Lower Temperature Terminations of the Three-phase Region Plagioclase-Alkali Feldspar-Liquid

Abstract

Geological and experimental evidence indicate that the three-phase field, plagioclase-alkalifeldspar-liquid, may terminate in several different ways. The possible terminations have been developed from Schreinemakers' rules governing the disappearance of three-phase fields. In igncous rocks, these different terminations may arise from variations in the relative amounts of additional components in magmas, or from changes of total pressure, or from structural changes that effect the extent of solid solution in feldspar.