercomplex. The complex is in­truded by bodies of gabbro (occasionally with ultramafic cumulates), diorites to granites (Struma diorite formation). U-Pb studies on zircons yielded Cadomian ages within the time span between c. 574 and 517 Ma. The Frolosh complex covers the ultrametamorphic (migmatized gneisses and amphibolites; tourma­line-biotite schists; quartzo-feldspathic gneisses; lensoid bodies of metaperidotites to norites) of the Ograzhdenian supercomplex. The Ograzhdenian rocks are intersected by diatectic metagranites over­printed by amphibolite-facies metamorphism. Dominant U-Pb ages vary between 470 and 430 Ma. The contact between the Frolosh complex and the Ograzhdenian supercomplex has been subject of long dis­cussion and controversial interpretations. Now we emphasize on the multistage developments of both complexes as demonstrated both by field evidence and isotopic dating. The Ograzhdenian supercomplex has been subject of Precambrian tectonometamorphism witnessed by Rb-Sr whole-rock isochron data and relict U-Pb zircon data. Ordovician to Silurian anatectites (metatectic migmatization, diatexis) are in­truded by Permo-Triassic granites. The contact between the Ograzhdenian supercomplex and the covering Frolosh complex is regarded as a thick complex zone of multistage tectonometamorphic development rather than a “razor-blade” surface of one-stage origin. As a boundary between suprastructure and infra­structure, it played an important role throughout the Phanerozoic, and acted as a screen with a steep ther­mal gradient during the Ordovician-Silurian anatexis and metamorphism in the Ograzhdenian supercom­plex. For to verify this hypothesis, new detailed structural and isotopic studies are needed

Geologic and Isotopic Models for the Carpathian Crystalline Evolution

The majority of Carpathian metamorphics protoliths have TDM model Sm/Nd ages between 1.6 and 2.0 Ga. This suggests an important episode of continental crust formation after the 2.0 Ga. The Biharia lithogroup (Apuseni Mountains) and the Tulghes lithogroup (East Carpathians) furnished Zircon U/Pb ages from metagranitoids and acid metavolcanics, respective, around 500 Ma; this is a sign of existence of some Lower Proterozoic protoliths among Carpathian metamorphics. The bimodal intrusions which are piercing the volcano-sedimentary sequence of Paiuseni lithogroup in Highiş Massif (Apuseni Mountains) have given Permian ages on Zircon U/Pb data. The Paiuseni lithogroup probably represents the fill of a rift basin of the same age. The Arieseni, Muntele Mare and Vinta granitoid intrusions from Apuseni Mountains, with U/Pb ages between Lower Devonian and Permian, indicates some contractional and extensional processes, in connection with Variscan Orogeny

Geologic and Isotopic Models for the Carpathian Crystalline Evolution

The majority of Carpathian metamorphics protoliths have TDM model Sm/Nd ages between 1.6 and 2.0 Ga. This suggests an important episode of continental crust formation after the 2.0 Ga. The Biharia lithogroup (Apuseni Mountains) and the Tulghes lithogroup (East Carpathians) furnished Zircon U/Pb ages from metagranitoids and acid metavolcanics, respective, around 500 Ma; this is a sign of existence of some Lower Proterozoic protoliths among Carpathian metamorphics. The bimodal intrusions which are piercing the volcano-sedimentary sequence of Paiuseni lithogroup in Highiş Massif (Apuseni Mountains) have given Permian ages on Zircon U/Pb data. The Paiuseni lithogroup probably represents the fill of a rift basin of the same age. The Arieseni, Muntele Mare and Vinta granitoid intrusions from Apuseni Mountains, with U/Pb ages between Lower Devonian and Permian, indicates some contractional and extensional processes, in connection with Variscan Orogeny