Accommodation of the Cenozoic Tunka Rift Valley at the Ordovician Slyudyanka Collision Zone: insight into volcanic sources, deep-seated inclusions, and seismic tomography models

On the one hand, Pb isotope data on 18–13 Myr volcanic rocks from the eastern part of the Tunka Valley yield age estimate of garnet-bearing source region in the viscous mantle of ca. 2.2 Byr that might correspond to the age of the Siberian craton mantle. On the other hand, inclusions from basanites show the pressure range that overlaps the pressure estimates for rocks of the Slyudyanka Ordovician collision zone. The lithospheric material corresponds to the transition from spinel-pyroxene to olivine-plagioclase facies of peridotites in the uppermost part of the mantle and lower-middle crust. V_S-data show a low-speed zone dipping from the central Tunka valley eastwards under Southern Baikal to a depth of 70 km. This zone ends at the South Baikal – Tunka Valley junction. We suggest that the eastern parts of the Tunka Valley has inherited the Early Paleozoic collision zone between the Hamar-Daban Terrane and Siberian Paleo-Continent and that the lithosphere of the collision zone overlays the viscous mantle related to the Siberian craton.

This work is supported by the RSF grant 18-77-10027.