Variable eruptive styles in an ancient monogenetic volcanic field: examples from the Permian Levín Volcanic Field (Krkono e Piedmont Basin, Bohemian Massif)

The Permian pyroclastic deposits of the Levín Volcanic Field within the Krkono e Piedmont Basin were studied in terms of volcanology. Pyroclastic rocks are exposed in two quarries and the study was supported with the 30 m deep borehole K1 penetrating these rocks. The pyroclastic rocks are altered but preserved textures enabled reconstruction of eruptive styles. The volcanic sequence exposed in the abandoned Hvězda quarry starts with a phreato-Strombolian pyroclastic rocks rich in basaltic scoriae, cuspate glass shards, armoured- and accretionary lapilli overlain with mafic lava. Subsequent activity was phreatomagmatic in style and produced fall-out of accretionary lapilli and accumulation of base surge deposits. Overlying subhorizontally bedded matrix-supported pyroclastic deposits are rich in scoria and contain spindle-shaped bombs. These rocks are interpreted as mafic pyroclastic flow deposits related to Strombolian eruptions. A similar succession capped by scoriaceous fall-out deposit was documented in the K1 borehole. A coherent mafic volcanic rock (lava or sill) terminates the succession exposed in the Hvězda quarry. Agglutinates at the base of the Studenec quarry were produced during Hawaiian eruptions building up a spatter cone. The cone most probably dammed a stream and created an ephemeral lake. Increasing influence of water on eruptive styles is documented in overlying pyroclastic deposits of phreatomagmatic eruptions. Subsequent lava flowed into the lake. Quenching of the lava resulted in formation of pillows enclosed in hyaloclastite breccia. Further up in the exposure, transition of pillow lava to massive lava has been recognized. Overlaying pyroclastic deposits are matrix-supported and rich in scoria and spindle-shaped bombs. Similarly to the Hvězda quarry, these are interpreted as mafic pyroclastic flow deposits. Volcanic activity in the Levín Volcanic Field was characterized by Hawaiian, Strombolian, phreato-Strombolian and phreatomagmatic eruptions accompanying lava effusions and possibly sills emplacement. The lavas were emitted in both subaerial and subaquatic conditions. The character and distribution of volcaniclastic facies suggests existence of several monogenetic volcanoes.