Purpose. We investigated secondary serpentines in order to reconstruct the geodynamic conditions of the formation and transformations of the peridotites (Uholskyi complex), which are localized in the Marmarosh rocky zone in the Inner Eastern Ukrainian Carpathians and are most widely spread in the interfluve of Velyka and Mala Uholka-rivers. Methods. The work is based on the results of geological observations of the Uholskyi complex rocks in natural outcrops, as well as petrographic, mineralogical (including X-ray diffraction, thermal and microprobe analysis), and geochemical studies. For comparison, literary data on peridotites of the Ukrainian Carpathians and some studied in detail orogenic peridotite complexes have been used. Results. Peridotites form olistoliths in the Soimulska olistostrome-conglomerate strata (K1) of the Marmarosh rocky zone (Vezhanskyi nappe) of the Inner Ukrainian Carpathians. The age of olistoliths of the Uholskyi complex peridotites of the Soimulska suite is T2–K1 (?). The rocks of the Uholskyi complex are represented by serpentinous peridotites and serpentinites. The metamorphic transformations of peridotites are revealed in the significant distribution of a- and β-lizardite and antigorite. Two groups have been identified among the studied serpentines. Serpentines of the first group have a lenticular-looped texture and are mainly represented by a-lizardite and bastite, which have high chromium content and contain large non-altered grains of chrome-spinellids. Serpentines of the second group have a striped-shale texture; they are represented mainly by β-lizardite and antigorite, which have high iron content and contain powdered particles of magnetite. Serpentines of the first group were formed under the conditions of regressive metamorphism of the greenschist facies upper part, which occurred under the geodynamic conditions of the spreading zone during raising and cooling of peridotites. Serpentines of the second group have the characteristics (albeit local) of progressive metamorphism of the lower greenschist–upper epidote-amphibolite facies. They were formed under the supersubduction conditions and confined to fragments of paleozones of shear-plastic deformations. This was accompanied by subduction-collision events between the terrains of Dacia and Tisza in the Jurassic–Early Cretaceous, which led to the closure of the Transylvanian-Mureş paleocean. Selected groups of serpentines, which differ in mineral, chemical composition and structural and texture peculiarities, belong also to various geodynamic and genetic groups: the first tend to primary mantle protoliths of the ultrabasic composition, and the second – to lithospheric protoliths of the basic composition. Scientific novelty. The research of serpentines, which developed on the peridotites of the Uholskyi complex, made it possible to divide them into two groups whose representatives have different thermodynamic and geodynamic history. It is determined that structural, textural, mineral, and other features of serpentines are the indicators of geodynamic conditions for the transformation of peridotites of the Marmarosh rocky zone as well as other regions. A model of the phased transformation of the Uholskyi complex peridotites has been proposed. Practical value. The study of serpentinites developed on peridotites of the Uholskyi complex is important for the determination of the types of metamorphism in primitive mantle protoliths and the stage of formation of fold-covering structures lithosphere (on the example of the Ukrainian Carpathians). The obtained results can be used for prediction of serpentinite mineralization, since lizardite rocks (group 1) contain elements of the platinum group, and antigorite rocks (group 2) – magnetite.
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