Page 227 - Microtectonics

7.6 · Problematic Porphyroblast Microstructures 217

Fig. 7.38. Two garnet porphyroblasts in a garnet-mica schist containing inclusion patterns similar to the pattern at right in Fig. 7.36c
(section normal to the S-axis of Fig. 7.36). In fact, the section is slightly inclined to the R(rotation)-axis (Fig. 7.36a). Leiden Collection.
Width of view 45 mm. CPL

Fig. 7.39. Development of deflection planes and truncation planes
around a syntectonic periodically growing porphyroblast in non-
coaxial progressive deformation. The foliation and the porphyro-
blast rotate with respect to each other. a Strain caps and strain shad-
ows develop around the porphyroblast during progressive deforma-
tion. After mica-rich strain caps are developed, they are overgrown
by the porphyroblast, forming a deflection plane (e.g. Fig. 7.32).
b If development of a syntectonic porphyroblast is temporarily inter-
rupted by local dissolution in the strain caps, renewed growth over the
strain caps causes development of truncation planes. The geometry
of deflection and truncation planes is shown in the enlarged insets