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

Figure 8

(a) Traverse showing Ca/Na ratio of the metabasic gneiss on either side of an epidote-bearing cataclasite (thin section H). Position of large fracture containing hornblende-epidote cataclasite marks the boundary between plagioclase (albite) gneiss to the right and epidote gneiss to the left; (b) X-ray distribution map showing Ca distribution in orange-red shades, Na distribution shown in dark green shades, and Mg distribution shown in blue (thin section H). Note the fracture trace itself has a similar composition to the epidote gneiss; (c) plot showing Na and Ca contents of different whole rock compositions of the gneisses relative to average metabasic gneiss (large red diamond) in the Lewisian [56] and metabasic gneisses lacking evidence of retrogression from Iona (black diamond with standard deviations represented by error bars, based on 16 samples) [40]. Cataclasite compositions within both albite- and epidote-gneisses are shown by orange diamonds. Epidote gneiss II represents gneiss composition immediately adjacent to epidosites; (d) comparison of major element chemistry of different retrogressed samples of metabasic gneisses with average Lewisian metabasic gneiss [56]. Values above the line represent enrichments; those below the line represent depletions.

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