The Late Paleozoic fold-thrust structure of the Tunka bald mountains, East Sayan (southern framing of the Siberian Platform)

Abstract

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 geometrical analysis of macro- and microstructures has revealed three development stages of the structures, which followed one another in progressive deformation. The first (thrust-fault) stage (316–310 Ma) comprised a group of N-verging thrust sheets. In 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 near-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 continental-margin 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.

Impact of seismic events in the southern Baikal region on the troposphere according to radiometer data ATMS/SNPP

“…The epicenters of the studied earthquakes were recorded in the southwest of the Baikal Rift Zone (BRZ) at the southeastern tip of the Main Sayan Fault. This is the largest discontinuous structure with a length of more than 1000 km and a width of about 10 km [7]. This fault retains high geodynamic activity and is included in the East Sayan earthquake source zone.…”

Late Paleozoic low-angle southward-dipping thrust in the Züünharaa area, Mongolia: tectonic implications for the geological structures in the Sayan-Baikal and Hangai-Daur belts

“…1b) (e.g., Zorin 1999; Ruzhentsev et al 2006Ruzhentsev et al , 2007Ruzhentsev et al , 2012Buslov et al 2009;Ryabinin et al 2011;Zhimulev et al 2011). Buslov et al (2009) andZhimulev et al (2011) reported that the Neoproterozoic-Cambrian formations overthrust upon the Middle Ordovician Tunka granite and the Late Devonian-Early Carboniferous Sagan-Sair Formation with an E-W trending plane and dipping less than 30° southward in the Tunka area (L.4; Fig.…”

“…The molasses-like Late Devonian-Early Carboniferous Sagan-Sair Formation overlaps the Tunka granite and Ordovician-Silurian sedimentary rocks (Buslov et al 2009;Zhimulev et al 2011). The rocks of the Tunka terrane form a complex N-verging fold-thrust structure (e.g., Ryabinin et al 2011;Zhimulev et al 2011).…”

“…The minerals (such as amphibole, biotite and muscovite) at the bottom of the tectonic sheet of the NeoproterozoicCambrian formations (dated at an U-Pb age of 2-1.7 Ga; Zhimulev et al 2010) yield an Ar-Ar age of 316-310 Ma, which correspond to the Late Carboniferous (e.g., Buslov et al 2009;Ryabinin et al 2011;Zhimulev et al 2011). Ryabinin et al (2011) andZhimulev et al (2011) interpreted this isotopic age as the timing of the low-angle southward-dipping thrusts.…”

“…Ryabinin et al (2011) andZhimulev et al (2011) interpreted this isotopic age as the timing of the low-angle southward-dipping thrusts.…”