ZONE-BLOCK TECTONICS AND ELEMENTS OF NEOTECTODYNAMICS OF THE SURKHANDARYA DEPRESSION (SOUTH UZBEKISTAN)

The paper presents the results of neotectonic and neotectodynamic studies of the Surkhandarya depression. The depression is a structure of post-platform orogeny, characterized by the imposition of tectonic movements and deformations of different genesis. Taking into account the new geological and geophysical data, cartographic models have been made for fault-block tectonics, neostructure, and neotectonic zoning.

The study area, spanning from the northwest to the southeast, shows the second-rank northeast-striking overthrust reverse step-like fault zones: Kugitang-Baysun and Kelif-Sherabad-Sarygamysh-Surkhantau, with the fault plane dipping northwest. There have been identified third-rank northwest-striking transverse fault zones. Among them are fault zones along the Sangardak – Kyzyljar – Denau – Zarkosa, Akkapchigai – North Dasmanaga, Urgilisai, and Sherabad – Dzharkurgan lines. They are the boundaries of uplifts (Kaymazar-Dalvarzin, Uchkyzyl) and adjacent depressions. There have been noted the left-lateral northwest-striking and right-lateral northeast-striking shears. They are clearly defined along the relative displacement of the Cenozoic outcrop ridges (Kelif-Sherabad-Sarykamysh, Babatag mountain ranges).

Two second-rank regional stress fields were obtained for the study area. The first is characterized by the northwest (southeast) orientation of the compressive principal normal stress axis (σ₃), with the southwest (northeast) direction of the extension axis (σ₁) and the subvertical direction of the intermediate axis (σ₂). This stress field is characteristic of the uplifts of the southwestern spurs of the Gissar Range and the piedmont Surkhandarya depression. The second stress field, within the Baysun basin and the Surkhandarya depression, is characterized by a sublatitudinal subhorizontal compressive stress axis (σ₃) and a submeridional orientation of the extension axis (σ₁), with a subvertical direction of the intermediate axis (σ₂). This stress field determines the deformations of the MZ-KZ cover, forming shear zones, and the structural paragenesis accompanying this dynamic environment. The analysis shows that the involvement in the process of uplift occurs during the rapid rise of the western and northwestern anticlinal folds with their rising centers moving from west to east.

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