Time-dependent formation of mantled inclusion structures for different rheologies under a simple shear

Mantled inclusions, commonly encountered in mylonites, sometimes represent the only recorders of the deformation history. Understanding the influence of rheology on the structure of mantled inclusion is important for its interpretation and also for the retrieval of the deformation regime. This paper is devoted to the 2D numerical investigation of time-dependent deformation behaviour of inclusion and its dependence on rheology under simple shear. The numerical model is based on an iterative finite-difference scheme. The inclusion is taken to be deformable and having its own intrinsic rheological properties differing from those of the matrix. The diffusion between the matrix and the inclusion is assumed to be insignificant. In order to emulate natural mantled inclusion, we imposed passive mantle around the inclusion, which efficiently monitors the deformation. The results of numerical modeling show that a key factor of structural appearance is the effective viscosity contrast (ratio of the inclusion to matrix effective viscosities). In the power-law rheology, even a small difference in rheological parameters may result in a high effective viscosity contrast of around 10 between matrix and inclusion. The high contrast inhibits stretching of the inclusion, preserving its round shape, which, in turn, may create an illusion of the seeming rigidity of the inclusion. Wings or tails are developed only in the systems with a high effective viscosity contrast. They are not influenced by whether the high viscosity contrast is produced by non-Newtonian medium or by the highly contrasting viscosity between the matrix and the inclusion in the linear rheology.