Discovery of metamorphosed Devonian volcanic rocks in the Prypyat-Dnieper-Donets Rift

The Late Devonian Prypyat-Dnieper-Donets Rift is a significant tectonic structure on the East European platform. Devonian salt domes are extensively developed within the Rift and create a system of associated traps, which often accommodate oil and gas fields. Associated with these salt domes hydrothermal deposits and occurrences of mercury and base metals are also found in the south-eastern part of the Rift, near the Donets inversion-folded structure. Diapiric breccias (cap rocks) frequently contain fragments of various rocks, which remain poorly studied. The authors examined a fragment of metamorphosed mafic rock collected from a cap rock of the Bantysheve salt dome, situated in north-western Donbas, at the transition zone to the Dnieper Basin. The rock was identified as hornblende schist, metamorphosed at a relatively high temperature of 775–730℃ and low pressure of 1.4–1.0 kBar, corresponding to the hornfels facies of metamorphism. The U-Pb age of the metamorphic crystallisation of titanite from the schist was determined at 370 ± 17 Ma. This age matches the magmatism in the Prypyat-Dnieper- Donets Rift. Data obtained suggest that the most probable protolith for the studied schist is the Late Devonian picritic basalt or picritic dolerite, which is associated with the development of the Rift.