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

Figure 6

Photomicrographs of veins. (a) Coarse-grained epidote vein, with central area containing quartz with actinolite needles, cutting across hornblende in altered gneiss (thin section I) (PPL); (b) quartz and epidote-filled vein cutting across epidosite. Marginal epidote shows euhedral shapes (thin section I) (PPL). Quartz has mylonite texture shown in Figure 4(f); (c) calcite-filled vein crosscutting thin epidote-bearing sheared vein (thin section G) (PPL); (d) complex fill of quartz-filled veins as they cut through a hornblende in the host altered gneiss (thin section I) (PPL). Vein on left shows quartz-fill cutting through epidote (top of view) and actinolite-fill, in optical continuity with the host hornblende, where the vein cuts the amphibole host. The vein on the right has quartz-fill at top and base of view where it cuts epidote and quartz in the wall rock and calcite-chlorite-actinolite-fill where it cuts through wall rock hornblende; (e) cartoon showing summary of mineral textures for the thick vein shown in (d); (f) quartz-filled vein transforming into calcite-filled vein with marginal actinolite, where it cuts hornblende in the host gneiss. Note thin epidote vein cuts across hornblende host (thin section I) (PPL); (g) actinolite- and epidote-filled fracture in the sample of gneiss from the southwest of Iona collected by Fiona Fraser (Sample F464, in Hunterian museum collection (Entry 666), Grid Ref NM253 221) showing variation in fracture fill controlled by the mineralogy of the adjoining host. The arrow shows clear albite at the edge of the vein with epidote fill.

(a)

(b)

(c)

(d)

(e)

(f)

(g)