Sequence of deformations in frame of Syum-Keu ultrabasic massif (Polar Urals)

Research subject . The Syum-Keu ultrabasic massif, located in the Polar Urals. Aim. Identification and disassembly of deformation events near the junction of different-age structures of the Urals, Pay-Khoy, and the northwestern part of Western Siberia. Materials and Methods . Geological interpretation of data on the geometric characteristics of fold structures, paleostress indicators, anisotropy of magnetic susceptibility, and 40 Ar/ 39 Ar dating of muscovite. Results. The study of the structural characteristics of rock complexes in the Syum-Keu ultrabasic massif and its framing confirmed the presence of several stages in their deformation: (1) a stage of plastic deformation (early collisional stage) and (2) two stages of brittle deformation (late collisional stage). During the early collisional stage, thrusting with a shear component took place, which is manifested in shallow folding hinges and orientations of the main axes of the anisotropy of magnetic susceptibility ellipsoid. The late collisional stage reveals early NE-SW strike-slip compressional stresses and late NW-SE strike-slip stresses corresponding to strike-slip and strike-slip displacements. The results of 40 Ar/ 39 Ar dating of granitoids indicate the Turnean age of metamorphic transformations. Conclusions . The conducted study of mesostructural elements revealed two types of deformations: early plastic deformations, attributed to the early collisional stage and reflecting regional thrusting, and late brittle deformations, attributed to the late collisional stage and reflecting thrust and thrust movements. The study of the orientation of the ellipsoid anisotropy axes of magnetic susceptibility of rocks in the western and eastern margins of the Syum-Keu massif showed thrusting and strike-slip kinematic characteristics of the complexes, which are typical of the early collisional stage and the formation of the Ural cover structure in accordance with the Hansen model. The results of 40 Ar/ 39 Ar dating may indicate metamorphic transformations of rocks in connection with the onset of collisional processes in the Polar Urals, presumably of the Turnean age.