Deformation-Induced and Reaction-Enhanced Permeability in Metabasic Gneisses, Iona, Scotland: Controls and Scales of Retrograde Fluid Movement

Figure 7

Photomicrographs of pervasive alteration textures in the gneiss. (a) Epidote vein marking sharply defined boundary between plagioclase (albite)-rich gneiss to the left and epidote-rich gneiss to the right (thin section I3) (PPL); (b) granular textured epidote replacement texture within granoblastic gneiss (thin section AH1) (XPL); (c) sericitization of plagioclase (thin section S) (XPL); (d) marginal alteration of albite to epidote along minor fractures and grain boundaries at margins of epidosite (thin section I) (PPL); (e) alteration of coarse-grained albite plagioclase within pegmatite to fine-grained epidote along feldspar twin planes (thin section F) (PPL); (f) complete alteration of coarse-grained plagioclase at the margin of pegmatite to a combination of fine-grained epidote and small elongate quartz “blebs” (thin section F). Adjacent albite has cataclastic texture (PPL); (g) relict plagioclase within epidote gneiss and large deformed hornblende with minor marginal alteration to chlorite (thin section I) (PPL); (h) secondary electron image of plagioclase grain boundary with thin sheets of chlorite coating the boundary (sample AH1).

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