Quantitative structural analyses and numerical modelling of ...

1. Quantitative analysis of deformation structures and their numerical modelling 9elevation and exhumation of rocks. The results of our model (Fig. 1.3) shows systematicvariability in strain pattern, depending on the convergence angle and strain-rate withinthe transpressive zones. This fundamental behaviour could be used to inverse field datainto controlling parameters in both active and fossil deformation zone.One of the most important published contributions to this topic (Lexa et al., 2003)is based on our detailed structural analysis of polyphase deformation within the Gemerunit in the Western Carpathians. Here, the Paleozoic rocks deformed during LowerCretaceous convergence form steep cleavage fan between the more rigid blocks of easternand western part of the Vepor crystalline basement. Moreover, the so-called Trans-Gemeric shear zone is developed along eastern margin of the Vepor promontory andfurther east separate Gemer unit into two domains. By contrast, the eastern part ofthe Vepor basement suffered more frontal convergence with Gemer unit documented bydevelopment of Eastern Gemer thrust (Fig. 1.4). We tried to justify this complicatedtectonic model using viscous sheet formulation modelled by finite element method, wherewe simulate deformation in front of the moving indenter, which progressively deformedviscous domain in between the stationary blocks of eastern and western Vepor basementand which was free to thicken and outflow among these blocks.The result of numerical modelling (Fig. 1.5) was more than surprising, since both thesymmetry and distribution of viscous deformation of thin viscous sheet corresponds withsufficient precision to our observations. We consider this model as particularly valuablecontribution to the simulation of continental deformation. This example suggests thatthe concept developed since the eighties of last century (England and Houseman, 1986,Houseman and England, 1986) for deformation lithospheric scale deformations (deformationof Tibet in front of India indenter) could be successfully applied to significantlysmaller scale of geological units.Our simulations showed that our model for transpression was satisfying startingestimate for the deformation evolution in areas with complex kinematic framework. Webelieve that the deformation of continental crust is dominantly controlled by the presenceof lateral inhomogeneities of different shape and that the deformation is subsequentlypartitioned and channelized into narrow zones. Understanding polyphase deformationas consequence of principles of continuum mechanics is a challenge that will be testedin the near future theoretically as well as on field examples.Our field studies and observations rise the question of understanding the flow kinematicsin anisotropic rocks. The most common kinematic indicators used by field geologistsare “extensional shear bands”, which form basis of argumentation in numberof kinematic orogenic models (e.g. Behrmann, 1988, Neubauer et al., 1999, Platt and