Tectonic Evolution of the Intra-plate Structures of Sarmatia in the Phanerozoic. 2. Tectonic frameworks of deformations

Objective. Based on data from the Dnieper-Donetsk Aulacogene, the role of different-age systems of crustal faults as tectonic frameworks of deformations of the Sarmatian plate was investigated. Methods. An integrated method for reconstructing the stress-strain state of the crust was proposed based on geoinformation technologies, morphometric, tectonophysical methods, and comparative structural analysis of discontinuous and folded deformations. Results. Four main fault systems were identified in the pre-Rifean basement and Phanerozoic sedimentary cover of the Aulacogene. There are pre-Rifean cratonic, Paleozoic riftogenic, and two post-rift systems of early (Laramian phase, Senonian-Early Eocene) and recent (Attic phase, Neogene-Quarter) Cenozoic activation. It is established that Paleozoic tectonites formed a riftogenic lattice and a framework of the Hercynian (Zaalian phase) folding of the Dnieper Graben cover. It is found that the inversion deformations of the Aulacogene are controlled by the frameworks of reactivated pre-Rifean and Cenozoic tectonites, which are unconformably superimposed on rift lines. Previous ideas about the direct reactivation of the latest tectonites with the inheritance of the directions and genetic types of Paleozoic tectonites were not confirmed. The coincidence of the directions of the latest tectonitic systems, reactivated in meridional directions, with the suture zones of the basement is due to their position on the moving boundaries of megablocks, which united in the core of Sarmatia as accretionary terranes. The original and reactivated genetic types of "reverse" tectonites were reconstructed: in the Paleozoic, under conditions of meridional stress and latitudinal extension of the Sarmatian crust, a thrust-shear rift framework was formed, while in the Cenozoic, a thrust-shear framework was formed in a regional shear field. Scientific novelty. The kinematic mechanism of the natural phenomenon of spatiotemporal inversion of stress field parameters was determined. Geodynamic axes in the Phanerozoic underwent a counterclockwise shift of ~15° during the tectogenesis epoch, which caused their general displacement from the Paleozoic to the Cenozoic by ~60°. Because of this, four deformation planes were formed in the Sarmatian crust: rift (D–С1), inversion (С2–P1), two collisional (Т–К1) and (К2–KZ). The distribution patterns of the latest tension/compression zones in the aulacogen in areas of increased density of certain genetic types of tectonites and deformation parageneses have been established. Conclusion. A theoretical conclusion has been obtained for understanding the patterns of formation and evolution of the Earth's crust: the restructuring of the platform infrastructure occurs in a variable stress field due to changes in the genetic type and kinematics of tectonites with the formation of "reverse" reactivated systems that constitute younger tectonic deformation frameworks. Practical significance. The application of the original method of reconstruction of the stress-strain state of the Earth's crust made it possible to identify tectonic modes and kinematic mechanisms of fault and fold deformations of the Earth's crust in Sarmatia.