The Strike-Slip and Tectonic-Gravitational Structural Ensembles of the Cimmerian Development of the Dakhov Crystalline Block (Western Pericline of the Paleozoic Core of the Greater Caucasus)

Using the Dakhov granitometamorphic block (Neoproterozoic – Paleozoic) as an example consideration is being given to exhumation mechanisms of the Hercynian basement complexes within the epi-platform orogen of the Greater Caucasus. The block forms a horst-like uplift and is located in the junction area between the Central and Western Caucasus segments, where the pericline of the Paleozoic core of the orogen is tectonically overlain by the Cimmerian (Lower to Middle Jurassic) and Alpine (Middle Jurassic to Cenozoic) structural-formational complexes. The geologicalstructural and particularly the structural-kinematic studies have shown that the Dakhov uplift sits in the transpressional dextral strike-slip fault zone that is a branch of the long-lived Pshekish-Tyrnyauz suture zone. The sandstones and shales of the Cimmerian complex commonly found north and south of the Dakhov uplift, are complicated by the nappeoverthrust structures with divergent displacements occurred relative to the axis of Dakhov block uplift and associated with sliding collapse of the overlying Jurassic strata into the adjacent depressions. The Dakhov block itself is a structural element of a shear zone, which forms a shear duplex and participates in the formation of large Z-shaped shear-contact axonoclines complicating the northern part and the eastern pericline of the uplift, as well as its bordering Jurassic strata. The northern part of the uplift still contains a fragment of a serpentinite-gneiss melange zone that formed during the Hercynian tectogenesis. This zone exhibits signs of kinematic inversions in fault structures, related to rotation phenomena of large domains of metamorphic rocks. The isolation of the Dakhov uplift within the Hercynian basement structure was caused by the presence of a rheologically weakened Hercynian suture zone (serpentinite-gneiss melange) therein. During the Cimmerian dextral slipstrike movements, this zone was reactivated and experienced planar bending, which gave rise to the formation of asymmetric Z-shaped axonoclines. Rotational shear deformations in the area of converging flanks of these axonoclines contributed to the development of an extensional shear duplex, in which the Dakhov crystalline block was uplifted. The Cimmerian exhumation of the Dakhov crystalline block occurred as a result of the combined action of two interconnected heterogeneous processes: transpressional deformation of the basement and gravity sliding of the Lower to Middle Jurassic cover sediments. The processes involved in the Late Alpine orogeny, which began at the Neogene-Quaternary boundary, proceeded simultaneously with the collapse of the growing Greater Caucasus orogen. One of the forms of collapse occurrence in the study area was the development of tectono-gravitational detachments and sliding of the Alpine cover sediment down the northern slope of the orogen that causes the pre-Alpine basement rocks, including the Dakhov crystalline block, to be exposed on the modern relief surface.