Results of gravity modeling of the central part of the Korsun-Novomyrhorod pluton (Ukrainian Shield)

Three-dimensional gravity modeling of the Gorodishchen and Smilyan gabbro-anorthosite massifs, located in the central part of the Korsun’-Novomirgorod pluton (Ukrainian shield), was performed. A three-dimensional model of the upper crust of the research area was developed using maps of the anomalous gravity field of 1:200 000 scale, taking into account the results of detailed seismic studies by the methods of the RWM (reflected wave method) and CDP (common depth point). Differences in the structure of the intrusive complex of the anorthosite-rapakivi granite formation and the gneisses of the Ingulo-Ingulets series surrounding it were reflected in the seismic wave fields, which made it possible to determine the boundaries of the entire intrusive. For separating the basic rocks and rapakivi granites that differ in their density, three-dimensional gravity modeling was performed using computer technology of automated interpretation of geophysical data based on the trial and error method. For the geological objects parameterization, an approximation model is proposed, which is represented by a set of three-dimensional rod bodies. In the process of solving the inverse problem, various criteria for local optimization of gravitaty field sources were implemented. Three different functionalswere calculated during the iterative process. It is proved that the joint use of the functionals allows to reduce various types of noise in the observed gravity data. During the solving the inverse problem we found out that using of various types of functionals in the algorithms of trial and error methods is quite appropriate. Three-dimensional gravity modeling made it possible to identify and outline gabbro-anorthosite bodies in the upper part of the section with maximum thickness of up to 4—5 km, to clarify the shape and dimensions of the rapakivi granites, and to study the contacts of the intrusive complex with the gneisses surrounding it. The obtained model, which takes into account all the available information on density and geometric parameters of the anomaly forming objects, could be used to obtain additional reliable geological information about the structure of the Gorodishchensk and Smilyan gabbro-anorthosite massifs. The reliability of this algorithm for three-dimensional trial and error gravity method, using an approximation model in the form of a three-dimensional rods construction, allows us to recommend it for the study of similar gabbro-anorthosite massifs of the Ukrainian Shield, primarily the Korosten pluton.