High-potassium rocks of the Late Riphean Mara paleovolcano, Biryusinsky ledge, South of the Siberian Platform

The research was focused on the Mara–Kamenka–Uvat interfluve of the Biryusinsky ledge of the Siberian Platform, where more than half a century ago, during prospecting works for manganese, the Marа paleovolcano was identified. However, specific volcanogenic-sedimentary rocks were considered as a part of the Karagas sedimentary series of the Late Riphean. Our mineralogical and petrographic studies have allowed us to establish the wide distribution of high-potassium pyroclastics, ignimbrites, and trachybasalts, indicating a subaerial explosive volcanic nature of the Mara volcano. The age of high-potassium volcanism has been determined based on U–Th–Pb zircon dating as 640 Ma. Lu–Hf isotope systematics of zircon indicate a relation of these volcanic rocks with mantle-derived magmas. The composition and time of formation of the studied rocks do not allow us to correlate them, as previously thought, with sedimentary Late Riphean quartz and quartz-feldspathic sandstones of the Karagas sedimentary series and dolerites of the Nersa intrusive complex. The specific mineralogical and petrographic features of the studied rocks make them suitable as a regional stratigraphic mark.