Figure F31. Photomicrographs illustrating the complex, multistage evolution of brown amphibole gabbro during deformation and metamorphism. A–C. Sample 209-1271B-14R-1, 25–29 cm (cross-polarized light [XPL]: blue filter). (A) Ductile deformation. Amphibole porphyroclast with wavy extinction (a(p)) represents a microboudin that has been syntectonically recrystallized to fine-grained amphibole neoblasts (a(n)) along its margins (sc(n) = sericite-altered plagioclase neoblasts) (field of view [FOV] = 5.5 mm; image 1271B_058). (B) Amphibole porphyroclasts (a(p)) have been partially replaced by amphibole neoblasts (a(n)). The amphibole is surrounded by bands of former plagioclase neoblasts that have been statically altered to sericite-bearing assemblages (sc(n)) (FOV = 5.5 mm; image 1271B_059). (C) Outline of a "ghost" plagioclase porphyroclast replaced by sericite-bearing assemblages (sc(p)). The original polysynthetic twinning of the plagioclase porphyroclasts (white arrows) is pseudomorphed by sericite, quartz, and secondary plagioclase. Former plagioclase neoblasts are also pseudomorphically replaced by sericite aggregates (sc(n); red arrows) (FOV = 2.75 mm; image 1271B

Figure F31. Photomicrographs illustrating the complex, multistage evolution of brown amphibole gabbro during deformation and metamorphism. A–C. Sample 209-1271B-14R-1, 25–29 cm (cross-polarized light [XPL]: blue filter). (A) Ductile deformation. Amphibole porphyroclast with wavy extinction (a(p)) represents a microboudin that has been syntectonically recrystallized to fine-grained amphibole neoblasts (a(n)) along its margins (sc(n) = sericite-altered plagioclase neoblasts) (field of view [FOV] = 5.5 mm; image 1271B_058). (B) Amphibole porphyroclasts (a(p)) have been partially replaced by amphibole neoblasts (a(n)). The amphibole is surrounded by bands of former plagioclase neoblasts that have been statically altered to sericite-bearing assemblages (sc(n)) (FOV = 5.5 mm; image 1271B_059). (C) Outline of a "ghost" plagioclase porphyroclast replaced by sericite-bearing assemblages (sc(p)). The original polysynthetic twinning of the plagioclase porphyroclasts (white arrows) is pseudomorphed by sericite, quartz, and secondary plagioclase. Former plagioclase neoblasts are also pseudomorphically replaced by sericite aggregates (sc(n); red arrows) (FOV = 2.75 mm; image 1271B_060). D, E, F. Sample 209-1271B-11R-1, 44–46 cm (XPL: blue + dark gray filters; FOV = 1.4 mm). (D) Intergrowth of fibrous amphibole (a2) and chlorite (ch) after former high-temperature amphibole. Fibrous amphibole and chlorite are stretched and deformed along shear bands (image 1271B_049). (E) Amphibole-chlorite schists after gabbroic protolith. The secondary fibrous amphibole (a2), sericite (sc), and chlorite (ch) are stretched and banded, defining the schistosity (image 1271B_048). (F) Fold of fibrous amphibole (a2) in a amphibole-chlorite schists after gabbro. Chlorite (ch) crystallized in the pressure shadow of the inner part of the fold. The matrix is composed of fine fibrous aggregates of secondary amphibole (a2) and chlorite (a2ch may replace former high-temperature amphibole) alternating with dark bands of sericite and hydrogrossular (sc & hgr; may by replacing former plagioclase) (Sample 209-1271B-11R-1, 55–57 cm) (XPL: blue + dark gray filters; FOV = 5.5 mm; image 1271B_053).