EFFECT OF EARTH SPHERICITY ON THE RESULTS OF AEROMAGNETIC MEASUREMENTS OVER PLATOBASALTS (ON THE EXAMPLE OF NORILSK REGION)

Abstract

The research relevance is caused by the expediency of using model concepts adequate to real physical and geological conditions, while reducing the results of magnetic prospecting in the areas of development of platobasalts. The aim of the research is to evaluate the influence of the Earth’s sphericity on the anomalous magnetic field under conditions of a sharply dissected relief of the day surface which is composed of magmatic mountain rocks that have an increased magnetization (on practical materials). Methods: calculation of corrections for the influence of magnetic terrain by solving the direct problem of magnetic exploration for a region with a radius of 20 km in two versions: for flat and spherical models of the Earth. Comparison of the results and spatial-statistical analysis of the identified differences were carried out. It was assumed that the magnetization vector of the rocks forming the relief is directed along the modern geomagnetic field of the region. Variable laterally effective magnetization of the upper part of the section was determined by solving the linear inverse problem of magnetic exploration. Results. The paper describes briefly the problem of taking into account the influence of the terrain relief in measuring the magnetic field over volcanogenic formations. On the example of materials of a large-scale high-precision aeromagnetic survey, performed in the central part of the Norilsk ore region, the nonlinear signal distortions associated with the curvilinearity of the earth's surface were shown. The amplitude of these distortions (absolute value) reaches 100–200 nT and more, with relatively small differences in elevations for different models. This is due to the high values of the vertical gradient of the magnetic field. Findings. In order to suppress the intense noise anomalies caused by magnetic rocks composing the upper part of the geological section, the author proposed the calculation of topographic corrections using the spherical model of the Earth. It also seems promising to use a statistical approach, implicitly taking into account the shape of the earth's surface, to isolate anomalies of «relief» nature. A comparison of the results obtained and a spatial-statistical analysis of the revealed differences are performed.

Keywords

• platobasalts
• terrain
• aeromagnetic survey
• anomaly
• topographic correction
• reduction
• model of the earth