Reconstruction of the paleostress field of the Kokdjot Block, Malyi Karatau ridge (South Kazakhstan)

Abstract

Paleozoic fields of the Kokdjot Block, Malyi Karatau ridge (South Kazakhstan) were reconstructed as a result of a detailed structural study. The main role in the structure of the Early Paleozoic complex of Malyi Karatau is played by large thrust plates composed of terrigenous Precambrian deposits and Cambrian and Ordovik carbonates. In the formation of the Caledonian structure of Malyi Karatau, four stages of deformation were distinguished. The first stage is characterized by the thrust of tectonic plates on each other in the southwest direction with amplitudes up to 15–20 km; the second is characterized by the formation of longitudinal folds of the northeastern vergence and longitudinal uplifts; the third is characterized by diagonal shifts and the folded forms associated with them; and the fourth is characterized by the development of longitudinal cleavage of the northwestern strike and accompanying shear folds in the most compressed parts of the structure. Kink-bands and fold-axes were used to indicate stress field reconstruction. Study areas of the Kokdjot Block are located from the northwest to the southeast of the Kokdjot plateau and are characterized as both clastic sedimentary rocks of greenschist and phyllite facies of metamorphism, and clastic and carbonate sedimentary rocks. Two stress fields have been identified as corresponding to Caledonian (Late Ordovician) and Hercynian deformations. The earlier tectonic event is characterized by horizontal compression of the northeastern trend, and the later tectonic event is characterized by the shear stress field at the west-north-west trend of the compression axis.