At 18:16 06/11/01 -0500, Dugald wrote :
At 08:31 AM 05/11/2001 +0100, prior to
provoking JC's defense of "the noble
discipline", Christian wrote:
>... Grt+Cpx+Pl+Q is a
>typical paragenesis of HP granulite facies and the transition between
HP
>granulite facies and amphibolite facies is reached by the
reaction
>Grt+Cpx+Q=Hb+Pl;...
Nomenclature aside, perhaps we can forge a link between the two
noble
disciplines (:-)) by recognizing that the reaction in question is
better
approximated by Hb + Pl + Qtz = Grt + Cpx + tonalitic liquid.
Indeed , it is, a good idea to forge a link
between the 2 noble disciplines since amphibolite-granulite transition is
precisely at a PT interval where the 2 kind of rocks often coexist.
Often, but not always! This transition does not necessarily imply
melting. Even if it‘s often true in Archean provinces. There are cases
where the transition amphibolite to granulite (and reversely) is reached
by subsolidus transformations, without melting.
In other words, granulites (sorry ! rocks in the conditions of granulite
facies: kinzigite, khondalite, pyribolite, pyrigarnite, …) are not
always, necessarily restites after (vapor-absent) partial melting…
;-))
CN
