Quantitative structural analyses and numerical modelling of ...

J. KonopaÂsek et al. / Journal of Structural Geology 23 2001) 1373±1392 13853X/Y2D2K=1D2D2D3Quartz - D2Quartz - D3K-feldspar - D2K-feldspar - D3D3D3D3dD211 2 3 4 5 6 7 8 910864Y/ZQuartz - D2Quartz - D3K-feldspar - D2K-feldspar - D3200 1 2 3 4 5kFig. 8. Flinn's graph and d/k plot obtained from measurements of K-feldspar and quartz aggregates in coarse-grained orthogneisses of the MeÏdeÏnec nappe. Inthe MeÏdeÏnec synformand northern part of the MeÏdeÏnec antiform D2 structures), both K-feldspar and quartz aggregates show plane strain to prolate symmetryat relatively low strain intensities. On the other hand, the same aggregates in the southern limb of the MeÏdeÏnec antiformand in the KlõÂnovec antiformD3structures) show oblate symmetry and higher strain intensities see text for methods and details). Grey areas represent starting and ending positions of the D2ellipsoids used for modelling of the D3 fabric. Results of this modelling are presented in Fig. 10.represented by late F 4 folds and kink bands Fig. 5f). Thelatest deformation in the metasediments is represented bysemi-brittle normal faults dipping to the SW. These occur onthe southern limb of the KlõÂnovec antiform. Evidence of theD4 deformation in orthogneisses is rare. The D4 structuresappear mostly in the southern limb of the KlõÂnovec antiformas discrete sets of brittle-ductile S 4 cleavage with homogeneousspacing obliquely oriented to the main S 2 foliationFig. 9).7.1. The D3 and D4kink-band folds in metasediments andorthogneissesIn several places, conjugate arrays of kink-band foldswere observed, but in most cases only one single set isdeveloped monoclinal kink-band folds after Ramsay andHuber 1987), p. 427). All these kink-band folds are ofcontractional type Ramsay and Huber, 1987, p. 427) andtheir common feature is an E±W orientation of their hinges.In the northern limb of the MeÏdeÏnec antiformclose to thehinge zone, Fig. 9) several localities with well-developedkink-band folds occur. These appear in both the metasedimentsand the orthogneisses in zones where the S 2 fabricdips gently Loc. 130, 130.V, 6, 138ÐFig. 9). The sametype of kink-band folds can be locally observed in zones of¯at lying S 2 metamorphic fabric south of the KlõÂnovec antiformLoc.307). These kink-band folds, which are eitherconjugate or forma single set with a uniformorientation ofthe kink-plane, are related to the D3 deformation.The D4 kink-band folds are developed exclusively inzones of steep S 2 ±S 3 fabric in both the plagioclase schistsand the garnetiferous micaschists, and are mostfrequently observed in close proximity to the allochthonousorthogneiss body. Three groups of D4 kink-band folds arerecognised and these are shown in Fig. 9. A group a) ismade up from a set of monoclinal kink-band folds, whichaffect foliations dipping steeply to the north. They indicatetop-to-the-north normal movement. Group b) consists of61