Computer modelling of mantled porphyroclasts in Newtonian and non-Newtonian simple shear viscous flows

In computer simulations based on creeping motion equations, the difference in stress sensitivity of strain rate between Newtonian rheology and non-Newtonian power-law rheology does not greatly influence the types of mantled porphyroclast developed in simple shear viscous flows. Porphyroclast type is determined by the radius of an initial spherical mantle. When a thin mantle lies within the separatrix, (δ2-objects develop at small γ, then complex porphyroclasts appear with increasing γ. When the mantle is thicker and transected by the separatrix, φ-objects form at small γ and δ2-objects appear with increasing γ during the same deformation. The transition from φ- to δ2-objects is gradual, the transition strain being dependent on the initial radius of the mantle. Our simulations did not produce θ-, δ1- or σ-objects.