GLG 301 Lecture Notes - Lecture 20: Hyperbola, Flat Earth, Love Wave
Document Summary
Metamorphic foliations in schists or gneiss (e. g. , schistosity): slaty cleavage (other cleavages exist) Smooth, penetrative cleavage planes that are very closely spaced (< 1 mm); dominates over primary fabric. Composed of subparallel grains of thin-layer (phyllo-) silicates (e. g. , chlorite, muscovite, clayey minerals) Best developed in fine-grained sedimentary rocks (shale, mudstone, argillite or layers containing them) and volcanic tuffs but not quartzites (no clay minerals ) Pressure dissolves ions which then re-precipitate in low stress directions (the plane perpendicular to compression, 1). Some crystals may rotate: relationship to folding. If slaty cleavage forms perpendicular to 1, it also should form parallel to the axial plane of the fold thus slaty cleavage is very often axial plane cleavage, that is, parallel to the axial plane. Since the fold axis (hinge line) is the intersection of bedding and the axial plane, it should also be the intersection of bedding and cleavage.
