Age and Tectonic Setting of Volcanic Rocks of the Olov Basin in the West Transbaikal Rift System

Geochemical and geochronological (U–Pb zircon method, ID-TIMS) studies of volcanic rocks of the Olov basin of the West Transbaikal Rift System within the western part of the West Stanovoy superterrane of the Central Asian Fold Belt are performed. It is established that the age of volcanic rocks of this basin is in the range of 178 ± 5–177 ± 5 Ma. Taking into account the results of earlier studies, this indicates the manifestation of two bursts of continental volcanism (Early Middle Jurassic and Early Cretaceous) in different geodynamic settings in this region. The first burst is revealed exclusively in the Olov basin, localized in the influence zone of the Mongol-Okhotsk suture, and is represented by differentiated basaltic trachyandesite-trachyandesite-trachyrhyolite association of the adakitic type, formed in a collisional geodynamic setting. The second one is represented by a bimodal basaltic trachyandesite-trachyrhyolite association formed under conditions of post-collisional continental rifting. The collision event is most likely associated with the closure of the central segment of the Mongol–Okhotsk Ocean and the collision of the continental masses of the North Asian and Sino-Korea continents at the turn of ~175 Ma. The subsequent collapse of the collisional orogen was accompanied by the large-scale Early Cretaceous lithospheric extension and rifting (~140 Ma).