Microstructures

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Post-tectonic Porphyroblasts

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70. Post-tectonic staurolite - Staurolite is a relatively rigid mineral during deformation. Pre-tectonic staurolite, where preserved, is generally boudinaged and cracked so that the pieces are rotated (e.g., image # 67) or are extended parallel to foliation. Syntectonic staurolite commonly shows the deflection of other minerals that grew around it. This example of post-tectonic staurolite, from Vermont, has overgrown a pre-existing, weak, left-lateral S-C fabric defined by quartz ribbons and white mica. The staurolite grain's inclusions mimic the curvature of the C-planes.

FOV 1.5 mm, Plane Light.

Click here to view Flash animation in a new window.

71. Post-tectonic garnet - Garnet from the Parry Sound shear zone, Ontario, Canada, has overgrown the deformation-related gneissic foliation. Although the large grain is very elongate, it is really a composite of many smaller grains that have coalesced. Well-developed crystal faces are visible on several of the garnet grains, especially at right of image.

FOV 1.5 mm, Plane Light.

Post-tectonic Porphyroblasts	Click image to enlarge
70. Post-tectonic staurolite - Staurolite is a relatively rigid mineral during deformation. Pre-tectonic staurolite, where preserved, is generally boudinaged and cracked so that the pieces are rotated (e.g., image # 67) or are extended parallel to foliation. Syntectonic staurolite commonly shows the deflection of other minerals that grew around it. This example of post-tectonic staurolite, from Vermont, has overgrown a pre-existing, weak, left-lateral S-C fabric defined by quartz ribbons and white mica. The staurolite grain's inclusions mimic the curvature of the C-planes. FOV 1.5 mm, Plane Light. Click here to view Flash animation in a new window.
71. Post-tectonic garnet - Garnet from the Parry Sound shear zone, Ontario, Canada, has overgrown the deformation-related gneissic foliation. Although the large grain is very elongate, it is really a composite of many smaller grains that have coalesced. Well-developed crystal faces are visible on several of the garnet grains, especially at right of image. FOV 1.5 mm, Plane Light.