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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]