Frank and others
I guess I should not keep silent this time. By the way the rumour
that I have retired is slightly exagerated.
Frank is correct in that I used P-T diagrams for CONSTANT BULK
COMPOSITION (ie. a rock or experimental charge),in which the position
and extent of divariant (sliding) reactions, and their relationship
to the (relevant sections of) univariant reactions in a system (eg
FMAS) to which the particular bulk composition (eg. Mg/Mg/Fe=0.8;
A/F+M+A=0.7) belongs. I never used the term pseudosection for this
or any other type of diagram.
As far as I know it was Roger Powell and co-workers that started
calling such sections pseudosections, and, until recently, added
Hensen (1971) in brackets. I must admit always having been rather
pleased that they bothered to acknowledge the fact that I brought the
"pseudosections", and their theoretical implications, into use in
These sections have proved their worth for working out what is ( or
should be) happening in a particular rock during its P-T history.
They also make one realise that univariant reactions are but rarely
intersected ("encountered" or "seen") by single rocks (fixed
bukcompositions) on their path through the earth, even in relatively
simple systems (eg KFMASH).
Because of Tim Holland's and Roger Powell's, and others , efforts the
pseudosections can now be calculated for an ever larger range of bulk
compositions. They are a very useful petrological tool, and clearly
here to stay. I think we need to have a simple term to describe them,
and do not see much point of changing the term at this stage.
School of Geology
The University of New South Wales,
Sydney 2052, NSW,
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