Quantitative structural analyses and numerical modelling of ...

1. Quantitative analysis of deformation structures and their numerical modelling 7Figure 1.2: Three stages of the mechanical and rheological evolution of orthogneissbodies and host metasedimentary migmatites: (a) Early stage of layer parallel shortening.(b) Later stage in the deformation when the margin of the orthogneiss body hasbeen transformed to an orthogneiss/granite multilayer. (c) In the final stage furtherhomogeneous deformation of host diatexites is accompanied by flattening and intensificationof the orthogneiss fabric.deformation overprints, otherwise we are exposed to the problem of strain compatibility(formation of open spaces within rock masses is not possible for obvious reasons). In thiswork, numerical models were set-up to reproduce the variation in the finite strain andorientation of the original mechanical anisotropy with respect to external stress field.Although the model successfully explained the structural zonality of rigid domains inthe migmatites, it was not robust enough to understand general dependencies of thefinite strain intensity and symmetry to the degree and symmetry of initial mechanicalanisotropy. In the following I will show some other perspectives of the problem.Relative motion of lithospheric plates on a spherical surface is such that the plateconvergence vectors are often not orthogonal to plate boundaries (Dewey, 1975, McKenzieand Parker, 1967). These plate boundaries experience combined transcurrent andconvergent displacements associated with development of deformation zones of differentsize. Within continental blocks, the deformation is not only restricted to active plate