A set of metamorphic mineral assemblages (produced by the metamorphism of a wide range of starting rock types under the same metamorphic conditions), typically characterized by the development of the mineral assemblage clinopyroxene–labradorite–quartz in rocks of basic igneous composition. Other rocks of contrasting composition, e.g. shales or limestones, would each develop their own specific mineral assemblage, even though they are all being metamorphosed under the same conditions. The variation of mineral assemblage with starting rock composition reflects a particular range of pressure, temperature, and P(H2O) conditions. Experimental studies of mineral pressure–temperature stability fields indicates that the facies represents a range of low pressures (0–2 kb) and moderate temperatures (550–750 °C) characteristic of contact metamorphic conditions.
Subjects: Earth Sciences and Geography.