Abstract

Rocks of the arendalite charnockitic suite are well exposed on numerous islands and along the coast near Arendal, Norway. Isoclinally folded interlayered hypersthene quartzite and pyroxene-amphibole-quartz-plagioclase gneiss were examined for major element variation with respect to structural setting. The hinge and limb samples are much the same in the gneiss, but show striking chemical differences in the quartzite. On the basis of equal aluminum, the hinge is enriched in SiO2, TiO2, Fe2O3, MnO, MgO, and CaO, with alkalies approximately constant. Textures and orientation of hypersthene crystals are also very different from limb to hinge, and suggest that stresses in the hinge had σ1 > σ2 > σ3 while stress in the limbs was less well defined and probably approached σ1 = σ2 = σ3.

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