Page 218 - Microtectonics

208 7 · Porphyroblasts and Reaction Rims
Fig. 7.26.
Schematic representation of
pre-, syn-, and post-tectonic
porphyroblast growth for por-
phyroblasts that lack passive
inclusions. Only distinction of
post-tectonic porphyroblasts is
relatively easy. Distinction of
pre-, inter- and syntectonic por-
phyroblasts is usually impossi-
ble, but they can commonly be
distinguished from post-tec-
tonic porphyroblasts by inter-
nal deformation features such
as undulose extinction

Fig. 7.27.
a Growth of a porphyroblast
over matrix material. Inclusions
are more rounded but of similar
size to those in the matrix. After
porphyroblast growth, grains in
the matrix may become coarser
by static recrystallisation and
grain growth (b), or smaller by
dynamic recrystallisation due
to deformation (c)