Petrohrad
Description
The study site is situated south of village Petrohrad, the Usti Region, Czech Republic. It is significant of natural granodiorite outcrops with several geological phenomenons - deformation fabrics, intrusions, frost cliff, rock crest, rock salient, rock wall, outcrop.
The area geologically belongs to the Bohemian Massif - crystalline complex and pre-Variscian Palaeozoic - Bohemicum (Central Bohemian region) - Magmatites in Bohemicum. Stratigraphy is Cambrian (Geological localities, 2012).
The medium grained biotite granodiorite in the study area is "Petrohrad type". Petrohrad granodiorite is mainly composed of quartz, plagioclase, potassium feldspar and biotite. For higher content of biotite granodiorite is darker than usual. Biotite aggregates in bands and lenses are typical for this rock, as possible evidence of an impact of metamorphic processes. Potassium feldspar phenocrysts also occur. Radiometric age of this granodiorite is 488 plus minus 24 mil. years (Geological localities, 2012).
References:
[1] BREITER, Karel. Zprávy o geologických výzkumech v roce 2003: Granitoidy tiského masivu. Praha, 2003, s. 13-16. http://www.geology.cz/zpravy/obsah/2003/zpravy-o-vyzkumech-2003-str-013-16.pdf.
[2] Kozinec - Granodiorite (Petrohrad type). CZECH GEOLOGICAL SURVEY. Geological localities [online]. 2012 [cit. 2015-01-02]. http://lokality.geology.cz/d.pl?vyb=1&text=Lokality%20v%20okresu:&item=7&odlok=1&lokalizace=1&Okres=LN&id=3523&l=e.