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A consistent integrated model of a medium is a model that conforms to all the observed geophysical fields and has definite relationships between the unknown medium properties. The simultaneous solution of the inverse problems for the seismic and gravity methods have been used as an iteration procedure. The results of the inversion in one geophysical method served as initial model for inversion task in another geophysical method and vice versa. As a result of one step of the integrated inversion the interrelated density and velocity models of the studied medium can be obtained. The solution precision is estimated from the discrepancy between the observed and calculated fields. If the precision of the solution does not satisfy to the a priori r.m.s. differences of the fields (travel time, gravity field), the interpretation may be repeated on the next step in order to ascertain the complex solution in velocity-density values. This process is, in general, convergent and allows us to obtain a satisfactorily precise solution of the integrated inverse problem, the number of iterations being low. This approaches based on interrelation between the physical properties of the medium. These interrelations should be determined a priori for the rock types that are found in the study region. In a general case, they have a probabilistic nature rather than functional one. The probabilistic characteristics of these interrelations are a basis for solving inverse problems with system of the weighting functions.
The results of the integrated 3D modelling for the entire region of Lapland Granulite Belt and adjacent areas, including the Pechenga structure and northern part of the Belomorian Belt are shown. For calculation of the 3D upper crust regional model, the integrated inversion for geothermal, gravity and seismic data was applied. When solving the inverse geophysical problems, we also used petrophysics data for crustal rocks. The calculated geophysical results for the 3D upper crust models show that the Lapland granulites and Pechenga structure form subhorizontal bodies gently dipping towards each other and are underlain by a lighter infrastructure. Their sublatitudinal structural trend changes into a submeridional one at a depth of 14 - 18 km. The obtained geophysical results allowed us to propose one of the possible models for formation of the Lapland Granulite Belt and Pechenga structure.
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