Quantitative structural analyses and numerical modelling of ...

Chapter 1Quantitative analysis ofdeformation structures and theirnumerical modellingFinite deformation modelling is an approach that is used in structural geology for decadesas a proxy to study distribution and nature of deformation within crustal collision zones,zones of transpression or transtension and lithospheric extension (Sanderson and Marchini,1984). The main question arises in situations, where rock masses do not behaveaccording to “simple rules” of homogeneous deformation, i.e. where considerablevariation in lithology and rheology introduce heterogeneities, which are likely to controltheir complex deformation behaviour accompanied with strain superposition (Burg,1999). Konopásek et al. (2001) described in western part of Erzgebirge steeply dippinglineations contained by steeply dipping eclogite foliations and horizontal lineations insurrounding structurally conformable orthogneisses. This conflict has led us to modelevolution of deformation pattern within “soft” incompetent orthogneiss during verticalflattening. In our model, these orthogneisses initially showed a similar orientation offinite strain axes as eclogites but after subsequent vertical shortening suffered viscousdeformations, which does not affected competent eclogites. Our numerical simulationshave shown conclusively that the superposition of deformation stages is a powerful mechanismthat allows us to understand some strain paradoxes as one described above. Theresult of our modelling (Fig. 1.1) shows that the contrast in deformation record of eclogitesand orthogneisses results from common deformation history, which is selectively andto different extent recorded in individual lithologies.Our results were challenged by German colleagues Krohe and Willner (2003) and wewere obliged to defend our hypothesis in the manuscript Konopásek et al. (2003) using5