The inner structure and kinematics of the Zvizdal-Zalisk and Brusyliv fault zones of the Ukrainian shield by the results of tectonophysical, magnetometrical data

Abstract

In 2021, the tectonophysical measurements of cracking, structural-textural elements of rocks near Malyn, Radomyshl, Pohrebyshche, Buky, Kashperivka and magnetometric field studies of Zvizdal-Zalisk dyke were carried out. And also the deep seismic sounding data along II and VI geotravers were analyzed in order to purpose to finding out of the internal structure and kinematics of Zvizdal-Zalisk and Brusyliv fault zones of the Ukrainian Shield. According to our tectonophysical data, the studied rocks were formed under landslide deformation processes with alternating sublatitudinal and submeridional compression regimes, which correspond to the youngest Subbottsi-Moshoryn stage of faulting formation within the Ukrainian Shield (1.80—1.77 Ga), with subhorizontal axes of compression σ1 — 315° and tensile σ3 — 45°. Cracks and bands of gneisses of moderate dip are also widely developed in the study area. Established, that it has deformation throw regime with σ1 — 100/85°, σ3 — 280/05°, σ2 — 10/02°. Authors of article associate this deformation with formation of the main breeds Zvizdal-Zalisk dikes. Deformations of the Nemyriv faulting stage (1.99 Ga) were fixed at the intersection node of the Zvizdal-Zalisk faulting zone with Nemyriv fault zone (1.99 Ga). Stress field is σ1 — 301°, σ3 — 31° at the intersection node the Brusyliv fault zone with Nemyriv fault zone and it repeat main deformation strains of the Novograd-Volyn and Uman massifs (~2.05 Ga). By the data of the deep seismic sounding along II and VI Geotraverses, the Zvizdal-Zalisk fault zone enters the mantle all along, in the north and in the south. The crust structure in the study area has two layers of upper crust (VР=5,9–6,4 km/s),with intermittent low- (5,8—6,2 km/s) and high-velocity (6,3—6,9 km/s) horizons, the middle crust (6,4—6,9 km/s), and lower crust (6,9—7,0 km/s) that has a wavy dome-like shape with high differentiated velocity picture differing on both sides of the Central faulting area. The Bug megablock has a dome-like structure along all VI Geotraverse and is divided in half by the Zvizdal-Zalisk fault zone at the Moho discontinuity according to the data of the tomographic inversion along the velocity change gradient. By the magnetometric data, the Zvizdal-Zalisk fault zone lies almost fully within the regional minimum of the magnetic field (∆В)а,reg, which encompasses areas of the crust with minimum values of magnetization. The dyke was formed at the same time of the Korosten pluton formation and at activation of the Zvizdal-Zalisk fault zone. Its small depth confirms its crust origin; the variable sharp incline of the dyke’s parts is evidence of its subvertical falling which corresponds to the vertical position of the Zvizdal-Zalisk fault zone. The data on the chemical-mineralogical composition and position of mineral deposits suggest that the main regional structures which have influenced the metallogenic specialization of the region are the Zvizdal-Zaliska, Brusyliv, Nemyriv, Khmelniksk, Central, and Sarnensko-Varvarivka fault zones.