>"The facies concept is robust also because it contains no implication of
>P,T or other physical conditions. It is simply an association of rocks or
>mineral assemblages, from which we infer physical conditions."
>If I understand this correctly: Facies has no implications of P or T. Yet,
>from facies (= an association of ...) we infer P and T (i.e., physical
>conditions). I have a problem with logic here. It may have been that at
>the time the facies concept had been devised, P and T could not be
>quantified so easily, but this has changed. Just about every modern
>textbook in Metamorphic Petrology has a facies diagram which is a
>quantitative P-T diagram (not that they would look the same, but
Of course you are correct about the problem with the logic. I should have
said that: "The facies concept is robust also because it is not defined by
P,T or other physical conditions. It is simply an association of rocks or
mineral assemblages, from which we may infer physical conditions."
We all include inferences about P,T etc in our thinking, but the beauty of
the concept is that it can be used independent of any knowledge of the
physical conditions of metamorphism.