The Jurassic-Cretaceous K-rich Volcanism of the Nercha Depression in Eastern Transbaikalia and Its Geodynamic Nature

The geochronological, geochemical, and Sr-Nd isotopic features of the Late Mesozoic volcanic rocks associated with the development of the Nercha Depression in the Eastern Transbaikalia are presented. The structure of the depression involves the sequences of K-rich subalkaline volcanic rocks with content of 55 to 73 wt % (SiO2.Ar)-Ar-40/Ar-39 isotope dating of bulk rock samples was conducted. Ar-40/Ar-39 dating gives a value of 150.8 +/- 1.8 Ma for K-rich andesibasalt and 131.0 +/- 1.6 Ma for latite. Volcanic rocks are characterized by depletion of hydrophobic Ti, Nb, and Ta, slightly negative epsilon Nd(T) values, but increased in epsilon Sr(T) values, which probably indicates contamination processes of primary melts by the crust component. In terms of their geological and geochemical characteristics, the volcanic rocks of the Nercha Depression belong to the shoshonite-latite series of the rear part of the Greater Khingan volcanic region, which formed in the subduction setting of the continental active margin.