We have analyzed the isotope-geochemical features of volcanosedimentary rocks of the Karsakpai Group in southern Ulutau (Central Kazakhstan): mafic volcanics, siliceous and siliceous-ferruginous sediments, and quartz–sericite–chlorite schists. The close association of ferruginous quartzites with intraplate volcanics indicates that they formed in a tectonically active basin. The Nd isotope composition of ferruginous quartzites was governed by synchronous underwater volcanism, whereas the 143Nd/144Nd value of schists was additionally controlled by the Nd isotope composition of older sources. The Mesoproterozoic Nd model ages and positive εNd(t) values of the metaterrigenous rocks of the Karsakpai Group indicate the presence of Mesoproterozoic juvenile material in the provenance. The minimum Nd model ages suggest the lower boundary of sedimentation of 1.3 Ga.