Page 240 - Microtectonics

230 7 · Porphyroblasts and Reaction Rims

Fig. 7.59. Symplectitic coronas of plagioclase, orthopyroxene and hornblende between garnet and clinopyroxene grains, reflecting the reac-
tion garnet +clinopyroxene +H 2 O → plagioclase + orthopyroxene + hornblende. Note that some orthopyroxene grains are aligned in the
coronas parallel to cracks in the garnet relicts; the coronas probably developed initially along cracks. The cracks therefore predate the
reaction. Bolingen Island, Prydz Bay, Antarctica. Width of view 5 mm. PPL. (Photograph courtesy P. Dirks)

Fig. 7.60. Pseudomorph of plagioclase-orthopyroxene symplectite after garnet. The grain size of the symplectite decreases inwards. Wu Li
Dong, N-Shanxi, China. Width of view 9 mm. PPL. (Photograph courtesy P. Dirks)