Abstract <p>The West Transbaikal rift region was formed in a continental setting in the Late Jurassic and has been developed until the Early Cenozoic. The Uda sector is one of its central fragments and includes the Uda, Eravnoe and Zaza depressions. New Sr, Nd, Pb, O isotopic data reported in this study in combination with geochemical signatures of Cretaceous basaltic rocks of each depression allowed us to estimate the compositions of mantle- and crustal-derived magmas and to propose their mixing model. During the formation of volcanics of the Uda sector within the age range of ∼143–71 Ma, the isotopic sources successively changed from enriched (EMI and EMII) to moderately depleted PREMA types. The Early Cretaceous primary magmas were derived from mantle sources that included subduction-enriched mantle, which resulted in the depletion of the basaltic rocks in Ta, Nb, Ti and in high (La/Ta)_N (2.2–4.9) and (La/Nb)_N (2.1–4.2) ratios at high contents of incompatible trace elements. Mantle magmas of the Uda depression were contaminated with a lower crustal component, which is characterized by the moderate or lowered contents of Zr and La, and low La/Yb and Rb/Sr ratios compared to the composition of basaltic melt. Compositions of basaltic rocks from the Eravnoe and Zaza depressions reflect the interaction of mantle magmas with upper crustal granitoids of the Angara–Vitim batholith. Mantle-crust interaction least affected the composition of Late Cretaceous volcanics, the geochemical characteristics of which are consistent with the dynamics of temporal isotope variations of mantle sources.</p>