We provide new geochemical and isotope-geochronological evidence for gabbro intrusions of the Krestovsky zone in the Olkhon composite terrane. The intrusions belong to the Birkhin (similar to 500 Ma) and Ust'-Krestovsky (similar to 470 Ma) complexes, which underwent several pulses of magmatism. Rock structures and textures record magma crystallization in tectonically turbulent conditions. The compositions of gabbro are similar to those of subduction-related basalts, but the Ust'-Krestovsky gabbro is richer in incompatible elements than the Birkhin rocks. A similar composition trend of gabbro is observed in other areas of the Central Asian Orogenic Belt (CAOB): southeastern Tuva, Gornaya Shoria, and western Mongolia. We suggest a model of regular composition changes in parental magmas during the interaction of a mantle plume with suprasubductional lithospheric mantle. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.