Geochronology of the Volyn volcanic complex at the western slope of the East European Craton – Relevance to the Neoproterozoic rifting and the break-up of Rodinia/Pannotia

Abstract

Thick Neoproterozoic rift sequences along the western margin of the East European Craton (EEC) are classically attributed to rifting leading to break-up of super-continent Rodinia/Pannotia. Rifting was associated with intense, mainly mafic, volcanism, known as the Volyn Series, in the Lublin-Podlasie Basin (LPB) and in the Orsha-Volyn Aulacogen. Legacy deep boreholes in Poland provide continuous section through the volcanic series. Zircon from nine samples of tuff layers interbedded with basalt, from four boreholes, were dated with the U–Pb method with SHRIMP. The samples contain syn-eruptive zircons, together with zircon recycled from previous ash falls and zircon from the surrounding Proterozoic basement. The youngest volcanic zircon cluster from each sample of the studied tuff samples yielded concordia ages stratigraphically consistent, which document eruption events that took place between 567.1 ± 4.7 Ma and 551.0 ± 4 Ma. The most intense development of lavas and pyroclastics took place at ca. 557–555 Ma and ca. 567–560 Ma. Older volcanogenic zircon grains, inherited from previous phases of volcanic activity, preceding actual eruptions, were are dated at 588.0 ± 8 Ma to 580 ± 8.1 Ma. Age spectrum of xenocrysts zircon grains, inherited from the crystalline basement rocks of the LPB, ranges from ca. 1830 Ma to ca. 1480 Ma, coherent with the known late Paleoproterozoic and Mesoproterozoic age of crust-forming events in the western part of the EEC. The late Ediacaran syn-rift igneous activity in the LPB continued over a time span of approx. 37 My. It developed along both the SW margin of emerging Baltica and in the western the Orsha-Volyn Aulacogen. The study area was located at the intersection of these regional structures, being thus a site of development of an incipient triple junction, related to Rodinia/Pannotia break-up. Further extension along the SW margin of Baltica led to its separation from the plate adjacent to the west, and to the subsequent development of continental passive margin. Final emergence of Baltica, as an individual palaeocontinent, took place at ca. 550 Ma.