Picritic dolerite dikes of the Naryn River: age, composition and position in the geological history of the Southeastern Tuva (Central Asian Orogenic Belt)

New evidence of the Early Silurian sublithospheric magmatic activity in the eastern part of the Altai-Sayan orogen has been obtained, which occurred between large-scale mantle magmatic episodes of the Middle–Late Ordovician and Devonian. These are the dikes of high-Mg (MgO 15–22 wt %) picritic dolerite of the Naryn complex in the western part of the Tuva-Mongolian superterrane. The dike complex consists of simple picritic dolerite dikes and combined dikes which compose a central picritic dolerite and granitoids along contacts with mingling zone between them. The picritic dolerite geochemical signature is similar to the enriched basalt of mid-ocean ridges or within-plate regions and indicates sublithospheric mantle source of therm. The origin of initial picritic dolerite melts occurred at depth about 120–140 km, temperature of 1600–1640°C and melting degree up to 20% of a dry peridotite. These values are consistent with the origin conditions of the hot spot magmas. The granitoids from combined dikes had crustal geochemical signature and were formed due to anatexis of the Tuva-Mongolian superterrane host rocks initiated by the picritic dolerite intrusion. The U–Pb zircon age (SHRIMP-II) of leucogranite from the combined dyke is 439±3 Ma witch interpreted as age of the Naryn dyke complex. Early Silurian mantle magmatic activity of the Southeastern Tuva most likely caused the migration of the Siberian paleocontinent over the African mantle hot field.