Quantitative structural analyses and numerical modelling of ...

1. Quantitative analysis of deformation structures and their numerical modelling 13Some models of viscous deformation of thin plates show the characteristic deformationgradient, which is generally difficult to identify. Are we able to recognise sucha gradient within anisotropic rock masses? And what is the effect of lateral temperaturegradient on deformation of the crust? We have tried to answer those interestingquestions in the paper Baratoux et al. (2005b), where we observed structural variationsin shape and flattening of mesoscopic folds across 40 km long section (Fig. 1.7). Thisprofile was characterized by buckle and chevron folds in the east, flattened buckle foldsin the centre and flow folds in the west. Quantitative analysis of fold shape in termsof Fourier harmonic analysis method and the Ramsay’s method of dip isogons pointedto systematic decay in degree of mechanical anisotropy from east to west. This trendwas correlated with PolyLX analyses of microstructures of amphibolites, which revealexistence of gradient in shape anisotropy on grain scale. This detailed quantitative workconcludes that the character of folding is directly controlled by degree of anisotropy ofmicrostructure, so that the grain shape anisotropy governed mechanical properties offolded macroscopic layers. In another words, lateral variations in fold style correlatewith lateral variations in the mechanical anisotropy which reflect metamorphic zonalityi.e. thermal history of previous tectonometamorphic event.1.1 Perspectives of numerical modelling of deformation ingeologyUse of numerical modelling in structural geology introduced new possibilities especiallyin the area of deformation overprints. The range of deformation structures, which aretraditionally explained as the result of “magic” deformation partitioning into zones ofpure shear (prolate and oblate) and simple shear dominated deformation can not explainfabric variations encountered in orogens. This concerns the problem of strain compatibilityand second the problem of significance of deformation intensities. Therefore wedecided to elaborate methods to quantify and numerically simulate these deformationprocesses (e.g. Kratinová et al., 2010). For example, long-standing study of Třebíč syenitemassif led us to conclude is that the magma body suffered multiple deformationsduring magmatic stage, which led to the distinctive variance of the magmatic fabricsthat are not explainable in terms of standard approaches (Lexa et al., in prep.). OurAMS study shows that northern part of the body exhibit NW-SE trending lineation accompaniedwith oblate shape of AMS ellipsoid, while the southern part is characterizedby NE-SW trending lineation and prolate shape of AMS ellipsoid (Fig. 1.9).Our numerical modelling revealed that the variance in the symmetry and direction oflineations could be successfully explained by the superposition of horizontal flow (within