Advanced Structural Geology (MOHR) / Продвинутая структурная геология

R ock masses deform under the action of forces. Rheology (from the Greek 'study of flow') is the branch of physics dealing with the deformation of materials. An understanding of rheology is a prerequisite for the study of deformed domains. Rheological properties of rocks can be described with or without reference to atomic processes (microrheology and macro-rheology). In the frame of ma cro-rheology, deforma tion can be des cr ibed physically in terms of three end-members: Elastic, Plastic or Viscous deformation. Those terms are explained in the chapter l of this course. In a purely descriptive point of view, deformation can be described in terms of discontinuous or continuous (continuous-homogeneous or continuous-heterogenous) deformation. R emarkably the character of the deformation is scale-dependent (sketch on the right). Continuous-homogeneous Discontinous Undeformed object

In general, deformation is partitioned between discontinuities (faults) that limit domains where deformation is continuous (sketch on the right). Finite strain analysis allows the characterization of the final product of deformation in domains where deformation is continuous. However, to be valid, this analysis must be applied at a scale where the deformation is continuous-homogeneous. Therefore, a complexly deformed domain (hand-specimen or a piece of continental crust) will be divided into small volumes where deformation can be considered to be homogeneous. In this condition, any imaginary sphere inserted into each elementary volume will be transformed after deformation into an ellipsoid. This ellipsoid is called the Finite Strain Ellipsoid (Chapter l) and characterises the strain. Fault analysis deals with that part of deformation accommodated by discontinuities. Faults can be reactivated or newly formed discontinuities. Both reactivation and formation of discontinuity planes strongly depend on the state of stress. T he state of stress is characterized by the stress ellipsoid (Chapter l) which is also responsible for strain. T he relationship between strain and stress is discussed in Chapter 1 <...>