PERMIAN-TRIASSIC TRANSCONTINENTAL SHEAR ZONES IN NORTHERN ASIA AND EASTERN EUROPE

During the Permian (270-250 Ma), the evolution of the Altaids was controlled by the sinistral Irtysh-Gornostaev and dextral Scytho-Turanian shear zones. In China and Mongolia, these shear zones merge with each other and exhibit reversals of shear sense– dextral for the earlier and sinistral for the later events. The Irtysh-Gornostaev shear zone stretches from Chinese Altay to the Polar Urals where it cuts the Uralide structures. The displacement along the Irtysh-Gornostaev shear zone may reach 2000 km as balancing of the tectonic units of the Altaids shows. The E-W trending Scytho-Turanian shear zone stretches from Beishan to the southeastern margin of the Russian craton and continues farther northwest as the Tornquist-Teisseyre lineament. Counterclockwise rotation of Permian declinations in the southern limb of the Kazakhstan orocline (southern Kazakhstan and Tien Shan) for 40-90° suggest ~1000 km displacement along the Scytho-Turanian shear zone. This zone marks the northern boundary of a number of en echelon, southwest-facing arc fragments belonging to the late Palaeozoic to Jurassic Silk Road arc. These fragments are distributed in northern Afghanistan and Iran, Turkmenistan, Caucasus and the northern Black Sea. They were stacked by large-scale, right-lateral strike-slip coastwise transport along arc-slicing and arc-shaving strike-slip faults in the Triassic and medial Jurassic simultaneously with the subductive elimination of Palaeo-Tethys.

The deformations along these shear zones are often considered as a results of frontal collisions of independent arcs or microcontinents even if their width is only 5-20 km (width of modern arc usually exceeds 50 km) and the rocks constituting the units have low strain being surrounded by boundary mylonites. Besides, the intense deformation along these shear zones did not often create a high topography (e.g. Sothern Mongolia, Iran, Turan, Caucasus), which is expected by collisional model – thick piles of coarse-grained clastics are absent. Finally, the strike-slip related shear zones are marked by mélanges, in which the age of matrix may be older than the age of inclusions (atypical for subduction mélange) or mélange is represented by fragments of arcs, continental basement, and carbonate platforms as it is observed in Sothern Mongolia.