Abstract
New data are reported on the age, composition and formation conditions of the Late Triassic granitoids of minor intrusions from the eastern part of the Bureya continental massif of the Central Asian fold belt, and their geodynamic interpretation is given. U-Pb geochronological studies on zircons indicate that the age of rocks of the Altakhta syenite-leucogranite complex is in the 235–224 Ma range, which intrusion proceeding in two phases. The formation of magmatites is associated with the first phase (235.3 ± 2.9–230 Ma), which by their geochemical features are similar to А1-type intraplate granitoids and by REE concentrations to subduction- and collision-related granitoids. Geochemical characteristics of А2-type and А2 + I & S-type granites (226–224 Ma) suggest their formation in a syncollisional setting. The evolution of the chemical composition of the Altakhta granitoids indicates a change in the geodynamic setting type, when the opposing (orthogonal) movement of the plates at the convergent boundary (subduction) changed to their sliding past each other (transform continental margin).
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