Late orogenic magmatism and sedimentation within Late Carboniferous to Early Permian basins in the Balkan terrane (Bulgaria): geodynamic implications

Abstract

The orogenic Balkanid belt, which developed between the Moesian Plate and the Moravian-RhodopiThracian Massifs, was affected by the Late Carboniferous and Early Permian opening of W-E oriented graben structures. The progressive tectonic rejuvenation of the basins is demonstrated by the deposition of repeated regional sedimentary cycles, associated with volcanism that was mostly localised along the tectonic boundaries, in an intramontane setting.The Late Carboniferous volcanism is represented by rhyodacitic explosive products and hyaloclastites, and by andesitic flows. During the Early Permian, subvolcanic rhyodacitic and rhyolitic bodies and the explosive products prevailed in the western sectors, whereas rhyolitic ignimbrites occur to the east.The tectonically active basins are interpreted due to late orogenic collapse, and the alternation of extensional tectonics and minor compressional phases is consistent with the regional transtensional regime, active along the Variscan suture of Pangaea. The volcanic activity associated with the evolution of the basins matches the petrogenetic features and the evolution from early daciticandesitic to late rhyolitic activity in the Southern European segment of the Variscan system.These Late Carboniferous-Early Permian sedimentary and tectono-magmatic events in Bulgaria are characterized, and compared with the homologous Permo-Carboniferous sequences along some western European segments of the Variscan belt.

The Atlas-East Variscan -Elbe shear system and its role in the formation of the pull-apart Late Palaeozoic basins

“…To account for the stratigraphic and tectonic constraints, the early interaction between subcrustal and crustal anatectic magmas, followed by assimilation and fractional crystallisation, has been proposed (Cortesogno et al 1998a;Buzzi et al 2007. Another important aspect is that the calc-alkaline magmatism changed into alkaline-type in the Upper Permian, although at the Mid-Permian the overlap of the two suites was locally evidenced and related with an important variation in the geodynamic framework (e.g., Deroin and Bonin 2003;Cortesogno et al 2004a;Cocherie et al 2005).…”

“…This structure was also active during the collapse of the Balkan orogen and formed a series of diachronic, mostly E-W or WNW-ESE-striking, Late Carboniferous-Early Permian basins with calc-alkaline volcanic rocks and subvolcanic bodies (e.g., Svoge, Sofia-Stara Planina, Godech and Buchino-Petrohan Pass Basins in Cortesogno et al 2004a). The Upper Permian continental red beds and overlying Triassic Buntsandstein sediments followed after a Mid-Late Permian stratigraphic gap.…”

Characterisation of igneous terranes by zircon dating: implications for UHP occurrences and suture identification in the Central Rhodope, northern Greece

“…Schermaier et al 1997;Finger and Steyrer 1990;Okay et al 2001;Carrigan et al 2003;Cortesogno et al 2004). Interpretations diverge between post-orogenic collapse to subduction-related magmatism.…”

Petrogenesis of post – orogenic Lower Permian andesites in southern Europe: insights into the collapse of the Variscan range

“…In analogy with other Variscan segments [40][41][42], the origin for intermediate-acid calc-alkaline volcanism in a transtensional -transpressive regime has been associated with partial melting in the lower continental crust previously thickened by the stacking of crustal nappes [23]. Mafic tholeiitic intrusions, dated to 305 -304 Ma in Corsica (U/ Pb, dissolution; [36]), with coeval to later emplacement than the main Sardo-Corsican batholith were ascribed to other sources than acid magmas [43].…”

“…% of quartz, and 10 vol. % of garnet (Alm 56-60 Py [34][35][36][37][38][39][40][41][42] ). Mixing and fractional crystallization (MFC) were modelled in a closed system under isobaric, isenthalpic conditions (P = 0.3 GPa).…”