Simulation of inclusion trail patterns within rotating synkinematic porphyroblasts

Abstract

The paper presents two-dimensional numerical simulations of inclusion trail patterns of spherical and non-spherical synkinematic porphyroblasts rotating and growing over a pre-existing, passive foliation during a single progressive deformation taking into account the effects of heterogeneous strain field around the rigid porphyroblast. The analysis is based on the velocity functions around a rigid object hosted in a Newtonian viscous medium. Using Visual Basic software, the trail patterns have been simulated in a PC assuming that the porphyroblast grows by increments of constant radius, over a pre-existing foliation, which simultaneously gets distorted due to heterogeneous strain field around the porphyroblast and included within the porphyroblast. The numerical simulations show that the trail patterns in spherical porphyroblasts are controlled by two factors: (1) the initial orientation of the foliation marker relative to the shear direction (θ) and (2) the ratio of pure shear and simple shear rates in the bulk deformation (S_r). Complex trail structures form when θ<0° and S_r≤0.75. The ratio of growth rates along axial directions of non-spherical porphyroblasts is an additional factor that controls the trail patterns.