Publication details

Orogenic collapse recorded in Benešov granodiorite, Bohemian Massif


BÁRTA Ondřej MELICHAR Rostislav

Year of publication 2018
Type Conference abstract
MU Faculty or unit

Faculty of Science

Description Magmatic rocks in the NE part of the Central Bohemian Plutonic Complex known as the "Benešov type" were affected by strong deformation during the Variscan orogeny. These rocks are represented especially by amphibole-biotite granodiorites. To determine deformation fabric of the "Benešov type", anisotropy of magnetic susceptibility (AMS) was used. AMS data were compared with similar structures found in the Bohemian Massif. Over 450 samples were collected. Recognized magnetic fabric is more-or-less homogenous through the study area. Magnetic lineation dips to the NW or N at low angles (Fig. 1). Magnetic foliations are less homogeneous but it trends to dip to the W-NW. The most of samples have prolate ellipsoid of AMS. The degree of anisotropy varies from 1.033 to 1.132. Relatively low bulk magnetic susceptibility of measured samples (0.23×10-4 – 4.08×10-4 SI) suggests that the AMS signal is caused by paramagnetic minerals. Microstructural observation confirmed top-to-the north tectonic movement. Equivalent shear zones with similar orientation as well as with similar sense of movement were found in this part of the Bohemian Massif in other units, such as Čertovo břemeno type, Miřetín pluton, Nové Město durbachite among others. Considering lithology, dating and tectonics of the surrounding units, these shear zones might be interpreted as ductile to brittle-ductile detachments originated during gravitational collapse of the Variscan orogenic belt.

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