Deformation fabrics in Earth's crust and mantle are commonly used to constrain the tectonic history, deformation mechanisms, and rheological properties of the lithosphere. Their formation involves heterogeneous and multiscale deformation processes that current single-scale models cannot capture. Here we present a micromechanics-based MultiOrder Power Law Approach (MOPLA) for the simulation of multiscale fabrics in crustal scale high-strain zones. We consider the progressive deformation in a crustal high-strain zone on three different scales. On the macroscopic scale, representing the average assemblage of rock units at a point, we regard the rock mass as a continuum made of many first-order elements. The progressive deformation of first-order elements in the macroscopic flow field simulates tectonic transposition. On the scale of an individual first-order element, we regard it as an Eshelby inhomogeneity embedded in a poly element continuum. We apply Eshelby's inhomogeneity formalism for power law materials to relate the flow field inside a first-order element to the macroscopic flow field. On the scale pertinent to structures observed on the outcrop or smaller scale, the partitioned flow fields inside individual first-order elements are used to examine the fabric development. We implement MOPLA in MathCad, apply the approach to a natural example of the Cascade Lake shear zone, and discuss the implications of multiscale deformation. Our model predicts lineation patterns observed in natural high-strain zones that have remained unexplained by single-scale models.