Deformation and metamorphic reactions in polyphase rocks
Figure caption
93
Plagioclase grain from granodiorite weakly deformed at low to mid greenschist conditions; recrystallization involved change of composition.
Weakly deformed granodiorite. Recrystallization of plagioclase has occurred along fractures which do not show major displacement. The left part of the porphyroclast is substantially recrystallized; the composition of the new grains is albite, whereas the host grain is an intermediate plagioclase. The recrystallization occurs through nucleation of new grains with a different chemical composition from that of the host grain; thus, it is better termed neo-mineralization. Small light specks are white mica, and the high-relief mineral is clinozoisite.