Three-dimensional density model of the Tarasivka structure of the Golovanivsk suture zone of the Ukrainian Shield

Abstract

For the first time, based on the data of three-dimensional density modeling, a diagram of the density distribution on the surface of the basement of the Tarasivka mafic-metamafic structure with an area of 2.5×5.5 km, extending to a depth of no more than 3—4 km, was constructed. The distribution of density to a depth of 5 km has been studied in detail, and the depths of occurrence of geological bodies have been determined. New in methodological terms is the use of a bypass step-like boundary from below, the form of representation of which is determined by the expected depth of occurrence of bodies with different densities. Thus, the depth of bodies with increased density near the basement surface is 2 km, of granitoids — 3 km, of undivided charnockites and enderbites — 4 km. It is shown that apogabbroids and aponorites with an average density of 2,80—2,90 g/cm3 (slightly altered rocks of mafic-metamafic composition), which form the central part of the Tarasivka mafic-metamafic structure, extend to a depth of 2 km without changing their angle fall, which is confirmed by seismic and electrical survey data. Based on the complex of available data, the selection and substantiation of the density of the host rocks of the charnockite-enderbite series, which are characterized by a density of 2,75—2,76 g/cm3 and form a ledge of about 1—2 km within the Tarasivka structure, were made. The marginal parts of the structure extend deeper than the central ones, which testifies against its synclinal structure. Along the latitudinal strike-slip fault, which passes through the central part, the Tarasivka structure is divided into two parts: the northern, less dense, and the compacted southern one. It is shown that in the eastern and northeastern parts of the structure, the fault zones are fragmented and compacted.In some of them, the density is 2,77 and 2,80 g/cm3 throughout the section, which can be explained by the intersection of high-density rocks by faults in such a places.The absence of supply channels and the shallow depth of the Tarasivka structure can be explained in two ways: either the channels of the mafic intrusion that forms the structure, most likely, have a small diameter (or diameters), that is why they cannot be fixed by gravimetry; or powerful strike-slip processes, which are fixed within the Golovanivsk suture zone, led to the formation of a detachment at a depth (modern) of 3—4 km, as a result of which the upper part of the Yatra block, together with the Tarasivka mafic-metamafic structure, moved quite strongly to the south, tearing it from root part. The last statement is considered the most probable.