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Anzhela Zhirova, Geological Institute KSC RAS (Russian Federation)
Victor Glaznev, Geological Institute (Russian Federation)
Alexey Raevsky, Geological Institute (Russian Federation)
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The purpose of this work was to construct a three-dimensional complex geophysical model of the structure of the upper crust of the central Kola Peninsula where alkaline Paleozoic massifs of Khibiny and Lovozero are located. In order to create of three-dimensional complex model of the structure of the earth's crust upper part in the Khibiny and Lovozero massifs regions have been used the following data: the data of a gravity field; the regional and detailed data of the refraction seismic wave traveltimes; the petrophysical properties of the surface rock of this region. As a basis for combining different methods of geophysics it has been used correlation of the petrophysical characteristics. The procedure of the complex interpretation included also the formalized description of geological structure of the surface of this region and the prediction data about deep position of geological boundaries in the upper crust. The initial seismic data were the first arrivals times of the weakly refracted waves. The digital map of the region with 1x1 km step in the plan was used as the initial gravity data. For exception of the regional trend of the gravity field the direct gravity problem for three-dimensional density models of the Fennoskandian lithosphere has been solved. The area of modelling (160 x 160 km in the plan and 20 km for the depth) has been filled with one-dimensional normal distribution of density. As a result of the decision of a complex inverse problem the detailed three-dimensional geophysical model of the upper part of an earth's crust in the Khibiny and Lovozero massifs regions is obtained. The model contains distribution of the velocity of the longitudinal waves and the density of rocks in the studied volume of medium. The obtained models of the velocity and density have been transformed to normal thermodynamic conditions. It has allowed proceed to lithological interpretation of results of the modelling. The analysis of the results of the three-dimensional complex geophysical modelling has allowed to reveal features of deep structure of the Khibiny and Lovozero alkaline massifs. The obtained results of complex interpretation demonstrate a coordination of the density and velocity models of the Lovozero massif and confirm the geological representations about the laccolith-like form of this massif. As for the Khibiny massif, the results of combined interpretation demonstrate its complex structure in the middle part of the section, distinguished from geological representations about the concentrically zonal conical form of the massif. Specificity of the deep structure of the Khibiny massif is presence of the anomaly objects, detected on 2-5 km depths, presumably connected with paleocaldera of the massif. The research was supported by Russian Foundation of Basic Research (grant 1 07-05-00397).
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