Gravity and magnetic studies of the Rhodope Region NE Greece

Gravity and magnetic studies have been carried out in order to investigate the structure of upper crustal bodies in the Rhodope region, NE Greece. Geologically, the area, which extends over 30000 km2, consists of a metamorphic basement containing granitic intrusions and tectonically emplaced ultramafic bodies, with superimposed Tertiary sedimentary basins. Analytical methods such as filtering and power spectral analysis have been applied to existing and composited aeromagnetic and Bouguer anomaly maps of the region. The resultant maps, together with the initial gravity and aeromagnetic maps and the available geological information, were used to delineate regional and local structures. Sedimentary basins, the formation of which is related to post-Alpine extension in the Aegean region, give rise to negative gravity anomalies. These anomalies have been identified and interpreted by 2D, 2 1/2D and 3D modelling, constrained by borehole information and limited seismic data. The maximum thickness of the sedimentary formations in the various basins studied was found to range between 2 and 6 km. Aeromagnetic anomalies associated with granitic intrusions of Tertiary age and ultramafic complexes have been interpreted by 2D forward modelling and non-linear optimization. Estimates of the magnetic properties of several of these bodies have been obtained from laboratory measurements on a number of samples selected from outcropping rocks. Interpretation of the aeromagnetic anomaly of the Esohi-Kimi ultramafic body has produced a model for its shape which differs from that suggested by the limited geological information about the region. The possibility of an additional source for this anomaly at depth is briefly discussed. The Soufli serpentinites are interpreted as occupying a thin-skinned tectonic setting. Modelling of the aeromagnetic anomalies associated with some of the Tertiary granitic intrusions has revealed a shallow depth to base in the range of 1.2 to 6.0 km. This can be interpreted to suggest that the intrusions are mainly of laccolithic form. Combined interpretations of sedimentary basins and granitic intrusions have highlighted their spatial association and the possibility of a common tectonic setting for these units is discussed. (D73966/87)