Pressure shadow explained

A pressure shadow (also called strain shadow) is a term used in metamorphic geology to describe a microstructure in deformed rocks that occurs adjacent to a relatively large, undeformed particle, such as a porphyroclast. Pressure shadows often appear in thin sections as pairs of roughly triangular regions that are elongated parallel to the foliation around a clast of a different mineral.[1] Pressure shadows that contain fibrous mineral textures are also termed pressure fringes or strain fringes.[2]

Formation

During deformation, minerals can migrate by plastic flow or may grow by diffusive mass transport into the lower-stress regions created by a rigid porphyroclast or porphyroblast.[3]

Notes and References

  1. Book: Passchier and Trouw . Microtectonics . 2005 . Springer . 978-3-540-29359-0 . 2nd.
  2. Müller, W.. Aerden, D.. Halliday, A. N.. Alexander Halliday. 2000. Isotopic dating of strain fringe increments: duration and rates of deformation in shear zones. Science. 288. 5474. 2195–2198. 10.1126/science.288.5474.2195. free. 10864865 . 2000Sci...288.2195M .
  3. Book: Blenkinsop, T.G. . Deformation Microstructures and Mechanisms in Minerals and Rocks . 2007 . Kluwer Academic Publishers . 978-0-306-47543-6 . 150.