Geometrie kvarcitových těles v okolí Příchovic

Abstract

Quarzite as a metasedimentary rock is usually figured in prolongated bands in geological maps. But muscovite quartzite from Krkonoše-Jizera Crystalline Unit in SE surrounding of Příchovice village forms irregular shapes in detailed geological maps (e.g., Mrázová – Štěpánek 2007, see Fig. 1), which do not allow simple interpretation of the geometry of quartzite bodies. To find correct 3D geometry of the bodies, we used standard methods of detailed mapping and documentation of outcrops as well as detailed structural analysis. Locations of terrain edges with quartzite outcrops have been indicated in the map (Fig. 3 –A, B, C). Generaly sub-horizontal to moderately dipping metamorphic foliation has been found. Foliation poles make wide girdle in the plot (Fig. 2) which indicates sub-cylindrical fold structure with horizontal axis in the NW–SE direction.Studied area can be geomorphologically divided into two different parts. The northeastern part of the territory is sub-horizontal plateau, while the southwestern part is generally inclined to the southwest. In the second part, the metamorphic foliation dips to the southwest under such angle, that it seems to be parallel to the inclination of the slope, see the old quarry (Fig. 3B) and SW part of Velká bílá skála (Fig. 3A). The last one show us bent outcrop respecting the change in slope inclination. Large shear bands were directly observed as a part of S-C structure. It indicates that SW limb of the fold was strained under simple shear condition with the drop SW kinematics (Fig. 4). Change in orientation of SW-dipping fold limb was produced by a ductile shear zone.Based on a combination of metamorphic foliation orientation of quartzite and field edges, we can interpret quartzite rocks as a part of one platy body, which forms the overall morphology of the landscape south of Příchovice. In the plateau, erosion stopped at subhorizontally oriented part of the quartzite layer, while denudation of the SW limb of the large fold predeterminates the inclined slope surface to the SW (Fig. 3D). Relics of thin overlying rocks remaining on quartzite in some places and erosion of the small creeks produce bizarre forms in geological map, which seems to be difficult to understand. This study has shown that such complex structure can be decrypted using the detailed structural analysis. In this case it was shown that quartzite forms a relatively simple body which was only slightly bent due to simple shear deformation.