3‐D density model for the lithosphere of Europe: construction method and preliminary results

Abstract

A map of the observed gravity field of Europe has been constructed by averaging anomalies on a 1° X 1° grid in a combined reduction of Bouguer anomalies on land and free‐air anomalies offshore. On the basis of the observed gravity field and recent seismic data on crustal structure, a 3‐D density model for the lithosphere of Europe has been calculated. The model is represented by two complementary parts, each obtained by its own specific method. For the south of Eastern Europe, the 3‐D density model of the Earth's crust comprising the sedimentary cover and three layers within the crystalline crust (upper, intermediate and lower crust) was obtained by the following procedure: (1) the velocity model was transformed into a density distribution using the velocity‐density relation; (2) the gravity field of this density distribution was calculated by solving the 3‐D direct gravity problem; (3) the residual gravity field was obtained by subtracting the total gravity effect of the model and the regional component from the oberved gravity field; (4) the isostatic equilibrium of the model was evaluated; (5) in accordance with the residual anomalies and isostasy estimates, some changes (mainly in density distribution within the sedimentary cover) were entered into the initial density model and the final version of the density model was obtained for the consolidated crust as well as for areas with density inhomogeneities within the upper mantle. The correlation between Moho traveltimes and crustal gravity influence obtained from the results of 3‐D modelling for the south of Eastern Europe, supplemented by 2‐D modelling data available over Western Europe, makes it possible to estimate (without solving the direct gravity problem) the crustal gravity field for the whole European continent. Residual anomalies due to subcrustal density inhomogeneities have been interpreted in the light of seismic tomography and heat‐flow distribution. For both parts of the model geological and geodynamical interpretations of the results have been made. In particular, differences in the deep structure of the two major geoblocks of the continent—the West and East European Platforms—have been confirmed. Regions of relatively light upper mantle have been outlined beneath the east and north‐west of the East European Platform, while a heavier upper mantle has been distinguished below the Alps, the Caucasus, and the Calabrian Arc, as well as under the South Caspian Depression. Copyright © 1995, Wiley Blackwell. All rights reserved