The greenschist-amphibolite transition in the CFM projection

The CFM projection (C = CaO+Na2O+K2O-AlzOr, F: FeO-FezO:, M = MgO) was originally designed for illustrating mineral assemblages in upper amphibolite and granulite facies quartz-feldspar-magnetite-bearing metabasites. By introducing chlorite, the projec-tion can also be used to illustrate mineral assemblages in greenschist facies quartz-feldspar-magnetite-bearing metabasites. The greenschist-amphibolite facies transition takes place in the context of Abbott's (1982) lowest grade CFM topology. In metabasites, the change from the greenschist facies to the amphibolite facies commonly proceeds with no change in the mineral assemblage other than (l) a change in the compositions of the minerals and (2) a change in the modal proportions of the minerals (Laird, 1980; Thomp-son et al., 1982; Laird in Robinson et al., 1982). The common assemblage is amphibole (Amp) + chlorite (Chl) + plagioclase (Pla) + epidote (Epi) + quartz (Qtz)+Fe3