Geochemistry of ancient ophiolites of the Sharyzhalgai uplift

Petrological, geochemical, and geochronological data for the basic-ultrabas ic rocks of the Bulun block from the Sharyzhalgai uplift are reported, and the age and geodynamic environments of these geologic structures are determ ined. The examined rocks are determined to be fragments of a reduced ophiol itic sequence, which included relics of a residual and a gabbroid complex. The metamorphosed ultramafic rocks of the residual complex exhibit petroche mical characteristics corresponding to those of the Fe-rich peridotites of mid-oceanic ridges and backarc spreading zones. The gabbroid complex is det ermined to consist of metapyroxenites, gabbro-pyroxenites, and metagabbroid s. All of the metabasic rocks affiliate with the tholeiite series. The gabb ro-pyroxenites correspond to N-MORB, whereas the metagabbroids are geochemi cally similar to T-MORB. Based on a complex of geological, petrological-geo chemical, and isotopic-geochemical criteria, a conclusion is drawn that the fragment of the metamorphosed mafic-ultramafic rock association of the Bul un block from the Sharyzhalgai uplift should be classified with Early Preca mbrian ophiolites.