Pressure anomalies around cylindrical objects in simple shear

We model the pressure distribution around cylindrical objects in simple she ar deformation using the finite element method in two dimensions and presen t an analytical solution for a special case. Parameter space is explored nu merically for viscosity contrast between object and matrix, eta, and for th e non-linearity of flow, as expressed by n. We show that the geometry and s ize of the pressure shadow is independent of eta, but strongly dependent on n. For example, at n = 1, pressure shadows are roughly circular in shape, while for, n > 1, pressure shadows disintegrate into two branches. We also show that pressure may only exceed 100 MPa in pressure shadows at resolvabl e distances from the object if eta > 4 for strain rates of 10(-14) s(-1) an d matrix viscosities around 10(22) Pa a. As these values for strain rate, v iscosity and viscosity contrast are geologically reasonable, we emphasise t hat it is conceivable that geobarometric results obtained from syndeformati onal mineral paragreneses near rigid porphyroblasts may be influenced by no n-lithostatic components of pressure. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.