Internal structure and kinematics of the Zvenyhorod-Brats’k fault zone of the Ukrainian shield according to geophysical data

Abstract

Complex geomagnetic and tectonophysical studies were performed in order to characterize in detail the heterogeneity of the Earth’s crust of the Zvenyhorod-Bratskfault zone and to clarify its internal structure and kinematics. Based on the results of magnetometric studies, maps of the different wavelength components of magnetic anomalies were obtained, the sources of which are associated with different layers of the crust; the magnetization of the upper, middle and lower parts of the crust was estimated; 2D and 3D magnetic models of individual structures and areas were developed; geological and tectonic interpretations were performed. The Zvenyhorod-Bratskfault zone is clearly manifested in the regional component of the geomagnetic field, separating its maxima and minima zones, and is also reflected by linear anomalies and bands of the short-wavelength component of the upper part of the crustal section. At the same time, it separates areas of the Earth’s crust with fundamentally different types of sources and their magnetization values: in the west, linear sources of the upper and middle crust of the GSZ are characterized by significant magnetization (up to 3—6 A/m) in contrast to the oval-shaped sources of the Ingul block with magnetization up to 1 A/m m. Tectonophysical measurements of structural and textural elements of rocks were carried out at four sites along the rivers Velyka Vys’, Kilten’, Suhyi Tashlyk and Mertvovid. Processing and interpretation of field measurements of structural textural elements of rocks were done by the structural-paragenetic method of tectonophysics for III-IV depth levels using the Stereonet program. It was established that the Zvenyhorod-Bratskfault zone was formed ≤2.45 billion years ago and consists of rectilinear shear zones related to different stages of fault formation. However, the main factor in the formation of the fault zone is the Pervomaisk stage, during which the L-shears with a strike azimuth of 345° and R-shears with a strike azimuth of 357° were formed. The presence of Archean phases of shear in it can testify to the earlier formation of the Zvenyhorod-Bratskfault zone relative to the Pervomaysk one. The Proterozoic cycle of activation (~2.1—1.70 billion years ago) contributed to the formation of deposits and ore manifestations of minerals within the Zvenyhorod-Bratskfaults zone.