At 18:16 06/11/01 -0500, Dugald wrote:

"At 10:54 AM 07/11/2001 +0100, Christian wrote:
>...This transition [amphibolite to granulite facies] 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.
>...
True in theory, but where has such a case been persuasively documented? "

Of course! it’s difficult simply for kinetic reasons;there is rarely arrested reactions in the prograde direction ! But you are right and your discussion is very interesting : the transition amphibolite to granulite facies is often reached with melting
generally, but not always.  You seem to exclude the formation of granulites without fusion??
There are huge proterozoic terranes with basic magmatic complex in granulitic conditions; In SW of Madagascar, the parageneses are 1 or 2prxs, Pl, with or without Q, Brown Hb, Grt in a space of a few hundred square meters. All the parageneses of the transition zones of the 3facies: amphibolite, HP and IP granulite facies in the domain of the multivariant (because of the variations of MG/Fe , Na/Ca ratios, asiO2, aH2O and/or CO2?) subsolidus reactions Cpx+Grt+Q+V = Hb +Pl, Cpx+Grt+Q = Opx +Pl, Cpx+Ox+Pl+V = Hb, The magmatic textures are sometimes preserved and there no melting of these rocks.

 Moreover, at first time, I have speak about the transition in the direction HP granulite to amphibolite facies.

“>... 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. In the
prograde direction this is a vapour-absent melting reaction”

But not in the retrograde direction.
In the paleozoic hercynian belt, pieces of the oceanic lithosphere are implied in the intracontinental collision. Relics (lenses) of eclogites and HP granulites  (1-2GPa  700-800°C) are preserved in amphibolites. The amphibolites are the products of the retrograde evolution of the HPgranulites (and eclogites) by the reaction Grt+Cpx+Q+V=Hb+Pl: there are splendid coronitic textures.
Cheers,

Christian
http://christian.nicollet.free.fr/