Geological interpretation of detailed gravity survey of the granulite complex in southern Bohemia and its structure


Authors: Vrána S, Šrámek J

Published in: Bulletin of Geosciences, volume 74, issue 3; pages: 261 - 278;

Keywords: detailed gravity survey, granulite complex of southern Bohemia, structural setting of granulites, Moldanubian Zone,

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The recent detailed gravity survey of a significant part of the granulite complex at the scale of 1 : 25 000 and use of existing older data provided basis for derivation of 1 : 100 000 gravity map of the complex. Geological interpretation of a number of positive and negative gravity anomalies is supported by data base on rock density. The five granulite massifs in the complex show differences in integrated density depending on the ratio of ultrabasic and basic rocks (peridotites, pyroxenites, basic granulites) to the predominant acidic granulites and on the total structural thickness of individual massifs. Acidic granulite masses nearly free of interlayered rocks with increased density, such as the Prachatice massif, represent particularly valuable objects for calculation of gravity model sections. A gravity model section indicates for this massif a total structural thickness of 8 km and a vertical jump of at least 7 km in relation to the neighbouring Lhenice belt of gneisses/migmatites and amphibolites. Interpretation of the geological structure of the complex, based on geological structural data from maps 1 : 25 000, published petrological and geochronological data indicates four successive stages of granulite uplift and their implantation in gneissic complexes of the middle/upper crust.