At 10:25 AM 2001/01/07 -0000, Joanie Marion asked:
>...
>As an aside, does anyone know the upper temperature limit on cleavage
>development?
Cleavage depends on planar preferred orientation of easily cleavable
phyllosilicates. In metapelites, prograde metamorphic reactions eliminate
chlorite at ~400, muscovite at ~700, and biotite at ~900 degrees C. In my
experience, cleavage becomes gradually less prominent across this whole
range of temperature. One of my favorite slides from a 1999
South-Australian field trip (led by Jeff Vassallo and Chris Wilson) shows a
locally strong axial-plane cleavage (defined by local concentrations of
coarse biotite) transecting tight upright minor folds in metapelitic gneiss
in granulite facies.
Dugald M Carmichael Phone/V-mail: 613-533-6182
Dept of Geological Sciences and Geological Engineering
Queen's University FAX: 613-533-6592
Kingston ON K7L3N6 E-mail: [log in to unmask]
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