| Summary: | Amphibolites were systematically sampled along s-surfaces from two outcrops in the Alabama and Georgia Piedmont. S-surfaces are planar features that pervade rocks. In this study the s-surfaces have a metamorphic origin. Compositional and textural effects of two phases of metamorphism (one of increasing temperature and one of decreasing temperature) were examined within distances of centimeters along s-surfaces. Mineral, chemical and textural parameters were measured and were found to vary along the s-surfaces. === Chemical variations between s-surfaces show chemical differentiation that could have been present in an original basaltic body. The s-surfaces are oriented at oblique angles to the direction of inferred differentiation in both outcrops. Although the amphibolites have been affected by two metamorphic events, the original chemical variations in the basalt have not been obliterated. Hornblende 2V variations and the presence of both epidote and clinozoisite within thin sections indicates that major elements are immobile within distances of millimeters along these s-surfaces. These findings do not support the development in amphibolites of metamorphically differentiated features, such as layering, by the diffusion of elements through longer ranged distances. The process of recrystallization, occurring crystal by crystal, in a sequence is implied by the absence of hornblende intercrystal equilibria. === The major mineral transformation recorded in these rocks is plagioclase changing to clinozoisite. The degree of this mineral reaction varies along s-surfaces. The dependence of this reaction on the presence of water indicates that fluid pressure varies along the same s-surfaces over distances less than centimeters. === Hornblende crystals that were originally more randomly distributed have rotated and translated to a less random arrangement due to the volume decrease that accompanied the retrograde plagioclase-clinozoisite reaction. === This study includes the most detailed quantitative description of metamorphic rock textures thus far described in the literature. Quantitative textural parameters include the distribution of hornblende and clinozoisite in the rock, hornblende sizes and shapes, dispersion of hornblende optic Z-axes and dispersion of the traces of hornblende crystallographic bc planes in the dominant and secondary lineations. These textural parameters vary in an unsystematic fashion along the s-surfaces. === The textural values obtained from amphibolites in Alabama and Georgia are comparable to those of amphibolites from New Mexico, Scotland and Wyoming. Therefore, regardless of variations of metamorphic grade and degrees of strain, amphibolite hornblendes have narrowly defined spatial distributions and optical and crystallographic orientations. === Source: Dissertation Abstracts International, Volume: 41-03, Section: B, page: 0859. === Thesis (Ph.D.)--The Florida State University, 1980.
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