Page 213 - Microtectonics

7.4 · Classification of Porphyroblast-Matrix Relations 203

Fig. 7.20. Post-tectonic chlorite crystal overgrowing a slaty cleavage. The cleavage structure is perfectly continuous without any deflec-
tion or development of strain shadows. Older strain shadows around opaque grains are included without modification. Example of
case g in Fig. 7.9. Araí, Goiás, Brazil. Width of view 0.6 mm. PPL

Fig. 7.21. Post-tectonic biotite porphyroblasts overgrowing a vertical crenulation cleavage (S ). Although no inclusion patterns have developed,
2
the lack of deflection of S 2 and the lack of strain shadows show that the biotite crystals grew after the crenulation cleavage development. The
opaque crystals at left are probably of the same age. However, very late syntectonic growth is also possible, as discussed in the text. Example of
cases c2 and d in Fig. 7.26. Ouro Preto, Minas Gerais, Brazil. Width of view 1.8 mm. PPL. (Thin section courtesy Hanna Jordt-Evangelista)