Abstract <p>Neoproterozoic (725–715 Ma) dolerite dikes ascribed either to the Sayan–Baikal dike belt or to the Irkutsk Large Igneous Province (LIP) are widespread in the southern part of the Siberian Craton. The age of the dolerites matches that of the Franklin LIP, indicating that the dikes formed during rifting associated with the breakup of the Rodinia supercontinent and the separation of the Siberian Craton from Laurentia. The chemical compositions of all dolerites of the Sayan–Baikal dike belt correspond to subalkaline tholeiitic basalts and basaltic andesites with low TiO₂ and P₂O₅ concentrations. However, the dolerites in the different parts of the belt differ in geochemical and isotopic characteristics. It is suggested that the dolerites may have formed either as a result of melting of a subcontinental lithospheric mantle source, or by mixing of mantle components in varying proportions, or by crustal contamination of the mantle source. Neoproterozoic dolerites of the Sayan–Baikal dike belt in different parts of the Siberian Craton were derived from heterogeneous mantle sources vaiably subjected to crustal contamination.</p>