Home – Home – Jornals – Russian Geology and Geophysics 2011 number 12

According to the new geological, geochronological, and structural data, the Tunka bald mountains (East Sayan) have a nappe structure, which formed in the Late Carboniferous-Early Permian. The deformations have been dated by the ⁴⁰Ar-³⁹Ar method on the basis of syntectonic micas and amphiboles, whose structural and spatial positions have been determined in oriented thin sections. The geometric analysis of macro- and microtextures has revealed three development stages of the deformation structures, which followed one another in progressive deformation. The first (thrust-fault) stage (316-310 Ma) comprised a group of north-verging thrust sheets. At the second (fold deformation) stage (305-303 Ma), they were folded. The third (strike-slip fault) stage (286 Ma) comprised high-angle shears, along which V-shaped blocks were squeezed westward from the most compressed areas. All the structures developed under N-S-trending compression. The thrusting in the Tunka bald mountains was coeval with the major shear structures in the eastern Central Asian Fold Belt (Main Sayan Fault, Kurai, Northeastern, and Irtysh crumpled zones, etc.). Also, it was simultaneous with the formation of continent-marginal calc-alkalic and shoshonite series (305-278 Ma) as well as that of the alkali and alkali-feldspar syenites and granites (281-278 Ma) of the Tarim mantle plume in the Angara-Vitim pluton located near and east of the studied region. Thus, the simultaneous development of the Late Paleozoic structures, active-margin structures, and plume magmatism in southern Siberia might have resulted from the global geodynamic events caused by the interaction between the tectonic plates which formed the Central Asian Fold Belt.