Genesis of Cenozoic Volcanism in the Baikal Rift: The Role of Garnet-Pyroxenite Source Melting in the Lithospheric Mantle

The Cenozoic volcanism of the Baikal Rift, associated with the Indo-Asian collision, exhibits geochemical signatures of melting from an olivine-free mafic source, excluding a significant contribution from a peridotitic mantle. Analysis of volcanic rock compositions (primarily basalts and trachybasalts) indicates that the magmas were generated by the melting of garnet-pyroxene lithologies, formed during the sinking of the thickened lower crust into the lithospheric mantle. Geophysical data confirm anomalous crustal thickening (up to 55 km) in the southwestern part of the rift, where the most extensive volcanic fields are observed. The proposed model explains the volcanism as a result of gravitational instability and lithospheric delamination triggered by collisional deformation. The passive nature of the magmatism implies its relation with tectonic processes rather than active upwelling of deep mantle material. This study presents the model for the formation of late Cenozoic basaltic melts in the Baikal Rift, attributing their origin to the remelting of lower crustal material within the lithospheric mantle.