A hand sample of the metamorphosed granitic rock outcroping near Charleston on the west coast of New Zealand (South Island). A well developed metamorphic fabric indicates that these rocks have been subjected to substantially higher P-T conditions than similar rocks at Cape Foulwind. The rock has been variably described as gneiss to mylonite in the literature. Can you identify any features that might suggest which is a better description?
Foliation surfaces are defined by the alignment of platey minerals (mostly muscovite and biotite in this rock), which glint in the light as the rock is ritated - this effect is missing from the model.
Clear crenulation lineations can be seen on the foliation surfaces, as well as a larger cm-scale open folding of the fabric. The difference in plunge direction of crenulations and larger fold axes is about 45 degrees.
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